Semiempirical orthogonalization-corrected methods (OM1, OM2, and OM3) go beyond the standard MNDO model by explicitly including additional interactions into the Fock matrix in an approximate manner (Pauli repulsion, penetration effects, and core-valence interactions), which yields systematic improvements both for ground-state and excited-state properties. In this Article, we describe the underl...

Metallothionein, a two-domain protein, naturally binds seven gram atoms of divalent ions such as Zn and Cd. Four of the metals (M1, M5, M6 and M7) are found in the alpha-domain and three (M2, M3 and M4) in the beta-domain. Previous studies have shown that metals in the beta-domain are more readily exchangeable, and the level of avidity is site specific. By semi-empirical MNDO modified neglect o...

Chelate complexes of 1,2-dimesitoylbenzene radical anion with alkali metal cations exhibit in aprotic solution extremely iarge ESR/ENDOR metal coupling constants. For rationaliza­ tion, structures of both the neutral molecule (H 3C)3H2C6C O C 6H4 C O C 6H2(CH3)3, in which the two carbonyl groups are twisted out of the benzene ring plane by dihedral angles of ± 37°, and a sodium contact ion quad...

As a starting reagent in organic synthesis, malononitr i le-dicyanomethylene has an established posit ion because of its reactivity in the addi t ion, self addi t ion, and condensation reactions leading to various carbocyclic and heterocyclic systems [1]. The a im of our work is to investigate the reaction path of malononitrile dimerizat ion and the structure of the reaction product using q u a...

The collective electronic oscillators (CEO) approach based on the TDHF approximation is combined with INDO/S, MNDO, AM1, and PM3 semiempirical Hamiltonians. This technique is applied to compute and analyze the electronic structure of acceptor-substituted oligomers and conjugated polymers. Calculated excited-state energies and oscillator strengths agree well with the experimental data and with e...

BACKGROUND The G52S mutation in the Arg50 loop of thymidylate synthase leads to decreased binding of FdUMP. It has been suggested that the mutation affects the Arg50 residue (within the Arg50 loop) responsible for binding the phosphate of FdUMP. The binding of the methylguanidinium moiety as a model for Arg50 to a methylphosphate entity as a model for FdUMP was investigated with theoretical cal...

A semiempirical AM1/d Hamiltonian is developed to model phosphoryl transfer reactions catalyzed by enzymes and ribozymes for use in linear-scaling calculations and combined quantum mechanical/molecular mechanical simulations. The model, designated AM1/d-PhoT, is parametrized for H, O, and P atoms to reproduce high-level density-functional results from a recently constructed database of quantum ...

Using a computer code called MOPAC, an acronym for a general Molecular Orbital Package (Quantum Chemistry Programme Exchange (QCPE) Programme No. 455), the geometries and heats of formation of the reactant, the products and the trdnsition state were computed by the MNDO semi- empiricalself consistent field (SCF) method for the pyrolysis of ethyl vinyl ether. ((Force))calculation on the reac...

Two new semiempirical methods employing a Pairwise Distance Directed Gaussian modification have been developed: PDDG/PM3 and PDDG/MNDO; they are easily implemented in existing software, and yield heats of formation for compounds containing C, H, N, and O atoms with significantly improved accuracy over the standard NDDO schemes, PM5, PM3, AM1, and MNDO. The PDDG/PM3 results for heats of formatio...