DIARYL NITRENIUM IONS: ELECTRONIC STATE REACTIONS, MECHANISTIC STUDIES, AND PEPTIDE LABELING

Abstract

Nitrenium ions are studied for their electronic properties, synthetic reactions, and their labeling of biomolecules. Diaryl nitrenium ions have sufficient conjugation to allow the nitrenium ions to both exist as a discrete structure and be directly observed by laser flash photolysis. In this dissertation the mechanisms and reactions of diaryl nitrenium ions will be examined. Further, the peptide WWCNDGR will be selectively labeled with a diaryl nitrenium ion.Chapter 1 reviews relevant photochemistry fundamentals and nitrenium ion basics. Chapter 2 describes the 10,11-dihydrodibenzo[b,f]azepinyl nitrenium ion 2 in comparison to the diphenyl nitrenium ion 1. It will be found that although the ethylene bridge 10,11-dihydrodibenzo[b,f]azepinyl nitrenium ion 2 raises the triplet state energy by approximately 8 kcal/mol, it’s singlet state reaction rates are only minorly decreased. Chapter 3 investigates diaryl nitrenium ions’ mechanism with H-atom donors as the parent amine has been reported in the literature as evidence of triplet state reactivity. It is concluded there are alternative mechanisms for formation of the parent amine through either reducing the nitrenium ion to the neutral radical or through direct hydrogen atom abstraction from the singlet state. Chapter 4 examines the antiaromaticity of 3,6-dibromocarbazolyl nitrenium ion’s mechanism with different electron donors and nucleophiles. It is concluded that the 3,6-dibromocarbazolyl nitrenium ion either gets trapped by a nucleophile or it gets reduced by an electron donor or the parent pyridinium ion to form the neutral radical. The neutral radical either gets protonated to form the parent amine or dimerizes to form the N-N dimer. Finally, chapter 5 shows that the diaryl nitrenium ion, N-(4,4’-dibromodiphenyl)nitrenium ion, can selectively label tryptophan on the peptide WWCNDGR.