International Journal of Molecular Sciences

179 KiB

Open AccessArticle

A Microscopic Study of Sodium Cluster Deposition on an Insulating Surface

by A. Ipatov, E. Suraud and P. G. Reinhard

Int. J. Mol. Sci. 2003, 4(5), 301-311; https://doi.org/10.3390/i4050301 - 15 Apr 2003

Cited by 7 | Viewed by 8828

We present microscopic calculations of the low energy deposition of small sodium clusters on NaCl surface. The substrate surface is taken as inert acting on the cluster through its interface potential. The time evolution of the cluster electronic system is described using the time-dependent density approximation. The dependence of the attachment process on the initial cluster orientation relative to the insulating surface is studied for the case of a Na₆ cluster. Full article

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205 KiB

Open AccessArticle

Conjugated Molecules for the Smart Filtering of Intense Radiations

by Danilo Dini

Int. J. Mol. Sci. 2003, 4(5), 291-300; https://doi.org/10.3390/i4050291 - 15 Apr 2003

Cited by 11 | Viewed by 7191

Abstract

The practical realization of smart optical filters, i.e. devices which change their optical transmission in a suitable way to keep a working state for a general light sensitive element , can involve the use of conjugated molecules whose light absorption properties are light- intensity dependent (nonlinear optical effect). The verification of optical limiting displayed by some particular conjugated molecules, e.g. phthalocyanines, is quite noteworthy and can be successfully exploited for the realization of such smart optical devices. In the present contribution the analysis of the relevant molecular feature of a phthalocyanine are analyzed with the aim of determining useful correlations between optical limiting performance and phthalocyanine chemical structure. In particular , the electronic nature of the substituent is considered as a key factor for the explanation of some observed optical limiting trends. Full article

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151 KiB

Open AccessArticle

Absolute Total Single–Electron–Capture Cross Sections of O₂⁺ with N₂ Gas

by A. T. Hasan and T. J. Gray

Int. J. Mol. Sci. 2003, 4(5), 284-290; https://doi.org/10.3390/i4050284 - 15 Apr 2003

Cited by 5 | Viewed by 8796

Abstract

Absolute total single-electron-capture cross sections have been measured for lowenergy O₂⁺ + N₂ system in the collision energy range between 0.50 to 2.0 keV. These cross sections are found to be in the range of 0.67 to 2.08 x10^-16 cm2. The measured total cross sections for single-electron- capture display a slowly increasing behavior as a function of the incident energy. Several measurements of total cross sections for electron-capture from N₂ by slow N₂⁺ and O⁺ ions, and from O₂ by slow O₂⁺ ions presently exist in the literature. In the measurements reported here, we measured the total cross sections for electron-capture from N₂ by slow O₂⁺ ions, such measurements are not found in the literature. The increasing availability of data on this system may stimulate work in this direction. Full article

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164 KiB

Open AccessArticle

Structure–Toxicity Relationships for Aliphatic Compounds Based on Correlation Weighting of Local Graph Invariants

by Andrey A. Toropov, Pablo Duchowicz and Eduardo A. Castro

Int. J. Mol. Sci. 2003, 4(5), 272-283; https://doi.org/10.3390/i4050272 - 15 Apr 2003

Cited by 29 | Viewed by 7711

Abstract

Quantitative Structure-Activity Relationships based on molecular descriptors calculated with Correlation Weights of Local Graph Invariants were developed to model the toxicity of aliphatic compounds to the 50% population growth inhibition. The relationships were computed on the basis of Labeled Hydrogen- Filled Graphs and correlation weights were obtained by an optimization to render as large as possible correlation coefficients between log(IGC₅₀^-1) and descriptors calculated with correlation weights. Morgan extended connectivity indices of zero, first, and second orders, paths of lengths two and three and valence shells of second and third ranges have been tested as local invariants of the Labeled Hydrogen-Filled Graphs. The best quantitative relationship obtained from the optimization of correlation weights is that one based on the valence shell of range two. First, second, and third order fitting equations were determined and statistical results are better than other similar data for the same molecular set. Full article

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171 KiB

Open AccessArticle

Electric Multipole Moments and (Hyper)Polarizability of X–C≡C–X, X = F, Cl, Br and I

by George Maroulis and Demetrios Xenides

Int. J. Mol. Sci. 2003, 4(5), 263-271; https://doi.org/10.3390/i4050263 - 15 Apr 2003

Cited by 7 | Viewed by 8410

Abstract

We have calculated self-consistent field (SCF) and second-order Møller-Plesset perturbation theory (MP2) for the dihaloethynes X–C≡C–X, X = F, Cl, Br and I. All calculations have been performed with carefully optimized, flexible basis sets of gaussiantype functions. Our best values for the quadrupole moment (Θ/ea₀²) are -0.6524 (FCCF), 3.6612 (ClCCCl), 5.8143 (BrCCBr) and 8.3774 (ICCI). The dipole polarizability is strongly anisotropic. For the mean (α /e²a0²Eh^-1) and the anisotropy (Δα/e²a0²Eh^-1) we obtain 23.58 and 15.09 (FCCF), 51.75 and 48.30 (ClCCCl), 66.53 and 60.04 (BrCCBr), 93.79 and 78.91 (ICCI). The mean dipole hyperpolarizability (γ /e⁴a0⁴Eh^-3) increases rapidly as 2932 (FCCF), 9924 (ClCCCl), 17409 (BrCCBr) and 35193 (ICCI). The transversal component of the hyperpolarizability is larger than the longitudinal one for FCCF, γxxxx > γzzzz but this is reversed for the other molecules in the series. Difluoroethyne is less (hyper)polarizable than ethyne. Full article

178 KiB

Open AccessArticle

Quantitative Structure-Activity Relationships of Noncompetitive Antagonists of the NMDA Receptor: A Study of a Series of MK801 Derivative Molecules Using Statistical Methods and Neural Network

by M. Elhallaoui, M. Elasri, F. Ouazzani, A. Mechaqrane and T. Lakhlifi

Int. J. Mol. Sci. 2003, 4(5), 249-262; https://doi.org/10.3390/i4050249 - 15 Apr 2003

Cited by 11 | Viewed by 9750

Abstract

From a series of 50 MK801 derivative molecules, a selected set of 44 compounds was submitted to a principal components analysis (PCA), a multiple regression analysis (MRA), and a neural network (NN). This study shows that the compounds' activity correlates reasonably well with the selected descriptors encoding the chemical structures. The correlation coefficients calculated by MRA and there after by NN, r = 0.986 and r = 0.974 respectively, are fairly good to evaluate a quantitative model, and to predict activity for MK801 derivatives. To test the performance of this model, the activities of the remained set of 6 compounds are deduced from the proposed quantitative model, by NN. This study proved that the predictive power of this model is relevant. Full article

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Int. J. Mol. Sci., Volume 4, Issue 5 (May 2003) – 6 articles , Pages 249-311

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