Potentiometric and (1)H NMR studies of complexation of Al(3+) with (-)-epigallocatechin gallate, a major active constituent of green tea.
J Inorg Biochem
; 88(1): 7-13, 2002 Jan 01.
Article
en En
| MEDLINE
| ID: mdl-11750019
The acid dissociation of (-)-epigallocatechin gallate (abbreviated as egcg) and its complexation with Al(3+) were studied by potentiometric titrations, and were compared with those of (-)-epicatechin (ec) and (-)-epigallocatechin (egc). In Al(3+)-ec and Al(3+)-egc reaction systems, [Al(LH(-2))](+), [Al(LH(-2))(OH)](0), and [Al(LH(-2))(2)](-) are formed, as reported for Al(3+)-catechin (c). Reactions between Al(3+) and egcg at pH <4.1 yield AlLH(-2) and AlLH(-3) species. The 1H NMR studies have shown that two hydroxyl groups of the gallate (D) ring are deprotonated and coordinated to an Al(3+) ion in [Al(egcgH(-2))](+). The AlLH(-3) species of egcg is supposed to be formulated as [Al(egcgH(-3))](0) in which one hydroxyl group of the pyrogallol (B) ring and two hydroxyl groups of the D ring are deprotonated; an Al(3+) ion is coordinated to two oxygen atoms of the D ring and one oxygen atom from the B ring of the neighboring chelate molecule, resulting in the formation of a polymeric structure. In the Al(3+) complex of egcg, the gallate group forms major coordinate bonds and results in solution properties that are different from those of ec, egc and c which have no gallate group.
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Té
/
Catequina
/
Aluminio
Idioma:
En
Revista:
J Inorg Biochem
Año:
2002
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Estados Unidos