Investigation of the structural stabilities chlorophyll A and B and pheophytin A and B

In this study, chlorophyll a and b were purified from grass and spinach, pheophytin a and b were prepared with demetalation of chlorophyll a and b, and then their structural stabilities in different medium and solutions, under nonoxidant condition and toward hydrogen peroxide, tert-butyl hydroperoxide and sodium hypochlorite were studied in various pH's at 30 °C. The degradation kinetics of these chlorophyll derivatives were determined by following the decrease of the Soret band intensities in the UV-Vis spectra. When chlorophyll a and b and pheophytin a and b were investigated in direct sun light, they were degradated very fast. When they were investigated in indirect sun light, they were degradated slower than in direct sun light, and in darkness no degradation was observed except in water. When chlorophyll derivates were investigated in different pH's, in nonoxidant medium and in acidic media, they had demetalation and degradation of their porphyrin ring. In addition in basic medium, their phytol group was broken and very slow degradation than in acidic medium except pheophytin a. In basic medium, pheophytin a was hydrolised and changed into pheophorbide a and it showed non degradation. When chlorophyll derivates were investigated toward oxidants, their structural stabilities increased as follow NaOCI < H202 <(CH3)3COOH for chlorophyll a, NaOCl < (CH3)3COOH < H202 for chlorophyll b, NaOCl < (CH3)3COOH < H202 for pheophytin a, (CH3)3COOH < H202 < NaOCI for pheophytin b. The degradation kinetics of these reactions showed the pseudo-first order rate kinetics and the degradation rate constants were calculated. Keywords: chlorophyll, pheophytin, structural stability, kinetics, oxidation