Spectrophotometric Studies on Complex Formation with Sulfosalicylic Acid. IV. With Iron(III) at Higher pH Values

1950 ◽  
Vol 72 (12) ◽  
pp. 5609-5612 ◽  
Author(s):  
Robert T. Foley ◽  
Robbin C. Anderson
Keyword(s):  
Complex Formation ◽  
Sulfosalicylic Acid ◽  
Ph Values

pH Effects in trypsin catalysis

1969 ◽  
Vol 47 (21) ◽  
pp. 4021-4029 ◽  
Author(s):  
H. P. Kasserra ◽  
K. J. Laidler
Keyword(s):  
Complex Formation ◽  
Ph Dependence ◽  
Specific Rotation ◽  
Ph Effects ◽  
Ph Values ◽  
A Value ◽  
Available Information ◽  
Hydrolysis Of ◽  
Substrate Concentrations ◽  
Covalent Complex

A kinetic study has been made of the trypsin-catalyzed hydrolysis of N-benzoyl-L-alanine methyl ester, at pH values ranging from 6 to 10. The substrate concentrations varied from 1.7 × 10−3 to 4.3 × 10−2 M. From the rates were calculated, at each pH, values of [Formula: see text] (corresponding to [Formula: see text]), [Formula: see text] (corresponding to [Formula: see text]) and [Formula: see text] The specific levorotation of trypsin was measured and found to vary with pH in the pH region 5–11, the change in specific rotation following the ionization of a single group with pK(app) of 9.4. At pH 11 the specific rotation of trypsin, its zymogen, and its phosphorylated derivative were approximately the same, suggesting similar conformations for all three forms of the protein.The kinetic results on the acid side were very similar to those obtained by other investigators for chymotrypsin; they imply that there is a group of [Formula: see text] in the free enzyme, presumably the imidazole function of a histidine residue, and that this group is involved in acylation and deacylation, which can only occur if it is unprotonated. The behavior on the basic side was found to be different from that with chymotrypsin revealing a decrease in [Formula: see text] at high pH corresponding to a value of [Formula: see text] whereas [Formula: see text] showed sigmoid pH-dependence. An interpretation of these results that is consistent with all available information is that a group of [Formula: see text] (presumably the —NH3+ function of the terminal isoleucine) controls the conformation and thereby the activity of the enzyme at different stages of complex formation. In contrast to chymotrypsin, the pK of this ionizing group appears to be generally lowered by covalent complex formation between trypsin and its substrates.

Stability and Complexation of Cyanidin-3-Giucoside and Raspberry Juice Extract in the Presence of Selected Cations

1981 ◽  
Vol 44 (7) ◽  
pp. 516-523 ◽  
Author(s):  
D. G. COFFEY ◽  
F. M. CLYDESDALE ◽  
F. J. FRANCIS ◽  
R. A. DAMON
Keyword(s):  
Complex Formation ◽  
Metal Ions ◽  
Ph Values ◽  
Hue Angle ◽  
The Stability ◽  
Similar Complex

The stability and color of purified cyanidin-3-glucoside and raspberry juice extract in the presence of selected metal ions was investigated. Production of metal-anthocyanin complexes was suggested by changes in color of the samples as shown by L, a, and hue angle values. Complex formation was indicated by HPLC in raspberry juice samples treated with Sn++ but not in samples of purified cyanidin-3-glucoside. According to the colorimetric values, complex formation occurs with cyanidin-3-glucoside and A1+++ at pH 2.0 and 3.0 and with Sn++ at pH 4.0 and 3.0. Similar complex formation occurs with these metals and raspberry juice extract at the same respective pH values.

