Introduction: Molecular and Biomolecular Electrochemistry

Maybe the most straightforward definition of “Molecular Electrochemistry” is through a double motto: “molecules for electrochemistry and electrochemistry for molecules”. As opposed to the equally important segment of electrochemistry that investigates or uses surface states directly involving the electrode material, molecular electrochemistry deals with the transformation of molecules triggered by electron transfer from or to an electrode and/or by the use of molecules dispersed in the solution or attached to the electrode surface to accelerate and optimize an electrochemical reaction. In such cases, the nature of the electrode material is expected to play a minor role, with the electrode serving essentially as an “innocent” electron reservoir or sink. Under these conditions, there is a strong link between molecular electrochemistry and other areas of electron transfer chemistry where the electron comes from or goes to a molecular reactant introduced in the solution as such or photogenerated from a stable ground state. The advantages of molecular electrochemistry is this respect are that imposing the electrode potential is an easy way of adjusting the driving force of the reaction and that the current flowing through the electrode is a convenient measure of the reaction kinetics. As in many other domains of physical chemistry, the motivations of the contemporary studies in molecular electrochemistry are increasingly directed toward natural systems in order to understand, imitate, or exploit them. This tendency is reflected in the title of this thematic issue, which was expanded to “Molecular and Biomolecular Electrochemistry”, even if it may appear redundant since biomolecules are molecules. Over the nineteen contributions to the issue, eight are indeed dealing directly with natural species or reactions and one is strongly inspired by the understanding and mimicking of biological reactions. Another major tendency in recent developments of molecular and biomolecular electrochemistry is downsizing, en route to nanoelectrochemistry or even to molecular electronics. Even though the perspectives and motivations of molecular and biomolecular electrochemistry have evolved over the last twenty years, the necessity of addressing fundamental problems of electron transfer chemistry through electrochemistry remains. This is the case with the question of oneelectron vs two-electron transfer, still of high current interest, which is treated in the contribution of Dennis H. Evans, OneElectron and Two-Electron Transfers in Electrochemistry and Homogeneous Solution Reactions. Another fundamental question concerns the association between electron transfer and proton transfer. This rather old problem is currently receiving much renewed attention in connection with the importance of such processes in biological reactions. Cyrille Costentin addresses the question under the electrochemical angle in his contribution Electrochemical Approach to the Mechanistic Study of Proton-Coupled Electron Transfer. How breaking and formation of bonds involving heavy atoms can be triggered by electron transfer, particularly electrochemical electron transfer, is a key question that, together with proton-electron transfer coupling, underlies the chemical transformations produced by means of electrochemistry and, more generally, by injection or removal of an electron. This topic is reviewed in Abdelaziz Houmam’s article Electron Transfer Initiated Reactions: Bond Formation and Bond Dissociation. Electrochemistry without solvent is another fundamental matter of timely interest, which may receive interesting clean-chemistry applications in the near future. It is scrutinized by Philippe Hapiot and Corinne Lagrost in their article Electrochemical Reactivity in RoomTemperature Ionic Liquids. Among the motivation and applications of molecular electrochemistry, electrochemical organic synthesis is a domain of continuously renewed interest. Jun-ichi Yoshida, Jean-Michel Savéant received his education in the Ecole Normale Supérieure in Paris, where he became the Vice-Director of the Chemistry Department before moving to the University Denis Diderot (Paris 7) as a Professor in 1971. He is, since 1985, Directeur de Recherche au Centre National de la Recherche Scientifique in the same university. In 1988-1989 he was a distinguished Fairchild Scholar at the California Institute of Technology. His current research interests involve all aspects of molecular and biomolecular electrochemistry as well as mechanisms and reactivity in electron transfer chemistry and biochemistry. Among many distinctions, Jean-Michel Savéant received the Faraday Medal of the Royal Chemical Society, the Olin Palladium Medal of the Electrochemical Society, la Medaglia Luigi Galvani della Società Chimica Italiana and the Manuel Baizer Award of the Electrochemical Society. Jean-Michel Savéant is a member of the French Academy of Sciences and foreign associate of the National Academy of Sciences of the United States of America. Volume 108, Number 7