Gold particles have been deposited at an immiscible electrolyte interface by electrochemical reduction of tetraoctylammonium tetrachloroaurate (TOAAuCl,) in 1,2-dichloroethane using potassium hexacyanoferrate(I1) [K,Fe(CN),] in water as the electrontransfer agent. The gold particles are formed at the interface and not in the bulk phases, and their growth was monitored in situ by transmission UV-VIS spectroscopy. The observed spectra have been qualitatively analysed using Mie's theory.

Ultrathin (<20 nm) polypeptide multilayer films are assembled by the electrostatic adsorption of alternating monolayers of poly(L-lysine) and poly(L-glutamic acid) onto carboxylic acid terminated alkanethiol-modified gold surfaces. These polypeptide multilayer films are hydrophilic, can bind electroactive anions such as ferri/ ferrocyanide, and are stable when immersed in organic solvents such as 1,2-dichloroethane (1,2-DCE). A combination of ex situ polarization-modulation Fourier transform infrared reflection-absorption spectroscopy (PM-FTIRRAS) and surface plasmon resonance (SPR) measurements is used to characterize the film deposition and the incorporation of D 2 O and electroactive ions. Electrochemical cycling of the polypeptide films in 1,2-DCE is used to reversibly oxidize the ferrocyanide ions in the film, and in situ PM-FTIRRAS measurements demonstrate that more than 95% of the ferrocyanide ions can be converted to ferricyanide without loss to the organic phase. These ultrathin films will be used to study both ion and electron transport across the film/ 1,2-DCE interface.

The a.c. impedance technique has been used for t h e measurement of electron-transfer rate constants between organic and inorganic redox couples at the water/l12-dichloroethane interface. The organic compounds studied were lutetium diphthalocyanine, bis(pyridine)(meso-tetraphenylporphyrinato)ruthenium(ii) and 7,7,8,8-tetracyanoquinodimethane; Fe(CN)z-'4-was in all cases t h e aqueous redox couple. Electron-transfer rate constants were calculated using recent theoretical developments based on a continuum media model. It is concluded that Marcus theory can be used to predict t h e rate constants for two-phase reactions. Potential-dependent transfer coefficients have been found and it is shown that the origin of this effect is ionic adsorption in the form of interfacial ion pairing.

The capacitance of the interface of immiscible electrolytes has been measured for the Li+, Na+, K+, Rb+ and Cs+ chlorides in 1,2-dichIoroethane and nitrobenzene. Evidence for ionic specific adsorption at the interface is presented. The nature of the specifically adsorbed charge is discussed in terms of the formation of interfacial ion pairs between the aqueous and the organic ions. The contribution of specific ionic adsorption to the interfacial capacitance is calculated on the basis of an ionic associated model using the Bjerrum theory of ion-pair formation. A mixed solvent region with varying penetration of the ion pairs into it, dependent on their ionic radii, best represents the structure of these interfaces.

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