Iron(III)- and copper(II) complexes of an asymmetric, pentadentate salen-like ligand bearing a pendant carboxylate group

The equilibrium and solution structural properties of the iron(III) and copper(II) complexes of an asymmetric salen-like ligand (N,N'-bis(2-hydroxybenzyl)-2,3-diamino-propionic acid, H(3)bhbdpa) bearing a pendant carboxylate group were characterized in aqueous solution by potentiometric, pH-dependent electron paramagnetic resonance (EPR) and UV-Vis (UV-Visible) measurements. In the equimolar systems the pentadentate ligand forms very stable, differently protonated mononuclear complexes with both metal ions. In the presence of iron(III) {NH, PhO(-), COO(-)}, {2NH, 2PhO(-), COO(-)} and {2NH, 2PhO(-), COO(-), OH(-)} coordinated complexes are dominant. The EPR titrations reflected the presence of microscopic complex formation pathways, leading to the formation of binding isomers in case of Cu(H(2)bhbdpa)(+), Cu(Hbhbdpa) and Cu(bhbdpa)(-). The {2NH, 2PhO(-)+COO(-)/H(2)O} coordinated Cu(bhbdpa) is the only species between pH 6-11. At twofold excess of metal ion dinuclear complexes were detected with both iron(III) and copper(II). In presence of iron(III) a mu-carboxylato-mu-hydroxo-bridged dinuclear complex (Fe(2)(bhbdpa)(OH)(3)) is formed from Fe(H(2)bhbdpa)(2+) through overlapping proton release processes, providing one of the rare examples for the stabilization of an endogenous carboxylate bridged diiron core in aqueous solution. The complex Cu(2)(bhbdpa)(+) detected in the presence of copper(II) is a paramagnetic (S=1) species with relatively weakly coupled metal ions.     

Potentiometric study of vitamin D3 complexes with manganese(II), iron(II), iron(III) and zinc(II) in water-ethanol medium.

Vitamin D3 (LH) complexes with manganese(II), iron(II), iron(III) and zinc(II) were identified in water-ethanol medium (30/70). Their stability constants were determined at 298 K and at a constant ionic strength of 0.100 M using potentiometric methods. The computerisation of the experimental data showed the presence of ML (M = metal, L = deprotonated vitamin D3) and ML2 species in all cases; in addition, the ML3 iron(III) complex was detected. The calculated overall stability constants beta for MnIIL, FeIIL, FeIIIL and ZnIIL are, respectively, in logarithms, 12.4, 16.5, 28.5 and 16.5. Under the experimental conditions, the only protonated species MLH detected was with iron(III).     

Synthesis and characterization of a series of new mixed ligand complexes of manganese(III), iron(III), nickel(II), copper(II) and zinc(II) with schiff bases of N,N-diethylamino-dithiocarbamate as ligands

Twenty new bioactive complexes of Mn(III), Fe(III), Ni(II), Cu(II) and Zn(II) have been prepared containing Schiff bases of N,N-diethylaminodithio- carbamate as ligands. These complexes have been characterized by elemental analyses, IR and UV-Vis spectroscopy as well as by magnetic susceptibility measurements. The spectra of the complexes suggest that the ligands are coordinated to the metal ions via the sulfur atoms of the dithiocarbamato group.     

Interaction between iron(II) and hydroxamic acids: oxidation of iron(II) to iron(III) by desferrioxamine B under anaerobic conditions

Interaction between iron(II) and acetohydroxamic acid (Aha), alpha-alaninehydroxamic acid (alpha-Alaha), beta-alaninehydroxamic acid (beta-Alaha), hexanedioic acid bis(3-hydroxycarbamoyl-methyl)amide (Dha) or desferrioxamine B (DFB) under anaerobic conditions was studied by pH-metric and UV-Visible spectrophotometric methods. The stability constants of complexes formed with Aha, alpha-Alaha, beta-Alaha and Dha were calculated and turned out to be much lower than those of the corresponding iron(II) complexes. Stability constants of the iron(II)-hydroxamate complexes are compared with those of other divalent 3d-block metal ions and the Irving-Williams series of stabilities was found to be observed. Above pH 4, in the reactions between iron(II) and desferrioxamine B, the oxidation of the metal ion to iron(III) by the ligand was found. The overall reaction that resulted in the formation of the tris-hydroxamato complex [Fe(HDFB)]+ and monoamide derivative of DFB at pH 6 is: 2Fe2+ + 3H4DFB+ = 2[Fe(HDFB)]+ + H3DFB-monoamide+ + H2O + 4H+. Based on these results, the conclusion is that desferrioxamine B can uptake iron in iron(III) form under anaerobic conditions.     

