Metal complexes of cyclic diamines,dissociation kinetics of bis(1,5-diazacyclo-octane)nickel(II) in acidic and basic solution,and electrochemical studies

The preparation of the planar yellow [Ni([8]aneN₂)₂](ClO₄)₂ is described. The complex dissociates in basic solution, with rate = k_OH[NiL][OH^?] (L = 1,5-diazacyclo-octane). At 25 °C, k_OH = 4.5 x 10^?2 M^?1 s^?1 and the corresponding activation parameters are ΔH^≠ = 69.2 kJ mol^?1 and ΔS₂₉₈^≠ = ?38.6 J K^?1 mol^?1. Acid catalysed dissociation in quite slow even in strongly acidic solutions. The kinetic data in this case can be fitted to the expression K_obs = k_o + K_H[H⁺], where k_o relates to a solvolytic pathway and k_H to the acid catalysed pathway. At 60 °C, K_o = 2 x 10^?5 s^?1 and k_H is 2 x 10^?5 M^?1 s^?1. Possible mechanisms for these reactions are considered.The Ni(II)/Ni(III) redox couple for NiLⁿ⁺ is irreversible on Pt using MeCN as solvent.     

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.     

Comparison of the SOD-like activity of hexacoordinate Mn(II), Fe(II) and Ni(II) complexes having isoindoline-based ligands

Recently, a series of Fe(II) complexes have been published by our group with 3 N-donor 1,3-bis(2′-Ar-imino)isoindoline ligands containing various Ar-groups (pyridyl, 4-methylpyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl). The superoxide scavenging activity of the compounds showed correlation with the Fe(III)/Fe(II) redox potentials. Analogous, electroneutral chelate complexes with Mn(II) and Ni(II) in 2:1 ligand:metal composition are reported here. Each Mn(II) complex exhibits one reversible redox wave that is assigned as the Mn(III)/Mn(II) redox transition. The E_1/2 spans a 180 mV range from − 98 (Ar = 3-methylpyridyl) to 82 mV (Ar = thiazolyl) vs. the Fc⁺/Fc depending on the Ar-sidearm. The SOD-like (SOD=superoxide dismutase)activity of all complexes was determined according to the McCord-Fridovich method. The Mn(II) isoindolinates have IC₅₀ values - determined with 50 μM cytochrome c Fe(III) - that range from (3.22 ± 0.39) × 10^− 6 (Ar = benzimidazolyl) to (10.80 ± 0.54) × 10^− 6 M (Ar = N-methylbenzimidazolyl). In contrast with the Fe(II) complexes, the IC₅₀ concentrations show no significant dependence on the E_1/2 values in this narrow potential range emphasizing that the redox potential is not the governing factor in the Mn(II)-containing scavengers. The analogous Ni(II) compounds show no redox transitions in the thermodynamically relevant potential range (− 0.40 to 0.65 V vs. SCE) and accordingly, their superoxide scavenging activity (if any) is below the detection level.     

Complexes of vitamin B6, part VII: Ternary complexes of cobalt(II), nickel(II), and copper(II) involving pyridoxamine and some amino acids

The stability constants of the ternary Cu(II), Ni(II), and Co(II) complexes containing pyridoxamine (PM) and as a second ligand (L) glycine, DL-alanine, DL-valine, and β-phenylalnine were determined by pH-metric titration in 0.50 M KNO₃ at 30°C. The corresponding constants of the equilibrium, log X, are greater than would be expected for purely statistical reasons (log X = 0.6), except for few complex cases of Co(II). It has been also concluded that amino acids compete more than pyridoxamine for Ni(II) and Co(II) through the formation of 1:2:1:0 species rather than 2:1:1:0 of PM⁻:L⁻:M²⁺:H⁺.     

