Temat: isotope effect - Prolib Integro

Skocz do pozycji: 1.

Tytuł:: Isotope effects of gallium and indium in cation exchange chromatography
Autorzy:: Dembiński, W.
Herdzik, I.
Skwara, W.
Bulska, E.
Wysocka, A.
Tematy:: isotope separation
chemical isotope effect
ion-exchange chromatography; Pokaż więcej
Wydawca:: Instytut Chemii i Techniki Jądrowej
Powiązania:: https://bibliotekanauki.pl/articles/146163.pdf Link otwiera się w nowym oknie
Opis:: The isotope effects of gallium (69/71Ga) and indium (113/115In) have been determined in the system: strong cation exchanger (Dowex 50-X8)/HCl. The sings of gallium and indium effects were opposite, i.e., the heavier isotope of gallium was fractionated into the resin phase, while the heavy isotope of indium was fractionated into the liquid phase. The values of unit separation gains were found to be +3.0 ´ 10-5 for gallium and –2.0 ´ 10-4 for indium. A possible explanation of the effects is proposed.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Tritium kinetic isotope effects on enzymatic decomposition of L-tryptophan
Autorzy:: Boroda, E.
Kański, R.
Kańska, M.
Tematy:: carbon-14
isotope effect
tritium
tryptophan
tryptophanase; Pokaż więcej
Wydawca:: Instytut Chemii i Techniki Jądrowej
Powiązania:: https://bibliotekanauki.pl/articles/148533.pdf Link otwiera się w nowym oknie
Opis:: The tritium kinetic isotope effect on position 2 has been determined in the reaction of decomposition of L-tryptophan, L-Trp, catalyzed by enzyme TPase, (EC 4.1.99.1). The numerical values of isotope effects in the course of reaction were obtained by the competitive method using [1-14C]-L-tryptophan as internal radiometric standard.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Isotope effects on enzymatic and nonenzymatic reactions of phosphorothioates
Autorzy:: Catrina, I.
Czyryca, P.
Hengge, A.
Tematy:: alkaline phosphatase
isotope effect
phosphoryl transfer
phosphorothioate
thio effect; Pokaż więcej
Wydawca:: Instytut Chemii i Techniki Jądrowej
Powiązania:: https://bibliotekanauki.pl/articles/146931.pdf Link otwiera się w nowym oknie
Opis:: Kinetic isotope effects have been measured for the aqueous hydrolysis reactions of p-nitrophenyl phosphorothioate (pNPPT) and the diester ethyl p-nitrophenyl phosphorothioate, and for the alkaline phosphatase-catalyzed reaction with pNPPT. The results show that the transition states of the uncatalyzed reactions of the phosphorothioate mono- and diesters are very similar to those of the corresponding phosphate ester reactions. The secondary 18O nonbridge isotope effects in reactions of phosphate esters become more normal as the mechanism changes from dissociative, metaphosphate-like to associative, phosphorane-like. The opposite trend occurs in phosphorothioate esters, due to differences in the relative contributions of bond-order changes and bending modes to this isotope effect. The KIEs for the alkaline phosphatase-catalyzed reaction of pNPPT are most consistent with a tight, triester-like transition state, probably a result of perturbations resulting from the larger size of sulfur that lead to a nucleophile attack angle that is unfavorable for an in-line process with a loose transition state.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Solvent deuterium isotope effect in the acid catalyzed decarboxylation of phenylpropiolic acid in 85% $D_{3}PO_{4}$ in $D_{2}O$
Autorzy:: Zielińska, A.
Zieliński, M.
Papiernik-Zielińska, H.
Dostawca treści:: Repozytorium Uniwersytetu Jagiellońskiego

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Skocz do pozycji: 5.

