Hamzeh M. Abdel-Halim

Electric field induced second harmonic generation: Second and third-order hyperpolarizabilities of 4-amino-4′-nitrodiphenyl sulfoxide

The second-order hyperpolarizability (β), and the third-order hyperpolarizability (γ) of 4-amino-4′-nitrodiphenyl sulfoxide (ANDSO) has been determined using the technique of electric field induced second harmonic (EFISH) generation in liquid. The third order macroscopic nonlinear susceptibility of ANDSO was first determined by comparing the intensity of the frequency doubled Nd:YAG laser pulse from the EFISH cell containing ANDSO solution to that of a reference material. The microscopic hyperpolarizabilities γ and β for ANDSO were extracted from the nonlinear susceptibility using local field factors, bond additivity concept and knowledge of the dipole moment of the molecule. Comparison of β and γ obtained in the present work to those obtained by other investigators for other molecules shows a superior microscopic nonlinear properties for ANDSO.

Molecular dynamics of nor-Seco-cucurbit[10]uril complexes

Molecular dynamics simulations were carried out to investigate the structure and dynamics of the 1:1 and 1:2 inclusion complexes formed by nor-Seco-cucurbit[10]uril (ns-CB[10]) with 1-adamantanmethylammonium in water. Two and three orientational isomers were considered for 1:1 and 1:2 complexes, respectively. These isomers are identified by the orientation/position of the ammonium group in the guest relative to the flexible and rigid carbonyl portals of the ns-CB[10] host. Results demonstrate that the inclusion of one guest molecule within one cavity in the host induces similar conformational changes in both the occupied and empty cavities. The average structure for each complex shows that the guest molecule is shifted closer to the side that lacks the CH2-bridge in the host, and that the ammonium group of the guest interacts with the oxygens of the host’s portals via ion–dipole interactions with the hydrophobic part of the guest molecule resides in the cavity of the host. Furthermore, the 1:1 complexes are found to interconvert over the time of the simulation. This observation is not found for 1:2 complexes. Finally, MM–PBSA calculations show that 1:2 complexes are significantly more stable than their 1:1 counterparts while two orientations of the 1:2 complexes are more stable than the third.

Kinetics of the Oxidation of L-Cysteine by trans- and cis-Cobalt(III) and Iron(III) Complexes

Kinetics of oxidation of L-cysteine by pairs of trans and racemic cis isomers of cobalt(III) and iron(III) based transition metal complexes have been studied in aqueous solution. Kinetics measurements were run under pseudo first order conditions in which the concentration of cysteine is between one and two orders of magnitude greater than that of the isomers of the transition metal complex. The orders of the reaction with respect to both cysteine and the isomer were determined. The observed rate constants and the overall rate constants of the oxidation process were measured. For all geometrical isomers, it was found that the rate constant of oxidation of L-cysteine by the trans isomer is between one to three orders of magnitude greater than that by the cis isomer. The difference in rates can be explained by a geometric factor around the metal ion center in the complex. The less crowded isomer (trans) makes electron transfer easier and hence facilitates the oxidation process which leads to a higher oxidation rate.

Synthesis of Cobalt(III), Iron(III), and Chromium(III) Complexes with Salicylaldiminato Ligands: Evaluation of the Complexes as Catalysts for Oxidation of L-Cysteine

A series of new cobalt(III)-, iron(III)-, and chromium(III)-based complexes of the general formula [M(N∩O)2Cl] (N∩O: N-salicylidene(X)amine and sodium N-(4-sulfonatosalicylidene(X)amine)) (X = cyclohexyl and 1-naphthyl) was prepared and characterized. Some of the isolated complexes have been evaluated as catalysts for the oxidation of L-cysteine. Preliminary results show that the rate of oxidation of L-cysteine is influenced by the nature of the metal center, the geometry of the complex, the auxiliary substituents, and the backbone of the ligand.

Effects of The Vibrational and Rotational Energy on Reaction Cross- Section in a Classical Trajectory Study of Atom-Diatomic Molecule Collisions

Effects of the initial vibrational and rotational energy of a diatomic molecule on reaction rates of atom-diatomic molecule reactions have been studied using classical trajectory calculations. The reaction probabilities, cross-sections and rate constants were calculated using the three-dimensional Monte-Carlo method. Equations of motion, which predict the positions and momenta of the colliding particles after each step in the trajectory, have been integrated numerically by the Runge-Kutta-Gill and Adams-Moulton methods. Morse potential energy surfaces were used to describe the interaction between the atom and each atom in the diatomic molecule. Several atom-diatomic molecule systems were studied. Variation of the reaction cross-section with both vibrational and rotational quantum numbers has been studied. For all systems studied, it was found that the cross-section increases with the vibrational quantum number. However, the effect of rotational quantum number on cross-section varies from one system to another. Results obtained in the present work were compared with experimental data and/or with results obtained theoretically. Good agreements were observed with experimental and with theoretical results obtained by other investigators using different calculation methods.

Reaction Rate Constants from Classical Trajectories of Atom-Diatomic Molecule Collisions

Classical trajectory calculations for various atom-diatomic molecules were preformed using the three-dimensional Monte Carlo method. The reaction probabilities, cross-sections and rate constants of several systems were calculated. Equations of motion, which predict the positions and momenta of the colliding particles after each step, have been integrated numerically by the Runge-Kutta-Gill and Adams-Moulton methods. Morse potential energy surfaces were used to describe the interaction between the atom and each atom in the diatomic molecules. The results were compared with experimental ones and with other theoretical values. Good agreement was obtained between calculated rate constants and those obtained experimentally. Also, reasonable agreement was observed with theoretical rate constants obtained by other investigators using different calculation methods. The effects of the temperature, the nature of the colliding particles and the thermochemistry were studied. The results showed a strong dependence of the reaction rates on these factors.