Chlorophyll and Related Compounds

The infrared spectrum of chlorophyll (1880-1600 cm ) gives evidence of aggregation effects in Fig. 14.1. Curve A of this figure is the spectrum of highly aggregated 

Compound Solvent NH OH C-H Phytol C—H Aldehyde Ester Ke- tone C=0 Car- boxyl C-7 Alde- hyde Che- late C=C 

Ethyl pheophorbide b-2,4-dinitrophenylhydrazone Bacteriochlorophyll Methyl bacteriochlorophyllide CHClj ecu CHCI, 3350 2916 1740 ester 1735 1727 1710 ketone 1683 1662 acetyl 1655 1662 1618 1610 1610 

Another argument against interpreting the solvent dependence of the infrared spectra of chlorophylls as being due to the enol form (Holt and Jacobs, 1955) is that infrared and NMR data show that chlorophylls a and b exist in solution predominantly in the keto form (/S-keto ester of ring V) (Pennington et a/., 1964). 

Boucher, L. J. and Katz, J. J. Abstracts of the I54th National Meeting of the American Chemical Society, Chicago, Sept. 1967a, Paper 250 C. 

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The main recovery of the IS was 100 12 per cent and the r values of the calibration curve were always over 0.9993. It can be concluded from the data that the method allows the reliable determination of chlorophylls and related compounds in various plant materials [303]. 

Molecular ions and protonated molecules of chlorophylls and related compounds will be formed during static FAB/LSIMS when using 3-nitrobenzyl alcohol as the matrix. Alternatively,... 

An important exception to this rule is provided by the magnesium complexes of tetrapyrrole systems, the parent compound of which is porphine (7-II). These conjugated heterocycles provide a rigid planar environment for Mg2+ (and similar) ions. The most important of such derivatives are the chlorophylls and related compounds,28 which are of transcendental importance in photosynthesis in plants.29 The structure of chlorophyll-a, one of the many chlorophylls, is (7-III). 

Granick, S., Beale, S. I. Hemes, chlorophylls, and related compounds biosynthesis and metabolic regulation. Adv. Enzymol. 46, 33-203 (1978)... 

Photoelectrochemical conversion from visible light to electric and/or chemical energy using dye-sensitized semiconductor or metal electrodes is a promising system for the in vitro simulation of the plant photosynthetic conversion process, which is considered one of the fundamental subjects of modern and future photoelectrochemistry. Use of chlorophylls(Chls) and related compounds such as porphyrins in photoelectric and photoelectrochemical devices also has been of growing interest because of its close relevance to the photoacts of reaction center Chls in photosynthesis. 

Because the four nitrogens form an optimal cavity, porphyrins can bind a wide variety of metal ions to form metalloporphyrins (MP). Iron porphyrins are found in many biological systems and act as electron transfer mediators (cytochromes) or oxygen transfer agents (hemoglobin). Modified porphyrins are found in nature also in the form of chlorophylls and vitamin B,2 and related compounds. 

Because of their extended 7r-system, porphyrins and related compounds absorb visible light. Therefore, their potential application as chromophores for harvesting solar energy, as a means to mimic the natural role of chlorophyll, has been under intense study. In addition, porphyrins can act as mediators of electron transfer, both as oxidants and as reductants. Therefore, the role of porphyrins as catalysts for various reductions and oxidations also has been studied by many authors. 

Most of the prenyUipids, such as chlorophylls, carotenoids, and prenylquinones, as well as tocopherols and vitamin Ki, which occur in plant hpid extracts, can be separated by TLC using sUica gel plates or special mixtures of silica gel with other adsorbents. But the compounds with one double bond per isoprene and others with a partially or fiiUy unsaturated isoprenoid chain can be separated efficiently by argentation TLC. The Rp values of selected hpophUic vitamins, their provitamins, and related compounds separated by argentation TLC using different mobile phases are listed in Table... 

Watanabe, N., Yamamoto, K., Ihshikawa, H., Yagi, A., Sakata, K., Brinen, L.S., and Clardy, J. (1993) New chlorophyll-A-related compounds isolated as antioxidants from marine bivalves. J. Nat. Prod., 56, 305-317. 

Duckweed (Lemna pausicostata L.) has proved to be a sensitive bioassay for AAL-toxin, FBj and related compounds (75). Duckweed is a small aquatic plant that can be easily grown in the laboratory (75). Phytotoxic effects can be easily quantified by measuring chlorophyll loss and cellular leakage (74). AAL-toxin was about 10-fold more active than FBj in the duckweed bioassay, causing maximal effect at a 0.1 pM concentration. FBi, FB2 and FB3 caused effects identical to those of AAL-toxin in duckweed at 1 pM. The hydrolysis products, APi and AP2 were much less active, and FAi and FA2 were completely inactive in the duckweed bioassay (75). 

Chlorophyll, as extracted from plants, is actually made up of two closely related compounds, chlorophyll A and chlorophyll B. These differ slightly in molecular structure and can be separated because they have different tendencies to be adsorbed on a finely divided solid (such as powdered sugar). 

All the analytical methods mentioned to separate, identify, and quantify chlorophylls and derivatives consume time, money, and samples. As alternatives, industries have been employing non-destructive methods for surface color measurements that are not only indirectly related to chlorophyll content, but may also estimate the pigments directly in tissues, leaving the sample intact and enabling serial analyses in a relatively short time. Eood color affects consumer acceptance and is an important criterion for quality control. Color vision is a complex phenomenon that depends on both the total content and number of pigments and also on absorption, reflectance and emission spectra of each compound present. 

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