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Density functional theory study on molecular structure and vibrational IR spectra of isocytosine

✍ Scribed by Józef S. Kwiatkowski; Jerzy Leszczynski

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
178 KB
Volume
61
Category
Article
ISSN
0020-7608

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✦ Synopsis

Density functional theory with the combined Becke3-LYP exchange᎐correlation energy w Ž .

x Ž . functional DFT B3-LYP method using the 6-31G d, p basis set is applied to predict Ž . molecular parameters geometries, rotational constants, dipole moments and vibrational Ž . IR spectra harmonic wavenumbers, absolute intensities of six tautomers of the isocytosine molecule. The results are compared with the corresponding data calculated at Ž . the conventional ab initio Hartree᎐Fock HF level using the same basis set and with Ž . available experimental data. Calculations show that a three amino tautomers are Ž . Ž slightly nonplanar species with, evidently, a distorted amino group, b the DFT B3-. Ž . LYP r6-31G d, p method predicts better molecular parameters, than do the HF Ž . Ž . calculations, and c the DFT B3-LYP -calculated vibrational IR spectra of isocytosine agree well with the available recorded IR spectra, and they show marked improvement Ž . over the IR spectra predicted at the HFr6-31G d, p level. Tautomeric stabilities of Ž . isocytosine are discussed on the basis of computed electronic energies by the DFT B3-LYP w Ž . and ab initio approaches including the MP2 and MP4 SDQ calculations of electronic x Ž . energies and predicted zero-point vibrational energies by DFT B3-LYP and HF methods. This relative energies at 0 K of the tautomeric forms of isocytosine predicted by both Ž . conventional ab initio and DFT B3-LYP methods correlate well with the experimental data, showing the predominance of the aminohydroxy tautomer of isocytosine for an isolated molecule.

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