Ohshiro T, Ito T, Bühlmann P, Umezawa Y
Department of Chemistry, School of Science, The University of Tokyo, Japan.
Anal Chem. 2001 Mar 1;73(5):878-83. doi: 10.1021/ac001056e.
STM gold tips chemically modified with 4-mercaptopyridine (4MP) were found capable of discriminating zinc(II) 5,15-bis(4-octadecyloxyphenyl)porphyrin (Por-Zn) from its metal-free porphyrin (Por-2H) and nickel(II) complexes (Por-Ni) in the mixed monolayers of these compounds, spontaneously formed at the solution/graphite interface. The porphyrin centers in STM images observed with 4MP-modified tips exhibited bright spots, while those measured with unmodified tips exhibited the porphyrin centers as dark depressions. The centers of Por-Zn were brighter than those of Por-2H and Por-Ni, thereby allowing the discrimination of Por-Zn from Por-2H or Por-Ni in mixed monolayers. The changes in the contrasts of porphyrin centers of Por-2H and Por-Zn/ Por-Ni were explained by facilitated electron tunneling due to hydrogen bond and metal coordination interactions, respectively, between porphyrin centers and the pyridyl group of 4MP on the tip.
研究发现，用4-巯基吡啶（4MP）进行化学修饰的扫描隧道显微镜（STM）金探针，能够在溶液/石墨界面自发形成的这些化合物的混合单分子层中，区分锌（II）5,15-双（4-十八烷氧基苯基）卟啉（Por-Zn）与其无金属卟啉（Por-2H）以及镍（II）配合物（Por-Ni）。用4MP修饰的探针观察到的STM图像中，卟啉中心呈现亮点，而用未修饰的探针测量时，卟啉中心呈现为暗凹陷。Por-Zn的中心比Por-2H和Por-Ni的中心更亮，从而能够在混合单分子层中区分Por-Zn与Por-2H或Por-Ni。Por-2H以及Por-Zn/Por-Ni的卟啉中心对比度变化，分别是由于卟啉中心与探针上4MP的吡啶基之间通过氢键和金属配位相互作用促进了电子隧穿所致。
