Nickel(II) binding to Cap43 protein fragments

Cap43 protein has been tested for metal binding domains. The protein, specifically induced by nickel compounds in cultured human cells, had a new mono-histidinic motif consisting of 10 amino acids repeated three times in the C-terminus. The 20-Ac-TRSRSHTSEG-TRSRSHTSEG (Thr(341)-Arg-Ser-Arg-Ser-His(346)-Thr-Ser-Glu-Gly-Thr-Arg-Ser-Arg-Ser-His(356)-Thr-Ser-Glu-Gly(360) - peptide 1) and the 30-Ac-TRSRSHTSEG-TRSRSHTSEG-TRSRSHTSEG (Thr(341)-Arg-Ser-Arg-Ser-His(346)-Thr-Ser-Glu-Gly-Thr-Arg-Ser-Arg-Ser-His(356)-Thr-Ser-Glu-Gly-Thr-Arg-Ser-Arg-Ser-His(366)-Thr-Ser-Glu-Gly(370) - peptide 2) amino acids sequence has been analyzed as a site for Ni(II) binding. A combined pH-metric and spectroscopic (UV-visible, CD, NMR) studies of Ni(II) binding to both fragments were performed. The 20-amino acid peptide can bind one and two metal ions while the 30-amino acid fragment one, two and three metal ions. At physiological pH, depending on the metal to ligand molar ratio, peptide 1 forms the Ni(2)L species while peptide 2 the NiL, Ni(2)L and Ni(3)L complexes where each metal ion is coordinated to the imidazole nitrogen atom of the histidine residue of the 10-amino acid fragment. Octahedral complexes at pH 8-9 and planar 4N complexes with (N(Im), 3N(-)) bonding mode at pH above 9, are formed. This work supports the existence of an interesting binding site at the COOH-terminal domain of the Cap43 protein.     

Complexes of Ni(II) and Cu(II) with ofloxacin. Crystal structure of a new Cu(II) ofloxacin complex

Several coordination compounds formed between Ni(II) or Cu(II) with ofloxacin have been synthesised and characterised. According to elemental chemical analysis and FT-IR spectroscopy data, direct reaction of Ni(II) and Cu(II) salts with ofloxacin leads to formation of precipitates for which mass spectrometry demonstrates their polymeric nature. However, crystalline [Cu(oflo)2(H2O)].2H2O is formed if the reaction is carried out in the presence of ammonia. This complex crystallises in the triclinic system, space group P-1 with a=9.2887(12), b=11.2376(14), c=17.874(2) A, alpha=92.12(3), beta=95.39(3), gamma=91.71(3) degrees and Z=2. The local geometry around the Cu(II) ion is a slightly distorted square base pyramid. Electronic spectra, magnetic susceptibility measurements and EPR spectra of the synthesised complexes indicate a tetragonal environment.     

Thermodynamic and spectroscopic study of Cu(II) and Ni(II) binding to bovine serum albumin

The thermodynamics of Cu(II) and Ni(II) binding to bovine serum albumin (BSA) have been studied by isothermal titration calorimetry (ITC). The Cu(II) binding affinity of the N-terminal protein site is quantitatively higher when the single free thiol, Cys-34, is reduced (mercaptalbumin), compared to when it is oxidized or derivatized with N-ethylmaleimide. This increased affinity is due predominantly to entropic factors. At higher pH (approximately 9), when the protein is in the basic (B) form, a second Cu(II) binds with high affinity to albumin with reduced Cys-34. The Cu(II) coordination has been characterized by UV-vis absorption, CD, and EPR spectroscopy, and the spectral data are consistent with thiolate coordination to a tetragonal Cu(II), indicating this is a type 2 copper site with thiolate ligation. Nickel(II) binding to the N-terminal site of BSA is also modulated by the redox/ligation state of Cys-34, with higher Ni(II) affinity for mercaptalbumin, the predominant circulating form of the protein.     

