TY - JOUR
T1 - Tautomeric transitions of isocytosine isolated in argon and neon matrices induced by UV irradiation
AU - Ivanov, Alexander Yu
AU - Stepanian, Stepan G.
AU - Adamowicz, Ludwik
N1 - Funding Information:
The present work was partly supported by the National Academy of Sciences of Ukraine (Grant No. 0110U007895 ). Authors acknowledge the Computational Centers at Institute for Low Temperature Physics and Engineering and at the University of Arizona for providing computer time for this work.
PY - 2012/10/10
Y1 - 2012/10/10
N2 - The tautomeric equilibrium of the isocytosine molecules in the low temperature Ar and Ne matrices has been investigated by the FTIR matrix isolation spectroscopy and quantum-chemical calculations at the DFT, MP2, and CCSD(T) levels of theory. Broad-band UV irradiation of matrix isolated isocytosine results in an increase of the abundance of the minor isocytosine tautomer, KA1. After UV irradiation the intensity of the spectral bands assigned to this tautomer increases more than 1.5 times and the bands of other minor conformers are not observed. The values of ΔH (6.6 kJ/mol) and ΔG (6.8 kJ/mol) determined based on the experimental data are close to the ΔE value (8.3 kJ/mol) calculated at the CCSD/aug-cc-pVDZ level of theory. Two Fermi resonances involving the νCO vibration of the minor tautomer KA1 (2-amino-4-oxo-pyrimidine or keto-amino) and four Fermi resonances involving the ring stretching vibrations of the most abundant tautomer EA1 (2-amino-4-hydroxy-pyrimidine or enol-amino) are found. The performance of the different computational methods in predicting the vibrational spectra of isocytosine is evaluated.
AB - The tautomeric equilibrium of the isocytosine molecules in the low temperature Ar and Ne matrices has been investigated by the FTIR matrix isolation spectroscopy and quantum-chemical calculations at the DFT, MP2, and CCSD(T) levels of theory. Broad-band UV irradiation of matrix isolated isocytosine results in an increase of the abundance of the minor isocytosine tautomer, KA1. After UV irradiation the intensity of the spectral bands assigned to this tautomer increases more than 1.5 times and the bands of other minor conformers are not observed. The values of ΔH (6.6 kJ/mol) and ΔG (6.8 kJ/mol) determined based on the experimental data are close to the ΔE value (8.3 kJ/mol) calculated at the CCSD/aug-cc-pVDZ level of theory. Two Fermi resonances involving the νCO vibration of the minor tautomer KA1 (2-amino-4-oxo-pyrimidine or keto-amino) and four Fermi resonances involving the ring stretching vibrations of the most abundant tautomer EA1 (2-amino-4-hydroxy-pyrimidine or enol-amino) are found. The performance of the different computational methods in predicting the vibrational spectra of isocytosine is evaluated.
KW - FTIR matrix isolation
KW - Fermi resonance
KW - Nucleic acid bases
KW - Tautomerism
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U2 - 10.1016/j.molstruc.2012.05.043
DO - 10.1016/j.molstruc.2012.05.043
M3 - Article
AN - SCOPUS:84866734259
VL - 1025
SP - 92
EP - 104
JO - Journal of Molecular Structure
JF - Journal of Molecular Structure
SN - 0022-2860
ER -