Quantum chemical MP2 results on some hydrates of cytosine: binding sites, energies and the first hydration shell.

A detailed quantum chemical investigation was undertaken to obtain the structure and energetics of cytosine hydrates Cyt·nH2O, with n = 1 to 7. The MP2(fc)/aug-cc-pVDZ level was used as the standard, with some DFT (B3LYP) and coupled cluster calculations, as well as calculations with the aug-cc-pVTZ basis set added for comparison. In a systematic search for microhydrated forms of cytosine, we have found that several structures have not yet been reported in the literature.

Benchmark studies on the building blocks of DNA. 2. Effect of biological environment on the electronic excitation spectrum of nucleobases.

In the first paper of this series (Szalay; et al. J. Phys.

Tautomers of cytosine and their excited electronic states: a matrix isolation spectroscopic and quantum chemical study.

We have measured the IR and UV spectra of cytosine in a low-temperature argon matrix. An attempt was made to determine the tautomeric ratios existing in the matrix, making use of the matrix-isolation IR spectrum and computed IR intensities of the tautomers in a least squares fitting procedure. The mole fractions are about 0.

Reinterpretation of the UV spectrum of cytosine: only two electronic transitions?

Theoretical vertical excitation energies and simulated UV spectrum are reported for the canonical (amino-oxo) form of cytosine. The calculations were performed by the EOM-CCSD and EOM-CC3 methods with basis sets up to triple-zeta quality. Beyond vertical excitations, the complete vibronic spectrum has been determined the first time, using the linear vibronic coupling (LVC) method.