Electronic structures for energy-rich phosphates

Abstract

The extended Huckel theory is applied to adenosine-5′-di- and triphosphate, and to the related molecules of adenosine-5′-monophosphate, inorganic ortho-, pyro- and triphosphate, adenine, D-ribose and adenosine. Charge distributions calculated for these three-dimensional molecules suggest that opposing resonance and electrostatic repulsions can contribute to the high free energies of hydrolysis of the polyphosphates near pH 7. Eigen-values from SCF calculations on small, related compounds are found to be useful as valence state ionization potentials. A procedure for obtaining total energies within the EH framework is described which approximates experimental values better than the sum of the orbital energies. The phosphorus 3d orbitals contribute significantly to the stability of the phosphates. The charges along the backbone of the condensed phosphates alternate in sign. Little interaction is found between the phosphate and base moieties of the nucleotides in folded conformations.