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Abstract

We describe the effect of three synthetic surfactants (anionic – sodium dodecyl sulfate (SDS), cationic – cetyltrimethylammonium bromide (CTAB) and nonionic – Triton X-100 (TX-100)) on surface properties of the type I calf skin collagen at the air/water interface in acidic solutions (pH 1.8). The protein concentration was fixed at 5 × 10⁻⁶ mol L⁻¹ and the surfactant concentration was varied in the range 5 × 10⁻⁶ mol L⁻¹–1 × 10⁻⁴ mol L⁻¹, producing the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:5, 1:10 and 1:20. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic surface tension and surface dilatational moduli of the mixed adsorption layers. Two spectroscopic techniques: UV–vis spectroscopy and fluorimetry allowed us to determine the effect of the surfactants on the protein structure. The thermodynamic characteristic of the mixtures was studied using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC).

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... Du et al. [18] found that the fluorescence intensity of collagen solutions varied with the types of surfactants. Recent studies by Kezwoń et al. [19,20] involved the effect of surfactants on surface properties of collagen by combination of spectroscopic techniques, calorimetry, and axisymmetric drop shape analysis. Their results demonstrated that the changes of surface activity and rheological properties of collagen solutions depended on the types of surfactants. ...
... It is well known that the interactions between surfactants and proteins involve very complex processes [29]. The changes of three-dimensional structure of proteins induced by surfactants are closely related to surfactants types and concentrations [18][19][20]. Herein, collagen-SDS system is of particular interest because collagen is a well-characterized protein with obvious conformational heat and SDS is a representative of anionic surfactants with appropriate charge density and hydrophobic chain [21]. In addition, SDS interacts more strongly with most proteins compared with cationic surfactants [29]. ...
... It is commonly accepted that the interaction between proteins and SDS are mainly electrostatic and hydrophobic interactions, always resulting in the formation of SDSprotein complex [19]. Besides, many studies further proposed that the binding of SDS with proteins including collagen takes place in two distinct stages [21,32]. ...
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In this communication, sulfate dodecyl sodium (SDS)-induced thermodynamics and conformational changes of collagen were studied. We used ultrasensitive differential scanning calorimetry (US-DSC) to directly monitor the thermal transition of collagen in the presence of SDS. The results show that SDS affects the conformation and thermal stability of collagen very differently depending on its concentrations. At C SDS ≤ 0.05 mM, the enhanced thermal stability of collagen indicates the stabilizing effect by SDS. However, a further increase of SDS leads to the denaturation of collagen, verifying the well-known ability of SDS to unfold proteins. This striking difference in thermodynamics and conformational changes of collagen caused by SDS concentrations can be explained in terms of their interactions. With increasing SDS, the binding of SDS to collagen can be dominated by electrostatic interaction shifting to hydrophobic interaction, and the latter plays a key role in loosening and unfolding the triple-helix structure of collagen. The important finding in the present study is the stabilizing effect of SDS on collagen molecules at extreme low concentration. Graphical abstract
... In contrast, very few studies have been performed exploring the fibrous protein-surfactant systems. Type I collagen, silk fibroin, and keratin are fibrous proteins that have been studied in combination with ionic and non-ionic surfactants (Maldonado et al. 1991;Mandal and Kund 2008;Kezwon et al. 2016;Kezwoń and Wojciechowski 2016;Pan et al. 2016;Park et al. 2014;Dubey et al. 2018). A few studies suggest that the molecular interactions presented by fibrous proteins (collagen, fibroin, keratin) in combination with ionic and non-ionic surfactants are similar to the globular protein-surfactant systems (Lee et al. 2011;Khan et al. 2015, Kezwon et al. 2016Kezwoń and Wojciechowski 2016;Pan et al. 2016). ...
... Type I collagen, silk fibroin, and keratin are fibrous proteins that have been studied in combination with ionic and non-ionic surfactants (Maldonado et al. 1991;Mandal and Kund 2008;Kezwon et al. 2016;Kezwoń and Wojciechowski 2016;Pan et al. 2016;Park et al. 2014;Dubey et al. 2018). A few studies suggest that the molecular interactions presented by fibrous proteins (collagen, fibroin, keratin) in combination with ionic and non-ionic surfactants are similar to the globular protein-surfactant systems (Lee et al. 2011;Khan et al. 2015, Kezwon et al. 2016Kezwoń and Wojciechowski 2016;Pan et al. 2016). Type I collagen interacts with Sodium Dodecyl Sulphate (SDS), Cetyl Trimethyl Ammonium Bromide (CTAB), and Triton X-100 through hydrophobic and electrostatic molecular interactions. ...
... Type I collagen interacts with Sodium Dodecyl Sulphate (SDS), Cetyl Trimethyl Ammonium Bromide (CTAB), and Triton X-100 through hydrophobic and electrostatic molecular interactions. The predominance of a particular molecular interaction depends on the type of surfactant, i.e. surfactants could produce changes in collagen secondary structure (Maldonado et al. 1991;Kezwon et al. 2016;Kezwoń and Wojciechowski 2016). ...
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Macromolecules are essential cellular components in biological systems responsible for performing a large number of functions that are necessary for growth and perseverance of living organisms. Proteins, lipids and carbohydrates are three major classes of biological macromolecules. To predict the structure, function, and behaviour of any cluster of macromolecules, it is necessary to understand the interaction between them and other components through basic principles of chemistry and physics. An important number of macromolecules are present in mixtures with surfactants, where a combination of hydrophobic and electrostatic interactions is responsible for the specific properties of any solution. It has been demonstrated that surfactants can help the formation of helices in some proteins thereby promoting protein structure formation. On the other hand, there is extensive research towards the use of surfactants to solubilize drugs and pharmaceuticals; therefore, it is evident that the interaction between surfactants with macromolecules is important for many applications which includes environmental processes and the pharmaceutical industry. In this review, we describe the properties of different types of surfactants that are relevant for their physicochemical interactions with biological macromolecules, from macromolecules–surfactant complexes to hydrophobic and electrostatic interactions.
