Silver complexes cyanines

By treating benzimidazole-phosphamethin-cyanines 8a with methanolic silver tetrafluoro-borate solutions, Greif isolated colorless, crystalline silver complexes. Their absorption bands lie at shorter wavelengths. The extinction coefficients are httle changed. Here, too, a clear dependence of the position of the absorption maxima on the nature of the N-alkyl substituents can be observed (Table 3). 

Addition of excess methanol destroys the silver complexes and regenerates the phosphamethin-cyanine salts. It is more advantageous to bind the Ag ions by addition of tris-j cyanoethyl-phosphine. 

The cyanine dye, 3,3 -diethyl-9-methylthiacarbocyanine chloride, had a much greater effect than gelatin in decreasing the reaction rate of the silver chloride. The rate of reduction of silver chloride varied linearly with the amount of silver chloride surface not covered by the dye, and the rate attained at complete coverage was of the order of one-thousandth that for the undyed precipitate. The dye exerted scarcely any effect upon the reduction of silver ions from silver sulfite complex solution. 

Non-specific complexes or associations between Ag1 and various cyanine spectral sensitizing dyes containing thiol or thione groups can be made by coating silver nitrate with a sensitizing dye. 

Several metal oxides (platinum, gold," nickel, copper, ) and cobalt phtalo-cyanine have been employed as surface bound mediators for carbohydrate detection. In a dc amperometric mode of operation detectors based on these mediators exhibit a significant loss of response with time and/or exposure to analyte. Various potential pulse programs have circumvented this stability problem, but at the expense of sensitivity and complexity of the instrumentation. Silver electrodes coated with electrogenerated silver oxide exhibit electrocatalytic activity with respect to carbohydrate oxidation. This paper describes our efforts to utilize an electrode as a carbohydrate detector in a dc amperometric mode. 

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