Solution properties of the nickel(II,III) and copper(II,III) complexes of trans-dioxocyclam (trans-dioxocyclam=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) and the X-ray crystal structure of the N-rac-isomer of the nickel(II) complex

The crystal and molecular structures of the N-rac-isomer of the nickel(II) complex of 14-membered amide-containing macrocycle [NiL¹] · 4H₂O (H₂L¹=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) have been determined. Two deprotonated amide and two amine donors co-ordinate to the nickel(II) in nearly square planar manner with Ni-N_amine bonds longer than Ni-N_amide ones (1.930 vs. 1.898 Å). Water molecules do not co-ordinate and form hydrogen bond bridges between macrocyclic units in the crystal lattice. The analysis of ¹H NMR data confirmed that the solid-state conformation of the macrocycle in N-rac[NiL¹] is retained in aqueous solution though equilibrated with some amount of N-meso isomer. The comparison of the spectroscopic characteristics of the M(II) and M(III) complexes and the redox potentials of M(III/II) couples (M=Ni and Cu) for ML¹ with those for ML²(H₂L²=5,7-dioxo-1,4,8,11-tetraazacyclotetradecane) revealed a rather small influence of the trans- vs. cis-arrangement of amide donors in co-ordination spheres of the metal ions.     

Structure and O2 uptake properties of a novel nickel(II) complex of pyridyl-pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane]

 Novel potentially five-coordinate pyridyl–pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (H₂L) and its homologs (6-methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple nickel(II) complex with a deprotonated amide (NiHL) was isolated from aqueous equimolar solution of H₂L and Ni(ClO₄)₂. A yellow nickel(II) complex with two deprotonated amides (NiL) was crystallized from an H₂O/CH₃CN solution of H₂L and Ni(OH)₂. The X-ray crystal study of NiL showed a square-planar nickel(II) complex with the pyridyl–pendant remaining uncoordinated. It is concluded from the visible absorption and NMR study of NiL in aqueous solution that the four-coordinate NiL is in equilibrium with a five-coordinate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl–pendant. A voltammetric study disclosed a low nickel(II/III) redox potential of +0.29 V vs SCE for NiL at pH 9.5 and 25  °C with 0.10 M Na₂SO₄. The nickel(II) complex NiL absorbed an equimolar amount of O₂ at pH 9.5 and 25  °C, and the O₂ was activated to cleave plasmid DNA. Received: 5 August 1996 / Accepted: 24 October 1996     

Specific nickel(II)-transfer process between the native sequence peptide representing the nickel(II)-transport site of human serum albumin and L-histidine.

The kinetics and mechanism for Ni(II)-transfer of the native sequence tripeptide, L-aspartyl-L-alanyl-L-histidine-N-methylamide (AAHNMA), representing the Ni(II)-transport site of human serum albumin (HSA) and L-histidine (L-His) was studied in forward and reverse reactions in the pH range 6.5 to 9.0 at I = 0.2 and 25 degrees C. For the Ni(II)-transfer from Ni(II)-(L-His)2 to native sequence peptide, the rate-determining step is the formation of a mixed-ligand complex of NiH-1AB by deprotonation of peptide nitrogen from NiAB where A and B denote the anionic forms of AAHNMA and L-His, respectively. For the Ni(II)-transfer from Ni(II)-peptide to L-His, the rate-determining step is a bond breaking between Ni(II) and peptide nitrogen to form NiH-1A by protonation to a peptide nitrogen of NiH-2A. The equilibrium constants for the metal-transfer reaction of MH-2A + 2HB in equilibrium MB2 + A (A = Ni(II), Cu(II] were 10(3.29) and 10(0.78) for Ni(II) and Cu(II), respectively. NiB2 is 324 times as stable as CuB2. Furthermore, the ratio of Ni(II)/Cu(II) in the rate constants for the reaction of MB2 with A was found to be 2.8 x 10(-4). Thus, despite the similarities of Cu(II) and Ni(II) in the metal-binding sites of HSA and in reaction mechanism, Ni(II)-(L-His)2 complex is so stable thermodynamically and kinetically, compared to the Cu(II)-(L-His)2 complex, that Ni(II) is hardly transferred from Ni(II)-(L-His)2 to native sequence peptide. These findings may support specificities in the Ni(II)-transfer, its organ distribution, and its excretion through urine in vivo.     

The kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) Complexes: a study on the reactivity of square-planar versus octahedral coordination

The bis(N-alkylsalicylaldiminato)nickel(II) complexes Ni(R-sal)₂ with R = CH(CH₂OH)CH(OH)Ph (I), R = CH(CH₃)CH(OH)Ph (II) and R = CH₂CH₂Ph (III; Ph = phenyl) were prepared and characterized. In the solid state I and II are paramagnetic (μ = 3.2 and 3.3 BM at 20 °C, respectively), whereas III is diamagnetic. It follows from the UV-Vis spectra that in acetone solution I is six-coordinate octahedral and III is four-coordinate planar, the spectrum of II showing characteristics of both modes of coordination. Vis spectrophotometry and stopped-flow spectrophotometry were applied to study the kinetics of ligand substitution in I–III by H₂salen (= N,N′-disalicylidene-ethylenediamine) in the solvent acetone at different temperatures. The kinetics follow a second-order rate law, rate = k[H₂-salen] [complex]. At 20 °C the sequence of rate constants is k(III):k(II):k(I) = 11 850:40.6:1. The activation parameters are ΔH^≠(I) = 112, ΔH^≠(II) = 40.7, ΔH^≠(III) = 35.7 kJ mol⁻¹ and ΔS^≠(I) = 92, ΔS^≠(II) = −103, ΔS^≠(III) = −89 J K⁻¹ mol⁻¹. The enormous difference in rate between complexes I, II and III, which is less pronounced in methanol, is attributed to the existence of a fast equilibrium planar ⇌ octahedral, which is established in the case of I and II by intramolecular octahedral coordination through the hydroxyl groups present in the organic group R. An A-mechanism is suggested to control the substitution in the sense that the entering ligand attacks the four-coordinate planar complex, the octahedral complex being kinetically inert.     

(1,3-Bis(2′-pyridylimino)isoindolinato)nickel(II) complexes of phenylcyanamido ligands: crystal structure, electronic absorption spectroscopy and solvent adduct studies

Complexes of the formula Ni(L)X, where L=1,3-bis(2′-pyridylimino)isoindolinato and X=Cl, Br, N₃, NCS, 2-Clpcyd, 4-Clpcyd, 2,3-Cl₂pcyd,2,6-Cl₂pcyd, 2,4,5-Cl₃pcyd and 2,3,5,6-Cl₄pcyd, have been synthesized and characterized by elemental analysis, and IR, ¹H NMR and UV---Vis spectroscopies. A crystal structure determination of Ni(L)(2-Clpcyd) showed nickel in a distorted square planar coordination sphere of nitrogen donor atoms in which the phenylcyanamido ligand is coordinated to Ni(II) via the terminal nitrogen. The solvent coordination equilibria of Ni(L)(pcyd) complexes was also investigated and the results suggest that both electronic and steric factors play important roles in determining the stability of the solvated complex.     

Chemical speciation of ternary complexes of L-dopa and 1,10-phenanthroline with Co(II), Ni(II) and Cu(II) in low dielectric media

Abstract

A computer assisted pH-metric investigation has been carried out on the speciation of complexes of Co(II), Ni(II) and Cu(II) with L-dopa and 1,10-phenanthroline. The titrations were performed in the presence of different relative concentrations (M:L:X = 1.0:2.5:2.5; 1.0:2.5:5.0; 1.0:5.0:2.5) of metal (M) to L-dopa (L) and 1,10-phenanthroline (X) with sodium hydroxide in varying concentrations (0-60% v/v) of 1,2-propanediol-water mixtures at an ionic strength of 0.16 mol L^-1 and at a temperature of 303.0 K. Stability constants of the ternary complexes were refined using MINIQUAD75. The species MLXH, MLX, ML₂X and MLX₂H for Co(II) and Cu(II) and MLXH, MLX and MLX₂H for Ni(II) were detected. The extra stability of ternary complexes compared to their binary complexes was believed to be due to electrostatic interactions of the side chains of ligands, charge neutralisation, chelate effect, stacking interactions and hydrogen bonding. The species distribution with pH at different compositions of 1, 2-propanediol-water mixtures and plausible equilibria for the formation of species were also presented. The bioavailability of the metal ions is explained based on the speciation.     

