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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 80 (1983), S. 151-157 
    ISSN: 1436-5073
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Kinetik der Oxydation der beiden Flavonole in alkalischem Milieu wurde untersucht. Die Fluoreszenz von Quercetin und Kämpferoi wurde nach Zugabe einer alkalischen Pufferlösung zu ihrer alkoholischen Lösung gemessen. Das pH, bei dem die Geschwindigkeit der Fluoreszenzabnahme ihr Maximum erreicht, liegt bei 11,0. Die Oxydation der beiden Flavonole in alkalischem Medium ist eine Reaktion erster Ordnung. Deren Geschwindigkeitskonstanten sind 27,5×10−3 sec−1 bzw. 1,22×10−3 sec−1 für Quercetin bzw. Kämpferoi. Eine kinetische Methode zur Bestimmung der beiden Flavonole in der Größenordnung 2,5–25μM auf der Basis der Fluoreszenzabnahme in alkalischem Milieu wurde ausgearbeitet.
    Notes: Summary In this work the kinetics of the oxidation of two flavonols in alkaline medium have been studied. The fluorescence of quercetin and kaempferol has been monitored by a fluorimetric technique after the addition of an alkaline buffer to their alcoholic solutions. The pH, at which the rate of their fluorescence decrease has its maximum, was 11.0. The oxidation of the two flavonols in alkaline medium follows a first order kinetic. The reaction rate constants of this reaction are 27.5×10−3 sec−1 and 1.22×10−3 sec−1 for quercetin and kaempferol respectively. Working curves in the range of 2.5–25μM for the determination of the two flavonols, based on the rate of their fluorescence decrease in alkaline medium, have been constructed and a kinetic method was developed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 941-948 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ascorbic acid present in natural products is often analyzed by its reducing effect on 2,6-dichlorophenolindophenol (DCPI). In case of coexistence of Fe(II) in natural samples and if oxalic acid is used for their extraction and stabilization, a significant interference is observed. The reaction of Fe2+ with 2,6-dichlorophenolindophenol (DCPI) in acidic solutions in the presence or absence of oxalate ions was investigated. The reaction was studied with a Stopped-Flow Spectrophotometer (S.F.S) equiped with a data acquisition system, which allows the determination of initial rates and reaction rate constants. Results for the effect of the concentrations of all the reagents of the reaction are presented. During the experimental work all concentrations of the reagents were kept in such levels to make the reaction first-order in respect of DCPI. An interesting finding is, that, although Fe2+ and C2O42- ions do not react separately with DCPI (or react very slowly), they react very rapidly in mixtures and show a strong synergetic effect. The experimental data fit with the mechanism of the formation of intermediates FeC2O4 and [Fe(C2O4)2]2-. The proposed rate law agrees with the above mechanism and the experimental results. The value kc=(1.6±0.2)×105 M-1·s-1 was calculated for the second-order rate constant of the reaction of FeC2O4 and DCPI. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 941-948, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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