Pentacopper(II) complexes of alpha-aminohydroxamic acids: uranyl-induced conversion of a 12-metallacrown-4 to a 15-metallacrown-5

Effects of uranyl on the pentacopper(II) complexes of alpha-leucinehydroxamic acid and alpha-tyrosinehydroxamic acid were studied in water and methanol by means of electrospray ionisation mass spectrometry (ES-MS), absorption spectrophotometry, circular dichroism spectroscopy and proton NMR spectroscopy. All the measurements were consistent with the complete conversion of a 12-metallacrown-4 to a 15-metallacrown-5 upon addition of one equivalent of the uranyl ion. The uranyl ion is accommodated in the cavity formed by five copper(II) ions and five alpha-aminohydroxamate ligands. The 15-metallacrown-5 inclusion complexes have a high affinity for the uranyl ion. Competition studies showed that even in the presence of a large excess of calcium(II), the 15-metallacrown-5 remained stable, and no exchange reactions between calcium(II) and uranyl were observed. Extraction of uranyl from the 15-metallacrown-5 was also not detected in the presence of a large excess of 18-crown-6. Trivalent lanthanide ions can be partially sequestered by the 15-metallacrown-5, however, even these trivalent ions are displaced by uranyl.     

Study of copper(II) ternary complexes with phosphocreatine and some polyamines in aqueous solution

Ternary systems of Cu(II) with phosphocreatine (PCr) and the polyamines (PAs), ethylenediamine (en), 1,3-diaminopropane (tn), putrescine (Put), spermidine (Spd), and spermine (Spm), were investigated in aqueous solution through potentiometry, ultraviolet-visible, EPR and Raman spectroscopy. The binary complex CuPCr was also studied by Raman spectroscopy, and the calculation of the minimum stabilization energy was done assuming this molecule in aqueous solution. The stability constants of the CuPCrPA ternary complexes were determined by potentiometry (T = 25 °C, I = 0.1 mol L^− 1, KNO₃). The stability order determined was CuPCrSpm > CuPCrSpd > CuPCren > CuPCrtn > CuPCrPut, the same order of the corresponding binary complexes of Cu(II) with these polyamines. The evaluation of intramolecular PA-PCr interactions in protonated and deprotonated species of ternary complexes was carried out using the equation Δlog K = log β_{CuPCrPAHq + p} − (log β_CuPAHq + log β_CuPCrHp). All of the CuPCrPA ternary complexes have a square planar structure and are bonded to PCr through the nitrogen atom of the guanidine group and the oxygen atom of the phosphate group, and to the PAs through two nitrogen atoms of the amine groups. The structure of the complex CuPCrSpm is planar with distortion towards tetrahedral. Calculation of the minimum stabilization energy for the CuPCr and CuPCrenH complexes confirmed the proposed coordination mode.     

Copper(II) complexes of 4-aminobenzoic and 4-aminosalicylic acids

Copper(II) complexes of 4-aminobenzoic (HAB) and 4-aminosalicylic (HAS) acids were prepared and characterized by means of thermal analysis, magnetic measurements, ESR, IR and electronic spectroscopy. Both ligands behave as monodentate (carboxylate bonded) or bridging bidentate (amino and carboxylate bonded) donors yielding two types of complexes having essentially planar CuO₄ and CuN₂O₂ chromophores, respectively.     

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.     

Unusual reactivity of cytotoxic cis-dihydrazide Pt(II) complexes in aqueous solution

Complexes of the general structure cis-[PtX(2)(hydrazide)(2)] and cis-[PtX(2)NH(3)(hydrazide)], where X=Cl(-), Br(-) and I(-), and hydrazide=cyclohexylcarboxylic acid hydrazide (chcah), cyclopentylcarboxylic acid hydrazide (cpcah), 3-aminocyclohexanspiro-5-hydantoin (achsh) and 3-aminocyclopentanspiro-5-hydantoin (acpsh), were investigated with respect to aqueous stability, DNA platination rates and cytotoxic activity on a panel of seven human cancer cell lines as well as a cisplatin-resistant cell line. Stabilities in aqueous solution, determined by RP-HPLC and UV-Vis methods, were highly dependent on the type of halide ligand, with stability decreasing in the order I(-)>Cl(-)>Br(-). Added chloride (100 mM) only stabilized the dichloro-Pt(II) complexes containing the hydrazide as part of a hydantoin ring (i.e., achsh). Platination of calf thymus DNA determined by AAS was most rapid with dichloro-Pt(II) complexes containing achsh ligand. The mixed-amine dichloro-Pt(II) complexes with either chcah or cpcah ligands also platinated DNA >80%, but at a slower rate, while dihydrazide dichloro-Pt(II) complexes with either chcah or cpcah ligands resulted in <25% DNA platination at 24 h. cis-[PtX(2)(hydrazide)(2)], where hydrazide=chcah or cpcah, were the most potent compounds (chcah>cpcah), but activity was independent of the halide ligand (I(-)=Cl(-)=Br(-)). These complexes showed no cross-resistance with cisplatin, but they also showed little differentiation in potency over the seven cell lines. Complexes with the hydantoin ligands achsh and acpsh were inactive in all cell lines. Thus, neither stability in aqueous media nor covalent binding to DNA are correlated with biological activity, suggesting that cis-dihydrazide Pt(II) complexes act by a unique mechanism of action.     

