Electron transfer, the process of moving an electron from one place to another, is vital to almost all chemical systems. It is a fundamental process in organic synthesis, in catalysis, and in the biochemistry of all living organisms. In biological systems, transition metal centers (such as iron and copper) often play the central role in an electron transfer protein, shuttling electrons within or between proteins. Electron transfer proteins are specially designed to do their jobs in a fast and efficient manner, and are often more efficient then any man-made counterparts. Hence, understanding biological electron transfer provides important insight not only into biological mechanisms, but also to a fundamental process of all chemical systems.

Photoelectron spectroscopy (PES) experiments conducted at SSRL have enabled researchers at Stanford University to gain fundamental insight into the changes that occur in small molecule model systems of the protein rubredoxin upon removal of an electron. These studies indicate that the electron transfer process is more complicated than the "one-electron" model that is often assumed. Rather, these studies show that there is a large change in the electronic structure upon removal of an electron. This change in electronic structure distributes the removal of the electron over a larger volume, thus decreasing the energy required to remove an electron and allowing the process to happen more quickly. Hence, these studies provide insight into the factors which allow electron transfer proteins to efficiently and effectively carry out their jobs.