Thermodynamic dissociation constants of benzoic and nitrobenzoic acids in binary mixtures of water with acetone and tetrahydrofuran at 25.degree.C

1992 ◽  
Vol 37 (4) ◽  
pp. 470-473 ◽  
Author(s):  
M. Sadiq Khan Niazi ◽  
A. Hassan ◽  
M. Zafar I. Khan ◽  
S. S. Shah ◽  
J. Ali
Keyword(s):  
Binary Mixtures ◽  
Dissociation Constants ◽  
Nitrobenzoic Acids

Chromatographic Determination of Thermodynamic Acid Dissociation Constants of Tetracycline Antibiotics and Their Epimers

2019 ◽  
Vol 57 (8) ◽  
pp. 745-750
Author(s):  
İlkay Konçe ◽  
Ebru Çubuk Demiralay ◽  
Hülya Yılmaz Ortak
Keyword(s):  
Experimental Data ◽  
Dissociation Constant ◽  
Binary Mixtures ◽  
Dissociation Constants ◽  
Reversed Phase ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Chromatography Method ◽  
Ph Values

Abstract The presented study describes the development of reversed-phase liquid chromatography method using a core-shell particle column with a pentafluorophenyl stationary phase for the dissociation constant (pKa) determination of the tetracycline group antibiotics (tetracycline, oxytetracycline, chlortetracycline) and their epimers (4-epitetracycline, 4-epioxytetracycline, 4-epichlortetracycline). The pH values were measured in the acetonitrile (ACN)–water binary mixtures, used as mobile phases, instead of in water and take into account the effect of the activity coefficients. Thermodynamic acid dissociation constant (pKa1) values of studied antibiotics and their epimers were calculated using retention factor (k) at different mobile phase pH values in studied binary mixtures with ACN percentages of 20, 25, 30 and 35% (v/v). Experimental data were analyzed by using an Origin 7.0 program to fit experimental data to the nonlinear expression derived. From calculated pKa1 values, the aqueous pKa values of studied compounds were calculated by different approaches and these values were compared.

scholarly journals THE ACTIVATION OF STARFISH EGGS BY ACIDS

1927 ◽  
Vol 10 (5) ◽  
pp. 703-723 ◽  
Author(s):  
Ralph S. Lillie
Keyword(s):  
Carbonic Acid ◽  
Dissociation Constants ◽  
Free Acid ◽  
External Solution ◽  
Chlorobenzoic Acid ◽  
Nitrobenzoic Acid ◽  
Molecular Concentration ◽  
Nitrobenzoic Acids ◽  
Effective Component ◽  
Rate Of Activation

1. Comparison of the rates of activation of unfertilized starfish eggs in pure solutions of a variety of parthenogenetically effective organic acids (fatty acids, carbonic acid, benzoic and salicylic acids, chloro- and nitrobenzoic acids) shows that solutions which activate the eggs at the same rate, although widely different in molecular concentration, tend to be closely similar in CH. The dissociation constants of these acids range from 3.2 x 10–7 to 1.32 x 10–3. 2. In the case of each of the fourteen acids showing parthenogenetic action the rate of activation (within the favorable range of concentration) proved nearly proportional to the concentration of acid. The estimated CH of solutions exhibiting an optimum action with exposures of 10 minutes (at 20°) lay typically between 1.1 x 10–4 M and 2.1 x 10–4 M (pH = 3.7–3.96), and in most cases between 1.6 x 10–4 M and 2.1 x 10–4 M (pH = 3.7–3.8). Formic acid (CH = 4.2 x 10–4 M) and o-chlorobenzoic acid (CH = 3.5 x 10–4 M) are exceptions; o-nitrobenzoic acid is ineffective, apparently because of slow penetration. 3. Activation is not dependent on the penetration of H ions into the egg from without, as is shown by the effects following the addition of its Na salt to the solution of the activating acid (acetic, benzoic, salicylic). The rate of activation is increased by such addition, to a degree indicating that the parthenogenetically effective component of the external solution is the undissociated free acid. Apparently the undissociated molecules alone penetrate the egg freely. It is assumed that, having penetrated, they dissociate in the interior of the egg, furnishing there the H ions which effect activation. 4. Attention is drawn to certain parallels between the physiological conditions controlling activation in the starfish egg and in the vertebrate respiratory center.

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