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Photooxidation of Guanine by a Ruthenium Dipyridophenazine Complex Intercalated in a Double‐Stranded Polynucleotide Monitored Directly by Picosecond Visible and Infrared Transient Absorption Spectroscopy
Author(s) -
Elias Benjamin,
Creely Caitriona,
Doorley Gerard W.,
Feeney Martin M.,
Moucheron Cécile,
KirschDeMesmaeker Andrée,
Dyer Joanne,
Grills David C.,
George Michael W.,
Matousek Pavel,
Parker Anthony W.,
Towrie Michael,
Kelly John M.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700564
Subject(s) - chemistry , ultrafast laser spectroscopy , photochemistry , aqueous solution , absorbance , reaction rate constant , ruthenium , guanine , absorption spectroscopy , infrared spectroscopy , phenazine , photoexcitation , analytical chemistry (journal) , spectroscopy , excitation , kinetics , organic chemistry , nucleotide , biochemistry , physics , chromatography , quantum mechanics , electrical engineering , gene , engineering , catalysis
Transient species formed by photoexcitation (400 nm) of [Ru(dppz)(tap) 2 ] 2+ ( 1 ) (dpp z =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)×10 9 s −1 ). The subsequent reformation of 1 proceeds with a rate constant of (1.1±0.2)×10 8 s −1 . When the process is carried out in D 2 O, the rates of formation and removal of [Ru(dppz)(tap) 2 ] + are reduced (rate constants (1.5±0.3)×10 9 and (0.7±0.2)×10 8 s −1 respectively) consistent with proton‐coupled electron transfer processes. Picosecond transient IR measurements in the 1540–1720 cm −1 region in D 2 O 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.