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Hydration of humic and fulvic acids studied by DSC
Abstract
Qualitative and quantitative aspects of hydra-
tion of four humic acids (HA) and three fulvic acids (FA)
originating from different sources were investigated. DSC
experiments at subambient temperatures were carried out
in order to monitor differences in ice behavior originating
from freezable water surrounding humic molecules. It was
found that kinetic effects play a significant role in hydra-
tion processes of both HA and FA. In fact, the hydration
took part over 21 days which was detected as a progressive
decrease in ice melting enthalpy. Simultaneously, the peak
shapes and positions changed indicating structural changes
in the physical structure of the humic substances. In case
of FA, the dependency of melting enthalpy on water con-
centration showed a linear trend resembling a complete
hydration previously observed for water-soluble hydro-
philic polymers. In contrast, the melting enthalpy of some
HA increased in a step-like way with increasing water
content, suggesting preservation of original hydrophobic
scaffold during the hydration. The differences between the
rather young FA and the rather old HA lead to the con-
clusion that water can play a significant role in processes of
humification. We assume that separation of hydrophobic and hydrophilic domains and thus increase in nanoscale
heterogeneity represents an important physical contribution
to the overall humification process. It was also demon-
strated that the higher content of oxygen in humic mole-
cules is not the only indicator of higher water holding
capacity. Instead the porosity of humic matrix seems to
contribute as additional parameter into these processes.
... Indeed, crosslinking is a natural process in stabilization of soil organic matter (Smejkalova et al., 2006) also playing a role in diagenesis of organic geopolymers (Grasset and Ambles, 1998;Grasset et al., 2002;Pignatello, 2012;Schneckenburger et al., 2012) and it is believed to protect soil organic matter against mineralization (Monreal et al., 2010). In HAs, the molecules of different polarity are separated forming hydrophobic and hydrophilic domains or " hotspots " stabilized by noncovalent interactions (Kucerik et al., 2012). Accordingly, the hydrophilic domains are formed by polar functional groups, which are too far from each other to form intermolecular crosslink (Schulten et al., 1998). ...
... The ability of HAs to uptake moisture is not frequently studied, but it is an important property, especially for application of HAs in water-limited ecosystems. Furthermore, excess of water can cause a collapse of HA physical structure due to a break of H-bond stabilizing HA segments (Kucerik et al., 2012). This leads to opening of less accessible parts of HAs. ...
... To complete the picture about hydration properties of derivatives, we analyzed the change in water holding capacity under watersaturated conditions. Hydration of organic molecules is frequently studied by means of freezing/thawing DSC experiments (Kucerik et al., 2012;Prusova et al., 2010). This approach allows the categorization of water types according to the melting enthalpy of ice formed in the HA structure upon cooling. ...
Polar and apolar moieties of humic acids are spatially separated forming domains of different polarity. In this work, we tested the procedures to crosslink functional groups in polar domains of humic acids by using carbodiimide coupling and analyzed to which extent influenced the modification their hydration properties and stability. For this reason, we prepared eight derivatives of lignite humic acids using either water-soluble N-Ethyl-N′-(3-dimethylaminopropyl)carbodiimide (EDC) or water-insoluble N,N′-dicyclohexylcarbodiimide (DCC) under various conditions. Characterization of prepared derivatives showed that both methods lead to formation of crosslinked humic structures. Using of EDC resulted in lower degree of crosslinking, but better hydration properties. Higher moisture uptake and water holding capacity were observed in humic acids, which were pre-wetted prior to crosslinking for at least 24 h. Although the EDC derivatives of humic acids contained only between 60 and 85% of original free carboxylic groups, they showed similar moisture uptake as parental humic acids by equilibration at relative humidities of both 94% and 76%. Under water-saturated conditions, the EDC derivatives showed faster swelling kinetics and reached almost the same water holding capacity as the original sample after 18 days. However, both the EDC and DCC derivatives began to degrade already after 3–9 days during swelling tests, which subsequently decreased their hydration. The results suggested that water holding capacity, swelling kinetics and moisture uptake of humic acids were not influenced significantly by the amount of polar groups, but also by their spatial arrangement and distribution.
... Increasing water content improves sorption capacity of organic matter towards the non-polar compounds (Borisover, 2013;Borisover and Graber, 2004), which underlines the importance of non-covalent polar links in stabilization of soil organic matter supramolecular structure. Excess of water content breaks those interactions (Kucerik et al., 2012) thereby decreasing the structural compactness. This might cause problems in humic-substances based amendments due to their fast desiccation and uncontrolled water release. ...
... 2.3.1. Differential scanning calorimetry (DSC) measurement TA Instruments Differential Scanning Calorimetry (DSC) Q200 equipped with a cooling accessory RCS 90 was employed in order to determine the melting enthalpy of freezable water into HA structure (Kucerik et al., 2012). The temperature and heat scale were calibrated using distilled water and In standards. ...
... It is recognized that after wetting stage, which can take from minutes to months in some organic substrates , water molecules penetrate and distribute into the structure causing its swelling . This is accompanied with the interruption of weak interactions stabilizing the supramolecular HS structure (Diehl, 2013;Jaeger et al., 2010;Kucerik et al., 2012). Fig. 7 reports distribution of longitudinal relaxation times obtained by applying the UPEN algorithm (see Materials and Methods). ...
Lignite and lignite humic acids, which are used as soil amendments sometimes, are supposed to improve soil properties such as water holding capacity. The structure of those materials is composed of various organic molecules stabilized mostly by weak interactions. Therefore, excess of water causes only partial swelling, but most of the physical structure is destabilized. This accelerates the desiccation and hampers their application as natural hydrogel-like substances. In order to stabilize the structure of lignite humic acids and improve the water holding capacity, we applied formaldehyde cross-linking procedure based on covalent coupling of aromatic humic acids moieties. By combining the 1H NMR relaxometry and methods of thermal analysis, the kinetics and degree of hydration, water distribution and moisture uptake were investigated. It was found that cross-linking induced a reduction in moisture sorption capacity at low relative humidity and an increase at higher relative humidity, which was attributed to the separation of functional groups and decreasing of structural compactness after cross-linking. As a result, the cross-linked humic acids, exhibited faster water uptake and approximately three-fold higher water holding capacity in comparison with the parental sample. The distribution of relaxation times of water protons in swollen humic acids revealed the unification of pore size distribution upon cross-linking. Although the improved hydration of cross-linked lignite humic acids already resembles the hydration of some hydrophilic polymers, the water holding capacity is still below the capacity of classical hydrogels. Nevertheless, the low price of lignite, sorption properties and its overall positive affect on soil quality and productivity give a promise in application of this material both in agriculture and remediation technologies.
... 16,17,65 At the same time, HAs show great affinity toward water because of their hydrophilic groups. 33,66 Therefore, HAs and gelatin might compete for interactions with water molecules. ...
... 65 Instead, this effect is not present in the DSC curve of bare HA (black curve), suggesting that water molecules are constrained by intimate interactions with HA moieties, which prevent them from crystallization. 66 Water affinity to HA must be larger than to bare gelatin, whose DSC profile shows an evident ice melting peak, suggesting the presence of a relevant amount of crystallized water. To highlight a significant change in crystallization water by varying HA concentration, a sample in which HA concentration is equal to that of gelatin (green curve) has been prepared. ...
Exploring the chance to convert biowaste into a valuable resource, this study tests the potential role of humic acids (HA), a class of multifunctional compounds obtained by oxidative decomposition of biomass, as physical agents to improve gelatin’s mechanical and thermal properties. To this purpose, gelatin–HA aqueous samples were prepared at increasing HA content. HA/gelatin concentrations changed in the range 2.67–26.67 (wt/wt)%. Multiple techniques were employed to assess the influence of HA content on the gel properties and to unveil the underlying mechanisms. HAs increased gel strength up to a concentration of 13.33 (wt/wt)% and led to a weaker gel at higher concentrations. FT-IR and DSC results proved that HAs can establish noncovalent interactions through H-bonding with gelatin. Coagulation phenomena occur because of HA–gelatin interactions, and at concentrations greater than 13.33 (wt/wt)%, HAs established preferential bonds with water molecules, preventing them from coordinating with gelatin chains. These features were accompanied by a change in the secondary structure of gelatin, which lost the triple helix structure and exhibited an increase in the random coil conformation. Besides, higher HA weight content caused swelling phenomena due to HA water absorption, contributing to a weaker gel. The current findings may be useful to enable a better control of gelatin structures modified with composted biowaste, extending their exploitation for a large set of technological applications.
... On farmland, water is an important medium for nutrient transport to maintain photosynthesis, respiration, and transpiration of crops. Indeed, a considerable amount of investigations has affirmed the positive effects of HSs on water retention ability, meaning that the application of HSs can enhance the water-holding capacity of soil and increase the drought stress tolerance of plants (Kučerík et al., 2012;Cihlář et al., 2014). ...
