Magnesium in chlorophyll

The reference is to ions of elements where charges are shown, i.e. not to magnesium in chlorophyll. Most elements are concentrated in combined forms. 

Naturally occurring compounds incorporating haem include vitamin Bi2, haemoglobin, and chlorophyll The central metal is iron in haemoglobin, magnesium in chlorophyll and cobalt in Bi2. 

Of the wide range of organo-metallic complexes likely to exist in natural waters only a small number have been structurally identified. Two examples of identified complexes found in sea water are cobalt(II)-containing cyanocobalamine or vitamin B,2 (Carlucci, 1970) and magnesium in chlorophyll a (Riley and Chester, 1971). Although a great deal is known about the properties of the unidentified complexes, it is not possible to classify them according to the systematic molecular nomenclature used in classical chemistry (lUPAC, 1973 Cahn, 1974). This undoubtedly has contributed... 

How is the magnesium in chlorophylls removed and how are vanadium and nickel introduced ... 

Adenosylcobalamin, cyanocobalamin (both active forms of vitamin B12), heme, and chlorophyll a aU enjoy the structural similarity of possessing a metal (cobalt in B12, iron in heme, and magnesium in chlorophyll a) centrally held in a core of four cojoined pyrrole (or pyrrole derived) rings. That these tetrapyrroUc systems are individually adorned with other substitution elements allows them and a large number of related materials, which are also composed of the same four pyrrole (or pyrrole-derived) rings, their respective functions. 

All organisms seem to have an absolute need for magnesium. In plants, the magnesium complex chlorophyll is the prime agent in photosynthesis. In animals, magnesium functions as an enzyme activator the enzyme which catalyses the ATP hydrolysis mentioned above is an important example. 

Another tetrahydroporphyrin derivative, porphodimethene (7), which consists of two dipyr-rylmethene halves is obtained in the photoreduction of magnesium-containing chlorophyll a (6) with hydrogen sulfide3211 42 as reductant and pyridine as base. 

Bohn, T. et al., Chlorophyll-bound magnesium in commonly consumed vegetables and fruits relevance to magnesium nutrition, J. Food Sci., 69, S347, 2004. 

The chlorophylls share a common tetrapyrrole stmcture and in their normal occurrence contain a chelated magnesium ion [28,29]. Structures for some chlorophyll a and b are shown in Figure 13.3. The structural difference is that there is a methyl group in chlorophyll a, whereas there is an aldehyde function in chlorophyll b. The... 

A prime example of this is the crucial ease of such oxidation in the magnesium(II) complex of the chlorin system present in chlorophyll during photosynthesis. Table 8 shows the half-wave potentials for the first ring oxidation of some metalloporphyrins, the examples chosen being based on 5,10,15,20-tetraphenyl porphyrin, TPP (2) and on 1,2,7,8,12,13,17,18-octaethylporphyrin, OEP (16). 

Magnesium has its role intimately intertwined with phosphate in many phosphoryl transfer reactions, as Mg-ATP in muscle contraction, in the stabilization of nucleic acid structures as well as in the catalytic activity of ribozymes (catalytic RNA molecules). It also serves as a structural component of enzymes, and is found as the metal centre in chlorophylls, which absorbs light energy in photosynthesis. 

Porphyrins 21 are the backbone of major players in life cycles—cytochromes (Scheme 8). There are three types of cytochromes, classified by their color, or more precisely by their long-wavelength absorption band, as a (600 mn), b (563 nm), and c (550 nm). They are protein conjugates of a porphyrin complex with iron(II), which is a coenzyme called heme (22). In plants, porphyrins form a complex with magnesium-(II) chlorophylls a and b (23), vital in photosynthesis. Porphyrin derivatives are used in photodynamic therapy for dermatological diseases such as psoriasis, and for skin or subcutaneous cancer.5c-e... 

In chlorophyll iron as complex-forming metal is replaced by magnesium (Willstatter). The structure of chlorophyll differs from that of haemin as follows. In chlorophyll one propionic acid chain (a) in oxidised form has condensed with a methine carbon atom to form a cyclopentane ring which takes the position at (c) of the vinyl ethyl. Further the two carbonyl groups are esterified and one of the four pyrrole rings is partially hydrogenated... 

Since magnesium is a constituent of the chlorophyll molecule, it is essential to the growth of all green plants (78). It occurs in all the cells and fluids of the human body, especially in bones and muscles (82). E. V. McCollum and his collaborators have proved that it is essential to animal life. The principal sources of magnesium in human diets are milk, vegetables, and green plants (128, 129). 

O. Lumpkin, Mg and N nuclear quadrupole resonances in chlorophyll-a and magnesium phthalocyanine. /. Chem. Phys., 1975, 62, 3281-3283. 

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