title: Conformational change in 4-pyridineethanethiolate self-assembled monolayers on Au(111) driven by protonation/deprotonation in electrolyte solutions.
abstract: Self-assembled monolayers (SAMs) of 4-pyridineethanethiol (4-PyEtS) formed on a Au(111) surface were investigated in aqueous electrolyte solutions by cyclic voltammetry and in situ scanning tunneling microscopy (STM). On the basis of reductive desorption of 4-PyEtS on Au(111), the reduction peak potential was found to be -0.86 V vs. Ag/AgCl (sat. KCl). The surface excess was calculated from the reductive desorption peak area to be 5.4 x 10(-10) mol cm(-2). High-resolution STM images revealed that a p(5 x radical3 R-30 degrees ) lattice including two molecules was found in 0.1 M NaClO(4), whereas the 4-PyEtS-SAMs formed a p(10 x radical3 R-30 degrees ) lattice constituting four molecules in 0.05 M HClO(4). The transition from a p(10 x radical3 R-30 degrees ) to a p(5 x radical3 R-30 degrees ) in the 4-PyEtS-SAMs was directly observed by changing pH of the electrolyte solution, indicating that the conformational change in 4-PyEtS-SAMs is driven by protonation/deprotonation. The present results obtained by STM observation are also supported by the clear pH dependence of the pyridine moiety in the surface-enhanced infrared spectrum.
authors.affiliation: Department of Applied Chemistry and Biochemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan. nisiyama@kumamoto-u.ac.jp
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Masashi
authors.initials: M
authors.lastname: Tsuchiyama
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kubo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Seriu
authors.forename: Susumu
authors.initials: S
authors.lastname: Miyazaki
authors.forename: Soichiro
authors.initials: S
authors.lastname: Yoshimoto
authors.forename: Isao
authors.initials: I
authors.lastname: Taniguchi
mesh_terms: D004566:Electrodes; D004573:Electrolytes / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008968:Molecular Conformation; D011522:Protons; D011725:Pyridines / Q000737:chemistry*; D012996:Solutions; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: C534755:4-pyridineethanethiolate; D004573:Electrolytes; D011522:Protons; D011725:Pyridines; D012996:Solutions; D013438:Sulfhydryl Compounds; D006046:Gold