The Chlorophylls

Electromagnetic energy lying mainly in the visible or near-infrared region is capable of initiating 

Chlorophyll contains a macrocyclic tetrapyrrole ring, with a structure similar to that of the prosthetic 

The tetrapyrrole ring of Chi [see Fig. 5 (A)] can be seen to differ from the heme in several aspects  

In chlorophyll, the optical transition axes x and y lie in the plane of the n-electron system of the tetrapyrrole ring along each ofthe N-N diagonals [see Fig. 5 (A)]. The absorption spectra of chlorophylls in solution show two main pairs ofbands, one pair in the blue region (So- S2, designated as the B-bands) and one pair in the red or far red (So- S, designated as the Q-bands). The subscripts x and y are used in Fig. 5 (D, b) as they were in Fig. 5 (A). 

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Chiorophyllin—copper complex, oil soluble—The chlorophyllin is obtained by extraction from a mixture of fescue and rye grasses. The chlorophyll is... 

Potassium sodium copper chlorophyllin (chiorophyllin—copper complex)—A green-black powder obtained from chlorophyll by replacing the methyl and phytyl ester groups with alkaH and replacing the magnesium with copper. The source of the chlorophyll is dehydrated alfalfa. 

Natural Sensitizing Dyes and Photodynamic Therapy. The chlorophylls are, of course, among the natural sensitizers for photosynthesis. Considerable iaterest exists ia chlorophyll and related pigments as photosensitizers ia biology and medicine (75), isomeric retinal chromophores as visual pigments (76,77), and the use of synthetic photosensitizers ia neurobiology (9), hematology (78), and photodynamic therapy (79). 

In this way, the near-linear chlorophyll-phosphorus relationship in lakes depends upon the outcome of a large number of interactive processes occurring in each one of the component systems in the model. One of the most intriguing aspects of those components is that the chlorophyll models do not need to take account of the species composition of the phytoplankton in which chlorophyll is a constituent. The development of blooms of potentially toxic cyanobacteria is associated with eutrophication and phosphorus concentration, yet it is not apparent that the yield of cyanobacterial biomass requires any more mass-specific contribution from phosphorus. The explanation for this paradox is not well understood, but it is extremely important to understand that it is a matter of dynamics. The bloom-forming cyanobacteria are among the slowest-growing and most light-sensitive members of the phytoplankton. ... 

Figure 12.16 View of the reaction center perpendicular to the membrane illustrating that the pigments are bound between the transmembrane helices. The five transmembrane-spanning a helices of the L (yellow) and the M (red) subunits are shown as well as the chlorophyll (green) and pheophytin (blue) molecules.

In the bacterial reaction center the photons are absorbed by the special pair of chlorophyll molecules on the periplasmic side of the membrane (see Figure 12.14). Spectroscopic measurements have shown that when a photon is absorbed by the special pair of chlorophylls, an electron is moved from the special pair to one of the pheophytin molecules. The close association and the parallel orientation of the chlorophyll ring systems in the special pair facilitates the excitation of an electron so that it is easily released. This process is very fast it occurs within 2 picoseconds. From the pheophytin the electron moves to a molecule of quinone, Qa, in a slower process that takes about 200 picoseconds. The electron then passes through the protein, to the second quinone molecule, Qb. This is a comparatively slow process, taking about 100 microseconds. 

The light-harvesting complex LHl is directly associated with the reaction center in purple bacteria and is therefore referred to as the core or inner antenna, whereas LH2 is known as the peripheral antenna. Both are huilt up from hydrophohic a and p polypeptides of similar size and with low hut significant sequence similarity. The two histidines that hind to chlorophyll with absorption maxima at 850 nm in the periplasmic ring of LH2 are also present in LHl, but the sequence involved in binding the third chlorophyll in LH2 is quite different in LHl. Not surprisingly, the chlorophyll molecules of the periplasmic ring are present in LHl but the chlorophyll molecules with the 800 nm absorption maximum are absent. 

