Article

Structural features of resorcinol-formaldehyde resin chars and interfacial behavior of water co-adsorbed with low-molecular weight organics

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Abstract

Products of resorcinol-formaldehyde resin carbonization (chars) are characterized by different morphology (particle shape and sizes) and texture (specific surface area, pore volume and pore size distribution) depending on water content during resin polymerization. At a low amount of water (Cw = 37.8 wt.%) during synthesis resulting in strongly cross-linked polymers, carbonization gives nonporous particles. An increase in the water content to 62.7 wt.% results in a nano/mesoporous char, but if Cw = 73.3 wt.%, a char is purely nanoporous. Despite these textural differences, the Raman spectra of all the chars are similar because of the similarity in the structure of their carbon sheets with a significant contribution of sp3 C atoms. However, the difference in the spatial organization of the carbon sheet stacks in the particles results in the significant differences in the textural and morphological characteristics and in the adsorption properties of chars with respect to water, methane, benzene, hydrogen, methylene chloride, and dimethylsulfoxide.

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... The properties of the final carbon materials are mainly determined by the structure of polymeric precursors prepared by polycondensation of resorcinol with formaldehyde in the aqueous media. During RFR preparation, water can play a role of both a solvent and a template regulating the textural characteristics of RFR and chars [14]. ...
... The D and G bands of RFR chars (Fig. 10a) include both narrow and broad components [14] related to more ordered and disordered carbon structures, respectively. The broad component of the G band can be assigned to amorphous graphite-like structures [48], which are out of the graphene planes (see, e.g., Fig. 4b). ...
... It can be assigned to mixed sp 2 -sp 3 bonding or to the C-C and C C stretching vibration modes of polyene-like structures [55], or structures with sp 3 C atoms in defects out of the planes. There is a certain difference in the D/G ratio for pure RFR chars [14] and ZnO doped RFR chars (Fig. 10), since the D band intensity increases for local structures with ZnO abundance (compare D band intensity for RFC2(1) and RFC2(2) in Fig. 10a). ...
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f polymerization of resorcinol-formaldehyde (RF) mixtures in water with addition of different amounts of zinc acetate and then carbonization of dried gels are studied to prepare ZnO doped chars. Zinc acetate as a catalyst of resorcinol-formaldehyde polycondensation affects structural features of the RF resin (RFR) and, therefore, the texture of chars prepared from Zn-doped RFR. The ZnO doped chars are characterized using thermogravimetry, low temperature nitrogen adsorption/desorption, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). At a relatively high content of zinc acetate ( Polycondensation polymerization of resorchial-formaldehyde (RF) mixtures in water with addition of different amounts of zinc acetate and then carbonization of dried gels are studied to prepare ZnO doped chars. Zinc acetate as a catalyst of resorcinol-formaldehyde polycondensation affects structural features of the RF resin (RFR) and, therefore, the texture of chars prepared from Zn-doped RFR. The ZnO doped chars are characterized using thermogravimetry, low temperature nitrogen adsorption/desorption, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). At a relatively high content of zinc acetate (1 mol per 10-40 mol of resorcinol) in the reaction mixture, the formation of crystallites of ZnO (zincite) occurs in a shape of straight nanorods of 20-130 nm in diameter and 1-3 mu m in length. At a small content of zinc acetate(1 mol per 100-500 mol of resorcinol), ZnO in composites is XRD amorphous and does not form individual particles. The ZnO doped chars are pure nanoporous at a minimal ZnO content and nano-mesoporousor nano-meso-macroporous at a higher ZnO content.
... The resorcinol-formaldehyde polymer was synthesized using the poly-condensation of resorcinol and formaldehyde in the aqueous solution. The morphological, structural and textural characteristics of polymers, as well the chars, depend strongly on the concentration of reagents, the presence of a catalyst and water content during co-polymerization [31]. Fumed Al 2 O 3 used as a catalyst can affect the structural features of polymer composites and, consequently, the texture of the chars. ...
... The defect degree of crystallite carbon was determined by measuring the integrated D to G peak area ratio (A D /A G ), via deconvolution of the spectra using Lorentzian functions. The obtained A D /A G values are in the range of 0.8, which is 3 times lower than disordered structures synthesized by carbonization of pure resorcinol-formaldehyde at different content of water [31]. These results indicate that alumina does not have a significant effect on carbon crystallinity degree in the selected concentration range of the as-obtained composites, but promotes the ordering in the carbon structures compared to unmodified chars. ...
