Matrix-isolation FT-IR studies and ab-initio calculations of hydrogen-bonded complexes of molecules modeling cytosine or isocytosine tautomers. 2. 4-aminopyridine and 4-aminopyrimidine complexes with H{sub 2}O in Ar matrices
- Univ. of Leuven, Heverlee (Belgium)
H-bonding interactions of the cytosine-modeling compounds 4-aminopyridine and 4-aminopyrimidine with water are investigated with the use of a combined experimental matrix-isolation FT-IR and theoretical ab-initio method. Both bases appear exclusively as the amino tautomers in low-temperature Ar matrices, in accordance with large ab-initio predicted energy differences with the rare imino forms. The most stable complex of water with 4-aminopyridine is the H-bonded N{sub 1}...HO-H structure, but the energy difference with the alternative N-H...OH{sub 2} complex is calculated to be only 6.7 kJ/mol. Both complexes are observed in the Ar matrix. In the case of 4-aminopyrimidine, the closed N-H...O-H...N{sub 3} structure containing two H-bonds is found to be significantly more stable than the singly H-bonded structures N{sub 1}...HO-H and N-H...OH{sub 2} by 8.0 and 10.2 kJ/mol, respectively. The previously suggested relation between the scaling factor for the theoretically-calculated $nu{sup b}{sub OH} mode of the H-bonded water and the proton affinity value of the proton-acceptor site in the base is developed further. 24 refs., 10 figs., 10 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG03-93ER61605
- OSTI ID:
- 50499
- Journal Information:
- Journal of Physical Chemistry, Vol. 99, Issue 17; Other Information: PBD: 27 Apr 1995
- Country of Publication:
- United States
- Language:
- English
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