International Journal of Molecular Sciences

55 KiB

Open AccessArticle

Collisional versus laser driven ionization in metal clusters

by P.-G. Reinhard and E. Suraud

Int. J. Mol. Sci. 2000, 1(4), 92-97; https://doi.org/10.3390/ijms1040092 - 14 Nov 2000

Cited by 2 | Viewed by 7605

We compare the capabilities of rapid highly charged projectiles and intense femtosecond lasers to ionize simple metal clusters while leaving as little intrinsic excitation as possible in the residue. We show that both excitation mechanisms are able to produce highly charged clusters. The deposited excitation energies increase with ionization but with different trends. Cold ionization, corresponding to moderate deposited excitation energy, is better attained with ionic projectiles for low charge states, and with lasers for high charge states. Full article

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238 KiB

Open AccessArticle

A New Graphical Model for Proton NMR (De)shielding over a Carbon-Carbon Double Bond to Replace the Shielding Cone Model

by Ned H. Martin and Justin D. Brown

Int. J. Mol. Sci. 2000, 1(4), 84-91; https://doi.org/10.3390/ijms1040084 - 14 Nov 2000

Cited by 11 | Viewed by 10475

Abstract

The long-held “shielding cone” model of the through-space NMR shielding effect of a carbon-carbon double bond predicts only the effect of the magnetic anisotropy of the double bond; it ignores other important contributors to the overall shielding. GIAO-SCF and GIAO-MP2 calculations have been performed on a simple model system, methane moved sequentially above ethene or 2-methylpropene. These calculations permit the net NMR shielding surface to be mapped. Based on those results, a new and very different graphical model for predicting the effect of a proton’s position relative to a carbon-carbon double bond on its chemical shift is presented. Full article

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60 KiB

Open AccessArticle

Modeling NMR chemical shifts: crystal potential derived point charge (CPPCh) model to calculate solid state effects on ³¹P chemical shifts tensors

by D. M. Schneider, M. C. Caputo, M. B. Ferraro and J. C. Facelli

Int. J. Mol. Sci. 2000, 1(4), 75-83; https://doi.org/10.3390/ijms1040075 - 13 Oct 2000

Cited by 5 | Viewed by 8415

Abstract

This paper presents a new method to calculate solid-state effects on NMR chemical shifts. Using full crystal potentials, this new method (CPPCh) eliminates the need to arbitrarily select the point charges that are included in the calculations of the NMR chemical shieldings to take into account intermolecular effects. By eliminating the arbitrary selection of the point charges, the method provides a mechanism to systematically improve the simulation of intermolecular effects on chemical shielding calculations. This new method has been applied to the calculation of the ³¹P NMR chemical shifts tensors in P₄S₃. The shielding calculations were done using the DFT approach with the BLYP gradient corrected exchange correlation functional. This method was selected to calculate the ³¹P chemical shifts because it includes electron correlation effects at a reasonable cost. Full article

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97 KiB

Open AccessArticle

Toxicity Assessment of Atrazine and Related Triazine Compounds in the Microtox Assay, and Computational Modeling for Their Structure-Activity Relationship

by P.B. Tchounwou, B. Wilson, A. Ishaque, R. Ransome, Ming-Ju Huang and Jerzy Leszczynski

Int. J. Mol. Sci. 2000, 1(4), 63-74; https://doi.org/10.3390/ijms1040063 - 13 Oct 2000

Cited by 51 | Viewed by 16981

Abstract

The triazines are a group of chemically similar herbicides including atrazine, cyanazine, and propazine, primarily used to control broadleaf weeds. About 64 to 80 million lbs of atrazine alone are used each year in the United States, making it one of the two most widely used pesticides in the country. All triazines are somewhat persistent in water and mobile in soil. They are among the most frequently detected pesticides in groundwater. They are considered as possible human carcinogens (Group C) based on an increase in mammary gland tumors in female laboratory animals. In this research, we performed the Microtox Assay to investigate the acute toxicity of a significant number of triazines including atrazine, atraton, ametryne, bladex, prometryne, and propazine, and some of their degradation products including atrazine desethyl, atrazine deisopropyl, and didealkyled triazine. Tests were carried out as described by Azur Environmental [1]. The procedure measured the relative acute toxicity of triazines, producing data for the calculation of triazine concentrations effecting 50% reduction in bioluminescence (EC₅₀s). Quantitative structure-activity relationships (QSAR) were examined based on the molecular properties obtained from quantum mechanical predictions performed for each compound. Toxicity tests yielded EC₅₀ values of 39.87, 273.20, 226.80, 36.96, 81.86, 82.68, 12.74, 11.80, and 78.50 mg/L for atrazine, propazine, prometryne, atraton, atrazine desethyl, atrazine deisopropyl, didealkylated triazine, ametryne, and bladex, respectively; indicating that ametryne was the most toxic chemical while propazine was the least toxic. QSAR evaluation resulted in a coefficient of determination (r²) of 0.86, indicating a good value of toxicity prediction based on the chemical structures/properties of tested triazines. Full article

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Int. J. Mol. Sci., Volume 1, Issue 4 (December 2000) – 4 articles , Pages 63-97

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