Kinetics and Equilibrium of Binding of Fe3+ by a Fulvic Acid: A Study by Stopped Flow Methods

1975 ◽  
Vol 53 (20) ◽  
pp. 2979-2984 ◽  
Author(s):  
Cooper H. Langford ◽  
Tahir R. Khan
Keyword(s):  
Ionic Strength ◽  
Complex Formation ◽  
Fulvic Acid ◽  
Metal Ion ◽  
Equilibrium Constants ◽  
Acid Dissociation ◽  
Stopped Flow ◽  
Solution Ph ◽  
Sulfosalicylic Acid ◽  
Flow Measurements

The first report of a rate of binding of a metal ion (Fe3+) by a soluble fulvic acid is derived from stopped flow measurements. The rate of complex formation is normal in Wilkins' sense and similar to that for sulfosalicylic acid. Dissociation is slow (t1/2 > 10 s). The binding of Fe3+ by the fulvic acid in acid solution, pH = 1–2.5, was investigated by kinetic analysis in which the reaction of free Fe3+ with sulfosalicylic acid was followed by stopped flow spectrophotometry on a time scale short compared to release of Fe3+ by fulvic acid. Conditional equilibrium constants found were 1.5 ± 0.3 × 104 at pH = 1.5 and 2.5, and 2.8 ± 0.3 × 103 at pH = 1.0 at 25 °C (ionic strength 0.1).

THE DISSOCIATION OF α- AND β-LIPOVITELLIN IN AQUEOUS SOLUTION: PART II. INFLUENCE OF PROTEIN PHOSPHATE GROUPS, SULPHYDRYL GROUPS, AND RELATED FACTORS

1962 ◽  
Vol 40 (3) ◽  
pp. 373-379 ◽  
Author(s):  
R. W. Burley ◽  
W. H. Cook
Keyword(s):  
Aqueous Solution ◽  
Complex Formation ◽  
Calcium Ions ◽  
Chromatographic Behavior ◽  
Related Factors ◽  
Sulphydryl Group ◽  
Ph Changes ◽  
Ph Values ◽  
Sulphydryl Groups ◽  
Phosphate Groups

Removal of protein phosphate groups from α- and β-lipovitellin by means of a phosphatase has shown that these groups do not take part in the dissociation–association process. They appear, however, to be responsible for a difference in their ease of complex formation with calcium ions, and also for their different chromatographic behavior on columns of hydroxyapatite.Both lipovitellins contain about 26 μmoles/g of sulphydryl groups. Sulphydryl group reagents had no effect on the dissociation of α-lipovitellin but markedly changed the behavior of β-lipovitellin. N-Ethylmaleimide and p-chloromercuribenzoate displaced the equilibrium towards the associated form at all pH values below pH 10, but iodoacetamide tended to stabilize the dissociated form against pH changes. The different behavior of these reagents indicates that the sulphydryl groups are not directly involved in the dissociation but their substitution probably causes other changes in β-lipovitellin that affect its dissociation.

Calculation by computer of individual concentrations in a simulated milk salt solution. I

1981 ◽  
Vol 48 (1) ◽  
pp. 77-83 ◽  
Author(s):  
Geoffrey B. Wood ◽  
David S. Reid ◽  
Roger Elvin
Keyword(s):  
Ionic Strength ◽  
Complex Formation ◽  
Computer Program ◽  
Calcium Ions ◽  
Salt Solution ◽  
Salt Solutions ◽  
Ph Values ◽  
Phosphoric Acids

SummaryA modegl is proposed for the equilibria between the components of the salts in milk. The model includes complex formation between calcium ions and the various ionized forms of citric, lactic and phosphoric acids, and makes allowance for the effect of ionic strength. A computer program has been written to calculate the pH of the milk salt solutions and the concentration of each of the complexes formed. Calculated pH values agree with observed values for solutions of known composition.

The preparation and kinetics of complex formation of hexadimethylsulfoxidovanadium(III) perchlorate

1970 ◽  
Vol 48 (19) ◽  
pp. 2969-2971 ◽  
Author(s):  
Cooper H. Langford ◽  
Fine Man Chung
Keyword(s):  
Complex Formation ◽  
Sulfosalicylic Acid ◽  
Kinetics Of

We report the synthesis of the ion V(DMSO)63+ and kinetics of its reactions with SCN−, sulfosalicylic acid, and 2,2-bipyridine. The complex formation rates show some dependence on the ligand. The value of ΔS≠ found for the reaction with bipyridine is quite negative. A definite mechanistic assignment cannot yet be made.

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