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... It was established that the structure and properties of the polymer depend strongly on conditions of the process and concentrations of the reagents. These factors influence the morphological and textural characteristics of both the untreated hybrid polymeric composites and their chars [14,15]. ...
... The morphology and texture of chars depend on the water content during the polymeric composite formation [15]. An increase in the water content leads to a decrease in the mesoporosity due to the formation of small-sized nanoparticles that leads to enhanced microporosity (Fig. 5). ...
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A series of organics mixed with kaolinite as well corresponding chars were synthesized by modification of kaolinite with resorcinol-formaldehyde polymer and subsequent carbonization under inert atmosphere at 800 °C. The hybrid organo-clay nanocomposites were prepared via two routes: (i) rapid simultaneous copolymerization of the components, (ii) through prolonged contact of monomer solutions with clay in order to improve morphological and structural characteristics of nanocomposites to be used as adsorbents. The composites were characterized using X-ray diffraction, Raman spectroscopy, thermal analysis (with simultaneous DSC), nitrogen adsorption-desorption, scanning electronic microscopy and small-angle X-ray scattering (SAXS) methods. It was shown that the nanohybrid polymeric composites are micro- and mesoporous. The adsorption ability of both polymer/kaolinite and carbonized composites was investigated using such cationic dyes as methylene blue (MB) and rhodamine 6G. There is an increase in adsorption affinity of nanocomposites toward MB. A low adsorption of rhodamine 6G could be explained by steric effects in narrow pores for relatively large molecules. The obtained results show that suggested synthesis method considerably improves the morphology and textural characteristics of nanocomposites. The characteristics of polymer/kaolinite and related carbon/metakaolinite nanocomposites confirm that the developed routes are promising to obtain high-performance adsorbents.
... Thus, the structure and properties of the RFR depend strongly on the conditions, at which the process occurs, and concentrations of the reagents. These factors influence the morphological and textural characteristics of the chars [18,19]. ...
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Carbon xerogel microspheres were synthesized by inverse emulsion polymerization of resorcinol with formaldehyde, followed by pyrolysis at 900 °C under nitrogen atmosphere. We have studied the effect of various synthesis parameters, including dilution ratio and hydrophilic−lipophilic balance (HLB) of nonionic surfactants, on the size and morphology of resulting structures. The average particle size of carbon microspheres could be modulated from 1 to 28 μm by varying the dilution ratio over 3 orders of magnitude. Increase in the HLB value and the amount of surfactants produced a variety of dense carbon, but open-architecture fractal-like structures. Three different methods of stirring, namely, magnetic, mechanical, and ultrasonication were applied during the inverse emulsification to produce carbon xerogel microstructures. Formation of a wide spectrum of nonporous carbon particle morphologies, including the highly branched, hierarchical microparticles, by tuning the synthesis conditions may have potential applications in printing technology, controlled drug delivery, biosensors, and carbon-based microelectromechanical systems (C-MEMS) including bio-MEMS.
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After curing, phenol-formaldehyde resins were post-cured at 160°C, and then carbonized and graphitized from 300°C to 2400°C. The structure of the resulting carbonized and graphitized resins were studied using X-ray diffraction and Raman spectroscopy. Thermal fragmentation and condensation of the polymer structure occurred above 300°C. The crystal size of the cured phenolic resins increased with an increase in temperature. The crystal size increased from 0.997 nm to 1.085 nm when the heat-treatment temperature rose from 160°C to 500°C. Above 600°C, the original resin structures disappeared completely. Below 1000°C, the stack size (Lc) increased very slowly. The values increased from 0.992 to 1.192 nm when the heattreatment temperature rose from 600°C to 1000°C. Above 1000°C, the stack size showed an increase with the increase in heat-treatment temperature. The values increased from 1.192 to 2.366 nm when the temperature rose from 1000°C to 2400°C. The carbonized and graphitized resins were characterized using Raman spectroscopy. The Raman spectrra were recorded between 700 and 2000 cm−1. Below 400°C, there were no carbon structures in the Raman spectra analysis. Above 500°C, G and D bands appeared. Raman spectra confirmed progressive structure ordering as heat-treatment temperature increased. The frequency of the G band of all carbonized and graphitized samples shifted to 1600 cm−1 from the 1582 cm−1 of graphite. At the same temperature, the D band shifted to 1330 cm−1 from the 1357 cm−1 of the imperfect carbon. In the curve fitting analysis of the Raman spectra, a Gaussian shaped band centered at 1165 cm−1 was included. This band has not been described before in the literature and is attributed to disordered structures, which are formed from the original polymeric structures. These polymeric structures formed unknown disordered structures and remained in the carbonized phenolic resins. Above 1800°C, this band disappeared completely. But, a weak peak is present near 1620 cm−1. This indicated that those disoriented molecules and some disordered carbons were removed as volatiles or repacked into the glassy carbon structures during graphitization. The carbonized and graphitized phenolic resins were found to correspond to low order sp2 bonded carbon, but cannot be considered as truly glassy or amorphous carbon materials since they have some degree of order in the basal plane.