Formation and structure of Cu(II)-poly(L-lysine) complexes in aqueous solution.

Cu(II)-poly(L-lysine) complexes have been studied using potentiometric titrations, optical absorption and circular dichroism spectra. As in the Cu(II)-poly(L-arginine) system studied previously potentiometric and spectral data consistently show that two types of complexes are formed. The first formed below pH 7.6 contains two amine nitrogens and two oxygen from water molecules at the corners of a square in which the metal occupies the center. The second is obtained at pH above 7.6 when the oxygen atoms are replaced by two adjacent peptide nitrogens.     

Synthesis and solution studies of Cu(II) complexes with pyridine derivatives of iminobisphosphonic acids

New 2-pyridyl, 3-pyridyl and 4-pyridyl derivatives of iminobisphosphonic acid were prepared by addition of tris(trimethylsilyl)phosphite to the corresponding derivatives of pyridineimine-methylphosphonates 3 and subsequent methanolysis of the silylated products 4. Solution studies on the coordination abilities of the ligands have shown that these compounds bind copper(II) ion through the tridentate {N,O,O} mode, where Cu(II) is stabilized by two five-membered chelate rings. The complexes obtained are very stable, with the pCu(II) value above 12, and therefore the ligands can be used as powerful chelating agents for copper ion.     

Reaction of a model siderophore with Ni(II), Co(II) and Zn(II) in aqueous solution: kinetics and spectroscopy

A spectroscopic study was performed showing that the [Fe(III)(L(2-))(2)](1-) (L(2-)=dopacatecholate) complex reacts with Ni(II), Co(II) and Zn(II) in an aqueous solution containing S(2)O(3)(2-) resulting in the soluble [M(L(1-))(3)](1-) (L(1-)=dopasemiquinone; M=Ni(II), Co(II) or Zn(II) complex species. The Raman and IR spectra of the [CTA][M(L(1-))(3)] complexes, CTA=hexadecyltrimethylammonium cation, in the solid state were obtained. The kinetic constants for the metal substitution reactions were determined at four different temperatures, providing values for DeltaH(not equal), DeltaS(not equal) and DeltaG(not equal). The reactions were slow (k=10(-11) Ms(-1)) and endothermic. The system investigated can be considered as a simplified model to explain some aspects of siderophore chemistry.     

Mercury(II) complex formation with glutathione in alkaline aqueous solution

The structure and speciation of the complexes formed between mercury(II) ions and glutathione (GSH = L-glutamyl-L-cysteinyl-glycine) have been studied for a series of alkaline aqueous solutions (\( C_{{{\text{Hg}}^{{2 + }}}}\,{\sim18\,{\rm{mmol}}\,{\rm{{dm^{-3}}}}}\) and C _GSH = 40–200 mmol dm^?3 at pH ～10.5) by means of extended X-ray absorption fine structure (EXAFS) and ¹⁹⁹Hg NMR spectroscopy at ambient temperature. The dominant complexes are [Hg(GS)₂]^4? and [Hg(GS)₃]^7?, with mean Hg–S bond distances of 2.32(1) and 2.42(2) Å observed in digonal and trigonal Hg–S coordination, respectively. The proportions of the Hg²⁺–glutathione complexes were evaluated by fitting linear combinations of model EXAFS oscillations representing each species to the experimental EXAFS spectra. The [Hg(GS)₄]^10? complex, with four sulfur atoms coordinated at a mean Hg–S bond distance of 2.52(2) Å, is present in minor amounts (<30%) in solutions containing a large excess of glutathione (C _GSH ≥ 160 mmol dm^?3). Comparable alkaline mercury(II) cysteine (H₂Cys) solutions were also investigated and a reduced tendency to form higher complexes was observed, because the deprotonated amino group of Cys^2? allows the stable [Hg(S,N-Cys)₂]^2? chelate to form. The effect of temperature on the distribution of the Hg²⁺–glutathione complexes was studied by comparing the EXAFS spectra at ambient temperature and at 25 K of a series of glycerol/water (33/67, v/v) frozen glasses with \( C_{{{\text{Hg}}^{{2 + }} }} \,{\sim7\,{\rm{mmol}}\,{\rm{{dm^{-3}}}}} \) and C _GSH = 16–81 mmol dm^?3. Complexes with high Hg–S coordination numbers, [Hg(GS)₃]^7? and [Hg(GS)₄]^10?, became strongly favored when just a moderate excess of glutathione (C _GSH ≥28 mmol dm^?3) was used in the glassy samples, as expected for a stepwise exothermic bond formation. Addition of glycerol had no effect on the Hg(II)–glutathione speciation, as shown by the similarity of the EXAFS spectra obtained at room temperature for two parallel series of Hg(II)-glutathione solutions with \( C_{{{\text{Hg}}^{{2 + }} }} \,{\sim7\,{\rm{mmol}}\,{\rm{{dm^{-3}}}}},\) with and without 33% glycerol. Also, the ¹⁹⁹Hg NMR chemical shifts of a series of ～18 mmol dm^?3 mercury(II) glutathione solutions with 33% glycerol were not significantly different from those of the corresponding series in aqueous solution.     

