Full geometry optimizations using the PM3, AMl, 3-21G*/HF and 6-31G*/HF levels of theory were conducted on the syn and anti conformations of cyclic 3’,5’-adenosine monophosphate (CAMP). Comparison of the anti crystal structures with the semiempirical and ab initio results revealed that the ab initio results agree well with the experimental results. The results of semiempirical calculations are ...

The study of a UV-VIS spectrum of 8-hydroxyquinoline (8HQ) in different solvents can provide relevant information concerning the influence of the medium on the electronic structure of the solute or the nature and strength of the specific solvent-solute intraor intermolecular interactions. The electronic absorption spectra of 8-hydroxyquinoline in various solvents have very different features du...

The semiempirical orthogonalization-corrected OMx methods (OM1, OM2, and OM3) go beyond the standard MNDO model by including additional interactions in the electronic structure calculation. When augmented with empirical dispersion corrections, the resulting OMx-Dn approaches offer a fast and robust treatment of noncovalent interactions. Here we evaluate the performance of the OMx and OMx-Dn met...

The lowest-energy conformations of four 2-chloroethylnitrososulfamides were determined using the MM+ molecular mechanics method as implemented in Hyperchem 6.0. Some of the calculated structural parameters, angles and bonds lengths were compared with the crystal structure data of N-nitroso-N-(2-chloroethyl)-N'-sulfamoyl- proline. Using MM+, AM1 and PM3 the anti conformation was predicted to be ...

The conversion of 4-chlorobenzoyl-CoA to 4-hydroxybenzoyl-CoA catalyzed by 4-chlorobenzoyl-CoA dehalogenase is investigated using combined QM/MM approaches. The calculated potential of mean force at the PM3/CHARMM level supports the proposed nucleophilic aromatic substitution mechanism. In particular, a Meisenheimer intermediate was found, stabilized by hydrogen bonds between the benzoyl carbon...

We have developed a simple convergent procedure for the synthesis of molecular rotors consisting of a central aromatic group coupled with two axially positioned ethynyltriptycenes. Molecular rotors with 1,4-phenylene (1), 1,4'-1,1'-biphenylene (2), 9,10-anthracenylene (3), and 2,7-pyrenylene (4) groups were prepared by Pd(0)-catalyzed coupling of ethynyl triptycenes with the corresponding dibro...

We introduce a framework to investigate ab initio the dynamics of rare thermally activated reactions, which cannot be studied using the existing techniques. The electronic degrees of freedom are described at the quantum-mechanical level in the Born-Oppenheimer approximation, while the nuclear degrees of freedom are coupled to a thermal bath, through a classical Langevin equation. This method is...

Single-photon ionization dynamics of two conformers of glycine is studied by classical trajectory simulations using the semiempirical PM3 potential surface in "on the fly" calculations. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for the initial vibrational ground state. Vertical ionization in the spirit of the classical Franck-Con...

Semi-empirical PM3 calculations are made for the electronic absorption spectra of colored forms nonmethylated anthocyanidins (aurantinidin, pelargonidin, cyanidin, and delphinidin). The position band peak is shown to depend on orientation hydroxyl groups in aglycone structure. observed tendency toward a bathochromic shift after ОН added ring generally corresponds experimental data. results unch...

Several density functional methods, the semiempirical methods AM1 and PM3, Hartree-Fock, and Gaussian3 theories were applied to compute the oxygen atom transfer enthalpies for 14 X/XO couples (inorganic and organic systems, charged and neutral species, light and heavy main group element containing molecules). The calculated reaction enthalpies were compared to available experimental data. The G...