Photooxidation of guanine by a ruthenium dipyridophenazine complex intercalated in a double-stranded polynucleotide monitored directly by picosecond visible and infrared transient absorption spectroscopy.
Transient species formed by photoexcitation (400 nm) of [Ru(dppz)(tap)2]2+ (1) (dppz = dipyrido[3,2-a:2',3'-c]phenazine; tap=1,4,5,8-tetraazaphenanthrene) in aqueous solution and when intercalated into a double-stranded synthetic polynucleotide, [poly(dG-dC)]2, have been observed on a picosecond timescale by both visible transient absorption (allowing monitoring of the metal complex intermediates) and transient infrared (IR) absorption spectroscopy (allowing direct study of the DNA nucleobases). By contrast with its behavior when free in aqueous solution, excitation of 1 when bound to [poly(dG-dC)]2 causes a strong increase in absorbance at 515 nm due to formation of the reduced complex [Ru(dppz)(tap)2]+ (rate constant=(2.0+/-0.2) x 10(9) s(-1)). The subsequent reformation of 1 proceeds with a rate constant of (1.1+/-0.2) x 10(8) s(-1). When the process is carried out in D2O, the rates of formation and removal of [Ru(dppz)(tap)2]+ are reduced (rate constants (1.5+/-0.3) x 10(9) and (0.7+/-0.2) x 10(8) s(-1) respectively) consistent with proton-coupled electron transfer processes. Picosecond transient IR measurements in the 1540-1720 cm(-1) region in D2O solution confirm that the reduction of 1 intercalated into [poly(dG-dC)]2 is accompanied by bleaching of IR ground-state bands of guanine (1690 cm(-1)) and cytosine (1656 cm(-1)), each with similar rate constants.
Elias
Benjamin
B
Service de Chimie Organique et Photochimie, CP 160/08, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, 1050 Bruxelles, Belgium.
Creely
Caitriona
C
Doorley
Gerard W
GW
Feeney
Martin M
MM
Moucheron
Cécile
C
Kirsch-DeMesmaeker
Andrée
A
Dyer
Joanne
J
Grills
David C
DC
George
Michael W
MW
Matousek
Pavel
P
Parker
Anthony W
AW
Towrie
Michael
M
Kelly
John M
JM
D006147:Guanine / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010619:Phenazines / Q000737:chemistry*; D010777:Photochemistry; D011119:Polynucleotides / Q000737:chemistry*; D017975:Ruthenium Compounds / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013997:Time Factors
D010619:Phenazines; D011119:Polynucleotides; D017975:Ruthenium Compounds; D006147:Guanine