Thermodynamic of metal complexation of the macrocyclic antibiotic rifampicin

2001 ◽  
Vol 79 (1) ◽  
pp. 42-49
Author(s):  
I Shehatta ◽  
I Kenawy ◽  
A H Askalany ◽  
Ayman A Hassan
Keyword(s):  
Binding Sites ◽  
Equilibrium Constants ◽  
Ionic Species ◽  
Ligand Field ◽  
Water Medium ◽  
Acid Base ◽  
Distribution Diagram ◽  
Macrocyclic Antibiotic ◽  
Transition Series ◽  
Different Temperatures

The acid-base and complexation equilibria of rifampicin with H+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+ were studied by means of potentiometry. The stoichiometric equilibrium constants were determined in 50% (v/v) methanol-water medium at different temperatures and constant ionic strength (0.05 M KCl). It was established that rifampicin has two proton-binding sites. The distribution diagram of the corresponding ionic species as a function of pH is given and indicated that rifampicin exists predominantly in the zwitterionic form at pH [Formula: see text] 5. The thermodynamic parameters of protonation and complexation were derived and discussed. The formation of the complexes is spontaneous, more favourable at lower temperatures, entropically unfavourable, and an enthalpy-driven process. The order of the changes in Gibbs energy and enthalpy accompanying the complexation was found to be Mn2+ < Co2+ < Ni2+ < Cu2+ > Pb2+ > Zn2+ > Cd2+ > Hg2+ in accordance with the well-known sequence of Irving and Williams. The transition series contraction energy (Er(Mn-Zn)), and the ligand field stabilization energy (δH) were calculated from the enthalpy changes.Key words: rifampicin, thermodynamics, potentiometry, and complexation.

scholarly journals Adsorption of strontium on manganese oxide (δ-MnO2) at elevated temperatures: experiment and modeling

2019 ◽  
Vol 64 (10) ◽  
pp. 1091-1104
Author(s):  
O. N. Karaseva ◽  
L. I. Ivanova ◽  
L. Z. Lakshtanov
Keyword(s):  
Ionic Strength ◽  
Elevated Temperatures ◽  
Equilibrium Constants ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Acid Base ◽  
Surface Complexes ◽  
Different Temperatures ◽  
Low Ionic Strength ◽  
Outer Sphere Complexes

Strontium adsorption has been studied by the method of acid-base potentiometric titrations at three different temperatures: 25, 50, 75C. The effect of pH, ionic strength, sorbate/sorbent ratio, and temperature on adsorption was investigated. Experimental data were simulated using two various surface complexation models, with two different electrostatic descriptions of the interface: the constant capacitance model (CCM) and the triple-layer model (TLM). Although the both models used are able to account for the acid-base reactions and surface complexation of strontium on birnessite, we consider that the TLM is more applicable for a description of heterophaseous system H+ MnOH Sr2+. Under conditions of low ionic strength and negatively charged surface, Sr2+ ions compete with the electrolyte ions and form outer-sphere complexes along with inner-sphere complexes. Consequently, using the CCM for description of strontium adsorption data could be mathematically satisfactory, but physically senseless. The equilibrium model proposed here consists of the complexes of inner (MnOHSr2+, MnOSr+, MnOSrOH0) and outer types ([MnO Sr2+]+). The corresponding intrinsic equilibrium constants of the formation of these surface complexes were calculated for 25,50, and 75C.

scholarly journals Acid-base behaviour of sanguinarine and dihydrosanguinarine

2009 ◽  
Vol 7 (4) ◽  
pp. 876-883 ◽  
Author(s):  
Helena Absolínová ◽  
Luděk Jančář ◽  
Irena Jančářová ◽  
Jaroslav Vičar ◽  
Vlastimil Kubáň
Keyword(s):  
Optical Properties ◽  
Acetic Acid ◽  
Ionic Strength ◽  
Equilibrium Constants ◽  
Ionic Species ◽  
Transport Proteins ◽  
Priority Effect ◽  
Acid Base ◽  
Strength Of Interaction ◽  
Transition Reaction

AbstractAcid-base and optical properties of sanguinarine and dihydrosanguinarine were studied in the presence of HCl, HNO3, H2SO4, H3PO4, CAPSO and acetic acid (HAc) of different concentrations and their mixtures. The equilibrium constants pKR+ of the transition reaction between an iminium cation Q+ of sanguinarine and its uncharged QOH (pseudo-base, 6-hydroxy-dihydroderivative) form were calculated. A numerical interpretation of the A-pH curves by a SQUAD-G computer program was used. Remarkable shifts of formation parts of absorbance-pH (A-pH) curves to alkaline medium were observed. The shifts depend on the type and concentration of inert electrolyte (the most remarkable for HNO3 and HCl). The corresponding pKR+ values ranged from 7.21 to 8.16 in the same manner (ΔpKR+ = 0.81 and 0.73 for HNO3 and HCl, respectively). The priority effect of ionic species and ionic strength was confirmed in the presence of NaCl and KCl. The strength of interaction of SA with bioactive compounds (i.e. receptors, transport proteins, nucleic acids etc.) may be affected because of the observed influence of both cations and anions of the inert electrolytes.

