SPECTROPHOTOMETRIC, VOLTAMMETRIC AND ELECTROSPRAY MASS-SPECTROMETRIC STUDY OF THE ASSOCIATION OF PYOCYANINE WITH MN(II) IN AQUEOUS-MEDIA

Spectrophotometry, voltammetry and electrospray mass spectrometry have been used to examine dilute aqueous solutions containing pyocyanine a nd manganous ions. Spectrophotometry shows no evidence of complex form ation between the two constituents in either non-buffered (pH similar to 5) or buffered (pH 6.4) media at concentrations up to 100 mu mol l( -1) pyocyanine and 150 mu mol l(-1) Mn2+. Direct voltammetry with buff ered solutions confirms the spectrophotometric results, however the re sults obtained with non-buffered solutions, although significantly dif ferent from those for the buffered solutions, do not provide unambiguo us evidence of complex formation. Complexes of Mn2+ with one, two and three pyocyanine molecules are present in high intensity in the electr ospray mass spectra obtained with unbuffered aqueous solutions but are almost entirely absent with the buffered solutions. It is concluded t hat the concentrations of complexes in the solutions are extremely low and that their mass spectrometric observation is due to their formati on in the electrospray process and not to their pre-formation in the s olutions. (C) 1998 Elsevier Science B.V. All rights reserved.