Ionization of 9-cyanofluorene in Me2SO–water mixtures. The role of solvent reorientation in proton tranfers

1986 ◽  
Vol 64 (6) ◽  
pp. 1273-1275
Author(s):  
Claude F. Bernasconi ◽  
François Terrier
Keyword(s):  
Rate Constants ◽  
Intrinsic Rate ◽  
Log P ◽  
Stopped Flow ◽  
Flow Method ◽  
Methoxide Ion ◽  
Carbon Acid ◽  
Role Of Solvent ◽  
Primary Aliphatic Amines

Rate constants of the reversible deprotonation of 9-cyanofluorene by primary aliphatic amines were measured in 10%, 50%, and 90% aqueous Me2SO (v/v) by the stopped-flow method. Intrinsic rate constants defined as k0 = k1B/q = k−1BH+/p at ΔpK + log (p/q) = 0 were obtained from Brønsted plots. The values for log k0 are 3.60 ± 0.15 in 10%, 3.81 ± 0.10 in 50%, and 3.61 ± 0.05 in 90% Me2SO. The constancy of k0 with increasing Me2SO content of the solvent contrasts with results obtained by Ritchie (C. D. Ritchie, J. Am. Chem. Soc. 91, 6749 (1969)) who found that k0 for the ionization of 9-carbomethoxyfluorene by carboxylate ions in Me2SO is much higher than for the ionization of the same carbon acid by methoxide ion in methanol. Our findings suggest that it is mainly early desolvation of the oxyanions in the hydroxylic solvent which accounts for Ritchie's results.

scholarly journals Phosphate has dual roles in cross-bridge kinetics in rabbit psoas single myofibrils

2021 ◽  
Vol 153 (3) ◽  
Author(s):  
Masataka Kawai ◽  
Robert Stehle ◽  
Gabriele Pfitzer ◽  
Bogdan Iorga
Keyword(s):  
Rate Constants ◽  
Striated Muscle ◽  
Intrinsic Rate ◽  
Isometric Tension ◽  
Force Generation ◽  
Skinned Fibers ◽  
Sinusoidal Analysis ◽  
Rabbit Psoas ◽  
Cross Bridge

In this study, we aimed to study the role of inorganic phosphate (Pi) in the production of oscillatory work and cross-bridge (CB) kinetics of striated muscle. We applied small-amplitude sinusoidal length oscillations to rabbit psoas single myofibrils and muscle fibers, and the resulting force responses were analyzed during maximal Ca2+ activation (pCa 4.65) at 15°C. Three exponential processes, A, B, and C, were identified from the tension transients, which were studied as functions of Pi concentration ([Pi]). In myofibrils, we found that process C, corresponding to phase 2 of step analysis during isometric contraction, is almost a perfect single exponential function compared with skinned fibers, which exhibit distributed rate constants, as described previously. The [Pi] dependence of the apparent rate constants 2πb and 2πc, and that of isometric tension, was studied to characterize the force generation and Pi release steps in the CB cycle, as well as the inhibitory effect of Pi. In contrast to skinned fibers, Pi does not accumulate in the core of myofibrils, allowing sinusoidal analysis to be performed nearly at [Pi] = 0. Process B disappeared as [Pi] approached 0 mM in myofibrils, indicating the significance of the role of Pi rebinding to CBs in the production of oscillatory work (process B). Our results also suggest that Pi competitively inhibits ATP binding to CBs, with an inhibitory dissociation constant of ∼2.6 mM. Finally, we found that the sinusoidal waveform of tension is mostly distorted by second harmonics and that this distortion is closely correlated with production of oscillatory work, indicating that the mechanism of generating force is intrinsically nonlinear. A nonlinear force generation mechanism suggests that the length-dependent intrinsic rate constant is asymmetric upon stretch and release and that there may be a ratchet mechanism involved in the CB cycle.

