SERS potential-depending

An interesting difference, however, is seen in the potential dependence of the SERS va and features, in that the latter is only observed at the least negative potentials (E > -0.2 V), where the surface infrared vaa band also appears, whereas the former band survives until the most negative potentials (E < -0.8 V),... 

Figure 3 also contains an example of an ISER-flrel plot for a simple specifically adsorbed species, bromide on silver (solid curve). This plot was extracted from bromide coverage-potential data, obtained from differential capacitance measurements, along with the corresponding potential-dependent intensity of the SERS bromide-surface stretching mode at ca. 160 cm"1 (19.). In this case, the maximum (i.e. unity) value of 0r>1 corresponds to a close-packed bromide monolayer, ca. 1.4 x 10"9 mol cm 2. Again, the ISER-0t 1... 

The adsorption mode of 2,6-dimethylphenyl isocyanide (DMPl) on Au electrodes [43] has been studied using potential-dependent SERS. The gold substrate... 

The mode of 2,6-dimethylphenyl isocyanide (DMPI) adsorption on Pt electrodes [43] has been studied using potential-dependent SERS. The Pt electrodes were obtained by depositing Pt nanoparticles ( 17nm) on a polycrystalline Pt film. Three bands appear, at 2166, 2124 and 1997cm" , when DMPI is adsorbed on the... 

Using SERS, Brolo et al. [249] have studied the potential-dependent orientation of 2,2 -bipyridine molecules adsorbed on a... 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

It is of interest to examine quantitatively such potential-dependent redox equilibria as determined by SERS in comparison with that obtained by conventional electrochemistry. Figure 1 shows such data determined for Ru(NH3 )6 3" 2+at chloride-coated silver. The solid curves denote the surface concentrations of the Ru(III) and Ru(II) forms as a function of electrode potential, normalized to values at -100 and -500 mV vs SCE. These are determined by integrating cyclic voltammograms for this system obtained under conditions [very dilute (50 yM) Ru(NH3)63 +, rapid (50 V sec-1) sweep rate] so that the faradaic current arises entirely from initially adsorbed, rather than from diffusing, reactant (cf. ref. 6b). The dashed curves denote the corresponding potential-dependent normalized Ru(III) and Ru(II) surface concentrations, obtained from the integrated intensities of the 500 cm 1 and 460 cm-1 SERS bands associated with the symmetric Ru(III)-NH3 and Ru(II)-NH3 vibrational modes.(5a)... 

Such conclusions are, however, extremely speculative at present. The Fe(CN) 3"/ system suffers from a number of complications, including the possibility of surface reactions to form Prussian Blue-like cyano-bridged chains. Details of these results will be given in a forthcoming publication. (14) This brief summary is included here in order to illustrate how information on electron delocalization effects for adsorbed redox couples might be obtained, at least in principle, by examining potential-dependent SERS frequencies. 

The foregoing has been concerned with the application of SERS to gain information on surface electronic coupling effects for simple adsorbed redox couples that are reversible in the electrochemical as well as chemical sense, that is, exhibit Nernstian potential-dependent responses on the electrochemical time scale. As noted in the Introduction, a major hoped-for application of SERS to electrochemical processes is to gain surface molecular information regarding the kinetics and mechanisms of multiple-step electrode reactions, including the identification of reactive surface intermediates. 

The average size of these small clusters is on the scale of 1. ..500 nm. One of the principal advantages of the use of electrodes is that it is possible to control the surface potential of the SERS substrate. In this way SERS becomes nearly an ideal structurally sensitive tool for in situ investigations of potential dependent effects on surfaces. For an overview of SERS on electrodes see also Chang, 1987. 

Ochsenkuhn MA, Borek J, Phelps R, Campbell CJ (2011) Redox potential dependence of peptide stmcture studied using SERS. Nano Lett 11 2684-2688... 

Not only can changes in orientation be studied and rationalized using SERS measurements but also the relative proportion of adsorbates can be determined. Watanabe and coworkers have studied potential-dependent changes in the spectra of adenosine, cytidine, and their mixtures among other derivatives of these nucleosides on Ag surfaces [221]. Cytidine displays weaker intensities than adenosine... 

Xiao, Y.-). and Markwell, J.P. (1997) Potential dependence of the conformations of nicotinamide adenine dinuceletide on gold electrode determined by FT-near-IR-SERS. Langmuir, 13, 7068-7074. 

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