No abstract

ABSTRACT:Optimal Gaussian-type orbital GTO basis sets of positron and electron in positron-molecule complexes are proposed by using the full variational treatment of Ž . molecular orbital FVMO method. The analytical expression for the energy gradient with respect to parameters of positronic and electronic GTO such as the orbital exponents, the Ž . orbital centers, and the linear combination of atomic orbital LCAO coefficients, is derived. Wave functions obtained by the FVMO method include the effect of electronic or positronic orbital relaxation explicitly and satisfy the virial and Hellmann᎐Feynman theorems completely. We have demonstrated the optimization of each orbital exponent in Ž . various positron-atomic and anion systems, and estimated the positron affinity PA as the difference between their energies. Our PA obtained with small basis set is in good agreement with the numerical Hartree᎐Fock result. We have calculated the OH y and w y q x OH ; e species as the positron-molecular system by the FVMO method. This result shows that the positronic basis set not only becomes more diffuse but also moves toward the oxygen atom. Moreover, we have applied this method to determine both the nuclear and electronic wave functions of LiH and LiD molecules simultaneously, and obtained the isotopic effect directly.

We constructed a model structure of Mg-adenosine triphosphate (MgATP) and the surrounding portion of myosin by using the X-ray crystal structure of the myosin motor domain bound to the stable MgATP analogue, MgADP-BeF x , and by adding hydrogen atoms and replacing beryllium with phosphorus and fluorine with oxygen. The positions of the hydrogen atoms were determined by optimization using the semiempirical molecular orbital program MOPAC 97. Analysis of the electronic states of the model structure revealed that the highest occupied molecular orbitals (HOMO) indicate that the reaction site of the ATP hydrolysis is the nonbridging γ-phosphoryl oxygen atoms and confirmed that H 2 O(1181) is the hydrolytic water. Thus, hypothetical mechanisms of the initial phase of the hydrolysis are proposed.