Modeling of the reaction center inside the hole of LHl shows that the primary photon acceptor—the special pair of chlorophyll molecules—is located at the same level in the membrane, about 10 A from the periplasmic side, as the 850-nm chlorophyll molecules in LH2, and by analogy the 875-nm chlorophyll molecules of LHl. Furthermore, the orientation of these chlorophyll molecules is such that very rapid energy transfer can take place within a plane parallel to the membrane surface. The position and orientation of the chlorophyll molecules in these rings are thus optimal for efficient energy transfer to the reaction center. 

Green, B. R., and Dnrnford, D. G., 1996. The chlorophyll-carotenoid proteins of oxygenic photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology 47 685—714. 

Preeminent in importance among the macro-cyclic complexes of Group 2 elements are the chlorophylls, which are modified porphyrin complexes of Mg. These compounds are vital to the process of photosynthesis in green plants (see Panel). Magnesium and Ca are also intimately... 

The influence of sunlight on vegetable growth, and the results of etiolation are, of course, well known to botanical students. There is no room for doubt that the production and evolution of the odour-bearing constituents of a plant are in direct relationship with the chlorophyll... 

One thing is certain, and that is that the chlorophyll-containing... 

If you wish to prepare some chlorophyll, grind up some fresh leaves and extract with alcohol. The alcohol dissolves the chlorophyll, as shown by the solution color. 

The chlorophylls produced by bacteria, algae and plants are a natural source of chlorins. The isolation of chlorophylls from natural material is known to be difficult because of their extreme sensitivity to various reactions, such as enolization, epimerization, allomerization, de-methoxycarbonylation, solvolysis, demctalation, dephytylation, photooxidation, etc. Often the... 

Electrochemical reduction has been studied intensively in the chlorophyll series due to the possibility to utilize the formed reduction products for the preparation of bacterio-chlorophylls.31c-d 41 For instance, methyl 3 -oxorhodochlorin-l5-acetate (4), a metal-free chlorin, can be electrochemically reduced to the corresponding chlorin 5 which is at the same oxidation level as a tetrahydroporphyrin. 

Nickel(II) chlorophyll derivatives undergo catalytic hydrogenation with Raney nickel as catalyst to yield stereoisomeric isobacteriochlorins in which ring A of the chlorophyll derivatives is reduced.16... 

The fluorescent lifetime of chlorophyll in vivo was first measured in 1957, independently by Brody and Rabinowitch (62) using pulse methods, and by Dmitrievskyand co-workers (63) using phase modulation methods. Because the measured quantum yield was lower than that predicted from the measured lifetime, it was concluded that much of the chlorophyll molecule was non-fluorescent, suggesting that energy transfer mechanisms were the means of moving absorbed energy to reactive parts of the molecule. 

Because of the role these algae play in the oceans biological productivity and their impacts on climate due to the removal of carbon dioxide, satellite sensors have been employed to measure the chlorophyll a contents in oceans, lakes, and seas to indicate the distribution and abundance of biomass production in these water bodies. Detection is set at the specific reflectance and absorption wavelengths of the light from the upper layer of the ocean where photosynthesis occurs. 

In a similar way, microalgal biomass on the sediment surface can be estimated by measuring the chlorophyll contents in benthic microalgae, which are single-celled microscopic plants that inhabit the top 0 to 3 cm of a sediment surface and are sometimes referred to as microphytobenthos. These organisms are the primary food resources of benthic grazers such as shellfish and numerous finfish species. 

Green, B.R. and Dunford, D.G., The chlorophyll-carotenoid proteins of oxygenic photosynthesis, Anmi. Rev. Plant Physiol. Plant Mol. Biol., 47, 685, 1996. 

Scheumann, V., Schoch, S., and Rudiger, W., Chlorophyll A formation in the chlorophyll b reductase reaction requires reduced ferredoxin, J. Biol. Chem., 273, 35102, 1998. 

Schluter, A. et al.. The chlorophyll-derived metabolite phytanic acid induces white adipocyte differentiation, Int. J. Obes., 26, 1277, 2002. 

Both chlorophylls and carotenoids occur in all green leaves, but their color is masked by chlorophyll in photosynthetic tissues. When the chlorophylls break down as leaves senesce (mature), the yellow and orange carotenoids persist and the leaves turn yellow. Carotenoids are responsible for the colors of familiar animals such as lobsters, flamingos, and fish. Often people are unaware of the chemical nature of food colorants. ... 

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