... Collagen has partially cationic behavior [42,43] but the dielectric properties of Poly(MMA-co-EA) covalently bonded on the surface of ASC as side chains, are more likely to overcome vigorously due to low electron mobile phase and electrostatic polarization under the influence of the external electric field that is considered here by means of the lowered conductivity of the CME solution in contrast with the other solution consisting of N6 polymer [7,33]. diameter is more likely to increase by increasing the electric field. ...
... Collagen has partially cationic behavior [42,43] but the dielectric properties of Poly(MMA-co-EA) covalently bonded on the surface of ASC as side chains, are more likely to overcome vigorously due to low electron mobile phase and electrostatic polarization under the influence of the external electric field that is considered here by means of the lowered conductivity of the CME solution in contrast with the other solution consisting of N6 polymer [7,33]. We applied coaxial electrospinning to consider the effect of the orientation polarization of the polymers in the core and the shell with a varied capacity of built-in dipoles that are independent of each other, i.e., they can move and align individually [44]. ...
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One step fabrication of the three dimension (3D) fibrous structure of Collagen-g-poly(MMA-co-EA)/Nylon6 was investigated by controlling the experimental conditions during coaxial electrospinning. This 3D fibrous structure is the result of interactions of two polymeric systems with a varied capability to be electrostatically polarized under the influence of the external electric field; the solution with the higher conductivity into the inner spinneret and the solution with the lesser conductivity into the outer capillary of the coaxial needle. This setup was to obtain bimodal fiber fabrication in micro and nanoscale developing a spatial structure; the branches growing off a trunk. The resultant 3D collagen-based fibrous structure has two distinguished configurations: microfibers of 6.9 ± 2.2 µm diameter gap-filled with nanofibers of 216 ± 49 nm diameter. The 3D fibrous structure can be accumulated at an approximate height of 4 cm within 20 min. The mechanism of the 3D fibrous structure and the effect of experimental conditions, the associated hydration degree, water uptake and degradation rate were also investigated. This highly stable 3D fibrous structure has great potential end-uses benefitting from its large surface area and high water uptake which is caused by the high polarity and spatial orientation of collagen-based macrostructure.
... The results can be used to derive the binding isotherm of a protein-surfactant system, facilitating its thermodynamic characterization such as the stoichiometry, enthalpy and entropy of binding, and association constant [33,34]. Differential scanning calorimetry (DSC) is a similar approach to determine the denaturation temperature, enthalpy, and entropy at fixed concentrations [35]. The technique is suitable for studying the equilibrium between the originally folded and denatured conformations of proteins and the stability of protein-surfactant complexes [36]. ...
Article
Protein surfactant (PS) interactions is an essential topic for many fundamental and technological applications such as life science, nanobiotechnology processes, food industry, biodiesel production and drug delivery systems. Several experimental techniques and data analysis approaches have been developed to characterize PS interactions in bulk and at interfaces. However, to evaluate the mechanisms and the level of interactions quantitatively, e.g., PS ratio in complexes, their stability in bulk, and reversibility of their interfacial adsorption, new experimental techniques and protocols are still needed, especially with relevance for in-situ biological conditions. The available standard techniques can provide us with the basic understanding of interactions mainly under static conditions and far from physiological criteria. Detailed measurements at complex interfaces can be formidable due to the sophisticated tools required to carefully probe nanometric phenomena at interfaces, however, without disturbing the adsorbed layer. Tensiometry-based techniques such as drop profile analysis tensiometry (PAT) have been among the most powerful methods for characterizing protein's and surfactant's adsorption layers at interfaces via measuring equilibrium and dynamic interfacial tension and dilational rheology analysis. PAT provides us insightful data such as kinetics mechanisms and isotherms of adsorption and related surface activity parameters. However, the data analysis and interpretation can be challenging for mixed protein–surfactant solutions via standard PAT experimental protocols. The combination of a coaxial double capillary (micro flow exchange system) with drop profile analysis tensiometry (CDC-PAT) is a promising tool to provide valuable results under different competitive adsorption/desorption conditions via novel experimental protocols. CDC-PAT provides unique experimental protocols to exchange the droplet subphase in a continuous dynamic mode during the in-situ analysis of the corresponding interfacial adsorbed layer. The contribution of diffusion/convection mechanisms on the kinetics of the adsorption/desorption processes can also be investigated using CDC-PAT. Here, firstly, we review the commonly available techniques for characterizing protein–surfactant interactions in the bulk phase and at interfaces. Secondly, we give an overview for applications of the coaxial double capillary PAT setup for investigations of mixed protein–surfactant adsorbed layers and address recently developed protocols and analysis procedures. Exploring the competitive sequential adsorption of proteins and surfactants and the reversibility of pre-adsorbed layers via the subphase exchange are the particular experiments we can perform using CDC-PAT. Also the sequential and simultaneous competitive adsorption/desorption processes of some ionic and nonionic surfactants (SDS, CTAB, DTAB, and Triton) and proteins (bovine serum albumin (BSA), lysozyme, and lipase) using CDC-PAT are discussed. Last but not least, the fabrication of micro-nanocomposite layers and membranes are additional applications of CDC-PAT discussed in this work.
... Considering wound dressing as a feasible application of these scaffolds, light barrier properties were analyzed by UV-Vis spectroscopy. As can be seen in Figure 8, control samples showed the characteristic UV light barrier of collagen with an absorbance maximum from 200 to 250 nm, associated with carbonyl, carboxyl and amide groups, and a small peak between 250 and 280 nm, related to chromophores groups of tyrosine and phenylalanine amino acids [52,53]. The addition of THC showed a slight increase of the absorbance in the visible light range (400-800 nm) and a strong increase in the UV range (200-400 nm) due to the absorption peak of THC around 280 nm with a shoulder at 310 nm [54]. ...
