One of the unresolved problems in the study of electron transfer mechanisms involves the methods of electron transport on a molecular level in the respiratory chain. Our objective is to construct models which will mimic the electronic pathways available for long distance transfers in proteins. An examination of simple systems and of proteins whose structures are well known (especially cytochrome c) leads us to postulate that electron rich functional groups such as aromatic rings and sulfur atoms may serve to mediate and guide the transferring electron. The approach to be used is quite original in that we assume that geometry of the metal in relation to that of the sulfur and aromatic ring is a critical factor in observing through-space interactions in proteins and that this preferred geometry can be found by an examination of the properties of simple model systems. At the same time, we propose to investigate small molecules designed to transfer electrons in a 'through-bond' manner. There is evidence from photoelectron spectroscopy that this occurs. Its importance in biological systems can only be assessed if quantitative data from simple well-defined systems are available. The methods used to explore the redox process will be primarily electrochemistry and near-infrared spectroscopy. The latter technique will be employed to measure the intervalence transition band which appears when an electron is optically transferred from one metal to another in the same molecule. The shape and intensity of the band provides information on the degree of electronic coupling between the metal centers. In the long-term, the model studies will serve to direct the approach to a study of the actual proteins since one might expect to observe intervalence transitions indicative of through-space interactions in proteins under the proper experimental conditions, yet to be determined.
