Gold sensitization

The discovery of gold sensitization stimulated interest in other noble metals. Interest has centered chiefly on iridium (177,178) and, to a lesser extent, on rhodium (179-181). Some studies have been made on platinum and palladium (182). 

The effect of gold sensitization of emulsions is to alter the shape of the curve shown in Figure 20 because of the incorporation of gold into the latent image. Gold is more active than silver as a catalyst for silver deposition [88] and also has been shown to be able to catalyze development with a two-atom center, compared with the minimum of four atoms for silver. The curve will now come down more steeply and not turn over to long induction periods until n is very small. 

Tani [90] has examined the properties of silver clusters by means of redox buffer solutions, and showed that the oxidation potential of latent images formed by sulfur-plus-gold sensitization was much more positive than for those formed in unsensitized, sulfur-sensitized, reduction-sensitized, and iridium-sensitized emulsions. The oxidation potential of fog centers with excessive sulfur sensitization was much more positive than that of fog centers with excessive reduction sensitization. In general this reflects the relative ease of bleaching of silver centers compared with silver sulfide centers. 

The best point of attack for a determination of the surface electrochemical properties of latent images is at the level of latent sub-images. There can hardly be more than three sizes (2, 3,4) without gold sensitization, and only one size (N=2) with gold. Indeed, the continued presence of optical latensification effects after the application of optimal gold sensitization established the development threshold at N=3, not 2, in the presence of gold atoms. 

Complexes of other metals are used to sensitize emulsions, and some are used to sensitize even further (supersensitize) gold-sensitized emulsions. " Among these are (NH4)2[PtCl4], (NH4)2[PdCl4], (NH4)2[PdCy, K2[IrCl6] and similar compounds with ruthenium and the other halides. Sensitization by iridium salts and complex ions has been reviewed recently. Mechanisms of action of palladium(II) salts and complex ions on gold-sensitized emulsions have been studied. Several phosphine complexes of palladium and platinum, for example (2), are reported to be effective sensitizers, as are many macrocyclic polyamine compounds and their metal complexes,for example the Cu", Ni", Fe " and Rh " chelates of the cyclen ligand, 1,4,7,10-tetraazacyclododecane (3). 

The net result is two electrons for one photon. An active area of current AgX research is the development of new sensitizing reagents which can produce this same effect without the drawbacks of reduction sensitization, which normally include elevated fog levels and incompatibility with gold sensitization. 

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Larsen W, Adams RM, Maibach HI (1992) Color text of contact dermatitis. Saunders, Philadelphia, pp 812-816 Leow Y-H, Ng S-K, Goh C-L (1998) A preliminary study of gold sensitization in Singapore. Contact Dermatitis 38 69-170 Marks JG Jr, Helm KF, Kreuger GG, Griffiths CEM, Guzzo CA, Leyden JJ (1995) Contact dermatitis from topical auranofin. J Am Acad Dermatol 32 813-814... 

Silvennoinen-Kassinen S, Niinim i A (1984) Gold sensitivity blast transformation. Contact Dermatitis 11 156-158 Somov BA, Khaimovskii GD (1964) Allergic dermatitis caused by aurum compounds in watch industry. Vestnik Dermatologii i Venerologii 10 33... 

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