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Native collagen doughs were processed using a syringe-based extrusion 3D printer to obtain collagen scaffolds. Before processing, the rheological properties of the doughs were analyzed to determine the optimal 3D printing conditions. Samples showed a high shear-thinning behavior, reported beneficial in the 3D printing process. In addition, tetrahydrocurcumin (THC) was incorporated into the dough formulation and its effect on collagen structure, as well as the resulting scaf-fold's suitability for wound healing applications, were assessed. The denaturation peak observed by differential scanning calorimetry (DSC), along with the images of the scaffolds' surfaces assessed using scanning electron microscopy (SEM), showed that the fibrillar structure of collagen was maintained. These outcomes were correlated with X-ray diffraction (XRD) results, which showed an increase of the lateral packaging of collagen chains was observed in the samples with a THC content up to 4%, while a higher content of THC considerably decreased the structural order of collagen. Furthermore, physical interactions between collagen and THC molecules were observed using Fou-rier transform infrared (FTIR) spectroscopy. Additionally, all samples showed swelling and a controlled release of THC. These results along with the mucoadhesive properties of collagen suggested the potential of these THC-collagen scaffolds as sustained THC delivery systems.
... The surface tension experiment can be explained as diffusion of macromolecules to the surface of a droplet and subsequent film creation on the water-air interface. This concept was used similarly for collagen self-assembly investigation [61,62]. Therefore, it was suggested that aggregates start to diffuse to the droplet surface at CAC1, and the compact film is created onto the interface at CAC2. ...
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The understanding how physicochemical properties of amphiphilic molecules influence the self-assembly process is crucial to control their final nanostructure. Furthermore, the relationship between the supramolecular structure and functional properties is of utmost importance for effective design towards specific applications. The hydrophobically modified hyaluronic acid was investigated as a representative of semi-flexible amphiphilic polyelectrolyte with the tremendous biomedical potential. The essential physicochemical characteristics were extracted from the interplay of multiple techniques such as rheology, fluorescence, dynamic light scattering, surface tension, and small-angle X-ray scattering. The correlation of used techniques allowed us to determine the size of hydrophobic domains and showed that aggregate size decrease with increasing chain flexibility. Furthermore, the ratio between the size of aggregates and hydrophobic domains was found to be crucial for curcumin loading efficiency and in vitro skin penetration. Moreover, critical aggregation concentration was determined using various techniques. However, aggregates were found below these concentrations. The rheological characterization identified different dynamical regimes that can define the preparation and application concentration range. The acquired supramolecular structure-property functions provides valuable information for the design of self-assembled nanostructures.
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Protein-surfactant interactions have been explored for decades owing to their widespread application in the pharmaceutical, food, and cosmetics industries and their importance to biochemical systems. However, they require further study owing to their compositional complexity and the innate limitations of current analytical approaches. In this review, we briefly introduce a series of individual approaches used for the qualitative and quantitative investigation of protein-surfactant interactions, including absorbance- or emission-based spectroscopy, scattering-based spectroscopy, mass spectrometry, calorimetry, computation and microscopy. More importantly, we then compare and evaluate various combinations of these approaches and provide comprehensive critical assessments and comments regarding their application to the advanced study of protein-surfactant interactions at the molecular level.
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Polyetheretherketone (PEEK) is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydrophobic interaction, collagen was cross-linked with N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). EDC/NHS system also contributed to the immobilization of rhBMP-2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.
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Background More and more evidences demonstrate the significance of Signal transducers and activators of transcription 3(STAT3) in oncogenesis and tumor development. However, little systematic researches have been reported on the correlation between STAT3 and thymic epithelial tumor (TET). Methods Expression of STAT3 protein in 80 thymic epithelial tumors was detected by immunohistochemistry (IHC). The difference of STAT3 expression was compared by the χ2 test. Estimation of survival was calculated using the Kaplan-Meier method, and the statistical differences were analyzed using the Log-rank test. Results Positive expression of STAT3 protein was significantly associated with Masaoka staging and WHO histological classification (P < 0.05), but not with age, gender, or tumor size. The rate of postoperative recurrence/metastasis was 33.33% in STAT3-positive tumors, compared with 4.55% in negative ones (P < 0.05). 5-year survival was significantly lower in STAT3-positive subjects (61.11%) than in negative ones (97.73%) (P < 0.01); In patients in Masaoka stage III or IV and WHO B3 or C, 5-year survival rate of subjects positive in STAT3 (35.00%, 35.00%) was statistically lower than that of the negative ones (92.31%, 91.67%). Cox regression analysis revealed that positive expression of STAT3 protein was an independent prognostic factor of thymic epithelial tumors (HR = 9.325, P = 0.044). Conclusion Positive expression of STAT3 protein increases along with the rising malignant degree of thymic epithelial tumors. It may be considered as an independent prognostic parameter with good prognostic value to evaluate the possibility of recurrence/metastasis in patients with thymic epithelial tumor.
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Surface modification of poly(ether ether ketone)(PEEK) was performed to increase the surface wettability. Acrylamide(AAm) was grafted on the surface of PEEK film by ultraviolet grafting to improve the hydrophilicity through the introduction of hydrophilic groups. Then, glutaraldehyde was used to immobilize collagen and hydrolyzed collagen on surface of the material. Fluorescein-labelled collagen was also used to verify the immobilization. The surfaces of PEEK film before and after modification were characterized by contact angle meter, scanning electron microscope, fluorescence spectrophotometer and X-ray photoelectron spectrometer. The results show that the surface morphology and the hydrophilicity are changed significantly after surface modification. Polyacrylamide grated on PEEK has a density of as high as 50.9 μg/cm2. PEEK-g-PAAm becomes hydrophilic with a decreased water contact angle of (22±3)°. Surface immobilized with hydrolyzed collagen labeled with fluorescein isothiocyanate exhibits strong fluorescence effect. Modified films immobilized with collagen showed nitrogen peak, which was not observed for unmodified PEEK film in X-ray photoelectron spectroscopy, indicating the successful immobilization of collagen. The concentration of collagen immobilized on PEEK was determined to be 10.2 μg/cm2.
