Metal Chelates of Cerium (III), Thorium(IV) and Dioxouranium(VI) with Some Heterocyclic AZO Dyes; Potentiometric and Spectrophotometric Studies

ABSTRACT

The stepwise formation constants of Ce³⁺, Th⁴⁺ and UO₂ ²⁺ complexes with four azo compounds based on I-phenyl-2, 3-dimethylpyrazoline-5-one nucleus namely; 4-phenylazo- (2-hydroxy, 5-x) 1-pheny1-2, 3-dimethy1-pyrazoline-5-one, where x= H (1), OH (II), COOH (III) and NH₂ (IV) have been determined potentiometrically at different temperatures and ionic strengths in 30% (v/v) ethanol-water solutions, then the thermodynamic parameters are calculated.

Negatives values of both ∠H and ∠G are obtained indicating the exothermic and spontaneous nature of complexation reactions, whereas positive values of ∠S show that entropy consideration favour complex formation. The study at different ionic strengths shows that an increase in the latter causes a decrese in the pK values. The azo compounds are also tested as new reagents for the spectrophotometric determination of Ce³⁺, Th4⁺ and UO₂ ²⁺ ions in synthetic and natural solutions by extensive investigation of the optimum conditions favoring the formation of colored complexes.     

ATMP(氨基三甲叉膦酸)及其顺磁性Co(Ⅱ)配合物的核磁共振研究

本文用¹H、³¹P和¹³C核磁共振谱研究了ATMP(氨基三甲叉膦酸,以简式H₆L表示)及其顺磁性Co(Ⅱ)配合物。测定了不同C_co/C_ATMP摩尔比在不同pH值下的各向同性位移。定性地讨论顺磁性Co(Ⅱ)配合物在不同pH条件下的组成、电荷和空间构型变化对化学位移的影响。运用快速交换反应中化学位移与配合物浓度的关系,确定不同pH下的条件稳定常数。     

Theoretical investigation on multinuclear NMR chemical shifts of some tris(trifluoromethyl)boron complexes

Tris(trifluoromethyl)boron complexes have unusual properties and may find applications in many fields of chemistry, biology, and physics. To gain insight into their NMR properties, the isotropic ¹¹B, ¹³C, and ¹⁹F NMR chemical shifts of a series of tris(trifluoromethyl)boron complexes were systematically studied using the gauge‐included atomic orbitals (GIAO) method at the levels of B3LYP/6‐31 + G(d,p)//B3LYP/6‐31G* and B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p). Solvent effects were taken into account by polarizable continuum models (PCM). The calculated results were compared with the experimental values. The reason that the structurally inequivalent fluorine atoms in a specific species give a same chemical shift in experimental measurements is attributed to the fast rotation of CF₃ group around the B? C(F₃) bond because of the low energy barrier. The calculated ¹¹B, ¹³C(F₃), and ¹⁹F chemical shifts are in good agreement with the experimental measurements, while the deviations of calculated ¹³C(X, X = O, N) chemical shifts are slightly large. For the latter, the average absolute deviations of the results from B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p) are smaller than those from B3LYP/6‐31 + G(d,p)//B3LYP/6‐31G*, and the inclusion of PCM reduces the deviation values. The calculated ¹⁹F and ¹¹B chemical shieldings of (CF₃)₃BCO are greatly dependent on the optimized structures, while the influence of structural parameters on the calculated ¹³C chemical shieldings is minor. Copyright © 2009 John Wiley & Sons, Ltd.     

Chromium Bis(anthracene‐η6) Complexes – A DFT Study

Chromium bisanthracene‐η⁶ complexes are considered within the framework of density functional theory using LANL2DZ and 6‐31+G(d) basis sets and B3LYP functional. The complexation with both the same types of rings of anthracene decks (AA‐ and BB‐type complexes) and with different rings (AB‐type complex) are considered. The optimized geometries and the associated quantum chemical properties are comparatively discussed for the both types of basis sets used. LANL2DZ basis set yielded some unreasonable results. B3LYP/6‐31+G(d) level of calculations yielded the stability order as AA > BB > AB. IR spectra of AA and BB‐type complexes resemble each other. The C–H frequencies are almost the same for both of the anthracene decks, whereas they differ in the case of AB‐type complex. UV/Vis spectra of the complexes all absorb above 500 nm. AA and AB‐type complexes in contrast to BB‐type display rather complex pattern. The NICS(0) values of various rings in the complexes considered are obtained and discussed.     

