Steroids and steroidases. IX. Activation parameters and the mechanism of base- and enzyme-catalyzed isomerizations of androst-5-ene-3,17-dione. The nature of the active center of the Δ5 → Δ4-3-ketosteroid isomerase of Pseudomonas testosteroni

1969 ◽  
Vol 47 (23) ◽  
pp. 4459-4466 ◽  
Author(s):  
J. Bryan Jones ◽  
Donald C. Wigfield
Keyword(s):  
Amino Acids ◽  
Active Center ◽  
Activation Parameters ◽  
Circumstantial Evidence ◽  
Kcal Mole ◽  
Acid Base ◽  
Ketosteroid Isomerase ◽  
Enzyme Action ◽  
Enthalpy Of Activation

Determination of the activation parameters for the acid-, base-, and enzyme-catalyzed isomerizations of androst-5-ene-3,17-dione has revealed that the facility of the enzymic process is mainly due to an extremely low enthalpy of activation of 5.0 kcal mole−1. Further circumstantial evidence regarding the nature of the reacting groups at the active center has also been obtained, and a mechanism of enzyme action is proposed employing tyrosine and histidine as the principal amino acids responsible for catalyzing the isomerization.

Applications of proton magnetic resonance to rotational isomerism in halotoluene derivatives. IV. α,α,2,4,6-Pentachlorotoluene in carbon disulfide, an exchanging ABC system

1970 ◽  
Vol 48 (24) ◽  
pp. 3877-3881 ◽  
Author(s):  
Helen G. Gyulai ◽  
B. J. Fuhr ◽  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Carbon Disulfide ◽  
Activation Parameters ◽  
Frequency Factor ◽  
Kcal Mole ◽  
Hindered Rotation ◽  
Line Shapes ◽  
Line Shape Analysis ◽  
Enthalpy Of Activation ◽  
Carbon Carbon Bond ◽  
Entropy Of Activation

The p.m.r. of α,α,2,4,6-pentachlorotoluene in carbon disulfide solution displays hindered rotation about the sp2–sp3 carbon–carbon bond, causing broadening and collapse of the proton resonance spectrum. A full line-shape analysis using the computer program DNMR gives an activation energy of 14.2 ± 0.3 kcal/mole, a frequency factor of 11.9 ± 0.2, an enthalpy of activation of 13.7 ± 0.3 kcal/mole, and an entropy of activation of −4.4 ± 1 e.u. These data are compared with the activation parameters obtained in methylcyclohexane and toluene-d8 solutions from different line shapes.

Titration – a rapid method for the determination of proteolysis in cheese

1990 ◽  
Vol 57 (1) ◽  
pp. 149-150 ◽  
Author(s):  
Pia Ollikainen
Keyword(s):  
Amino Acids ◽  
Rapid Method ◽  
Acid Base ◽  
End Products ◽  
Acid Base Titration ◽  
Lactic Acids ◽  
Titration System

Titration is an old method used for the determination of acidic and basic groups of a molecule. Several metabolic end-products in cheese are compounds with acidic or basic groups, e.g. propionic, acetic and lactic acids, amino acids, amines and ammonia. A number of colorimetric and fluorometric methods have been used to study proteolysis in cheese; some are time-consuming with several steps, and certain of the reagents are hazardous.We have used acid-base titration for analysis of the products of proteolysis in Swiss-type cheese. The titration system was that originally developed for use in silage analysis (Moisio & Heikonen, 1989) and applied to cheese it has proved to be useful, easy and rapid with an accuracy similar to that achieved by colorimetry.

Kinetics and mechanism of redox reactions of U(III) ions with monochloroacetic and dichloroacetic acids

1979 ◽  
Vol 44 (2) ◽  
pp. 401-405 ◽  
Author(s):  
Ľubica Adamčíková ◽  
Ľudovít Treindl
Keyword(s):  
Redox Reactions ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Alcohol Concentration ◽  
Kinetics And Mechanism ◽  
Solvent Structure ◽  
Influence Of Ph ◽  
Sphere Mechanism

The kinetics and mechanism of the redox reactions of U3+ ions with mono- and dichloroacetic acids were studied. The influence of pH was observed mainly in the second case and led to the determination of the rate constants and activation parameters corresponding to two parallel steps, namely oxidation of U3+ with CHCl2COO- ions and oxidation of U3+ with CHCl2.COOH molecules. The influence of binary mixtures of water with methanol, ethanol, isopropanol, or tert-butenol on the reaction rate was followed. Increasing alcohol concentration influences the rate constant not only through changing dielectric constant and solvation of the reactants but also through a change of the solvent structure which plays a role in reactions with an outer sphere mechanism of the electron transfer.

Spectrophotometric study of the acid-base and optical properties of the 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-(diethylamino)phenol (BrPADAP, ClPADAP) and their complexation equilibria with zinc(II) ions

1982 ◽  
Vol 47 (10) ◽  
pp. 2676-2691 ◽  
Author(s):  
Miroslav Macka ◽  
Vlastimil Kubáň
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Alkaline Media ◽  
Acid Base ◽  
Ethanol Medium ◽  
Triton X ◽  
Mixed Water ◽  
Derivatives Of

The optical and acid-base characteristics of BrPADAP and ClPADAP were studied in mixed water-ethanol and water-DMF media and in 10% ethanol medium in the presence of cationic, anionic and nonionic tensides. The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the ML and ML2 complexes with zinc(II) ions were found by graphical analysis and numerical interpretation of the absorbance curves by the modified SQUAD-G program. Optimal conditions were found for the spectrophotometric determination of Zn(II) in the presence of 0.1% Triton X-100 or 1% Brij 35 in alkaline media with pH = 6.5-10. BrPADAP and ClPADAP are the most sensitive reagents (ε = 1.3-1.6 . 105 mmol-1 cm2 at 557 and 560 nm, respectively) for the determination of zinc with high colour contrast of the reaction (Δλ = 104 nm) and selectivity similar to that for the other N-heterocyclic azodyes (PAN, PAR, etc.).

scholarly journals Rapid Organocatalytic Chirality Analysis of Amines, Amino Acids, Alcohols, Amino Alcohols and Diols with Achiral Iso(thio)cyanate Probes

2021 ◽  
Author(s):  
Eryn Nelson ◽  
Jeffrey S. S. K. Formen ◽  
Christian Wolf
Keyword(s):  
Amino Acids ◽  
Absolute Configuration ◽  
Rapid Determination ◽  
Amino Alcohols ◽  
Enantioselective Synthesis ◽  
Widespread Occurrence ◽  
Chiral Compounds ◽  
New Methods ◽  
The Absolute

The widespread occurrence and significance of chiral compounds does not only require new methods for their enantioselective synthesis but also efficient tools that allow rapid determination of the absolute configuration,...

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