Barbara Kurzak

X-Ray and potentiometric studies on a pentanuclear copper(II) complex with β-alaninehydroxamic acid

Potentiometric and X-ray studies on the system copper(II)–L-β-alaninehydroxamic acid have shown the formation of a very stable pentanuclear complex [Cu5A4H–4]2+ at pH around 4. In this species all donor atoms of the aminohydroxamic acid are involved in the metal ion co-ordination. Four peripheral metal ions form an almost planar structure and the central metal ion is 0.4 A above this plane. There are twelve five- and six-membered chelate rings with different conformations. The X-ray structure results support earlier suggestions based on potentiometric and spectroscopic data for the formation of oligomeric structures at relatively low pH.

Interactions of zinc(II), magnesium(II) and calcium(II) with aminomethane-1,1-diphosphonic acids in aqueous solutions

Abstract Complex formation equilibria of the aminomethane-1,1-diphosphonic acids with Zn II , Mg II and Ca II have been studied by potentiometric pH titrations and by means of NMR spectroscopy. The ligands exhibit a strong tendency to form protonated species over a wide range of pH. The most efficient binding mode in all the studied systems is the formation of the six-membered chelate ring involving oxygens of both phosphonate groups. An evident preference for the formation of multinuclear complexes is noted in the case of zinc(II). Magnesium demonstrates preference for mononuclear complexes, whereas calcium(II) tends to form insoluble species with most of the studied ligands. The structures of the main complex species are discussed with respect to the priorities in the hydrogen-bond network organization in solid state.

Mixed-ligand copper(II) complexes with diethylenetriamine and histidine- or methioninehydroxamic acids in water solution

Abstract Stability of the mixed-ligand complexes of Cu2+ ion with diethylenetriamine [bis(2-aminoethyl)amine, dien] as a primary ligand and histidinehydroxamic acid [2-amino-3-(4′-imidazolyl)propanehydroxamic acid, Hisha] or methioninehydroxamic acid [2-amino-4-(methylthio)butanehydroxamic acid, Metha] as a secondary ligand L and their absorption and EPR spectra at various pH values are reported. The visible spectra exhibit a characteristic red shift and a shoulder at lower energies indicating a five-co-ordinate structure of the formed complexes. The EPR spectral parameters support formation of mixed-ligand complexes which geometry is slightly deviated from square pyramidal.

Role of the NH3+ moiety in iron(III)–, aluminium(III)– and gallium(III)–aminohydroxamate interactions

Stability constants have been determined and the bonding modes and effects caused by the side-chain NH3+ moiety in aminohydroxamic acids evaluated for complexes formed in aqueous solution in between iron(III), aluminium(III) and gallium(III) with α-alaninehydroxamic acid (α-Alaha), β-alaninehydroxamic acid (β-Alaha), aspartic acid-β-hydroxamic acid (Asp-β-ha) and glutamic acid-γ-hydroxamic acid (Glu-γ-ha). The iron(III)–, aluminium(III)– and gallium(III)–acetohydroxamic acid (aha) systems were studied as models. Co-ordination of hydroxamate oxygens occurs in the cases of aha, α- and β-Alaha, while Asp-β-ha and Glu-γ-ha are co-ordinated via their hydroxamate and carboxylate oxygens. The OH– ion was found to be an effective ligand in these systems (especially for GaIII) causing the formation of both binary and ternary hydroxo complexes. The presence of NH3+ in the hydroxamic acids favours the hydrolysis to an extent which depends on the distance between the hydroxamate moiety and NH3+. These findings can be explained by the electron-withdrawing effect of NH3+ and electrostatic repulsion between it and the co-ordinating M3+ ion.

Potentiometric and spectroscopic studies of the copper(II) complexes with some aminodiphosphonic acids in aqueous solution

The stoichiometries and stability constants of the copper(II) complexes with seven aminodiphosphonates [R–N(CH2PO3H2)2, L] containing iminomethylenephosphonate moieties have been determined pH-metrically at 25°C and at an ionic strength of 0.20 mol dm−3 (KCl). The results suggest for L=1–6 only equimolar species: [Cu(H2L), [Cu(HL), [CuL] and two hydroxo [CuH−1L] and [CuH−2L], in the pH range of 2–11.5, the only difference is the presence of an additional [Cu(H3L)] species (∼15%) at low pH for N-3-picolyliminodi(methylenephosphonic) acid. For L=7 the model contains protonated and non-protonated 1:2 species. From the comparative analysis of the stability and the spectroscopic (UV–VIS and EPR) data it has been established that the ligands in [CuHL] and [CuL] are tridentate; the formation of two five-membered chelate rings leads to very stable complexes. The LMCT bands from O− (PO32−) and Nimino to Cu2 are at 225–231 and 302–277 nm.

