Pigments from natural systems

A series of hydroretinals were synthesized and were bound to bovine opsin to form visual pigment analogs, the hydrorhodopsins [92]. Model protonated Schiff bases were also prepared from each of these retinals, and the magnitudes of the opsin shifts were determined. Table 1 summarizes the data obtained and shows the opsin shift for bovine rhodopsin for comparative purposes. Binding studies were also carried out to ascertain that the hydroretinals occupy the same binding site as 11-cK-retinal in rhodopsin. This is required to show the relevance of the data to the natural system. 

There are many valid approaches to the preparation and study of manmade systems which mimic some aspects of natural photosynthesis. In this article, we shall focus on our results with one of these the synthesis and spectroscopy of multicomponent molecular devices constructed from organic pigments, electron donors, and acceptors whose structures resemble those found in the natural system. In these artificial photosynthetic species, the organizational constraints imposed by the protein environment in natural photosynthesis are provided instead by covalent linkages. 

Related systems to the naphthazarines are perylenequinones 33, which are biologically active pigments obtainable from natural sources. These compounds are of interest not only because of their peculiar structure features, but also owing to their photodynamic activity. 

Carotenoids are natural pigments characterized by a tail to tail linkage between two C20 units and an extended conjugated system of double bonds They are the most widely dis tributed of the substances that give color to our world and occur m flowers fruits plants insects and animals It has been estimated that biosynthesis from acetate produces approximately a hundred million tons of carotenoids per year The most familiar carotenoids are lycopene and (3 carotene pigments found m numerous plants and easily isolable from npe tomatoes and carrots respectively... 

The reduced symmetry of the chromophore, which still contains 187t-electrons and is therefore an aromatic system, influences the electronic spectrum which shows a bathochromic shift and a higher molar extinction coefficient of the long-wavelength absorption bands compared to the porphyrin, so that the photophysical properties of the chlorins resulting from this structural alteration render them naturally suitable as pigments for photosynthesis and also make them of interest in medical applications, e.g. photodynamic tumor therapy (PDT).2... 

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