Tytuł:: Sulfur isotope effects for the SO2(g)-SO2(aq) system
Autorzy:: Chmielewski, A.
Derda, M.
Wierzchnicki, R.
Mikołajczuk, A.
Tematy:: istotopic fractionation of SO2
mass spectrometer
sulfur isotope effect; Pokaż więcej
Wydawca:: Instytut Chemii i Techniki Jądrowej
Powiązania:: https://bibliotekanauki.pl/articles/146983.pdf Link otwiera się w nowym oknie
Opis:: Sulfur isotope fractionation (34S/32S) factors were determined for the SO2(g)-SO2(aq) system. The influence of temperature on the investigated sulfur isotopes separation between phases was studied as well.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Modeling of the Reaction Mechanism of Enzymatic Radical C–C Coupling by Benzylsuccinate Synthase
Autorzy:: Heider, Johann
Szaleniec, Maciej
Wydawca:: MDPI
Cytata wydawnicza:: Szaleniec, Maciej, and Johann Heider. “Modeling of the Reaction Mechanism of Enzymatic Radical C-C Coupling by Benzylsuccinate Synthase.” International journal of molecular sciences vol. 17,4 514. 7 Apr. 2016, doi:10.3390/ijms17040514
Opis:: MNiSW/SGI4700/PAN/038/2007, MNiSW/IBM_BC_HS21/PAN/038/2007 the Deutsche Forschungsgemeinschaft (He2190/7-2) the state of Hessen via the LOEWE Center for Synthetic Microbiology, Marburg
Molecular modeling techniques and density functional theory calculations were performed to study the mechanism of enzymatic radical C–C coupling catalyzed by benzylsuccinate synthase (BSS). BSS has been identified as a glycyl radical enzyme that catalyzes the enantiospecific fumarate addition to toluene initiating its anaerobic metabolism in the denitrifying bacterium Thauera aromatica, and this reaction represents the general mechanism of toluene degradation in all known anaerobic degraders. In this work docking calculations, classical molecular dynamics (MD) simulations, and DFT+D2 cluster modeling was employed to address the following questions: (i) What mechanistic details of the BSS reaction yield the most probable molecular model? (ii) What is the molecular basis of enantiospecificity of BSS? (iii) Is the proposed mechanism consistent with experimental observations, such as an inversion of the stereochemistry of the benzylic protons, syn addition of toluene to fumarate, exclusive production of (R)-benzylsuccinate as a product and a kinetic isotope effect (KIE) ranging between 2 and 4? The quantum mechanics (QM) modeling confirms that the previously proposed hypothetical mechanism is the most probable among several variants considered, although C–H activation and not C–C coupling turns out to be the rate limiting step. The enantiospecificity of the enzyme seems to be enforced by a thermodynamic preference for binding of fumarate in the pro(R) orientation and reverse preference of benzyl radical attack on fumarate in pro(S) pathway which results with prohibitively high energy barrier of the radical quenching. Finally, the proposed mechanism agrees with most of the experimental observations, although the calculated intrinsic KIE from the model (6.5) is still higher than the experimentally observed values (4.0) which suggests that both C–H activation and radical quenching may jointly be involved in the kinetic control of the reaction
Maciej Szaleniec
Dostawca treści:: Repozytorium Centrum Otwartej Nauki

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Skocz do pozycji: 7.