The puzzle posed by COMMD1, a newly discovered protein binding Cu(II)

Copper is critically important for cellular metabolism. It plays essential roles in developmental processes, including angiogenesis. The liver is central to mammalian copper homeostasis: biliary excretion is the major route of excretion for ingested copper and serves to regulate the total amount of copper in the organism. An extensive network of proteins manipulates copper disposition in hepatocytes, but comparatively little is known about this protein system. Copper exists in two oxidation states: most extracellular copper is Cu(II) and most, if not all, intracellular copper is Cu(I). Typical intracellular copper-binding proteins, such as the Cu-transporting P-type ATPases ATP7B (Wilson ATPase) and ATP7A (Menkes ATPase), bind copper as Cu(I). Accordingly, the recent discovery that the ubiquitous protein COMMD1 binds Cu(II) exclusively raises the question as to what role Cu(II) may play in intracellular processes. This issue is particularly important in the liver and brain. In humans, Wilson’s disease, due to mutations in ATP7B, exhibits progressive liver damage from copper accumulation; in some Bedlington terriers, mutations in COMMD1 are associated with chronic copper-overloaded liver disease, clinically distinct from Wilson’s disease. It seems unlikely that Cu(II), which generates reactive oxygen species through the Fenton reaction, has a physiological role intracellularly; however, Cu(II) might be the preferred state of copper for elimination from the cell, such as by biliary excretion. We argue that COMMD1 participates in the normal disposition of copper within the hepatocyte and we speculate about that role. COMMD1 may contribute to the mechanism of biliary excretion of copper by virtue of binding Cu(II). Additionally, or alternatively, COMMD1 may be an important component of an intracellular system for utilizing Cu(II), or for detecting and detoxifying it.     

Inter- and intra-octarepeat Cu(II) site geometries in the prion protein: implications in Cu(II) binding cooperativity and Cu(II)-mediated assemblies

Cu(II) binding to the alpha prion protein (alphaPrP) can be both intramolecular and intermolecular. X-ray absorption spectroscopy at the copper K-edge has been used to explore the site geometry under each binding mode using both insoluble polymeric Cu(II).alphaBoPrP-(24-242) (bovine PrP) complexes and soluble Cu(II) complexes of peptides containing one, two, and four copies of the octarepeat. Analysis of the extended region of the spectra using a multiple scattering approach revealed two types of sites differing in the number of His residues in the first coordination shell of Cu(II). Peptides containing one and two-octarepeat copies in sub-stoichiometric Cu(II) complexes showed the direct binding of a single His in accord with crystallographic intra-repeat geometry. Alternatively, the polymeric Cu(II).alphaBoPrP-(24-242) complex and Cu(II) in its soluble complex with a four-octarepeat peptide at half-site-occupancy showed Cu(II) directly bound to two His residues, consistent with an inter-repeat binding mode. Increasing the Cu(II) site occupancy from 0.5 to 0.75 in the peptide containing four octarepeats resulted in spectral features that are intermediate to those of the inter- and intra-repeat modes. The transition from His-Cu-His (inter-repeat) to Cu-His (intra-repeat) on increasing Cu(II) saturation offers a structural basis for the positive cooperativity of the cation binding process and explains the capacity of alphaPrP to participate in Cu(II)-mediated intermolecular interactions.     

Structural characterization of binding of Cu(II) to tau protein

Transition metals have been frequently recognized as risk factors in neurodegenerative disorders, and brain lesions associated with Alzheimer's disease are rich in Fe(III), Zn(II), and Cu(II). By using different biophysical techniques (nuclear magnetic resonance, circular dichroism, light scattering, and microcalorimetry), we have structurally characterized the binding of Cu(II) to a 198 amino acid fragment of the protein Tau that can mimic both the aggregation behavior and microtubule binding properties of the full-length protein. We demonstrate that Tau can specifically bind one Cu(II) ion per monomer with a dissociation constant in the micromolar range, an affinity comparable to the binding of Cu(II) to other proteins involved in neurodegenerative diseases. NMR spectroscopy showed that two short stretches of residues, (287)VQSKCGS (293) and (310)YKPVDLSKVTSKCGS (324), are primarily involved in copper binding, in agreement with mutational analysis. According to circular dichroism and NMR spectroscopy, Tau remains largely disordered upon binding to Cu(II), although a limited amount of aggregation is induced.     

Dinuclear Ni(II) and Cu(II) complexes with indolecarboxamide ligand: Synthesis, structure and properties

