Biopolym. Cell. 1995; 11(1):36-39.
http://dx.doi.org/10.7124/bc.0003CF
Acidic-basic properties of molecular hypoxanthine in vacuum
1Govorun D. M., 1Kondratyuk I. V., 1Zheltovsky N. V.
  1. Institute of Molecular Biology and Genetics, NAS of Ukraine
    Kiev, Ukraine

Abstract

By means of semiempirical quantum mechanical AMI method with full parameters optimization there were calculated the energies of protonation of exocyclic oxygen atom of «carbonyi group and of endocyclic proton free nitrogen atoms as well as energy of depro-Uonation NH- and CH-groups for two energetically prevalent hypoxanthine's (Hyp) tau-tomers N7H and N9H in vacuum. It was established, that endocyclic proton free nitrogen atom of imidazole ring is the most probable site of protonation; «amide» group H1N1C606 of Hyp has the better protonodonor and protonoacceptor properties than the «amide» groups H3N3C404, H3N3C202 of uracile and H1N1C606, H1N1C2O2 of xanthine. The most probable schemes for Hyp interaction through two cyclic H-bonds with neutral and deprotonated carboxylic group are proposed; they are in agree with experimental results (N. V. Zheltovsky et al., 1993).
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References

[1] Govorun D. M., Kondratyuk I. V., Zheltovsky N. V. Prototropic molecular-zwitterion tautomerism of hypoxanthine: AMI calculation in vacuum. Biopolym Cell. 1995; 11(1):30-5.
[2] Bell R. Proton in Chemistry. Springer; 1973, 310 p.
[3] Tupitsyn I. F., Popov A. S, Shibayev A. YU. Aromatic heterocycles as CH acid. 1. The methyl derivatives of five-and six-membered heterocycles. Zhurn. obshch. khimii. 1992. 62(124), 9: 2100-2111.
[4] Del Valle JC, De Paz JLG. A theoretical study of the acidity of nitrogen heterocycles. J Mol Struct. 1992; 254:481-491.
[5] Zheltovsky N. V., Samiylenko S. P., Kolomiets I. N., Kondratyuk I. V., Stepanyugin A. V. The investigation of interactions of hypoxanthine, xanthine and their methyl and glycosyl derivatives with amino acid carboxylic group by spectroscopic methods. Biopolym. Cell. 1993; 9(3):17-22.
[6] Sheina GG, Radchenko YeD, Stepanian SG, Ivanov AYu, Blagoi YuP. Vibration spectra of hypoxanthine. Biofizika. 1986; 31(4):555-60.
[7] Sheina GG, Stepanian SG, Radchenko ED, Blagoi YP. IR spectra of guanine and hypoxanthine isolated molecules. J. Mol. Struct. 1987;158:275–92.
[8] Govorun D. M., Kondratyuk I. V., Zheltovsky N. V. Acidic-basic properties of molecular xanthine and its complex formation ability. Biopolym. Cell. 1994; 10(6):61-64.
[9] Petrov ES. The Equilibrium NH Acidity of Organic Compounds. Russ. Chem. Rev. 1983; 52(12) 1144-1155.
[10] Romm IP, Guryanova EN pπ-Conjugation in Aromatic Compounds of Group V and VI Elements. Russ. Chem. Rev. 1986. 55(2):83-98.
[11] Vereshchagin A. N. Inductive effect. M.: Nauka, 1988. 110 p.