(Q)SAR Modelling of Nanomaterial Toxicity - A Critical Review

There is an increasing recognition that nanomaterials pose a risk to human health, and that the novel engineered nanomaterials (ENMs) in the nanotechnology industry and their increasing industrial usage poses the most immediate problem for hazard assessment, as many of them remain untested. The large number of materials and their variants (different sizes and coatings for instance) that require testing and ethical pressure towards non-animal testing means that expensive animal bioassay is precluded, and the use of (quantitative) structure activity relationships ((Q)SAR) models as an alternative source of hazard information should be explored. (Q)SAR modelling can be applied to fill the critical knowledge gaps by making the best use of existing data, prioritize physicochemical parameters driving toxicity, and provide practical solutions to the risk assessment problems caused by the diversity of ENMs. This paper covers the core components required for successful application of (Q)SAR technologies to ENMs toxicity prediction, and summarizes the published nano-(Q)SAR studies and outlines the challenges ahead for nano-(Q)SAR modelling. It provides a critical review of (1) the present status of the availability of ENMs characterization/toxicity data, (2) the characterization of nanostructures that meets the need of (Q)SAR analysis, (3) the summary of published nano-(Q)SAR studies and their limitations, (4) the in silico tools for (Q)SAR screening of nanotoxicity and (5) the prospective directions for the development of nano-(Q)SAR models

Multi-parameter correlations of solvent effects on kinetics of 1,3-dipolar cycloaddition reaction of C, N-diphenylnitrone with fumaronitrile: An experimental and theoretical study

1478-1484Solvent effects on kinetics of 1,3-dipolar cycloaddition reaction between C,N-diphenylnitrone and fumaronitrile have been studied spectrophotometrically at 65°C. Second-order rate constants of the reaction decrease with increasing normalized polarity parameter ( E ). Therefore, polarity of the reactants is higher than that of the activated complex of the reaction. Linear correlation of the logk2 vs E gives acceptable result (r = 0.978; s.e = 0.098; F1,14 = 310.54). Single-parameter correlations of log k2 vs π* (dipolarity/polarizability) and a (hydrogen-bond donor acidity) do not give satisfactory results; therefore, π* and α are not individually important factors in determining solvent effects on the reaction rate. Dual-parameter correlation of log k2 vs π* and α gives interesting result (r= 0.994; s.e = 0.056; F2,13 = 495.85). Dipolarity/polarizability and hydrogen-bond donor acidity of media have parallel effects on decreasing of the reaction rate; therefore, the reactants of reaction are stabilized via hydrogen-bonding and dipole-dipole interactions with solvent molecules major than the activated complex. The values of log k2 correlate well with three sets of theoretical (computational) molecular parameters using theoretical linear solvation energy relationship. The theoretical descriptors are calculated by two semiempirical methods (MNDO and AM1 algorithm) and one ab initio method (with 6-31 G* basis set). The correlation equations are physically reasonable and may be used as probes for solute-solvent interactions. Statistically, suggested multi-parameter correlation equation, in which the theoretical descriptors were calculated by MNDO algorithm, is better than the other equations

Correlation between vapour pressure of organic compounds and semiempirical theoretical descriptors

1504-1526A quantitative structure-property treatment of vapour pressure has been performed for a structurally wide variety of organic compounds using theoretical descriptors, which are calculated by semiempirical molecular orbital methods (MNDO and AM1 algorithm). From the eight theoretical descriptors, in model I, Mw (molecular weight), q+(the most positive charge of a hydrogen atom), ɛA and ɛB (the covalent acidity and basicity terms), π1 (polari zability term) and μ (dipole moment) have major effects on the vapour pressure. In the models, vapour pressure of the compounds decreases with increasing Mw, q+, ɛB, π1 and μ Effects of Mw and π1 on the vapour pressure arc higher than those of the other theoretical descriptors. The suggested multi-parameter equations are statistically acceptable (in model I: n = 246, r = 0.972, s.e = 0.259, F6.239 = 673.85 and in model II:n = 247, r = 0.973, s.e = 0.251 , F7.239 = 615.39)

Effect of aqueous solutions of various alcohols on kinetics of aromatic nucleophilic substitution reaction of 1-fluoro-2,4-dinitrobenzene with piperidine

895-899Reaction kinetics of 1-fluoro-2, 4-dinitrobenzene with piperidine has been studied spectrophotometrically in aqueous solutions of methanol, ethanol, propan-2-ol and 2-methylpropan-2-ol at 10°C. The reaction in the aqueous solutions is not catalyzed by nucleophile(piperidine). Second-order rate constants of the reaction decrease with increasing mole fraction of water and ETN(normalized polarity parameter). Therefore, polarity of the reactants of the reaction is higher than that of the activated complex. Single-parameter correlations of log kA vs ETN give satisfactory results (regression coefficients in aqueous solutions of methanol, ethanol, propan-2-ol and 2-methylpropan-2-ol are 0.988, 0.994, 0.995 and 0.996, respectively). Single-parameter correlations of log kA vs π*(dipolarity/ polarizability) and a ( hydrogen-bond donor acidity) do not give acceptable results(fore example, in the all aqueous solutions regression coefficients are 0.893 and 0.789, respectively), hence π* and α are not individually major factors in determining the reaction rate. Dual-parameter correlations of log kA vs π* and α in the all solutions represent significant improvement in statistical factors with regard to the single parameter models. Dipolarity/polarizability and hydrogen-bond donor acidity (HBD) of media have parallel and approximately equal effects on the reaction rate. Increasing of hydrogen-bond donor acidity of media stabilizes piperidine via hydrogen bonding interactions (one of the reactants) and hence the reaction rate decreases. A dual -parameter equation of log kA vs π* and α is obtai ned in the all aqueous solutions (n = 41, r= 0.990, s.e = 0.070, F2,38 = 968.10) in which π* and α have parallel and approximately equal effects on the reaction rate

Prediction of acidity constant for substituted acetic acids in water using artificial neural networks

478-487Linear and non-linear quantitative structure-activity relationships have been successfully developed for the modelling and prediction of acidity constant (pKa) of 87 substituted acetic acids with diverse chemical structures. The descriptors appearing in the multi-parameter linear regression (MLR) model are considered as inputs for developing the back-propagation artificial neural network (BP-ANN). ANN model is constructed using two molecular descriptors; the most positive charge of acidic hydrogen atom (q⁺) and most negative charge of the carboxylic oxygen atom (q⁻) as inputs and its output is pKa. It has been found that properly selected and trained neural network with 53 substituted acetic acids could fairly represent dependence of the acidity constant on molecular descriptors. For evaluation of the predictive power of the generated ANN, an optimized network has been applied for prediction pKa values of 17 compounds in the prediction set. Mean percentage deviation (MPD) for prediction set using the MLR and ANN models are 9.135 and 1.362, respectively. These improvements are due to the fact that the pKa of substituted acetic acids demonstrates non-linear correlations with the molecular descriptors

Electronic structure of ZnO(0001)/AgBr(111) heterojunction interface based on the TB-mBJ approximation

In this paper, we investigate the electronic structure of the ZnO and the AgBr semiconductors, in bulk and thin slab structures and in ZnO(0001)/AgBr(111) heterojunction interface, based on full-potential density functional theory and using the Tran and Blaha modified Beck Johnson potential. We obtain energy band gaps in excellent agreement with experiments. By analyzing the surface and interface states, it is found out that there is a wide two-dimensional n-type s-band at the surface of the nano-structures which grabs electrons from the bulk valence p–d band. The build-up potential at the interface is also determined which is 2.3 eV, higher at the AgBr side