科研之友
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摘要
The adsorption of glycine at gold single crystal and evaporated thin-film electrodes with preferential (111) orientation was studied in perchloric acid solutions by cyclic voltammetry experiments combined with external reflection infrared spectroscopy (gold single crystals) and surface-enhanced infrared reflection absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) (gold thin films). Theoretical harmonic vibrational frequencies obtained from B3LYP/LANL2DZ, 6-31 +G(d) calculations for glycinate species adsorbed on Au clusters with (111) orientation were used to interpret the experimental spectra. The optimized geometry obtained from DFT calculations for zwitterionic glycine plus a water molecule corresponds to a bidentate asymmetrical bridge configuration under the application of an external electric field of 0.01 atomic units. The absence of an adsorbate band for the asymmetric OCO stretching in the experimental infrared spectra confirms the bidentate bonding of glycinate anions through the oxygen atoms of the carboxylate group irrespective of the crystallographic orientation of the electrode surface, the glycinate coverage, and/or the electrode potential. The ATR-SEIRA spectra show an important coadsorption of perchlorate anions that compensates the positive charge of the protonated ammonium group. In addition to typical interfacial water bands associated to perchlorate anions, the spectra also show bands around 2800 cm(-1) that can be related to the formation of hydrogen bonds between interfacial water and the ammonium group of the adsorbed glycinate species. The infrared experimental study is extended to the oxidation of glycine at potentials above 1.10 V, showing the formation of carbon dioxide and adsorbed cyanide.
- 出版日期2011-8-25
