Chapter 4: Electron Transfer Reactions in Enzymes: Seven Things that Might Break Down in Vanilla Marcus Theory and How to Fix Them if They Do

Marcus theory (MT) is the governing paradigm for electron transfer (ET) reactions in solution and its power has also been brought to bear on biological ET. However, MT may mean different things to different people, depending on the particular variant of MT they have in mind. In this chapter, we take Marcus’ work as it stood in 1965 to represent the standard or ‘vanilla’ MT. After describing the salient features of vanilla MT, we then attempt to provide a pedagogical review from the perspective of features that might break down in real applications, focusing mainly on enzymes, and we discuss available fixes. The chapter is meant to provide a rigorous graduate-level review of both theoretical and computational issues.