The Photochemistry of Animal Vision

Example The four chromophores of animal vision are resonant conjugate retinoids that only exhibit their unique spectral performance when in the liquid crystalline state. They must not be attacked by strong detergents or either oxidizing or reducing agents. Their spectra can only be measured in the transient mode unless they are in quantum contact with another material that can continually de-excite the excitons created by the incident photons. 

This Chapter will present the actual chromophores of vision, labeled the Rhodonines and derivable from a number of feedstocks, including the retinol family, consist of relatively small molecules with a molecular weight of either 285 (R5 R9) or 299 (R7 R11). They are retinoids of the resonant conjugate type. They are also carboxylic-ion systems and exhibit a negative charge in their fundamental form. The molecules are relatively easily generated in the laboratory in pure form. However, they exhibit a number of unique properties that have made their isolation difficult. They only exhibit the properties of a visual chromophore when in the liquid crystalline state. Their absorption characteristic is a transient one unless a means of de-exciting the molecules of the liquid crystal is present. Finally, they are extremely sensitive to destruction by oxidants and alkali metal ions. 

2Gutmann, F. Keyzer, H. Lyons, L. (1981) Organic semiconductors Part B Malabar, FL RobertE. Krieger Publishing Co. Pg. 319 

3Saari, J. in Spom, M. Roberts, A. Goodman, D. (1984) The retinoids. NY Academic Press pg. 351 

The Rhodonine chromophores consist of a family of twelve, four related to Retinol (Vitamin A1 and found in saline-based animals), four related to 3,4 dehydroietinol (Vitamin A2 and associated with the freshwater-based animals) and four related to 3-hydroxyretinol (Vitamin A3 and found primarily in the two-winged flies, the Diptera Order of Arthropoda). The functional absorption spectra of these three sets, when in the liquid crystalline state, are virtually identical. This is due to the primary quantum-mechanical mechanism involved and the identical form of their chromophoric structure. The members of each set are spaced at 95 2 nm. 

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