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1

Tritium kinetic isotope effects on enzymatic decomposition of L-tryptophan

Boroda E., Kański R., Kańska M.

Nukleonika

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2006

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Vol. 51,suppl.2

17-19

EN

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.

2

Low-Barrier Hydrogen Bonds in Pyridine-Dichloroacetic Acid Complexes

Perrin C., Lau J. S., Ohta B. K.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 11

1693-1702

EN

Amixture of Cl2CHCOOH-16O2 and Cl2CHCOOH-18O2 was combined with an excess of a pyridine and studied by NMR at 23_C, -43_C, and -81_C. The 1:1 complexes were analyzed by isotopic perturbation of equilibrium. Plots of OH chemical shift and of 13C isotope shift vs. pKa of the pyridinium ion both exhibit maxima ~ 5, when the basicities of the hydrogen-bond acceptors become matched, the hydrogen bond is strongest, and the equilibrium is maximally perturbed by the isotope. In contrast, for the complexes of pyridine and 3-picoline the isotopic perturbation seems to disappear, consistent with a low-barrier hydrogen bond in a single structure, rather than a hydrogen that can take either of two positions in a mixture of two tautomers.

3

Differences between DeltaH and DeltaS Values of the 1:2 Complexes of Camphor Enantiomers with alfa-Cyclodextrin Determined by NMR Titrations and by Other Techniques

Dodziuk H., Kozminski W., Dolgonos G.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 2

251-255

EN

DeltaH12 andDeltaS12 values for the 1:2 complexes of camphor enantiomers with alfa-cyclodextrin by NMR titrations, carried out from 25 to 48 graduateC, yielded -16.0 +-0.2 kcal/mol and 28.3 0.3 e.u. for 1a@2 and -9.8 0.2 kcal/mol and 9.10.2 e.u. for 1b@2. A comparison of the values obtained by other groups, using isothermal titration calorimetry and reversed-phase liquid hromatography, showed considerable differences except the Delta H12 and DeltaS12 for 1a@2, obtained by NMR and ITC methods. The reason of the differences, involving RPLC, are not discussed in view of internal inconsistencies of this method. On the other hand, the disagreement between the ITC andNMRresults seems to be due to the difference in solvents (H2O and D2O, respectively) used in both methods, which causes deuteration of all 36 OH groups of the host cyclodextrins. Interestingly, the deuteration causes a lowering of the absolute values of DeltaH12 and DeltaS12 for 1b@2, while the corresponding values of the complex with the second enantiomer are either unchanged or undergo only small changes upon the complexation.

4

Kinetic Isotope Effect in Hydrogen Isotope Exchange Between Hydrogen Sulphide or Thiol and Alcohol in Gas and Solution

Wawer A., Szydłowski J.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 1

117-121

EN

The kinetic parameters of the tritium exchange between H2 * S(D2 * S) or MeSH*(MeSD*) and MeOH(MeOD) vapours on PTFE and glass surface were measured. The *HH/*DD kinetic isotope effects are significantly lower than those for the reaction of phosphines with methanol. The kinetics of deuterium exchange between ButSH and EtOD in solutions of C6D12 and CD3CN had been studied and HH/DD isotope effect was evaluated. It appeared to be smaller than that in the vapours. These results suggest that contrary to the exchange reactions in phosphine, the elementary reaction of HH-transfer in four center transition state is not the rate limiting step and H-bond formation as well as diffusion controlled processes should be taken into account.

5

Isotope effects on enzymatic and nonenzymatic reactions of phosphorothioates

Catrina I., Czyryca P., Hengge A.

Nukleonika

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2002

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Vol. 47,suppl.1

17-23

EN

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.

6

Interpretation of isotope effects on the solubility of gases

Jancsó G.

Nukleonika

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2002

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Vol. 47,suppl.1

53-57

EN

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.

7

Lattice Cluster Theory for Copolymer Blends : General Theory in the Incompressible System, Long Chain Limit

Dudowicz J., Freed K. F.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 4

527-545

EN

The lattice cluster theory is developed for binary blends of two structured monomer copolymers in the simplifying limit of an incompressible system and high molecular weights. The major advance in the present theory is the inclusion of nonrandom mixing effects that lead to a monomer sequence dependence of the Helmholtz free energy without the introduction of new adjustable parameters beyond those present in descriptions of binary homopolymer blends formed from the constituent monomers. Equivalently, the sequence dependent contributions are shown to emerge from a proper determination of the "surface fractions" in individual copolymer chains. The general theory applies to blends of random copolymer, diblock copolymers, alternating copolymers, as well as of copolymers with kinetically controlled monomer sequences. The theory is illustrated for purely random copolymer blends of deuterated and hydrogenated polybutadienes, where the computed phase boundaries depart qualitatively from those predicted by random copolymer Flory-Huggins theory.