... Porosity plays an important role in water-holding capacity. Kučerík et al. (2012) found that in HSs structures, hydrophobic domains are surrounded by hydrophilic moieties, which can form a hydrophobic scaffold via non-specific weak interactions. Cihlář et al. (2014) employed a formaldehyde cross-linking method to increase the porosity of HAs, showing a three-fold increase in the water-holding capacity of the products. ...
Aerobic composting is a typical biochemical process of stabilization and harmlessness of organic wastes during which organic matter degrades, and then aggregates, to produce humic substances (HSs). HSs are a core product of—and a crucial indicator of—the maturation of compost that can be used in soil amendments. The formation of HSs is affected by the characteristics of the raw materials involved, the presence of compost additives, microbial activity, temperature, pH, the C/N ratio, moisture content, oxygen content and particle size, all of which can interact with each other. The formation of HSs is therefore complex. Moreover, it is difficult to identify definitive structures of humic acids (HAs) and fulvic acids (FAs), which are the two major components of HSs. However, HSs represent the same functional groups and structural arrangements, which helps to predict their structures. Functional groups represented by phenol and carboxylic acid groups of HAs and FAs can provide various agronomic functions, such as plant growth enhancement, water and nutrient retention, and disease suppression capacity. Overall, HSs can act as a soil amendment, fertilizer, and plant growth regulator. These functions of HSs enhance the reuse potential of organic waste compost products; however, this requires scientific control of various composting parameters and appropriate application of final products.
... On farmland, water is an important medium for nutrient transport to maintain photosynthesis, respiration, and transpiration of crops. Indeed, a considerable amount of investigations has affirmed the positive effects of HSs on water retention ability, meaning that the application of HSs can enhance the water-holding capacity of soil and increase the drought stress tolerance of plants (Kučerík et al., 2012;Cihlář et al., 2014). ...
... Porosity plays an important role in water-holding capacity. Kučerík et al. (2012) found that in HSs structures, hydrophobic domains are surrounded by hydrophilic moieties, which can form a hydrophobic scaffold via non-specific weak interactions. Cihlář et al. (2014) employed a formaldehyde cross-linking method to increase the porosity of HAs, showing a three-fold increase in the water-holding capacity of the products. ...
Aerobic composting is a typical biochemical process of stabilization and harmlessness of organic wastes during which organic matter degrades, and then aggregates, to produce humic substances (HSs). HSs are a core product of—and a crucial indicator of—the maturation of compost that can be used in soil amendments. The formation of HSs is affected by the characteristics of the raw materials involved, the presence of compost additives, microbial activity, temperature, pH, the C/N ratio, moisture content, oxygen content and particle size, all of which can interact with each other. The formation of HSs is therefore complex. Moreover, it is difficult to identify definitive structures of humic acids (HAs) and fulvic acids (FAs), which are the two major components of HSs. However, HSs represent the same functional groups and structural arrangements, which helps to predict their structures. Functional groups represented by phenol and carboxylic acid groups of HAs and FAs can provide various agronomic functions, such as plant growth enhancement, water and nutrient retention, and disease suppression capacity. Overall, HSs can act as a soil amendment, fertilizer, and plant growth regulator. These functions of HSs enhance the reuse potential of organic waste compost products; however, this requires scientific control of various composting parameters and appropriate application of final products.
... The formed organo-mineral complexes interact further within each other or with soil biota exudates [3,16,17], forming aggregates which hinder fast degradation of soil organic matter [18]. In addition, regular wetting and drying cause separation of organic molecules according to their polarity, i.e. polar and degradable molecules are separated from hydrophobic, microbiologically more stable ones [18,19]. As a result, the stabilization of soils can be considered, among others, as a result of continuous interplay between water (physicochemical contribution) and soil microorganisms (microbiological contribution), both processes taking simultaneously part on soil organic and inorganic surfaces. ...
... Therefore, the statistical significance of results reported in this work is even higher. Correlation between TML and moisture evaporation confirmed that water binding is one of the key factors regulating microbiological transformation of soils and thereby the soil forming processes [19,33] as well. In principle, water evaporated up to 150°C can be adsorbed on functional groups of soil organic matter [34,35], physically and chemically bound on clay minerals [36] or it can be physically trapped in the soil pores [37][38][39]. ...
Properties and compositions of soils originating
from different sources usually vary, depending largely on
the conditions of soil forming processes and parent mate-
rials. Our previous investigations of soils from contrasting
localities showed linear correlations between carbon
dioxide produced by soil microorganisms and thermal mass
losses of air-dried soils recorded using thermogravimetry.
The correlations were observed at temperatures corre-
sponding both to moisture evaporation and thermal deg-
radation of soil organic matter. In this work, those soils
were combined into one group and the correlation analysis
was repeated using both linear and power functions.
Whereas the linear dependency between respiration and
water evaporation was confirmed; the connection between
respiration and thermal decay of organic matter appeared to
follow power function. These findings indicate the exis-
tence of fundamental unifying principles in soil forming
processes, in terms of water binding and clay-dependent
organic carbon sequestration, notwithstanding the fact, that
soils develop under contrasting conditions. Additional soils
were analyzed in order to test the applicability of obtained
models for prediction of soil respiration using thermo-
gravimetry. The results indicate a promising potential of
this method mainly for soils originating from areas undis-
turbed by anthropogenic activity.
... Ultrasonic velocity in combination with the density measurement allowed for the determination of adiabatic compressibility, which was used to determine the hydration water in a set of chemically treated lignite HA. The determined values ranged from 0.45 to 0.95 g of water per 1 g of DOM at the concentration of HS 0.25 g/L [192]. Interestingly, these values are similar to those reported by Kučerík et al. [193] in a study on IHSS standard HS using differential scanning calorimetry. ...
Natural organic matter, including humic substances (HS), comprises complex secondary structures with no defined covalent chemical bonds and stabilized by inter- and intra-molecular interactions, such as hydrogen bonding, Van der Waal’s forces, and pi-pi interactions. The latest view describes HS aggregates as a hydrogel-like structure comprised by a hydrophobic core of aromatic residues surrounded by polar and amphiphilic molecules akin a self-assembled soft material. A different view is based on the classification of this material as either mass or surface fractals. The former is intended as made by the clustering of macromolecules generating dendritic networks, while the latter have been modelled in terms of a solvent-impenetrable core surrounded by a layer of lyophilic material. This study reviews the evolution of the increasingly refined models that appeared in the literature, all capable to describing the physicochemical properties of HS. All the models are critically examined and revisited in terms of their ability to provide key information on the structural organization of HS. Understanding how the molecular association pathway influences aggregation of HS also provides a key acknowledgment of their role in the environment.
... The SOM is a supramolecular mixture of various molecules, 59 which form domains of various polarities. 60 Additionally, the mixture includes amphiphilic and hydrophobic molecules and moieties, which can adsorb on the PHB surface. The high affinity of liposoluble compounds such as chlorobenzene (CB) and o-nitrochlorobenzene (o-NCB) to PHB were demonstrated in an earlier report. ...
Adverse effects of microplastics on soil abiotic properties have been attributed to changes in the soil structure. Notably, however, the effects on the supramolecular structure of soil organic matter (SOM) have been overlooked, despite their key role in most soil properties. This work accordingly investigated the influence of plastic residues at various concentrations on the SOM supramolecular structure and soil water properties. To model plastic residues of micro-bioplastics, spherical or spherical-like poly-3-hydroxybutyrate (PHB) was used, while polyethylene terephthalate (PET) was used as a model of conventional microplastics. The results suggest that both types of plastic residues affect SOM properties, including physical stability (represented by water molecule bridges), water binding (represented by decreased desorption enthalpy or faster desorption), and the stability of SOM aliphatic crystallites. The results further showed that the polyester-based microplastics and micro-bioplastics affected the SOM abiotic characteristics and that therefore the observed effects cannot be attributed solely to changes in the whole soil structure. Notably, similar adverse effects on SOM were observed for both tested plastic residues, although the effect of PHB was less pronounced compared to that of PET.
... This reversible red-ox behavior accounts for their ability to scavenge reactive oxygen species (ROS), exerting antioxidant action (Aeschbacher et al., 2012;Scott et al., 1998). Structural reorganization of hybrid samples is strongly dependent on water absorption kinetics of HA, which are influenced by their nature as well as by their supramolecular arrangement (Kučerík et al., 2012). Water uptake as well as swelling kinetics of HA_Art and HA_Cof must be slower than that of HA_Man due their greater hydrophobicity, as indicated by NMR data elaboration (Table S1) and to their different pore morphology, as evidenced by N 2 physisorption (Table S2). ...
