Synthesis and flash-quench studies of ruthenium-modified oligonucleotides

The notion that DNA may be capable of electron transfer (ET) over many base pairs at meaningful rates has inspired numerous experimental and theoretical studies of electron transfer reactions through DNA. The structure of DNA, with noncovalently-stacked pi orbitals, has been proposed as a medium for extending the electronic coupling between an electron donor and acceptor pair.;This thesis focuses on the synthesis and flash-quench investigations of ruthenium-modified oligonucleotides for intramolecular, ground-state electron transfer studies in DNA. The site-selectively modified oligonucleotides with covalently bound donor and acceptor ruthenium complexes would allow the examination of the ground state electron transfer rates and the variation of these rates with distance through DNA.;The first part of this thesis (Chapter 2) describes the synthesis and characterization of [Ru(tol-acac)2(IMPy-T)] (tol-acac = tolyl-acetylacetonate, IMPy = 2'-iminomethylpyridine, T = thymidine) and [Ru(bpy)2(IMPy-T)] 2+ with spectroscopically unique properties that are covalently attached to the 5'-position of DNA ribose rings. Various lengths (10-, 11-, and 12-mer) of the ruthenium-modified duplex DNA have been synthesized and characterized, demonstrating successful incorporations of ruthenium complexes into DNA duplexes. Photochemistry and the flash-quench studies in these synthesized metalated oligonucleotides are discussed in the second part of this thesis (Chapter 3). Time-resolved spectroscopy and transient absorption spectroscopy are used to explore the kinetics of the quenching processes of the metalated oligonucleotides. The synthesis of a novel bimetalated single strand (ss) DNA with the modification of ruthenium complexes at the 3'- end and the 5'- end are discussed in Chapter 4.