8

Influence of H/D Isotope Substitutio on Physicochemical Properties of Aqueous Solutions of Urea and Thiourea

Jelińska-Kazimierczuk M., Szydłowski J.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 1

115-125

EN

The influence of the H/D isotope substitution on excess volumes, partial molar volumes, viscosity and ultrasound speed in aqueous solutions of urea and thiourea are studied at 20 C. The excess volume of the solutions studied is relatively small - however, it is negative in urea and positive in thiourea solutions. On the other hand, the deuteration affects the excess volume in both solutions in the same way: deuterated systems show smaller deviation from additivity than regular ones. The speed of sound in the systems studied increases monotonously with concentration, but its isotope effect decreases as the concentration increases. The curves of viscosity are monotonous too, but isotope effect of kinematic viscosity is practically the same in the whole concentration range studied. The present results for urea and thiourea aqueous solutions are compared with those previously obtained for amide-water systems.

9

Acid-Catalyzed Cleavage of Some Chromone, Coumarin and Pyrone Derivaties of Aminomethylphosphonic Acid. Products and Kinetics of the ReactionB

Boduszek B., Latajka R., Walkowiak U.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 1

63-69

EN

Treatment of chromone-2, coumarin-4 and pyrone-2 derivatives of N-benzylaminomethylphosphonic acid with strong mineral acids leads to formation of the corresponding heterocyclic amines and phosphoric acid. Kinetic studies of this cleavage reaction demonstrate that protonation has a remarkable influence on a cleavage of C-P bonds. In aq. H2SO4, cleavage of the acids 1-3 exhibits a kinetic dependence on [H+]. The measured solvent isotope effect (kH/kD) was about 1.5 for the 1 and 2 and only 1.1 for the 3. The existence of the isotope effect shows that protons are involved on the rate-determining step. The data obtained suggest that the protonated phosphonate molecule is split by a dissociative mechanism with A-SE2 character and this is combined with an elimination of the phosphonate group as a positive-charged phosphorus moiety.

10

The Effect of Deuteron Substitution in Wated on the Speed of Sound in Aqueus Solutions of 1-Propanol

Marczak W., Spurek M.

Molecular and Quantum Acoustics

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2001

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Vol. 22

157-163

EN

Aqueous solutions of 1-alkans are often regarded as model systems in the investigation of hydration phenomena. The deuteron substitution in water changes the properties of aqueous alkans solutions as well as thode of such more complicated systems: cells, tissues and organs of living organisms. In this work, the speed of sound in mixtures of 1-propanol with D2O was compared with the speeds in binary solutions of methanol, ethanol and 1-propanol in H2O. A somewhat more pronounced hydrophobic hydration in D2O than in H2O is manifested by an effect similar to that resulting from the elongation of the alcohol molecule.

11

The Influence of (O, N)-Deuteration on the Crystal and Molecular Structure, Thermal Stability and Spectroscopic Properties of 1,3-Propanediammonium Hydrogenphosphate Monohydrate

Bartoszak-Adamska E., Figlerowicz M., Wiewiórowski M., Gustaffson T., Olovsson I., Jaskolski M.

Polish Journal of Chemistry

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2000

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Vol. 74, nr 3

393-402

EN

Exchange of mobile hydrogen atoms in 1,3-propanediammonium hydrogenphosphate for deuterium (OH-OD, NH-ND) affects the thermal stability of the salt. Additionally, (O,N)-deuteration induces some unexpected changes in the -CH2-vibrations in the IR spectrum of this compound. The structure of the title compound has been determined by single crystal X-ray diffraction analysis at 290 K (protonated as well as deuterated crystals) and at 25 K (deuterated crystal). In all cases, the crystals are monoclinic, space group, P21/c. The 1,3-propanediammonium dication has the extended all-trans conformation. The structure contains a three-dimensional network of hydrogen bonds, in which all available proton donors are engaged. The phosphate groups are linked through relatively strong H bonds to form infinite chains along c. The water molecule is closely associated with these chains by donating H bonds to two consecutive phosphate units along the chain.

