From Enzyme to Molecular Device. Exploring the Interdependence of Redox and Molecular Recognition

Abstract

Angelika Niemz was born in Rheinfelden, Germany, in 1970. After receiving her B.Sc. in chemistry at the University of Konstanz in 1993, she came to the United States through the Baden Wu ¨rttemberg-Massachusetts exchange program. Currently a Ph.D. student in the Rotello group at the University of Massachusetts, her interests span the areas of biological, organic, and physical chemistry. Her current research focuses on the characterization of host-guest systems using an array of magnetic resonance, electrochemical, spectroelectrochemical, and surface characterization methods. Vincent M. Rotello received his B.S. from the Illinois Institute of Technology in 1985. He obtained a Ph.D. with Harry Wasserman from Yale University in 1990, and then did an NSF Postdoctoral Fellowship with Julius Rebek at MIT. He is currently an Associate Professor in the Department of Chemistry and the Program in Molecular and Cellular Biology at the University of Massachusetts. His principle motivation in research is the fundamental understanding of noncovalent interactions, and the application of this knowledge to biological and materials issues. Scheme 1. Common Redox and Protonation States of the Flavin Cofactor (lumiflavin, R ) CH 3 ; FMN, R ) CH 2 ((CHOH) 4 -phosphate; FAD, R ) CH 2 ((CHOH) 4 -pyrophosphate-adenosine; flavin 1, R ) CH 2 CH(CH 3 ) 2 )

Hydrogen bond-free flavin redox properties: managing flavins in extreme aprotic solvents

“…This suggests that flavin reduction evinces a significant increase in the electron density at each carbonyl group, and that the increased ligand affinity of anionic flavin semiquinone radical is principally mediated by hydrogen bonding contacts of these carbonyls, as previously noted. 22 …”

Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

“…[1][2][3][4][5] Hydrogen-bonding and proton transfer are of key importance for controlling the reduction potential and reaction path. [5][6][7][8][9][10][11][12][13][14][15] In well-buffered aqueous media, quinone-hydroquinone couples provide familiar, reversible two-electron redox systems in which half-wave reduction potentials vary with the pH in a straightforward Nernstian manner. 16 On the other hand, in dry, neutral aprotic media, quinones typically show two cathodic waves corresponding to reversible formation of the radical anion and the dianion.…”

“…[6][7][8][9][10][11][12][13][14][15]17 Much attention has been paid to the characteristics of the redox behavior of quinones by hydrogen-bonding with weakly interacting proton donors, such as CH3OH and C2H5OH, [6][7][8][9][10][11][12][13][14][15] which is implicated in controlling both intra-and intermolecular structures in biological systems and biological function as an active site of quinoenzymes. [3][4][5] Such studies demonstrate that the first and second reduction waves of quinones move towards less-negative potential values as the concentration of the proton donor is increased, with no loss of reversibility. We first considered the models used to describe this type of interaction involving the hydrogen-bonding of unreduced and reduced quinones with CH3OH, and evaluated the hydrogen-bond formation constants using electrochemical techniques.…”

Ethanol Concentration Dependence of Photoinduced Charge Separation Reaction between Zinc Tetraphenylporphyrin and Duroquinone Studied by Laser Flash Photolysis

“…[5][6][7][8][9][10][11] Recent time-resolved electron paramagnetic resonance (EPR) studies on solvent-separated radical ion pairs generated by photoinduced CS reactions suggest that values are also increased by solute-solvent hydrogen-bonding interactions in polar solvents. 12 The results were interpreted with a change of chemical equilibrium for the hydrogen-bonding complex during the ET reactions; 13 however, the ET reaction rates have not been evaluated directly.…”