Electrostatic effects in myoglobin. pH and ionic strength variations of ionization equilibria for individual groups in sperm whale ferrimyoglobin

Biochemistry ◽  
1974 ◽  
Vol 13 (14) ◽  
pp. 2974-2979 ◽  
Author(s):  
S. J. Shire ◽  
G. I. H. Hanania ◽  
F. R. N. Gurd
Keyword(s):  
Ionic Strength ◽  
Sperm Whale ◽  
Electrostatic Effects ◽  
Ionization Equilibria

scholarly journals Electrostatic effects on the kinetics of bound enzymes

1975 ◽  
Vol 145 (3) ◽  
pp. 431-435 ◽  
Author(s):  
J M Engasser ◽  
C Horvath
Keyword(s):  
Enzyme Activity ◽  
Ionic Strength ◽  
Substrate Concentration ◽  
Simple Expression ◽  
Inhibitor Concentration ◽  
Electrostatic Effects ◽  
Strength Change ◽  
Electrostatic Effect ◽  
Kinetics Of

1. The effect of the interaction between the charged matrix and substrate on the kinetic behaviour of bound enzymes was investigated theoretically. 2. Simple expression is derived for the apparent Km. 3. The apparent Km can only be used for the characterization of the electrostatic effect of the ionic strength does not vary with the substrate concentration. 4. The deviations from Michaelis-Menton kinetics are graphically illustrated for cases when the ionic strength varies with the substrate concentration. 5. The inhibition of the bound enzyme by a charged inhibitor at constant ionic strength is characterized by an apparent Ki. 6. When both the inhibitor concentration and the ionic strength change there is no apparent Ki, and the inhibition profile is graphically illustrated for this case. 7. Under certain conditions the electrostatic effects manifest thenselves in a sigmoidal dependence of the enzyme activity on the concentration of the substrate or inhibitor.

Electrostatic effects on ionization equilibria: Solvent dependence

1984 ◽  
Vol 49 (1) ◽  
pp. 179-189 ◽  
Author(s):  
Karel Kalfus ◽  
Zdeněk Friedl ◽  
Otto Exner
Keyword(s):  
Gas Phase ◽  
Carboxylic Acids ◽  
Dissociation Constants ◽  
Aprotic Solvents ◽  
Benzoic Acids ◽  
Cavity Model ◽  
Electrostatic Effects ◽  
Solvent Dependence ◽  
Ionization Equilibria ◽  
Substituted Benzoic Acids

Apparent dissociation constants of 3-substituted bicyclo[2,2,2]-octane-1-carboxylic acids I-III and of several substituted benzoic acids were measured in four pure solvents. The results - together with numerous literature data concerning dissociation in other solvents and in the gas phase - were compared with the prediction of the electrostatic theory. The theory fails to reproduce the essential features of the solvent dependence as it predicts generally too small effects and does not differentiate between protic and aprotic solvents. The mentioned goal cannot be achieved by any more sophisticated cavity model or by any other theory as far as it characterizes the solvent only through its bulk permittivity.

Electrostatic effects on ionization equilibria. 3-Substituted bicyclo[2,2,2]octane-1-carboxylic acids

1979 ◽  
Vol 44 (10) ◽  
pp. 2928-2945 ◽  
Author(s):  
Zdeněk Friedl ◽  
Jaroslav Hapala ◽  
Otto Exner
Keyword(s):  
Carboxylic Acids ◽  
Substituent Effects ◽  
Molecular Size ◽  
Geometrical Parameters ◽  
Electrostatic Effects ◽  
Ellipsoidal Cavity ◽  
Theoretical Predictions ◽  
Ionization Equilibria ◽  
The One

Nine 3-substituted (I-IX) and one 2-substituted (XI) bicyclo[2,2,2]octane-1-carboxylic acids were prepared as model compounds for verification of the electrostatic theory of substituent effects. On the one hand they are regular-shaped and suitable for calculations, on the other hand they allow to evaluate the role of the angle θ of the substituent dipole. The apparent pK values in 50% ethanol and 80% methyl cellosolve were correlated with σI constants (ρI 1.18 and 1.42, respectively) and compared with theoretical predictions based on the spherical and ellipsoidal cavity models. The agreement is very good with the new Ehrenson model but still satisfactory with some others not matching exactly the actual molecule shape. The substituent effects are resonably correlated with the substituent dipoles and with the geometrical parameters but exceptions are notable. Comparison with the previous results implies that the theory reproduces fairly the substituent effects in carboxylic acids of a given molecular size and not too unsymmetrical shape; the cavity model is, however, sufficiently flexible to compensate partly even for some non-electrostatic effects neglected by the basic theory.

Electrostatic Effects in Ionization Equilibria: An AM1 Study of Reversed Substituent Effect in 5-Fluorobicyclo[3.3.3]undecane-1-carboxylic Acid

1994 ◽  
Vol 59 (7) ◽  
pp. 1467-1471
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm
Keyword(s):  
Carboxylic Acid ◽  
Proton Transfer ◽  
Substituent Effect ◽  
Am1 Method ◽  
Electrostatic Effects ◽  
Ionization Equilibria ◽  
Electrostatic Theory

Relative proton transfer enthalpies δ ∆H0 of sp and ap conformers of 5-fluorobicyclo[3.3.3]undecane-1-carboxylic acid have been calculated by the AM1 method and the results were compared with the prediction of the electrostatic theory. It is shown that the great reversed substituent effect in the sp conformer (δ ∆H0 = 32.1 kJ mol-1) is substantially overestimated largely due to sterical Baeyer strain and non-bonded interactions.

scholarly journals Grand-Reaction Method for Simulations of Ionization Equilibria and Ion Partitioning in a Broad Range of pH and Ionic Strength

2019 ◽  
Author(s):  
Jonas Landsgesell ◽  
Oleg Rud ◽  
Pascal Hebbeker ◽  
Raju Lunkad ◽  
Peter Košovan ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Reaction Method ◽  
Corrected Version ◽  
Major Flaw ◽  
Ion Partitioning ◽  
Original Manuscript ◽  
Ionization Equilibria

On 16th September 2019 we found a major flaw in the original manuscript, that has been uploaded to ChemRXiv. To prevent readers from implementing and using a flawed algorithm, we decided to replace the manuscript with this notice. We anticipate to upload a corrected version within few weeks.<br><br>

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

1986 ◽  
Vol 64 (12) ◽  
pp. 2310-2314
Author(s):  
Martino Paventi ◽  
Fenton Heirtzler ◽  
John T. Edward
Keyword(s):  
Ionic Strength ◽  
Dissociation Constants ◽  
High Ionic Strength ◽  
Amide Group ◽  
Electrostatic Effects ◽  
Ammonium Group ◽  
Group A ◽  
Electrostatic Theory

The first dissociation constants pK1of four diprotonated α-aminothionamides, determined spectrophotometrically, are between −8.1 to −8.8; the second dissociation constants pK2, of three of these compounds, determined titrimetrically, are between 7.3 and 7.7. Both pK1and pK2 values are close to those calculated from current electrostatic theory for equilibria in solutions of zero ionic strength, in spite of the fact that data for pK1values were obtained in solutions of high ionic strength. Results indicate a much larger effect of the charged ammonium group on the basicity of the thionamide group than on the basicity of the amide group. A possible explanation based on the greater hydration of the protonated amide group is advanced.

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