A multi-scale time-resolved study of photoactivated dynamics in 5-benzyl uracil, a model for DNA/protein interactions

Phys Chem Chem Phys. 2019 Dec 11;21(48):26301-26310. doi: 10.1039/c9cp03839f.

Abstract

We combine fluorescence up-conversion and time correlated single photon counting experiments to investigate the 5-benzyl uracil excited state dynamics in methanol from 100 fs up to several ns. This molecule has been proposed as a model for DNA/protein interactions. Our results show emission bands at about 310 and 350 nm that exhibit bi-exponential sub-ps decays. Calculations, including solvent effects by a mixed discrete-continuum model, indicate that the Franck Condon region is characterized by significant coupling between the excited states of the benzyl and the uracil moieties, mirrored by the short-lived emission at 310 nm. Two main ground state recovery pathways are identified, both contributing to the 350 nm emission. The first 'photophysical' decay path involves a ππ* excited state localized on the uracil and is connected to the ground electronic state by an easily accessible crossing with S0, accounting for the short lifetime component. Simulations indicate that a possible second pathway is characterized by exciplex formation, with partial benzene → uracil charge transfer character, that may lead instead to photocyclization. The relevance of our results is discussed in view of the photoactivated dynamics of DNA/protein complexes, with implications on their interaction mechanisms.

MeSH terms

  • Cyclization
  • DNA / chemistry*
  • Density Functional Theory
  • Kinetics
  • Methanol / chemistry
  • Proteins / chemistry*
  • Spectrometry, Fluorescence
  • Uracil / chemistry*

Substances

  • Proteins
  • Uracil
  • DNA
  • Methanol