New Au(III), Pt(II) and Pd(II) complexes with glycyl-containing homopeptides

Twelve new Au(III), Pt(II) and Pd(II) complexes with glycyl-containing homopeptides glycyl-glycine (G2), glycyl-glycyl-glycine (G3), glycyl-glycyl-gycyl-glycine (G4), glycyl-glycyl-glycyl-glycyl-glycine (G5) and glycyl-glycyl-glycyl-glycyl-glycyl-glycine (G6) have been synthesized, isolated and characterized spectroscopically and structurally by means of solid-state linear-dichroic infrared (IR-LD) spectroscopy of oriented colloids in nematic liquid crystal host, ¹H- and ¹³C-NMR, TGA and DSC, UV–Vis spectroscopy, EPR, ESI- and FAB mass spectrometry and HPLC tandem mass spectrometry (HPLC-MS/MS). Quantum chemical calculations are carried out with a view to obtain the structures and spectroscopic properties of the ligand and newly synthesized metal complexes.     

Complex formation in nickel(II)-glycine-β-lactam antibiotic systems

Complex formation in solutions containing Ni²⁺ cations, glycine anions (Gly^?), and β-lactam antibiotics, namely, ampicillin (Amp), amoxicillin (Axn), and cephalexin (Cpx), is studied by pH-metric titration at 20°C and an ionic strength of 0.1 (KNO₃). Mixed-ligand complexes [NiGlyAmp], [NiGlyAxn], and [NiGlyCpx], which are in equilibrium with the [NiGly]⁺ complexes, are formed in the systems studied in a weakly alkaline medium. The formation constants of the complexes are determined. The distribution diagrams of the complex Ni(II) forms at different pH values of the solutions are constructed.     

Chemical reactivity of analogous technetium(V) and rhenium(V) dioxo complexes

All complexes of the series [MO₂L₂]⁺ (M=Tc, Re; L=ethylenediamine (en), 1,3-diaminopropane (1,3-dap)) have been synthesized and their chemical reactivities investigated. The following properties were studied: stability of the aqueous solutions at different pH values, substitution kinetics, lipophilicity and protein binding. The complexes show very similar reactivity in aqueous solution. From a radiopharmaceutical point of view, no significant difference in their in vivo behavior is expected.     

Investigation on transition States of [Alanine + M2+] (M = Ca,Cu, and Zn) complexes: A quantum chemical study

The ground state geometries of [Alanine (Ala) + M²⁺] [M = Ca, Cu, and Zn) complexes were calculated in gas phase at B3LYP/6‐311++G(d,p) level of theory. Transition states (TSs) between different stable conformers of [Ala + M²⁺] complexes were also calculated. Among the different [Ala + M²⁺] complexes, the complex where metal cations coordinated to carboxylate group (? COO^?) is found to be energetically most favorable. To calculate TSs, the ground state structures of any two conformers of [Ala + M²⁺] complexes were used. The ground state energies of two stable conformers and their TS structures were used to calculate the activation energy. The reactivity of different conformers of [Ala + M²⁺] complexes have been discussed in terms of energy difference between their highest occupied molecular orbital and lowest unoccupied molecular orbital. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Synthesis and vibrational study of platinum(II) and palladium(II) complexes of glyoxilic acid oxime

New platinum(II) and palladium(II) complexes of glyoxilic acid oxime (gao) have been prepared and characterised by infrared (4000–150 cm⁻¹) and Raman (4000–200 cm⁻¹) spectra. The gao acts as bidentate ligand bonding through the oxime nitrogen and carboxyl oxygen atoms to form neutral bis-chelate square-planar complexes. The lowest energy conformer of the gao ligand (ectt) was selected among 16 theoretically possible conformers on the basis of ab initio calculations at HF/3-21G*, HF/6-31G* and HF/6-311** levels of the theory from which structural parameters and conformational stabilities have been obtained. A complete vibrational assignment of the gao was performed for the lowest energy ectt conformer on the basis of ab initio optimised parameters and normal coordinate analysis calculations (PED). NCA calculations of the complexes studied were also performed.     

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p, H₆ L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H₄dota and H₈dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several Ln^III–H₆ L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H₂O)]^3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the ¹H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H₂O)]^2? and [Yb(H L )]^2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between ³¹P/¹H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N₄ and O₄ planes.     