Metal--glutathione interaction in aqueous solution. Nickel(II), cobalt(II) and copper(II) complexes with oxidized glutathione.

The interaction of copper(II), nickel(II) and cobalt(II) ions with oxidized glutathione in aqueous solutions have been examined by spectroscopic methods. Cu(II) is the only ion which interacts with disulphide bridge and forms dimeric species containing the Cu(II)-S-S-Cu(II) unit. Ni(II) and Co(II) bind mainly with the terminal NH2 and COO- groups of glutamic acid, and the complexes formed are of nearly octahedral symmetry. At high pH, in the Co(II)-GSSG solution Co(II) is oxidized to Co(III) with the concomitant reduction of GSSG to GSH. Considerable differences were observed between the oxidized and reduced form of glutathione in the coordination ability towards metal ions.     

Antimicrobial, spectral, magnetic and thermal studies of Cu(II), Ni(II), Co(II), UO(2)(VI) and Fe(III) complexes of the Schiff base derived from oxalylhydrazide

The Schiff base ligand, oxalic bis[(2-hydroxybenzylidene)hydrazide], H(2)L, and its Cu(II), Ni(II), Co(II), UO(2)(VI) and Fe(III) complexes were prepared and tested as antibacterial agents. The Schiff base acts as a dibasic tetra- or hexadentate ligand with metal cations in molar ratio 1:1 or 2:1 (M:L) to yield either mono- or binuclear complexes, respectively. The ligand and its metal complexes were characterized by elemental analyses, IR, (1)H NMR, Mass, and UV-Visible spectra and the magnetic moments and electrical conductance of the complexes were also determined. For binuclear complexes, the magnetic moments are quite low compared to the calculated value for two metal ions complexes and this shows antiferromagnetic interactions between the two adjacent metal ions. The ligand and its metal complexes were tested against a Gram + ve bacteria (Staphylococcus aureus), a Gram -ve bacteria (Escherichia coli), and a fungi (Candida albicans). The tested compounds exhibited high antibacterial activities.     

Complexation of the fungal metabolite tenuazonic acid with copper (II), iron (III), nickel (II), and magnesium (II) ions

Tenuazonic acid (TA) is a phytotoxin produced by a fungal pathogen of rice, Pyricularia oryzae. We have synthesized and characterized the metal complexes of TA with copper (II), iron (III), nickel (II), and magnesium (II). The stoichiometry of the complexes determined by microanalysis and mass spectroscopy (D/CI) are Cu(II)TA2, Fe(III)TA3, Ni(II)TA2, and Mg(TA)2. Voltammograms of Fe(III)TA3, and Cu(II)TA2 in methanolic solutions confirmed this stoichiometry. Ni(II)TA2 paramagnetism and visible absorption data suggest an octahedral geometry. Fe(III)TA3 showed a characteristic visible absorption at 450 nm. Addition of Fe(III)Cl3 and Mg(II)Cl2 did not reverse the toxicity of NaTA to rice and bacterial cells, showing that this toxicity is not due to the privation of the cells of these metals essential for cell growth.     

Iron transfer from urate-Fe(III) to citrate and ATP.

1. Urate, citrate and ATP, which form stable complexes with ferric ions, are proposed to function as low mol. wt iron binding agents in humans. 2. Citrate and ATP were found to readily take up iron from the urate-Fe(III) complex; the study suggests that citrate and ATP may be physiologically more important iron binding agents than urate.     

