Issue 21, 2003
From the journal:

Physical Chemistry Chemical Physics

The nucleobase cytosine and the cytosine dimer investigated by double resonance laser spectroscopy and ab initio calculations

E. Nir,a   I. Hünig,b   K. Kleinermannsb  and  M. S. de Vriesc  

a Department of Chemistry, The Hebrew University, Jerusalem, Israel

b Institut für Physikalische Chemie und Elektrochemie I, Heinrich Heine Universität Düsseldorf, Düsseldorf, Germany

c Dept. of Chemistry and Biochemistry, Santa Barbara, California, USA

Abstract

The vibronic spectrum of laser desorbed and jet cooled cytosine consists of bands from two major tautomers (keto and enol) as revealed by UV-UV and IR-UV double resonance spectroscopy and methyl blocking experiments. Only one isomer each was observed for the cytosine dimer and for the cytosine - 1-methylcytosine mixed dimer. These isomers form C[double bond, length as m-dash]O⋯HNH/NH⋯N hydrogen bonds. Cytosine - 5-methylcytosine exhibits three isomers: one again with C[double bond, length as m-dash]O⋯HNH/NH⋯N connectivity, the second with C[double bond, length as m-dash]O⋯HNH/NH⋯N interaction but one cytosine in the enol form and the third with symmetrical C[double bond, length as m-dash]O⋯NH/NH⋯O[double bond, length as m-dash]C bonds. These are also the most stable clusters according to molecular dynamics/quenching and ab initio quantum chemical calculations. The experimental IR spectra of these isomers agree well with the calculated normal mode vibrational spectra. The vibronic spectra of the clusters are blue shifted relative to the monomer spectra by more than 1000 cm−1 indicating a considerable reduction of dimer stability upon electronic excitation.

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Article information

DOI
https://doi.org/10.1039/B310396J
Article type
Paper
Submitted
27 Aug 2003
Accepted
29 Aug 2003
First published
24 Sep 2003

Phys. Chem. Chem. Phys., 2003,5, 4780-4785

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The nucleobase cytosine and the cytosine dimer investigated by double resonance laser spectroscopy and ab initio calculations

E. Nir, I. Hünig, K. Kleinermanns and M. S. de Vries, Phys. Chem. Chem. Phys., 2003, 5, 4780 DOI: 10.1039/B310396J

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