modeling of the hydration shell of adenine

the molecular geometry of complex of adenine with 8 water molecules was calculated with hartree-fock (hf). the standard 6-31g(d) basis set has been employed. the existence of c-h…o hydrogen bonds between the water molecules and the hydrophobic part of nucleobase is stablished. we optimized structures and computed interaction energies of all complexes of adenine with water molecules step by step, and finally compared them. moreover, a theoretical investigation of the complex of adenine with 8 water molecules has led to the conclusion that the molecular structure of this molecule cannot be described by conventional chemical formula. the result of an ab initio hartree-fock study of the structural parameters, atomic charge, dipole moment and thermodynamic change for isolated and poly hydrated adenine complexes are reported. finally the gauge-invariant atomic orbital (giao) method was employed to calculate isotropic atomic shielding of complex using hf theory.