Antimicrobial,spectral, magnetic and thermal studies of Cu(II), Ni(II), Co(II), UO2(VI) and Fe(III) complexes of the Schiff base derived from oxalylhydrazide

The Schiff base ligand, oxalic bis[(2-hydroxybenzylidene)hydrazide], H₂L, and its Cu(II), Ni(II), Co(II), UO₂(VI) and Fe(III) complexes were prepared and tested as antibacterial agents. The Schiff base acts as a dibasic tetra- or hexadentate ligand with metal cations in molar ratio 1:1 or 2:1 (M:L) to yield either mono- or binuclear complexes, respectively. The ligand and its metal complexes were characterized by elemental analyses, IR, ¹H NMR, Mass, and UV-Visible spectra and the magnetic moments and electrical conductance of the complexes were also determined. For binuclear complexes, the magnetic moments are quite low compared to the calculated value for two metal ions complexes and this shows antiferromagnetic interactions between the two adjacent metal ions. The ligand and its metal complexes were tested against a Gram + ve bacteria (Staphylococcus aureus), a Gram -ve bacteria (Escherichia coli), and a fungi (Candida albicans). The tested compounds exhibited high antibacterial activities.     

Synthesis of rhodium(III), iridium(III) and osmium(III) complexes with tris(2-aminoethanethiolato)cobalt(III)

Polynuclear sulfur bridged complexes where the neutral complex tris(2-aminoethanethiolato)cobalt(III) acts as a tridentate ligand to rhodium(III), iridium(III) and osmium(III) have been prepared. These complexes have been characterized by electronic spectroscopy, vibrational spectroscopy and nuclear magnetic resonance spectroscopy. Along with the previously prepared complexes of iron(III), ruthenium(III) and cobalt(III), these complexes form two series of complexes with the group 8 and group 9 elements from all three transition series.     

Reaction of iron(III)-polyaminocarboxylate complexes with hydrogen peroxide: Correlation between ligand structure and reactivity

Reactions of iron(III) complexes with five polyaminocarboxylates and hydrogen peroxide in an alkaline solution were investigated. Iron(III) complexes of which the ring including two nitrogen and iron atoms is five-membered formed a well-known stable side-on peroxo adduct. On the other hand, iron(III) complexes which have a six-membered ring formed a short-lived side-on peroxo adduct and then changed to iron(II) complex and superoxide. Electrochemical measurements showed that the redox potentials of the iron complexes having a six-membered ring are higher than those of the complexes having a five-membered ring. These results indicate that the chelate size is an important factor for tuning the redox potential of the iron center and for the reactivity toward hydrogen peroxide.     

Metalloantibiotics: synthesis and antibacterial activity of cobalt(II), copper(II), nickel(II) and zinc(II) complexes of kefzol

Kefzol (kzl), a beta-lactam antibiotic, possesses various donor sites for interaction with transition metal(II) ions [Co(II), Cu(II), Ni(II) and Zn(II)] to form complexes of the type [M(kzl)2]Cl2 and [M(kzl)Cl], with molar ratio of metal: ligand (M:L) of 1:2 and 1:1 respectively. These complexes were prepared and characterized by physicochemical and spectroscopic methods. Their IR and NMR spectra suggest that kefzol potentially acts as a bidentate, tridentate as well as monoanionic tetradentate ligand. The complexes have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus mirabilis. The metal complexes were found to be more potent against one or more bacterial species than the uncomplexed kefzol.     

Potentiometric and spectrophotometric equilibrium study on Fe(III) and new catechol-bisphosphonate conjugates

The coordination properties of mixed catechol-bisphosphonates towards Fe(III) are presented. From the potentiometric and spectroscopic results it was possible to state that iron coordination takes place only on the bisphosphonate moiety at acidic pH, and involves both catechol and bisphosphonate groups on two different iron(III) ions at higher pH values. Steric constracts keep both groups from chelating the same metal ion. Quantum mechanical calculations confirm this statement and allow to determine the minimum length of the linker for a stable conformation of complexes in which the same iron(III) ion is coordinated by both catechol and bisphosphonate.     