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Collagen, gelatin and collagen hydrolysate were prepared from bovine limed split wastes by different preparative processes. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the molecular weight distribution of collagen was very narrow (about 200 and 100kDa for β and α chains respectively) compared with those of gelatin (less than 300kDa and wide distribution) and collagen hydrolysate (less than 50kDa and wide distribution). The isoelectric points of collagen, gelatin and collagen hydrolysate were 8.26, 4.88 and 4.54 respectively determined by Zeta potential titration. Circular dichroism (CD) spectra revealed that there were two peaks, a positive peak around 221nm and a negative peak around 192nm for collagen, which are the characteristics of collagen triple helix. However, gelatin and collagen hydrolysate lacked any positive peaks around 220nm, suggesting random coils. The denaturation temperature of collagen was about 37.5°C determined by the viscosity method, the helix-coil transitions for gelatin and collagen hydrolysate were not present in the heating process. Collagen reaggregated to fibrils at 35°C monitored at 313nm. In contrast, gelatin and collagen hydrolysate lost the ability of fibril formation. Collagen was more resistant to trypsin hydrolysis compared with gelatin and collagen hydrolysate. In addition, the collagen membrane exhibited superior features such as higher enthalpy, greater network structure and better physical/mechanical properties compared with those of the gelatin membrane. Therefore, collagen isolated from limed split wastes can be a high value product due to its special characteristics and has many potential future applications in biomaterials, functional additives, cosmetics and pharmaceutical industries.
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We describe the adsorption behaviour and rheological properties of a calf skin type I collagen, and of its hydrolysates obtained using a Clostridium histolyticum collagenase (CHC) under moderate conditions (pH 7, 37°C). The effect of CHC concentration (2×10(-9)-2×10(-6)M) and incubation time (35-85min) was studied and optimised to achieve the highest decrease of surface tension and the highest dilational surface viscoelasticity of the adsorbed layers. SDS-PAGE electrophoresis and reverse-phase high performance liquid chromatography (RP-HPLC) were used to characterise the hydrolysis products. The results show that even simple modifications (heat treatment, pH change, partial hydrolysis) of collagen enhances its surface properties, especially in terms of surface dilational elasticity modulus. The use of low enzyme concentration (CHC-to-collagen molar ratio of 4×10(-3)) and short incubation time (<45min) results in moderately hydrolysed products with the highest ability to lower surface tension (γ=53.9mNm(-1)) forming highly elastic adsorbed layers (surface dilational elasticity, E'=74.5mNm(-1)). Copyright © 2015 Elsevier B.V. All rights reserved.
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The dynamic surface tension and surface dilational rheology of native collagen (type I, from bovine calf skin) were analyzed in the temperature range from 21 to 34.5 °C. In addition, the effect of heating the collagen solutions up to 90 °C followed by cooling down to room temperature, on surface tension and rheological parameters of the adsorbed layers was studied. As a water-soluble fibrous protein with little exposed hydrophobicity, native collagen is weakly surface active. However, its layers formed by spontaneous adsorption on the water/air surface display exceptional dilational rheology parameters, comparable with those of globular proteins: at high frequency limit (0.1 Hz) the layers are predominantly elastic, with the storage modulus, E′ = 58 mN/m for collagen concentration of 1.3 × 10−5 M (4 g/L). Increasing temperature during adsorption helps to reduce the surface tension, but the resulting layers show diminished surface elastic response. On the other hand, the samples heated at elevated temperatures and measured after cooling down to the room temperature maintain their high surface elasticity. The results suggest that collagen, even in its native form (not processed to gelatin) has a potential to stabilize biocompatible foams/emulsions by forming mechanically strong adsorbed layers.
Article
Polyetheretherketone (PEEK) is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydrophobic interaction, collagen was cross-linked with N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide hydrochloride (EDC) and N-hydro-xysuccinimide (NHS). EDC/NHS system also contributed to the immobilization of rhBMP-2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.
Article
Effect of a model bovine milk protein, β-casein, on surface activity of Quillaja bark saponin (QBS) from Sigma was studied at three fluid/fluid interfaces: air/water, tetradecane/water and olive oil/water. In all cases, the protein concentration was fixed at 10−6 mol L−1, and QBS concentration was varied between 5·10−7 and 1·10−3 mol L−1. Dynamic interfacial tension on the timescale 5 s–3600 s was measured using a drop shape analysis technique. For the air/water system, they were complemented with short-term (50 ms–5 s) measurements using a maximum bubble pressure technique. The dynamic results together with the extrapolated equilibrium surface pressures are discussed from the point of view of a complexation between β-casein and QBS, with the surface activity of the complex changing with its stoichiometry. At low biosurfactant/protein ratios, the interfacial tension at all three interfaces passes through a maximum, corresponding to a transient decrease of both foam and emulsion formation ability. In addition, the effect of QBS on deterioration of β-casein's surface activity upon ageing at room temperature is discussed.
Article
In this study, acid-soluble (ASC) and pepsin-soluble (PSC) collagens with triple helical structures were successfully extracted from the skin of grass carp (Ctenopharyngodon idella) by two different extraction approaches. SDS-PAGE pattern revealed that ASC and PSC are type I collagens with typical α1, α2 and β-chains. In addition, the intensity of χ-chain (trimer) in ASC was higher than that of PSC, representing the presence of the high proportion of intra- and intermolecular cross-links of extracted collagens with large molecular weight using the acid method. Differential scanning calorimetry (DSC) results demonstrate that Td (69.04 °C) of ASC was higher than Td (62.20 °C) of PSC. Both ASC and PSC had the highest solubility at acidic pHs or at a low concentration of NaCl (<2%, w/v). The results of FTIR suggested the ASC and PSC maintained in the helical secondary structure at high degree.
Article
A series of collagen hydrolysate-based surfactants (CHBS) were prepared by grafting different amount of oleoyl group onto collagen hydrolysate (CH). Their physicochemical properties and surface activities were investigated, and their emulsifying ability on rapeseed oil–water emulsion was evaluated. The results showed that, as increasing grafting degree of oleoyl group, the free amino content and isoelectric point of CHBSs and the size of CHBS particles formed in aqueous solution declined, while their molecular weight and surface hydrophobicity increased. The CHBSs with high grafting degree, such as CHBS-30, CHBS-40, and CHBS-50 (postfix datum represents mmol amount of oleic acid chloride to react with 10 g collagen hydrolysate), exhibited satisfactory wetting capacity and foaming capacity, and the CHBSs with low grafting degree, such as CHBS-10 and CHBS-20, presented good emulsifying capacity. The surface activity of CHBSs was closely correlated with the hydrophobicity of their molecules, as well as their capacity to reduce the surface tension of air–water interface. In addition, CHBS-20 showed good emulsifying ability on rapeseed oil–water emulsion in neutral and alkaline pH, even in the condition of low salt concentration.
