Molecular configuration of gelatin–water suspensions at low concentration (original) (raw)
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Molecular configuration of gelatinewater suspensions at low concentration
Direct assessment of gelatin molecular configuration has been difficult due the complexity of the molecule and limitations of analytical techniques. The objective of this work was the molecular characterization of bovine gelatin as a function of temperature, concentration and time. Diluted suspensions were prepared at different concentrations (7.5 Â 10 À5 to 1.5 g/l) and kept at temperatures above (S1) (40 C) and below (S2) (5 C) the gelling point as determined by Differential Scanning Calorimetry. Circular dichroism measurements showed the secondary structure of a polyproline II like spectra similar to native collagen at S1 and a denaturated configuration at S2 conditioning. Atomic Force Microscopy (AFM) at S1, using a HOPG substrate, showed single strands segments with two marked distributions in heights, w0.6 nm and w1.6 nm, indicating possible helical configurations even at high temperatures. At S2, AFM showed only one height distribution in the range of w0.9 nm but wider (0.3e1.6 nm range). At increasing gelatin concentration (12 g/l) and annealing time (48 h), a well-defined network was detected with narrow height distribution (w1.0 nm) featuring aggregates and highly ordered structure zones. An analysis of gelatin strand interactions, showed a network linked by knots with a coordination number Z ¼ 3 (strands) with a bond length of w50 nm. The gel network formation and aggregation was consistent with molecular size increase observed by Dynamic Light Scattering, showing variations in hydrodynamic dimensions from w10 nm (S1) to w100 nm (S2). This experimental approach has allowed to pinpoint differences in molecular configuration of gelatin, which may be applied in the study the structuring pathway of other biopolymers and the association kinetics during storage for a wide range of temperatures.
Influence of Weak and Covalent Bonds on Formation and Hydrolysis of Gelatin Networks
Biomacromolecules, 2004
The relative influence of physical and chemical bonds to overall gel properties are explored in gelatin gels. Physical, chemical, chemical-physical, and physical-chemical gels are obtained by cooling the protein solution and/or by transglutaminase reaction. Each type of network is characterized by rheology and polarimetry. It is shown that the overall properties as well as the dynamics inside the gels are dependent upon the order of formation and on the relative amount of triple helices and covalent bonds. Enzyme hydrolysis of covalent gels is slower than that of physical gels, as confirmed by the kinetics of helix release and degradation. A scheme is proposed to explain the results at both the physicochemical and the molecular levels.
2007
his research work focuses on the changes in molecular dynamics of gelatin in the early stages of gelation under temperature variations (273-330 K), pHs (3, 6.5, and 11) and concentrations (1, 3, and 5 %w/w). The early stage of gelation occurs at temperature well above the sol-gel transition point and is accompanied by increasing the viscosity of the solution. The induced variations of the local mobility of the macromolecules are detected by measurements of the spin-spin relaxation time of 1 H nuclei of different amino acids. Changes in the rheological characteristics of the gelatin solutions are measured and the effects of acidity, temperature, and concentration on the early stages of the gelatin gelation process are evaluated. The experimental results were analyzed for the mobility of the individual amino acids and of the complete gel network at different temperatures and acidities. Spin-spin relaxation data indicate that the mobility of amino acids in this siane of gelation is not affected by the gelatin concentration, indicating that it is predominantly governed by intra-molecular interactions. As expected, the influence of this interaction on individual amino acids strongly depends on the polarity and their ability to form hydrogen bonds. The variation of the relaxation times reflects the specific role of each individual amino acid during the gelation process. Any deviation from the neutral pH conditions causes a strong increase in the local molecular dynamic, presumably caused by electrostatic repulsion under acidic or basic conditions. At the same time, it leads to decrease in the solution viscosity originally observed under neutral conditions.
We present a systematic investigation of hydration and gelation of the polypeptide gelatin in water–glycerol mixed solvent (glycerol solutions). Raman spectroscopy results indicated enhancement in water structure in glycerol solutions and the depletion of glycerol density close to hydration sheath of the protein molecule. Gelation concentration (cg) was observed to decrease from 1.92 to 1.15% (w/v) while the gelation temperature (Tg) was observed to increase from 31.4 to 40.7 °C with increase in glycerol concentration. Data on hand established the formation of organogels having interconnected networks, and the universal gelation mechanism could be described through an anomalous percolation model. The viscosity of sol diverged as η (1 – cg/c)−k as cg was approached from below (c < cg), while the elastic storage modulus grew as G′ (c/cg – 1)t (for c > cg). It is important to note that values determined for critical exponents k and t were universal; that is, they did not depend on the microscopic details. The measured values were k = 0.38 ± 0.10 and t = 0.92 ± 0.17 whereas the percolation model predicts k = 0.7–1.3 and t = 1.9. Isothermal frequency sweep studies showed power-law dependence of gel storage modulus (G′) and loss modulus (G′′) on oscillation frequency ω given as G′(ω) ωn′ and G′′(ω) ωn′′, and consistent with percolation model prediction it was found that n′ ≈ n′′ ≈ δ ≈ 0.73 close to gelation concentration. We propose a unique 3D phase diagram for the gelatin organogels. Circular dichroism data revealed that the gelatin molecules retained their biological activity in these solvents. Thus, it is shown that the thermomechanical properties of these organogels could be systematically tuned and customized as per application requirement.
