Intermolecular Forces (intermolecular + force)

Distribution by Scientific Domains

Selected Abstracts

Photoinitiated polymerization of methacrylic monomers in a polystyrene matrix: Kinetic, mechanistic, and structural aspects

J. L. Mateo
Abstract The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6-hexanediol dimethacrylate (HDDMA) and 2-ethylhexyl methacrylate (EHMA)] in a polystyrene (PS) matrix were studied. The aggregation state, vitreous or rubbery, of the monomer/matrix system and the intermolecular strength of attraction in the monomer/matrix and growing macroradical/matrix systems are the principal factors influencing the kinetics and mechanism. For the PS/HDDMA system, where a relatively high intermolecular force of attraction between monomer and matrix and between growing macroradical and matrix occurs, a reaction-diffusion mechanism takes place at low monomer concentrations (<30,40%) from the beginning of the polymerization. For the PS/EHMA system, which presents low intermolecular attraction between monomer and matrix and between growing macroradical and matrix, the reaction-diffusion termination is not clear, and a combination of reaction-diffusion and diffusion-controlled mechanisms explains better the polymerization for monomer concentrations below 30,40%. For both systems, for which a change from a vitreous state to a rubbery state occurs when the monomer concentration changes from 10 to 20%, the intrinsic reactivity and kp/kt1/2 ratio (where kp is the propagation kinetic constant and kt is the termination kinetic constant) increase as a result of a greater mobility of the monomer in the matrix (a greater kp value). The PS matrix participates in the polymerization process through the formation of benzylic radical, which is bonded to some extent by radical,radical coupling with the growing methacrylic radica, producing grafting on the PS matrix. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2049,2057, 2001 [source]

Hierarchical Structures in Tin(II) Oxalates

Padmini Ramaswamy
Abstract Six new SnII oxalates exhibiting a hierarchy of structures have been prepared employing hydrothermal methods. The compounds I [C10N2H10][Sn(C2O4)2], II [C10N2H10][Sn2(C2O4)3], and III [C8N4H26][Sn(C2O4)2]2·2H2O possess zero-dimensional molecular structures; IV [C10N2H8]2[Sn(C2O4)]2 and V [C12N2H8][SnC2O4] have one-dimensional chain structures; and compound VI [C5N2H14]2[Sn4(C2O4)6]·7H2O has a two-dimensional layer structure. The SnII ions have 4- and 6-coordination with square-pyramidal or pentagonal-bipyramidal geometry, in which the lone pair of electrons also occupies one of the vertices. Weak intermolecular forces such as hydrogen-bond interactions, ,···, interactions, and lone-pair,, interactions have been observed and appear to lendstructural stability. Theoretical studies indicate that the ,···, interaction energy between the bound 1,10-phenanthroline molecules is of the order of 5,6 kcal,mol,1 in V. Natural bond orbital (NBO) analysis on two model compounds, II and IV, indicates reasonable lone-pair,, interactions. The close structural relationship between all the compounds indicates that a building-up process from the zero-dimensional monomer can be considered. The present structures provide opportunities for evaluating the structure-directing role of the lone pair of electrons of SnII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Range and strength of intermolecular forces for van der Waals complexes of the type H2Xn -Rg, with X = O, S and n = 1,2

Patrícia R. P. Barreto
Abstract This study is intended as a continuation of previous experimental and theoretical works on the systems H2O-Rg, H2S-Rg, H2O2 -Rg, and H2S2 -Rg, where Rg = He, Ne, Ar, Kr, Xe. For the H2O-Rg and H2S-Rg systems, molecular and atomic polarizabilities have been calculated and from them, using phenomenological correlation formulas modeling the dispersion-repulsion (van der Waals) forces, the isotropic interaction parameters have been determined and compared with experimental data from this laboratory. For the H2O2 -Rg and H2S2 -Rg systems, the molecular polarizabilities have been calculated and used in correlation formulas to predict well depths and positions of van der Waals forces and a comparison made with the corresponding potential energy surfaces calculated in previous works. The approach correctly predicts the interaction parameters, except for H2O and H2O2 with the heavier rare gases. The correlation formulas have been then extended to include an attractive induction contribution accounting for the interaction between the permanent molecular dipole moment and the instantaneous induced atomic dipole moment, to improve the predicted parameters for H2O and H2O2 -Ar, Kr and Xe. The agreement with experimental and theoretical data is improved but the predicted data still underestimate the interaction. This is probably due to the presence of a significant non van der Waals contribution to the interaction for the heavier gases, as suggested by analogy with the previously studied water-Rg case. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

