Differences between the structure of the anti-arthritic gold drug “myocrisin” in the solid state and in solution: a kinetic study of dissolution

Abstract

Detailed analyses of changes in the ultraviolet-visible absorption spectra of the anti-aithritic gold drug disodium gold(I) thiomalate·0 3 glycerol·2H 2O with time, suggest that the solid may contain about 23% of a species with λ max of 337 and 370 nm. This disappears in a two-step process soon after dissolution in water. The reaction was monitored at a variety of temperatures (20–47°C), pH's (6–11), and ionic strengths (0.05–0.61 M). The first step is complete in ca. 3 min. The second step is independent of Au(tm) concentration with k o' = 8.5 × 10 −2min −1 and activation parameters of Δ H ± = 82.1 ≠ 4.1 kJmol −1 and Δ S ≠ = 13.65 KJ −1 mol −1. The logarithm of the rate of this step increases linearly with the square root of the ionic strength. The reaction is readily reversed at high ionic strengths and is interpreted as a cooperative structural transition of polymeric gold( I) thiomalate, possibly involving Au(I)-Au(I) bonding. The relationship of these observations to reactions of other 1:1 Au(I) thiolate complexes and their method of preparation is discussed.