Aromatic sulphonates and the hydrolysis of 2-(p-nitrophenoxy)tetrahydropyran

1984 ◽  
Vol 62 (7) ◽  
pp. 1320-1324 ◽  
Author(s):  
Stella O'Leary
Keyword(s):  
Ionic Strength ◽  
Rate Constant ◽  
Polyacrylic Acid ◽  
Order Rate Constant ◽  
High Ionic Strength ◽  
Buffer Concentration ◽  
Salt Effects ◽  
Low Ionic Strength ◽  
Hydrolysis Of ◽  
Aromatic Sulphonates

The rate of hydrolyis of 2-(p-nitrophenoxy)tetrahydropyran was measured in a variety of buffers in water at 30 °C. At low ionic strength (μ = 0.05), 3,6-disulphonaphthoxyacetic acid catalysed the reaction. The second-order rate constant was 20 times faster than predicted from pKa. At high ionic strength (μ = 0.5), plots of kobs vs. total buffer concentration for both 3,6-disulphonaphthoxyacetic acid and 6,8-disulphonaphthyoxyacetic acid go through a maximum. Polyacrylic acid catalysed the reaction. The results are discussed in terms of aggregation and salt effects.

scholarly journals Multiple supramolecular structures formed by interaction of actin with protamine

1982 ◽  
Vol 205 (1) ◽  
pp. 31-37 ◽  
Author(s):  
Enrico Grazi ◽  
Ermes Magri ◽  
Ivonne Pasquali-Ronchetti
Keyword(s):  
Ionic Strength ◽  
Exchange Reaction ◽  
Dead Time ◽  
High Ionic Strength ◽  
Supramolecular Structures ◽  
Molar Ratio ◽  
First Case ◽  
Atpase Reaction ◽  
Low Ionic Strength ◽  
Millipore Filters

When protamine is added to actin, different supramolecular structures are formed depending on the molar ratio of the two proteins and of the ionic strength of the medium. At low ionic strength, and going from a molar ratio of protamine to G-actin of 4:1, 2:1 and 1:1, globular aggregates are first converted into extended structures and then to long threads in which the constituent ATP–G-actin is rapidly exchangeable with the actin of the medium. At high ionic strength {Tyrode [(1910) Arch. Int. Pharmacodyn. Ther.20, 205–212] solution}, starting from G-actin and protamine in the 1:1 molar ratio, long ropes are formed that can be resolved into intertwining filaments of 4–5nm diameter. The addition of protamine in a 1:1 molar ratio to a solution of F-actin in Tyrode solution causes the breakage of the actin filaments, which is also revealed by the decrease of the viscosity of the solution and the formation of ordered latero-lateral aggregates. The structures formed by reaction of protamine with G-actin can be separated from free G-actin and protamine by filtration through 0.45μm-pore-size Millipore filters. This technique has been exploited to study the exchange reaction between free actin and the actin–protamine complexes. For these studies the 1:1 actin–protamine complex formed at low ionic strength and the 2:1 actin–protamine complex formed in the presence of 23nm-free Mg2+ have been selected. In the first case the exchange reaction is practically complete in the dead time of the experiment (20s). In the second case, where the complex operates like a true ATPase, the rate of the exchange is initially comparable with the rate of the ATP cleavage. Later on, however, the complex undergoes a change and the rate of the exchange between free actin and the actin bound to protamine becomes lower than the rate of the ATPase reaction. It is proposed that the ATP exchanges for ADP directly on the G-actin bound in the complex.

The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100 °C

2005 ◽  
Vol 83 (9) ◽  
pp. 1483-1491 ◽  
Author(s):  
Eduardo Humeres ◽  
Maria de Nazaré M. Sanchez ◽  
Conceição ML Lobato ◽  
Nito A Debacher ◽  
Eduardo P. de Souza
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Base Catalysis ◽  
Hydrolysis Rate ◽  
Negative Slope ◽  
General Base ◽  
Order Rate ◽  
Basic Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100 °C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pH–rate profile showed that the hydrolysis occurred through specific acid catalysis at pH < 2, spontaneous hydrolysis at pH 2–6.5, and specific basic catalysis at pH > 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The Bunnett–Olsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an A1 mechanism. The neutral species hydrolyzed with general base catalysis shown by the Brønsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 10–7 s–1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 1–3 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 10–4 (mol/L)–1 s–1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.Key words: alkylthioncarbamate esters, ethyl N-ethylthioncarbamate, ethyl N,N-diethylthioncarbamate, hydrolysis, mechanism.

