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1,422 results on '"Liebman, Joel"'

14. Mononuclear Aluminum–Fluoride Ions, AlF x (+/−) —Study of Plausible Frameworks of Complexes with Biomolecules and Their In Vitro Toxicity.

Author

Pavlovič, Anja, Janžič, Larisa, Sršen, Lucija, Kopitar, Andreja Nataša, Edwards, Kathleen F., Liebman, Joel F., and Ponikvar-Svet, Maja

Abstract

The importance of fluorine and aluminum in all aspects of daily life has led to an enormous increase in human exposure to these elements in their various forms. It is therefore important to understand the routes of exposure and to investigate and understand the potential toxicity. Of particular concern are aluminum–fluoride complexes (AlFx), which are able to mimic the natural isostructural phosphate group and influence the activity of numerous essential phosphoryl transferases. Our review of salts of ionic AlFx species, which plausibly form the framework of complexes with biomolecules, revealed that the octahedral configuration of aluminum in the active site of the enzyme is preferred over the trigonal-bipyramidal structure. The effects of varying concentrations of fluoride, aluminum and AlFx—from micromolar to millimolar levels—on the viability and apoptosis rate of THP-1 monocytes were investigated using phosphate buffer solution as a culture media to simulate physiological conditions. Our results suggest that aluminum can reduce the direct toxicity of fluoride through the formation of AlFx. In view of the results found, further in vitro studies are required to clarify the toxicity mechanisms of these species. [ABSTRACT FROM AUTHOR]

Published
2025
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30. The heats of formation of the haloacetylenes XCCY [X, Y = H, F, Cl]: basis set limit ab initio results and thermochemical analysis

Author

Parthiban, Srinivasan, Martin, Jan M. L., and Liebman, Joel F.

Subjects
Physics - Chemical Physics, Physics - Atmospheric and Oceanic Physics
Abstract

The heats of formation of haloacetylenes are evaluated using the recent W1 and W2 ab initio computational thermochemistry methods. These calculations involve CCSD and CCSD(T) coupled cluster methods, basis sets of up to spdfgh quality, extrapolations to the one-particle basis set limit, and contributions of inner-shell correlation, scalar relativistic effects, and (where relevant) first-order spin-orbit coupling. The heats of formation determined using W2 theory are: \hof(HCCH) = 54.48 kcal/mol, \hof(HCCF) = 25.15 kcal/mol, \hof(FCCF) = 1.38 kcal/mol, \hof(HCCCl) = 54.83 kcal/mol, \hof(ClCCCl) = 56.21 kcal/mol, and \hof(FCCCl) = 28.47 kcal/mol. Enthalpies of hydrogenation and destabilization energies relative to acetylene were obtained at the W1 level of theory. So doing we find the following destabilization order for acetylenes: FCCF $>$ ClCCF $>$ HCCF $>$ ClCCCl $>$ HCCCl $>$ HCCH. By a combination of W1 theory and isodesmic reactions, we show that the generally accepted heat of formation of 1,2-dichloroethane should be revised to -31.8$\pm$0.6 kcal/mol, in excellent agreement with a very recent critically evaluated review. The performance of compound thermochemistry schemes such as G2, G3, G3X and CBS-QB3 theories has been analyzed., Comment: Mol. Phys., in press (E. R. Davidson issue)

Published
2001
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31. Definitive heat of formation of methylenimine, CH2=NH, and of methylenimmonium ion, CH2NH2+, by means of W2 theory

Author

de Oliveira, Glenisson, Martin, Jan M. L., Silwal, Indira K. C., and Liebman, Joel F.

Subjects
Physics - Chemical Physics, Physics - Computational Physics
Abstract

A long-standing controversy concerning the heat of formation of methylenimine has been addressed by means of the W2 (Weizmann-2) ab initio thermochemical approach. Our best calculated values, DeltaHf298(CH2NH)=21.1+/-0.5 kcal/mol and DeltaHf298(CH2NH2+)=179.4+/-0.5 kcal/mol, are in good agreement with the most recent measurements but carry a much smaller uncertainty. As a by-product, we obtain the first-ever accurate anharmonic force field for methylenimine: upon consideration of the appropriate resonances, the experimental gas-phase band origins are all reproduced to better than 10 cm-1. Consideration of the difference between a fully anharmonic zero-point vibrational energy and B3LYP/cc-pVTZ harmonic frequencies scaled by 0.985 suggests that the calculation of anharmonic zero-point vibrational energies can generally be dispensed with, even in benchmark work, for rigid molecules., Comment: RevTeX, 20 pages. J. Comput. Chem., in press JCC10266/F-204 (Paul von Ragu\'e Schleyer festschrift) Supplementary material: complete CCSD(T)/cc-pVTZ quartic force field available at http://theochem.weizmann.ac.il/web/papers/ch2nh.html

Published
2001

37. Paradoxes and paradigms: elements and compounds – similar names, very different energetics

Author

Ponikvar‑Svet, Maja, Edwards, Kathleen Frances, and Liebman, Joel F. Liebman

Abstract

In this paper we continue to review the phonetic similarity of trivial names of chemical substances and the names of the elements in the periodic table. Thermochemical properties are explicitly considered. We review elements from cesium to radon (Cs-Rn) Z = 55–86.

Published
2023
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