Humic acids (HA) are considered a promising and inexpensive source for novel multifunctional materials for a huge range of applications. However, aggregation and degradation phenomena in aqueous environment prevent from their full exploitation. A valid strategy to address these issues relies on combining HA moieties at the molecular scale with an inorganic nanostructured component, leading to more stable hybrid nanomaterials with tunable functionalities. Indeed, chemical composition of HA can determine their interactions with the inorganic constituent in the hybrid nanoparticles and consequently affect their overall physico-chemical properties, including their stability and functional properties in aqueous environment. As a fundamental contribution to HA materials-based technology, this study aims at unveiling this aspect. To this purpose, SiO2 nanoparticles have been chosen as a model platform and three different HAs extracted from composted biomasses, manure (HA_Man), artichoke residues (HA_Art) and coffee grounds (HA_Cof), were employed to synthetize hybrid HA-SiO2 nanoparticles through in-situ sol-gel synthesis. Prepared samples were submitted to aging in water to assess their stability.
Furthermore, antioxidant properties and physico-chemical properties of both as prepared and aged samples in aqueous environment were assessed through Scanning Electron Microscopy (SEM), N2 physisorption, Simultaneous Thermogravimetric (TGA) and Differential Scanning Calorimetric (DSC) Analysis, Fourier Transform Infrared (FT-IR), Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR) spectroscopies.
The experimental results highlighted that hybrid HA-SiO2 nanostructures acted as dynamic systems which exhibit structural supramolecular reorganization during aging in aqueous environment with marked effects on physico-chemical and functional properties, including improved antioxidant activity. Obtained results enlighten a unique aspect of interactions between HA and inorganic nanoparticles that could be useful to predict their behavior in aqueous environment.
Furthermore, the proposed approach traces a technological route for the exploitation of organic biowaste in the design of hybrid nanomaterials, providing a significant contribution to the development of waste to wealth strategies based on humic substances.
... Thus, the high activities of the TiO 2 /HA-NDL samples towards the removal of antibiotics could be due to the larger surface areas of the nanohybrids compared to that of bare TiO 2 and, concurrently, to the presence of pores in the hydrated nanohybrids with sizes that are compatible with the molecular dimensions of the investigated antibiotics (Fig. 1). Water uptake of HA moieties could play a key role in influencing the organization of their supramolecular structures, which undergo swelling (Kučerík et al., 2012). This phenomenon is expected to produce larger pore sizes that can host organic molecules. ...
Humic acids (HAs) provide an important bio-source for redox-active materials. Their functional chemical groups are responsible for several properties, such as metal ion chelating activity, adsorption ability towards small molecules and antibacterial activity, through reactive oxygen species (ROS) generation. However, the poor selectivity and instability of HAs in solution hinder their application. A promising strategy for overcoming these disadvantages is conjugation with an inorganic phase, which leads to more stable hybrid nanomaterials with tuneable functionalities. In this study, we demonstrate that hybrid humic acid/titanium dioxide nanostructured materials that are prepared via a versatile in situ hydrothermal strategy display promising antibacterial activity against various pathogens and behave as selective sequestering agents of amoxicillin and tetracycline antibiotics from wastewater. A physicochemical investigation in which a combination of techniques were utilized, which included TEM, BET, ¹³C-CPMAS-NMR, EPR, DLS and SANS, shed light on the structure-property-function relationships of the nanohybrids. The proposed approach traces a technological path for the exploitation of organic biowaste in the design at the molecular scale of multifunctional nanomaterials, which is useful for addressing environmental and health problems that are related to water contamination by antibiotics and pathogens.
... The DSC thermogram of FA (Fig. 2 C) exhibited two endothermic peaks initially a minor curve at 60°C (not interpreted in the graph) it corresponds to the evaporation of incorporated water or adsorbed onto FA (Kucerik et al., 2012). Subsequently,a broad endotherm at 229°C may be attributed to the decomposition of simple and labile organic structures. ...
Fulvic acid, a humic substance often considered as a geopolymer, extracted from different natural resources like Shilajit, Peat, dissolved organic matters, etc. There are several reports of its pharmacological properties and its potential as pharmaceutical excipients. So, we have devised a project to strengthen its claim as a functional excipient. For the given project, lyophilized sample of a dietary supplement product (an aqueous solution of peat derived Fulvic acid) was used. The selected studies were typical for an excipient development like physico-chemical properties, flow properties, compatibility with other excipient and stability studies, non-clinical safety studies (acute toxicity in mice whereas sub-acute toxicity in rats) and some functionality tests. We also suggest its ability to form co-crystal with natural phytochemicals. Our group has already reported its ability to enhance solubility and or bioavailability of different BCS class II drugs. Henceforth, we can propose that Fulvic acid appears a good candidate to be further explored as a functional excipient and should be evaluated as per the remaining recommendations of IPEC, USFDA, and USP.
... The DSC thermogram of FA (Fig. 2 C) exhibited two endothermic peaks initially a minor curve at 60°C (not interpreted in the graph) it corresponds to the evaporation of incorporated water or adsorbed onto FA (Kucerik et al., 2012). Subsequently,a broad endotherm at 229°C may be attributed to the decomposition of simple and labile organic structures. ...
Fulvic acid, a humic substance often considered as a geopolymer, extracted fromdifferent natural resourceslike Shilajit, Peat, dissolved organic matters, etc. There are several reports of its pharmacological properties and its potential as pharmaceutical excipients. So, we have devised a project to strengthen its claim as a functional excipient. For the given project, lyophilized sample of a dietarysupplement product (an aqueous solution of peat derived Fulvic acid) was used. The selected studies were typical for an excipient development like physicochemical properties, flow properties, compatibility with other excipient and stability studies, non-clinical safety studies (acute toxicity in mice whereas sub-acute toxicity in rats) and some functionality tests. We also suggestits ability to form co-crystal with natural phytochemicals.Our group has already reported its ability to enhance solubility and or bioavailability of differentBCS class II drugs. Henceforth, we can propose that Fulvic acid appears agood candidate to be further explored as a functional excipient and should be evaluated as per the remaining recommendations of IPEC, USFDA, and USP.
... . 59 In terms of binding energy, and thus desorption enthalpy, it is expected that water of type 1 is dominated by strong SOM− water interactions, resulting in a comparably high binding energy. In contrast, both WaMB water and phase water are expected to be dominated by water−water interactions, thus having a desorption enthalpy close to that of pure water. ...
Adsorption is the main mechanism of capturing water in soil organic matter (SOM) under arid conditions. This process is assured by hydrophilic sites, which are gradually bridged via water molecule bridges (WaMB). Up to now, the link between WaMB and other types of water molecules occurring in SOM during sorption has not been systematically investigated. In this work, we compared the formation and stability of WaMB simultaneously with the total water content, strength of water binding, kinetics of water sorption in a vacuum dried model SOM (sapric histosol) exposed to different relative water pressures. The same parameters were then determined in SOM exposed to reduced relative pressures. The adsorption resulted in an isotherm with Langmuir-like part below 0.5 relative pressure and BET-like isotherm at higher relative pressures. The WaMB formation was observed at relative pressure of 0.32, which represented the pressure at which Langmuir-like reached a plateau. The binding energy showed a linear decrease with increasing pressure, the slope increased at relative pressure of 0.46. Reduction of relative pressures above relative pressure of 0.46 showed that the water content remained constant, but binding energy was lowered. Conversely, below 0.46 water content decreased, but binding energy was not changed. The results indicate that in SOM exposed to different relative pressures, water exists bound strongly on primary sorption sites (Langmuir-like), water in WaMB, which bridges functional groups and where predominates water-water interactions and phase-water, located in larger pores similar to pure water phase. The latter either surrounds the WaMB and destabilizes it, or for higher water content, links individual WaMB and successively reduces their stabilizing effect. Formation of phase water leads to swelling processes including plasticizing effects and potential volume changes of SOM. Accordingly, the results suggest that at lower water relative pressures WaMB stabilizes the SOM structure, while at higher water relative pressures influence the formation of phase water and thereby the total water content in SOM.
... In the last years, some studies regarding the (de)hydration of materials [48][49][50][51] and more specifically of boron-based materials [52,53] were reported in the literature. The first thermal and kinetic study of the stability and dehydration of boric acid was carried out by Sevim et al. [54], followed by the studies of Balci et al. [55] and Zhang et al. [56]; Sevim et al. [54] have found two thermal processes (by TG and DTA) for which they have assumed two kinetic studies by Coats-Redfern [57] and by Suzuki methods [58]. ...
Boric acid is a very important inorganic material with diverse uses in optoelectronics, petroleum industry, medicine, agriculture, etc. Recently, it was reported on the modification of the crystallization system of the triclinic boric acid (TBA) to hexagonal boric acid (HBA), when a special obtaining procedure is applied. In this paper, the thermokinetic stability of HBA novel material was comparatively studied with respect to the well-known TBA, in air flow atmosphere. Both HBA and TBA undergo a three-step overall thermal decomposition reaction (dehydration), following similar pathways; from the thermodynamic point of view HBA is more stable—decomposition temperatures and ΔH are higher in this case compared to those of TBA. The kinetic analysis was performed by means of the isoconversional methods, for each step of dehydration observing different thermokinetic regions. Higher thermal stability for HBA enables it to be employed at higher temperatures instead of TBA, explaining why the triclinic symmetry enhances the formation actually of the pseudo-hexagonal crystals as crystal habit at the macroscopic scale. Lower thermodynamic and kinetic stability of HBA makes it easier to be activated and thus more instable at the microstructural scale: this is an indirect proof of the TBA presence in the usual surrounding conditions and in the same time raises the probability for HBA molecules to slide onto their crystalline layers due to the lability of hydrogen bonds keeping them and thus increased potential to intercalate with other molecules. The present results open the possibility for promising applications of HBA as a better lubricant for various industries, while in the medical sector superior cleanser, antifungal and antibacterial properties may be foreseen.
