Force field calculations (MM3) on glyoxal,quinones, and related compounds

A general force field type of calculation has been devised in connection with MM3 to treat 1,2- and 1,4-diketones, both when they are not conjugated (as in derivatives of glyoxal) and when they are conjugated (as in derivatives of ortho- and para-benzoquinone). The molecular structures, moments of inertia, dipole moments, and vibrational spectra have been examined for about 15 compounds, some in several conformations. Ab initio calculations (6-31G*) have been used to determine quantities that have not been previously defined by experiment. In general, the force field permits the calculation of the structures with high accuracy, and the spectroscopic and conformational energy data with fair accuracy. © 1994 by John Wiley & Sons, Inc.     

On thermodynamic similarity of the stability boundaries of metastable metal states

The data on the thermodynamic and kinetic stability boundaries of liquid and solid Pb, Li, Al, Cu, and Fe metals over a wide range of pressures and temperatures accumulated by the authors are analyzed and compared. Molecular-dynamics models using the embedded atom and Lennard-Jones potentials are considered. Examples of assuredly absent similarity are given, and the possibility of constructing approximate similarity is discussed. The following variants for constructing dimensionless parameters are considered: the use of critical point parameters (for the liquid phase), the use of Simon parameters, and the use of parameters reached at the stability boundary at zero pressure (the latter variant was most effective for ordering the stability boundaries of crystals).     

Molecular mechanics (MM2) calculations on peptides and on the protein Crambin using the CYBER 205

The MM2 potential functions for amides and peptides have been further extended by examining the experimental crystal structures for cyclo-(-Ala-Ala-Gly-Gly-Ala-Gly-), I, and cyclo-(-Ala-Ala-Gly-Ala-Gly-Gly-), II. The force field obtained was then applied to a study of the structure of the hydrophobic protein Crambin, for which a high resolution crystal structure is available. The energy minimization was carried out using a version of MM2 adapted to the CYBER 205.     

VESCF calculations of the spectra of some hydrocarbons containing triple bonds

The ultraviolet spectra of acetylene, diacetylene, triacetylene, allene, and their alkyl derivatives were calculated by a modified Pariser-Parr method using VESCF orbitals and including all singly and doubly excited states in the CI matrix, a method which has given good results in previous calculations on compounds containing only ethylenic carbon atoms. In the present work two new parameters were introduced, namely, the effective nuclear charge of an acetylenic carbon, and the integral (ie261-01). The calculated spectra agreed well with experiment for transitions observed above 190 m (< 6.53 eV). For transitions observed near or below 170 m (> 7.3 eV), the calculated energies were always too high. Agreement with experiment was improved by the inclusion of triply excited configurations, particularly in the case of acetylene.This research was supported by Grant GP 6763 from the National Science Foundation.     

Degradation of epoxy polymers: 3—Photo-degradation of bisphenol-A diglycidyl ether

The principal characteristics and products of photo-degradation of a commercial epoxy resin, bisphenol-A diglycidyl ether, have been studied. Comparison with the results of thermal degradation shows that many of the products are identical, especially the phenols and derivatives of phenol. The principal differences are the appearance of hydrogen in the photo, but not in the thermal, reaction and a series of aromatic hydrocarbons, including xylenes and/or ethyl benzene, styrene, isopropyl benzene and isopropenyl benzene, which are completely absent from the products of thermal degradation. Mechanisms are outlined.     

Aqua­bis(3‐meth­oxy‐2‐pyridonato)­(2,2′:6′,2′′‐terpyridine)ruthenium(II)–acetonitrile–water (1/1/1)

The title compound, [Ru(C₆H₆NO₂)₂(C₁₅H₁₁N₃)(H₂O)]·CH₃CN·H₂O, is a transfer hydrogenation catalyst supported by nitro­gen‐donor ligands. This octa­hedral Ru^II complex features rare monodentate coordination of 3‐meth­oxy‐2‐pyridonate ligands and inter­ligand S(6)S(6) hydrogen bonding. Comparison of the title complex with a structural analog with unsubstituted 2‐pyridonate ligands reveals subtle differences in the orientation of the ligand planes.     

A comparison of different methods in determining energies and geometries of open-shell systems

Three methods of obtaining eigenvectors for open-shell systems, namely the Roothaan restricted open-shell method, the “half-electron” method, and the use of ground state orbitals, are compared with each other both on a formal basis, and by contrasting theab initio energies predicted by these schemes for a series of radicals and triplets. The r.m.s. improvement in the energy of eight radicals by use of the Roothaan method rather than the half-electron approximation amounts to 4.8 kcal mole^?1, whereas the r.m.s. improvement for nineteen triplet states is 8.2 kcal mole^?1. Optimum geometries predicted by these two methods do not differ appreciably. The use of closed-shell eigenvectors rather than those of the half-electron method leads to very large errors for triplet states whose electron density distributions differ appreciably from those of the ground state.