Flavoenzymes comprise a group of biological molecules that utilize the flavin cofactor to catalyze a large variety of oxidation and reduction reactions. The protein constituent of these redox-active enzymes regulates the activity of the flavin apoenzyme, mainly through non-covalent interactions. Some of these non-covalent interactions that have been previously isolated and investigated include hydrogen bonding, π-π aromatic stacking, dipolar and steric effects. We have focused our efforts in gaining better understanding on hydrogen bonded interactions utilizing a combination of 1H-NMR, electrochemistry, SEEPR and B3LYP computational techniques. In the present manuscript we have studied the interplay between hydrogen bond formation and redox activity in redox-active model systems. Specifically, we have used cyclic voltammetry and chemical modification of the flavin cofactor to understand better the influence of hydrogen bonding on the redox properties of the flavin cofactor. We have concluded that hydrogen bond formation at the N(3)-H position of the cofactor modulates the reduction potential by 80 mV (1.8 kcal/mol), making the flavin harder to reduce. This effect is similar in effect and magnitude to methylating the N(3) position of the cofactor. Our next goal was to investigate how far the electronic modulation is transmitted from the binding site. For this project we have utilized the flavin cofactor and a group of chemically related triazine hosts with different functionality and electronic donating and withdrawing capabilities. We analyzed the effects of the electronic requirements of the functional groups on the association constants between flavin and 5 different triazine-based complexes. Further insight on the systems under study was obtained through DFT-B3LYP computational studies. Our results show that electronic modulation extend more than 11 Å from the binding site, providing further knowledge useful in designing molecular wires and sensing devices. Finally, we have utilized the redox-active compound 1,8-naphthalimide and two chemically related hosts to study the recognition-controlled modulation in hydrogen bond formation. In this project we have employed diaminotriazine and diaminopyridine hosts to examine the interplay between polarizability and electrostatic interactions on the formation of hydrogen bonds. We have concluded that in the naphthalimide-triazine pair, the recognition is mainly driven by electrostatic interaction. However, in the naphthalimide-diaminopyridine complex, the hydrogen bond formation is due to polarization of the N-H bonds.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-3496 |
| Date | 01 January 2001 |
| Creators | Cuello, Alejandro Oscar |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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