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

100%
Jančářová I., Jančář L., Náplavová A., Kubáň V.
Open Chemistry
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2013
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vol. 11
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issue 10
1575-1582
EN
Changes 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). [...]
2
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Acid-base behaviour of sanguinarine and dihydrosanguinarine

88%
Absolínová H., Jančář L., Jančářová I., Vičar J., Kubáň V.
Open Chemistry
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2009
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vol. 7
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issue 4
876-883
EN
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. [...]
3
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Spectrophotometric study of time stability and acid-base characteristics of chelerythrine and dihydrochelerythrine

88%
Absolínová H., Jančář L., Jančářová I., Vičar J., Kubáň V.
Open Chemistry
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2010
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vol. 8
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issue 3
626-632
EN
Time 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. [...]
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