A potential tetradentate indolecarboxamide ligand, H₄L³ is synthesized and investigated for its coordination abilities towards Ni(II) and Cu(II) ions. Two H₄L³ ligands in their tetra-deprotonated form [L³]⁴⁻, were found to coordinate two metal centers resulting in the formation of [Ni₂(L³)₂]⁴⁻ (5) and [Cu₂(L³)₂]⁴⁻ (6) complexes. The crystal structure of 6 displays the formation of a dinuclear structure where two fully deprotonated ligands, [L³]⁴⁻ hold two copper(II) ions together. Even more interesting is the fact that both deprotonated ligands, [L³]⁴⁻ coordinate the copper ions in an identical and symmetrical fashion. The Na⁺ cations present in the complex 6 stitch together the dinuclear units resulting in the formation of a coordination chain polymer. Four sodium ions connect two dinuclear units via interacting with the O_amide groups. Further, Na⁺ cations were found to coordinate several DMF molecules; some of them are terminal and a few are bridging in nature. The solution state structure (determined by the NMR spectral analysis) of the diamagnetic complex 5 also supported the fact that two deprotonated ligands, coordinate two nickel ions in an identical and symmetrical fashion. Absorption spectral studies reveal that the solid-state square-planar geometry is retained in solution and both complexes do not show any tendency to coordinate potential axial ligands. The variable-temperature magnetic measurements and EPR spectra indicate spin-spin exchange between two copper centers in complex 6. The electrochemical results for both complexes show three irreversible oxidative responses that correspond to the oxidation of first and second metal ion followed by the ligand oxidation, respectively.     

Thermodynamic and spectroscopic studies of Cu(II) and Ni(II) complexes with a new proline-threonine dipeptide ligand

The interactions between a new proline-threonine dipeptide ligand with two metallic cations were investigated in aqueous solution. The metallic cations studied were the copper(II) and the nickel(II), which are involved in many biological processes. The combination of potentiometry, UV-visible spectrophotometry, EPR, and mass spectrometry was used to determine the formation constants of the complexes and their structure in solution. The complexation sites were identified using electronic absorption and EPR spectroscopies. Copper complexes were obtained as square planar or square pyramidal mononuclear species, whereas nickel complexes were obtained as dinuclear species with an octahedral geometry.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Presence of a poly(A) binding protein and two proteins with cell cycle-dependent phosphorylation in Crithidia fasciculata mRNA cycling sequence binding protein II

Crithidia fasciculata cycling sequence binding proteins (CSBP) have been shown to bind with high specificity to sequence elements present in several mRNAs that accumulate periodically during the cell cycle. The first described CSBP has subunits of 35.6 (CSBPA) and 42 kDa (CSBPB). A second distinct binding protein termed CSBP II has been purified from CSBPA null mutant cells, lacking both CSBPA and CSBPB proteins, and contains three major polypeptides with predicted molecular masses of 63, 44.5, and 33 kDa. Polypeptides of identical size were radiolabeled in UV cross-linking assays performed with purified CSBP II and 32P-labeled RNA probes containing six copies of the cycling sequence. The CSBP II binding activity was found to cycle in parallel with target mRNA levels during progression through the cell cycle. We have cloned genes encoding these three CSBP II proteins, termed RBP63, RBP45, and RBP33, and characterized their binding properties. The RBP63 protein is a member of the poly(A) binding protein family. Homologs of RBP45 and RBP33 proteins were found only among the kinetoplastids. Both RBP45 and RBP33 proteins and their homologs have a conserved carboxy-terminal half that contains a PSP1-like domain. All three CSBP II proteins show specificity for binding the wild-type cycling sequence in vitro. RBP45 and RBP33 are phosphoproteins, and RBP45 has been found to bind in vivo specifically to target mRNA containing cycling sequences. The levels of phosphorylation of both RBP45 and RBP33 were found to cycle during the cell cycle.     

The binding of Mg(II) and Ni(II) to synthetic polynucleotides

Equilibria and kinetics of the interactions of Mg2+ and Ni2+ with poly(U), poly(C) and poly(I) have been investigated at 25 degrees C, an ionic strength of 0.1 M, and pH 7.0 or 6.0. Analogous studies involving poly(A) were reported earlier. All binding equilibria were studied by means of the (usually small) absorbance changes in the ultraviolet range. This technique yields apparent binding constants which are fairly large for the interaction of Ni2+ with poly(A) (K = 0.9 X 10(4) M-1) and poly(I) (K approximately equal to 2 X 10(4) M-1) but considerably lower for the corresponding Mg2+ systems, Mg2+-poly(A) (K = 2 X 10(3) M-1) and Mg2+-poly(I) (K = 280 M-1). Each of the two pyrimidine nucleotides binds both metal ions with about the same strength (K approximately equal to 65 M-1 for poly(U) and K near 600 M-1 for poly(C]. In the case of poly(C) the spectral changes deviate from those expected for a simple binding equilibrium. In addition, the binding of Ni2+ to the four polynucleotides was measured by using murexide as an indicator of the concentration of free Ni2+. The results obtained by this technique agree or are at least consistent with those derived from the ultraviolet spectra. Complications are encountered in the binding studies involving poly(I), particularly at higher metal ion concentrations, obviously due to the formation of aggregated poly(I) species. Kinetic studies of the binding processes were carried out by the temperature-jump relaxation technique. Measurable relaxation effects of time constants greater than 5 microseconds were observed only in the systems Ni2+-poly(A) and Ni2+-poly(I). Such not-too-fast reaction effects are expected for processes which include inner-sphere substitution steps at Mg2+ or Ni2+. The relaxation process in Ni2+-poly(I) is characterized by (at least) four time constants. Obviously, the complicated kinetics again include reactions of aggregated poly(I). The absence of detectable relaxation effects in all other systems (except Mg2+-poly(I), the kinetics of which was not investigated) indicates that inner-sphere coordination of the metal ions to specific sites of the polynucleotides (site binding) does not occur to a significant extent. Rather, the metal ions are bound in these systems mainly by electrostatic forces, forming a mobile cloud. The differences in binding strength which are nevertheless observed are attributed to differences in the conformation of the polynucleotides which result in different charge densities.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.     