scholarly journals The Use of 2-Chloroethanol for Reversible Depolymerisation of the Protein Shell of Bacteriophage fr

1970 ◽  
Vol 25 (7) ◽  
pp. 711-713 ◽  
Author(s):  
D. Schubert ◽  
H. Frank
Keyword(s):  
Acetic Acid ◽  
Ionic Strength ◽  
Organic Solvent ◽  
High Ionic Strength ◽  
Protein Subunits ◽  
Viruslike Particles ◽  
Low Ionic Strength ◽  
Protein Shell

In mixtures of 1 volume of buffer and 2 volumes of 2-chloroethanol, the icosahedral bacteriophage fr is split into RNA and monomeric protein subunits. After removal of the RNA and after replacement of the organic solvent by water, viruslike particles can be obtained by dialysis of the protein against neutral buffers of high ionic strength, whereas multishell particles are formed in buffers of low ionic strength. All results achieved by the use of 2-chloroethanol are very similar to those obtained using acetic acid.

scholarly journals Proteolytic removal of three C-terminal residues of actin alters the monomer-monomer interactions

1993 ◽  
Vol 289 (3) ◽  
pp. 897-902 ◽  
Author(s):  
M Mossakowska ◽  
J Moraczewska ◽  
S Khaitlina ◽  
H Strzelecka-Golaszewska
Keyword(s):  
Electron Microscopy ◽  
Steady State ◽  
Ionic Strength ◽  
Rate Constants ◽  
Initial Rate ◽  
Critical Concentration ◽  
Rate Of Polymerization ◽  
Low Ionic Strength ◽  
Hydrolysis Of

Homogeneous preparations of actin devoid of the three C-terminal residues were obtained by digestion of G-actin with trypsin after blocking proteolysis at other sites by substitution of Mg2+ for the tightly bound Ca2+. Removal of the C-terminal residues resulted in the following: an enhancement of the Mg(2+)-induced hydrolysis of ATP in low-ionic-strength solutions of actin; an increase in the critical concentration for polymerization; a decrease in the initial rate of polymerization; and an enhancement of the steady-state exchange of subunits in the polymer. Electron microscopy indicated an increased fragility of the filaments assembled from truncated actin. The results suggest that removal of the C-terminal residues increases the rate constants for monomer dissociation from the polymer ends and from the oligomeric species.

scholarly journals The composition of cartilage proteoglycans. An investigation using high-and low-ionic-strength extraction procedures

1973 ◽  
Vol 131 (3) ◽  
pp. 541-553 ◽  
Author(s):  
Robert W. Mayes ◽  
Roger M. Mason ◽  
David C. Griffin
Keyword(s):  
Amino Acid ◽  
Ionic Strength ◽  
Density Gradient ◽  
Amino Acid Analysis ◽  
Chondroitin Sulphate ◽  
High Ionic Strength ◽  
Guanidinium Chloride ◽  
Equilibrium Conditions ◽  
Chondroitin Sulphate Proteoglycans ◽  
Low Ionic Strength

1. A proteoglycan fraction (the proteoglycan subunit fraction) was prepared from extracts, with 0.15m-KCl (low-ionic-strength) and 0.5m-LaCl3, 2.0m-CaCl2 and 4.0m-guanidinium chloride (high-ionic-strength), of bovine nasal cartilage by equilibrium-density-gradient centrifugation, essentially as described by Hascall & Sajdera (1969). 2. The use of different centrifugation times showed that near-equilibrium conditions were reached by 48h for the fractions prepared from the high-ionic-strength extracts. The fraction isolated from the low-ionic-strength extract required a longer centrifugation time to reach equilibrium conditions. 3. The composition of the proteoglycan fractions from the various extracts was compared by analyses of their carbohydrate and amino acid contents. Difference indices were calculated from the amino acid analysis to compare the degree of compositional relationship between the protein components of the proteoglycans. 4. Small compositional differences were found between the proteoglycans isolated from the various high-ionic-strength extracts. The protein content of the fractions from the CaCl2 extract and the guanidinium chloride extract showed the greatest difference in this respect, although their amino acid analysis was similar. 5. The proteoglycan fraction isolated from the low-ionic-strength extract shows marked differences in composition from the fractions isolated from the high-ionic-strength extracts. Its protein and glucosamine contents were lower whereas its hexuronic acid and galactosamine contents were higher than those of the latter. It also exhibits major differences in its amino acid composition. The glucosamine:galactosamine ratio of the fraction from the low-ionic-strength extract indicates that it may be an almost exclusively chondroitin sulphate–proteoglycan. Its analysis correlates closely with that of a low-molecular-weight proteoglycan isolated from pig laryngeal cartilage by Tsiganos & Muir (1969). 6. The proteoglycan fractions from both the low- and high-ionic-strength extracts migrate as a single band in zone electrophoresis carried out in a sucrose-density gradient at both pH3.0 and pH7.0, although each showed evidence of band widening during the electrophoresis. All the proteoglycan fractions migrated with the same electrophoretic mobility at pH3.0, irrespective of the differences in composition between them. 7. The differences between the proteoglycans from the low- and high-ionic-strength extracts are discussed and the view is advanced that they may be due to association between predominantly chondroitin sulphate–proteoglycans and a keratan sulphate-enriched proteoglycan species.

