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Redox Reactions Involving Chlorophyll

Timiryazev has already suggested that participation of chlorophyll in photosynthesis is due to its reversible redox transformations. Excited chlorophyll molecules can act as electron acceptors and donors [35, 36]. [Pg.148]

Rabinovich and Weiss [35, 36] investigated a homogeneous dark redox reaction of chlorophyll with ferric chloride  [Pg.148]

An asymmetric chlorophyll molecule consists of a hydrophihc head formed by four pyrrole rings arranged around magnesium and a long tail - a hydrophobic chain (phytol residue). The hydrophihc head seems to be turned into water and the hydrophobic tail attaches chlorophyll to the nonaqueous phase. [Pg.148]

A number of studies are concerned with the adsorption of chlorophyll in monolayers at the water/nitrogen and water/heptane interfaces [39-41]. Comparison of the areas per chlorophyll molecule for the nitrogen/water and heptane/water interface shows that at the interface with a hydrocarbon, the molecules are less inclined toward the interface. Upon illumination of the interface, the area per chlorophyll molecule changes slightly [41]. [Pg.148]

During chlorophyll adsorption at the octane/water interface, the interfacial tension changes markedly. This fact was utilized in determining the surface excess of chlorophyll by the Gibbs equation. From the slope of the initial section of the isotherm, [Pg.148]


This raises the electrochemical potential, of these molecules and alters the formal value of electrode potential in redox reactions involving the chlorophyll (see Section 29.4). [Pg.587]

Linschitz and Rennert (80) showed that the chlorophyll photobleaching reaction was not restricted to liquid systems. They observed a similar rapid reversible photobleaching of chlorophyll a in a solid solution of ether iso pentane alcohol at liquid nitrogen temperature. A mechanism involving either electron or hydrogen transfer was postulated as the initial step. Although further identification of the intermediates is necessary, it appears likely that a one-electron redox reaction is at least involved in the primary process. [Pg.296]

If the involvement of a pair of chlorophyll molecules as the reaction initiator signifies the fact that a large distance of charge separation is necessary for redox reactions to compete significantly with charge return, perhaps the role of Mg is to control the degree of association between the two molecules... [Pg.179]

Organic Systems. The photooxidation and reduction reactions for most organic compounds require two electron processes and are generally irreversible. However, several phenothiazine dyes, such as Thionine and Methylene Blue, function as reversible two electron redox systems. The reversible photobleaching of chlorophyll may also involve a one or two electron process although the exact mechanism is still in doubt. One electron redox processes for organic molecules are possible... [Pg.294]

Based upon a detailed analysis of reaction transients, a mechanism was proposed for chlorophyll a-photosensitized transmembrane oxidation-reduction of aqueous phase donors and acceptors that included electron transfer between juxtaposed Chi a+ r-cations and Chi a molecules as the transmembrane charge-transfer step [112]. The maximum apparent first-order rate constant for this step was 10 s , which seems large for thermal electron transfer between chlorophyll molecules located at the opposite membrane interfaces, even considering that nuclear activation barriers may be relatively small for this reaction. Transverse flip-flop diffusion of Chi b across the membrane is 10 -fold slower than transmembrane redox under these conditions, so this alternative mechanism is almost certainly unimportant. Kinetic mapping studies have shown that some of the Chi a becomes localized within the membrane at sites that are inaccessible to aqueous phase electron acceptors, presumably within the membrane interior [114]. This suggests the possibility of a transverse hopping mechanism involving electron transfer over relatively short distances from buried Chi a to interfacial Chi a+, followed by electron transfer from Chi a at the opposite interface to the buried Chi a" ". [Pg.2985]


See other pages where Redox Reactions Involving Chlorophyll is mentioned: [Pg.148]    [Pg.148]    [Pg.865]    [Pg.92]    [Pg.2977]    [Pg.865]    [Pg.224]    [Pg.4485]    [Pg.716]    [Pg.199]    [Pg.499]    [Pg.220]    [Pg.182]    [Pg.60]    [Pg.288]    [Pg.320]    [Pg.217]    [Pg.110]    [Pg.364]    [Pg.382]    [Pg.199]    [Pg.499]    [Pg.2359]    [Pg.10]    [Pg.2972]    [Pg.127]    [Pg.579]    [Pg.587]    [Pg.588]    [Pg.522]    [Pg.1970]    [Pg.2545]    [Pg.4055]    [Pg.522]    [Pg.312]    [Pg.24]    [Pg.201]    [Pg.60]    [Pg.280]    [Pg.113]    [Pg.1560]    [Pg.1867]    [Pg.181]    [Pg.126]    [Pg.93]    [Pg.331]   


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