ELECTRONICALLY ACTIVE AIB HELICES

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The proposed research program is to design and synthetic specific synthetic helical oligopeptides containing beta-(aromatic)- alanines and to measure light-induced electron dynamics from singlet and triplet excited states of these multicomponent covalent assemblies using nanosecond and picosecond transient absorption methods. Natural aromatic amino acids will be introduced in intervening positions along the helix to test theories for their participation in long range electron transfer. Theoretical approaches based on the recently developed quantum path integral Monte Carlo approach to electron tunneling in complex structured environments will also be pursued and will be applied to these molecular systems. The diverse techniques of synthetic chemistry, oligopeptide synthesis, time-resolved laser spectroscopy, and theoretical quantum simulation methods together will enable an intense study of the role of polypeptide structure in modulating long range electron transfer interactions. The immediate aim is to design and build a novel system in which to observe complex electronic interaction phenomena; this program was developed to advance the confluence of two long range goals: to understand the participation of intermediary residues in accelerating, controlling, or directing electron transfer reactivity, and to design synthetic electron transfer proteins. Specifically, donor and acceptor redox centers will be included within the sequence of a series of hydrophobic oligopeptides rich in alpha-aminoisobutyric acid (Aib) which will be synthesized by known methods. Aib-rich oligopeptides form 310 helices and occur naturally in microbial peptide antibiotics. Transient absorption spectrometers based on Q-switched YAG/dye and flash-pumped mode-locked YAG lasers will provide the capability to follow electron transfer kinetics over a very wide range of time scales (distances). The ability to synthesize families of related oligopeptides will be extensively exploited and represents a significant advantage of this polymeric approach to structured electron donor/perturbant/acceptor complexes.