Binding abilities of dehydropeptides towards Cu(II) and Ni(II) ions. Impact of Z-E isomerization on metal ion binding

The study on the binding ability of dehydro-tri- and tetrapeptides has shown that the ,β-double bond has a critical effect on the peptide coordination to metal ions. It may affect the binding of the vicinal amide nitrogens by the electronic effect and stabilize the complex due to steric effects. The (Z) isomer is the most effective in stabilizing of the complexes formed. The presence of large side chain in the dehydroamino acid residue may also be critical for the coordination mode in the metallopeptide systems.     

Adsorption of Cu(II), Ni(II) and Zn(II) on modified jute fibres

The potential of a lignocellulosic fibre, jute, was assessed for adsorption of heavy metal ions like Cu(II), Ni(II) and Zn(II) from their aqueous solutions. The fibre was also used as adsorbent after chemically modifying it by two different techniques viz, loading of a dye with specific structure, C.I. Reactive Orange 13, and oxidising with hydrogen peroxide. Both the modified jute fibres gave higher metal ion adsorption. Thus, the dye loaded jute fibres showed metal ion uptake values of 8.4, 5.26 and 5.95 mg/g for Cu(II), Ni(II) and Zn(II), respectively, while the corresponding values for oxidised jute fibres were 7.73, 5.57 and 8.02 mg/g, as against 4.23, 3.37 and 3.55 mg/g for unmodified jute fibres. Adsorption isotherm models indicated best fit for Langmuir model for the modified jute fibres. The adsorption values decreased with lowering of pH. The desorption efficiency, regenerative and reuse capacity of these adsorbents were also assessed for three successive adsorption-desorption cycles. The adsorptive capacity was retained only when the caustic soda regeneration is carried out as an intermediate step after desorption. Possible mechanism has been given.     

E.s.r., visible and SOD studies of imidazolate bridged Cu(2)(II,II), Cu(II)Zn(II) and Cu(II)Ni(II) complexes with pentamethyldiethylenetriamine as capping ligand: a plausible model for superoxide dismutase

X-band e.s.r. and electronic spectra of imidazolate bridged homobinuclear Cu-Cu complex, [(PMDT)Cu-Im-Cu(PMDT)](ClO(4))(3) and heterobinuclear Cu-Zn and Cu-Ni complexes, viz. [(PMDT)Cu-Im-Zn(PMDT)](ClO(4))(3), [(PMDT)Cu-Im-Ni(PMDT)] (ClO(4))(3), where PMDT=pentamethyldiethylenetriamine, Im=Imidazolate ion and related mononuclear complexes, [(PMDT)Cu(OH(2))](2+) and [(PMDT)Cu(ImH)](2+) have been described. Superoxide dismutase activities of these complexes have also been measured.     

Acetazolamide-M(II) [M(II) = Co(II),Ni(II),Cu(II)] complexes with ethylamine, diethylamine, triethylamine, and potassium hidroxide

Complexes of Co(II), Ni(II), and Cu(II) with dideprotonated Acm are synthesized and characterized. Acm acts as bidentate ligand through the N-sulfonamido atom and the N-thiadiazole atom except for K6CoAcm4.6H2O in which Acm behaves as monodentate through the N-sulfonamido atom.     