Article
Rapid urbanization and improvement in living standard skyrocket the demand for washing machines in Chinese households, especially in urban households. This paper discusses the owning rate of different types of washing machines, using frequency, load capacity, factors affect choices of washing machines, etc. in Chinese households and suggest possible strategies in choosing washing machines considering economic expenditure. Quantitative information relates to choice and use of household washing machines was collected through in‐depth interview of the key person who carried out household laundering. A total of 993 households that were randomly selected in eight provinces and a municipality were successfully interviewed. Impeller washing machine is still in a dominate place whereas drum washing machine increasing steadily. Households with higher income tend to buy drum washing machines for their better performances in detergency and superior quality. Load capacity between 4 and 6 kg is very common at present. Larger load capacity is a trend of washing machine choices in Chinese households. Washing machine with better energy efficiency is more popular for its lower expenditure in use. This is more obvious for drum washing machine. Washing machines are often used once every 1 or 2 days in summer, whereas one wash per week and two washes per week are very common in winter. Consumer will expend much more money with the choice of a drum washing machine, not only for paying for the machine, but also for the consumed electricity and water and wastewater discharges in every use.
Article
Study focused on interaction of collagen fibres of collagen I with anionic surfactants sodium dodecylbenzene sulphonate (SDBS), sodium dodecyl sulphate (SDS) and their mixtures at pH = 6, at two ionic strengths (I = 0.06 mol L(-1) and I = 0.4 mol L(-1)) and laboratory temperature. Surfactants and their mixtures were characterised by their critical micelle concentration (c.m.c.), composition of mixed micelles and interaction factor beta according to Rubingh. Dependency of c.m.c. on mixture composition has an opposite tendency at both ionic strengths, which proves the greater influence of added electrolyte on behaviour of SDS than of SDBS. Interaction was evaluated by means of binding isotherms and mass swelling degree alpha(m). The bound quantity partly depends on mixture composition, partly on ionic strength. SDS and mixtures containing its greater quantities are bound more than SDBS (approx. 150% related to SDBS). Increased ionic strength of the environment increases bound quantity in approximately same manner, heedless of adsorbate composition. Even composition of the mixture after interaction with fibres does not markedly alter from initial composition. Fibre swelling is affected by composition of swelling mixture similarly to binding - it increases with growing quantity of surfactants. Greater ionic strength acts against collagen swelling, and at given ionic strength (I = 0.4 mol L(-1)) swelling attains half values compare to swelling at low ionic strength (I = 0.06 mol L(-1)). There are characteristic concentrations of both surfactants and their mixtures (c(s) approximately 0.5 - 1.0 mmol L(-1)) that do not produce swelling. It is assumed that this range of concentrations corresponds to amount of surfactants bound to collagen through electrostatic forces and thus to temporary increase in fibre hydrophobity.
Article
The surface activity of pepsin-solubilized type I collagen acylated by lauroyl chloride and succinic anhydride was investigated in this article. Compared with native collagen, acylated collagen exhibited better surface activity such as oil absorption capacity, emulsion activity and stability, foam expansion, and foam stability but presented lower water absorption capacity. Acylated collagen also had higher emulsion activity and stability than Tween 80, whereas Tween 80 displayed higher foam expansion and stability than acylated collagen. After acylation, the surface tension of collagen decreased with the storage time increased, the hydrophobicity and the wetting power increased with the increase of the concentration. Meanwhile, the emulsion activity and stability of acylated collagen decreased with the increase of NaCl concentration ranging from 20 to 100 mmol/L. Under neutral pH value, acylated collagen reached higher emulsion activity and stability at acylated collagen concentration of 0.4 mg/mL and lower temperature (<35°C). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40174.
Article
The collagen in Amur sturgeon skin was isolated using sodium chloride (SSC, 4.55%), acetic acid (ASC, 37.42%) and pepsin (PSC, 52.80%), respectively. The collagens appeared to be dense sheet-like film linked by random-coiled filaments under SEM. The denaturation and melting temperature were 32.15 °C and 116.62 °C for SSC, 32.78 °C and 120.66 °C for ASC, 32.46 °C and 115.42 °C for PSC, assessed by CD and DSC. SDS-PAGE showed that the collagens were mainly type I with two different α chains. The amino acid profiles of them was similar to each other with high imino acid content and hydroxylation degree. FTIR confirmed the triple helical structure of the collagens, and indicated more hydrogen bond in PSC and more intermolecular crosslinks in ASC. These results suggested that the collagens have potential in commercial applications as alternatives to mammalian collagen.
Article
One of the major constituents of the synovial fluid that is thought to be responsible for chondroprotection and boundary lubrication is the glycoprotein lubricin (PRG4); however, the molecular mechanisms by which lubricin carries out its critical functions still remain largely unknown. We hypothesized that the interaction of lubricin with type II collagen, the main component of the cartilage extracellular matrix, results in enhanced tribological and wear properties. In this study, we examined: i) the molecular details by which lubricin interacts with type II collagen and how binding is related to boundary lubrication and adhesive interactions; and, ii) whether collagen structure can affect lubricin adsorption and its chondroprotective properties. We found that lubricin adsorbs strongly onto denatured, amorphous, and fibrillar collagen surfaces. Furthermore, we found large repulsive interactions between the collagen surfaces in presence of lubricin, which increased with increasing lubricin concentration. Lubricin attenuated the large friction and also the long-range adhesion between fibrillar collagen surfaces. Interestingly, lubricin adsorbed onto and mediated the frictional response between the denatured and native amorphous collagen surfaces equally and showed no preference on the supramolecular architecture of collagen. However, the coefficient of friction was lowest on fibrillar collagen in the presence of lubricin. We speculate that an important role of lubricin in mediating interactions at the cartilage surface is to attach to the cartilage surface and provide a protective coating that maintains the contacting surfaces in a sterically repulsive state.