Structure‐Based Design of Platinum(II) Complexes as c‐myc Oncogene Down‐Regulators and Luminescent Probes for G‐Quadruplex DNA

A series of platinum(II) complexes with tridentate ligands was synthesized and their interactions with G‐quadruplex DNA within the c‐myc gene promoter were evaluated. Complex 1 , which has a flat planar 2,6‐bis(benzimidazol‐2‐yl)pyridine (bzimpy) scaffold, was found to stabilize the c‐myc G‐quadruplex structure in a cell‐free system. An in silico G‐quadruplex DNA model has been constructed for structure‐based virtual screening to develop new Pt^II‐based complexes with superior inhibitory activities. By using complex 1 as the initial structure for hit‐to‐lead optimization, bzimpy and related 2,6‐bis(pyrazol‐3‐yl)pyridine (dPzPy) scaffolds containing amine side‐chains emerge as the top candidates. Six of the top‐scoring complexes were synthesized and their interactions with c‐myc G‐quadruplex DNA have been investigated. The results revealed that all of the complexes have the ability to stabilize the c‐myc G‐quadruplex. Complex 3 a ([Pt^II L2R ] ⁺ ; L2 =2,6‐bis[1‐(3‐piperidinepropyl)‐1H‐enzo[d]imidazol‐2‐yl]pyridine, R =Cl) displayed the strongest inhibition in a cell‐free system (IC₅₀=2.2 μM ) and was 3.3‐fold more potent than that of 1 . Complexes 3 a and 4 a ([Pt^II L3R ]⁺; L3 =2,6‐bis[1‐(3‐morpholinopropyl)‐1H‐pyrazol‐3‐yl]pyridine, R =Cl) were found to effectively inhibit c‐myc gene expression in human hepatocarcinoma cells with IC₅₀ values of ≈17 μM , whereas initial hit 1 displayed no significant effect on gene expression at concentrations up to 50 μM . Complexes 3 a and 4 a have a strong preference for G‐quadruplex DNA over duplex DNA, as revealed by competition dialysis experiments and absorption titration; 3 a and 4 a bind G‐quadruplex DNA with binding constants (K) of approximately 10⁶–10⁷ dm³ mol^?1, which are at least an order of magnitude higher than the K values for duplex DNA. NMR spectroscopic titration experiments and molecular modeling showed that 4 a binds c‐myc G‐quadruplex DNA through an external end‐stacking mode at the 3′‐terminal face of the G‐quadruplex. Intriguingly, binding of c‐myc G‐quadruplex DNA by 3 b is accompanied by an increase of up to 38‐fold in photoluminescence intensity at λ_max=622 nm.     

Dinuclear Ruthenium(II) Complexes That Induce and Stabilise G‐Quadruplex DNA

A series of dinuclear ruthenium(II) complexes were synthesised, and the complexes were determined to be new highly selective compounds for binding to telomeric G‐quadruplex DNA. The interactions of these complexes with telomeric G‐quadruplex DNA were studied by using circular dichroism (CD) spectroscopy, fluorescence resonance energy transfer (FRET) melting assays, isothermal titration calorimetry (ITC) and molecular modelling. The results showed that the complexes 1 , 2 and 4 induced and stabilised the formation of antiparallel G‐quadruplexes of telomeric DNA in the absence of salt or in the presence of 100 mM K⁺‐containing buffer. Furthermore, complexes 1 and 2 strongly bind to and effectively stabilise the telomeric G‐quadruplex structure and have significant selectivity for G‐quadruplex over duplex DNA. In comparison, complex 3 had a much lesser effect on the G‐quadruplex, suggesting that possession of a suitably sized plane for good π–π stacking with the G‐quadruplets is essential for the interaction of the dinuclear ruthenium(II) complexes with the G‐quadruplex. Moreover, telomerase inhibition by the four complexes and their cellular effects were studied, and complex 1 was determined to be the most promising inhibitor of both telomerase and HeLa cell proliferation.     

Reactivity Tracers of the Hydrolysis of Fe(II)‐Bis(salicylidene) Complexes: Initial–Transition States Analysis and Enhanced Impact of Tensides on the Kinetic Trends

The kinetics of the acid hydrolysis reaction of Fe(II)‐bis(salicylidene) complexes were followed under pseudo–first‐order conditions ([H⁺] >> [complex]) at 298 K. The ligands of the studied azomethine complexes were derived from the condensation of salicylaldehyde with different five α‐amino acids. The hydrolysis reactions were studied in acidic medium at different ratios (v/v) of aqua–organic mixtures. The decrease in the dielectric constant values of the reaction mixture enhances the reactivity of the reaction. The transfer chemical potentials of the initial and transition states (IS–TS) from water into mixed solvents were determined from the solubility measurements combined with the kinetic data. Nonlinear plots of logk_obs versus 1/D (the reciprocal of the dielectric constant) suggest the influence of the solvation of IS–TS on the reaction reactivity. Furthermore, the acid hydrolysis reactions were screened in the presence of different concentrations of cationic and anionic tensides. The addition of surfactants to the reaction mixture accelerates the reaction reactivity. The obtained kinetic data were used to determine the values of δ_mΔG^# (the change in the activation barrier) for the studied complexes when transferred from “water to various ratios (v/v) of water–co‐organic binary mixtures” and from “water to water containing different [surfactant].” It was found that the reactivity of the acid hydrolysis reaction was controlled by the hydrophobicity of the studied chelates.     

