Extraction, isolation and physicochemical studies of natural pheophytin complexes

Abstract

A simple, rapid and efficient method for the extraction and purification of chlorophyll-a from plant sources has been developed. And with it, a new method for the -extraction of chlorophyll in winter, which has been previously problematic, has been developed. The methods are summarized in flow diagrams showing the elimination of carotene and xanthophylls. The chlorophyll-a isolated has been demetallated to obtain pheophytin-a that in tum has been complexed with cobalt(II), copper(II), zinc, nickel(II) and chromium(Ill) ions. The resulting metal pheophytin complexes, chlorophyll-a and pheophytin-a have been fully characterized by ultraviolet-visible and Fourier transform infrared spectroscopies, electrospray ion mass spectrometry and elemental analysis. For the first time, the kinetics of the oxidation of cobalt(II) pheophytin-a by chromium(III) has been followed spectrophotometrically at temperatures ranging from 313 to 333 K. The reaction has been found to be first order in the concentration of the hexaaquachromium(III) cation. The oxidation-reduction mechanism proposed for the reaction is an outer-sphere electron tunnelling mechanism. The ease of demetallation and complexation of chlorophyll-a has highlighted the problem caused by acidity and the presence of these metal ions in soils, on the chlorophyll content of leaves.