title: Molecular switch based on a biologically important redox reaction.
abstract: Building on our earlier report of a single-molecule probe, we show how biologically important redox centers, nicotinamide and quinone, incorporated into a fluorophore-spacer-receptor molecular structure, form redox active molecular switches, with the photoinduced electron-transfer behavior of each depending on the oxidation state of the receptor subunit. The switch based on nicotinamide (3/6) is strongly fluorescent in its oxidized state (Phi(F) approximately 1.0) but nonfluorescent in the reduced state (Phi(F) < 0.001) due to electron transfer from the reduced nicotinamide to the photoexcited fluorophore. The fluorescence can be reversibly switched off and on chemically by successive reduction with NaBH(3)CN and oxidation with tetrachlorobenzoquinone and switched electrochemically over 10 cycles without significant degradation. A similar switch based on quinonimine turned out to be nonfluorescent in both reduced and oxidized states: in addition to a similar quenching mechanism in the reduced state, quenching also occurs in the oxidized state, due to electron transfer from the fluorophore to the receptor. Ab initio quantum chemical calculations of orbital energy levels were used to corroborate these quenching mechanisms. Calculations predicted photoinduced electron transfer to be energetically favorable in all cases where quenching was observed and unfavorable in all cases where it was not. Application of the perylene analogue as a biosensor has also been demonstrated by coupling the switch to the catalytic pathway of yeast alcohol dehydrogenase, a common NADH/NAD(+)-utilizing enzyme.
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Yan
authors.forename: Michael W
authors.initials: MW
authors.lastname: Holman
authors.forename: Paul
authors.initials: P
authors.lastname: Robustelli
authors.forename: Arindam
authors.initials: A
authors.lastname: Chowdhury
authors.forename: Fady I
authors.initials: FI
authors.lastname: Ishak
authors.forename: David M
authors.initials: DM
authors.lastname: Adams
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry*; D001894:Borohydrides / Q000737:chemistry; D004563:Electrochemistry; D005453:Fluorescence; D015394:Molecular Structure; D009243:NAD / Q000138:chemical synthesis / Q000737:chemistry*; D009536:Niacinamide / Q000737:chemistry*; D010084:Oxidation-Reduction; D010569:Perylene / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry*; D013997:Time Factors
chemical_list: D016227:Benzoquinones; D001894:Borohydrides; D009243:NAD; D009536:Niacinamide; C004532:quinone; D010569:Perylene; C009282:sodium cyanoborohydride; D000426:Alcohol Dehydrogenase