Zinc(II) porphyrins at the air-water interface as studied by polarized total-reflection X-ray absorption fine structure
Zinc(II) porphyrins at the air-water interface as studied by polarized total-reflection X-ray absorption fine structure
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DOI：
10.1021/la0519204
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发表时间：
2006-01-03
期刊：
影响因子：
3.9
通讯作者：
Watanabe, I
中科院分区：
文献类型：
--
作者：
Nagatani, H;Tanida, H;Watanabe, I
采用偏振全反射x射线吸收精细结构方法对空气-水界面处的卟啉锌进行了表征。近边结构的x射线吸收随x射线偏振度的不同表现出显著的差异。在9662 eV下观察到无轴向配位的方形平面金属配合物的1s-4p跃迁对应的Zn k边肩峰，这表明所检测的卟啉锌分子的轴向配位位点在空气-水界面处没有完全水化。通过分析过渡峰强度的极化依赖性，确定了锌卟啉的分子取向。中取代卟啉衍生物5,10,15,20-四苯基卟啉锌（II） （ZnTPP）取向与溶液表面相当平行。与ZnTPP相比，分子一侧具有亲水性羧基的锌（II）原卟啉IX （ZnPP）相对于溶液表面是直立的，卟啉平面与表面的平均倾斜角在57°到43°之间。此外，ZnPP的轴向配位随表面浓度的变化而改变，在压缩的表面层中，锌中心的轴向水化被有效抑制。
The polarized total-reflection X-ray absorption fine structure method was applied to characterize zinc porphyrins at the air-water interface. The X-ray absorption near edge structure exhibited a significant difference depending on the polarization of the X-ray. A shoulder peak of the Zn K-edge corresponding to the 1s-4p, transition for a square planar metal complex without axial coordination(s) was observed at 9662 eV, which indicates that the axial coordination sites of zinc porphyrin molecules examined are not fully hydrated at the air-water interface. The molecular orientation of zinc porphyrins was determined by analyzing the polarization dependence of the transition peak intensity. The meso-substituted porphyrin derivative 5,10,15,20-tetraphenylporphyrinatozinc(II) (ZnTPP) orients rather parallel to the solution surface. In contrast to ZnTPP, the zinc(II) protoporphyrin IX (ZnPP) with hydrophilic carboxyl groups at one side of the molecule stands up with respect to the solution surface, and the average tilting angle of the porphyrin plane to the surface was evaluated to be between 57 degrees and 43 degrees. In addition, the axial coordination of ZnPP is modified depending on the surface concentration, in which the axial hydration to the zinc center is effectively inhibited in the compressed surface layer.