Spectroscopic Determination of Metal-Ligand Coordination by Biologically Active 2-Picolinehydroxamic Acid with Iron(III) and Oxidovanadium(IV) in Aqueous Solutions

Abstract

The complexing properties of 2-picolinehydroxamic acid towards iron(III) as well as oxidovanadium(IV) were characterized in aqueous solutions by the UV-Vis spectrophotometric method. The speciation models have been confirmed and even extended by electrospray-ionization mass spectrometry (ESI-MS) studies. For both systems, mononuclear complexes were formed below a pH of 1 and coordination by {O,O-} chelation mode leading to the formation of five-membered rings was confirmed. The overall stability constant values were determined and compared with other similar systems, indicating more effective binding of the ligand by Fe(III) than VO(IV). The acidic medium of the reaction in the VO(IV)-2-picolinehydroxamic acid system prevented the oxidation of VO(IV) to V(V). 2-Picolinehydroxamic acid was chosen because of its previously evidenced biological properties. As a result of acidification, reversible dissociation of the complexes in both systems was observed, indicating the action of 2-picolinehydroxamic acid as a potential siderophore.

Complex-Forming Properties of Ceftazidime with Fe(III) Ions in an Aqueous Solution

“…The hydrolysis of the Fe(III) ions was already observed above pH 1.0 and corresponded to the literature data. As indicated by the reference data, the formation constants of the aqua-hydroxido complexes [Fe(OH)] 2+ and [Fe(OH) 2 ] + are equal to log β 10-1 = −2.68 and log β 10-2 = −6.48, respectively [ 15 , 16 , 17 , 18 , 19 ].…”

“…In the Hyperquad model were used the dissociation constants of ceftazidime, previously determined by pH-metric titration (log β [LH 3 ] 2+ = 9.23, log β [LH 2 ] + = 7.62, log β [LH] = 4.82) [ 13 ], where [LH 3 ] 2+ non-deprotonated all active groups, viz., two carboxyl (at the six-membered dihydrothiazine ring and at the methyl-ethoxy group), amine, and amide groups; [LH 2 ] + deprotonated a carboxyl group at the six-membered dihydrothiazine ring; and [LH] deprotonated two carboxyl groups. The hydrolysis constants of Fe(III) (log β [Fe(OH)] 2+ = −2.68; log β [Fe(OH) 2 ] + = −6.48) were taken from the data [ 15 ]. The ionic product of water pK w included in the equilibrium model was 13.77 [ 20 ].…”