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DOI

Determination of ionisation constants of nitrobenzidines

01 Aug 1982-Vol. 91, Iss: 4, pp 311-314
Abstract: The ionisation constants of 2-nitrobenzidine, 2,2’-dinitrobenzidine and 2,3’-dinitrobenzidine were determined spectrophotometrically in 33-3% (w/w) methanol. The low pK value obtained for 2,3’-dinitrobenzidine when compared to that of 2-nitro and 2,2’-dinitrobenzidines is explained on the basis of electron withdrawing nature of the nitrogroup and intramolecular hydrogen bonding.

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Abstract: The quantification of metal-chelating activity of caffeic and ferulic acids( 1 and 2, resp.) was successfully performed by using a potentiometric system with data-analysis computer programs. The method was applied to two phenolic models, which have been systematically reported as antioxidants. Although a chain-breaking mechanism was proposed, several studies pointed out the possibility of complexation of transition metals that can participate in single-electron reactions and mediate the formation of oxygen-derived free radicals. In this work, the complexation propertiestowardsCu II were investigated by potentiometry with a glass electrode. Acidity constants of the ligands (phenolic acids) and the formation constants of the ligandmetal complexes were evaluated by potentiometry. The modeling of the titration curvesand the data treatment were performed with the computer programsSuperquad and Bes t. A detailed quantitative examination of the complexation species formed in the Cu II /caffeic acid (1) and Cu II /ferulic acid (2) systems is presented together with the formation constants (log ). Results have shown that the complexation properties of the two phenolic acids towardsthe trans ition metal are quite different: the activity of caffeic acid ( 1) wasfound higher than that of ferulic acid (2). The data are important to get insight into the mechanism of action of antioxidants, and, in this case, could partially explain the efficacy of caffeic acid in the protection of LDL oxidative damage. In addition, the analytical method developed could be applied to quantify the chelating activity of important biological compounds, such as allopurinol, uric acid, cinnamic acids, flavonoids, and anthocianins, and, in that way, could be a valuable tool to understand the mechanisms underlying their protective effects.

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32 citations


Cites methods from "Determination of ionisation constan..."

  • ...The errors reported were calculated by the method of Albert and Serjeant [26], as the maximum difference between the logarithm of the average of the antilogarithms of the calculated pKa values and their individual values....

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  • ...The errors reported were calculated by the method of Albert and Serjeant [26], as the maximum difference...

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References
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Journal ArticleDOI
07 Feb 1959-Angewandte Chemie
Abstract: Die Farbe organischer Verbindungen hangt von strukturellen Einzelheiten des Molekuls ab. Es werden Elektronengasmodelle von Farbstoffen (Cyanine, Polyene, Polyacetylene, Acridine, Xanthene, Oxazine, Azine, Bacteriochlorophyll, Phthalocyanin, Azulen) beschrieben. Die Zustande von π-Elektronen werden durch eindimensionale Elektronenwellen entlang der Molekulkette (eindimensionales Modell) bzw. durch Wellenfunktionen, die sich uber die Molekulebene erstrecken, (zweidimensionales Modell) dargestellt. Energiewerte und Wellenfunktionen der Elektronen lassen sich mit Hilfe eines neu entwickelten Analogrechners ermitteln, und daraus konnen Lage, Starke und Form der Absorptionsbanden berechnet werden. Beide Modelle zeigen, das z. B. in langkettigen Polyenen ein ebenso ausgepragter Unterschied zwischen alternierend auftretenden langen und kurzen Bindungen vorhanden ist wie im Butadien.

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73 citations