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 Development of Methods for the Determination of pKa Values

2013 ◽  
Vol 8 ◽  
pp. ACI.S12304 ◽  
Author(s):  
Jetse Reijenga ◽  
Arno van Hoof ◽  
Antonie van Loon ◽  
Bram Teunissen
Keyword(s):  
Dissociation Constant ◽  
Conceptual Development ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Future Developments ◽  
Research Fields ◽  
Current State ◽  
Wide Range ◽  
Pka Determination

The acid dissociation constant (pKa) is among the most frequently used physicochemical parameters, and its determination is of interest to a wide range of research fields. We present a brief introduction on the conceptual development of pKa as a physical parameter and its relationship to the concept of the pH of a solution. This is followed by a general summary of the historical development and current state of the techniques of pKa determination and an attempt to develop insight into future developments. Fourteen methods of determining the acid dissociation constant are placed in context and are critically evaluated to make a fair comparison and to determine their applications in modern chemistry. Additionally, we have studied these techniques in light of present trends in science and technology and attempt to determine how these trends might affect future developments in the field.

scholarly journals Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

2015 ◽  
Vol 15 (17) ◽  
pp. 24217-24249 ◽  
Author(s):  
N. Borduas ◽  
B. Place ◽  
G. R. Wentworth ◽  
J. P. D. Abbatt ◽  
J. G. Murphy
Keyword(s):  
Acid Dissociation ◽  
Enthalpy Of Dissolution ◽  
Ionization Mass ◽  
Acid Dissociation Constant ◽  
Henry's Law ◽  
Analytical Technique ◽  
Henry’S Law ◽  
Ph Values ◽  
Ambient Measurements

Abstract. A growing number of ambient measurements of isocyanic acid (HNCO) are being made, yet little is known about its fate in the atmosphere. To better understand HNCO's loss processes and particularly its atmospheric partitioning behavior, we measure its effective Henry's Law solubility coefficient KHeff with a bubbler experiment using chemical ionization mass spectrometry as the gas phase analytical technique. By conducting experiments at different pH values and temperature, a Henry's Law coefficient KH of 26 ± 2 M atm-1 is obtained, with an enthalpy of dissolution of −34 ± 2 kJ mol-1. Our approach also allows for the determination of HNCO's acid dissociation constant, which we determine to be Ka = 2.1 ± 0.2 × 10-4 M at 298 K. Furthermore, by using ion chromatography to analyze aqueous solution composition, we revisit the hydrolysis kinetics of HNCO at different pH and temperature conditions. Three pH dependent hydrolysis mechanisms are in play and we determine the Arrhenius expressions for each rate to be k1 = (4.4 ± 0.2) × 107 exp (−6000 ± 240/T) M s-1, k2 = (8.9±0.9) × 106 exp (−6770 ± 450/T) s-1 and k3 = (7.2±1.5) × 108 exp (−10 900 ± 1400/T) s-1 where k1 is for HNCO + H+ + H2O → NH4+ + CO2, k2 is for HNCO + H2 O → NH3 + CO2 and k3 is for NCO- + 2H2 O → NH3 + HCO3-. HNCO's lifetime against hydrolysis is therefore estimated to be 10 days to 28 years at pH values, liquid water contents, and temperatures relevant to tropospheric clouds, years in oceans and months in human blood. In all, a better parameterized Henry's Law coefficient and hydrolysis rates of HNCO allow for more accurate predictions of its concentration in the atmosphere and consequently help define exposure of this toxic molecule.

scholarly journals Synthesis, structure elucidation and determination of acid dissociation constant, tautomerism of pyrido [1,2-a] benzimidazole-2,4-dione

2016 ◽  
Vol 54 (1) ◽  
pp. 23
Author(s):  
İsmail Kayağil ◽  
Naime Funda Tay ◽  
Hüseyin Kemal Yaşar Konak ◽  
Cihan İspir ◽  
Şeref Demirayak
Keyword(s):  
Dissociation Constant ◽  
Structure Elucidation ◽  
Acid Dissociation ◽  
Acid Dissociation Constant
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