Second order charge overlap effects and damping functions for isotropic atomic and molecular interactions

Second order charge overlap effects and the related dispersion energy damping functions have been evaluated for the H-(1s)-H(1s) interaction through partial wave indices l_a+l_b such that (l_a+l_b) ? 13. These results are a substantial improvement on, or addition to, previous literature results and are important since they can be used, following several available scaling approaches, to construct damping functions for other interactions. They also indicate that the “spherical” energies are not an insignificant part of the total second order Coulomb energy until R becomes reasonably large. The various approaches for evaluating the non-expanded second order Coulomb energy are compared and the difficulties associated with the accurate determination of these energies, and the related damping functions, for general interactions are discussed in some detail.     

Application of response surface methodology to optimize the process variables for fluoride ion removal using maghemite nanoparticles

Adsorption of fluoride ion was done from its aqueous solution by using maghemite (γ-Fe₂O₃) nanoparticles. Effects of the major independent variables (temperature, adsorbent dose and pH) and their interactions during fluoride ion adsorption were determined by response surface methodology (RSM) based on three-level three-factorial Box–Behnken design (BBD). Optimized values of temperature, maghemite nanoparticle dose and pH for fluoride sorption were found as 313 K, 0.5 g/L, and 4, respectively. In order to investigate the mechanism of fluoride removal, various adsorption isotherms such as Langmuir, Freundlich, Temkin and Florry–Huggins were fitted. The experimental data revealed that the Langmuir isotherm gave a more satisfactory fit for fluoride removal. The adsorption process was rapid and obeyed pseudo-second-order kinetics. The values of thermodynamic parameters ΔG°, ΔH° and ΔS° indicated that adsorption was spontaneous and endothermic in nature.     

Approaches to charge calculations in molecular mechanics. 2 Resonance effects in conjugated systems

A previously published scheme of estimating atomic charges in haloalkanes is extended to include olefines, alcohols amines, acids, ethers, and amides. In the conjugated systems the effects of mesomeric transfer of charge are explicitly included. Generally good agreement with the observed dipole moments of these compounds and their substituted derivatives is found. The atomic charges so obtained are compared with those of other semiempirical and quantum-mechanical calculations for the amide group. The charges so obtained fall within the range of values obtained by these other schemes, supporting the general validity of this approach.     

Relationship of charge to antiaromaticity in bis-fluorenyl dications and fluorenyl monocations: experimental support for theoretical calculations

The antiaromaticity of fluorenyl cations is dependent on the magnitude of the charge of the system. Theoretical assessments of antiaromaticity and charge were supported by experimental NMR chemical shifts. Delocalization was related to antiaromaticity, and evaluated through the standard deviation of the charges on carbons of the fluorenyl systems.     

New sensing material of molecularly imprinted polymer for the selective recognition of sulfamethoxazole in foods and plasma and employing the Taguchi optimization methodology to optimize the carbon paste electrode

A new man-tailored biomimetic sensor for sulfamethoxazole host–guest interactions and potentiometric transduction is presented. The host cavity was shaped on a polymeric surface assembled with methacrylic acid monomers by radical polymerization. Molecularly imprinted particles (MIP) were mixed with graphite powder, paraffin oil and ionic site. Using the Taguchi method, this study analyzed the optimum conditions for preparing the carbon paste electrode. The controllable factors used in this study consisted the weights of (1) MIP, (2) paraffin oil, (3) graphite, and (4) the ionic site. The percentage contribution of each controllable factor was also determined. MIP-modified electrode exhibited a Nernstian response (57.2 mVdecade^?1) in a wide concentration range of 6.0 × 10^?8 to 3.1 × 10^?3 mol L^?1 with a lower detection limit of 3.5 × 10^?9 mol L^?1. The sensor was successfully applied to the determination of sulfamethoxazole concentrations in foods and plasma.     

Smooth solvation method for d-orbital semiempirical calculations of biological reactions. 2. Application to transphosphorylation thio effects in solution

Density-functional and semiempirical quantum methods and continuum dielectric and explicit solvation models are applied to study the role of solvation on the stabilization of native and thio-substituted transphosphorylation reactions. Extensive comparison is made between results obtained from the different methods. For the semiempirical methods, explicit solvation was treated using a hybrid quantum mechanical/molecular mechanical (QM/MM) approach and the implicit solvation was treated using a recently developed smooth solvation model implemented into a d-orbital semiempirical framework (MNDO/d-SCOSMO) within CHARMM. The different quantum and solvation methods were applied to the transesterification of a 3'-ribose,5'-methyl phosphodiester that serves as a nonenzymatic model for the self-cleavage reaction catalyzed by the hammerhead and hairpin ribozymes. Thio effects were studied for a double sulfur substitution at the nonbridging phosphoryl oxygen positions. The reaction profiles of both the native and double sulfur-substituted reactions from the MNDO/d-SCOSMO calculations were similar to the QM/MM results and consistent with the experimentally observed trends. These results underscore the need for a d-orbital semiempirical representation for phosphorus and sulfur for the study of experimentally observed thio effects in enzymatic and nonenzymatic phosphoryl transfer reactions. One of the major advantages of the present approach is that it can be applied to model chemical reactions at a significantly lower computational cost than either the density-functional calculations with implicit solvation or the semiempirical QM/MM simulations with explicit solvent.     

Search for a structural change in concentrated sodium sulfate solutions around the transition point temperature using the charge transfer to solvent spectrum of lodide ion as a probe

Claims have been made that aqueous sodium sulfate solutions exhibit an anomalous temperature dependence close to the transition point of the solid decahydrate (Na₂SO₄·10H₂O), viz., 32.38°C. In studies of dilute solutions these claims have been queried. Concentrated solutions, where this effect might be more readily detected, have not been investigated. A very accurate analysis of the shift of the charge transfer to solvent spectrum of iodide, a sensitive probe of its environment, (6×10^?5 M) in concentrated (1 and 2 M) sodium sulfate solutions, as a function of temperature has not evinced any support for a structural change in solution on traversing the transition point temperature.     

Metal to ligand charge transfer induced DNA photobinding in a Ru(II)-Pt(II) supramolecule using red light in the therapeutic window: a new mechanism for DNA modification

The Ru(II)-Pt(II) supramolecular complex, [(Ph(2)phen)(2)Ru(dpp)PtCl(2)](2+), displays a new mechanism for DNA modification: photobinding through a (3)MLCT excited state. Gel shift analysis, selective DNA precipitation, and DNA melting point experiments support efficient covalent DNA binding following visible light excitation.