scholarly journals Acid-Base Chemistry of White Wine: Analytical Characterisation and Chemical Modelling

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Enrico Prenesti ◽  
Silvia Berto ◽  
Simona Toso ◽  
Pier Giuseppe Daniele
Keyword(s):  
Ionic Strength ◽  
Carboxylic Acids ◽  
Ionic Species ◽  
White Wine ◽  
Chemical Model ◽  
Water Mixture ◽  
Acid Base ◽  
Chemical Equilibria ◽  
Chemical Modelling ◽  
Strong Electrolytes

A chemical model of the acid-base properties is optimized for each white wine under study, together with the calculation of their ionic strength, taking into account the contributions of all significant ionic species (strong electrolytes and weak one sensitive to the chemical equilibria). Coupling the HPLC-IEC and HPLC-RP methods, we are able to quantify up to 12 carboxylic acids, the most relevant substances responsible of the acid-base equilibria of wine. The analytical concentration of carboxylic acids and of other acid-base active substances was used as input, with the total acidity, for the chemical modelling step of the study based on the contemporary treatment of overlapped protonation equilibria. New protonation constants were refined (L-lactic and succinic acids) with respect to our previous investigation on red wines. Attention was paid for mixed solvent (ethanol-water mixture), ionic strength, and temperature to ensure a thermodynamic level to the study. Validation of the chemical model optimized is achieved by way of conductometric measurements and using a synthetic “wine” especially adapted for testing.

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.

scholarly journals On the cataphoresis of gliadin Part II—The effect of strong electrolytes upon the mobility

1934 ◽  
Vol 147 (860) ◽  
pp. 11-24
Keyword(s):  
Ionic Strength ◽  
Colloidal Particle ◽  
Electrolyte Concentration ◽  
Electrolyte Solutions ◽  
Ionic Species ◽  
Colloid Particle ◽  
Wide Range ◽  
Strong Electrolytes ◽  
Set Up ◽  
Good Agreement

Careful analyses of the cataphoretic velocity of a colloid particle suspended in an electrolyte solution have been made by Smoluchowski, by Debye and Hückel, and by Henry. No actual test of their theoretical conclusions over a sufficiently wide range of ionic strength appears yet to have been made, with the exception of some experimental work recorded by Audubert, whose results indicate good agreement for particles of radius 60 - 130 A, but not for particles of radius 2-8 μ. Unfortunately, no details are given of the measurement of the sizes of such small particles. In adopting the hypothesis of Pauli that a colloidal particle behaves like a large polyvalent ion, it is assumed that on altering the electrolyte concentration there is no change in valency of the ion when the theory of Debye-Hückel and of Henry is applied. In practice those colloids whose charge is derived mainly from adsorption of ions do not exhibit constant valency on variation of the ionic strength of the electrolyte. According to Abramson, quartz particles covered with protein behave as ions of constant valency in solutions of the same ionic strength and hydrion activity. This assumption can be valid only over a restricted range of concentrations. Thus, at high ionic strengths, the valency may be altered appreciably by the adsorption of electrolyte ions, whilst it may reasonably be anticipated that at small ionic strengths the effect of the restriction of ions inside the double layer will lead to an alteration in the effective valency of the particle. In general a Donnan equilibrium is set up wherever one ionic species is constrained in any manner from free diffusion; modification of the effective valency of the colloid ion may be expected in very dilute electrolyte solutions on this account.

Stability of White Wine Proteins: Combined Effect of pH, Ionic Strength, and Temperature on Their Aggregation

2012 ◽  
Vol 60 (5) ◽  
pp. 1308-1319 ◽  
Author(s):  
Marie Dufrechou ◽  
Céline Poncet-Legrand ◽  
François-Xavier Sauvage ◽  
Aude Vernhet
Keyword(s):  
Ionic Strength ◽  
White Wine ◽  
Combined Effect ◽  
Effect Of Ph

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.

Spectrophotometric study of the effect of sodium dodecyl sulphate on the acid-base behaviour of 4-(2-pyridylazo)-resorcinol

1991 ◽  
Vol 56 (4) ◽  
pp. 785-795 ◽  
Author(s):  
Jiří Bílý ◽  
Ludmila Čermáková ◽  
Jiří Knapp
Keyword(s):  
Surface Tension ◽  
Critical Micelle Concentration ◽  
Sodium Dodecyl Sulphate ◽  
Azo Dye ◽  
Dissociation Constants ◽  
Sodium Dodecyl ◽  
Spectrophotometric Study ◽  
Acid Base ◽  
Strong Electrolytes ◽  
The Given

The values of the apparent dissociation constants of the azo dye 4-(2-pyridylazo)-resorcinol (PAR) have been found in the presence of sub- and supercritical concentrations of the anionogenic tenside sodium dodecyl sulphate (SDS) and the effects of the strong electrolytes NaCl and NaNO3 were also evaluated. In both electrolytes, the pKan values initially are independent of the SDS concentration and then increase. Spectrophotometric and surface tension measurements were employed to determine the critical micelle concentration (cmc) of SDS alone and in the presence of PAR and the given electrolytes. The determined cmc values were in the range 0.20–3.02 mmol l-1 and dependent on the type and concentration of the particular additive.

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