12

Carbon-13 Isotope Fractionation in the Decarboxylation of Phenypropiolic Acid in Orthophosphoric Acid and in Diphosphoric Acid

Zieliński M., Ogrinc N., Zielińska A., Koblyuk N., Papiernik-Zielińska H.

Polish Journal of Chemistry

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2000

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Vol. 74, nr 5

707-715

13

Deuterium kinetic isotope effect for oxidation of perdeuteriated sodium butyrate with manganate in 3 M sodium hydroxide solution

Zielińska A., Zieliński M.

Nukleonika

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1999

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Vol. 44, nr 4

529-538

EN

Deuterium kinetic isotope effect, D-KIE, for oxidation of perdeuteriated sodium butyrate, CD3(CD2)2COONa, with manganate in the aqueous solution of 3 M NaOH has been determined in the temperature range 323-373 K. The temperature dependent k[indeks dolny]H/k[indeks dolny]D ratios are in the range from 17.59 at 323 K to 11.25 at 373 K. The activation energy difference, ΔQ[indeks dolny]o = Q[indeks dolny]oDD - Q[indeks dolny]oHH = ΔH#[indeks dolny]oDD - ΔH#[indeks dolny]oHH = 9.20 kJ mol-1, and the Arrhenius preexponential factors ratio A[indeks dolny]oDD/A[indeks dolny]oHH is equal to 1.76, corresponding to ΔS[indeks górny]≠[indeks dolny]oDD - ΔS[indeks górny]≠[indeks dolny]oHH = 4.70 J K[indeks górny]-1as deduced from the Arrhenius and Eyring diagrams. This is the main evidence of tunnelling in the transfer of methylene hydrogens of butyrate to the negatively charged oxygens of manganate in very basic solutions. The k[indeks dolny]oHH/k[indeks dolny]oDD ratios, corrected for the ionic strengh, have been reproduced by multiplying the (k[indeks dolny]C-H/k[indeks dolny]C-D)KIE value, caused by zero point energy differences, by the Bell tunnel correction Q[indeks dolny]tHH/Q[indeks dolny]tDD. The half width of the energy barrier, as approximated by an inverted parabola, was found to be equal to 5ź10[indeks górny]-11 m. The physicochemical origin of the energy barrier for the oxidation of n-chain aliphatic carboxylates with MnO[indeks dolny]4[indeks górny]2- ions in strongly alkaline solutions has been discussed. The mechanisms of the permanganate versus manganate oxidation i.e., in acidic versus alkaline media are compared.

PL

Zbadano kinetyczny efekt izotopowy deuteru (D-KlE) w reakcji utleniania deuterowanego całkowicie maślanu sodu, CD3(CD2)2COONa, manganianem (VI) w 3M roztworze wodnym wodorotlenku sodu w temperaturze od 323 do 373° K. Zależne od temperatury reakcji stosunki k[indeks dolny]oH/k[indeks dolny]oD zawierają się w granicach od 17,59 w 323° K do 11,25 w 373° K. Wyznaczone z wykresów Arrheniusa i Eyringa różnice energii aktywacji i entalpii aktywacji: ΔQ[indeks dolny]o = Q[indeks dolny]oDD - Q[indeks dolny]oHH = ΔH[indeks górny]≠[indeks dolny]oDD - ΔH[indeks górny]≠[indeks dolny]oHH = 9.20 kJ mol-1oraz stosunki czynników przedwykładniczych Arrheniusa A[indeks dolny]oDD/A[indeks dolny]oHH = 1,76, odpowiadające różnicy entropii aktywacji ΔS[indeks górny]≠[indeks dolny]oDD - ΔS[indeks górny]≠[indeks dolny]oHH = 4,70 J K[indeks górny]-1 wskazują na występowanie efektu tunelowego w toku przenoszenia wodoru od grup metylenowych maślanu do ujemnie naładowanych atomów tlenu utleniacza, tj. jonów MnO[indeks dolny]4[indeks górny]2- w środowisku silnie alkalicznym. Zgodność między wyznaczonymi doświadczalnie wartościami D-KlE (tj. stosunkami (k[indeks dolny]oH/k[indeks dolny]oD)) i tymiż wartościami obliczonymi teoretycznie otrzymano, mnożąc w każdej temperaturze efekty kinetyczne uwarunkowane różnicami energii punktu zerowego wiązań C-H/C-D przez poprawki na efekt tunelowy, Q[indeks dolny]tHH/Q[indeks dolny]tDD. Te ostatnie oszacowano metodą Bella, przyjmując dla szerokości połówkowej a paraboli odwróconej wartość 5.10[indeks górny]-11 m. Omówiono oddziaływania fizykochemiczne, warunkujące występowanie dużych efektów tunelowych deuteru w reakcjach utleniania alifatycznych kwasów karboksylowych jonami MnO[indeks dolny]4[indeks górny]2- w środowisku silnie zasadowym oraz brak takich efektów w reakcjach utleniania nadmanganianem, zachodzących w środowisku kwaśnym. Zaproponowano strukturę kompleksu stanu przejściowego w badanej reakcji utleniania maślanu manganianem w 3M NaOH.

