The Structure of Adenine Adsorbed at Sub-Saturation Coverage at Au(110)/Electrolyte Interfaces

Abstract

It is demonstrated using Reflection anisotropy spectroscopy (RAS) that at sub-saturation coverage adenine adsorbs on the Au(110)/electrolyte interface in a base-stacking configuration with the plane of the bases orientated vertically on the surface and with the long axis of the molecules parallel to the [110] direction. This orientation is the same as that determined for saturation coverage. We also show that RAS can be used to determine the adenine coverage of the Au(110) surface.

The influence of pH on the structure of adenine monolayers adsorbed at Au(110)/electrolyte interfaces

“…The complexity of this process will be discussed in detail in a future publication [14]. The RAS profile observed from adenine adsorbed from a solution of pH 7.1 is, as expected, almost identical to those obtained in the earlier studies [3,4]. It is clear from Fig.…”

“…2 that varying the pH of the solution has dramatic effects on the RAS of adenine adsorbed at the Au(110)/electrolyte interface. These effects are much stronger than the effects on the RAS of adsorbed adenine arising from variations in the concentration of the solution, the degree of surface coverage or the application of varying potentials to the Au(110) electrode [3,4]. In order to deduce further information about the orientation of the adsorbed adenine, it is necessary to consider the dipole transitions that are expected to contribute to the optical response of the molecules.…”

“…Of course, the two low energy transitions are expected to be indistinguishable in the RAS system. The energies of these transitions are probably modified by both the interaction between the dipole transitions in the molecule and the dielectric response of the Au substrate and the surrounding environment [15] [3,4,16,17]. Changes to the RA profiles produced by variations in adenine concentration and applied electrode potential whilst leaving the adsorption structure unaffected were interpreted as rotations of the base stacking structure in the surface plane as characterised by the angle a in Fig.…”

“…The earlier analysis [3,4] established that the change in the RAS profile of adenine adsorbed on Au(110) at pH 7.1 as the potential applied to the gold crystal was varied is due to a change in the orientation of the molecules on the surface. It is difficult to be sure of the adsorption geometry obtained at pH 1.2 and 12.8 without obtaining the dependence of the spectral profiles on the azimuthal angles and carrying out the spectral modelling applied in the earlier studies.…”

“…In a previous work [3] it was shown that at saturation coverage adenine adsorbs at the Au(110)/electrolyte interface in a base stacking configuration with the plane of the bases orientated vertically on the surface and with the long axis of the molecules parallel to the [110] direction. At subsaturation coverage the adenine molecules have been shown to adopt the same base stacking configuration as at saturation coverage and it is possible to determine the percentage of the Au(110) surface that is covered by adenine using reflection anisotropy spectroscopy (RAS) [4].…”