Polymer and Biophysics Laboratory, School of Physical Sciences, Jawaharlal Nehru University, New Delhi, India.
J Phys Chem B. 2011 Jun 9;115(22):7332-40. doi: 10.1021/jp201877d. Epub 2011 May 12.
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 (c(g)) was observed to decrease from 1.92 to 1.15% (w/v) while the gelation temperature (T(g)) 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 - c(g)/c)(-k) as c(g) was approached from below (c < c(g)), while the elastic storage modulus grew as G' ∼ (c/c(g) - 1)(t) (for c > c(g)). 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) ∼ ω(n') and G''(ω) ∼ ω(n''), 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.
我们对多肽明胶在水-甘油混合溶剂（甘油溶液）中的水合和凝胶化进行了系统研究。拉曼光谱结果表明，甘油溶液中水分子结构增强，靠近蛋白质分子水合鞘的甘油密度耗尽。随着甘油浓度的增加，凝胶化浓度（c(g)）从 1.92%（w/v）降低到 1.15%（w/v），而凝胶化温度（T(g)）从 31.4°C 增加到 40.7°C。现有的数据建立了具有相互连接网络的有机凝胶的形成，并且通用的凝胶化机制可以通过异常渗流模型来描述。溶胶的粘度随着 η ∼ (1 - c(g)/c)(-k)发散，当 c(g)从下方接近（c < c(g)）时，而弹性储能模量随着 G' ∼ (c/c(g) - 1)(t)增长（c > c(g)）。值得注意的是，确定的临界指数 k 和 t 值是通用的；也就是说，它们不依赖于微观细节。测量值为 k = 0.38 ± 0.10 和 t = 0.92 ± 0.17，而渗流模型预测 k = 0.7-1.3 和 t = 1.9。等温频率扫描研究表明，凝胶储能模量（G'）和损耗模量（G'')对振荡频率ω的幂律依赖关系为 G'(ω) ∼ ω(n')和 G''(ω) ∼ ω(n'')，并且与渗流模型预测一致，发现 n'≈n''≈δ≈0.73 接近凝胶化浓度。我们提出了一个独特的明胶有机凝胶三维相图。圆二色性数据表明，明胶分子在这些溶剂中保留了它们的生物活性。因此，表明这些有机凝胶的热机械性能可以根据应用要求进行系统地调整和定制。