An investigation of Cu(II) and Ni(II)-catalysed hydrolysis of (di)imines

The reactions of six diimine ligands with Cu(II) and Ni(II) halide salts have been investigated. The diimine ligands were Ph₂CN(CH₂)_nNCPh₂ (n = 2 (Bz₂en, 1a), 3 (Bz₂pn, 1b), 4 (Bz₂bn, 1c)), N,N′-bis-(2-tert-butylthio-1-ylmethylenebenzene)-2,2′diamino-biphenyl (2), N,N′-bis-(2-chloro-1-ylmethylenebenzene)-1,3-diaminobenzene (3) and N,N′-bis-(2-chloro-1-ylmethylenebenzene)-1,2-ethanediamine (4). Reactions of 1a-c, 2-4 with CuCl₂·2H₂O in dry ethanol at ambient temperature led to complete or partial hydrolysis of the diimine ligands to ultimately form copper diamine complexes. The non-hydrolyzed complexes of 1b and 1c, [Cu(L)Cl₂] (L = 1b, 1c), could be isolated when the reactions were carried out at low temperatures, and the half-hydrolyzed complex [Cu(Bzpn)Cl₂] could also be identified via X-ray crystallography. Similarly, reactions of 1a or 1b with NiCl₂·6H₂O or [NiBr₂(dme)] led to rapid hydrolysis of the imines and Ni complexes containing half-hydrolyzed 1a (Bzen; [trans-[Ni(Bzen)₂Br₂]) and 1b (Bzpn; [Ni(Bzpn)Br₂] could be isolated and identified via single crystal X-ray analysis. Kinetic studies were made of the hydrolyses of 1a, 1b in THF and 2 in acetone, in the presence of Cu(II), and of 1a in acetonitrile, in the presence of Ni(II). Activation parameters were determined for the latter reaction and for the copper-catalyzed hydrolysis of 2; the relatively large negative activation entropies clearly indicate rate-determining steps of an associative nature.     

Interaction of water-soluble Cu(II), Ni(II), and Co(III) porphyrins with polynucleotides

The interaction of the Cu(II), Ni(II) and Co(III) complexes of the following six water-soluble cationic porphyrins with calf thymus DNA, poly(dG-dC)2 and poly(dA-dT)2 was studied by UV-visible and resonance Raman spectroscopy: tetrakis(2-N-) and (3-N-methylpyridyl) porphyrin (1, 2); monophenyl-tris(4-N-methylpyridyl)porphyrin (4); cis- and trans-diphenyl-bis (4-N-methylpyridyl)porphyrin (5, 6). The binding to nucleic acids was compared with that of tetrakis(4-N-methylpyridyl)porphyrin (3). If the N(+)-CH3 group is moved from the para (3) to the meta position (2), binding of the free porphyrin as well as that of the metal complexes is only gradually modified; thus, the square-planar Cu- and Ni-2 are intercalated at the G-C site whereas Co-2 is groove-bound at A-T. Additionally, Ni-2 is probably also intercalated at the A-T site. When the N(+)-CH3 group is located at ortho position (1), the high rotation barrier of the 2-N-methylpyridyl group prevents intercalation of Cu- and Ni-1, resulting in weak outside binding. At ionic strength mu = 0.2, there is no evidence of significant interaction of Co-1 with any of the polynucleotides. When the charged N-methylpyridyl groups in 3 are subsequently replaced by phenyl groups (4, 5/6), the tendency of the Cu(II) and Ni(II) complexes to bind to the outside of the helix or to intercalate only partially increases at the expense of full intercalation. The coulombic attraction remains strong, no significant differences can be detected between 3, 4, 5, and 6. Ni-4 binds to poly(dA-dT)2 in the same complicated manner as Ni-3. The outside-binding in Co-4, -5 and -6 differs slightly from that in Co-2 and Co-3.     

Iminodiacetyl-hydroxamate derivatives as metalloproteinase inhibitors: equilibrium complexation studies with Cu(II), Zn(II) and Ni(II)

Two new iminodiacetyl-hydroxamate derivatives, the N-benzyl-N-carboxymethyl-iminoacetohydroxamic acid (H(2)L(1)) and the N-benzyl-N'-hydroxypiperazine-2,6-dione (HL(2)), have been recently reported as very effective inhibitors against a set of zinc-containing matrix metalloproteinases (MMPs). Herein, aimed at understanding that inhibitory function, these compounds are studied in their complex formation equilibria with three biologically relevant first-row transition M(2+) metal ions (M=Cu, Zn, Ni) by using potentiometric and spectroscopic techniques. At physiological conditions, complexation of these metal ions by H(2)L(1) mostly occurs with formation of 1:1 species by tridentate co-ordination (O,N,N) (carboxylate-amino-hydroxamate), whereas complexation with HL(2) mainly involves the formation of 1:2 (M:L) species with normal (O,O) hydroxamate coordination. Moreover, at higher pH, H(2)L(1) is able to form a pentanuclear tetrameric copper complex with an interesting 12-metallacrown-4 structure.