MINDO/3 and MNDO studies of some thio analogues of nucleic acid bases

Singh, Kamalendra; Rai, D.K.; Yadav, Janardan

doi:10.1016/0166-1280(91)85208-o

Cited by 12 publications

(1 citation statement)

References 15 publications

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“…Therefore, 6-thioguanine can exist in several tautomeric forms that will play important roles in the replication process and spontaneous mutation of DNA and RNA. Investigations were devoted to the physical chemistry properties of 6-thioguanine either experimentally or theoretically [3][4][5]. The experimental results indicate that 6-thioguanine exists as the N(7)H thione-amino tautomer in the crystal structure.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Investigation on Tautomerization Mechanism of 6-Thioguanine

Ren

2013

AMR

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The tautomerization reaction mechanisms between three stable 6-thioguanine tautomers were investigated theoretically using B3LYP/6-311+G(d,p) method. The results show that the pathway P(1) is to isomerize from TG(9,10,10,11) to TG(1,9,10,10) and the needed activation Gibbs free energy barrier is 112.7 kJ/mol with the rate constant of 1.12×10-7 s-1. Another two pathways P(2) and P(3) are to isomerize from TG(1,9,10,10) to TG(1,7,10,10) and the activation Gibbs free energy barriers of the rate-determining steps are 227.4 and 281.6 kJ/mol, respectively, with the related rate constants of 8.96×10-28 s-1 and 2.86×10-37 s-1, these results implying the intramolecular proton transfer reactions are infeasible in the gas phase.

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Section: Introductionmentioning

confidence: 99%

Theoretical Investigation on Tautomerization Mechanism of 6-Thioguanine

Ren

2013

AMR

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AM1 and PM3 studies of some thio analogues of pyrimidine bases in the gas and aqueous phases

Civcir¹

2001

J of Physical Organic Chem

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Heats of formation, entropies, Gibbs free energies, relative tautomerization energies, dipole moments, and ionization potentials for the tautomers of 2‐thiocytosine, 2,4‐dithiouracil and 2,4‐dithiothymine and their 1‐methyl analogues were studied by using semiempirical AM1 and PM3 quantum‐chemical calculations at the SCF level both in the gas phase and in aqueous solution, with full geometry optimization. The COSMO solvation model was employed for aqueous solution calculations. The calculations show that the thiol‐amino tautomer of 2‐thiocytosine is the most stable in the gas phase whereas the thione‐amino tautomer is the most stable in the aqueous phase. For 2,4‐dithiouracil and 2,4‐dithiothymine, dithione tautomers are the most stable in both phases. The results are in good agreement with available experimental and theoretical results. The entropy effect on the Gibbs free energy of the thiopyrimidine bases is very small and has practically no significance for the tautomeric equilibria of thiopyrimidine bases. The enthalpic term is dominant in the determination of the equilibrium constant. Copyright © 2001 John Wiley & Sons, Ltd.

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AM1 studies on the prototropic tautomerism of 6-thioguanine

Contreras

Alderete

1993

Journal of Molecular Structure: THEOCHEM

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MINDO/3 and MNDO studies of some thio analogues of nucleic acid bases

Cited by 12 publications

References 15 publications

Theoretical Investigation on Tautomerization Mechanism of 6-Thioguanine

Theoretical Investigation on Tautomerization Mechanism of 6-Thioguanine

AM1 and PM3 studies of some thio analogues of pyrimidine bases in the gas and aqueous phases

AM1 studies on the prototropic tautomerism of 6-thioguanine

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