Article
Recent progress in syntheses of porous carbons with designed pore architecture has rejuvenated the field of carbon chemistry and promises to provide new advanced materials. In order to reap the full benefit of designer carbons, it is necessary to develop chemistries for functionalizing the porous carbon surfaces. This Review examines methods of functionalizing porous carbon through direct incorporation of heteroatoms in the carbon synthesis, surface oxidation and activation, halogenation, sulfonation, grafting, attachment of nanoparticles and surface coating with polymers. Methods of characterizing the functionalized carbon materials and applications that benefit from functionalized nanoporous carbons with designed architecture are also highlighted.
Article
The near-i.r. and i.r. spectra of various coals have been measured using a diffuse reflectance method. In the near-i.r. region, anthracite and some bituminous coals were observed to have broad absorption bands whose intensities increased with wavenumber. Brown coals did not show such bands. From the size-effect of coal powders on the diffuse reflectance spectra, the broad absorption bands can be attributed to the real electronic transitions of polycondensed aromatic hydrocarbons. The intensity of the broad absorption band increases with the rank of coalification and degree of carbonization. Since the broad bands change with coal treatments, including solvent extraction and maceral separation, they afford a new measure of the coal study.
Article
The behaviour of water and water/organic mixtures adsorbed onto activated microporous carbons or a carbon adsorbent with narrow intraparticle micropores and broad mesopores and macropores between nanoparticles was studied using low-temperature adsorption method and 1H NMR spectroscopy with layer-by-layer freezing-out of liquids at 190–273 K. These investigations revealed concentration-dependent effects of benzene, DMSO, acetone, chloroform, methane and acetonitrile on the characteristics of adsorbed water and the influence of this water on the interfacial behaviour of adsorbed organics. The influence of organics causes the structural and energetic differentiations of adsorbed water. The latter can be displaced by organics from micropores into broader pores and/or form mixture with polar solvents in meso and macropores. Freezing of adsorbed water can affect the adsorbent structure because ice crystallites have a larger size than that of liquid water droplets that lead to changes in the behaviour of adsorbed water/organic mixtures observed by the 1H NMR and adsorption methods.
Article
A brief overview on the preparation and properties of resorcinol–formaldehyde organic and carbon gels reveals very interesting features about their structural and performance characteristics. The resulting nanostructure was very sensitive to the various synthesis and processing conditions. This leads to a remarkable potential for designing and tailoring these materials to fit specific applications. Based on step-by-step comparisons of the published studies, approximate generalizations on the specific roles the synthesis and processing conditions play on the final properties are provided. Overall, resorcinol–formaldehyde organic gels undergo two main stages during synthesis. The first stage is associated with the preparation of the sol mixture, and the subsequent gelation and curing of the gel. The second stage is associated with the drying of the wet gel. The most important factors that affect the properties of the organic gel during the first stage are the catalyst concentration, the initial gel pH, and the concentration of the solids in the sol. The most important factors that affect the properties of the organic gel during the second stage are the drying procedure (e.g., super- or subcritical drying), and the difference between the surface tensions of the solvent before and after drying. The corresponding resorcinol–formaldehyde carbon gels are produced from the organic gels during a third stage, which is associated with carbonization or activation. Depending on the conditions, carbonization and activation both impact the structural and performance characteristics significantly.
