Sensitizing action

The detection of spectral sensitizing action often depends on amplification methods such as photographic or electrophotographic development or, alternatively, on chemical or biochemical detection of reaction products. Separation of the photosensitization reaction from the detection step or the chemical reaction allows selection of the most effective spectral sensitizers. Prime considerations for spectral sensitizing dyes include the range of wavelengths needed for sensitization and the absolute efficiency of the spectrally sensitized process. Because both sensitization wavelength and efficiency are important, optimum sensitizers vary considerably in their stmctures and properties. 

NGF, in addition to its direct sensitizing action in the peripheral terminal, is retrogradely transported to the cell body, where, via the ERK MAPK and CREB pathways, it increases expression of substance P (sub P), CGRP, BDNF, ASIC and Navl-8, and produces an increase in TRPV1 translation. Navl-8, ASIC and TRPV1 are shipped to the periphery, where their increased levels further augment peripheral sensitivity. After peripheral inflammation, substance P and BDNF are expressed in low threshold... 

The sensitizing action of gold can be interpreted by postulating that the gold particles act as electron traps. 

When green leafy vegetables are under analysis, the carotenoids are prone to photoisomerization by the sensitizing action of coextracted chlorophylls. 

Many sensitizing dyes, including dyes used in commercial emulsions, can decrease the sensitivity for radiation absorbed by the silver halide. This desensitization extends to the region of spectral absorption by the dyes, and thereby competes with the spectral sensitizing action. 

The discovery of the sensitizing properties of dyes that formerly had been considered as strictly desensitizing dyes, and the high efficiency with which some of these dyes can spectrally sensitize under proper conditions, requires reconsideration or extension of earlier theories of spectral sensitization. Unless previous estimates of the position of the singlet excitation level of these dyes relative to the conduction band of the silver halide are in serious error, these dyes should not be able to photoinject electrons directly into the conduction band from the level. The clue to their sensitizing action, I think, is contained in an explanation offered by Sturmer, Gaugh, and Bruschi for the "abnormal" spectral sensitization obtained with one of the desensitizing dyes used in their study of the effect of chemical sensitization on the efficiency of spectral sensitization (273). They wrote that... 

Bruevich TS, Bogomolets NN, Berezovskii AD. 1980. [Sensitizing action of precious metal compounds Gold, platinum, ruthenium, rhodium and silver]. Gig Tr Prof Zabol 42-44. (Russian). 

This production of a peculiar degree of instability in the silver bromide, close to the atoms of sulphur in the sulphide, seems closely analogous to the other cases of promoter action, and the effects of a one-dimensional interface in a solid surface, which were considered in 3. It may be an effect of the same nature as the increased ease of decomposition of the calcium carbonate group, when this has calcium oxide groups adjacent to it. There is some evidence that the silver sulphide crystal lattice is rather more easily disorientated than the silver bromide, but since silver sulphide is, alone, not particularly sensitive to light, it seems certain that the sensitizing action of the sulphide speck must be due to a boundary action between the sulphide and the bromide.8... 

Although these effects were considered by McNamara et al. (1975) to be unrelated to the exposure to sulfur mustard, they are consistent with the known vesicant and sensitization actions of the agent. It is possible that the HD condensed on the fur of the animals and was subsequently ingested as a result of grooming behavior. Gastroenteritis could then have resulted from direct contact of the vesicant with the gastrointestinal epithelium. 

In course of subsequent work Bubeck, Tieke, and Wegner discovered that the action spectrum for photopolymerization of undoped diacetylene multilayers extends into the visible provided some polymer formed in course of previous UV-irradiation is present. Since obviously excitation of the polymer can sensitize the reaction this effect has been termed self-sensitization. Checking the absorption spectrum of the polymer produced via self-sensitization assured that the final product is identical with the product obtained under UV excitation of the monomer. Later work by Braunschweig and Bassler demonstrated, that the effect is not confined to multilayer systems but is also present in partially polymerized single crystalline TS-6, albeit with lower efficiency. Interestingly, the action spectrum of self-sensitization follows the action spectrum for excitation of an electron from the valence band of the polymer backbone to the conduction band rather than the excitonic absorption spectrum of the polymer which is the dominant spectral feature in the visible (see Fig. 21). The quantum yield is independent of the electric field, whereas in a onedimensional system the yield of free carriers, determined by thermal dissociation of optically produced, weakly bound geminate electron-hole pairs, is an linear function of an applied electric field 29.30,32,129) Apparently, the sensitizing action does not... 

C. Lamont and D.J. Miller, Calcium-sensitizing action of carnosine and other endogenous imidazoles in chemically skinned striated muscle. J. Physiol, 454 (1992) 421-434. 

Data on the photochemical stability and stabilizing action of HB s, benzotriazoles, and related compounds have been reported on several occasions (6,9,70,71,7,82,87). In order to be a good stabilizer, it is not sufficient that a compound does not decompose if dissolved for example, in a plastic, it is equally important that it does not act as a sensitizer. Investigations on the sensitizing action of HB s compared to that of benzophenone and nonchelated derivatives are, therefore, of interest. Such studies are Included by Lamola (8), A. Heller (80), and Hammond (74). Cls-trans isomerization of piperylene (1,3-pentadiene) in benzene is easily sensitized by benzophenone via triplet transfer... 

Troponin T subfragments (residues) Ca -sensitizing action Immobilized proteins ... 

The SDS-gel electrophoretic pattern of tropomyosin showed two bands, designated a and /8, around 35,000 Da (Cummins and Perry, 1973). The ratio of the two subunits varied from tissue to tissue mostly a subunit in fast skeletal muscle, equimolar a and )8 subunits in slow skeletal muscle, and exclusively a subunit in cardiac muscle (Bronson and Schachat, 1982). The tropomyosin molecule consists of aa or ajS dimers. A )8/8 molecule produced in vitro showed the same Ca -sensitizing action as that of aj8- or aa-tropomyosin (Cummins and Perry, 1973). Hence physiologically both a and /3 subunits are identical. 

It seems likely that the sensitizing action of the transition metals for photodegradation of polymers could be attributed to UV light absorption and the generation of free radicals which initiate degradation (16, 32,33). 

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