Chlorophyll modification

Hynninen PH (1991) Chemistry of Chlorophylls Modifications. Scheer H (ed) Chlorophylls. CRC Press, Boca Raton, p 145... 

Agostiano, A., Catucci, L., Colafemmina, G., deUa Monica, M., and Scheer, H., Relevance of the phytyl chain of the chlorophylls on the lamellar phase formation and organization, Biophys.J., 84,189, 2000. Van Rossum, B.-J., Steensgaard, D.B., Mulder, EM., Boender, G.J., Schaffner, K., Holzwarth, A.R., and de Groot, H.J.M., A refined model of the chlorosomal antennae of the green bacterium Chlorobium tepidum from proton chemical shift constraints obtained with high-field two-dimensional and three-dimensional MAS NMR dipolar correlation. Biochemistry, 40, 1587, 2001. Hynninen, RH., Chemistry of chlorophylls modifications, in Chlorophylls, Scheer, H., Ed., CRC Press LLC, Boca Raton, FL, 1991, p. 145. 

The typical isocyclic ring E present in chlorophylls is susceptible to a number of different modifications such as epimerization, which produces stereoisomers by inversion of the configuration at C-13 of their parent pigments. These 13 -epichlorophylls, known as chlorophylls a and b, are minor pigments. They are considered artifacts produced in the course of handling plant extracts and sometimes are also found in small amounts in heated and deep-frozen vegetables, hi the old Fischer systan of nomenclature that can still be found in some literature, these epimers were named 10-epichlorophylls. 

Allomerized chlorophylls are oxidized compounds at C-13, forming theC-13 OH-chlorophyU catabolites. Other common positions for modifications and/or oxidation have been found at C-3, C-7, and C-8. Pyroderivatives of chlorophylls and their degradation products, usually found in heated and processed vegetables, lack the carbomethoxy group (-COOCH3) at C-13 of ring E, which is replaced by hydrogen. 

Commercially produced metal-substituted chlorophylls such as copper chlorophylls and copper chlorophyllins that can be obtained by chemical modification of natural chlorophylls have better stability, solubility, and tinctorial strength, but they cannot be considered natural food colorants and will be discussed later. 

Copper Chlorophyll (E141). This is made from chlorophyll it is more blue than natural chlorophyll. The chemical modification makes it much more stable to heat and light. It is a more useful material than natural chlorophyll. 

The widespread application of HPLC methodology to chlorophyll analysis demonstrates its flexibility, effectiveness, and reliability. Methods described in this unit are based on the work of Schwartz et al. (1981). This original method allows for resolution of twelve chlorophyll derivatives in 30 min. While minor modifications were made to this method to further simplify the analysis, the final resolution and sensitivity were not compromised. Based on a commercially available reversed-phase column and an aqueous mobile phase, the method can be easily altered for specific separations. This is demonstrated in the Alternate Protocol, where the Basic Protocol was adjusted for the analysis of polar and Cu2+- and Zn2+-containing chlorophyll derivatives. The method for polar derivatives is based on the separation of Can-jura and Schwartz (1991), while the method for... 

Hotchandani, S. Kamat, P. V. Modification of electrode surface with semiconductor colloids and its sensitization with chlorophyll a, Chem. Phys. Lett. 1992, 191, 320. 

Itoh, S., Iwaki, M., and Ikegami, I. (2000) Modification of photosystem I reaction center by the extraction and exchange of chlorophylls and quinines, Biochim. Biophys. Acta 1507, 115-138. 

The basis of the concept of a dimer of chlorophyll a in P-700 rests on evidence obtained with optical or ESR spectroscopy. In the P-700 redox difference spectrum, although very similar to that obtainable upon chemical oxidation of chlorophyll a, there are significant differences in the red region, which presents a splitting of the peak (at 685 and 700 nm) which is absent in chlorophyll a [53]. Moreover, the ESR and ENDOR spectra also present characteristics that have been interpreted as due to a dimeric arrangement [16]. Alternative interpretations have been offered suggesting that the spectral distortions are caused by a modification of the chemical environment of chlorophyll a in the RC complex. Definitively not in line with the dimer hypothesis is the spectrum of the light-induced triplet state of P-700, that can be observed when the intermediate acceptor is prereduced chemically in this spectrum the zero field parameters are the same as those of chlorophyll a monomers [54]. It is not clear, however, whether the triplet state resides on P-700 or on other chlorophylls of the RC complex. 

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