Volume 223, Issue 7

We approach the dynamics of adiabatic charge transfer through bridged triarylamine cations by a direct molecular dynamics simulation involving classical and quantum mechanical degrees of freedom. Within a simple yet chemically specific model, the quantum mechanical subsystem is described by a tight-binding Hamiltonian, which is coupled to a classical force field. From a population analysis of the quantum part, the charge transfer rate can be readily extracted, including the influence of memory effects. The direct computation of the associated thermodynamic potential establishes a close link to analytical rate concepts. The theoretical data are compared to experiments, and the limits and possible extensions of our approach are discussed.

Cyclic voltammetry, fluorescence and viscosity measurements were carried out to study the effect of various glycol additives such as EG, DEG, TEG, EGMME and EGMEE on the micellar properties of zwitterionic surfactants, DPS, TPS and HPS. Cyclic voltammetry has been used to determine the diffusion coefficient ‘D’ values by the use of well known Randles-Sevcik equation. The decrease in the ‘D’ values on addition of glycol additives has been explained on the basis of hydration effect and obstruction effect which is more in case of TEG and EGMEE. The destabilization of micelles of zwitterionic surfactants with the addition of glycol additives is explained on the basis of decrease in transfer of free energy (∆Gº t ). In case of TEG the change in intensity ratios (∆ I 1 /I 3 ) determined by fluorescence measurements become more negative with its increasing concentration which indicates that the zwitterionic surfactants are becoming more hydrophobic in its presence. The determination of relative viscosity (η r ) for each system indicates the surfactant-glycol oligomer interaction in the micellar state.

Two newly synthesized Enaminone compounds ethyl-3-[(2-aminoethyl) amino]-2-butenoate (compound I) and ethyl-3-(2-aminoanilino)-2-butenoate (compound II)) in 0.5 M H 2 SO 4 on AISI 316 have been investigated at 20 to 50 ºC using weight loss and potentiostatic polarization techniques. The percentage inhibition efficiencies and surface coverage degrees increase with increasing additive concentration. The inhibition is in both cases of a mixed anodic-cathodic nature. Differences in inhibition efficiency between compound I and II are correlated with their chemical structures. The inhibitors function through adsorption following Temkin isotherm in acid media. Activation energy ( E a ) and Gibbs free energy ( ∆G ads ) for adsorption of inhibitors are calculated. The values of ∆G ads decreased (attained more negative values) with increasing temperature.

The densities (ρ mix ) and viscosities (η mix ) of binary mixtures between n-butylethanoate and several non-polar hydrocarbon solvents viz; cyclohexane, benzene, 1,4-dimethylbenzene and 1,3,5-trimethylbenzene have been measured at 308.15 K for the whole composition range. From the experimental densities values, excess molar volumes(V E ) have been estimated. V E values are found to be large positive for mixtures with cyclohexane for entire range of concentration while small positive for benzene and 1,3,5-trimethylbenzene except a negative value at lower concentration of both hydrocarbons and at higher concentration of latter hydrocarbon only. Almost all the V E values are negative for mixtures with 1,4-dimethylbenzene. Deviations in viscosities (Δη) from ideal behaviour have been calculated from the experimental viscosities values. Δη values are large negative for mixtures with cyclohexane. The negative Δη values gradually decreases from benzene, 1,4-dimethylbenzene to 1,3,5-trimethylbenzene respectively. Experimental viscosities values have been analysed on the basis of several viscosities models. The results have been discussed in terms of molecular interactions between unlike molecules.

The topology of ternary phase diagrams of systems that are forming salts, cocrystals, solvates, or hydrates is discussed based on a simple mathematical model. The considerations include the thermodynamic stability of the multi-component crystal relative to the individual components, the character of the interactions in solution, the effect of relative solubility of the components, the consequences of using liquid components, the formation of multi-component crystals with different stoichiometry, and the competition between cocrystals or salts and solvates. Based on the characteristics of the phase diagrams, recommendations are provided as to an efficient design of salt formation and cocrystallization experiments.

The electronic structure properties of two pristine and defected models of zigzag and armchair boron nitride nanotubes (BNNTs) are computationally studied. Chemical shielding (CS) tensors at the sites of various boron-11 (B-11) and nitrogen-15 (N-15) nuclei in each of the optimized structures are calculated and converted to isotropic and anisotropic chemical shieldings (ICS and ACS, respectively). The ACS values revel that boron atoms at the end of nanotube play the major role in determining the characteristic properties of the BNNTs. Defects are considered by removing a B-N bond from the pristine models yielding B-B and N-N bonds in the zigzag but not in the armchair BNNT. The changes of the CS tensors at the sites of those B-11 and N-15 nuclei in the B-B and N-N bonds are the most significant among other nuclei. The calculations are performed employing BLYP method and 6–31G* standard basis set using GAUSSIAN 98.