scholarly journals Microtubule assembly kinetics. Changes with solution conditions

1987 ◽  
Vol 247 (3) ◽  
pp. 505-511 ◽  
Author(s):  
J S Barton ◽  
D L Vandivort ◽  
D H Heacock ◽  
J A Coffman ◽  
K A Trygg
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Low Temperature ◽  
Number Concentration ◽  
High Ionic Strength ◽  
Microtubule Assembly ◽  
Microtubule Protein ◽  
Assembly Kinetics ◽  
Low Ionic Strength ◽  
Kinetics Of

The assembly kinetics of microtubule protein are altered by ionic strength, temperature and Mg2+, but not by pH. High ionic strength (I0.2), low temperature (T less than 30 degrees C) and elevated Mg2+ (greater than or equal to 1.2 mM) induce a transition from biphasic to monophasic kinetics. Comparison of the activation energy obtained for the fast biphasic step at low ionic strength (I0.069) shows excellent agreement with the values obtained at high ionic strength, low temperature and elevated Mg2+. From this observation it can be implied that the tubulin-containing reactant of the fast biphasic event is also the species that elongates microtubules during monophasic assembly. Second-order rate constants for biphasic assembly are 3.82(+/- 0.72) x 10(7) M-1.s-1 and 5.19(+/- 1.25) x 10(6) M-1.s-1, and for monophasic assembly the rate constant is 2.12(+/- 0.56) x 10(7) M-1.s-1. The microtubule number concentration is constant during elongation of microtubules for biphasic and monophasic assembly.

Breakdown and reassociation of bacterial spinae

1982 ◽  
Vol 28 (7) ◽  
pp. 795-808
Author(s):  
K. B. Easterbrook ◽  
R. W. Coombs
Keyword(s):  
Ionic Strength ◽  
Protein Conformation ◽  
High Ionic Strength ◽  
Random Coil ◽  
Temperature Dependent ◽  
Calcium Effect ◽  
Α Helix ◽  
Low Ionic Strength ◽  
Β Sheet ◽  
Polymeric Structures

The tubular appendage, spina (Easterbrook and Coombs. 1976. Can. J. Microbiol. 22: 438–440), dissociates most efficiently under conditions of low ionic strength (0.01 M), high pH (10), and high temperature (95 °C). The protomer, spinin, thus produced is stable under these conditions and reassociates on cooling to give two distinct filamentous polymeric structures that differ in their stability, protein conformation, and reassociation characteristics. Under conditions of low ionic strength (0.01 M), reassociation is relatively slow and leads to a product that has significant amounts of α-helix in addition to the high β-sheet component; under conditions of high ionic strength (1 M), reassociation is rapid and the non-β-sheet component is in the random coil configuration. Since polymerization of the latter structure is "seeded" by either endogenous or exogenously supplied spina fragments, the protomers comprising it are assumed to be in the same conformation as in the spinae. High ionic strength induces folding of the protomer, multimeric association, and finally, elongation by a temperature-dependent process. Reassociation appears to be pH (6–10) independent and, apart from a possible minor calcium effect, cation nonspecific.

Studies on Horseradish Peroxidase. VII. A Kinetic Study of the Oxidation of Iodide by Horseradish Peroxidase Compound II

1971 ◽  
Vol 49 (18) ◽  
pp. 3059-3063 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford ◽  
M. Evett
Keyword(s):  
Ionic Strength ◽  
Horseradish Peroxidase ◽  
Kinetic Study ◽  
Rate Constant ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Acid Dissociation ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of iodide ion by horseradish peroxidase compound II have been studied as a function of pH at 25° and ionic strength of 0.11. The logarithm of the second-order rate constant decreases linearly from 2.3 × 105 to 0.1 M−1 s−1 with increasing pH over the pH range 2.7 to 9.0. The pH dependence of the reaction is explained in terms of an acid dissociation outside the pH range of the study.