Article
Devising directions for surfactant assisted effective controlled release of drugs requires a quantitative and qualitative understanding of the drug-protein, drug-surfactant, and surfactant-protein interactions. In this work, the effect of micellar environment on the binding of naproxen and diclofenac sodium with bovine serum albumin has been studied. The isothermal titration calorimetric (ITC) results suggest that the binding of naproxen is reduced with the protein when it is delivered from micellar media. However, the binding is observed to be strengthened for diclofenac sodium. The differential scanning calorimetric results suggest that the integrity of the binding sites is not altered under the employed micellar conditions. The ITC results further suggest that the numbers of naproxen and diclofenac sodium molecules partitioning/binding per micelle of HTAB are 15 and 38, respectively. In the micelles, naproxen is restricted to the surface of the micelles whereas diclofenac sodium is able to partition in the palisade layers. A detailed understanding of the energetics of the drug-protein interactions under different conditions helps in devising directions for effective drug delivery. The ITC and DSC results have shown that the micelles assisted drug-protein interactions are modified depending on the hydrophobic content of the drug.
Article
Mixed protein–surfactant adsorption layers at liquid interfaces are described including the thermodynamic basis, the adsorption kinetics and the shear and dilational interfacial rheology. It is shown that due to the protrusion of hydrophobic protein parts into the oil phase the adsorption layers at the water–hexane interface are stronger anchored as compared to the water-air surface. Based on the different adsorption protocols, a sequential and a simultaneous scheme, the peculiarities of complexes between proteins and added surfactants are shown when formed in the solution bulk or at a liquid interface. The picture drawn from adsorption studies is supported by the findings of interfacial rheology.
Article
The adsorption kinetics of four Tritons (TX45, TX100, TX165 and TX405) was studied by using the complementary drop and bubble profile and maximum bubble pressure tensiometry methods. While TX45 and TX100 can be quantitatively described by a diffusion controlled adsorption mechanism, based on the reorientation model for describing the equilibrium state of adsorption, the results for TX165 and TX405 deviate significantly from this adsorption mechanism. With additional assumptions, such as a finite rate constant for the transition of adsorbed molecules between states of different molar area, and effects of the composition of the Triton samples by many compounds of different ethylene oxide chains, a much better description of the experimental data is possible.
Article
Extensive research has indicated that the electrostatic attraction between polysaccharides and proteins on the oil–water interface can improve the stability of emulsions. However, this electrostatic effect will be weakened or even eliminated as the solution pH or ionic strength of emulsions change, resulting in the shedding of the polysaccharide layer. We prepared primary oil-in-water emulsions at pH 7.0 using whey protein isolate (WPI) as an emulsifier and then beet pectin was added to form secondary emulsions. After the pH of emulsions was adjusted to 4.0 to promote electrostatic attraction between the beet pectin molecules and the protein-coated droplets, horseradish peroxidase was added to generate a cross-linked beet pectin coating. Results show that stable emulsions coated with WPI and cross-linked beet pectin interfaces could be formed. The sensitivity of the emulsions to the environmental stresses of pH changes, ions addition, thermal processing and freezing was also characterized in this work. Our results support the view that cross-linked beet pectin improves the stability of emulsions and is superior to simple deposition on the surface of lipid droplets. The interfacial engineering technology used in this study could be used to create food emulsions with improved stability to environmental stresses.
Article
Drop and bubble shape tensiometry is a modern and very effective tool for measuring dynamic and static interfacial tensions. An automatic instrument with an accurate computer controlled dosing system is discussed in detail. Due to an active control loop experiments under various conditions can be performed: constant drop/bubble volume, surface area, or height, trapezoidal, ramp type, step type and sinusoidal area changes. The theoretical basis of the method, the fitting procedure to the Gauss-Laplace equation and the key procedures for calibration of the instrument are analysed and described.The interfacial tension response to transient and harmonic area perturbations yields the dilational rheological parameters of the interfacial layer: dilational elasticity and exchange of matter function. The data interpretation with the diffusion-controlled adsorption mechanism based on various adsorption isotherms is demonstrated by a number of experiments, obtained for model surfactants and proteins and also technical surfactants. The application of the Fourier transformation is demonstrated for the analysis of harmonic area changes. The experiments shown are performed at the water/air and water/oil interface and underline the large capacity of the tensiometer.
Article
The influence of UV radiation (254nm) on collagen from rat tail tendon in the absence and presence of melanin was investigated. It was found that the relative viscosity and fluorescence of collagen decreased, whereas the absorption/scattering of collagen solution increased during irradiation of the sample. Such changes in the physical properties indicate that photodegradation, phototransformation and changes in the conformational state of collagen take place during UV irradiation. The changes in the above properties in the presence of melanin suggest that it makes collagen more resistant to the action of UV radiation.
Article
A quantitative analysis of the long time period approximation of the diffusion-controlled model is presented and the interval of its validity is defined to interpret adsorption kinetics data. An estimate is also given of the error which results from linear extrapolation of equilibrium surface tension values.
Article
Proteins are of great interest due to their amphiphilic nature, which allows them to reduce the interfacial tension at the oil-water interface. The incorporation of proteins at the oil-water interface has allowed scientists to utilise them to form emulsions (O/W or W/O), which may be used in food formulations, drug and nutrient delivery. The systematic study of the proteins at the interface and the factors that affect their stability (i.e., conformation, pH, solvent conditions, and thermal treatment) has allowed for a broader use of these emulsions tailored for various applications. In this review, the factors affecting the stability of emulsions using food proteins will be discussed. The use of polysaccharides to complex with proteins will also be explored in relation to enhancing emulsion stability.
Article
A new kind of acylated collagen with water solubility and better surface activity was prepared via reaction of pepsin-solubilized calf skin collagen with lauroyl chloride and succinic anhydride in this paper. The equilibrium surface tension and the isoelectric point were 55.92 mN/m and 4.93 respectively, suggesting that acylated collagen had surface activity as well as water solubility. Meanwhile, the results of Fourier transform infrared spectroscopy analyses and electrophoresis patterns demonstrated that the triple helix conformation of collagen was not destroyed, but the subunits of acylated collagen shifted to higher molecular weight than those of native collagen. Scanning electron microscope and differential scanning calorimeter measurements revealed that lyophilized acylated collagen exhibited relatively well-distributed pore structure and its denaturation temperature was ahout 9.0°C higher than that of native collagen. Additionally, the increase of the diameter of the fibrils was observed by atomic force microscopy. Acylated collagen with water solubility and better surface activity might broaden the application of collagen-based materials to cosmetics, drug delivery and pharmacotherapy.
