Alkanethiol Molecules Research Articles

Scanning Tunneling Microscope Image of Thioguanine Molecules on Au(111) Surface

We have studied 6-thioguanine, a substituent of deoxyribonucleic acid (DNA) bases, adsorbed on a Au(111) surface by scanning tunneling microscopy (STM) under ambient condition in air. Observation of the STM image of the molecule suggests that thioguanine is bound to the Au substrate through the Au-S bond formation described in STM studies of alkanethiolate molecules. Our STM images obtained under ambient condition are much more similar to those of a planar two-dimensional hydrogen-bonded array of guanine molecules on a MoS2 substrate rather than those of a disordered array of guanine on a Au substrate in solution.

Packing and molecular orientation of alkanethiol monolayers on gold surfaces

Preliminary calculations based on a simple model give a good description of the molecular orientation and packing of akanethiol monolayers on gold surfaces. These calculations suggest that alkanethiol molecules on gold have a total alkyl chain axis tilt of approximately 38' in a plane that bisects the methylene H-C-H angles, followed by a rotation about the alkyl chain axis of -46'. The alkyl chain tilt is a function of the sulfur-sulfur spacing in a hexagonal crystal lattice layer and maximizes the attractive interactions between neighboring molecules. These results are in agreement with the molecular orientations obtained from grazing angle FTIR experiments on dodecanethiol monolayers on a (111) gold surface.

A molecular mechanics force field for conformational analysis of alkanethiols and thioethers

A molecular mechanics force field for conformational and vibrational studies on alkanethiols and thioethers is developed. The final set of force field parameters reproduces molecular structures adequately and provides a good fit for energy differences between conformers and barriers to internal rotation for a large number of alkanethiol and thioether molecules. In addition, vibrational frequencies are calculated in reasonable agreement with available experimental data.