scholarly journals Spectrophotometric study of time stability and acid-base characteristics of chelerythrine and dihydrochelerythrine

2010 ◽  
Vol 8 (3) ◽  
pp. 626-632 ◽  
Author(s):  
Helena Absolínová ◽  
Luděk Jančář ◽  
Irena Jančářová ◽  
Jaroslav Vičar ◽  
Vlastimil Kubáň
Keyword(s):  
Ionic Strength ◽  
Spectral Properties ◽  
Equilibrium Constants ◽  
Ionic Species ◽  
Spectrophotometric Study ◽  
Time Stability ◽  
Priority Effect ◽  
Acid Base ◽  
Strength Of Interaction ◽  
Transition Reaction

AbstractTime stability, acid-base and UV-VIS spectral properties of dihydrochelerythrine (DHCHE) were studied spectrophotometrically in water:methanol and water:ethanol media. DHCHE is stable in strongly acid milieu (pH HCl, HNO3, H2SO4, H3PO4 and their mixtures. Remarkable shifts of formation parts of absorbance-pH (A-pH) curves to the alkaline medium were observed depending on the type and concentration of inert electrolyte (most remarkable for HNO3 and HCl). The corresponding equilibrium constants pKR+ of the transition reaction between charged iminium Q+ and uncharged QOH (pseudo-base, 6-hydroxy-dihydro derivative) forms of chelerythine were calculated using a numerical interpretation of A-pH curves by a SQUAD-G computer program which ranged from 8.51–9.31. The highest changes of ΔpK R+ (0.75 and 0.53) were observed for H3PO4 and H2SO4, respectively. The priority effect of ionic species and ionic strength was confirmed in the presence of additions of NaCl and KCl. The strength of interaction of CHE with biomacromolecular compounds (i.e., peptides, proteins, nucleic acids etc.) may be affected because of the observed influence of both cation and anion of the inert electrolyte on acid-base behavior.

Determining Acid Equilibrium Constants by Means of Chromatic Parameters

1996 ◽  
Vol 50 (10) ◽  
pp. 1290-1294 ◽  
Author(s):  
D. Escolar ◽  
Ma R. Haro ◽  
A. Saucedo ◽  
J. Ayuso ◽  
A. Jimenez ◽  
...  
Keyword(s):  
Ph Value ◽  
Equilibrium Constants ◽  
Bromophenol Blue ◽  
Acid Base ◽  
Acidity Constants ◽  
Spectrophotometric Methods ◽  
Acid Base Equilibrium ◽  
Different Temperatures ◽  
Entire Spectral Range

A method has been developed for the determination of acid-base equilibrium constants, which is applicable to compounds that absorb in the visible. The tristimulus (X, Y, Z) and the colorimetric coordinate values ( L, a, b) of the chromatic space CIELAB 1976 are calculated by means of the transmittances of the entire spectral range. The curves, in the a,b plane, of chromatic differences vs. pH intersect at a pH value agreeing with the p Ka; this configuration occurs because a chromatic equilibrium of both species takes place at this point, which corresponds to the chemical equilibrium. With this method, the acidity constants are found easily and quickly, and they yield very good results. The validity of the method has been tested with the acid-base indicator bromophenol blue, obtaining p Ka= 3.943 at 25 °C; this result is compared with those obtained through the usual spectrophotometric methods. Also, thermodynamic magnitudes obtained from p Ka values at different temperatures from 20 to 70 °C have been determined, resulting in Δ H0 = -(13.93 ± 0.88) kj mol−1 Δ S0 = -(122.6 ± 2.8) J K−1 mol−1.

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 Thermodynamic Investigations on the Inclusion Complexation of Piroxicam with Cyclodextrin Derivatives

2005 ◽  
Vol 73 (3) ◽  
pp. 147-161 ◽  
Author(s):  
Charumanee S. ◽  
Weiss-Greiler P. ◽  
Wolschann P. ◽  
Viernstein H. ◽  
Titwan A. ◽  
...  
Keyword(s):  
Ph Value ◽  
Equilibrium Constants ◽  
Inclusion Complexation ◽  
Solubility Diagram ◽  
Phase Solubility ◽  
Cyclodextrin Derivatives ◽  
Ph Values ◽  
Solubility Behavior ◽  
Solubility Method ◽  
Different Temperatures