Nickel(II)-baicalein complex modified multiwall carbon nanotube paste electrode and its electrocatalytic oxidation toward glycine

A modified electrode, nickel(II)-baicalein complex modified multiwall carbon nanotube paste electrode (Ni(II)-BA-MWCNT-PE), has been fabricated by electrodepositing Ni(II)-BA complex on the surface of MWCNT-PE in alkaline solution. The Ni(II)-BA-MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)-BA-carbon paste electrode (CPE). It also shows better electrocatalytic activity toward the oxidation of glycine than Ni(II)-MWCNT-PE. Kinetic parameters such as the electron transfer coefficient α, rate constant k_s of the electrode reaction, the diffusion coefficient D of glycine, and the catalytic rate constant k_cat of the catalytic reaction are determined. Moreover, the catalytic currents present linear dependence on the concentration of glycine from 20 μM to 1.0 mM by amperometry. The detection limit and sensitivity are 9.2 μM and 3.92 μA mM⁻¹, respectively. The modified electrode for glycine determination is of the property of simple preparation, fast response, and good stability.     

Studies on the formation of a complex of Cu(II) with sodium 1,4-dihydroxy-9,10-anthraquinone-2-sulphonate - An analogue of the core unit of anthracycline anticancer drugs and its interaction with calf thymus DNA

Copper(II) forms a complex with sodium 1,4-dihydroxy-9,10-anthraquinone-2-sulphonate (sodium quinizarin-2-sulphonate, NaQSH₂), an analogue of the core unit of anthracycline antibiotics used in the treatment of cancer. The 1:2 metal-ligand complex is formed in aqueous solution at neutral and acidic pH while in alkaline pH both 1:1 and 1:2 species are formed. The effective stability constant of the 1:2 metal-ligand complex is 9.64 × 10¹⁶ while that of the 1:1 metal-ligand complex is 9.4 × 10⁹. The 1:2 complex Cu(NaQSH)₂(H₂O)₂ was synthesized and characterized by different techniques in solid state and in solution. The complex Cu(NaQSH)₂(H₂O)₂ interacts with calf thymus DNA which was studied by fluorescence spectroscopy. The binding constant and site size for the interaction with DNA were determined.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Chronotolerance of a Nickel (II) Complex with the 5-Methyl 2-Furaldehyde Thiosemicarbazone Ligand in Male Swiss Mice

In vitro nickel (II) complex presents antimitotic effects. In this work, we have studied the in vivo seasonal effects of nickel (II), ligand and the complex [NiCl₂(M5FTSC)₂] in male Swiss mice. During spring, an intra peritoneal (i.p.) injection of NiCl₂ in aqueous NaCl up to 1.0.10^-2 mmol.kg^-1 body weight (b.w.) killed 10% of the rodents after 6 days. Lethal dose 100% (LD100) was up 1.91.10^-2 mmol.kg^-1 b.w.; ligand was less toxic than Ni (II), while the complex was 25% lethal at 1.37.10^-2 mmol.kg^-1 b.w. In autumn, mice were less sensitive to NiCl₂. The ligand and the complex, on the contrary, were more toxic. This leads us to the conclusion that, in vivo, chronotolerance of nickel (II), ligand and complex in aqueous solution, are quite different in spring and autumn seasons.     