Studies on Sulphamic Acid and Related Compounds. II. Kinetics and Mechanism of Hydrolysis of Trimethylamine- and of Triethylamine Sulphur Trioxide Addition Compounds

1962 ◽  
Vol 15 (2) ◽  
pp. 251 ◽  
Author(s):  
BE Fleischfresser ◽  
I Lauder
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Aqueous Acetone ◽  
Second Order ◽  
Fluoride Ions ◽  
Order Rate ◽  
Mechanism Of Hydrolysis ◽  
Reaction With Water ◽  
Sulphamic Acid ◽  
Hydrolysis Of

The kinetics of hydrolysis of trimethylamine- and of triethylaminesulphur trioxide addition compounds have been studied in water and in aqueous acetone. Reaction occurs according to the equation,������������� f - + R,N.SO,+H,O-tR,XH+HSO~.The solvolysis reactions are first-order and are not catalyzed by acids. The halide ions, Cl', Br', and 1', show only a normal salt effect on the rate of hydrolysis of + - (CH,),N.SO, but in the presence of fluoride ions, the rate constant for the production + - of acid from (C,H,),N.SO, in water at 95 OC is about one-seventh of that in the absence of fluoride under the same conditions. It is suggested that the fluorosulphonate ion is formed rapidly, and that this ion then undergoes slow hydrolysis :�In the presence of alkali, using water as the solvent, second-order kinetics are observed, the equation for the reaction being,�������������� + - R,N.SO,+~OH-+R,X+SO~= +H,O. Assuming the reaction with water is bimolecular, the ratio of the (bimolecular) rate constants at 35 OC, ko~-/k~,o is approximately lo8 for each complex. In aqueous acetone, at low water concentrations, the hydrolysis reactions of the trialkylaminesulphur trioxide complexes show second-order kinetics. At 35 OC for the hydrolysis of + - (CH,),N.SO, the ratio of the second-order rate constant in aqueous acetone to the + - (calculated) second-order rate constant in water is approximately 550 ; for (C,H,),N.SO, the same ratio is 6900. It is considered that hydrolysis occurs in water and in aqueous acetone via a bi- molecular attack at sulphur.

scholarly journals Kinetic and Thermodynamic Study of Oxidative Decolourisation of a Typical Food Dye (Tartrazine) in an Aqueous Environment

2020 ◽  
Vol 24 (6) ◽  
pp. 1021-1026
Author(s):  
F.O. Okeola ◽  
E.O. Odebunmi ◽  
M.A. Amoloye ◽  
H.F. Babamale ◽  
S. Thema ◽  
...  
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Rate Constant ◽  
Metal Ion ◽  
Reaction Medium ◽  
Order Rate Constant ◽  
Aqueous Environment ◽  
Food Dye ◽  
Typical Food ◽  
Homogenous Catalyst

The study was carried out to describe the kinetics and thermodynamics of hydrogen peroxide oxidation of a typical food dye (Tartrazine). The effect of different operational factors were investigated spectrophotometricallyat wavelength460 nm under pseudo first order reaction.These included concentration of the oxidant and the dye, the pH, ionic strength and temperature of the reacting medium and the presence of transition metal ion as homogenous catalyst. A complete and smooth decolourisation was observed. The results showed that the rate of oxidation of dye increased with increasing in concentration of substrate and oxidant. Increasing in temperature, ionic strength and pH of the basic reaction medium also raised the reaction rate. The rate of oxidation also increased with increasing in the concentration of Fe (III) ion. Pseudo second order rate constant (k2) obtained was 1.95 x 10-3 M-1s-1 and 3.8 x10-3M-1s-1 in the absence and presence of Fe (III) ion respectively. The Arrhenius activation energy for the oxidation in the absence and presence of Fe (III) ion were 47.23 kJmol-1 and 42kJmol-1 respectively. Other thermodynamic parameters showed entropy of activation (ΔS#), free energy of activation (ΔG#) and Enthalpy of activation of the reaction (ΔH#) in the presence of Fe (III) as -34.7  JK-1mol-1, 48.4 kJmol-1 and 40.30 kJmol-1 respectively. The results in the absence of Fe (III) ion were -24.6 JK-1mol-1, 51.2 kJmol-1 and 44.0 kJmol-1respectively. The relative lower activation energy (Ea),fairly higher negative value of (ΔS#) and higher (ΔG#) , with higher rate constant in the presence of Fe(III) ion showed Fe(III) ion enhancement of rate of decolourisation. Keywords: Tartrazine Food dye, Kinetics, Thermodynamics, Hydrogen Peroxidede colourisation,

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