Pyropheophorbides Chlorophylls

Chlorophyll-a Pheophytin-a Pyropheophitin- a Pheophorbide-a Pyropheophorobide-a Isofucoxanthin-dehydrate Fucoxanthin dehydrate Fucoxanthin-hemiketal Isofucoxanthin dehydrate pheophorbide a ester Isofucoxanthin dehydrate pheophorbide a ester Isofucoxanthin dehydrate pyropheophorbide a ester 23.5 26.4 28.1 5.0 6.9 10.7 12.0 6.4 24.4 22.9 25.4... 

Figure F4.4.2 HPLC chromatogram of chlorophyll derivatives separated using the Alternate Protocol. Peak identifications 1, chlorophyllide if 2, chlorophyllide a 2, chlorophyllide a" 3, pheophorbide tr, 3, pheophorbide if 4, pyropheophorbide b 5, pheophorbide a 5, pheophorbide a 6, pyropheophorbide a 7, chlorophyll tr, 7, chlorophyll if 8, chlorophyll a 8, chlorophyll a 9, pheophytin tr, 9, pheophytin tf 10, pyropheophytin tr, 11, pheophytin a 11, pheophytin a 12, pyropheophytin a. Reproduced from Canjura et al. (1991) with permission from the Institute of Food Technologists.

Although covalently linked donor-acceptor systems of small organic chromo-phores have been studied for some time in order to uncover the basic principles of electron and energy transfer, the first covalently linked cyclic tetrapyrroles were reported by Gouterman, Dolphin and coworkers in 1972 [27]. In 1976 the first dimeric chlorophyll-based models were reported. Structure la, based upon pyropheophorbide-a, was prepared by Boxer and Closs [28], whereas the pheo-phorbide-a derivative lb was reported by Wasielewski, Studier and Katz [29]. 

As mentioned above, the natural photosynthetic reaction center uses chlorophyll derivatives rather than porphyrins in the initial electron transfer events. Synthetic triads have also been prepared from chlorophylls [62]. For example, triad 11 features both a naphthoquinone-type acceptor and a carotenoid donor linked to a pyropheophorbide (Phe) which was prepared from chlorophyll-a. The fluorescence of the pyropheophorbide moiety was strongly quenched in dichloromethane, and this suggested rapid electron transfer to the attached quinone to yield C-Phe+-Q r. Transient absorption studies at 207 K detected the carotenoid radical cation (kmax = 990 nm) and thus confirmed formation of a C+-Phe-QT charge separated state analogous to those formed in the porphyrin-based triads. This state had a lifetime of 120 ns, and was formed with a quantum yield of about 0.04. The lifetime was 50 ns at ambient temperatures, and this precluded accurate determination of the quantum yield at this temperature with the apparatus employed. 

Figure 9.37 Chemical structures of chlorophylls-a and b which contain a propionic acid esterified to a C20 phytol chlorophylls-cj and C2 have an acrylic acid that replaces the propionic acid. Also included are the pheopigments, the four dominant tetrapyrrole derivatives of chloropigments (pheopigments) found in marine and fresh-water/estuarine systems (chlorophyllide, pheophorbide, pheophytin, pyropheophorbide.) More specifically, chlorophyllase-mediated de-esterification reactions (loss of the phytol) of chlorophyll yield chlorophyllides. Pheophytins can be formed when the Mg is lost from the chlorophyll center. Pheophorbides are formed from removal of the Mg from chlorophyllide or removal of the phytol chain from pheophytin, and pyrolyzed pheopigments, such as pyropheophorbide and pyropheophytin, are formed by removal of the methylcarboxylate group (-COOCH3) on the isocylic ring from the C-13 propionic acid group.

Pheophorbide-fc Chlorophyllide-a Blue-green chl-a derivatives (lactones, 10-hydroxy chlorophylls) Pyrochlorophyll-a Pyropheophytin-a Pyropheophorbide-a Mesopheophorbide-a... 

A high concentration of chlorophyll catalyzes photosensitized reaction (photooxidation) in the product fried and stored in clear packages. In addition, extra bleaching of the oil can decompose chlorophylls into pheophytenes, pheophorbides, and pyropheophorbides, which do not have visual green color but are ten times more active photosensitizers than their parent compounds (44- 6). 

The crude oil with high nonhydratable phospholipids requires acid pretreatment before refining. This may increase the chlorophyll breakdown, forming pheophy-tenes, pheophorbides, and pyropheophorbides and make the finished oil more susceptible to photooxidation (44). 

Chlorophyll itself is rather unstable due to facile reactions at the 10 position. Pyropheophorbides, which lack substituents at this position, are much more stable and synthetically tractable. Thus, pyropheophorbide a, prepared from natural chlorophyll a, was used as the basis for triad 13 [58]. 

Ziegler, R., A. Blaheta, N. Guha and B. Schonegge (1988) Enz5tmatic formation of pheophorbide and pyropheophorbide during chlorophyll degradation in a mutant of Chlorella fusca Shihira et Kraus. PL Physiol. 132, 327-32. 

Doi M, Inage T, Shioi Y (2001) Chlorophyll Degradation in a Chlamydomonas reinhardtii Mutant An Accumulation of Pyropheophorbide a by Anaerobiosis. Plant Cell Physiol 42 469... 

PENNINGTON F c, STRAIN H H, SVEC w A and KATZ J J (1964), Preparation and properties of pyrochlorophyll a, methyl pyrochlorophyllide a, pyropheophytin a, and methyl pyropheophorbide a derived from chlorophyll by decarbomethoxylation , J Am Chem Soc, 86, 1418-1426. 

Thirty-nine chlorophyll transformation products were separated on a C g colunw (. = 400nm) using a 40-min gradient from 90/10 methanol/water to 90/5/5 acetone/methanol/wato- [457]. Positive identification of methylated compounds within fiactions was made by thermospray MS. Pheophoibide a methyl ester, zeaxanthin, pyropheophorbide a methyl ester, isorenieratene, pheophytin a and b and pyiopheoph5 in a and b were confirmed. 

Chlorins 10 (Figure 10.2) were prepared using a similar route, from methyl pyropheophorbide-a (a chlorophyll-a derivative) by functionalization of the vinyl group using various alcohols ROH (R = methyl, propyl, pentyl, heptyl, nonyl), followed by cleavage of the ester group, activation with oxalyl chloride, and reaction with the tetramethylammonium salt of Chlorins 10... 

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