Mixed ligand complexes of osmium(II)-2,2-bipyridine: synthesis, spectral characterization and electrochemical properties of bis-chelated-arylazoimidazole-bipyridine-osmium(II) and X-ray crystal structure of [(2,2-bipyridine)-bis-{1-methyl-2-(p-tolylazo)imidazole}osmium(II) hexafluorophosphate

Reaction of ctc-OsBr₂(RaaiR^′)₂ [RaaiR^′=1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-NN-C₃H₂-NN-1-R^′, where R=H (a), Me (b), Cl (c) and R^′=Me (2), Et (3) and CH₂Ph (4)] with 2,2^′-bipyridine (bpy) in presence of AgNO₃ in EtOH followed by the addition of NH₄PF₆ afforded a mixed ligand complex [Os(bpy)(RaaiR^′)₂](PF₆)₂. The structure of the complex, in one case [Os(bpy)(MeaaiMe)₂](PF₆)₂ · 4H₂O, has been confirmed by X-ray crystallography. The complexes are diamagnetic (low spin d⁶, s=0) and they show intense MLCT transition in the visible region (480-525 nm) and a weak transition at longer wavelength (>850 nm) in CH₃CN solution. Cyclic voltammetry of the complexes show two metal oxidation, Os(II)/Os(III) at 0.72-0.76 V and Os(III)/Os(IV) at 1.34-1.42 V and three successive ligand reductions.     

Oxidation of copper(II)-coordinated diethylenetriamine by hexacyanoferrate(III) ion. A kinetic investigation

The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]⁺ and [Fe(CN)₆]³⁻ in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k₁[OH⁻]²[[Cu(dien)(OH)]⁺] + k₂[OH⁻] × [[Cu(dien)(OH)]⁺]²}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)₆]³⁻; Fe(II) = [Fe(CN)₆]⁴⁻, the 4:4:1 OH⁻/Fe(III)/[Cu(dien)(OH)]⁺ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H₂NCH₂CH₂NCHCHNH.The [[Cu(dien)(OH)]⁺]² term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen.     

Nickel(II) complex with a tridentate ONS-Schiff base ligand: X-ray structure,VIS and NIR solution spectra and kinetics of ligand substitution

The ligand N-(3-thia-n-pentyl)salicylaldimine (Hsalen-SEt) and its green nickel(II) complex Ni(salen-SEt)₂ was prepared. The complex crystallizes in the orthorhombic space group Pbca with a a = 2538.3(4) pm, b = 1490.0(3) pm, c = 1163.5(2) pm and Z = 8. The coordination sphere of the nickel is a distorted octahedron with two oxygen atoms in a cis-position, two nitrogen atoms in a trans-position and two sulfur atoms in a cis-position. The two NiO distances were 197.8 and 198.1 pm, the two NiN distances 201.8 and 200.6 pm, whereas the two NiS distances are 272.0 and 266.3 pm. The magnetic susceptibility of Ni(salen-SEt)₂ was measured in the temperature range 2.6-281 K, the magnetic moment being μ_eff=3.02μ_B.The VIS and NIR solution spectra of the complex in different solvents indicate that the two tridentate ONS-ligands are coordinated as bidentate ON-ligands, the coordination geometry being square-planar (trans- N₂O₂) in non-coordinating solvents (e.g., toluene) and octahedral in coordinating solvents (e.g., pyridine), due to addition of two solvent molecules. From spectrophotometric titration the individual complex formation constants for the species Ni(salen-SEt)₂·py (K₁ and Ni(salen-SEt)₂·2py (K₂) were found to be K₁ = 1.76 ± 0.40 M^-1 and K₂ = 145 ± 34 M^-1. The kinetics of the reaction Ni(salen-SEt)₂ + H₂salen → Ni(salen) + 2Hsalen-SEt as studied in acetone by stopped-flow spectrophotometry follow the rate law, rate = (k^S = k_H2^salen H₂salen]) × [Ni(salen-SEt)₂] with k_S = 0.038 ± 0.013 s^-1 and k_H2^salen = 17.2 ± 0.4 M^-1 s^-1 at 25°C. The spectroscopic and kinetic properties of Ni(salen-SEt)₂ are compared with those of bis(N-alkyl-salicylaldiminato)nickel(II) complexes     

Anti-cancer study and whey protein complexation of new lanthanum(III) complex with the aim of achieving bioactive anticancer metal-based drugs