Copper(II) complexes with uridine,uridine 5'-monophosphate,spermidine, or spermine in aqueous solution

Molecular complexes of the types (Urd)H(x)(PA) and (UMP)H(x)(PA) are formed in the uridine (Urd) or uridine 5'-monophosphate (UMP) plus spermidine or spermine systems, as shown by the results of equilibrium and spectral studies. Overall stability constants of the adducts and equilibrium constants of their formation have been determined. An increase in the efficiency of the reaction between the bioligands is observed with increasing length of the polyamine. The pH range of adduct formation is found to coincide with that in which the polyamine is protonated while uridine or its monophosphate is deprotonated. The -NH(x)(+) groups from PA and the N(3) atom of the purine base as well as phosphate groups from the nucleotides have been identified as the significant centres of non-covalent interactions. Compared to cytidine, the pH range of Urd adduct formation is shifted significantly higher due to differences in the protonation constants of the endocyclic N(3) donor atoms of particular nucleosides. Overall stability constants of the Cu(II) complexes with uridine and uridine 5'-monophosphate in ternary systems with spermidine or spermine have been determined. It has been found from spectral data that in the Cu(II) ternary complexes with nucleosides and polyamines the reaction of metallation involves mainly N(3) atoms from the pyrimidine bases, as well as the amine groups of PA. This unexpected type of interaction has been evidenced in the coordination mode of the complexes forming in the Cu-UMP systems including spermidine or spermine. Results of spectral and equilibrium studies indicate that the phosphate groups taking part in metallation are at the same time involved in non-covalent interaction with the protonated polyamine.     

Interaction of copper(II) and nickel(II) with a bis-amide ligand functionalized with pyridine moieties: Thermodynamic and spectroscopic studies in aqueous solution

We synthesized a new bis-amide ligand derived from the l(+)-tartaric acid. We then determined its protonation constants and the stability constants of the copper(II) and nickel(II) chelates by potentiometry as well as ESI-MS and UV-Vis spectroscopy. We found that both metal ions are able to induce the deprotonation and the coordination of an amide nitrogen donor atom. In the case of copper complexes, the data show the formation of two major species: Cu₂(L₂H₋₃)⁺ and Cu₂(LH₋₄). EPR and XAS experiments led us to precise the relative structure of these compounds. In Cu₂(L₂H₋₃)⁺, each metal center is coordinated by pyridinic and amidic nitrogen atoms of one ligand and by nitrogen and oxygen atoms from pyridine and hydroxyl moieties from the other one. In Cu₂(LH₋₄), the copper centers are coordinated by pyridinic and amidic nitrogen atoms, as well as a deprotonated hydroxyl group of the ligand. In this latter complex, the lower value of the Cu-Cu distance determined from EXAFS experiments and compared to the one of the solid species likely involve the formation of an exogeneous hydroxyl bridge between the two copper centers. With Ni(II) ions, the only one major species is the mononuclear Ni(LH₋₂) complex, in which Ni(II) is held in an octahedral environment with the metal center chelated by the two pyridinic and the two amidic nitrogen atoms, and two oxygen atoms from water molecules.     