14

Carbon-13 isotope effect for decarboxylation of phenylpropiolic acid (PPA) in orthophosphoric acid

Zielińska A., Zieliński M., Zielińska-Papiernik H.

Nukleonika

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1999

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Vol. 44, nr 3

403-410

EN

The carbon-13 isotope effect accompanying decarboxylation of phenylpropiolic acid in 85% orthophosphoric acid has been studied in the temperature range 323-353 K. The first fraction of CO2 was found to be generated at 323 K in 85% H3PO4 with the carbon-13 isotope effect, k[indeks dolny]12/k[indeks dolny]13, equal to 1.011-1.015. The subsequent fractions of carbon dioxide produced in the temperature range 323-353 K have shown none but about 0.2% per cent kinetic isotope effect (KIE). It has been suggested that the initial larger carbon-13 fractionation, accompanying the decarboxylation of PPA in 85% orthophosphoric acid, is caused by isotopic equilibra linking decarboxylating monomeric species of PPA with dimeric and larger units formed during solvation and dissolving of solid PPA in orthophosphoric acid. The solvated PPA molecules are decarboxylated in the homogeneous solution with a negligible carbon-13 KIE. The triple bond of phenylpropiolic acid is attacked by the hydrated protons, H3O⊕aq, and formation of the Calpha-H bond is the rate determining step. The bond rupture between the alpha carbon and the carboxyl group is the next fast reaction step. The enthalpy of activation, ΔH[indeks górny]≠ = 123.4 kJ/mol, and the positive entropy of activation, ΔS≠ = +30 e.u.(SI), exclude the chelate like structure of the transition state. This suggests a flexible structure of the transition state complex which must be less solvated than in the initial state. Some further studies of the carbon-13 KIEs in phosphoric acid environment are suggested.

PL

Zbadano efekt izotopowy 13C w reakcji dekarboksylacji kwasu fenylopropiolowego (PPA) w 85% H3PO4 w 323-373 K. Delta (PDB) pierwszej porcji dwutlenku węgla, przy stopniach dekarboksylacji około f= 0.1, wskazuje na jej początkowe wzbogacenie w 13C o około 1,0-1,5%. Spowodowane jest to prawdopodobnie procesami równowagowymi, zachodzącymi między ulegającymi dekarboksylacji monomerami PPA a większymi agregatami, powstającymi w wyniku oddziaływania kryształów PPA z uwodnionymi cząsteczkami kwasu ortofosforowego. Dalsza dekarboksylacja PPA przebiega w roztworze homogenicznym bez wyraźnego rozfrakcjonowania izotopów węgla. Przyłączenie protonów do wiązania potrójnego i tworzenie wiązania Calfa-H zachodzi w etapie krytycznym reakcji, poprzedzającym właściwą dekarboksylację, tj. utratę cząsteczki dwutlenku węgla przez kwas fenylopropiolowy. Entalpia aktywacji ΔH[indeks górny]≠ = 123,4 kJ/mol i dodatnia entropia aktywacji ΔS[indeks górny]≠ = +30 e.u.(SI) sugerują niecykliczny, swobodny, stan przejściowy kompleksów reakcji dekarboksylacji PPA w 85% kwasie ortofosforowym. Zaproponowano dalsze badania efektu izotopowego 13C w środowisku kwasów fosforowych.

