Liu Huijin, Zheng Haifu, Miao Wangen, Du Xuezhong
MOE Key Laboratory of Mesoscopic Chemistry, State Key Laboratory of Coordination Chemistry, and School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, People's Republic of China.
Langmuir. 2009 Mar 3;25(5):2941-8. doi: 10.1021/la803976c.
The surface behaviors of monolayers of amino-acid-derived Schiff bases, namely, 4-(4-(hexadecyloxy)benzylideneamino)benzoic acid (HBA), at the air-water interface on pure water and ion-containing subphases (Cu2+, Ca2+, and Ba2+) have been clarified by a combination of surface pressure-area isotherms and surface plasmon resonance (SPR) technique, and the metal coordinations and molecular orientations in the monolayers have been investigated using in situ infrared reflection absorption spectroscopy (IRRAS). The presence of metal ions gives rise to condensation of the monolayers (Cu2+, pH 6.1; Ca2+, pH 11; Ba2+, pH 10), even leading to the formation of three-dimensional structures of the compressed monolayer in the case of Ba2+ (pH 12). The metal coordinations with the carboxyl groups at the interface depend on the type of metal ions and pH of the aqueous subphase. The orientations of the aromatic Schiff base segments with surface pressure are elaborately described. The spectral behaviors of the Schiff base segments with incidence angle in the case of Ba2+ (pH 12) have so far presented an excellent example for the selection rule of IRRAS at the air-water interface for p-polarization with vibrational transition moments perpendicular to the water surface. The chain orientations in the monolayers are quantitatively determined on the assumption that the thicknesses of the HBA monolayers at the air-water interface are composed of the sublayers of alkyl chains and Schiff base segments.
通过表面压力-面积等温线和表面等离子体共振（SPR）技术相结合，阐明了氨基酸衍生席夫碱单层，即4-(4-(十六烷氧基)亚苄基氨基)苯甲酸（HBA）在纯水和含离子亚相（Cu2+、Ca2+和Ba2+）上的空气-水界面的表面行为，并使用原位红外反射吸收光谱（IRRAS）研究了单层中的金属配位和分子取向。金属离子的存在导致单层凝聚（Cu2+，pH 6.1；Ca2+，pH 11；Ba2+，pH 10），在Ba2+（pH 12）的情况下甚至导致压缩单层形成三维结构。界面处羧基与金属的配位取决于金属离子的类型和水相亚相的pH值。详细描述了芳香席夫碱链段随表面压力的取向。到目前为止，在Ba2+（pH 12）情况下，席夫碱链段随入射角的光谱行为为空气-水界面处p偏振且振动跃迁矩垂直于水面的IRRAS选择规则提供了一个很好的例子。在假设空气-水界面处HBA单层的厚度由烷基链和席夫碱链段的子层组成的前提下，定量确定了单层中的链取向。