Ternary copper(II) complexes with diethylenetriamine and α-(or β-) alaninehydroxamic acids in water solution

Abstract Stabilities of the mixed-ligand complexes of Cu 2+ ion with diethylenetriamine [bis(2-aminoethyl) amine, dien)] as a primary ligand and α-alaninehydroxamic acid [2-amino-N-hydroxypropanamid, α-Alaha] or β-alaninehydroxamic acid [3-amino-N-hydroxypropanamid, β-Alaha] as a secondary ligand L and their absorption and EPR spectra at various pH values are reported. The visible spectra exhibit a characteristic red shift and a shoulder at lower energies indicating a five-coordinate structure of the formed complexes. The change of the EPR spectral parameters as a function of pH reflects two modes of an equatorial-axial chelation by aminohydroxamic acid ligand L in [Cu(dien)(HL)] 2+ and [Cu(dien)(L)] + species, while the diethylenetriamine nitrogens are coordinated at three equatorial positions in each case. α-Alaha is a more effective chelating ligand than β-Alaha in the Cu 2+ -dien-L ternary system. This is reflected in the much higher basicity-adjusted stability constants, logK Cudien)(α-Alaha)(β-Alaha) ∑pK H .

Potentiometric and spectroscopic studies of the cobalt(II), nickel(II) and manganese(II) complexes with some aminodiphosphonic acids in aqueous solution

Abstract The stoichiometries and stability constants of the manganese(II), cobalt(II) and nickel(II) complexes with seven aminodiphosphonates [RN(CH 2 PO 3 H 2 ) 2 , L] containing iminomethylenephosphonate moieties have been determined pH-metrically at 25°C and at an ionic strength of 0.20 mol dm −3 (KCl). The results suggest for L= 1 – 6 only equimolar species: [M(H 2 L)], [M(HL)] − , [ML] 2− and hydroxo [MH −1 L] 3− , in the pH range of 3–11.5, the only difference is the presence of an additional [M(H 3 L)] + species at low pH for N -3-picolyliminodi(methylenephosphonic) acid. For L= 7 the models contain protonated and non-protonated 1:2 species. From the comparative analysis of the stability and the spectroscopic (UV–VIS) data it has been established that the ligands coordinate to the metal ions only by the phosphonate group(s) in a monodentate or bidentate manner. The LMCT bands from O − (PO 3 2− ) to Ni 2+ are at 222–211 nm.

Potentiometric and spectroscopic studies of binary and ternary copper(II) complexes with histidinehydroxamic acid

Abstract Because the results concerning the Cu(II)-histidinehydroxamic acid (Hisha) system are somewhat controversial, we have performed a new study of the Cu(II)-Hisha binary system, using potentiometry and e.p.r. techniques. Since the occurrence of ternary complexes in natural systems is very probable, we have also undertaken potentiometric and spectroscopic studies of the Cu(II)-Hisha-His ternary system, where His is histidine.

Potentiometric and spectroscopic study of mixed-ligand copper(II) complexes with N,N,N′,N″,N″-pentamethyldiethylenetriamine and α- (or β-) alaninehydroxamic acids in water solution

Abstract Stabilities of the mixed-ligand complexes of Cu2+ ion with N,N,N′,N″,N″-pentamethyldiethylenetriamine [N,N,N′,N″,N″-pentamethyl-{bis(2-aminoethyl)amine}, Me5dien] as a primary ligand and α-alaninehydroxamic acid [2-amino-N-hydroxypropanamid, α-Alaha] or β-alaninehydroxamic acid [3-amino-N-hydroxypropanamid, β-Alaha] as a secondary ligand L and their absorption and EPR spectra at various pH values are reported. The visible spectra exhibit a characteristic red shift and a shoulder at lower energies indicating a five-coordinate structure of the formed complexes. The change of the EPR spectral parameters as a function of pH reflects two modes of an equatorial–axial chelation by the aminohydroxamic acid ligand L in the [Cu(Me5dien)(HL)]2+ and [Cu(Me5dien)(L)]+ species.

Potentiometric and proton NMR studies on zinc(II)-aminohydroxamic acids

Abstract Potentiometric and NMR studies on Zn(II) ions interaction with alaninehydroxamic acid, leucinchydroxamic acid, sarcosinehydroxamic acid, and histidinehydroxamic acid have shown that metal ion initiates its coordination with two oxygens of the hydroxamic group. The deprotonation of the amino group leads to formation of dinuclear species Zn2L3 in the case of the three former ligands and the tridentate coordination involving side-chain imidazole nitrogen in the case of histidine derivative. The formed complexes are very stable although in very basic solutions the hydroxy-species may be formed.