Leslie Glasser

Ab initio molecular orbital calculations of the infrared spectra of interacting water molecules. Part 4. Interaction energies and band intensities of the complexes of water with carbon dioxide and nitrous oxide

Abstract The interaction energies and the infrared band intensities in the vibrational spectra of a number of different isomers of the binary complexes formed between water and carbon dioxide, and water and nitrous oxide, have been predicted by means of ab initio molecular orbital theory. The results are discussed in the light of our recently reported studies of the structures and the infrared band wavenumbers of these species, using the same theoretical approach.

Ab initio calculations of the structural, energetic and vibrational properties of some hydrogen bonded and van der Waals dimers Part 3. The formaldehyde dimer

Abstract The structures, energies and atomic charges of five dimers of formaldehyde have been examined by means of ab initio molecular orbital theory, using the Gaussian-90 computer program at the second-order level of Moller-Plesset perturbation theory and the 6-31G split valence Gaussian basis set, augmented with polarization and diffuse functions (6-31++G ∗∗ ). These dimers are distinguished by the relative orientations of the monomer planes (coplanar, parallel or perpendicular) and dipoles (collinear, parallel or antiparallel). Three of the dimers were found to be genuine minima on the potential energy surface. These are a C s structure with its dipoles antiparallel and its molecular planes perpendicular; a coplanar species of C 2h symmetry with antiparallel monomer dipoles; and a C 21 . adduct with the dipoles collinear and the molecular planes perpendicular. The infrared spectra (wavenumbers and intensities) of these three dimers were computed, and the wavenumber shifts and intensity changes on dimerization were derived. The perturbations of these spectroscopic properties are compared with those observed for formaldehyde isolated in argon and nitrogen matrices at cryogenic temperatures, and the most probable structure is deduced in the light of all the available spectroscopic evidence.

An automated continuous-flow dynamic dialysis technique for investigating protein-ligand binding☆

Abstract An automated, continuous-flow dynamic dialysis technique has been developed to investigate protein-ligand binding. The method depends on a comparison of the diffusion of the low molecular mass ligand, in the presence and absence of protein, through a semipermeable membrane. The ligand passes from the sample compartment of a dialysis cell into the sink compartment through which a constant flow of eluting buffer is maintained. Digitized spectrophotometric determinations of the ligand concentration in the eluting buffer at successive, equally spaced time intervals, punched onto paper tape, provide the primary data (normally about 1000 data points). A mathematical treatment of the data based on a model of the diffusion system, whereby the protein-ligand binding isotherm may be evaluated, is discussed. The validity of the method is demonstrated from studies of the binding of phenol red to bovine serum albumin (BSA) at 15, 20, and 25°C. The method yields a large number of points on the binding isotherm (usually several hundred) which, in terms of a Scatchard model, provide values for the number of binding sites on the BSA molecule and binding constants for the phenol red-BSA interaction. The results obtained are consistent with values reported in the chemical literature but which are based on much scantier data.

Studies in hydrogen-bonding: Association in methylamine using an empirical potential

Abstract The empirical potentials EPEN and EPEN/2 have been used to establish the structures of isolated hydrogen-bonded clusters in methylamine. The most stable form of the dimer has an open structure with high dipole moment, the most stable trimer has a cyclic structure with low dipole moment and the tetramer has a cyclic structure with zero dipole moment. The results are compared, and generally agree, with experimental findings on clusters of methylamine in the vapour state.

Empirical energy parameters for structural modelling of alkali metal thiocyanate crystals in a standard formalism

Abstract Potential energy parameters describing Coulombic, van der Waals, and repulsion energies have been established for the thiocyanate ion in the EPEN/2 form of the exp-6 potential, with three ambient-stable alkali metal thiocyanate crystal structures for reference. A high temperature CsSCN structure is used as a test for the potential.

Studies in hydrogen bonding: simulation of the crystalline solids of ice, ammonia, and ammonia hydrate

Abstract The crystal structures of ice, ammonia and ammonia hydrate have been simulated with rigid molecules using the interatomic potential function EPEN/2 and the computer program WMIN. Structural parameters were adjusted to give structures with minimum energy. The hydrogen bonding in the simulated structures is compared with that in the experimental structures.

Studies in hydrogen bonding: the enthalpy of hydrogen bond formation of ethanol in carbon tetrachloride solutions

Abstract Enthalpy of dilution data reported by Stokes and Burfitt for ethanol in carbon tetrachloride are discussed in terms of alcohol self-association. The data in the low concentration range are found to be well represented by a monomer—dimer—tetramer alcohol association model; equilibrium constants and also enthalpies of formation of ethanol dimers and tetramers in carbon tetrachloride are calculated.

Ab Initio Molecular Orbital Calculations of the Infrared Spectra of Interacting Water Molecules. Complexes of Water with Carbon Dioxide and Nitrous Oxide

The molecular structures and infrared band wavenumbers of a number of different isomers of the binary complexes formed between water and carbon dioxide, and water and nitrous oxide, have been predicted by means of ab initio molecular orbital theory. The results are discussed in the light of high resolution gas phase infrared and microwave, and matrix isolation infrared spectroscopic studies, and of theoretical calculations on these and on a wide variety of similar complexes containing carbon dioxide and nitrous oxide.

PACKING MOLECULES AND IONS INTO CRYSTALS

It is a matter of great interest and significance to be able to predict the packing of molecules, especially of flexible molecules, and of ions into crystals. Packing may affect physical properties such as rate of solution, hardness, crystal shape, and so forth; these properties may be of crucial consequence in chemical reactivity and pharmacological activity.

Molecular geometry and substituent generation: A mathcad program

Abstract A MathCAD program, SUBSGEN, is presented. This program uses the standard mathematical vector and matrix notation of MathCAD to perform the following functions: (i) read in crystal lattice constants and atom positions in fractional coordinates; (ii) convert to orthonormal Cartesian coordinates; (iii) generate substituents in arbitrary positions; (iv) generate substituents in symmetry-defined positions; and (v) calculate internal geometry: bond lengths, bond angles and torsion angles.