Imre Labádi

Chloroplastic glutamine synthetase is activated by direct binding of aluminium

Acidification of soils may release water soluble, toxic aluminium species from clay minerals. Al interferes with a wide range of physical and cellular processes. Glutamine synthetase (GS, EC 6.3.1.2) is the key enzyme of primary N assimilation, as well as ammonia reassimilation and detoxification. Plant GS requires two magnesium ions per subunit for activity, which makes GS a potential target of metal stress. The objective of this investigation was to prove that Al from an organic metal complex is able to activate GS, and Al becomes bound to the polypeptide structure of the GS molecule. Aluminium(III)-nitrilotriacetic acid complex (Al(III)NTA) activated the GS prepared from wheat (Triticum aestivum L.) leaves, as Al(3+) did in vivo, but could not functionally substitute magnesium ions, which were also necessary for the activity in the in vitro GS assay. GS2 was isolated by non-denaturing polyacrylamide gel electrophoresis, and the Al and Mg content of the enzyme was determined by inductively coupled plasma atomic emission spectroscopy. The GS octamer remained intact and contained Mg(2+) bound to its specific sites after the electrophoretic separation. Al was detected in the Al(III)NTA-treated sample bound to the structure of the enzyme protein, potentially occupying one of the specific metal-binding sites of the subunits. Our results indicate that the activatory effect of the Al(III)NTA complex is because of specific binding of aluminium to the polypeptide chain of GS2, however presence of magnesium at least on one of the metal-binding sites is essential to the active state of the enzyme.

Superoxide dismutase activity of a Cu–Zn complex—bare and immobilised

A binuclear, imidazolato-bridged complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(aminoethyl)amine perchlorate) was prepared and immobilised on silica gel or among the layers of montmorillonite. Immobilisation occurred via hydrogen bonding for the silica gel and through electrostatic forces for the montmorillonite. The obtained substances were characterised by EPR and FT-IR spectroscopies and their thermal behaviour was studied by thermogravimetry. The superoxide dismutase (SOD) activity of the complex before and after immobilisation was studied by a SOD assay. It was found that the SOD activity of the host-free complex increased by more than an order of magnitude and approached the efficiency of the real enzyme when silica gel was used as host. The enhanced activity could be assigned to the formation of magnetically isolated centers in the silica pores. On the other hand, the immobilisation with montmorillonite slightly reduced the SOD activity.

Montmorillonite intercalated Cu(II)-histidine complex- synthesis, characterisation and superoxide dismutase activity

Cu(II)-L-histidine complex was prepared between the layers of montmorillonite by introducing the Cu 2+ ions by ion exchange first, then allowing complexation by adding the ligand molecules to the suspension of the host. Structural characterisation was performed by FT-IR and EPR spectroscopies and thermal analysis. Two types of intercalated complex were identified: mainly pentacoordinated complex was formed with the Cu 2+ ions coordinating to skeletal oxygens of the host accompanied by small amount of tetracoordinated complex anchored to the host via hydrogen bond through a COO − — skeletal OH interaction. The montmorillonite intercalated complexes displayed superoxide dimutase activity. Although it was lower than that of the host-free complex, the host-guest substance could be easily separated from the reaction mixture and could be used several times without significant loss of activity.

Lanthanide complexes of ethylenediaminotetramethylene-phosphonic acid

Ethylenediaminotetramethylenephosphonic acid (EDTMP, H8L) was prepared and its complexes with some lanthanide ions (La, Eu, Gd and Sm) were isolated under various conditions. IR spectra and thermal stabilities of EDTMP and its complexes were studied. The experimental conditions of the preparation influence to the composition of the complexes were shown. In alkaline solution (pH=8) deprotonated (P(O)(O−)2), and in acidic solution (pH=3–4) deprotonated and partly protonated (P(O)(O−)(OH)) and non-protonated (P(O)(OH)2) phosphonic groups are present in the complexes. All the complexes contain coordinated water molecules. The complexes containing a protonated phosphonic group contain coordinated and hydrogen-bonded water molecules.

Superoxide dismutase mimicking Cu(II)-mixed amino acid complexes covalently grafted onto silica gel--an FT-IR study.