In this study, a new lanthanum (III)-amino acid complex utilizing cysteine has been synthesized and characterized. The anticancer activities of the prepared La(III) complex against MCF-7 cell lines were studied. Results of MTT assay showed that at all three incubation times, the cytotoxic effect of prepared La(III) complex on MCF-7 breast cancer cell lines displays a time- and dose-dependent inhibitory effects. The interactions of the La(III) complex with two whey proteins (bovine serum albumin, BSA, and Bovine β-lactoglobulin, βLG) have been explored by using spectroscopic and molecular dicking methods. The obtained results indicated that La(III) complex strongly quenched the fluorescence of two carrier proteins in static quenching mode and also, BSA hah stronger binding affinity toward studied complex than βLG whit binding constant values of K_{BSA-La?Complex}?～?0.11?×?10⁴ M^?1 and K_{βLG-La?Complex}?～?0.63?×?10³ M^?1 at 300 K. The thermodynamic parameters revealed the contribution of hydrogen bond and Vander Waals interactions in both systems. The distances of the La(III) complex whit whey proteins were calculated using Förster energy transfer theory and proved existence of the energy transfer between two proteins and prepared La(III) complex with a high probability. FT-IR and UV–Vis absorption measurements indicated that the binding of the La(III) to BSA and βLG may induce conformational and micro-environmental changes of the proteins. The docking results indicate that the La(III) complex bind to residues located in the site II of BSA and second site of βLG.

Communicated by Ramaswamy H. Sarma     

The structures of bis(1H,5H-S-methylisothiocarbonohydrazidium) di-μ-chloro-octachlorodibismuthate(III) tetrahydrate and tris(1H-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III)

The structures of bis(1H⁺,5H⁺-S-methylisothiocarbonohydrazidium) di-μ-chlorooctachlorodibismuthate(III) tetrahydrate: (C₂H₁₀N₄S)₂(Bi₂Cl₁₀)· 4H₂O (compound [I]) and of tris(1H⁺-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III): (C₂H₉N₄S)₃(BiCl_5.67I_0.33) (compound [II]) were determined from single crystal X-ray diffractometer data. Both compounds crystallize as triclinic (P ); crystals [I] with Z = 1 formula unit in a cell of constants: A = 10.621(3), B = 9.989(5), C = 7.439(3) Å, α = 88.31(2), β = 84.51(2), γ = 68.88(2)°, final R = 0.0427 for 2229 unique reflections with I 2σ(I); crystals [II] with Z = 2 and cell dimensions: A = 14.109(4), B = 12.209(9), C = 8.206(7) Å, α = 103.54(3), β = 104.95(2), γ = 81.96(2)°, final R = 0.0411 for 3637 unique reflections (1 2σ(I)). The structure of [I] is built up of diprotonated organic cations, water molecules and dinuclear centrosymmetric [Bi₂Cl₁₀]⁴⁻ anions held together by N-HCl, N-HO, O-HCl hydrogen bonds and Van der Waals interactions. The [Bi₂Cl₁₀]⁴⁻ complex consists of two edge-sharing octahedra in which three pairs of bonds of similar length are observed (Bi-Cl_av = 2.602(5), 2.712(4), 2.855(5) Å). The structure of [II] consists of monoprotonated cations and [BiCl_5.67I_0.33]³⁻ anions held together by a tridimensional network of hydrogen bonds. Each bismuth atom is octahedrally surrounded by six chlorine atoms, one of which is statistically substituted by a iodine atom.     

nmr and infrared spectroscopic investigations of the Al(III), Ga(III), and Be(II) complexes of ATP

The interaction of Al(III) with ATP has been examined by ³¹P and ¹H nmr and infrared spectroscopy. At pH 6.2, Al(III) forms a long-lived complex with ATP, in which chemical exchange between free and complexed ATP is slow on the nmr time scale. Infrared spectra of the Al(III)-ATP complex exhibit large perturbations in the band corresponding to the -PO₃^2? antisymmetric stretching mode. At higher pH values, equilibria involving Al(III) and OH^? become favored with the result that Al(III) no longer influences the spectroscopic properties of ATP. Similar spectroscopic results are obtained for the Ga(III) and Be(II) complexes of ATP.