Coordination mode of adenosine 5'-diphosphate in ternary systems containing Cu(II), Cd(II) or Hg(II) ions and polyamines

The interactions of adenosine 5'-diphosphate (ADP) with some polyamines (PA) (1,3-diaminopropane (tn), 1,4-diaminobutane (Put), 1,7-diamino-4-azaheptane (3,3-tri) and 1,8-diamino-4-azaoctane (Spd)) both in presence and in the absence of metal ions (Cu(II), Cd(II) and Hg(II)) have been studied. In the metal-free systems the formation of adducts (ADP)Hx(PA) has been observed, in which the main reaction centres are the endocyclic nitrogen atoms of the purine ring, the phosphate group of the nucleotide and the protonated nitrogen atoms of the polyamine. The effectiveness of the phosphate group in formation of adducts has been found to decrease in the series Put > Spd > Spm and to be lower than in the reactions with shorter homologues of biogenic amines. In the ternary systems with metal ions the formation of molecular complexes (ML L' type) has been evidenced in which the protonated polyamine interacts with the nitrogen atoms N(1) or N(7) of the purine ring of the nucleotide. In the ternary systems Cu(II)/ADP/polyamine the coordination dichotomy observed in the binary system Cu(II)/ADP disappears. In the systems with Hg(II) ions the pH range of the dichotomy is extended, while for the systems Cd(II)/ADP/polyamine no changes of the range relative to the binary system Cd(II)/ADP have been noted.     

Heterogenized polymetallic catalysts Part II. Oxidation of 3,5-di-t-butylphenol by Cu(II), Fe(III) and Pd(II) complexed to a polyphenylene polymer containing ß-di- and triketone surface ligands; an improved catalyst system

Polyphenylene polymer preparation involves the cyclic trimerization polymerization of acetylated methyl benzoate with diacetyl benzene. Since the methyl benzoate groups do not take part in the polymerization they are present in high concentration. The ß-diketone ligands were placed on the surface by reaction of the methylbenzoate group with base and a methyl ketone and the triketone by reaction with base to give the ß-triketone. The ß-triketones can bind two metal ions in a known geometry that is suitable for bimetallic catalysis of the rapid polyelectron oxidation of catechols. The final catalytic surfaces were prepared by treating the chemically modified polymer with copper(II), iron(II) and palladium(II) acetonitrile complexes with non-coordinating BF₄⁻ as the anion. Since the metal ions contain no strongly coordinating ligand, they are very reactive species. These surfaces catalyzed the rapid air oxidation of 3,5-di-tert-butylcatechol (DTBC). The diketone surfaces gave only 3,5-di-tert-butyl-o-quinone (DTBQ) while the triketone surfaces gave ring-cleaved products, confirming the special catalytic effect of the triketone surface. Also, only the triketone catalysts showed any activity for ring cleavage oxidation of DTBQ. These catalysts were much more reactive than previous ones using the same polyphenylene polymer but without the methyl benzoate groups. With these polymers the di- and triketone groups were placed on the surface by chemical modification of the unpolymerized acetyl groups.     

Metalloantibiotics: Synthesis and Antibacterial Activity of Cobalt(II), Copper(II), Nickel(II) and Zinc(II) Complexes of Kefzol

Kefzol (kzl), a β-lactam antibiotic, possesses various donor sites for interaction with transition metal(II) ions [Co(II), Cu(II), Ni(II) and Zn(II)] to form complexes of the type [M(kzl)2]Cl2 and [M(kzl)Cl], with molar ratio of metal: ligand (M:L) of 1:2 and 1:1 respectively. These complexes were prepared and characterized by physicochemical and spectroscopic methods. Their IR and NMR spectra suggest that kefzol potentially acts as a bidentate, tridentate as well as monoanionic tetradentate ligand. The complexes have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus mirabilis. The metal complexes were found to be more potent against one or more bacterial species than the uncomplexed kefzol.     