Article
Collagen molecules, self-assembled into macroscopic hierarchical tissue networks, are the main organic building block of many biological tissues. A particularly common and important form of this self-assembly consists of type I collagen fibrils, which exhibit a nanoscopic signature -D-periodic gap/overlap spacing - with a distribution of values centered at approximately 67 nm. In order to better understand the relationship between type I collagen self-assembly and D-spacing distribution, we investigated surface-mediated collagen self-assembly as a function of substrate and incubation concentration. Collagen fibril assembly on phlogopite and muscovite mica, as well as fibrillar gel coextrusion in glass capillary tubes, all exhibited D-spacing distributions similar to those commonly observed in biological tissues. The observation of D-spacing distribution by self-assembly of type I collagen alone is significant as it eliminates the necessity to invoke other pre-assembly or post-assembly hypotheses, such as variation in the content of collagen types, enzymatic cross-linking, or other post-translational modifications, as mechanistic origins of D-spacing distribution. The D-spacing distribution on phlogopite mica is independent of type I collagen concentration, but on muscovite mica, D-spacing distributions showed increased negative skewness at 20 µg/ml and higher concentrations. Tilted D-spacing angles were found to correlate with decreased D-spacing measurements, an effect that can be removed with a tilt angle correction, resulting in no concentration dependence of D-spacing distribution on muscovite mica. We then demonstrated that tilted D-spacing is uncommon in biological tissues and it does not explain previous observations of low D-spacing values in ovariectomized dermis and bone.
Article
The aggregation behavior of type I collagen in acid solutions with the concentrations covering a range of 0.06-1.50mg/mL was studied utilizing both of the fluorescence resonance energy transfer (FRET) between the phenylalanine and tyrosine residues and the external probing of 1,8-anilinonaphthalene sulfonate (ANS). FRET at 0.30mg/mL showed the distance among collagen monomers was within 10nm without the obvious aggregates formed. The predominance of tyrosine fluorescence in FRET in the range of 0.45-0.75mg/mL identified the existence of collagen aggregates companied with the formation of hydrophobic microdomains revealed by the change of the fluorescence of ANS. The blue-shift of tyrosine fluorescence from 303 to 293nm for 0.90-1.50mg/mL dedicated the formation of high order aggregates. The results from the two-phase diagrams of the intrinsic fluorescence for the guanidine hydrochloride-induced unfolding of collagen confirmed these conclusions. By the two-dimensional correlation analysis for the intrinsic fluorescence of collagen solutions of 0.45, 0.75 and 1.05mg/mL, the probable characteristic fluorescence peaks for the interactions of proline-aromatic (CH∼π) among the collagen molecules were found at 298 and 316nm.
Article
Sodium n-alkyl sulfates (n-decyl, n-dodecyl, n-tetradecyl) have been found to be degraded when they are contained in aqueous suspensions of acidic aluminum oxide. The decomposition of the alkyl sulfate molecules in aqueous suspensions was followed by the dynamic surface tension behavior. Decomposition performance depends on the concentration and on the surface activity of the alkyl sulfates as well as on the time of treating the solutions with acidic alumina. The parent 1-alkanols could be detected in the corresponding alkyl sulfate suspensions by thin-layer chromatography. Acidic, surface chemically pure solutions of the alkyl sulfates (4 less-than-or-equal-to pH less-than-or-equal-to 7) did not reveal decompositional effects within a few hours provided that acidic alumina was excluded. The results are interpreted in terms of a surface-enhanced hydrolysis at the acidic alumina interface. Hydrolysis has not been observed in basic alumina suspensions.
Article
The selective determination of phenols in the presence of nonionizing interfering substances by ultraviolet difference spectroscopy is discussed. The difference spectrum of the alkaline form of a phenolic substance in water or alcohol is recorded directly in an ultraviolet recording spectrophotometer against an identical concentration of the substance in neutral or slightly acidified solvent. The resulting difference spectrum is a characteristic and useful indication of the concentration and chemical identity of the phenolic substance. Possible interferences due to nonionizing, nonphenolic species are usually canceled out in the difference spectrum. Applications to the polymer field of analysis are discussed.
Article
The drive for industrial sustainability has pushed biosurfactants to the top of the agenda of many companies. Biosurfactants offer the possibility of replacing chemical surfactants, produced from nonrenewable resources, with alternatives produced from cheap renewable feedstocks. Biosurfactants are also attractive because they are less damaging to the environment yet are robust enough for industrial use. The most promising biosurfactants at the present time are the glycolipids, sophorolipids produced by Candida yeasts, mannosylerythritol lipids (MELs) produced by Pseudozyma yeasts, and rhamnolipids produced by Pseudomonas. Despite the current enthusiasm for these compounds several residual problems remain. This review highlights remaining problems and indicates the prospects for imminent commercial exploitation of a new generation of microbial biosurfactants.
Article
The adsorption of the non-ionic surfactants Triton X-45, Triton X-100, Triton X-165, and Triton X-405 can be described by a reorientation model, assuming that molar area required by adsorbed molecules depends on the surface coverage. The surface tension isotherms we measured by drop and bubble profile tensiometry, where it was shown that at low surfactant bulk concentrations, significant differences in the measured equilibrium tensions are due to depletion effects from the volume of a single drop. This difference in equilibrium surface tensions, observed between data from drop and bubble experiments, is a good tool to determine the adsorbed amount from the total mass balance. An intersection point of all surface tension isotherms at about 1 μmol/l is explained by a respective displacement of the ethylene oxide chain from the interface by the hydrocarbon chain.
Article
The adsorption dynamics and equilibrium properties of hen egg-white lysozyme at the air/water interface is studied using bubble and drop profile analysis technique, ellipsometry and infrared reflection absorption spectroscopy (IRRAS). The set of equilibrium data can be described by a recently developed thermodynamic model. Using the equilibrium adsorption parameters the adsorption dynamics can be well described by a diffusion controlled mechanism at the lower concentrations and a mixed model at higher lysozyme concentrations where conformational changes in the surface layer become time determining.
