Department of Bioengineering, University of California-Berkeley, Berkeley, California 94720, USA.
Langmuir. 2012 Jun 12;28(23):8721-9. doi: 10.1021/la300769d. Epub 2012 May 24.
A systematic study of the interfacial energy (γ) of polypeptide complex coacervates in aqueous solution was performed using a surface forces apparatus (SFA). Poly(L-lysine hydrochloride) (PLys) and poly(L-glutamic acid sodium salt) (PGA) were investigated as a model pair of oppositely charged weak polyelectrolytes. These two synthetic polypeptides of natural amino acids have identical backbones and differ only in their charged side groups. All experiments were conducted using equal chain lengths of PLys and PGA in order to isolate and highlight effects of the interactions of the charged groups during complexation. Complex coacervates resulted from mixing very dilute aqueous salt solutions of PLys and PGA. Two phases in equilibrium evolved under the conditions used: a dense polymer-rich coacervate phase and a dilute polymer-deficient aqueous phase. Capillary adhesion, associated with a coacervate meniscus bridge between two mica surfaces, was measured upon the separation of the two surfaces. This adhesion enabled the determination of the γ at the aqueous/coacervate phase interface. Important experimental factors affecting these measurements were varied and are discussed, including the compression force (1.3-35.9 mN/m) and separation speed (2.4-33.2 nm/s). Physical parameters of the system, such as the salt concentration (100-600 mM) and polypeptide chain length (N = 30, 200, and 400) were also studied. The γ of these polypeptide coacervates was separately found to decrease with both increasing salt concentration and decreasing polypeptide chain length. In most of the above cases, γ measurements were found to be very low, <1 mJ/m(2). Biocompatible complex coacervates with low γ have a strong potential for applications in surface coatings, adhesives, and the encapsulation of a wide range of materials.
采用表面力仪（SFA）对多肽复合凝聚物在水溶液中的界面能（γ）进行了系统研究。聚（L-赖氨酸盐酸盐）（PLys）和聚（L-谷氨酸钠盐）（PGA）被用作一对带相反电荷的弱聚电解质模型对。这两种合成的天然氨基酸多肽具有相同的骨架，仅在其带电侧基上有所不同。所有实验均使用等链长的 PLys 和 PGA 进行，以分离并突出带电基团在复合物形成过程中的相互作用的影响。复合凝聚物是由混合 PLys 和 PGA 的非常稀的水溶液盐制成的。在使用的条件下，两种平衡相演化：一种是聚合物富有的凝聚相，另一种是聚合物贫的稀水溶液相。当两个表面分离时，测量与两个云母表面之间的凝聚物弯月面桥相关的毛细粘附。这种粘附使我们能够确定水/凝聚相界面处的γ。影响这些测量的重要实验因素有所变化，并进行了讨论，包括压缩力（1.3-35.9 mN/m）和分离速度（2.4-33.2 nm/s）。系统的物理参数，如盐浓度（100-600 mM）和多肽链长（N = 30、200 和 400）也进行了研究。分别发现，这些多肽凝聚物的γ随盐浓度的增加和多肽链长的减小而减小。在大多数情况下，γ的测量值都非常低，<1 mJ/m2。具有低γ的生物相容的复合凝聚物在表面涂层、粘合剂和广泛材料的封装方面具有很强的应用潜力。