Interactions of nitric oxide with copper(II) dithiocarbamates in aqueous solution

This is the first report on the formation of air-stable copper nitrosyl complexes. The interaction of nitric oxide, NO, with Cu(DTC)(2).3H(2)O (DTC: dithiocarbamate) and was studied in aqueous solution at pH 7.4 and 293 K. The stability constants were determined from UV-Vis data, using LETAGROP program. The high values obtained, log beta(1)=9.743(5) and log beta(2)=15.44(2) for Cu(ProDTC)(2)-NO, (ProDTC=L-prolinedithiocarbamate) and log beta(1)=8.723(5) and log beta(2)=11.45(2) for Cu(MorDTC)(2)-NO system, (MorDTC=morpholyldithiocarbamate), indicate the formation of two stable nitrosyl complexes, Cu(DTC)(2)NO and Cu(DTC)(2)(NO)(2). Coordinated NO is neither affected by the presence of air nor when the solution is purged with Ar. Cu(MorDTC)(2)NO.3H(2)O was isolated in the solid state and its nuNO (IR) band at 1682 cm(-1), but affected by temperature variations over 333 K.     

Copper(II) and lead(II) sorption from aqueous solution by non-living Spirogyra neglecta

Dried biomass of Spirogyra neglecta rapidly sorbed the test metals and the process became saturated in 10-20min. Maximum sorption of Pb(II) [116.1mgg(-1)] and Cu(II) [115.3mgg(-1)] occurred at 0.1gl(-1) biomass and 100mgl(-1) metal concentration in the solution. Sorption of Cu(II) and Pb(II) occurred optimally at pH 4.5 and 5.0, respectively. Lead(II) and Cu(II) sorption were lesser from binary metal solution than from single metal solution. Lead(II) more severely inhibited Cu(II) sorption than vice versa thus reflecting greater affinity of Pb(II) for the biomass. NaOH pretreatment slightly enhanced the metal removal ability of the biomass. During repeated sorption/desorption cycles, Pb(II) and Cu(II) sorption decreased by 11% and 27%, respectively, at the end of the fifth cycle due inter alia to 10-15% loss of biomass. Nevertheless, Spirogyra appears to be a good sorbent for removing metals Cu(II) and Pb(II) from wastewaters.     

Speciation study of an imidazolate-bridged copper(II)-zinc(II) complex in aqueous solution

The solution equilibrium and the binding mode of the species in the five-component system containing two metal ions (copper(II) and zinc(II)) and three ligands (A=diethylenetriamine, B=imidazole, C=tris(2-aminoethyl)amine) were investigated by pH-potentiometric titration, UV-visible spectrophotometry and EPR (electron paramagnetic resonance) spectroscopic titration in aqueous solution in the 2-11 pH range. An imidazolate-bridged heterobinuclear complex (ACuBH(-1)ZnC) was found to evolve above pH=7 and was stable between pH 7 and 11. The existence of the ACuBH(-1)ZnC complex (by determination of its molecular weight) was proved by mass spectrometry (ESI-MS (electrospray ionization mass spectrometry) and MALDI (matrix-assisted laser desorption/ionization) techniques). The electrochemical behaviour and the superoxide dismutase activity of this complex were also tested by cyclic voltammetry and the Riboflavin/NBT (nitro blue tetrazolium) assay, respectively.     

Field-dependent proton relaxation in aqueous solutions of some manganese(II) complexes: a new interpretation

Field-dependent measurements of the paramagnetic relaxation enhancement for water protons in the presence of Mn(II) complexes ( S=5/2), reported recently, are re-interpreted using theoretical models that take into consideration the fact that the relaxation of the electron spin for S>1 is multiexponential (even in the Redfield limit) and that are valid for an arbitrary relation between the electronic Zeeman interaction and the zero-field splitting in the complex.     

4-Nitrocatechol as a probe of a Mn(II)-dependent extradiol-cleaving catechol dioxygenase (MndD): comparison with relevant Fe(II) and Mn(II) model complexes