Article
Analysis of the results of calorimetric study of reconstituted collagen (type I) fibrils, in particular, the half-width of the temperature transition, shows that the collagen packing density in the fibrils and the size of cooperative blocks therein depend on the assembly temperature and on the initial collagen concentration. The least dense fibrils are formed at subphysiological temperatures (25° or 30°C) and low concentration (0.3 mg/ml). The extent of ordering does not change upon doubling the concentration but increases upon quadrupling it. At physiological temperature (35°C) the fibrils are densely packed regardless of collagen concentration. The enthalpy of fibril assembly is minimal at 35°C, 1.2 mg/ml, and ionic strength of 0.17 M. The influence of temperature on particular steps of fibrillogenesis and the role of water in these processes are discussed.
Article
Glycolipid biosurfactants produced by bacteria and yeasts provide significant opportunities to replace chemical surfactants with sustainable biologically produced alternatives in bulk commercial products such as laundry detergents and surface cleaners. Sophorolipids are already available in sufficient yield to make their use feasible while rhamnolipids and mannosylerythritol lipids require further development. The ability to tailor the biosurfactant produced to the specific needs of the product formulation will be an important future step.
Article
The adsorption kinetics, adsorption isotherm and the dilational surface rheology at low oscillation frequencies of sodium dodecyl sulphate (SDS) were studied by drop and bubble profile, and bubble pressure tensiometry. The effect of the inevitably present dodecanol in any SDS solution is taken into account by interpreting the experimental data with theoretical models valid for mixed surfactant solutions. In particular the dilational rheology method appears to be very suitable for demonstrating the continuously on-going hydrolysis reaction in a SDS solution, as the resulting dilational elasticities and viscosities change from a frequency dependencies characteristic to SDS to those expected for dodecanol adsorption layers. For surfactants as active as dodecanol, it turns out that all adsorption and rheological quantities depend significantly on the use of drop or bubble profile tensiometry, i.e. the small reservoir of available surface active molecules in a single droplet has to be considered quantitatively to obtain reliable data.
Article
The knowledge of the stability of foams and emulsions is very important for the control of a large number of technological processes. However, in spite of much intense research, the mechanism of foam stability is still not completely clear. Foam stability depends on many parameters but the type of the added surfactant and the surface rheological properties of the adsorption layers play the most important role. Because of the lack of reliable surface rheological data a comprehensive investigation of this problem was not yet possible. However, we can now present measurements of surface dilational properties of soluble adsorption layers in a frequency range of 1–500 Hz using a new version of the oscillating bubble method. The results are compared with measurements of foam stability. This indicates that the surface dilational viscosity plays an important role in the stability of foam films. A direct relation between surface dilational elasticity values and foam stability could not be detected for the examined systems. Pure elastic adsorption layers were not able to stabilize foam lamellas.
Article
Type I collagen is an important biopolymer and has been widely used in biomaterials due to its excellent biocompatibility and biodegradable properties. However, only a few studies have been reported on its comparison in different species. The amino acid composition, SDS-PAGE, UV–Vis spectrum, thermal transition temperatures, extractable uronic acid/protein ratio and enzymatic sensitivity of type I collagen from bird feet (BF), bovine skin (BS), frog skin (FS), porcine skin (PS) and shark skin (SS) were evaluated. The amino acid composition of type I collagens were different from different species, BF collagen contained higher glutamic acid (Glu) and aspartic acid (Asp), SS collagen contained lower aspartic acid and hydroxyproline (Hyp). Similar SDS-PAGE profiles were found from different animal’s collagen, all samples were composed of two α1-chain and one α2-chain. All UV–Vis spectrums exhibited a typical absorption peak at 218 nm. The UV absorption spectrum of BF collagen ranged from 190 to 340 nm, FS collagen ranged from 190 to 270 nm; the other species collagen ranged from 190 to 240 nm. Thermal transition temperatures of type I collagen from different animals decreased in the order of BF > BS > PS > FS > SS. PS collagen had higher extractable uronic acid/protein ratio and the lowest enzymatic sensitivity. Summarizing these results, the BF collagen had higher hyproxyproline (Hyp) + proline (Pro) value and exhibited higher thermal stability; the PS collagen contained larger amount of glycosaminoglycan and resulted in a high enzymes resistance. However, the BF and PS collagen should be used as a suitable material in biomaterial utilitys because of its better biostability.
Article
The surface tension isotherms of β-lactoglobulin and β-casein in mixtures with sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), respectively, strongly indicate the formation of surface-active complexes. These complexes saturate the adsorption layer at concentrations lower than the saturation concentrations of the individual components. Further increases of surfactant concentration lead to the formation of less-surface-active complexes which compete with free surfactant molecules and are replaced at sufficiently high surfactant concentrations. The surface shear viscosity is progressively decreased by the addition of the surfactants.
Article
While the adsorption dynamics of surfactants is quantitatively understood, the formation of protein adsorption layers is in a premature state yet. The same is true for mixed protein–surfactant layers at liquid interfaces. However, there are first theoretical models which allow a quite good description for mixtures of proteins and nonionic surfactants. For such surface layers, theoretical models (for the equilibrium state as well as for the adsorption kinetics) have to be developed yet.
Article
Surface and interfacial tension measurements have been performed at the water/air and water/hexane interface by drop profile analysis tensiometry for a series of alkyl trimethylammonium bromides with different chain lengths (C10, C12, C14 and C16). The effect of neutral phosphate buffer (10 mM, pH 7) has been investigated and the results have been compared with literature data obtained for the same surfactants in the absence of salt. The use of a modified Frumkin isotherm (Ionic Compressibility) taking into account the mean activity of all ions in solution leads to a real improvement of the data interpretation, while the classical Frumkin Compressibility model yields similar results but overestimates the adsorption parameters. At the water/hexane interface, the hexane molecules are incorporated in the surfactant layer and it results a kind of competitive adsorption for the shortest chain surfactant (10 carbons). For the longest chains, the attractive interactions between the hydrophobic chains of the adsorbed surfactants are strong enough to replace the solvent molecules from the interface.
Article
A bibliographic review of hydrocarbon emulsifiers produced through biological processes.