scholarly journals Determination of the kinetics underlying the pKa shift for the 2-aminoanthracenium cation binding with cucurbit[7]uril

2015 ◽  
Vol 185 ◽  
pp. 381-398 ◽  
Author(s):  
Suma S. Thomas ◽  
Cornelia Bohne
Keyword(s):  
Rate Constants ◽  
Cation Binding ◽  
Stopped Flow ◽  
Ph Values ◽  
Pka Shift ◽  
Changes Over Time ◽  
Initial Binding ◽  
Flow Experiments ◽  
Over Time

The binding dynamics of the 2-aminoanthracenium cation (AH+) and 2-aminoanthracene (A) with cucurbit[7]uril (CB[7]) was studied using stopped-flow experiments. The kinetics was followed by measuring the fluorescence changes over time for AH+ and A, which emit at different wavelengths. The studies at various pH values showed different mechanisms for the formation of the AH+@CB[7] complex, with this complex formed either by the binding of AH+ or by the initial binding of A followed by protonation. In the latter case, it was possible to determine the protonation ((1.5 ± 0.4) × 109 M−1 s−1) and deprotonation (89 ± 7 s−1) rate constants for complexed A/AH+, which showed that the pKa shift of +3.1 for A/AH+ in the complex is mainly due to a lower deprotonation rate constant.

scholarly journals Determination of Rate Constants for the Activation Step in Atom Transfer Radical Polymerization Using the Stopped-Flow Technique

2004 ◽  
Vol 37 (8) ◽  
pp. 2679-2682 ◽  
Author(s):  
Tomislav Pintauer ◽  
Wade Braunecker ◽  
Edmond Collange ◽  
Rinaldo Poli ◽  
Krzysztof Matyjaszewski
Keyword(s):  
Atom Transfer Radical Polymerization ◽  
Radical Polymerization ◽  
Rate Constants ◽  
Stopped Flow ◽  
Atom Transfer

The dependence of the rates of reduction of cobalt(III)-μ-peroxo complexes on isomeric structure

1984 ◽  
Vol 62 (11) ◽  
pp. 2127-2130 ◽  
Author(s):  
Steve C. F. Au-Yeung ◽  
Donald R. Eaton
Keyword(s):  
Rate Constants ◽  
Chemical Shifts ◽  
Cobalt Complex ◽  
Stopped Flow ◽  
Ferrous Ions ◽  
Point Charge Model ◽  
Isomeric Structure ◽  
Initial Reduction ◽  
Charge Model ◽  
Flow Experiments

The reaction of μ-peroxybis(ethylenediamine)bis(diethylenetriamine)cobalt(III) with ferrous ions has been studied by stopped flow spectrophotometry and by 59Co nmr. Two separate initial reduction steps with second order rate constants of 1.07 and 3.04 M−1 s−1, respectively, can be discerned in the stopped flow experiments. These two rate constants are assigned to inner sphere reduction of the aef,cd,b and edf,ac,b isomers of the peroxy cobalt complex, respectively. The different isomers can be distinguished by 59Co nmr. If there is insufficient Fe2+ present to completely reduce the complex to Co(II) and water, the change in the relative intensities of the 59Co resonances after partial reduction shows that one isomer has reacted faster than the other. The 59Co resonances can be assigned to the different isomers on the basis of a point charge model for the chemical shifts and line widths. Based on this model it is concluded that the isomer with the central NH of the diethylenetriamine trans to the peroxy ligand reacts faster. This result is compared to literature reports on the relative rates of substitution of isomers of Co(III) complexes with ethylenediamine and diethylenetriamine ligands.

scholarly journals Inhibitory efficiencies for mechanism-based inactivators of sialidases

2015 ◽  
Vol 93 (11) ◽  
pp. 1207-1213 ◽  
Author(s):  
Kobra Khazaei ◽  
Juliana H.F. Yeung ◽  
Margo M. Moore ◽  
Andrew J. Bennet
Keyword(s):  
Sialic Acid ◽  
Aspergillus Fumigatus ◽  
Kinetic Parameters ◽  
Rate Constants ◽  
Catalytic Efficiency ◽  
Fluoride Ion ◽  
Stopped Flow ◽  
Leaving Group ◽  
Inhibitory Efficiency ◽  
Flow Experiments

Here we describe the measurement of the inactivation rate constants for the mechanism-based inactivator 2,3-difluorosialic acid acting upon the sialidase from Micromonospora viridifaciens. Using double mixing stopped-flow experiments conducted in a 3-(N-morpholino)propanesulfonic acid buffer (100 mmol/L, pH 7.00) at 25 °C, the derived kinetic parameters are kinact/Ki = (3.9 ± 0.8) × 106 (mol/L)–1 s–1 and Ki = 1.7 ± 0.4 μmol/L. We demonstrate that the inhibitory efficiency of the inactivation event is similar to the catalytic efficiency for this sialidase acting upon a typical substrate, 4-methylumbelliferone α-d-sialoside, kcat/Km = (7.2 ± 2.8) × 106 (mol/L)–1 s–1. Furthermore, we show that the catalytic efficiencies for inactivation and hydrolysis by the Kdnase from Aspergillus fumigatus are similar for the corresponding Kdn-analogues. We conclude that the deactivating effect of incorporating an axial 3-fluoro substituent onto the sialic acid scaffold is comparable to the enhanced activation that occurs when the 4-methylumbelliferone leaving group is changed to the more nucleofugal fluoride ion.

