Flash quenching

Fig. 13 DNA-protein CT reactions. The DNA-bound protein, methyltransferase Hhal (mutant Q237W), flips a base out of the DNA double helix and inserts a trytophan side chain leaving the /r-stack largely unperturbed. This intercalated trytophan moiety transfers an electron to [Ru(bpy )(dppz)(phen)]3+, generated by flash quench, over 50 A away. Adapted from [164]... 

Nguyen KL, Steryo M, Kurbanyan K, Nowitzki KM, Butterfield SM, Ward SR, Stemp EDA (2000) DNA-protein cross-linking from oxidation of guanine via the flash-quench technique. J Am Chem... 

Figure 8 Illustration of the flash-quench technique for measuring intramolecular ET rates. Photoexcitation of Ru(II)(bpy)2(imidazole)(amine)2+, Ru(II)(bpy), bound to ferro-cytochrome c, Fe(II)P, produced an 80-ns lived metal-to-ligand charge transfer (MLCT) excited state, Ru(III)(bpy -), which was oxidatively quenched by bimolecular reaction with Ru(NH3) +. The resulting Ru(III)-complex was then reduced by the Fe(II)P through thermal, protein-mediated ET. Finally bimolecular reaction of the Ru(II)/Fe(III)P product with Ru(NH3) + re-formed the starting Ru(II)-protein-Fe(II)P complex.

Figure 13.1 Scheme for (a) the reduction or (b) the oxidation of the iron centre of haemo-proteins with photoexcited ruthenium complex, using flash quench procedure. (Adapted from Szacilowski et al. [124])... 

Figure 14.4 Molecular mechanism of the flash quench method applied for photo-oxidation of guanine by generated in situ Pu1" complex. Q denotes a quencher...

Stemp EDA, Arkin MR, Barton JK. Oxidation of guanine in DNA by Ru(phen)2dppz3+ using the flash-quench technique. J Am Chem Soc 1997 119 2921-5. 

On the basis of the strong photo-oxidising behaviour of [Re(phen)(CO)3(imidazole)]+ (9) (Re(I) /Re(0) = ca. +1.3 V vs. NHE in CH3CN), Gray and co-workers reacted [Re(phen)(C0)3(H20)]+ with azurin, resulting in the formation of [Re(phen) (CO)3(His83)]+-AzCu+, and studied the electron-transfer in this mutant [28], Excitation of the rhenium(I) complex leads to direct oxidation of the copper centre of the protein to copper(II). Using the flash-quench technique with... 

The rates of intramolecular Fe2+ - Ru3+ electron transfer were measured by a flash-quench technique (33) the results are listed in Table I along with other pertinent ET parameters. Measured ET rates span 2... 

Jay Winkler Flash-quench method for measurements of electron tunneling over long distances... 

As noted above, MLCT excited states of diimine metal complexes are both better reductants and oxidants than the ground-state species. This property has been exploited by Gray, Barton, and others for the study of proteins, DNA, and other biological molecules. Flash/quench experiments were first developed to provide a high driving force method to measure rates of electron transfer in proteins. In these experiments an excited diimine complex, typically a member of the Ru(bipy)2(diimine) + family of complexes, is oxidatively quenched with Ru(NH3)6 +, Co(NH3)5CP+, or methyl viologen, or reductively quenched with / -methoxy-A,A-dimethylaniline to yield a highly active redox species. 

Barton has carried out extensive studies into the transport of charge through DNA utilizing the flash/quench method to inject charge. In the absence of imperfections to the DNA stack, electron transport to sites 200 A away from the point of charge injection have been observed. These studies, which have been extensively reviewed, forced a significant... 

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