Article
Three sets of activated carbons (ACs) were prepared with the same precursor but activated differently (by CO2 or water vapour) with various burn-off levels. The ACs demonstrate increased deviation of the pore shape from the slitshaped model with increasing burn-off and contributions of pores of different sizes depending on the activation type. Significant re-arrangement of adsorption complexes, especially of the Van der Waals type characteristic for nonpolar or weakly polar adsorbates (H2, CH4, CH2Cl2, CHCl3), occurs in both micropores and mesopores of ACs with decreasing temperature. The behaviour of their mixtures with water and DMSO can strongly differ from that of individual adsorbates. KeywordsActivated carbons–CO2 activation–H2O activation–Structural characteristics–Particle morphology–Interfacial behaviour
Article
The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer clusters. The covalent crosslinking of these clusters produces gels which are processed under supercritical conditions to obtain low density, organic aerogels ( 0.1 g cm–3). The aerogels are transparent, dark red in colour, and consist of interconnected colloidal-like particles with diameters of approximately 10 nm. The polymerization mechanism, structure and properties of the resorcinol-formaldehyde aerogels are similar to the sol-gel processing of silica.
Article
A method is proposed for the calculation of the distribution functions for the pore size, the adsorption energy, and the fractal dimensionality with due regard to the multicomponent nature of complex adsorbents based on a combined approach, including calculation of the constants of the equations in the approximation of the local adsorption isotherm for individual adsorbents with allowance for their specific characteristics (e.g., the type of pores). The integral equation, in which the kernel is the sum of the local adsorption isotherms with weighting factors determining the accessibility of the various phases in the multicomponent adsorbent, is solved using the method of constrained regularization.
Article
Raman spectra of activated carbon materials have been investigated by a peak-deconvolution technique. It has been found as a result of our fitting trials that four Gaussians and a linear background are necessary and enough to reproduce the spectral data throughout our experiment, with a pair of relatively sharp peaks at about 1600  cm <sup>-1</sup> and about 1350  cm <sup>-1</sup>, namely G1 and D1, and a pair of relatively broad peaks around 1560  cm <sup>-1</sup> and 1340  cm <sup>-1</sup>, namely G2 and D2. From the characteristic behavior of these paired peaks, it has been concluded that the structure of activated carbon materials is schematically classified into two parts. The former part, represented by sharp G1 and G2 peaks, arises from winding short basal planes with bond angle order, while the latter, by broad G2 and D2 peaks, sp<sup>2</sup> clusters like a- Cs with bond angle disorder. We have found the peak intensity ratio of G2 to G1, the I(G1)/I(G2) ratio, as a useful parameter expressing the relative content of the disorder part to the order part in the activated carbons, revealing the structural changes induced by anneal or activations. Since the changes of fitting parameters including the I(G2)/I(G1) ratio were completely opposite for H <sub>2</sub> O and KOH activation, it has been clarified that the part with bond angle disorder is selectively removed or become ordered by H <sub>2</sub> O activation, whereas induced by KOH activation, though both activation methods yield similar surface area. © 2002 American Institute of Physics.
Article
Spherical resorcinol–formaldehyde (RF) aerogel particles were synthesized by emulsion polymerization of resorcinol with formaldehyde in a slightly basic aqueous solution, followed by supercritical drying with carbon dioxide. RF carbon aerogel particles were prepared by carbonizing of the RF aerogel particles at a high temperature under a nitrogen atmosphere. By changing the viscosity of the RF sol added to the cyclohexane containing a surface-active agent for preparation of the spherical RF hydrogels, we investigated the influence of the apparent viscosity of the RF sol on the size of the generated RF carbon aerogel particles. We could successfully prepare the RF carbon aerogel particles with a truly spherical shape and control their size in the range from about 10 to 500 μm by changing the apparent viscosity of the RF sol. The spherical RF carbon aerogel particles with an average diameter of 20 μm have a BET surface area of about 800 m2/g and a uniform mesopore radius of 1.78 nm.
Article
The sol–gel transition of organic gels prepared by polycondensation of resorcinol (R) with formaldehyde (F) in presence of sodium carbonate (C) was monitored by small amplitude oscillatory measurements, at a single frequency. The gelation time (tg) was determined from the evolution of the storage (G′) and loss (G″) moduli versus time. The influence of two synthesis variables, the resorcinol/sodium carbonate ratio (R/C) and the synthesis temperature (T), was investigated. The gelation time was found to decrease with increasing synthesis temperature and decreasing R/C ratio. The apparent activation energy of the reactional system leading to the gelation, calculated from the gelation times obtained between 50 and 90 °C, was found to be close to 80 kJ mol−1 and independent of the R/C ratio.