Mn(II)-dependent 3,4-dihydroxyphenylacetate 2,3-dioxygenase (MndD) is an extradiol-cleaving catechol dioxygenase from Arthrobacter globiformis that has 82% sequence identity to and cleaves the same substrate (3,4-dihydroxyphenylacetic acid) as Fe(II)-dependent 3,4-dihydroxyphenylacetate 2,3-dioxygenase (HPCD) from Brevibacterium fuscum. We have observed that MndD binds the chromophoric 4-nitrocatechol (4-NCH(2)) substrate as a dianion and cleaves it extremely slowly, in contrast to the Fe(II)-dependent enzymes which bind 4-NCH(2) mostly as a monoanion and cleave 4-NCH(2) 4-5 orders of magnitude faster. These results suggest that the monoanionic binding state of 4-NC is essential for extradiol cleavage. In order to address the differences in 4-NCH(2) binding to these enzymes, we synthesized and characterized the first mononuclear monoanionic and dianionic Mn(II)-(4-NC) model complexes as well as their Fe(II)-(4-NC) analogs. The structures of [(6-Me(2)-bpmcn)Fe(II)(4-NCH)](+), [(6-Me(3)-TPA)Mn(II)(DBCH)](+), and [(6-Me(2)-bpmcn)Mn(II)(4-NCH)](+) reveal that the monoanionic catecholate is bound in an asymmetric fashion (Delta r(metal-O(catecholate))=0.25-0.35 A), as found in the crystal structures of the E(.)S complexes of extradiol-cleaving catechol dioxygenases. Acid-base titrations of [(L)M(II)(4-NCH)](+) complexes in aprotic solvents show that the p K(a) of the second catecholate proton of 4-NCH bound to the metal center is half a p K(a) unit higher for the Mn(II) complexes than for the Fe(II) complexes. These results are in line with the Lewis acidities of the two divalent metal ions but are the opposite of the trend observed for 4-NCH(2) binding to the Mn(II)- and Fe(II)-catechol dioxygenases. These results suggest that the MndD active site decreases the second p K(a) of the bound 4-NCH(2) relative to the HPCD active site.     

Electrochemical study of the complexes of aspartame with Cu(II), Ni(II) and Zn(II) ions in the aqueous medium

The voltammetric behaviours of aspartame in the presence of some metal ions (Cu(II), Ni(II), Zn(II)) were investigated. In the presence of aspartame, copper ions reduced at two stages with quasi-reversible one-electron and, with increasing the aspartame (L) concentration, Cu(II)L(2) complex reduces at one-stage with irreversible two-electron reaction (-0.322 V). Zn(II)-aspartame complex (logbeta=3.70) was recognized by a cathodic peak at -1.320 V. Ni(II)-aspartame complex (logbeta=6.52) is reduced at the more positive potential (-0.87 V) than that of the hydrated Ni(II) ions (-1.088 V). In the case of the reduction of Ni(II) ions, aspartame serves as a catalyst. From electronic spectra data of the complexes, their stoichiometries of 1:2 (metal-ligand) in aqueous medium are determined. The greatness of these logarithmic values is agreement with Irwing-Williams series (NiZn).     

Binding of palladium(II) complexes to guanine, guanosine or guanosine 5-monophosphate in aqueous solution: potentiometric and NMR studies

The interaction of guanine, guanosine or 5^′-GMP (guanosine 5^′-monophosphate) with [Pd(en)(H₂O)₂](NO₃)₂ and [Pd(dapol)(H₂O)₂](NO₃)₂, where en is ethylenediamine and dapol is 2-hydroxy-1,3-propanediamine, were studied by UV-Vis, pH titration and ¹H NMR. The pH titration data show that both N1 and N7 can coordinate to [Pd(en)(H₂O)₂]²⁺ or [Pd(dapol)(H₂O)₂]²⁺. The pK_a of N1-H decreased to 3.7 upon coordination in guanosine and 5^′-GMP complexes, which is significantly lower than that of ∼9.3 in the free ligand. In strongly acidic solution where N1-H is still protonated, only N7 coordinates to the metal ion, but as the pH increases to pH ∼3, ¹H NMR shows that both N7-only and N1-only coordinated species exist. At pH 4-5, both N1-only and N1,N7-bridged coordination to Pd(II) complexes are found for guanosine and 5^′-GMP. The latter form cyclic tetrameric complexes, [Pd(diamine)(μ-N1,N7-Guo]₄⁴⁺ and [Pd(diamine)(μ-N1,N7-5^′-GMP)]₄H_x^(4−x)−, (x=2,1, or 0) with either [Pd(en)(H₂O)₂](NO₃)₂ or [Pd(dapol)(H₂O)₂](NO₃)₂. The pH titration data and ¹H NMR data agree well with the exception that the species distribution diagrams show the initial formation of the N1-only and N1,N7-bridged complexes to occur at somewhat higher pH than do the NMR data. This is due to a concentration difference in the two sets of data.     

Mixed-ligand complex formation of mercury (II) ethylenediaminetetraacetate with cysteine and methionine in aqueous solution

The mixed-ligand complex formation in the systems Hg²⁺-Edta⁴⁻-L (L = Cys²⁻, Met⁻) has been studied by means of calorimetry, pH-potentiometry and NMR spectroscopy in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of the HgEdtaL, HgEdtaHL and (HgEdta)₂L complexes have been determined. The most probable coordination mode for the complexone and the amino acid in the mixed-ligand complexes is discussed.