2007
This study focuses on the early stages of the gelation of an aqueous type A (pig skin) gelatin solution. The thermoreversible mono and triple helix formation was observed by rheology and proton NMR relaxation measurements. At high temperatures (T > 330 K), gelatin molecules form flexible random coils of small hydrodynamic radius, the elastic modulus of the solution is relatively low. On decreasing the temperature (330-320 K), mono helix formation begins, connected with an increase of the storage modulus and the hydrodynamic radius. The absence of a significant concentration dependence of this early variation of the modulus indicates the intramolecular nature of this structural change. The simultaneous decrease of the spin-spin relaxation times of the 1 H signals of certain aminoacids confirms its effect on the molecular mobility. As this affects especially the signals of arginine and lysine, we conclude that these basic aminoacids play a significant role in forming the intramolecular interactions. The formation of a three-dimensional network occurs at a point at which the viscosity begins to increase rapidly near the gel point (T < 320 K). This process is clearly dominated by intermolecular interactions, as the slope as well as the starting point of the rapid increase significantly depends on the concentration.
The effects of low molecular weight diluents (namely water and glycerol) on the nanostructure and thermodynamic state of low water content gelatin matrices are explored systematically by combining positron annihilation lifetime spectroscopy (PALS) with calorimetric measurements. Bovine gelatin matrices with a variation in the glycerol content (0-10 wt.%) are equilibrated in a range of water activities (a w = 0.11-0.68, T = 298 K). Both water and glycerol reduce the glass transition temperature, T g , and the temperature of dissociation of the ordered triple helical segments, T m , while having no significant effect on the level of re-naturation of the gelatin matrices. Our PALS measurements show that over the concentration range studied, glycerol acts as a packing enhancer and in the glassy state it causes a nonlinear decrease in the average hole size, v h , of the gelatin matrices. Finally, we report complex changes in v h for the gelatin matrices as a function of the increasing level of hydration. At low water contents (Q w ⇠ 0.01-0.10), water acts as a plasticizer, causing a systematic increase in v h .
Hydrodynamic Properties of Gelatin – Studies from Intrinsic Viscosity Measurements
Gelatin is a natural polymer widely used in pharmaceutical, cosmetic, photographic, and food industries. It is obtained by denaturation and partial hydrolysis of fibrous collagen. Collagen is the most abundant structural protein of animals and by far the main organic component of skin and bone of vertebrates. However, collagen is standing for a family of proteins with 21 different types of aminoacids described to date. Skin and bones, the raw materials for gelatin manufacture, mainly consist of type I collagen and a small fraction of type III collagen. Each type I collagen molecule consists of polypeptide chains are twisted into left-handed helices. The rod like triple-helical collagen molecules is arranged in a parallel but staggered orientation to form fibrils.
Evolution of water structure in biopolymer solutions during the gelation process
Chemical Physics Letters, 2004
The evolution of water structure in train of gelation process is examined in aqueous solution of gelatin using Raman spectroscopy of the O-H stretching band. The measurements have been performed at room temperature for four concentrations of gelatin, which yields different dimensions of nanopores in the network of the created gel. We have found that during the sol-gel transition the number of molecules that participate in the regular tetrahedral H-bond structure increases, and the effect is stronger for higher concentration of the biopolymer.
Phase Separation Induced by Conformational Ordering of Gelatin in Gelatin/Maltodextrin Mixtures
Macromolecules, 2001
Mixtures of gelatin and maltodextrin in aqueous solution have been quenched to temperatures at which they are initially miscible but where gelatin ordering is initiated. In many cases phase separation was observed to occur after a significant time delay, and the dependence of these delays on quench temperature and biopolymer concentration has been studied in detail using turbidity measurements and confocal laser scanning microscopy (CLSM). Furthermore, by observing the optical rotation (OR) and turbidity of the system simultaneously, the gelatin helix content and the time delay before the onset of phase separation were monitored concurrently. The observed delay times were found to correspond to the time taken for the development of a certain degree of gelatin ordering, which drives the separation process. A further consequence of gelatin ordering is the viscosifying of the solution and, at sufficient concentrations, the formation of a gel. Therefore, rheological measurements have been used in addition to turbidity measurements and CLSM in order to monitor further the structural development of the systems. A comparison of the data obtained from these techniques shows that while the development of a certain elasticity will trap the system morphology, this elasticity is not directly related to that found at the gel point. At low maltodextrin concentrations, where phase separation was not detected by turbidity, transmission electron microscopy (TEM) has been used to examine the microstructure on a smaller length scale.