scholarly journals KINETIC STUDY ON ANIONIC σ-COMPLEX FORMATION BETWEEN 2,4,6-TRINITROANISOLE AND METHOXIDE ION BY HIGH PRESSURE STOPPED-FLOW METHOD

1979 ◽  
Vol 8 (6) ◽  
pp. 671-674 ◽  
Author(s):  
Noboru Takisawa ◽  
Muneo Sasaki ◽  
Fujitsugu Amita ◽  
Jiro Osugi
Keyword(s):  
High Pressure ◽  
Complex Formation ◽  
Kinetic Study ◽  
Stopped Flow ◽  
Flow Method ◽  
Methoxide Ion

Mechanism of bromination of a quaternary pyrimidinium cation. Change of rate determining step with acidity

1978 ◽  
Vol 56 (23) ◽  
pp. 2970-2976 ◽  
Author(s):  
Oswald S. Tee ◽  
David C. Thackray ◽  
Charles G. Berks
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Aqueous Media ◽  
Stopped Flow ◽  
Flow Method ◽  
High Acidity ◽  
Rate Determining Step ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of bromination of the 1,2-dihydro-1,3-dimethyl-2-oxopyrimidinium cation (Q+) in aqueous media (pH 0–5) have been studied using the stopped-flow method. At the higher acidities (pH < 2) the results are consistent with rate determining attack by bromine upon the pseudobase (QOH), whereas at low acidities (pH > 4) it appears that pseudobase formation is rate determining. The change occurs because at high acidity the reversal of the pseudobase QOH to the cation is fast relative to bromine attack, whereas at low acidity the converse is true. Results obtained at intermediate acidities (pH 2–4) are consistent with this interpretation.A separate kinetic study of pseudobase formation (and decomposition) yielded rate constants in good agreement with those derived from the bromination study.

scholarly journals Kinetics of the Reversible Transformation of 2,3-Dioxogulonic Acid into its Enol as a Function of the pH of the Medium

1978 ◽  
Vol 33 (10) ◽  
pp. 1184-1189
Author(s):  
J. Zuluaga ◽  
P. Martínez
Keyword(s):  
Kinetic Study ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Disodium Salt ◽  
Stopped Flow ◽  
Free Energies ◽  
Reversible Transformation ◽  
Flow Method ◽  
Kinetic Coefficients ◽  
Kinetics Of

Abstract 2,3-dioxogulonic acid and the disodium salt of its enol were synthesised, isolated and identified both chemically and spectroscopically. A kinetic study was carried out on its equilibrium by means of the “stopped flow” method for rapid processes, and the rate constants for the forward and backward reaction were determined as a function of the pH of the medium. The kinetic coefficients involved, equilibrium constant and Gibbs free energies were also determined.

scholarly journals Competitive kinetics versus stopped flow method for determining the degradation rate constants of steroids by ozonation

SpringerPlus ◽  
2016 ◽  
Vol 5 (1) ◽  
Author(s):  
Alberto López-López ◽  
Valentín Flores-Payán ◽  
Elizabeth León-Becerril ◽  
Leonel Hernández-Mena ◽  
Ramiro Vallejo-Rodríguez
Keyword(s):  
Rate Constants ◽  
Degradation Rate ◽  
Stopped Flow ◽  
Flow Method ◽  
Competitive Kinetics

scholarly journals The intrinsic rate constants in diffusion-influenced reactions

2016 ◽  
Vol 195 ◽  
pp. 421-441 ◽  
Author(s):  
Adithya Vijaykumar ◽  
Peter G. Bolhuis ◽  
Pieter Rein ten Wolde
Keyword(s):  
Rate Constants ◽  
Explicit Knowledge ◽  
Dominant Role ◽  
Rare Event ◽  
Intrinsic Rate ◽  
Interacting Particles ◽  
Complex Processes ◽  
Rare Event Simulations ◽  
Event Simulations

Intrinsic rate constants play a dominant role in the theory of diffusion-influenced reactions, but usually as abstract quantities that are implicitly assumed to be known. However, recently it has become clear that modeling complex processes requires explicit knowledge of these intrinsic rates. In this paper we provide microscopic expressions for the intrinsic rate constants for association and dissociation processes of isotropically interacting particles and illustrate how these rates can be computed efficiently using rare event simulations techniques. In addition, we address the role of the orientational dynamics, for particles interacting via anisotropic potentials.

