Thiol with an Unusual Adsorption-Desorption Behavior: 6-Mercaptopurine on Au(111)

E. PENSA; P. CARRO; ALDO A. RUBERT; G. BENITEZ; C. VERICAT; R.C. SALVAREZZA

LANGMUIR

AMER CHEMICAL SOC

Año: 2010 vol. 26 p. 17068 - 17074

0743-7463

A multitechnique study of 6-mercaptopurine (6MP) adsorption on Au(111) is presented. The molecule adsorbs on Au(111), originating short-range ordered domains and irregular nanosized aggregates with a total surface coverage by chemisorbed species smaller than those found for alkanethiol SAMs, as derived from scanning tunneling microscopy (STM) and electrochemical results. X-ray photoelectron spectroscopy (XPS) results show the presence of a thiolate bond, whereas density functional theory (DFT) data indicate strong chemisorption via a S-Au bond and additional binding to the surface via aN-Au bond. FromDFT data, the positive charge on theAu topmost surface atoms is markedly smaller than that found for Au atoms in alkanethiolate SAMs. The adsorption of 6MP originates Au atom removal from step edges but no vacancy island formation at (111) terraces. The small coverage of Au islands after 6MP desorption strongly suggests the presence of only a small population ofAu adatom-thiolate complexes.Wepropose that the absence of theAu-S interface reconstruction results from the lack of significant repulsive forces acting at the Au surface atoms.