Paper Information

Journal:   JOURNAL OF PHYSICAL AND THEORETICAL CHEMISTRY   winter 2018 , Volume 14 , Number 4; Page(s) 331 To 341.
 
Paper: 

Using Implicit/Explicit Salvation Models to Theoretical Study Tautomerism in 7H-purine-2, 6-diamine

 
 
Author(s):  HOSSEINI SEYED JAVAD*, farahandoz Sona
 
* Chemistry Department, Shahrood Azad University, Shahrood, Iran
 
Abstract: 
A theoretical study at the B3LYP/6-31++G(d, p) level was performed on the tatumerization of 7H-purine-2, 6-diamine into 9H-purine-2, 6-diamine. Such a tautomerism can take place via three different pathways namely A, B, and C. The energetic results associated with the gas phase reveal that pathways A, B, and C display a very high activation Gibbs free energy of 45. 1, 68. 6 and 48. 9 kcal/mol, respectively, indicating this process cannot take place in the gas phase. When solvent effects of water are taken into account through a continuum of a uniform dielectric constant, the gas phase activation Gibbs free energies increase to 58. 8, 70. 6, and 52. 4 kcal/mol along pathway A, B, and C, respectively, emphasizing long range solute-solvent interactions do not play a key role in the considered tautomerization. The studied process can easily take place by inclusion of three molecules of water in which a significantly reduced activation Gibbs free energy of 24. 8 kcal/mol indicates the predominance of short range solute-solvent interactions over the long range ones. Combination of short range and long range solute-solvent interactions lead to an activation Gibbs free energy of 23. 5 kcal/mol for tatumerization of 7H-purine-2, 6-diamine into 9H-purine-2, 6-diamine. This value clearly points out that employing a polar and protic solvent is able to noticeably reduce the barrier of tatomerization.
 
Keyword(s): Tautomerism,purines,DFT,Explicit and implicit solvation models
 
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