... Thus, additional methods should be conducted in order to evaluate the real swelling state of a hydrogel in soil and to verify our assumptions. In this context, the standard one-dimensional 1 H NMR relaxometry should be extended by two-dimensional (2D) correlation maps (T 1 -T 2 , T 2 -D and T 2 -T 2 ) (Hills, 2009;Jaeger et al., 2010;Song et al., 2012) and thermo-analytical methods such as differential scanning calorimetry (DSC) (Kucerik et al., 2012;Schaumann, 2005) as they could possibly discriminate between soil pore water and water in hydrogels due to differences in the rotational mobility and freezing behaviour of water molecules in different environments. ...
Moisture dynamics can favour the formation of stable soil structure by reorientation of soil particles and their gluing by organic structures. While soils are naturally exposed to moisture dynamics, structural stabilization is rather low if the soil organic matter (SOM) or clay content is insufficient. Although it is accepted that hydrogel-forming, swellable organic substances can enhance structural stabilization, the underlying mechanisms are not yet fully understood due to the lack of appropriate testing methods. The objective of our study was to understand the impact of soil moisture dynamics on the swelling properties of an incorporated hydrogel and their implications for soil structural properties. A physically unstable, silty sand soil was treated with polyacrylic acid (PAA) as highly swellable model polymer and subjected either to drying/remoistening cycles or to constant moisture. At certain measurement points, we investigated swelling processes and water binding using 1H nuclear magnetic resonance relaxometry (1H NMR relaxometry) in order to characterize the state of water entrapped in the hydrogel and soil pores and combined this information with rheological characteristics of the soil sample. Contrary to the untreated soil, the polymer-treated soil revealed both higher deformation (γ) at the yield point and higher maximum shear stress (τmax), which reacted dynamically, but not reversibly on moisture dynamics and water redistribution. Structural stability clearly increased with the proportion of PAA-associated water assessed by 1H NMR relaxometry. This relation suggests that swelling–shrinking processes in the hydrogel could explain the hysteretic and time-dependent nature of hydrogel-induced soil structural stabilization. All in all, the combination of 1H NMR relaxometry and rheology will help to investigate mechanisms governing the development of soil structural stability and SOM-associated water in dependence of environmental dynamics.
... KHA, KRHA30N, KRHA40N, KRHA50N, KRHA5P, and KRHA10P) were found to lie relatively high, i.e. between 0.45 and 0.95 grams of water per gram of humate (Figure 6), similar in magnitude to those found for hyaluronan, which is considered to be the most hydrated polysaccharide (Davies et al. 1982;Průšová et al. 2010). This was probably a consequence the high porosity of the humic aggregates (Drastík et al. 2013;Kučerík et al. 2012): the water trapped in their interior contributed to the measured hydration value. ...
The positive effect of humic acids on the growth of plant roots is well known, however, the mechanisms and role of their physical structure in these processes have not been fully explained yet. In this work, South-Moravian lignite was oxidized by means of nitric acid and hydrogen peroxide to produce a set of regenerated humic acids. The elemental composition, solid state stability and solution characteristics were determined and correlated in vitro with their biological activity. A modified hydroponic method was applied to determine the effects of their potassium salts on Zea mays seedlings roots with respect to the plant weight, root length, root division, and starch and protein content. The relations between the determined parameters were evaluated through Principal Component Analysis and Pearson's correlation coefficients. The results indicated that the most important factor determining the biological activity of South-Moravian lignite potassium humates is related to the nature of self-assemblies, while the chemical composition had no direct connection with the root growth of Zea mays seedlings. It was demonstrated a controlled processing that provided humic substances with different chemical and physicochemical properties and variable biological activity.
... Linear dependences were obtained for all polysaccharides measured in this study. The linear behavior is typical for hydrophilic biopolymers (e.g., [34]) while it differs in comparison with mixtures of amphiphilic and hydrophobic molecules for example humic acids [35]. ...
The hydration of cellulose, chitosan, schizophyllan, hyaluronan, and carboxymethyl cellulose was studied using differential scanning calorimetry (DSC). In the first part, the classical freezing/thawing approach was used to determine the amount of non-freezing water. The inconsistency in enthalpies obtained during crystallization and melting of freezable water was discussed with respect to the DSC experimental conditions. Our interpretation questions the recent conclusions about competitive processes occurring during melting which are hypothesized to influence the determined melting enthalpy. In the second part, the hydration and drying were studied using the evaporation enthalpy of water. The dry mass normalized dependency of vaporization enthalpy on water content confirmed an abrupt break at low water content in hyaluronan sample which was attributed to the sudden appearance of a parallel process taking part during the drying. The rest of polysaccharide samples showed only a linear decrease in evaporation enthalpy. The renormalization of enthalpies by the water content revealed the increase in evaporation enthalpy with decreasing water content in most samples which was ascribed to the strong interaction between polysaccharide and water. The exceptions were carboxymethyl cellulose which showed a decrease in evaporation enthalpy. This indicates the existence of a simultaneous process occurring during drying, but unlike in hyaluronan, the processes do not appear abruptly but accompany the evaporation in the wide concentration range. Comparison of determined hydration numbers showed that part of non-freezing water in hyaluronan is not bound to sorption sites but occurs presumably in small temporary pores. In contrast, water-soluble schizophyllan forms temporary pores as well but presumably with higher dimension and the non-freezing water is formed mostly by water molecules interacting with sorption sites.
Engineered and anthropogenic nanoparticles represent a new type of pollutants. Up until now, many studies have reported its adverse effect on biota, but the potential influence on the properties and functions of environmental compartments has largely been ignored. In this work, the effect of Pt nanoparticles on the functions and properties of model soil organic matter has been studied. Using differential scanning calorimetry and molecular modeling, the effect of a wide range of 3 nm Pt nanoparticles concentrations on water holding capacity, the strength of water binding, the stability of water molecule bridges and the content of aliphatic crystallites was studied. It was found that strong hydration of the nanoparticles influences the 3D water structural network and acts as kosmotropic agents (structure-forming) in water bridges and as chaotropic agents (i.e. water destructuring) in larger water volumes. Contrarily, the interaction with soil organic matter moieties partially eliminates these effects. As a result, the 3 nm Pt nanoparticles decreased the evaporation enthalpy of water in soil organic matter and supported soil desiccation. They also increased the strength of water molecule bridges and increased the soil structural rigidity even at low concentrations. Additionally, at high concentrations, they decreased the water content in soil organic matter and induced the aliphatic moieties' crystallization. It is concluded that the small-sized Pt nanoparticles, and perhaps other types as well, may affect the local physicochemical processes in soils and may consequently contribute to enhanced evapotranspiration and deterioration of soil functions.
Natural organic matter (NOM) is an important component in many near-surface geochemical environments, and its properties are greatly affected by the incorporation of water. Because of its importance, the macroscopic behavior and effects of water in NOM and soil organic matter (SOM) have been extensively studied using a wide range of experimental and computational methods. The molecular scale structural and dynamical behavior of water in these materials, however, is less well understood. This paper presents a variable temperature ²H NMR and XRD study of water in Suwannee River NOM and its fulvic acid (FA) and humic acid (HA) fractions that provides new insight into the dynamical behavior of structurally different types of water and exchangeable hydrogen environments in NOM. The results provide a basis for future studies of more complex natural organic materials and the interaction of organic materials with mineral surfaces. Room temperature ²H NMR spectra of samples hydrated in ²H2O and then dehydrated, distinguish ²H2O molecules that are in rapid reorientational motion (correlation times, νc > 10⁵ Hz), ²H exchanged onto carboxylic sites of the NOM that do not undergo rapid reorientation at frequencies >∼10³ Hz, and ²H exchanged onto phenolic and possibly other alcohol sites of the NOM that undergoes rapid, but anisotropic, dynamical reorientation. For samples exposed to water and not dried, the XRD results collected at temperatures from 173 to 298 K show the formation of ice-1h in samples exposed to 100% relative humidity (R.H.) but not in samples exposed to 43% R.H. ²H NMR of those samples collected at temperatures from 313 K to 173 K show the presence of multiple sites. Near room temperature, the spectra contain a narrow resonance for mobile water undergoing rapid isotropic motion, and a broader symmetrical resonance probably due to a combination of more dynamically restricted water molecules and ²H exchanged onto phenolic and alcohol functional groups undergoing rapid anisotropic motion. The 43% R.H. samples also yield a broader, quadrupole-dominated, resonance for ²H exchanged onto functional groups of the NOM. With decreasing temperature the resonances for dynamically restricted water molecules and ²H exchanged onto phenolic and alcohol functional groups become broader, reflecting a decreasing rate of exchange between the water molecules and functional groups and a decreasing rate of reorientation of the ²H2O molecules. The formation of ice-1h is directly reflected in the ²H spectra of the 100% R.H. samples as a resonance with a quadrupole coupling constant (QCC) of ∼180 kHz. For the 43% R.H. samples, there is also a broad, poorly resolved resonance with typical QCCs of ∼180 kHz for which the relative signal intensity increases with decreasing temperature. This signal represents ²H2O molecules that are not crystallized in ice-1h but have greatly reduced reorientation frequencies at low temperature and a hydrogen bonding network with hydrogen bond strengths similar to, but somewhat weaker than, ice-1h. Such molecules are also likely to be present in the 100% R.H. samples. At both R.H.s, some of the ²H2O molecules do not freeze and retain their isotropic motion down to 173 K, the lowest temperature investigated.
