Chlorophyll absorption band

Photoexcited fluorescence from spread monolayers may be studied [158,159] if the substance has both a strong absorption band and a high emission yield as in the case for chlorophyll [159]. Gaines and co-workers [160] have reported on the emission from monolayers of Ru(bipyridine)3, one of the pyridine ligands having attached C g aliphatic chains. Ruorescence depolarization provides information about the restriction of rotational diffusion of molecules in a monolayer [161], Combining pressure-area... 

One of the absorption bands in chlorophyll a appears at about 700 nm. What energy does this correspond to in kj/mol Would this energy be sufficient to break an OH bond See Table 4.1. 

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... 

The new absorption band at 435 ran in the C60 spectrum has been attributed to the 1,2 addition to the fullerene cage to the fatty acid chains either across to the double bonds by a Diels-Alder addition or, more simply, by radical addition (Cataldo and Braun, 2007). Thus, fatty acid esters are able to not only dissolve C60, but also react with this molecule causing the addition of the fatty chain to the fullerene cage. In fact, the bands at 435 ran shown in Fig. 13.3 appear only when C60 is stirred at 75°C for a couple of hours in the esters of fatty acids. Only for olive oil the new band appears much weaker than in the other cases and displaced at 450 ran (Fig. 13.3B). Since this oil contains chlorophyll, the displacement may be probably due also to a charge-transfer interaction between C60 and chlorophyll or with other impurities. 

Bacteriochlorophyll in Chromatium has three absorption bands with peak positions at 800, 850, and 890 nm. The last includes the reaction center bacteriochlorophyll and is the only form that fluoresces. Recent studies have established that most if not all chlorophyll is bound to specific proteins, a fact that can account for the various overlapping absorption bands. 

The photooxidation of chlorophyll indicated in Eq. 23-31 is accompanied by bleaching in the principal light absorption band. However, since there is so much light-gathering chlorophyll for each reaction center, the effect is small. The study of the process has been aided greatly by preparation of isolated bacterial photochemical reaction centers. 

The reduction of ring IV in chlorophylls a or b changes the optical absorption spectrum of the molecule dramatically. Whereas the long-wavelength absorption band of a cytochrome is relatively weak (see fig. 14.4), chlorophyll a has an intense absorption band at 676 nm (fig. 14.5). Chlorophyll b has a similar band at 642 nm. Bacteriochlorophylls a and b have strong absorption bands in the region of 770 nm (see fig. 15.5). The chlorophylls thus absorb red or near-infrared light very well. 

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