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The interaction between bacterial cells of Pseudomonas fluorescens(ATCC 17552) and gold electrodes was analyzed by cyclic voltammetry (CV) and attenuated total reflection−surface-enhanced infrared absorption spectroscopy (ATR−SEIRAS). The voltammetric evaluation of cell adsorption showed a decrease in the double-layer capacitance of polyoriented single-crystal gold electrodes with cell adhesion. As followed by IR spectroscopy in the ATR configuration, the adsorption of bacterial cells onto thin-film gold electrodes was mainly indicated by the increase in intensity with time of amide I and amide II protein-related bands at 1664 and 1549 cm-1, respectively. Bands at 1448 and 2900 cm-1corresponding to the scissoring and the stretching bands of CH2were also detected, together with a minor peak at 1407 cm-1due to the vsCOO-stretching. Weak signals at 1237 cm-1were due to amide III, and a broad band between 1100 and 1200 cm-1indicated the presence of alcohol groups. Bacteria were found to displace water molecules and anions coadsorbed on the surface in order to interact with the electrode intimately. This fact was evidenced in the SEIRAS spectra by the negative features appearing at 3450 and 3575 cm-1, corresponding to interfacial water directly interacting with the electrode and water associated with chloride ions adsorbed on the electrode, respectively. Experiments in deuterated water confirmed these assignments and allowed a better estimation of amide absorption bands. In CV experiments, an oxidation process was observed at potentials higher than 0.4 V that was dependent on the exposure time of electrodes in concentrated bacterial suspensions. Adsorbed bacterial cells were found to get closer to the gold surface during oxidation, as indicated by the concomitant increment in the main IR bacterial signals including amide I, a sharp band at 1240 cm-1, and a broad one at 1120 cm-1related to phosphate groups in the bacterial membranes. It is proposed to be due to the oxidation of lipopolysaccharides on the outermost bacterial surface. [ABSTRACT FROM AUTHOR]

Classical electroanalytical techniques and in situ FTIR are used to study the oxidative chemisorption of catechol (o-H2Q) and the hydrogen-assisted reductive desorption of catechol-derived adlayers (o-Q(ads)) at nearly defect-free Pt(111) single-crystal electrodes in 0.5 M H2SO4. At near equilibrium conditions (lim→0) the cyclic voltammetric response does not conform to the behavior expected from classical models of molecular adsorption at electrochemical interfaces. Instead, attractive interactions play a controlling role, i.e., hydrogen-assisted displacement of o-Q(ads)takes place as an electrochemically reversible two-dimensional (2D) phase transition controlled by collision-nucleation-growth phenomena in the presence of 2 mM o-H2Q(aq). In contrast, different desorption dynamics are observed when the reductive desorption of the adlayers is carried out in clean (0 mM o-H2Q(aq)) supporting electrolyte. Donor−acceptor (DA) interactions between the Pt(111)/o-Q(ads)surface adduct and o-H2Q(aq)are postulated as a possible intervening mechanism leading to the observed differences in the macroscopic electrochemical responses. The results also demonstrate that in aqueous solutions it is thermodynamically feasible to shift the formal oxidation potential of catechol−metal adducts to potentials near those of molecular hydrogen via chemically reversible, nondissociative interactions, taking place as a 2D phase transition. [ABSTRACT FROM AUTHOR]