Thermodynamic studies of piroxicam in aqueous solution complexed with β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD) and two β-cyclodextrin derivatives, hydroxypropyl-β-cyclodextrin (HP-P-CD) and methyl-β-cyclodextrin (Me-β-CD) were performed at different temperatures and pH values using the phase solubility method. The phase solubility diagrams of β-CD, γ-CD and HP-β-CD is of AL-type behavior, indicating the formation of 1:l complexes. The related stability constants range from β-CD > γ-CD > Me-β-CD > HP-β-CD, respectively. An Ap-type solubility diagram is observed for Me-β-CD, indicating the formation of 1:2 complexes at higher CD concentrations. From the temperature dependence of the equilibrium constants the reaction enthalpies and entropies have been determined. The contributions of the reaction entropies are small and no enthalpy-entropy-compensation is observed, except for γ-CD, where a very small negative reaction entropy could be estimated. Moreover, the influence of the pH value is rather high because the differently charged forms of piroxicam show different solubility behavior in water.

Acid−Base Equilibrium Constants and Distribution Coefficients of Aminopyrene between the Surface and Bulk of Liquid Water as Studied by a Laser Two-Photon Ionization Technique

2004 ◽  
Vol 108 (32) ◽  
pp. 12111-12115 ◽  
Author(s):  
Miki Sato ◽  
Akira Harata ◽  
Yoshihiko Hatano ◽  
Teiichiro Ogawa ◽  
Takeshi Kaieda ◽  
...  
Keyword(s):  
Liquid Water ◽  
Equilibrium Constants ◽  
Distribution Coefficients ◽  
Acid Base ◽  
Ionization Technique ◽  
Two Photon ◽  
Base Equilibrium ◽  
Acid Base Equilibrium ◽  
Photon Ionization

scholarly journals Predictive models for the phase behaviour and solution properties of weak electrolytes: nitric, sulphuric, and carbonic acids

2021 ◽  
Author(s):  
Maximilian Kohns ◽  
Georgia Lazarou ◽  
Spiros Kournopoulos ◽  
Esther Forte ◽  
Felipe A. Perdomo ◽  
...  
Keyword(s):  
Equilibrium Constants ◽  
Ion Pairing ◽  
Ionic Species ◽  
Phase Behaviour ◽  
Solution Properties ◽  
Science And Engineering ◽  
Degree Of Dissociation ◽  
Hydronium Ion ◽  
Weak Electrolytes ◽  
Carbonic Acids

The distribution of ionic species in electrolyte systems is important in many fields of science and engineering, ranging from the study of degradation mechanisms to the design of systems for electrochemical energy storage. Often, other phenomena closely related to ionic speciation, such as ion pairing, clustering and hydrogen bonding, which are difficult to investigate experimentally, are also of interest. Here, we develop an accurate molecular approach, accounting for reactions as well as association and ion pairing, to deliver a predictive framework that helps validate experiment and guides future modelling of speciation phenomena of weak electrolytes. We extend the SAFT-VRE Mie equation of state [D. K. Eriksen et al., Mol. Phys., 2016, 114, 2724–2749] to study aqueous solutions of nitric, sulphuric, and carbonic acids, considering complete and partially dissociated models. In order to incorporate the dissociation equilibria, correlations to experimental data for the relevant thermodynamic equilibrium constants of the dissociation reactions are taken from the literature and are imposed as a boundary condition in the calculations. The models for water, the hydronium ion, and carbon dioxide are treated as transferable and are taken from our previous work. We present new molecular models for nitric acid, and the nitrate, bisulfate, sulfate, and bicarbonate anions. The resulting framework is used to predict a range of phase behaviour and solution properties of the aqueous acids over wide ranges of concentration and temperature, including the degree of dissociation, as well as the activity coefficients of the ionic species, and the activity of water and osmotic coefficient, density, and vapour pressure of the solutions. The SAFT-VRE Mie models obtained in this manner provide a means of elucidating the mechanisms of association and ion pairing in the systems studied, complementing the experimental observations reported in the literature.

Theoretical Calculations of Heteroconjugation Equilibrium Constants in Systems Modeling Acid−Base Interactions in Side Chains of Biomolecules Using the Potential of Mean Force

2004 ◽  
Vol 108 (32) ◽  
pp. 12222-12230 ◽  
Author(s):  
Joanna Makowska ◽  
Mariusz Makowski ◽  
Artur Giełdoń ◽  
Adam Liwo ◽  
Lech Chmurzyński
Keyword(s):  
Theoretical Calculations ◽  
Equilibrium Constants ◽  
Potential Of Mean Force ◽  
Side Chains ◽  
Systems Modeling ◽  
Acid Base

Determination of acid-base equilibrium constants in the excited state

1979 ◽  
Vol 31 (4) ◽  
pp. 1317-1319
Author(s):  
L. M. Rubeko ◽  
B. M. Uzhinov
Keyword(s):  
Excited State ◽  
Equilibrium Constants ◽  
Acid Base ◽  
Base Equilibrium ◽  
Acid Base Equilibrium
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