Inhibitor release mechanisms

Although the varied uses for which DIR couplers are employed call for precise control over where the inhibitor diffuses, the very complexation mechanism by which inhibitors work would seem to preclude such control. The desired ability to target the inhibitor can be attained by the use of delayed release DIR couplers, which release not the inhibitor itself, but a diffusable inhibitor precursor or "switch" (Fig. 16) (98). Substituents (X, R) and stmctural design of the precursor permit control over both diffusivity and the rate of inhibitor release. Increasing the effective diffusivity of the inhibitor, however, means that more of it can diffuse into the developer solution where it can affect film in an undesirable, nonimagewise fashion. This can be minimized by the use of self-destmcting inhibitors that are slowly destroyed by developer components and do not build up or "season" the process (99). 

Muller reported that black mustard (Brassica nigra) can form almost pure stands after invading annual grasslands of coastal southern California (25). This was attributed to inhibitors released from the dead stalks and leaves which do not permit germination and growth of other plants. These observations provide agronomists hope that similar results could be exploited with crops, specifically to achieve almost pure stands of crops (over weeds) by use of an allelopathic mechanism. 

After more than a decade of use, bupropion (24) is considered a safe and effective antidepressant, suitable for use as first-line treatment. In addition, it is approved for smoking cessation and seasonal affective disorder. It is also prescribed off-label to treat the sexual dysfunction induced by SSRIs. Bupropion is often referred to as an atypical antidepressant and has much lower affinity for the monoamine transporters compared with other monoamine reuptake inhibitors. The mechanism of action of bupropion is still uncertain but may be related to inhibition of dopamine and norepinephrine reuptake transporters as a result of active metabolites [71,72]. In a recently reported clinical trial, bupropion extended release (XL) had a sexual tolerability profile significantly better than that of escitalopram with similar re-... 

G. Paliwoda-Porebska, M. Rohwerder, M. Stratmann, U. Rammelt, L.M. Due, and W. Plieth, Release mechanism of electrodeposited polypyrrole doped with corrosion inhibitor anions, J. Solid State Electrochem., 10, 730-736 (2006). 

The present work confirmed the layer by layer assembly of ZMP nanocontainers and the release mechanism of corrosion inhibitor. FTIR and TEM study confirms the successful formation of ZMP nanocontainer as a layer by layer system with the aid of ultrasonic irradiation. Zeta potential and particle size analysis also shows the formation of layers and shows appropriate change in the surface charge, which could be responsible for the release mechanism initiated by the change in pH. Release study and corrosion results from Tafel plot and corrosion rate analysis showed significant improvement in the anticorrosion properties of coatings due to the optimum loading of the ZMP nanocontainers. 

The delivery of inhibitors can be based on different possible release mechanisms that depend upon the encapsulation approaches. The simplest example is uncontrollable leakage of active ingredients from a polymer capsule ruptured under mechanical stresses. This approach was used by Yang and Van Ooij when triazole inhibitor was encapsulated using plasma polymerization to produce PP-perfluorohexane and PP-pyrrole layers employing RF plasma discharge (Yang and Van Ooij, 2004). The release of the inhibitor from such a capsule is possible only when it is mechanically mptured. 

Replenishment of the inhibitor in the depletion zone. This function will be inextricably keyed into the self-repair mechanism of the polymer coating so that the new pigment distribution will allow further release of the inhibitor if mechanical damage occurs again (Fig. 9.2c). 

The question as to whether a flame retardant operates mainly by a condensed-phase mechanism or mainly by a vapor-phase mechanism is especially comphcated in the case of the haloalkyl phosphoms esters. A number of these compounds can volatilize undecomposed or undergo some thermal degradation to release volatile halogenated hydrocarbons (37). The intact compounds or these halogenated hydrocarbons are plausible flame inhibitors. At the same time, thek phosphoms content may remain at least in part as relatively nonvolatile phosphoms acids which are plausible condensed-phase flame retardants (38). There is no evidence for the occasionally postulated formation of phosphoms haUdes. Some evidence has been presented that the endothermic vaporization and heat capacity of the intact chloroalkyl phosphates may be a main part of thek action (39,40). 

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