Itoh K, Tokumi S, Kimura T, Nagase A
Department of Chemistry and Biochemistry, Advanced School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan.
Langmuir. 2008 Dec 2;24(23):13426-33. doi: 10.1021/la8015832.
The buildup mechanism of polypeptide multilayers prepared by the layer-by-layer deposition of a polyanion (poly(L-glutamic acid) (PGA)) and polycations (poly(L-lysine) (PLL), poly(D-lysine) (PDL), and copoly(DL-lysine)(PDLL)) was reinvestigated by using in situ ATR-IR spectroscopy. A difference spectral technique applied to analyze the spectra indicated that the deposition of both the PGA and PLL (PDL) layers accompanies the formation of secondary structures consisting mainly of the antiparallel pleated sheet (the beta-sheet) structure, and that the formation of the beta-sheet structure cannot always be explained in terms of polyanion/polycation complex formation or charge compensation between the polyanion and polycations, although it has been considered as a major process in the multilayer buildup process. Instead, the present paper proposes the following mechanism. During the deposition of the polyelectrolyte, a small amount of the beta-sheet structures are produced at the interface as a result of charge compensation between a polyelectrolyte and an oppositely charged polyelectrolyte in the multilayer. The beta-sheets act as nuclei from which further propagation of the structure takes place at the solution/multilayer interfaces. The driving force of the buildup process in the new mechanism is a kinetically favorable insolubilization of each polyelectrolyte in solution at the interfaces.
通过原位衰减全反射红外光谱（ATR-IR）对聚阴离子（聚（L-谷氨酸）（PGA））和聚阳离子（聚（L-赖氨酸）（PLL）、聚（D-赖氨酸）（PDL）以及聚（DL-赖氨酸）（PDLL））逐层沉积制备的多肽多层膜的形成机制进行了重新研究。应用差分光谱技术分析光谱表明，PGA和PLL（PDL）层的沉积都伴随着主要由反平行褶皱片层（β-片层）结构组成的二级结构的形成，并且β-片层结构的形成不能总是用聚阴离子/聚阳离子复合物的形成或聚阴离子与聚阳离子之间的电荷补偿来解释，尽管它一直被认为是多层膜形成过程中的主要过程。相反，本文提出了以下机制。在聚电解质沉积过程中，由于多层膜中聚电解质与带相反电荷的聚电解质之间的电荷补偿，在界面处产生少量的β-片层结构。β-片层作为核，结构在溶液/多层膜界面处从这些核进一步扩展。新机制中多层膜形成过程中的驱动力是各聚电解质在界面处的溶液中动力学上有利的不溶性。
