Chlorophyll structural modification

FIG. 2 Spectral modifications in the absorbance spectrum of chlorophyll a (full line) triggered by the replacement of the methyl side-group at the C7 position by an aldehyde side-group, yielding chlorophyll b (<dashed line). The structures of chlorophyll a and chlorophyll b molecules are also presented. 

There are several well known examples where modified porphyrins are used in biology, and in these cases the changes to the macrocycle structure do result in improved properties. The chlorophylls and chlorins are both porphyrinoids that are reduced at P pyrrolic positions (16). The effect of this modification is an increase in excited state lifetimes and quantum yields of... 

The modification of these residues would be only on the peripheral proteins as we have used BBY particles. The exposed polypeptides are the oxygen evolving polypeptides (33, 24 and 18 kDa) and the chlorophyll antenna proteins, but not the reaction centre core (D-l/D-2 proteins). However, it may be possible that modification of peripheral polypeptides caused some structural alterations in... 

There are four points at which the main stracmral modifications of the chlorophyll molecule start (1) the chelate, (2) the ester bond of the phytol alcohol (C-17 ), (3) the isocyclic ring (C-13 ), and (4) the basic porphyrin structure. Rgure 7.4 shows the possible transformations of the chlorophyll molecule. 

The charge separation processes in photosynthesis involve photoinduced electron transfer from chlorophyll to quinone derivatives. A popular methodology of biomimetic chemistry for biological active sites is assembly of supposedly essential components via covalent linkage. TTius, a variety of covalently linked porphyrin-quinone derivatives such as 1 and 2 below have been prepared and photoinduced electron transfer therein investigated as models of photosynthetic electron transfer [12]. There are two major difficulties in the covalent approach to the preparation of this type of face-to-face porphyrin-quinone derivatives. The first is synthetic problems associated with the preparation of highly substituted quinone precursors and the porphyrin-quinone double coupling reactions. Second, there is little room for the systematic modification of the electtonic/steric structures of quinones. 

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