Open AccessEXCITED-STATE TWO-PROTON TAUTOMERISM IN HYDROGEN-BONDED N-HETEROCYCLIC BASE PAIRS
Author(s) -
Carl Al Taylor,
M. Ashraf ElBayoumi,
Michael Kasha
Publication year - 1969
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.63.2.253
Subject(s) - tautomer , photochemistry , chemistry , excimer , excited state , fluorescence , dimer , proton , luminescence , base pair , hydrogen bond , monomer , absorption spectroscopy , molecule , dna , stereochemistry , materials science , atomic physics , organic chemistry , biochemistry , physics , optoelectronics , quantum mechanics , polymer
The optical absorption and luminescence spectra of 7-azaindole and its doubly hydrogen-bonded dimer were investigated as a model for the study of electronic interactions in DNA base pairs. It is demonstrated that a biprotonic phototautomerism occurs in the dimer and in suitable ethanol solvates in fluid solvents but that the phenomenon is not observed in a rigid solvent matrix. The normal violet structured fluorescence of 7-azaindole monomer becomes a broad green fluorescence in the tautomer. It is shown that spectral band interchanges, excimer formation, excited-state single-proton transfer, and proton tunneling cannot account for the luminescence change, but that the molecular exciton effect facilitates the cooperative two-proton reversible transfer. It is proposed that biprotonic phototautomerism with molecular environmental sensitivity could provide a mechanism for the initial step in ultraviolet mutagenic effects in DNA.