Abstract

CRITICAL REVIEW ON COMPUTATIONAL STUDY OF [1,3]SIGMATROPIC HYDROGEN MIGRATION IN PYRIMIDINES AND PURINES OF NUCLEIC ACIDS BY AUSTIN MODEL-1 METHOD

Bojja Rajeshwar Rao*

ABSTRACT

Photochemical and thermal [1,3]sigmatropic hydrogen migration in the formation of tautomers of pyrimidines (cytosine, thymine and uracil) and purines (adenine and guanine) play a vital role in changing the base sequence to cause chromosomal mutations, sometimes useful and occasionally harmful. The electronic structure and [1,3] sigmatropic hydrogen migration in the formation of tautomers, which have been optimized and evaluated by semi-empirical molecular orbital AM1 method. In this connection, the heats of formation (ΔHfo), dipole moment (μ), quantum chemical descriptors, full atomic charges and energies of frontier molecular orbitals (EHOMO and ELUMO) have been performed. The mechanistic investigation of [1,3] sigmatropic hydrogen shift have been studied by the comparison of net charges of hetero atoms in different positions of the molecule. It is observed that all tautomers exist within the range of heats of formation (ΔHfo) as +2.635 to +24.301 kcal/mol (Cytosine), -61.241 to -33.187 kcal/mol (Thymine), -53.964 to -33.395 kcal/mol (Uracil), +86.667 to +110.636 kcal/mol (Adenine) and +48.703 to+83.039 kcal/mol (Guanine). All tautomers also exist within the range of dipole moment (μ) as 1.447 to 6.389 D (Cytosine), 2.507 to 8.107 D (Thymine), 2.838 to 7.085 D (Uracil), 2.180 to 8.527 D (Adenine) and 1.683 to 9.484 D/mol (Guanine). Furthermore, and atomic charges of all tautomers indicated that the dipole-dipole interactions play a vital role during the synthesis of proteins and enzymes. The effect of changes and electronic properties of stable tautomers have been discussed.

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