Biohydrogels such as microbial exudates and root-derived mucilage are soil-born cross-linked polymers, able to form porous three-dimensional networks during water uptake. The gel effect is the variation of soil properties, such as soil hydrology and soil structural stability, resulting from biohydrogel swelling in soil. Conventionally, soil–water–hydrogel interactions are investigated by measuring soil bulk properties such as water retention curves and porosity, without further analyzing the effect of biohydrogel phases in soil on a quantitative basis. Therefore, the evaluation of advanced and novel methods for the characterization of biohydrogel phases in soil and soil–water–hydrogel interactions is necessary. This review evaluates currently available methods for their potential to analyze processes associated to the gel effect.
A promising approach to investigate the spatio-temporal distribution of biohydrogel phases in porous media is based on Nuclear Magnetic Resonance (NMR) such as 1H-NMR relaxometry, as well as on imaging techniques such as Environmental Scanning Electron Microscopy (ESEM). Especially NMR techniques enable the identification of different water populations based on their differences in the relaxation, and thus the mobility of water molecules in biohydrogels and non-gel water in soil pores.
Rheology measures the flow behavior of biohydrogels, providing information on the structural behavior of the hydrogel network and its gelling mechanism. Soil rheology further quantifies the effect of the biohydrogel phases on the interactions between soil particles, and thus the impact on soil microstructural stability. However, rheology does not elucidate the spatio-temporal distribution and structural state of biohydrogel phases in soil.
All in all, a systematic combination of rheology, NMR and suitable imaging methods seems promising and necessary in order to elucidate the still widely unknown gel effect in soil.
Physicochemical aging of soil organic matter is
assured by the dynamic character of weak interactions
stabilizing its supramolecular structure. However, aging is
difficult to monitor, due to low organic matter content in
most soils and relatively large time constants. In order to
overcome those problems, a model soil, sapric histosol,
was exposed to the accelerated aging after a short heating
event to 110 �C, and its thermal characteristics were
monitored over several months. Classical and temperature
modulated differential scanning calorimetry, microcalori-
metry and solid-state NMR were used to elucidate the
character of involved transitions. The heating event caused
separation of an initially broad transition into two pro-
cesses; a melting, which showed almost no response on the
previous heating and a step transition, which is associated
with the disruption of water molecule bridges (WaMB)
between molecular segments of organic matter. Both pro-
cesses are preceded by a preparatory phase, starting at
subambient temperatures, in which aliphatic domains
probably recrystallize and water molecules condensate
forming WaMB stabilizing the physical structure of sapric
histosol. The aliphatic moieties showed a particular
behavior reflected in higher imperfection in crystallite
structure upon slow cooling, which was attributed to their interaction with surrounding porous and heterogeneous
structures. The results show that soil organic matter aging,
considered as a natural process driven by thermodynamic
principles, is caused by successive development of WaMB.
This is potentially accompanied by recrystallization of
aliphatic structures and both processes lead to higher
physicochemical stability of soil organic matter.
Thermal analysis is primarily used in the field of materials science, but has a long history in the geosciences. Soil organic
matter (SOM) has received a great deal of recent scientific interest because of its role in the global carbon cycle. Conventional
methods of characterizing SOM quality are unsatisfactory because they do not adequately capture the complete quality continuum
that SOM comprises or the various mechanisms that act to stabilize it in the soil matrix. Thermal analysis techniques have
the potential to capture this quality continuum, but are dependent on numerous experimental conditions that limit the comparability
of results among different studies. Published methodology on thermal analysis of soils and sediments has largely focused on
the characterization of the mineral component, while the organic component has received little attention. We tested several
experimental conditions for their effects on the exothermic region of curves generated by thermal analysis of easily dispersed
soil clay fractions and non-protected light-density particulate organic matter fractions isolated from the surface horizon
of a forest soil. Results were found to be highly repeatable but strongly sensitive to crucible material, heating rate, and
sample amount, and relatively insensitive to the use of a reference material. Thermal analysis is an important addition to
the set of analytical tools used to characterize SOM quality because it provides direct, quantitative information of the energy
potentially available for microbial metabolism. However, users will need to balance the needs of specific scientific objectives
with the need for standardized methods and comparability between studies.
Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H2O molecules by using 1H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1 – T2 and T2 – D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H2O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5 – 50 kJ mol-1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soils.
Biological transformation of organic matter in soil is a crucial factor affecting the global carbon cycle. In order to understand these complex processes, soils must be investigated by a combination of various methods. This study compares the dynamics of biological mineralization of soil organic matter (SOM) determined via CO2 evolution during an 80-day laboratory incubation with their thermo-oxidative stability determined by thermogravimetry (TG). Thirty-three soil samples, originating from a wide range of geological and vegetation conditions from various German national parks were studied. The results showed a correlation between the amount and rate of respired CO2 and thermal mass losses of air-dried, conditioned soils occurring around 100 °C with linear coefficients of determination up to R
2 = 0.85. Further, correlation of soil respiration with thermal mass losses around 260 °C confirmed previous observations. The comparison of TG profiles from incubated and non-incubated soils underlined the importance of thermal mass losses in these two temperature intervals. Incubated soils had reduced thermal mass losses above 240 °C and conversely an increased mass loss at 100–120 °C. Furthermore, the accurate determination of soil properties by TG such as soil organic carbon content was confirmed, and it was shown that it can be applied to a wider range of carbon contents as was previously thought. It was concluded that results of thermal analysis could be a helpful starting point for estimation of soil respiration and for development of methods revealing processes in soils.
Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H2O molecules by using 1H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1 – T2 and T2 – D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H2O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5 – 50 kJ mol-1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soils
Water in sludge appears to be of four kinds; free water which freezes at normal freezing temperatures; interstitial water, which freezes at lower temperature due to high dissolved solids concentrations; vicinal water which is associated with solid surfaces and freezes only at very low temperatures; and water of hydration, which does not enter the ice crystal and which can be removed from the sludge only by thermal means. Using the classical technique of freezing in dilatometers, unfrozen water is measured in sludge at different temperatures and at different solids concentrations. Not all water appears to be frozen even down to −30°C. At low solids concentrations, where the sludge does not form large flocs, the only unfrozen water is most likely vicinal water and the water of hydration. At intermediate solids concentrations, the flocs capture the interstitial water which does not freeze, apparently due to its high dissolved solids concentration. At high solids concentrations, the interstitial water is squeezed out of the flocs and only the vicinal water and the water of hydration remain unfrozen. It is not possible to remove vicinal water or the water of hydration by mechanical means, but it is theoretically possible to remove the interstitial and free water. A knowledge of these fractions of water can provide practical limits of mechanical dewatering.
By studying the drying characteristic curve, the moisture in sludge is classified into four categories: free moisture, interstitial moisture, surface moisture and bound moisture. The effects of three dewatering procedures: gravity drainage, vacuum filtration, and centrifugation, as well as chemical conditioning by a cationic polymer, and physical conditioning by freeze-thaw on the moisture distribution, are investigated. It is found that the dewatering procedures studied by only remove part of the free and interstitial moisture; surface and bound moisture are not affected. Part of the free and interstitial moisture also remains with the sludge cake, which can be considered as the inherent inefficiency of the dewatering process. The complete removal of all the free moisture can be considered as the theoretical best performance any mechanical dewatering device can achieve. Polymer addition is found to improve the dewaterability of the sludge by reducing the inherent inefficiency, primarily by reducing the amount of free moisture retained in the cake. Freeze-thaw is found to effect the removal of free, interstitial and surface moisture, bringing about a dramatic increase in dewaterability. The treated sludge cake drains readily and retains no free moisture.
