Redox redux

The passage of 20 years since Rudy Marcus' 1992 Nobel Prize for electron transfer (ET) theory provides an opportunity to celebrate and to reflect on the emergence of the modern understanding of electron and proton flow in chemical, biological, and physical systems. Rudy's contributions – warmly recalled in his accompanying editorial – provided the torch that lit the way for generations. This volume celebrates this happy anniversary and also aims to highlight the stunningly diverse role that is played by charge transfer in the molecular sciences, from the most fundamental to the most applied areas of study. Indeed, the broader field of charge transfer has been punctuated by seminal developments, at least five of which led to the awarding of Nobel Prizes. Peter Mitchell's brilliant recognition of the coupling between electron and proton motion in biology, driving molecular bioenergetics, led to his 1978 Prize. Henry Taube's 1983 Prize was awarded for his understanding of electron transfer reaction mechanisms. Binning and Rohrer's spatial resolution of single atoms and molecules via scanning tunneling microscopy opened up entirely new fields of science and technology, leading to the 1986 Prize. Johann Diesenhofer, Robert Huber, and Hartmut Michel were awarded the 1988 Prize for determining the structure of the ultimate electron transfer engine, the photosynthetic reaction center. And many other Nobel Prize winning advances in Chemistry, Biology, and Physics have intellectual threads linking them to this field. Looking to the future, the relationship between redox stress in cells and cancer is placing ET in the forefront of biomedicine, and critical advances seem likely to be built on the deep foundations of this field.

The papers in this volume reflect the vibrancy and excitement surrounding charge-transfer processes today. Papers span all fields, including theory (studies of few and multi-state models for charge flow, inelastic transport through molecules, open system quantum dynamics, quantum dissipation, linkage of ET to energy transfer, the theory of transport though nucleic acids, and the possible role of inelastic tunneling in olfaction), novel synthetic frameworks for charge separation (peptides, nanoparticle–molecule hybrids, buckyballs, and single molecule junction structures), and biological redox machines, chains, and catalysts (DNA, microbial redox chains, hydrogenases, and interprotein ET couples).

It is startling to reflect on how rapid the progress has been in this field. Indeed, about 100 papers were published on “electron transfer” from 1950–1960; 1000 followed in the next decade, and over 9000 appeared in 2011 alone (according to ISI). Following the seminal contributions punctuated by the Nobel Prizes of Marcus and the others, a deepened understanding of ET mechanisms has unfolded. To name a few, solvent dynamical control and broader understanding of ET reaction dynamics, electronic tunneling pathways, proton-coupled ET mechanisms, DNA damage and repair, hopping–tunneling transitions, single-molecule junction phenomena, and electron transfer application in photobiology, nanoscience and energy science have provided tremendously rich challenges and opportunities for discovery; many of these exciting frontier research directions are represented in this volume.

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