Recent developments in the excited states of nucleic acids

A TDDFT Study of the Optical Response of DNA Bases, Base Pairs, and Their Tautomers in the Gas Phase

We present calculations of the optical response of the DNA bases and base pairs both in their normal and tautomeric forms in the gas phase, using time-dependent density functional theory (TDDFT). These calculations are performed in real time within the adiabatic approximation with a basis of local orbitals. Our results for the individual bases are in good agreement with experiment and computationally more demanding calculations of chemical accuracy. The optical response of base pairs indicates that the differences between normal and tautomeric forms in certain cases are significant enough to provide a means of identification.

Vacuum UV--photophysics and photochemistry of biomolecules

The vacuum UV radiation absorbed by biomolecules may initiate luminescence, photodestruction and photoionization processes which lead to distortions or damage of the molecular structure. To explain the mechanisms of the processes in question and the role of different molecular fragments, it is necessary to analyse the absorption spectra. The accurate determination of the photoproducts is necessary when discussing the possible scission of molecular bonds. A knowledge of the quantum yields of vacuum UV-induced processes provides information on the relative effectiveness of different processes. In particular, the most efficient destruction of purine-pyrimidine bases, nucleotides and DNA is caused by irradiation of aqueous solutions rather than solid compounds. Additional information on molecular damage mechanisms may be obtained by comparison of data obtained using ionizing UV and UV laser irradiation.