Polymer and Biophysics Laboratory, School of Physical Sciences, Jawaharlal Nehru University, New Delhi-110 067, India.
J Phys Chem B. 2010 Sep 23;114(37):12027-35. doi: 10.1021/jp105431t.
Coacervate is defined as a polymer-rich dense phase, which remains in thermodynamic equilibrium with its low concentrated phase called the supernatant. The effect of ionic strength (I = 0-0.1 M NaCl) on the mechanism of surface patch binding-induced protein-polysaccharide interaction leading to complex coacervation, between agar (a polyanionic polysaccharide) and gelatin B (a polyampholyte protein), both having similar net charge, at a particular mixing ratio, [gelatin]/[agar] = 1, was studied at various temperatures (20-40 °C). The coacervation transition was probed by turbidity and zeta-potential measurements. The intermolecular association had the signature of surface-selective binding, and a model calculation could explain the potential energy of interactions operative in such processes. The thermo-mechanical features of the coacervates were found to be strongly dependent on ionic strength, which has been interpreted as originating from formation of salt-bridges between the biopolymers. The microstructure of the coacervate materials was analyzed using rheology and small angle neutron scattering (SANS) techniques, which probed the heterogeneity prevailing in the system that had characteristic length in the range 1.3-2.0 nm, and the same data yielded the correlation length of concentration fluctuations, which was estimated to lay in the range 2.4-4 nm. It is concluded that the coacervation transition driven by surface-selective binding is not influenced by the ionic strength of the solution, but the mobile ions participate in the structural organization of the interacting polyions in the coacervate.
凝聚物被定义为富含聚合物的致密相，它与低浓度相（称为上清液）处于热力学平衡状态。离子强度（I = 0-0.1 M NaCl）对表面斑块结合诱导的蛋白质-多糖相互作用导致复杂凝聚的机制的影响，在特定混合比（[明胶]/[琼脂]= 1）下，琼脂（多阴离子多糖）和明胶 B（多两性电解质蛋白）之间发生，两者具有相似的净电荷，在不同温度（20-40°C）下进行了研究。通过浊度和 ζ 电位测量探测凝聚转变。分子间缔合具有表面选择性结合的特征，模型计算可以解释在这些过程中起作用的相互作用势能。凝聚物的热机械特性强烈依赖于离子强度，这可以解释为生物聚合物之间形成盐桥所致。使用流变学和小角中子散射（SANS）技术分析了凝聚物材料的微观结构，这些技术探测到系统中普遍存在的非均相性，其特征长度在 1.3-2.0 nm 范围内，相同的数据还得出了浓度波动的相关长度，估计在 2.4-4 nm 范围内。结论是，由表面选择性结合驱动的凝聚转变不受溶液离子强度的影响，但可移动离子参与凝聚物中相互作用聚离子的结构组织。