scholarly journals Om lenkefeil og ekvivaleringsmetoder på nasjonale prøver: Evaluering av endring over tid

2018 ◽  
Vol 12 (4) ◽  
pp. 16 ◽  
Author(s):  
Julius Kristjan Björnsson
Keyword(s):  
Item Response Theory ◽  
Item Response ◽  
Unbiased Estimate ◽  
Response Theory ◽  
Item Characteristics ◽  
National Tests ◽  
Changes Over Time ◽  
Design And Methods ◽  
Over Time

Nasjonale prøver i nåværende form, hvor Item Response Theory (IRT) benyttes for å bestemme oppgavenes egenskaper og hvor man måler utvikling over tid, har vært gjennomført siden 2014. Prøvene har vist seg å være stabile over tid, og en lenking og ekvivalering er blitt gjort siden 2014 for å gjøre sammenlik-ninger over tid mulige. For å kunne avgjøre om endringer over tid er signifikante, er det nødvendig å kvantifisere den usikkerheten som er knyttet til prosedyren for lenking fra år til år. Denne usikkerheten betegnes som lenkefeilen. Denne artikkelen gjør rede for ulike måter å gjøre dette på, og med bakgrunn i dette beregnes størrelsen av den lenkefeilen som er til stede i regning og engelsk for 5. og 8. trinn. I tillegg presenteres resultater fra en undersøkelse av mulig bias i lenkingen. Konklusjonen er at lenkefeilen er akseptabel, men likevel såpass stor at evaluering av endring over tid må ta hensyn til den. Det blir derfor viktig å ha et prøvedesign og bruke metoder som gir riktige (unbiased) estimater og som bidrar til å minimere lenkefeilen.Nøkkelord: IRT, nasjonale prøver, ekvivalering, lenkefeilLinking error and equating methods on the national tests:Estimating change over timeAbstractThe Norwegian national tests, utilizing Item Response Theory (IRT) to determine item characteristics and measure changes over time, have been administered since 2014. The tests have turned out to be stable over time, and linking and equating has been done each year to make comparisons over time possible. Central for these methods is to quantify the uncertainty in the linking from year to year, as this must be known to determine whether a change from year to year is significant or not. This article presents some often-used methods to estimate the linking error. Based on this, the size of the error due to linking is estimated for English and Numeracy for the 5th and 8th grades. The article also presents an examination of possible bias in the linking. The main conclusion is that the linking error is acceptable, but nevertheless so large that a determination of changes over time must take it into account. It remains important to make use of a test design and methods that result in an appropriately small and unbiased estimate of the linking error.Keywords: IRT, national tests, equating, linking error

RADIOACTIVE REMEDIATION OF AQUATIC ECOSYSTEMS USING MICROALGAE

2019 ◽  
Vol 186 (2-3) ◽  
pp. 296-300
Author(s):  
Dušan Galanda ◽  
Dominika Tatarová ◽  
Jozef Kuruc ◽  
Barbora Gaálová ◽  
Jana Slimáková
Keyword(s):  
Aquatic Ecosystems ◽  
Dunaliella Salina ◽  
Nuclear Accidents ◽  
Suitable Alternative ◽  
Ph Values ◽  
Nuclear Weapon Tests ◽  
Over Time ◽  
Optimal Ph ◽  
Radionuclide Activity

Abstract Radionuclides that have entered the environment through nuclear weapon tests, nuclear accidents or other human activities represent an ecological hazard. Many decontamination techniques are technically and financially demanding and often not environmentally beneficial. A suitable alternative is bioremediation techniques. One of them, phycoremediation utilizes the metabolic activity of microorganisms that degrade or eliminate contaminants from the environment. In our work, we focused on phycoremediation with microalgae Dunaliella salina and Chlorella vulgaris. An important parameter was the determination of the optimal pH values of the environment and subsequent monitoring of the radionuclide activity decline over time.

scholarly journals Determination of rapid chlorination rate constants by a stopped-flow spectrophotometric competition kinetics method

2014 ◽  
Vol 55 ◽  
pp. 126-132 ◽  
Author(s):  
Dean Song ◽  
Huijuan Liu ◽  
Zhimin Qiang ◽  
Jiuhui Qu
Keyword(s):  
Rate Constants ◽  
Stopped Flow ◽  
Chlorination Rate

The kinetics of partial processes in the oxidation of ascorbic acid catalyzed by vanadyl tetrasulphophthalocyanine

1982 ◽  
Vol 47 (3) ◽  
pp. 744-754 ◽  
Author(s):  
Dana M. Wagnerová ◽  
Jaroslav Votruba ◽  
Jürgen Blanck ◽  
Josef Vepřek-Šiška
Keyword(s):  
Experimental Data ◽  
Ascorbic Acid ◽  
Reaction Mechanism ◽  
Rate Constants ◽  
Stopped Flow ◽  
Adaptive Identification ◽  
Flow Method ◽  
Acid Catalyzed ◽  
Kinetics Of

The rapid partial reactions of the oxidation of ascorbic acid by dioxygen with vanadyl tetrasulphophthalocyanine as a catalyst were studied by the stopped-flow method. The experimental data were treated on a computer and compared with the kinetic implications resulting from the proposed mechanism. Application of the adaptive identification method led to quantitative solution of the mechanism, i.e. determination of the values of all the isolated rate constants of the reaction mechanism.

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