Article
The distribution of coke inside the pellets of several industrial spent hydroprocessing catalysts was analyzed using Raman spectroscopy. The shape of the coke profiles gives us information on the deactivation mechanism and the magnitude of diffusion limitations. Samples taken at the end of run showed the most pronounced coke profiles. Typical M-shaped profiles observed in a guard bed catalyst suggest a sequential deactivation mechanism and a strong diffusion resistance. Consequently, it is concluded that near the end of life the catalyst effectiveness factor can be significantly reduced by coke deposition.
Article
A nano-porous carbon was prepared by carbonization of a novel synthetic resorcinol–formaldehyde (RF) polymer without any additional activation process, and used as electrode materials for aqueous electric double-layer capacitors (EDLCs). This novel RF polymer-based carbon shows high specific surface area with large carbonization yield (∼50%), and excellent specific dc capacitance over 200 F/g. The effect of R/CA ratio (i.e. molar ratio of resorcinol to curing agent) on the specific surface area, pore size distribution, nanostructure and electrochemical capacitance was studied, respectively. The results showed that a higher R/CA ratio yielded carbon with higher specific surface area, larger specific capacitance, and broader pore size distribution. The highest specific surface area of 825 m2/g and specific capacitance exceeding 200 F/g were found to occur at R/CA ratio of 50. The electrochemical behaviors were characterized by means of galvanostatic charging/discharging, cycle voltammetry and impedance spectroscopy. The correlation between electrochemical properties and pore structure was investigated. Due to the excellent capacitance properties, low cost and simple process, this RF polymer-derived carbon would be a promising material for EDLCs applications.
Article
Spherical resorcinol–formaldehyde (RF) aerogel particles were synthesized by emulsion polymerization of resorcinol with formaldehyde in a slightly basic aqueous solution, followed by supercritical drying with carbon dioxide. The carbon aerogel particles were prepared by carbonizing the RF aerogel particles at a high temperature under a nitrogen atmosphere. We investigated the influence of the surface-active agents applied upon emulsion polymerization on the form, the size, and the characteristic pore structure of the generated carbon aerogel particles. We found an important relationship between the surface-active agents and the pore structure of the carbon aerogel particles; a lower hydrophile–lipophile balance (HLB) value of the surface active agent leaded to large micro and mesopore volumes and also a large specific surface area in the generated spherical carbon aerogel particles.
Article
Non-graphitic carbon materials produced by pyrolyzing wood at temperatures from 400 to 2400 °C and various types of commercial carbon fibers were examined by X-ray diffraction and Raman spectroscopy. The specimens cover a wide range of crystallite sizes La, in particular also very small sizes below 2 nm. The X-ray data were evaluated using the Scherrer equation and by an advanced approach using full curve fitting. The ratio of the D/G band intensities was determined from the Raman data by different evaluation techniques. A critical assessment of the classical linear relationship between 1/La and the D/G ratio shows that the relationship breaks down for crystallite sizes below 2 nm in accordance with recent theoretical predictions. The results are compared with data from the literature, showing that there are additional discrepancies between the data from various carbon types at large La due to different methods of data evaluation.
Article
Deviations of a pore shape from a slitlike one were analyzed for a variety of carbon adsorbents on the basis of calculations of pore size distributions (PSDs) with respect to the pore volume (fV(x)) used for estimation of the PSDs related to the specific surface area (fS(x)) applying several models of pores: individual slitlike pores and mixtures of slitlike and cylindrical pores and gaps between spherical particles. The use of complex pore models allows us to diminish the difference between SBET and the specific surface area (Ssum) calculated from fS(x).
Article
Carbon materials have attracted intense interests as electrode materials for electrochemical capacitors, because of their high surface area, electrical conductivity, chemical stability and low cost. Activated carbons produced by different activation processes from various precursors are the most widely used electrodes. Recently, with the rapid growth of nanotechnology, nanostructured electrode materials, such as carbon nanotubes and template-synthesized porous carbons have been developed. Their unique electrical properties and well controlled pore sizes and structures facilitate fast ion and electron transportation. In order to further improve the power and energy densities of the capacitors, carbon-based composites combining electrical double layer capacitors (EDLC)-capacitance and pseudo-capacitance have been explored. They show not only enhanced capacitance, but as well good cyclability. In this review, recent progresses on carbon-based electrode materials are summarized, including activated carbons, carbon nanotubes, and template-synthesized porous carbons, in particular mesoporous carbons. Their advantages and disadvantages as electrochemical capacitors are discussed. At the end of this review, the future trends of electrochemical capacitors with high energy and power are proposed.
