Oxygen transport photosynthesis

Many important natural substances are metal complexes." Examples of this important class of natural materials include the chlorophyll, which is the base of photosynthesis, and hemoglobin, which is the prerequisite for respiration and the medium for the oxygen transport in the blood (Figure 6). 

Coordination compounds play important roles in nature. Chlorophyll, which is involved in photosynthesis in plants, is a coordination complex of magnesium. Hemoglobin, the oxygen transporter in the human body, is a coordination complex of iron. Vitamin B12, necessary for the prevention and cure of pernicious anemia, is a coordination complex of cobalt. In all three compounds, the metal ion is in an approximately octahedral environment, its coordination number is 6, and bonded to it are the four nitrogen atoms of a planar porphyrin-hke ring. The basic planar ring structure is closely related to that of the extremely stable blue pigment, Cu(II)phthalo-cyanine. 

Although not related to iron and oxygen transport, it should be mentioned that synthetic biomimetic models of special pair bacteriochlorophyll a have also been prepared (247). The reason is that, in the molecular organization of chlorophyll in the photoreaction centers of both green plants and photosynthetic bacteria, it is believed that special pairs of chlorophyll molecules are oxidized in the primary light conversion event in photosynthesis. Dimeric chlorophyll derivatives such as the one in Fig. 6.6 in which the porphyrin... 

Living systems contain many molecules based on metal complexes. Hemoglobin (involved in oxygen transport), cytochrome c (involved in electron transport), carbonic anhydrase (involved in respiration), and chlorophyll (involved in photosynthesis) aU have coordinated metal ions that are critical to their structure and function. Table 24.7 sununarizes the biological significance of many of the other first-row transition metals. 

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