Tytuł:: Interpretation of isotope effects on the solubility of gases
Autorzy:: Jancsó, G.
Tematy:: gas solubility
isotope effect
isotopic fractionation
Henry's law constant
partition function; Pokaż więcej
Wydawca:: Instytut Chemii i Techniki Jądrowej
Powiązania:: https://bibliotekanauki.pl/articles/146951.pdf Link otwiera się w nowym oknie
Opis:: Experimental results concerning the isotope effect on the solubility of gases are reviewed and the theory of the isotope effect on Henry's law constants is derived in terms of the statistical mechanical theory of condensed phase isotope effects. The performance of the method is demonstrated by detailed analysis of some of the available experimental data on solubility isotope effect.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Carbon-14 kinetic isotope effects in the debromination of p-nitrodibromocinnamic acid
Autorzy:: Bukowski, J.
Kanski, R.
Kanska, M.
Tematy:: bromine
carbon-14
elimination
kinetic isotope effect
mechanism
p-nitrodibromocinnamic acid; Pokaż więcej
Wydawca:: Instytut Chemii i Techniki Jądrowej
Powiązania:: https://bibliotekanauki.pl/articles/147051.pdf Link otwiera się w nowym oknie
Opis:: The kinetic isotope effect (KIE) method was applied to study the mechanism of elimination of bromine from p-nitro-erythro-alfa,beta-dibromocinnamic acid labeled at the alfa-carbon. This compound was obtained starting from [2-14C]malonic acid via [2-14C]cinnamic acid and subsequent addition of bromide. The value of 14C KIE determined for alfa-position of side chain of p-nitro-erythro-alfa,beta-dibromocinamic acid proves that elimination of bromine leading to formation of (E)-p-nitrocinnamic acid proceeds via E2 mechanism.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: Carbon isotope distribution along pine needles [Pinus nigra Arnold]
Autorzy:: Barszczowska, L
Jedrysek, M.O.
Tematy:: Croatia
pine
inhomogeneity
needle
growth
distribution
kinetic isotope effect
black pine
Spain
Pinus nigra
carbon isotope; Pokaż więcej
Wydawca:: Polskie Towarzystwo Botaniczne
Powiązania:: https://bibliotekanauki.pl/articles/57836.pdf Link otwiera się w nowym oknie
Opis:: In this paper we show spatial carbon isotope variations in black pine (Pinus nigra Arnold) needles, collected in spring 2001 and autumn 2003, from trees at the coast of south-western Croatia island (Žirje) and southern Spain (Benalmadena near Malaga), respectively. Needles were segmented perpendicularly to the longer axis (base, middle and top) and each segment was analysed separately. d13C values in needles from Croatia varied between -26.65‰ to -24.43‰ (2 months old needles) and from -28.25‰ to -25.21‰ (1 year old needles), while d13C values in needles from Spain varied from -27.58‰ to -25.27‰. The difference between d13Cb (base) and d13Ct (top) in the same needle (D13Cb-t) varied from 1.85 to 2.05‰ (in young needles from Croatia), from 0,02 to 1,80‰ (young needles from Spain), and 1.16 to 2.32‰, (in old needles from Croatia). The average D13Cb-t values were 0.78‰ and 1.73‰ in Spain and Croatia, respectively. In each needle the base of the needle was always 13C-enriched as compared to the top of the same needle. This evidences that carbon isotopes are not retranslocated after its fixation into the leaf structure (after the growth process is over). Temperature variation was most probably negligible for the discovered intraneedle carbon isotope distribution. Although, the intraneedle carbon isotope inhomogeneity can be partly the result of seasonal variation in d13C of atmospheric CO2, most probably the remarkably high D13Cb-t values, and regular pattern, are predominantly resulting from isotopic and chemical composition of primary and secondary products contained in the growin part of needle and kinetic isotope fractionation during decomposition of storage materials at the base.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Role of Thermochemical Decomposition in Energetic Material Initiation Sensitivity and Explosive Performance
Autorzy:: Shackelford, S. A.
Tematy:: energetic material
thermochemical decomposition
kinetic deuterium isotope effect
KDIE
initiation sensitivity
performance; Pokaż więcej
Wydawca:: Sieć Badawcza Łukasiewicz - Instytut Przemysłu Organicznego
Powiązania:: https://bibliotekanauki.pl/articles/358845.pdf Link otwiera się w nowym oknie
Opis:: Catastrophic initiation of an energetic material consists of a complex, interactive, sequential train of mechanistic mechanical, physical, and chemical processes which occur over a finite time period and proceed from macroscopic into sub-microscopic composition levels (bulk > crystalline > molecular > atomic). Initiation results when these processes proceed at a rate which generates sufficient energy (heat) to reach a threshold stage within this finite time period. Thus, the rate at which these mechanistic processes occur defines initiation sensitivity and affects performance. Thermochemical decomposition processes regulate the rate at which heat energy is released at the molecular level, and therefore to some extent, control energetic material initiation sensitivity and performance characteristics. Kinetic deuterium isotope effect (KDIE) data, obtained during the ambient pressure thermochemical decomposition process, identifies the mechanistic rate-controlling bond rupture which ultimately regulates the energy release rate of a given energetic material. This same rate-controlling bond rupture also appears as a significant rate-limiting feature in higher order deflagration, combustion, and explosion phenomena. The effect the KDIE-determined rate-controlling bond rupture exerts on initiation sensitivity, and its potential influence in combustion and explosion performance is delineated.
Dostawca treści:: Biblioteka Nauki

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