Mohanty B, Bohidar H B
School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110016, India.
Biomacromolecules. 2003 Jul-Aug;4(4):1080-6. doi: 10.1021/bm034080l.
Turbidity measurements performed at 450 nm were used to follow the process of simple coacervation when 1% (w/v) aqueous alkali processed gelatin (type-B) solutions were titrated with methanol, ethanol, propanol, and tert-butyl alcohol at various pHs of the solution ranging from pH = 5 to 8 and ionic strengths varying from I = 0.01 to 0.1 M NaCl. The titration profiles clearly established the transition points in terms of the percentage of volume of alcohol added relative to that of solvent corresponding to the first occurrence of turbidity (Vt) and a point of turbidity maximum (Vp). Addition of more alcohol drove the system toward precipitation. The values of Vt and Vp characterized the initiation of intramolecular folding and intermolecular aggregate formation of the charge neutralized gelatin molecules and the subsequent micro coacervate droplet formation. The state of intermolecular aggregates and that of folded gelatin molecules could be characterized by dynamic laser light scattering experiments, which implied spontaneous segregation of particle sizes preceding coacervation. The aggregates constitute the coacervate phase while the folded gelatin molecules mostly stay dispersed in the supernatant. The data taken together reveal the role played by solution entropy in addition to that of electrostatic and solute-solvent interactions, which had been overlooked hitherto.
当用甲醇、乙醇、丙醇和叔丁醇在溶液pH值从5到8、离子强度（I）从0.01到0.1 M NaCl的不同条件下，对1%（w/v）碱处理的B型明胶水溶液进行滴定时，通过在450 nm处进行的浊度测量来跟踪简单凝聚过程。滴定曲线根据相对于溶剂体积的醇添加体积百分比，明确确定了对应于首次出现浊度（Vt）的转变点和浊度最大值点（Vp）。加入更多的醇会使系统趋向于沉淀。Vt和Vp的值表征了电荷中和的明胶分子的分子内折叠和分子间聚集体形成的起始以及随后的微凝聚液滴形成。分子间聚集体的状态和折叠的明胶分子的状态可以通过动态激光光散射实验来表征，这意味着在凝聚之前颗粒尺寸的自发分离。聚集体构成凝聚相，而折叠的明胶分子大多保持分散在上清液中。综合这些数据揭示了溶液熵除了静电和溶质 - 溶剂相互作用之外所起的作用，而这一点迄今一直被忽视。
