Luděk Jančář

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

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 < 3) and at the higher amounts (60% v/v) alcohol. Acid-base characteristics and UV-VIS spectral properties of chelerythrine (CHE) were studied in aqueous solutions in the presence of different concentrations of 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 ΔpKR+ (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.

Acid-base behaviour of sanguinarine and dihydrosanguinarine

Acid-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.

Effect of scaling regimes on the prediction of analytical results from multivariate calibration

Abstract Multivariate calibration has become indispensable for many analytical methods which suffer from insufficient selectivity. One of the practical limitations of multivariate calibration is the unfavourable error propagation for minor and trace components. For partial least-squares regression (PLS), it is shown that the accuracy and ruggedness of results depend critically on the scaling of the concentration matrix. When the scales for each chemical component are changed separately, the weighting schemes obtained reduce the relative error for minor components without negative effects on the results for major components. The conclusions drawn from simulation studies were confirming by testing mixtures of organic dyes (chromazurol S, phenyl red, bromocresol green and 2-(2-pyridylazo)-1-naphthol-4-sulphonic acid).

Changes of organic acids and phenolic compounds contents in grapevine berries during their ripening

AbstractChanges of total content of phenolic substances, alteration in total titratable acidity and differences in tartaric acid content in grapes of four white (Müller-Thurgau — MT, Pinot Blanc — Rulandské bílé in Czech, RB, Sauvignon (Sg), and Muscat Ottonel — Muškát Ottonel in Czech, MO) and two blue (Dornfelder — Df and Blue Frankish — Frankovka in Czech, Fr) grapevine varieties throughout their growth, ripening and maturing (July–November). Potentiometric titration was applied for the determination of total titratable acids in grapes (expressed as tartaric acid equivalents in g L−1). A spectrophotometric method according Rebelein based on the formation of a colored complex of ammonium metavanadate and tartaric acid was used for determination of tartaric acid in green juice made by pressing unripe grapes. A spectrophotometric method based on reduction of phosphomolybdato-tungsten complex in alkaline solution using Folin-Ciocalteau reagent was applied for determination of total content of phenolic substances (TCP).

PLS “self-calibration” method for the evaluation of rate constants and/or initial concentrations in multicomponent kinetic analysis

An algorithm is presented where the Partial Least Squares (PLS) regression estimation calibration method is used to calculate initial concentrations or rate constant parameters. The calibration matrix is obtained by a “selfmodeling” process calculating theoretical curves, while following two, three or more levelfactorial design. The new calibration objects are included in the calibration matrix or replacing the old ones and the calibration space is eventually reduced until satisfactory results are obtained. Prediction of the kinetic parameters as good as that achievable by the traditional minimizing routines can be obtained. The properties, behavior, advantages and problems of the proposed PLS “self-calibration” method are discussed. It has been shown that it is possible to determine analytes in mixtures quite rapidly and precisely without prior knowledge of the initial concentrations of components.