15

Kinetic isotope effects of atomic hydrogen in condensed phases

Plonka A.

Nukleonika

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1998

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Vol. 43, nr 4

415-422

EN

Accounting for the dynamical effects of the host matrix on the guest movements in terms of dispersive kinetics, one finds the rationalization of the inverse isotope effects of atomic hydrogen in condensed media in the vicinity of break points on the Arrhenius plots of rate parameters.

PL

W ramach kinetyki dyspersyjnej, uwzględnienie wpływu dynamiki matrycy na ruchliwość wskaźnika tłumaczy odwrotne efekty izotopowe wodoru atomowego występujące w fazach skondensowanych w otoczeniu załamań wykresów Arrheniusa dla parametrów szybkości badanych procesów.

16

III. Carbon-13 fractionation in the decomposition of formic acid initiated by phosphoric anhydride. (sup 13)C fractionation in the decomposition of HCOOH initiated by P2O5

Zieliński M., Zielińska A.

Nukleonika

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1998

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Vol. 43, nr 1

57-64

EN

(sup 13)C isotope effects in the decarbonylation of formic acid of natural isotopic composition initiated by phoshorus pentoxide have been studied in a large temperature range (-5°C) - (+90°C). The (sup 13)C fractionation in the carbon monoxide production at -5°C increased from a low value of 1.2% characteristic of the first fractions of consecutively collected portions of carbon monoxide to higher values of (sup 13)C KIE observed in the decarbonylation of pure formic acid at corresponding temperatures. The temperature and time dependences of the measured (sup 13)C fractionations are functions of the relative number of millimoles of formic acid and the dehydrating phosphoric anhydride, P2O5. The addition of metaphosphoric acid reagent to unreacted formic acid containing H3PO4 significantly increased the (sup 13)C fractionation in subsequent decarbonylations at 70.4°C but to a slightly less degree than expected (sup 13)C KIE=1.0503 instead of 1.0535). The addition of metaphosphoric acid reagent to formic acid saturated with NaCl results in the experimental (sup 13)C fractionation of a value of 1.0534 very close to the theoreticall one. An explanation of the low values of (sup 13)C KIE in the initial stages of HCOOH/P2O5 decarbonylations has been presented.

PL

Efekt izotopowy (sup 13)C obserwowany w reakcji dehydratacji kwasu mrówkowego inicjowanej pięciotlenkiem fosforu wzrasta w czasie od dolnej wartości granicznej charakterystycznej dla pierwszych frakcji tlenku węgla, wynoszącej około 1,2% w temperaturze -5°C, do wartości maksymalnych obserwowanych w reakcji dekarbonylacji czystego HCOOH przy różnych temperaturach. Kształt zależności czasowych i temperaturowych mierzonego efektu (sup 13)C jest zależny od wzajemnego stosunku początkowego substratów, tj. (HCOOH)/(P2O5). Podano interpretację uzyskanych wyników pomiarowych. Dolna wartość początkowa efektu (sup 13)C pokrywa się z wartością oczekiwaną, jeśli przyjąć, że tlenek węgla powstaje w początkowym stadium reakcji heterogenicznej poprzez produkt przejściowy, bezwodnik kwasu mrówkowego, ulegający rozpadowi wewnątrzcząsteczkowemu na tlenek węgla i HCOOH. Górną granicę efektu (sup 13)C, osiąganą w powolnym stadium końcowym dekarbonylacji podniesiono do wartości oczekiwanej teoretycznie wprowadzając do roztworu nadmiar odczynnika analitycznego o nazwie "kwas metafosforowy", zawierający metafosforan sodu jako czynnik stabilizujący (36.5% HP03+63.0% NaPO3).

17

Carbon-13 isotope effects in the decarbonylation of liquid formic acid in the presence of pyrophosphoric acid II. (sup 13)C KIE in the decarbonylation of HCOOH in the presence of H4P2O7

Zieliński M., Zielińska A., Paul H., Papiernik-Zielińska H.