Free metal ion depletion by "Good's" buffers. III. N-(2-acetamido)iminodiacetic acid, 2:1 complexes with zinc(II), cobalt(II), nickel(II), and copper(II); amide deprotonation by Zn(II), Co(II), and Cu(II)

Potentiometric, visible, infrared, electron spin, and nuclear magnetic resonance studies of the complexation of N-(2-acetamido)iminodiacetic acid (H2ADA) by Ca(II), Mg(II), Mn(II), Zn(II), Co(II), Ni(II), and Cu(II) are reported. Ca(II) and Mg(II) were found not to form 2:1 ADA2- to M(II) complexes, while Mn(II), Cu(II), Ni(II), Zn(II), and Co(II) did form 2:1 metal chelates at or below physiological pH values. Co(II) and Zn(II), but not Cu(II), were found to induce stepwise deprotonation of the amide groups to form [M(H-1ADA)4-(2)]. Formation (affinity) constants for the various metal complexes are reported, and the probable structures of the various metal chelates in solution are discussed on the basis of various spectral data.     

Metalloantibiotics: synthesis, characterization and in-vitro antibacterial studies on cobalt (II), copper (II), nickel (II) and zinc (II) complexes with cloxacillin

The synthesis and characterization of cloxacillin (clox) complexes with divalent metal ions [Co (II), Cu (II), Ni (II) and Zn (II)] is described. The nature of bonding of the chelated cloxacillin and the structures of the metal complexes have been elucidated on the basis of their physical and spectroscopic data. In all the complexes, the cloxacillin acts as a uninegatively charged bidentate ligand with coordination involving the carboxylate-O and endocyclic-N of the beta-lactam ring. The new compounds have been screened for in-vitro antibacterial activity against Escherichia coli (a), Klebsiella pneumonae (b), Proteus mirabilis (c), Pseudomonas aeruginosa (d), Salmonella typhi (e), Shigella dysentriae (f), Bacillus cereus (g), Corynebacterium diphtheriae (h), Staphylococcus aureus (j) and Streptococcus pyogenes (k) bacterial strains. The brine shrimp bioassay was also carried out to study their in-vitro cytotoxic properties. All compounds, respectively, showed a promising activity (90%) against five bacterial species at 10 microg/ml concentration and a significant activity (52%) against the same test bacteria at 25 microg/ml concentration.     

Coordination abilities of piperyd-1-yl-methane-1,1-diphosphonic acids towards zinc(II), magnesium(II) and calcium(II): potentiometric and NMR studies

The combination of the pH-metric and NMR studies is used to examine the stabilities and coordination modes as well as related structural aspects of zinc(II), magnesium(II) and calcium(II) complexation to piperyd-1-yl-methane-1,1-diphosphonic acid (1) and its derivatives containing a topologically modified piperidine ring (2-7). The studied compounds coordinate metal ions exclusively via the phosphonate functions with a nitrogen atom remaining protonated over the whole range of studied pH. Compounds 1-6 readily form soluble multinuclear complexes of type [M(3)(HL)(2)] and [M(3)(HL)(3)](3-) with Zn(2+) or [M(2)(H(2)L)(2)] with Ca(2+) and Mg(2+). These species are formed based on dimers consisting of two head-to-head arranged molecules linked by strong symmetrical hydrogen bonds. The placement of the two methyl groups at 2- and 6-positions on the piperidine ring precludes the molecular recognition via similar hydrogen bonds and accounts for different complexation properties of 7 compared to 1-6. The role that the metal coordination plays on conformation dynamics in 1-7 is also discussed.     

Hg(II)-coordination by sugar-acids: role of the hydroxy groups

A solution study on the ability of some derivatised sugars [glucuronic acid (GluA), galacturonic acid (GalA) and glucosaminic acid (GlNA)] to complex the Hg(II) ion is reported. The stability constants of the complex species were determined by potentiometric measurements while (1)H NMR experiments allow to define the coordination sites of sugar molecules. GluA coordinates the metal ion through the carboxylic oxygen and the O-4 hydroxyl group and is found to form more stable complexes with respect to GalA in which metal ligation is from the carboxylic oxygen and the O-5 ring oxygen. GlNA forms stable complexes chelating Hg(II) ion through carboxylic oxygen and the alpha-amino group. The ternary 2,2'-bipyridine containing systems were also investigated by means of potentiometric studies. The ML(2) complexes were also isolated in the solid state and characterised by IR spectroscopy.