Sensitisation Mechanism

Lazarides, T., Alamiry, M.A.H., Adams, H., et al (2007) Anthracene as a sensitiser for near-infrared luminescence in complexes of Nd(III), Er(III) and Yb(III) an unexpected sensitisation mechanism based on electron transfer. Dalton Transactions, 1484. 

As in the case of photoisomerisations, the reaction can proceed either via the singlet or the triplet intermediate. The component B is part of the reaction in contrast to the sensitisation mechanism discussed above. In addition both pathways via the singlet or triplet state can be quenched. The photophysical steps are summarised in Table 3.2 and the reaction scheme is derived in Appendix 6.6.1.1. In the following examples this information is used to derive the time laws and the quantum yields for 4 types of photoaddition reactions according to either the normal addition reaction... 

Recently the Rotter test has been used to assess the sensitising effect of diethylene triamine on a number of crystalline explosives. The detailed results of these tests have been reported elsewhere (Ref 23), but the main points are summarised here as they provide additional support for the proposed sensitisation mechanism. The first crystalline explosive we studied in the Rotter test was 2,4,6-trinitrotoluene (TNT). This showed a marked sensitisation... 

Figure 5.10 (a) Structure of the coordination polymer, Ln = Eu, Tb. (b) Three-photon excited emission of the Eu(lll) (dotted) and Tb(lll) (straight) complexes (RT, kex = 845nm). (c) Proposed sensitisation mechanism (from Reference [65])... 

Raymond, E. L., Mechanism of Sensitisation and Stabilisation of Incoloy Nickel-lron-Chromium Alloy 825 , Corrosion, 24, 180 (1968)... 

Hydrogen ions accumulate in tissue damaged by inflammation and ischaemia and so pH is lowered. These protons may activate nociceptors directly via their own family of ion channels as well as sensitising them to mechanical stimulation. Acid-sensing ion channels (ASICS) are a family of sodium channels that are activated by protons — of special interest is one type found only in small dorsal root ganglion neurons that possibly are responsible for activation of nociceptors. Although the transduction of mechanical stimuli is poorly understood, ASICs are closely related to channels that respond to stretch. 

A mechanism which has been proposed for the operation of this type of photocell is illustrated in Figure 10.7, although it is not fully established in detail. In the proposed mechanism, it is suggested that absorption of light by the dye (or sensitiser, S) raises the dye to its first excited state S. In the excited state, S releases an electron into the conducting band of the titanium dioxide electrode, at the same time forming oxidised sensitiser, S +. At the counter-electrode, an electron is transferred to the... 

Figure 10.7 Proposed mechanism for the operation of a dye-sensitised photocell...

Elahi, E.N., et al., Protein binding and metabolic inhibition reveals clues on the mechanisms surrounding relative potency of sensitising cinnamic compounds. Toxicology, 178, 43, 2002. 

Mutagenicity and carcinogenicity are generally considered to be non-threshold effects, unless a non-genotoxic mechanism can be established with a NOEL (or NOAEL or LOAEL). Risk assessment is based on establishing whether exposure is prevented. A similar process of preventing exposure also applies for skin and respiratory sensitisers, since there is no means of identifying a dose or concentration below which adverse effects will not occur in someone already sensitised to a particular substance. 

P-type delayed fluorescence is so called because it was first observed in pyrene. The fluorescence emission from a number of aromatic hydrocarbons shows two components with identical emission spectra. One component decays at the rate of normal fluorescence and the other has a lifetime approximately half that of phosphorescence. The implication of triplet species in the mechanism is given by the fact that the delayed emission can be induced by triplet sensitisers. The accepted mechanism is ... 

Photochemical addition of ammonia and primary amines to aryl olefins (equation 42) can be effected by irradiation in the presence of an electron acceptor such as dicyanoben-zene (DCNB)103-106. The proposed mechanism for the sensitised addition to the stilbene system is shown in Scheme 7. Electron transfer quenching of DCNB by t-S (or vice versa) yields the t-S cation radical (t-S)+ Nucleophilic addition of ammonia or the primary amine to (t-S)+ followed by proton and electron transfer steps yields the adduct and regenerates the electron transfer sensitizer. The reaction is a variation of the electron-transfer sensitized addition of nucleophiles to terminal arylolefins107,108. 

The neurobiological mechanisms that mediate the sensitised response to nicotine remain to be estabhshed. Mansvelder and colleagues (2000, 2002) have suggested... 

H-atom abstraction has been demonstrated to be the mechanism of action of excited uranyl ions, and in this case negligible base oxidation is found. Nucleo-base (especially guanine) oxidation is the principal reaction caused by singlet oxygen and this reactive species can be generated by a number of the complexes (e.g. many Ru(II)polypyridyls and porphyrins). It is worth pointing out, however, that the yield of may be lower when the sensitiser is bound to DNA, and it is the authors view that some of the reactions claimed to proceed via 62 may be caused by direct reaction of the photo-oxidised sensitiser with the DNA. 

Kimber I. Skin sensitisation immunological mechanisms and novel approaches to predictive testing. In Balls M, Van Zeller A-M, Haider M, eds. Proceedings of the Third World Congress on Alternatives and... 

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