Article
An overview on the preparation and properties of resorcinol-formaldehyde (RF) organic and carbon gels reveals the fascinating and remarkably flexible properties of RF carbon and organic gels and how these properties are related to the synthesis and processing conditions. The structural properties can be easily tailored by rigidly controlling such conditions. However, slight variations in some conditions may cause drastic variations in the structural characteristics, and hence properties. Therefore, the effects of different conditions must be well-understood before attempting to tailor organic or carbon gels to specific applications. The most important factors that affect the properties of an organic gel are the precursor concentrations, the catalyst type and concentration, the time and temperature of curing, and the drying method. In addition to these factors, characteristics of activated carbon gels also depend on the pyrolysis temperature and the activation method. These conditions impact the structural and performance characteristics significantly.
Article
The comparative analysis of the most widely used methods of mesoporosity characterization of two activated carbon fibers is presented. Not only the older methods are used, i.e. Barrett, Joyner and Halenda (BJH), Dubinin (the so-called first variant-D-1ST and the so-called second variant-D-2ND), Dollimore and Heal (DH), and Pierce (P) but the recently developed ones, i.e. the method of Nguyen and Do (ND) and that developed by Do (Do) are also applied. Additionally, the method of the characterization of fractality is put to use (fractal analog of FHH isotherm). The results are compared and discussed. (C) 2002 Elsevier Science B.V. All fights reserved.
Article
A carefully chosen set of experimental techniques applied to porous media characterization provides results that can be much greater than the sum of the individual parts. The inter-relation and complementarity of a number of techniques will be considered. NMR cryoporometry provides a valuable method of pore size measurement. An NMR method that is more widely used to assess pore dimensions relies on relaxation time analysis of a liquid that fills the pores and the enhanced relaxation that occurs in a liquid at the solid/liquid interface. Thermoporometry, a method based on the application of Differential Scanning Calorimetry (DSC), is closely related to cryoporometry, but employs a different set of assumptions to evaluate pore size distributions. Comparison of the results obtained on the same samples using all these methods together with gas adsorption serves to validate the methods and provide significantly more information about surface-fluid interaction and the behavior of nano-scale material within pores than each method employed in isolation. Technique developments will be discussed and applications of these methods to ideal silicas will be used to illustrate their power, particularly in combination.
Article
The behaviour of water at mosaic hydrophilic/hydrophobic surfaces of different silicas and in biosystems (biomacromolecules, yeast cells, wheat seeds, bone and muscular tissues) was studied in different dispersion media over wide temperature range using 1H NMR spectroscopy with layer-by-layer freezing-out of bulk water (close to 273 K) and interfacial water (180 < T < 273 K), thermally stimulated depolarization current (TSDC) (90 < T < 270 K), infrared (IR) spectroscopy, and quantum chemical methods. Bulk water and water bound to hydrophilic/hydrophobic interfaces can be assigned to different structural types. There are (i) weakly associated interfacial water (1H NMR chemical shift delta(H) = 1.1-1.7 ppm) that can be assigned to high-density water (HDW) with collapsed structure (CS), representing individual molecules in hydrophobic pockets, small clusters and interstitial water with strongly distorted hydrogen bonds or without them, and (ii) strongly associated interfacial water (delta(H) = 4-5 ppm) with larger clusters, nano- and microdomains, and continuous interfacial layer with both HDW and low-density water (LDW). The molecular mobility of weakly associated bound water is higher (because hydrogen bonds are distorted and weakened and their number is smaller than that for strongly associated water) than that of strongly associated bound water (with strong hydrogen bonds but nevertheless weaker than that in ice Ih) that results in the difference in the temperature dependences of the 1H NMR spectra at T < 273 K. These different waters are also appear in changes in the IR and TSDC spectra.
Article
The paper describes the generation of four types of three-dimensional molecular field descriptors or 'field points' as extrema of electrostatic, steric, and hydrophobic fields. These field points are used to define the properties necessary for a molecule to bind in a characteristic way into a specified active site. The hypothesis is that compounds showing a similar field point pattern are likely to bind at the same target site regardless of structure. The methodology to test this idea is illustrated using HIV NNRTI and thrombin ligands and validated across seven other targets. From the in silico comparisons of field point overlays, the experimentally observed binding poses of these ligands in their respective sites can be reproduced from pairwise comparisons.