ISSN:
1573-904X
Keywords:
DuP 925
;
heteropolyanion
;
keggin anion
;
solution stability
;
ion pair behavior
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Hexapotassium-α-vanado-11-tungstoborate (DuP 925) is a yellow irregular-shaped crystalline powder. The DSC thermogram indicates that decomposition begins to occur above 250°C. The compound exhibits a volatile loss of 3.7% by thermogravimetric analysis. The drug substance adsorbs water reaching a 7.1% volatile loss after 3 weeks at 85% relative humidity. The solubility of DuP 925 in water is high (1.6 g/ml at pH 4.8). Changes in pH have a negligible effect on the solubility with values of 1.3 g/ml in 0.1 N HC1 and 1.4 g/ml in 0.1 N NaOH. The solubility is minimally affected by changes in sodium ion concentration. The compound ion pairs with tetrabutyl-ammonium ions at 1:2 and 1:6 ratios, with the 1:6 ion pair having an affinity over six orders of magnitude greater than that of the 1:2 ion pair. The degradation of DuP 925 in solution follows apparent first-order kinetics over the pH range of 0.6 to 12.6 at 80°C. Citrate, EDTA, and phosphate buffers are catalytic at the pH minimum, with citrate and EDTA being stronger catalysts than phosphate. Acetate buffers appear to have negligible catalytic effects at pH 4 to 5. The degradation proceeds through the formation of the symmetrical dodecatungstoborate [BW12O40]−5. In acid, the dodecatungstoborate is stable, while in base it degrades further. Increasing the ionic strength has a catalytic effect on the degradation of DuP 925, while changes in the initial concentration of DuP 925 have a negligible effect on the stability. The pH-rate profile indicates a pH minimum of approximately 3.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1015813018400
Permalink