First reaction steps and intermediates of the oxidation of ascorbic acid by dioxygen. Catalysis by cobalt(II) tetrasulphophthalocyanine

1982 ◽  
Vol 47 (3) ◽  
pp. 755-765 ◽  
Author(s):  
Dana M. Wagnerová ◽  
Jürgen Blanck ◽  
Josef Vepřek-Šiška
Keyword(s):  
Ascorbic Acid ◽  
Rate Constants ◽  
Reactive Intermediates ◽  
Stopped Flow ◽  
Absorption Bands ◽  
Flow Method ◽  
The Individual

The oxidation of ascorbic acid by dioxygen catalyzed by cobalt(II) tetrasulphophthalocyanine (CoTSP) has been studied by the stopped-flow method. Two reactive intermediates, [O2.CoTSP. ascorbic acid] and [O2.CoTSP], characterized by separate absorption bands at 570 nm and 634 nm, respectively, have been proved to form in the reaction. The individual steps of the reaction have been elucidated, and their rate constants have been determined or estimated.

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.

Plant Resistance in Some Modern Soybean Varieties May Favor Population Growth and Modify the Stylet Penetration of Bemisia tabaci (Hemiptera: Aleyrodidae)

2021 ◽  
Author(s):  
Mauricélia F Almeida ◽  
Clébson S Tavares ◽  
Euires O Araújo ◽  
Marcelo C Picanço ◽  
Eugênio E Oliveira ◽  
...  
Keyword(s):  
Population Growth ◽  
Bemisia Tabaci ◽  
Intrinsic Rate ◽  
Reproductive Rate ◽  
Genetically Engineered ◽  
Population Increase ◽  
Net Reproductive Rate ◽  
Bt Toxin ◽  
Demographic Performance

Abstract Complaints of severe damage by whiteflies in soybean fields containing genetically engineered (GE) varieties led us to investigate the role of transgenic soybean varieties expressing resistance to some insects (Cry1Ac Bt toxin) and to herbicide (glyphosate) on the population growth and feeding behavior of Bemisia tabaci (Gennadius) MEAM1 (Hemiptera: Aleyrodidae). In the laboratory, the whiteflies reared on the GE Bt soybeans had a net reproductive rate (R0) 100% higher and intrinsic rate of population increase (rm) 15% higher than those reared on non-GE soybeans. The increased demographic performance was associated with a higher lifetime fecundity. In electrical penetration graphs, the whiteflies reared on the GE soybeans had fewer probes and spent 50% less time before reaching the phloem phase from the beginning of the first successful probe, indicating a higher risk of transmission of whitefly-borne viruses. Data from Neotropical fields showed a higher population density of B. tabaci on two soybean varieties expressing glyphosate resistance and Cry1Ac Bt toxin. These results indicate that some GE soybean varieties expressing insect and herbicide resistances can be more susceptible to whiteflies than non-GE ones or those only expressing herbicide resistance. Most likely, these differences are related to varietal features that increase host-plant susceptibility to whiteflies. Appropriate pest management may be needed to deal with whiteflies in soybean fields, especially in warm regions, and breeders may want to consider the issue when developing new soybean varieties.

scholarly journals Dye-Surfactant Interaction: Role of Solvent

2013 ◽  
Vol 25 (18) ◽  
pp. 10499-10503 ◽  
Author(s):  
Ziya Ahmad Khan ◽  
Abdullah S. Al-Bogami
Keyword(s):  
Role Of Solvent
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