Sensitization supersensitization

Energy transfer in the photosensitization of silver halide photographic emulsions Optical sensitization, supersensitization and antisensitization. J. chem. Physics 19, 417 (1950-... 

The pyrazolinones and pyrazolidinones are extensively employed in photography as color couplers, sensitizers, supersensitizers, developers and antihalation agents. A number of pyrazolinones which have been prepared for use as sensitizers are listed in Tables LI and LIL... 

Another common loss process results from electron—hole recombination. In this process, the photoexcited electron in the LUMO falls back into the HOMO rather than transferring into the conduction band. This inefficiency can be mitigated by using supersensitizing molecules which donate an electron to the HOMO of the excited sensitizing dye, thereby precluding electron—hole recombination. In optimally sensitized commercial products, dyes... 

Fig. 6. Effect of added supersensitizers on a J-aggregated spectral sensitizing dye, l,l -dieth5i-2,2 -quinocyariine chloride [2402-42-8] (1), for which...

FIG. 11 General mechanism for the heterogeneous photoreduction of a species Q located in the organic phase by the water-soluble sensitizer S. The electron-transfer step is in competition with the decay of the excited state, while a second competition involved the separation of the geminate ion-pair and back electron transfer. The latter process can be further affected by the presence of a redox couple able to regenerate the initial ground of the dye. This process is commonly referred to as supersensitization. (Reprinted with permission from Ref. 166. Copyright 1999 American Chemical Society.)... 

Succinylcholine produces muscle fasciculation, which may result in myoglobinuria and postoperative muscle pain. The amount produced depends on the level of physical fitness. Succinylcholine causes contractions of extraocular muscles, posing the danger of transient elevated intraocular pressure. Succinylcholine may produce hyperkalemia in patients with large masses of traumatized or denervated muscle (e.g., spinal cord injury). Denervated muscle is especially sensitive to depolarizing drugs because of the increased number of AChRs on the sarcolemma (denervation supersensitivity). Succinylcholine also causes prolonged contraction of the diseased muscles of patients with myotonia or amyotrophic lateral sclerosis. 

While much emphasis has been placed on alterations in noradrenergic neurotransmission, TCA drugs are not without effect on serotonin (5-HT) neurotransmission. Long-term studies with TCA drugs in animals have demonstrated postsynaptic supersensitivity to serotonin (5-HTia) receptor agonists at serotonin synapses, with an associated enhancement of serotonergic neurotransmission. The sensitization to 5-HTia agonists is mediated in part by an increase in the density of postsynaptic 5-HTia receptors. Enhancement of trans-... 

On balance, these actions could support a decrease rather than an increase in the functional state of CNS NE transmission, because depression can be conceptualized as a state of supersensitive catecholamine receptors secondary to decreased NE availability. This reasoning is consistent with the original hypothesis of diminished NE functioning, with antidepressants returning receptors to a more normal state of sensitivity. Siever and Davis ( 41) further elaborated on this concept by suggesting the possibility of dysregulation in the homeostatic mechanisms of one or more neurotransmitter systems, culminating in an unstable or erratic output. 

Early research at our institute found that treatment with lithium decreased the b-adrenergic receptor number, consistent with the noradrenergic down-regulation hypothesis but difficult to reconcile with a complementary theory of mania ( 25). Lithium can also block dopamine receptor supersensitivity, and this is consistent with the postulate that mania is associated with an increased sensitivity of catecholamine receptors. 

Reducing agents, such as hydroquinone, Br , I, SCN- ions, and others, are used as supersensitizers for electron photoinjection reactions. Figure 28 illustrates how an admixture of hydroquinone affects photocurrent in the system CdS—rhodamine B. In certain cases the solvent, water, can also act as a supersensitizer. For example, if the bipyridyl complex of Ru(II) is a sensitizer, the oxidized form, the complex of Ru(III), can oxidize water to oxygen... 

Diaz, A., Ruiz, F., Florez, J., Pazos, A., Hurle, M.A. Regulation of dihydropyridine-sensitive Ca++ channels during opioid tolerance and supersensitivity in rats, J. Pharmacol. Exper. Ther. 1995, 274, 1538-1544. 

In photography, a technique called supersensitization with supersensitizer (SS) is used to improve the quantum yield of spectral sensitization. The SS dye molecules co-adsorbed on the AgBr grains in much smaller concentration than the sensitizing dye improve the sensitization. The shortening of the fluorescence lifetimes by addition of SS is observed and this phenomenon is explained by the hole-trapping mechanism [10,11]. 

Two main mechanisms were proposed for the supersensitization effect. One is the hole-trapping mechanism in which the electron from SS fills the hole in the highest occupied molecular orbital (HOMO) of the excited sensitizing dye, since the HUMO level of SS is chosen to be higher than that of the sensitizer (Fig. 5) [2,10,11]. The resultant ionic state gives up an electron to the conduction band of silver halide with much higher quantum yield. 

The other is the aggregate-partitioning mechanism [2,15], where it is considered that the SS molecules work as J-aggregate partitioners, which decrease the size of the aggregates. This causes an increase in the fluorescence lifetime and/or an increase in the electron injection rate, and hence an increase in the quantum yield of the electron injection [2], In the present work the sensitization and supersensitization processes are described below by the hole-trapping supersensitization. 

Improvement of spectral sensitization can be accomplished by dye combinations. The effect has been found to often be greater than the predicted additive sensitivity increase. This phenomenon is called supersensitization (94), which is applied most effectively to polymethine aggregates (96). 

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