Matrix-isolation FT-IR studies and ab initio calculations of hydrogen-bonded complexes of molecules modeling cytosine or isocytosine tautomers. 5. 1-CH{sub 3}-cytosine complexes with H{sub 2}O in Ar matrices
Journal Article
·
· Journal of Physical Chemistry
- Univ. of Leuven, Heverlee (Belgium)
- Universite Paul Sabatier, Toulouse (France)
The combined experimental and theoretical ab initio method for investigation of hydrogen-bonded complexes between water and molecules modeling cytosines has been applied to 1-CH{sub 3}-cytosine. An approximate value of 7.2 is obtained for the tautomerization constant K{sub T}(a-o/i-o) using the infrared intensity measurement. The most stable H-bonded complex of the abundant a-o tautomer with water is the closed N{sub 3}...H-O...H-N{sub 14} structrue, which shows cooperativity between the two H-bonds. Less stable complexes are the closed N{sub 3}...H-O-H...OH{sub 7} complex and the open N{sub 14}-H...OH{sub 2} and N{sub 14}...H-OH structures. In the experimental FT-IR spectra, the closed N{sub 3}...H-O...H-N{sub 14} and open O{sub 7}...H-OH complexes are identified based on characteristic absorptions predicted by ab initio calculations or based on earlier obtained experimental results for similar structures. Despite some trace amounts of the i-o Epsilon tautomer in the Ar matrix, H-bonding of this rare form with water was detected in the form of the closed N{sub 14}...H-O...H-N{sub 3} structure. A preliminary correlation between the frequency shifts of the bonded water stretching mode and the proton affinities of the C=O group is presented for the open C=...H-OH complexes of 1-CH{sub 3}-cytosine and some related compounds. 44 refs., 6 figs., 11 tabs.
- DOE Contract Number:
- FG03-93ER61605
- OSTI ID:
- 263153
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 16 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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