PRIMARY LIGHT REACTION OF CHLOROPHYLL AND PHEOPHYTIN WITH WATER. (VOLUME I AND VOLUME II)
Abstract
The in vitro light reaction of chlorophyll a and its demetallated derivative pheophytin with water have been investigated. The characteristics of the photoreactions have led to proposed mechanisms and demonstrated the catalytic nature of chlorophyll a dihydrate in water photolysis. In reviewing the development of the role of chlorophyll as the primary light reactant in plant photosynthesis, it is clear that the primary light reaction in photosynthesis is not well understood. In order to more fully understand this reaction, this study of the in vitro reactions was undertaken. The role of water on the in vitro photochemical activity of chlorophyll a is investigated using a photogalvanic cell consisting of two platinum electrodes, one plated with chlorophyll a and one chlorophyll-free. The photoactivity of chlorophyll dihydrate and P700 dimer is shown to require excess water. A dual beam spectrometer was constructed to further investigate the photocurrents that were observed to consist of transient and irreversible component. The irreversible component is attributable to the photolysis of water by chlorophyll dihydrate. Analysis of the flux dependence of the response is made in terms of a biphotonic excitation mechanism. Utilizing mass spectrometry, it is shown that pure chlorophyll dihydrate is capable of catalyzing water photolysis utilizing red photons. Although Pt is not photochemically reactive with water in the visible wavelength region, the catalytic ability of chlorophyll dihydrate is greatly enhanced by platinization of the chlorophyll. The investigation of the photochemical reaction of pheophytin with water indicates that in this reaction pheophytin is reduced indicating the role of Mg in protecting the catalytic properties of chlorophyll.
Degree
Ph.D.
Subject Area
Chemistry
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