AbstractOur recent work concerning the synthesis, characterisation and testing of bioinspired electron transfer catalysts is described in this contribution. The catalysts were various Cu(II) complexes having mixed C- or N-protected amino acids (l-histidine and l-tyrosine) as ligands covalently grafted onto surface-modified silica gel. The resulting materials were structurally characterised by FT-IR spectroscopy, and their superoxide dismutase activities were tested. The covalently anchored Cu(II) complexes displayed appreciable activities in the test reaction; thus, they may be considered as promising candidates as durable electron transfer catalysts approaching the efficiency of the enzyme mimicked. FigureAlthough the active site mimicking, covalently anchored Cu-mixed amino acid complexes are less effective catalysts than the superoxide dismutase enzyme, but they can work under harsh experimental conditions as well

Mimicking catalase and catecholase enzymes by copper(II)-containing complexes

An imidazolate-bridged copper(II)-zinc(II) complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(2-aminoethyl)amine perchlorate (denoted as “Cu,Zn complex”) and a simple copper(II) complex (Cu(II)-tris(2-aminoethyl) amine chloride (“Cu-tren”) were prepared and immobilised on silica gel (by hydrogen or covalent bonds) and montmorillonite (by ion exchange). The immobilised substances were characterised by FT-IR spectroscopy and their thermal characteristics were also studied. The obtained materials were tested in two probe reactions: catalytic oxidation of 3,5-di-tert-butyl catechol (DTBC) (catecholase activity) and the decomposition of hydrogen peroxide (catalase activity). It was found that the catecholase activity of the Cu,Zn complex increased considerably upon immobilization on silica gel via hydrogen bonds and intercalation by ion exchange among the layers of montmorillonite. The imidazolate-bridged copper(II)-zinc(II) complex and its immobilised versions were inactive in hydrogen peroxide decomposition. The Cu(II)-tris(2-aminoethyl)amine chloride complex displayed good catalase activity; however, immobilisation could not improve it.

Modeling superoxide dismutase: Immobilizing a Cu−Zn complex in porous matrices and activity testing in H2O2 decomposition

A bimetallic bridged complex, the Cu(II)-diethylene-triamino- μ -imidazolato-Zn(II)- tris -aminoethylamine triperchlorato complex, was prepared and immobilized in A1MCM-41 and montmorillonite. The host-guest materials were intended to be superoxide dismutase mimics, however, only the complex intercalated in montmorillonite proved to be active in oxygen transfer reaction. The inability of the complex immobilized in A1MCM-41 to decompose an aqueous solution of H 2 O 2 might be due to diffusional constraints exerted on the reactants and/or the products by the relatively more regulated environment of molecular sieve than that of the layered clay.

Mixed-Ligand Complexes of Co(II) and Cu(II) with Pyrazoeon1C Mannich Bases and 2-aminobenzothiazole

Abstract Mixed-ligand complexes of the type M2L(TAB)nX4 [L = N,N′-bis(4-antipyryl-methyl)piperazine (BAMP), or N,N′-tetra(4-antipyrylmethyl)-l,2-diaminoethane (TAMEN) and 2-aminobenzothiazole (TAB), X - NCS or CIO4, M - Co, n - 2, or M - Cu, n = 4] were synthesized and investigated. The IR and Raman spectra revealed that the ligands L are coordinated through the carbonyl oxygen atom of the antipyrine and the nitrogen atom of the piperazine or 1,2-ethanediaminc bridge, except in Cu2(TAMEN)(TAB)4(ClO4)4, in which case TAMKN is coordinated to the metal only through the carbonyl oxygen. Steric considerations explain the bonding of TAB through the exocyclic or endocyclic nitrogen.

Preparation and characterization of Mg(II)-, Ca(II) and Cd(II) complexes of 1,2-ethanediol and water

Mixed ligand complexes of different compositions were prepared with water, sulfate ion and 1,2-ethanediol as ligand. IR spectra and the thermoanalytical curves of the complexes were recorded. Oxygen atoms bound by one or two coordinate bonds to the metal ion, or by hydrogen-bonds in the crystal, were observed. As for the water molecule, 1,2-ethanediol molecules of ‘crystal’ and ‘monohydrate’ type were found, depending on the type of binding of the oxygen atoms.

SYNTHESIS, CHARACTERIZATION, AND THERMAL STUDIES OF NEW TETRANUCLE AR OXOVANADIUM(IV)-COPPER(II) COMPLEXES CONTAINING OXALATE AND SULFIDE AS BRIDGING LIGANDS

ABSTRACT The new sulfide bridged-polynuclear complexes Cu2(VO)4- (C2O4)4S2L4ċnH2O, where for L=1, 10-phenanthroline, n=5 and for L=2, l0-bipyridine, n=7, have been synthesized and characterized by elemental and thermal analyses, electronic and IR spectroscopy. These data as well as magnetic moments and EPR spectra strongly support a structure in which four [VO(L)(C2O4)(H2O)] units act as ligands toward the two copper(II) centers through the oxalate anion. Each of the oxalate anions act as a tridentate ligand and the core of the complexes involve a copper-sulfide-copper moiety.