While the dewatering of wastewater sludges has received considerable research attention, it has been assumed that the water continuum surrounding the sludge particles has the physical properties of bulk water. This paper suggests that such an assumption may not be valid. The existence of vicinal water, consisting of ordered and layered water molecules on the surfaces of submerged solids, is demonstrated using research from various disciplines. The meaning of 'bound water' as used in sludge technology is discussed, and it is shown that bound water can be defined in several ways, depending on the test used. It seems reasonable that bound water as it is usually defined actually consists of three different types of water-water captured in the interstitial spaces within flocs and within cells, vicinal water on the surfaces of solids, and water of hydration. Only some of the interstitial water can be removed by mechanical dewatering. Because of the large surface area of sludge particles, including living cells, it is likely that much of the bound water is vicinal water, and this cannot be removed mechanically. The determination of the various fractions of these waters may lead to a better understanding of mechanical sludge dewatering.
Water in sludge appears to be of four kinds; free water which freezes at normal freezing temperatures; interstitial water, which freezes at lower temperature due to high dissolved solids concentrations; vicinal water which is associated with solid surfaces and freezes only at very low temperatures; and water of hydration, which does not enter the ice crystal and which can be removed from the sludge only by thermal means. Using the classical technique of freezing in dtlatometers, unfrozen water is measured in sludge at different temperatures and at different solids concentrations. Not all water appears to be frozen even down to −30°C. At low solids concentrations, where the sludge does not form large flocs, the only unfrozen water is most likely vicinal water and the water of hydration. At intermediate solids concentrations, the flocs capture the interstitial water which does not freeze, apparently due to its high dissolved solids concentration. At high solids concentrations, the interstitial water is squeezed out of the flocs and only the vicinal water and the water of hydration remain unfrozen. It is not possible to remove vicinal water or the water of hydration by mechanical means, but it is theoretically possible to remove the interstitial and free water. A knowledge of these fractions of water can provide practical limits of mechanical dewatering.
The ability of hylan, the formaldehyde cross-linked derivative of hyaluronan, to interact with water has been studied using differential scanning calorimetry (DSC). Three types of water can be distinguished: non-freezing, freezing-bound and free. When the water content of the system is increased, even by up to 10%, almost all the water remains in the freezing-bound state, with a ΔH value less than free water. Several metastable states of water can be detected within the structured hylan-water matrix, indicative of defects in the frozen-bound ice structure. The maximum amount of non-freezing water, intimately associated with the hydrophilic groups of hylan, corresponds to 13 mol water per disaccharide unit of the hyaluronan chain. The large capacity shown by hyaluronan entangled networks to build water into their structure could also be responsible for their unusually high viscosity and elasticity after the onset of entanglement. Such viscoelastic properties are the basis for their use in viscosupplementation of arthritic diseased joints.
The thermodynamic stability of lignite humic acids (sodium salt) aggregates was studied by high resolution ultrasonic spectroscopy within the temperature interval from 5 to 90°C. The changes in differential ultrasonic velocity (U12) showed strong differences among humic solutions within the concentration range from 0.005 to 10 g L−1. Measurement revealed several transitions which were attributed to the weakening of humic secondary structure. Concentration around 1 g L−1 seemed to be a limit under which the change of the prevalence and importance of hydration occurred. Above this concentration the difference in U12 decreased following the temperature increase which was explained as a dominance of hydrophilic hydration. In contrast, below this concentration, the temperature dependence of U12 resulted in increasing tendency which was attributed to the prevalence of hydrophobic hydration, i.e. uncovering of apolar groups towards surrounding water. Additional experiments in which the humic sample was modified by hydrochloric acid resulted in a slight structural stabilization which lead to the conclusion that humic micelle-like subaggregates form an open-layer assemblies easily accessible for interaction with an extraneous molecule. That was partly verified by addition of propionic acid which brought about even larger reconformation of humic aggregates and exhibition of polar groups towards hydration water.
The reversible changes in humate solutions induced by elevated temperatures provided the evidence about the existence of significant physical interactions among humic molecules resulting in formation of various kinds of aggregates. The nature of aggregates, mainly the stability and conformation, strongly depends on the concentration. Evidently, the changes observed in this work cannot be simply explained as expansions or conformational changes of macromolecular coils.
Under field conditions, soil is subjected to continuous moisture variations. This affects the state of swelling of soil organic matter. Although it is expected that the state of swelling of SOM alters other soil parameters and such effects have recently been published, very little is known about the process of swelling of soil organic matter itself.
In this contribution, results from a study on the swelling of soil organic matter by several methods are presented with a special emphasis on 1H-NMR Relaxation. We investigated peat samples and soil samples from Ah horizons and observed a gradual change in the pore size distribution and the amount of absorbed water during swelling, which went on for at least two to three weeks. The change could be described by a first order process with time constants up to 6 days. We also found an effect of the initial state before moistening, of the final water content and of the hydration time on the extractibility of PAH. These observations are supplemented by other studies showing an effect of the state of moisture on binding and sorption of organic compounds to soil.
The results show that swelling of soil organic matter is a slow process and lasts for at least two to three weeks. It influences at least the pore size distribution and the state of binding of organic chemicals in soil. Thus, swelling has to be taken into consideration when sorption and transport phenomena under field conditions are a central point of interest. The method of 1H-NMR Relaxation is an important and powerful method for the investigation of swelling of soil organic matter in whole soil samples.
The hydration kinetics of soil organic matter (SOM) are influential factors for transport and sorption processes in soil. Nevertheless, our knowledge about wetting and swelling processes, which both control the overall hydration kinetics, is limited. In this study, we observed the hydration process of actually water repellent and wettable soil samples with three independent methods. The rate of water uptake by water repellent samples was distinctly lower than that of wettable samples when the water was supplied in liquid phase, but was comparable when water was supplied in gas phase. Gravimetric measurements of the water uptake and 1H NMR Relaxometry showed that wetting of water repellent soils may last up to three weeks. This duration is distinctly longer than the WDPT of the samples, which consequently only reflects the first wetting step of the soil surface and does not consider infiltration of larger amounts of water. Since the achievement of equilibrium conditions is a slow process, the hydration kinetics of SOM may control transport and sorption kinetics in water repellent soils. Differences in the freezing, melting and evaporation processes of soil water of actually water repellent and wettable soil samples, observed by Differential Scanning Calorimetry (DSC), are most probably only a consequence of different water contents under field conditions. Consequently, the DSC measurements provided no evidence of a general difference in the way of water binding in water repellent and wettable soil samples.
Site-specific interactions between organic compounds and soil organic matter (SOM) may occur at surface sites or limited interior sites; limited sites can have either a specific force component (e.g., hydrogen bonding) or a nonspecific force component (van der Waals) or both. This research addresses sorption specificity to gain an understanding of SOM structure. Sorption of phenol, pyridine, and atrazine on Pahokee peat, a mineral-free SOM endmember, was measured as a function of solute activity in hydrated and dehydrated conditions. Sorption of phenol and pyridine from water at low solute activities was the same as from n-hexadecane; sorption at high solute activities was much greater from water than from n-hexadecane. Uptake of atrazine at high activities was not influenced by peat hydration. Sorption isotherms measured in nonaqueous systems were more nonlinear than those measured in water. The increase in sorption on hydrated peat at high pyridine and phenol activities is attributed to an increase in sorption sites resulting from penetration of solute molecules between polar peat contacts which are either previously solvated by water or solvated during penetration of the solute. High solute activities are neces sary for simultaneous disruption of multiple points of contact in the hydrated SOM macromolecular complex.
The scientific understanding of the molecular size and shape of humic substances (HS) is critically reviewed. The traditional view that HS are polymers in soil is not substantiated by any direct evidence but is assumed only on the basis of laboratory experiments with model molecules and unwarranted results produced by incorrectly applying either analytical procedures or mathematical treatments developed for purified and undisputed biopolymers. A large body of evidence shows an alternative understanding of the conformational nature of HS, which should be regarded as supramolecular associations of self-assembling heterogeneous and relatively small molecules deriving from the degradation and decomposition of dead biological material. A major aspect of the humic supramolecular conformation is that it is stabilized predominantly by weak dispersive forces instead of covalent linkages. Hydrophobic (van der Waals, π-π, CH-π) and hydrogen bonds are responsible for the apparent large molecular size of HS, the former becoming more important with the increase of pH. This innovative understanding of the nature of HS implies a further development of the science and technology for the control of the chemistry and reactivity of natural organic matter in the soil and the environment.