Nukleonika

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1998

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Vol. 43, nr 1

49-56

EN

Carbon-13 isotope fractionation in the decomposition of liquid formic acid of natural isotopic composition in the presence of pyrophosphoric acid has been studied in the temperature range 20-70°C. The initial fractionation of (sup 13)C in the decarbonylation of formic acid catalyzed by dehydrating species depends on the initial ratio of the substrate-formic acid to the dehydrating pyrophosphoric acid introduced into the reaction vessel. The (sup 13)CO fractionation increases with reaction time from the lowest value, which is close to that (sup 13)C KIE expected for the (sup13)C-(sup 1)H bond rupture in the rate determining step, to the highest boundary values observed in the thermal decomposition of pure liquid formic acid and approaching gradually the values of (sup 13)C KIE expected for the (sup 13)C-(sup 16)OH bond splitting in the rate determining step. The observed time and temperature dependences of the (sup 13)C fractionation are explained by the dependence of the (sup 13)C fractionation in catalysed dehydration of F.A. on the degree of solvation of dehydrating species with water molecules derived from the decomposing formic acid.

PL

Przeprowadzono trzy serie doświadczeń mających na celu wyznaczenie zależnego od czasu i temperatury efektu izotopowego 13C w reakcji dekarbonylacji kwasu mrówkowego zachodzącej w obecności kwasu pirofosforowego. Wyjaśniono, że początkowe wartości stosunku k12/k13 wyznaczone na podstawie składu izotopowego (tj. stosunków izotopowych 13C/12C) pierwszych porcji tlenku węgla zbieranych w toku dekarbonylacji HCOOH, określonego na spektrometrach masowych FINNIGAN i FISONS OPTIMA, są zbliżone do współczynników rozfrakcjonowania 13C w reakcjach, w których rozerwanie wiązania 13C-1H zachodzi w etapie krytycznym reakcji chemicznej. Te początkowe dolne wartości k12/k13 wzrastają w toku dalszej dekarbonylacji kwasu mrówkowego do wartości efektu kinetycznego 13C obserwowanego w reakcji rozpadutermicznego czystego kwasu mrówkowego w fazie ciekłej. Wyjaśniono, że systematyczny spadek stałej szybkości reakcji dekarbonylacji w miarę jej postępu i regularny wzrost efektu izotopowego13C jest spowodowany zmianą stopnia solwatacji/uwodnienia cząsteczek kwasu fosforowego i zmianą ich struktury. Uwodnione cząsteczki kwasu ortofosforowego, powstające z rozpadu kwasu pirofosforowego w toku dehydratacji HCOOH nie wpływają w sposów znaczący na efekt kinetyczny 13C w badanej reakcji.

18

A contribution to studies of carbon-13 kinetic isotope effect of the decarbonylation of liquid formic acid in the presence of phosphoric acids I. (sup 13)C KIE in the decarbonylation of HCOOH in the presence of phosphoric acids and P2O5

Zieliński M., Zielińska A., Papiernik-Zielińska H.

Nukleonika

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1998

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Vol. 43, nr 1

41-48

EN

A brief review of earlier (sup 13)C KIE studies of the decarbonylation of liquid formic acid (F.A.) and supplementary data concerning the (sup 13)C fractionation observed in the decomposition of this acid in the presence of inorganic dehydrating phosphoric acids and phosphoric anhydride are presented and discussed. The previous ad hoc interpretations of the experimental results are supported by more extensive numerical calculations relating to the cumulative (sup 13)C fractionation found in the carbon monoxide production in the presence of orthophosphoric acid, pyrophosphoric acid and P2O5 in liquid F.A. The full paper is given in the four internally related parts.

PL

Zbadano efekt kinetyczny (sup 13)C w reakcji dekarbonylacji ciekłego kwasu mrówkowego o naturalnym składzie izotopowym, zachodzącej w obecności 85% kwasu ortofosforowego, w obecności kwasu pirofosforowego oraz w obecności czystego bezwodnika kwasu fosforowego i P2O5 uwodnionego częściowo 85% kwasem ortofosforowym. Wyniki doświadczalnych oznaczeń (sup 13)C KlE przedstawionych w trzech pierwszych częściach poddano szczegółowej analizie teoretycznej w części czwartej pracy.

19

On isotope effect in superconducting materials with singular energy spectra

Rogula D.

Journal of Technical Physics

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1998

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Vol. 39, no 1

149-153

EN

The isotope mass effect in generalized BCS-like model of superconductor with singularities in energy spectrum is considered. The calculations are performed for logarithmic and square-root van Hove singularities corresponding to quasi-2D and quasi-1D systems. The effects of finite life-times of electronic states are taken into account by shifting the singularities off the rreal axis in the complex energy plane.