Adenine Adsorption at Single Crystal and Thin-Film Gold Electrodes: An In Situ Infrared Spectroscopy Study

Abstract

Adenine adsorption at gold electrodes is studied in neutral sodium fluoride solutions by cyclic voltammetry and in situ infrared spectroscopy. External reflection measurements were performed with Au(111) and Au(100) single crystal electrodes in D2O solutions, whereas surface enhanced infrared reflection absorption spectroscopy experiments under attenuated total reflection conditions were carried out with sputtered gold thin-film electrodes, both in D2O and H2O solutions. The results clearly show the specific adsorption of the molecule providing significant surface enhancement of the strong ring stretching band and the scissoring mode of the amino group. On the basis of the results, an adsorption model is proposed in which the molecular plane and the C−N(H2) bond are tilted on the electrode surface. Coordination is proposed to take place via the N(amino) atom upon sp3 hybridization and the N7 atom of the ring. The model applies irrespective of the surface crystallographic orientation of the electrode or the applied potential. The influence of the reconstructed or the unreconstructed state of the surface is inferred from the analyses of the spectra recorded while scanning the potential in opposite directions.

Electrochemical detection of cytosine and 5-methylcytosine on Au(111) surfaces

“…On the other hand, it is also known that DNA bases (nucleobases) can be adsorbed on some metal solid surfaces, particularly, on Au electrodes [22][23][24][25][26][27][28][29][30].…”

In situ Fourier transform infrared reflection absortion spectroscopy study of adenine adsorption on gold electrodes in basic media

“…Our previous in situ FT-IRRAS studies of adenine adsorption on gold electrodes in neutral and in acid media [3,4] showed that only the neutral form of adenine (AdH 3 ) is chemisorbed on the electrode under these conditions, even at pH values as low as pH . Recent in situ electrochemical STM experiments also suggest the weak adsorption of the protonated adenine [5].…”

“…On the other hand, the comparison of adenine adsorption in acid and in neutral media also reveals differences in the spectral signals corresponding to the solvent and to the anion of the supporting electrolyte [3,4], that indicate that the co-adsorption of these species with adenine takes place only in acid media.…”

“…We have previously studied the adsorption of adenine on gold single crystal and gold nanostructured electrodes, in neutral and acid media by means of different electrochemical, spectroscopic and microscopic techniques, [1][2][3][4][5]. The characterisation of the adsorption process by cyclic voltammetry and differential capacitance in neutral media on the low index gold single crystal electrodes [1] showed that the adsorption phenomena is strongly dependent not only on the crystallographic orientation, but also on the reconstructed or unreconstructed state of the surface.…”

“…In situ IRRAS measurements can provide information about the nature of the adsorbates, their orientation relative to the electrode surface, the atoms involved in the interactions with the metal surface, the nature of the intermolecular interactions at the interface and the influence of the solvent. In a previous work, the adsorption of adenine on gold single crystal and gold thin-film electrodes was studied in neutral media by means of in situ FT-IRRAS measurements [3]. The spectroscopic results obtained were analysed on the basis of previously published data for the -scheme 1 -Adenine has two pKa values in aqueous media [45,46] as is shown in scheme 1.…”