Phase transition behaviour of sorbed water in Konjac mannan (KM)-water system with various water contents (Wc) was investigated using differential scanning calorimetry (DSC). The measurements were performed repeatedly for 3 cycles. At least six types of sorbed water together with glassy water can be identified in the KM-water system: (1) non-freezing water (Wnf), (2) four types of freezing bound water (Wfb), designated Wfb1, Wfb2, Wfb2* and Wfb3 and (3) free water (Wf). Glassy water was closely related to Wnf and the amount of glassy water was influenced by the cooling rate. The cold crystallization (Tcc) of glassy water caused an under estimation of the weight of sorbed water when calculated for the first cycle. Thereafter, the effect of Tcc was eliminated by cyclic measurements and the transition of Wfb2* could be readily observed. The proportion of each type of sorbed water changed with increasing Wc. The equivalent value of Wnf per pyranose ring was ca. 5.2 (mol/mol). Wfb1, Wfb2 and Wfb2* were the Wfb that were influenced by interaction with the KM matrix at lower Wc regions and were transferred to Wf in the high Wc regions. Wfb3 was strongly bound water, maintaining interaction with KM chains even in the high Wc region; the equivalent value of Wfb3 per pyranose ring was ca. 1.4 (mol/mol). Most of the sorbed water in the system with high Wc was held as Wf.
In this study, hydration of a peat sample was investigated with differential scanning calorimetry (DSC) in terms of glass transition behavior and the formation of freezable and unfreezable water. Special attention was drawn to the development of these characteristics in the course of hydration and to plasticizing and antiplasticizing effects of water. Freezable water was formed above a water content threshold of Θcrit = (23 ± 7)% and revealed structured melting peaks indicating freezable bulk-like water and freezable bound water. The freezable bound water revealed a broad, kinetically controlled melting endotherm, and the melting barrier increased with increasing hydration time. Glass transitions were found in between 43 °C and 68 °C with a change in heat capacity of ΔC = (0.13 ± 0.08) J g−1 K−1. Glass transition behavior does not fully match the theoretical expectations and is linked with water binding. Water reveals a short-term plasticizing function in the range of days as well as a slow antiplasticizing function in the range of weeks or even months. The findings are consistent with the hydrogen bond based cross-linking model (HBCL) suggested in a previous study. Non-equilibrium and matrix relaxation are considered the rule rather than the exception in nature and underline the ecological relevance of hydration, the relevance for sorption and transport phenomena was well as possibly for soil development.
One of the most valuable ecological potentials of soil organic matter (SOM) is based on its highly dynamic nature, which enables flexible reactions to a variety of environmental conditions. SOM controls a large part of the processes occurring at biogeochemical interfaces in soil and may contribute to sequestration of organic chemicals. This contribution focuses on dynamics in SOM from a viewpoint that regards SOM as an amorphous matrix, in which weak intermolecular interactions rather than covalent binding are considered. This view is based on the conception of SOM as a supramolecular assembly, which was first suggested in studies by A. Piccolo and R. L. Wershaw. Based on our recent results on thermal analysis of SOM, our central hypothesis is that regardless of the individual molecular mass, SOM undergoes physicochemical matrix aging, driven by dynamics in intermolecular cross-linking via bridges of water molecules. In this study, we have made the first efforts to evaluate the water-bridge hypothesis with proton NMR relaxation and proton wideline NMR. The results clearly indicate changes in relaxation time and proton line shape induced by manipulations of thermal history, which suggests an increase in side-chain mobility upon heating that remains after cooling. Side-chain mobility slowly decreases again within at least 1–2 weeks. Our current results strongly suggest even longer aging periods. This observation supports the hypothesis that water molecules bridge molecular segments of SOM. The bridges may be easily disrupted, while re-formation is slow due to diffusion limitation in the SOM matrix.
The freezing and melting of water in semi-dilute (0.5–3.0%) solutions of the polysaccharide hyaluronanhave been investigated by modulated differential scanning calorimetry.
High molecular weight hyaluronan inhibited nucleation of ice and significantly depressed thefreezing temperature in a dynamic scan conducted at −3.0°C min−1. Low molecular weight hyaluronan had a weaker and more variable effect on nucleation. Theeffects on nucleation, especially by the high molecular weight hyaluronan, are attributed tothe influence of a hyaluronan network on the formation of critical ice nuclei.
Both high and low molecular weight hyaluronan reduced the melting temperature of ice by 0.4–1.1°C, depending on concentration. The enthalpy change associated with this transitionwas significantly reduced. If all of the enthalpy difference is attributed to the presence of non-freezing water, approximately 3.65 g water/g hyaluronan would be non-freezing. This result appears incompatible with published studies on hyaluronan samples of low water content. An alternative hypothesis and quantitative approach to analysis of the data are suggested. The data are interpreted in terms of a small amount of non-freezing water, and amuch larger boundary layer of water surrounding hyaluronan chains, which has slightly altered thermodynamic properties relative to those of bulk water. The boundary layer water behaves similarly to water trapped in small pores in solid materials and hydrogels.
Water molecules in hydrogels were classified into three categories according to phase transition behavior; non-freezing, freezing
bound and free water. Melting, crystallization, and glass transition of water in hydrogels reflected the state of the water
interacting with polysaccharides. Freezing bound water formed metastable ice by slow cooling and formed amorphous ice by quenching.
From the isothermal crystallization measurement, nucleation rate and crystal growth rate were obtained. The crystal growth
rate of freezing bound water was about ten times slower than that of free water. The DSC characterization of water in hydrogels
was summarized.
In Übereinstimmung mit dem Phasenum wandlungsverhalten werden Wassermoleküle in Hydrogelen in drei Kategorien eingestuft;
nicht gefrierendes, gefrierendes gebundenes und freies Wasser. Das Schmelzen, die Kristallisation und die Glasumwandlung von
Wasser in Hydrogen wiederspiegeln den Zustand von Wasser, welches in Wechselwirkung mit Polysacchariden tritt. Gefrierendes
gebundenes Wasser bildet metastabiles Eis durch langsames Abkühlen und amorphes Eis durch Abschrecken. Anhand isothermer Kristallisationsmessungen
wurden Keimbildungsgeschwindigkeit und Kristallwachstumsgeschwindigkeit erhalten. Die Kristallwachstumsgeschwindigkeit von
gefrierendem gebundenem Wasser liegt zehnmal niedriger als die von freiem Wasser.
Various natural and synthetic polymers with hydrophilic groups, such as hydroxyl, carboxyl and carbonyl groups, have either a strong or weak interaction with water. Thermal properties of polymers and water are both markedly influenced through this interaction. The first-order phase transition of water fractions closely associated with the polymer matrix is usually impossible to observe. Such fractions are called non-freezing water. Less closely associated water fractions exhibit melting/crystallization, showing considerable supercooling and significantly smaller enthalpy than that of bulk water. These water fractions are referred to as freezing bound water. The sum of the freezing bound and non-freezing water fractions is the bound water content. Water, whose melting/crystallization temperature and enthalpy are not significantly different from those of normal (bulk) water, is designated as freezing water. Bound water in the water-insoluble hydrophilic polymers, such as cellulose, lignin and poly(hydroxystyrene) derivatives, breaks hydrogen bonding between the hydroxyl groups of the polymers. The bound water content depends on the chemical and high-order structure of each polymer. Aqueous solutions of water-soluble polyelectrolytes, such as hyaluronic acid, gellan gum, xanthan gum and poly(vinyl alcohol) form gels above a threshold concentration. In the above gels, water mostly exists as the freezing bound water, playing an important role in the junction zone formation. It has also been observed that various kinds of polysaccharide polyelectrolytes with mono- and divalent cations, and other polyelectrolytes, such as polystyrene sulfonate, form thermotropic/lyotropic liquid crystals in the water content, ranging from 0.5 to ca. 3.0 g of water/g of polymer.
Differential scanning calorimetry (DSC) was used to determine the number of water molecules in the hydration shell of hyaluronan of different molecular weights and counterions. First, traditional experiments including freezing/thawing of free water in semi-diluted solutions were carried out leading to the determination of melting enthalpy of freezable water. Non-freezing water was determined using extrapolation to zero enthalpy. For sodium hyaluronan within the molecular weight range between 100 and 740 kDa the hydration shell was determined as 0.74 g g−1 HYA. A larger hydration shell containing 0.84 and 0.82 g g−1 HYA was determined for hyaluronan of 1390 kDa in its sodium and protonized form, respectively. Second, melting enthalpy of freezing water was further studied applying water evaporation experiments. Resulted plot of enthalpy vs concentration indicated an additional heat evolution process which occurs at specific concentration and decreases the measured evaporation enthalpy. The heat evolution was attributed to the mutual approaching of hyaluronan molecular chains, their mutual interactions and formation of the ordered hyaluronan structure which starts immediately when the hydration water is desorbed from the hyaluronan surface. The concentration at which the process occurred was related to “non-evaporable water” which was determined as 0.31–0.38 g g−1 for sodium hyaluronan and 0.84 g g−1 for its protonized form. The second approach provides additional information enabling a deeper insight into the problem of hyaluronan hydration.
