Pigments light absorbers

Figure 12.4 The light-absorbing pigment retinal undergoes a conformational change called isomerization, when it absorbs light.

Figure 12.13 Photosynthetic pigments are used hy plants and photosynthetic bacteria to capture photons of light and for electron flow from one side of a membrane to the other side. The diagram shows two such pigments that are present in bacterial reaction centers, bacteriochlorophyll (a) and ubiquinone (b). The light-absorbing parts of the molecules are shown in yellow, attached to hydrocarbon "tails" shown in green.

Bacteriochlorophyll- Light-absorbing pigment found in green sulfur and purple sulfur bacteria. 

The photosynthetic apparatus in green plants and algae is located in the chloroplast, which is a flattened, double-membraned structure about 150-200 A thick/4,5 The two flat membranes lie one above the other and are united at their peripheries. These double-membraned structures have been termed thylakoids (from the Greek sacklike )/ Each membrane of the thylakoid consists of a water-insoluble lipoprotein complex which contains the light-absorbing chlorophyll and other pigments utilized in photosynthesis. 

Most materials exhibit specific colors because they absorb certain wavelengths (colors) from white, ordinary light. A red object exposed to white light, for example, appears red because atoms on its surface absorb all the other colors in the beam and reflect only red. If transparent materials contain coloring materials, such as dyes or pigments, they absorb the characteristic color of the coloring material. 

Light-absorbing pigments differentiate rod cells for black-white vision and three types of cone cells for color vision 807... 

The light-absorbing part of a rod cell contains the pigment rhodopsin, which consists of the opsin attached to the 11-cis-retinal molecule (1) (Figure 12.3). Free 11-cis-retinal absorbs in the ultraviolet, but when attached to opsin the absorption is in the visible region. 

An elegant publication from Aman and Thoma [84] outlined the various options open to the stabilisation of photolabile oral products. The addition of lightabsorbing agents is a well-established approach to stabilising photolabile products [85]. Aman and Thoma [84] reported that the incorporation of light-absorbers and pigments considerably improved the photostability of the very light sensitive... 

A method for determining the alteration of the refractive index of a medium as a result of the temperature rise in the path of a beam of coherent light absorbed by the medium. Thermal lensing can also occur with pigmented proteins, and this phenomenon can influence the accuracy of concentration gradient measurements in small aperture flow cuvettes as well as in ultracentrifugation. 

Hao W, Fong HK 1996 Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium. Biochemistry 35 6251—6256... 

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