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1

Charge Localization in Monothiophosphate Monoanions

Rostkowski M., Paneth P.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 5-6

711-720

EN

We have examined charge distribution between exocyclic oxygen and sulfur atoms in 5,5-dimethyl-1,3,2-dioxaphosphorinan-2-oxy-2-thio monoanion. Our results indicate that while solvent polarity and substituents have minor effect, the presence of a counter- ion results in relative increase of the partial atomic charge on the oxygen atom. Thus it seems that change in the reactivity of this anion observed experimentally can be ascribed to ion pairing in low polarity solvent.

2

Equilibrium Isotope Effects on the Crotonase Reaction

Kołodziejska-Huben M., Anderson V. E., Paneth P.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 10

1467-1480

EN

Equilibrium isotope effects on the enoyl-CoA hydratase (crotonase, ECH) - catalyzed reaction were modeled by a mixed QM/MM method. The classical region (27 aminoacids essential for the catalysis) was treated at the MM level using universal force field UFF. The quantum atoms of 4-(N,N-dimethylamino)cinnamoyl-CoA (DAC-CoA), one water molecule, and two glutamate residues (Glu164 and Glu144) in the active site were treated at the PM3 level.

3

Carbon and Chlorine Kinetic Isotope Effects and Solvent Effects on the Hydrolysis of Chloroformates

Swanson S., Rudziński J., Paneth P., O'Leary M. H.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 12

1721-1731

EN

Carbon and chlorine kinetic isotope effects and pseudo-first order rate constants were measured for the hydrolysis of ethyl, benzyl, and isopropyl chloroformate in various mixtures of the binary solvent water-1,4-dioxane. Rate constants decreased as the percentage of 1,4-dioxane increased for all three chloroformates. Carbon-13 kinetic isotope effects (k12/k13) for hydrolysis of these compounds were 1.039-1.042 for ethyl chloroformate (0-75% 1,4-dioxane), 1.034-1.039 for benzyl chloroformate (15-75% 1,4-dioxane), and 1.025-1.037 for isopropyl chloroformate (25-75% 1,4-dioxane). Chlorine-37 kinetic isotope effects (k35/k37) were measured for benzyl and isopropyl chloroformates in 25% 1,4-dioxane (1.0088, benzyl; 1.0080 isopropyl) and 75% 1,4-dioxane (1.0090, benzyl; 1.0102 isopropyl). These data are consistent with an associative mechanism for benzyl and ethyl chloroformates, but hydrolysis of isopropyl chloroformate appears to be dissociative in polar solvents.

4

A Theoretical Study on (eta5-C5H5)Fe(CO)(PPh3)(C(O)CHMe) Anion Structure and Stereoselectivity

Anisimov V., Bartnicka E., Dybała-Defratyka A., Paneth P.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 5

737-744

EN

Organometallic systems provide an exceptional tool in the stereoselective synthesis. The source of this selectivity, however, frequently remains a challenging question. In recent years, theoretical studies of mechanisms of organometallic and metalloprotein catalysis have received considerable attention. The density functional theory (DFT) methods have been shown to be very successful in these studies. Their application, however, is still limited by the performance of the present computers. As the result, a new class of methods, which employ quantum mechanical calculations combined with either semiempirical and/or molecular mechanics levels (QM/MM), has been developed. This stimulated development of a number of new semiempirical methods, which can handle metals. We present a comparison of a few of these new methods with the DFT level on the example of the acetyliron. In addition, the DFT calculations are used to shed some light on the mechanism of the stereospecific catalysis by acetyliron.

5

Preface

Paneth P., Anderson V.

Nukleonika

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2002

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Vol. 47,suppl.1

1-2