Photooxidation of chlorophyll B by quinones studied by chemically-induced dynamic nuclear polarization.

The photooxidation of chlorophyll b by 1,4-benzoquinone and 2,6-dimethyl-1,4-benzoquinone was investigated by the technique of chemically-induced dynamic nuclear polarization. Polarization of the proton magnetic resonance lines of the quinone was detected. A mechanism for the photooxidation was postulated that invokes the reaction of the quinone with the excited singlet state of the chlorophyll to form a radical pair. This mechanism, together with a theoretical model and parameters taken from the literature, yields a theoretical proton magnetic resonance spectrum for the polarized quinone that agrees well with that observed experimentally.