Effect of metal ions on the quantitative determination of hydroxamic acids

The hydrolysis of hydroxamic acids to hydroxylamine is an important first step in the quantitative analysis of hydroxamate siderophores. The rate of this hydrolysis can be increased by the addition of ferric iron and the metals Mn(II), Cu(II), Ni(II), Cd(II), Cr(III), and Al(III). The maximum hydrolysis rate is obtained at iron to desferal ratios greater than 40:1. Using these conditions, >75% hydrolysis of the siderophores desferal, rhodotorulic acid, and scbizokinen was obtained in 2 h at temperatures as low as 70°C. These low temperatures make possible the direct analysis of hydroxamates in culture media containing high concentrations of carbohydrates. An example of this technique showing increased siderophore formation in low-iron cultures of Bacillus megaterium upon exposure to aluminum is presented.