Characterization of asphaltene structure using atomic force microscopy

Summary In this study, at the first stage, asphaltene was extracted. The roughness of asphaltene coating at different rpm was studied using an image analysis confocal microscopy. The basics of quantum mechanics and statistical thermodynamics are used to predict the potential energy and the intermolecular forces of asphaltene molecules. The functional forms for the potential energy and intermolecular forces are evaluated. Our final goal is to be able to observe and determine the surface structures of asphaltene micelles with scanning probe microscopes. So, the focus of the work on these unusual molecules is to characterize their structure, dynamics and thermodynamics and to establish the relationship between these properties and petroleum fluid behaviour. The existence of various nanostructures of asphaltene in petroleum has been extensively discussed. A set of fitted data is used to check the validity of the calculated results. The good agreement between the proposed models and the data is promising. [source]

A QM/MM Study of Cisplatin,DNA Oligonucleotides: From Simple Models to Realistic Systems

Arturo Robertazzi
Abstract QM/MM calculations were employed to investigate the role of hydrogen bonding and , stacking in several single- and double-stranded cisplatin,DNA structures. Computed geometrical parameters reproduce experimental structures of cisplatin and its complex with guanine,phosphate,guanine. Following QM/MM optimisation, single-point DFT calculations allowed estimation of intermolecular forces through atoms in molecules (AIM) analysis. Binding energies of platinated single-strand DNA qualitatively agree with myriad experimental and theoretical studies showing that complexes of guanine are stronger than those of adenine. The topology of all studied complexes confirms that platination strongly affects the stability of both single- and double-stranded DNAs: PtNH,,,X (X = N or O) interactions are ubiquitous in these complexes and account for over 70,% of all H-bonding interactions. The , stacking is greatly reduced by both mono- and bifunctional complexation: the former causes a loss of about 3,4 kcal,mol,1, whereas the latter leads to more drastic disruption. The effect of platination on Watson,Crick GC is similar to that found in previous studies: major redistribution of energy occurs, but the overall stability is barely affected. The BH&H/AMBER/AIM approach was also used to study platination of a double-stranded DNA octamer d(CCTG*G*TCC),d(GGACCAGG), for which an experimental structure is available. Comparison between theory and experiment is satisfactory, and also reproduces previous DFT-based studies of analogous structures. The effect of platination is similar to that seen in model systems, although the effect on GC pairing was more pronounced. These calculations also reveal weaker, secondary interactions of the form Pt,,,O and Pt,,,N, detected in several single- and double-stranded DNA. [source]

Multipolar Ordering in Electro- and Magnetostatic Coupled Nanosystems

CHEMPHYSCHEM, Issue 9 2008
Elena Y. Vedmedenko Dr. habil.
Abstract Electric and magnetic multipole moments and polarizabilities are important quantities in studies of intermolecular forces, non-linear optical phenomena, electrostatic, magnetostatic or gravitational potentials and electron scattering. The experimental determination of multipole moments is difficult and therefore the theoretical prediction of these quantities is important. Depending on purposes of the investigation several different definitions of multipole moments and multipole,multipole interactions are used in the literature. Because of this variety of methods it is often difficult to use published results and, therefore, even more new definitions appear. The first goal of this review is to give an overview of mathematical definitions of multipole expansion and relations between different formulations. The second aim is to present a general theoretical description of multipolar ordering on periodic two-dimensional lattices. After a historical introduction in the first part of this manuscript the static multipole expansion in cartesian and spherical coordinates as well as existing coordinate transformations are reviewed. On the basis of the presented mathematical description multipole moments of several symmetric charge distributions are summarized. Next, the established numerical approach for the calculation of multipolar ground states, namely Monte Carlo simulations, are reviewed. Special emphasis is put on the review of ground states in multipolar systems consisting of moments of odd or even order. The last section is devoted to the magnetization reversal in dense packed nanomagnetic arrays, where the magnetic multipole,multipole interactions play an important role. Comparison between the theory and recent experimental results is given. [source]