The stabilizing effect of water molecule bridges on polar regions in humic substances (HSs) has been investigated by means of molecular dynamics (MD) simulations. The purpose of these investigations was to show the effect of water molecular bridges (WAMB) for cross-linking distant locations of hydrophilic groups. For this purpose, a tetramer of undecanoid fatty acids connected to a network of water molecules has been constructed, which serve as a model for spatially fixed aliphatic chains in HSs terminated by a polar (carboxyl) group. The effect of environmental polarity has been investigated by using solvents of low and medium polarity in force-field MD. A nonpolar environment simulated by n-hexane was chosen to mimic the stability of WAMB in a hydrophilic hotspot surrounded by a nonpolar environment, while the more polar acetonitrile environment was chosen to simulate a more even distribution of polarity around the carboxylic groups and the water molecules. The dynamics simulations show that the rigidity of the oligomer chains is significantly enhanced as soon as the water cluster is large enough to comprise all four carboxyl groups. Increasing the temperature leads to evaporization processes which destabilize the rigidity of the tetramer-water cluster. Embedding it into the nonpolar environment introduces a pronounced cage effect which significantly impedes removal of water molecules from the cluster region. On the other hand, a polar environment facilitates their diffusion from the polar region. One important consequence of these simulations is that although the local water network is the stabilizing factor for the organic matter matrix, the degree of stabilization is additionally affected by the presence of nonpolar surroundings.
Freezing of solutions including disaccharides (trehalose, sucrose, and maltose) has been investigated by microscopic observations of freeze-fractured replicas using FE-TEM. Three typical features were observed: the smooth surface considered as the ice crystal, fine particles as the precipitated disaccharide molecules, and remaining part as the glass state of the solution. The expanded observations of fine-particle and its distribution investigations suggested that it was larger than 10 nm in size and averaged approximately 20-30 nm in diameter. The smallest particle was estimated to include several hundred disaccharide molecules. Based on systematic observations of trehalose solutions regarding concentrations and freezing rates, we concluded that ice crystal growth was inhibited by trehalose molecules. Since the ice crystal size reduced exponentially with increase in trehalose concentration, we could control ice crystal size formed in the frozen material. The growth inhibition of ice crystals with trehalose resulted both from a reduction in the free water in the solution due to a significant hydration effect and from an enhancement of nucleation of the ice crystals. It was confirmed that trehalose was more effective than the other disaccharide solutions examined for inhibiting the growth of ice crystals.
We examine sorption of pyridine by soil organic matter (SOM) from different organic media including n-hexadecane, acetonitrile, acetone, and n-hexadecane mixtures with either acetonitrile or acetone and compare it with sorption from water. By using an activity-based comparison, we distinguish between solvent-assisted and solvent-competitive sorption behavior. Pyridine was selected because it forms strong complexes with phenolic and carboxylic groups, such that site interactions should dominate interactions in SOM. It is anticipated that pyridine sorption will be illustrative of the importance of disrupting strong interactions in a condensed, shrunken SOM phase for many organic compounds. It was generally found that activity-normalized pyridine uptake was assisted by polar solvent molecules rather than suppressed due to competition. An explanation is tendered on the basis of our earlier hypothesis of water-assisted disruption of polar SOM contacts. Certain polar moieties of dry SOM are unavailable for compound sorption due to strong interactions between them. By penetrating SOM structure, solvent molecules (and water) solvate (hydrate) polar moieties creating new sorption sites. Solvent molecules must solvate both moieties of the polar contact, such that the driving force for solvent-assisted sorption is solvation of the partner of the disrupted contact that does not directly interact with the sorbate.
According to a recent conceptual model for hydration-assisted sorption of organic compounds in natural organic matter (NOM), certain polar moieties of dry NOM are unavailable for compound sorption due to strong intra- and intermolecular NOM interactions. Water molecules solvate these moieties creating new sorption sites at solvated contacts. It is expected that the greater a compound's ability to undergo specific interactions with NOM, the greater will be the hydration-assisted sorption effect, because penetration of compounds into solvated contacts must involve competition with water at the solvated contact. To test this model, we compare the hydration effect on sorption kinetics and equilibrium for 4 compounds with differing abilities to undergo specific interactions with NOM. Sorption measured on Pahokee peat in aqueous systems was fast compared with n-hexadecane (dry) systems. No concentration effect on attainment of sorption equilibrium was observed. m-Nitrophenol exhibited the greatest hydration-assisted sorption effect, benzyl alcohol showed an intermediate effect and acetophenone and nitrobenzene showed no hydration-assisted sorption, on an activity scale. The extent of hydration-assisted sorption effect correlates with compound ability to undergo specific interactions. These results support the conceptual model and demonstrate the importance of polar NOM noncovalent links in organizing the NOM phase and in controlling the hydration effect on sorption of organic compounds.
The dewatering of residual sludges is a current problem due to the huge production of this waste. Activated sludges are generally hard to dewater, and the design and the control of the separation operations are often quite difficult. In order to better understand this problem, pertinent indices are needed. The knowledge of how water is distributed within activated sludge is an interesting approach. Current literature dealing with this topic is, however, relatively difficult to apply. This work presents a review of the problem of moisture distribution classification and measurement within activated sludge. The main techniques used for this analysis are compared and discussed in detail. The estimation of the water binding energy is also extremely commented upon. Finally, the paper discusses the utility of this type of analysis to examine the conditioning and dewatering of activated sludge.
This contribution aims to expand the macromolecular view of fractionated natural organic matter (NOM)to organic matter in whole soils. It focuses on glass transition behavior of whole soil organic matter (SOM) and its interrelation with water through use of differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Three processes of structural relaxation related to macromolecular mobility were distinguished. Process I occurs in thermally pretreated and very low water-content samples and corresponds to classic glass transition behavior. Process II occurs in water-containing samples, where water is believed to act as an antiplasticizing agent in the peat at water contents below 12%, causing decreased macromolecular mobility and increased glass transition temperature. We suggestthe formation of hydrogen bond-based cross-links being responsible for this antiplasticizing effect. Process III represents a slow swelling process induced by water uptake with a time constant of swelling in the order of days, with water acting as a plasticizing agent. Results from this work are of particular importance for environmental systems as changes in environmental conditions (e.g., water content, temperature) may induce slow structural relaxation processes in NOM over periods of time ranging from days to weeks. These influences on NOM macromolecular mobility lead to continuous changes in physicochemical properties that may greatly influence sorbate-sorbent interactions in surface and subsurface environments.
A critical examination of published data obtained primarily from recent nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization-mass spectrometry, and pyrolysis studies reveals an evolving new view of the molecular structure of soil humic substances. According to the new view, humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules intimately associated with a humic substance, such that they cannot be separated effectively by chemical or physical methods. Thus biomolecules strongly bound within humic fractions are by definition humic components, a conclusion that necessarily calls into question key biogeochemical pathways traditionally thought to be required for the formation of humic substances. Further research is needed to elucidate the intermolecular interactions that link humic components into supramolecular associations and to establish the pathways by which these associations emerge from the degradation of organic litter.
Sorption isotherms of phenol on Pahokee Peat as model natural organic matter(NOM) have been measured at different partial NOM hydrations (water activities). Sorption at a given phenol solution concentration is substantially smaller in the lower water activity systems than in higher water activity systems, reaching a sorption maximum at an intermediate water activity. Such cooperative phenol uptake at interim water activities as a result of NOM hydration (hydration-assisted sorption) is predicted by the link solvation model (LSM), whereby water enhances the disruption of the noncovalently cross-linked NOM structure, creating new sorption sites. The LSM is herein extended to account for the observed direct relationship between isotherm linearity and water activity. The extended LSM provides an excellent description of phenol sorption isotherm data at nine different NOM hydration levels with a single set of three unique parameters. The successful fit of the LSM supports the conceptual model of creation of new sorption sites for sorbate molecules in the hydrated organic matter sorbent, accompanied by competition for those new sites by water molecules at high water activities.
Do water molecules bridge soil organic matter molecule segments? Glass transitions in peat: their relevance and the impact of water
- Ge Schaumann
- Bertmer
- Ge Schaumann
- Leboeuf
Schaumann GE, Bertmer M. Do water molecules bridge soil organic matter molecule segments? Eur J Soil Sci. 2008;59: 423–9. 458 J. Kučerík et al. 123 18. Schaumann GE, Leboeuf EJ. Glass transitions in peat: their relevance and the impact of water. Environ Sci Technol. 2005;39: 800–6.
The thermodynamic stability and molecular feature of lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy Morphological investigation of disaccharide molecules for growth inhibition of ice crystals
- J H Kučerík
- P Bursáková
- Pekař
- T Uchida
- M Nagayama
- T Shibayama
- Gohara
Kučerík J, Č echlovská H, Bursáková P, Pekař M. The thermodynamic stability and molecular feature of lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy. J Therm Anal Cal. 2009;96:637–43. 24. Uchida T, Nagayama M, Shibayama T, Gohara K. Morphological investigation of disaccharide molecules for growth inhibition of ice crystals. J Cryst Growth. 2007;299:125–35.
Hydration characteristics of the cross-linked hyaluronan derivative hylan
- S Takigami
- M Takigami
- G O Phillips
Takigami S, Takigami M, Phillips GO. Hydration characteristics
of the cross-linked hyaluronan derivative hylan. Carbohydr
Polym. 1993;22:153-60.