Coordination properties of N,O-carboxymethyl chitosan (NOCC). Synthesis and equilibrium studies of some metal ion complexes. Ternary complexes involving Cu(II) with (NOCC) and some biorelevant ligand

In the present study, the acid-base equilibria of N,O-carboxymethy chitosan abbreviated as (NOCC), is investigated. The complex formation equilibria with the metal ions Cu^(II), Ni^(II), Co^(II), Mn^(II), and Zn^(II) are investigated potentiometrically. The stability constant values of the binary and ternary complexes formed in solution were determined and the binding centers of the ligands were assigned. The relationships between the properties of the studied central metal ions as ionic radius, electronegativity, atomic number, and ionization potential, and the stability constants of the formed complexes were investigated in an effort to give information about the nature of chemical bonding in complexes and make possible the calculation of unknown stability constants. Cu^(II), Ni^(II), and U^(VI) complexes with NOCC are isolated as solid complexes and characterized by conventional chemical and physical methods. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. The ternary copper(II) complexes involving NOCC and various biologically relevant ligands containing different functional groups, as amino acids and DNA constituents are investigated. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated.     

Polarography of uranium(VI) and lead(II) complexes with l-glutamine

The complexes of uranium(VI) and lead(II) with 1-glutamine were investigated polarographically. For uranium(VI), the complexes UO(2)G(+2), UO(2)G(2)(+2) and UO(2)(OH)Ga(2)(+) were identified at pH < 2.5, pH 2.5-4.1 and pH 4.1-5.2 respectively. With lead(II), complexes PbG(+2), Pb(OH)G(+) and Pb(OH)G(2)(+) were formed at pH 2.0-5.0, pH 5.0-7.0, and pH 7.0-8.5, respectively. The concentration dissociation constant of Pb(OH)G(2)(+) was found to be pK(c) = 10.16 +/- 0.04 at ionic strength 0.6.     

Spectroscopic characteristics of dimethylsulfoxide molecules coordinated to Mg2+ cation. structure of complexes [Mg(DMSO)i(CH3CN)6-i]2+ from the data of quantum-chemical calculations and IR spectra of Mg(ClO4)2-DMSO-CH3CN Solutions

By the DFT B3LYP/6-31G** method the geometry was optimized and IR spectra were calculated of complexes [Mg(DMSO) _i (CH₃CN)_6-i ]²⁺ (i = 1–6). The values of free energy ΔG in the reaction of ligands substitution in the coordination sphere of the cation were determined. A satisfactory agreement between experimental and calculated values of structural parameters and infrared spectra of free molecules and coordinated to the cation DMSO was obtained. The regularities in the changes of the spectroscopic and structural characteristics of [Mg(DMSO) _i (CH₃CN)_6-i ]²⁺ complexes at varying their composition were revealed. The frequencies and absolute integral intensities of DMSO bands in the IR spectra of pure liquid, solutions in acetonitrile, and in three-component solutions Mg(ClO₄)₂-DMSO-CH₃CN were measured. A correspondence between the calculated change of the frequency and absolute intensity of the IR bands v(C≡N), v(C-C), v(S=O), and v(SC) of the complexes and the corresponding values in the IR spectra of the solutions with different content of components of binary solvent was found.     

Complexation dans le méthanol anhydre de Cu (II) et Zn (II) par des ligands diaza-polyoxamacrocycliques

Complexation in anhydrous methanol of Cu (II) and Zn (II) with diaza-polyoxamacrocyclic ligands Protonation of five diaza-polyoxamacrocyclic ligands, (L = [2.1], [2.2], [2.1.1.], [2.2.1], [2.2.2]), and their complexing properties towards Cu²⁺ and Zn²⁺ cations have been studied in anhydrous methanolic solutions. Potentiometric measurements have been carried out at 25°, using 5 · 10^?2MEt₄N⁺ClO as support-electrolyte, in order to determine the nature of the species formed upon complexation and their stability constants. The results were confirmed by spectrophotometry, for the cupric complexes of [2.1] and [2.2.2], and the electronic spectra of the different complexes were calculated. Comparison between complexation in aqueous and methanolic solutions have been made: as in water, ML²⁺ species and sometimes protonated MHL³⁺ species, with higher stability constants, are present in methanol; but the main difference is the formation of dinuclear complexes M₂L⁴⁺, between Cu²⁺ and all ligands except [2.1]. In these complexes the Cu²⁺ cations cannot be both ‘encaged’ in the ligand cavity because of its small size. The different possible structures are discussed in terms of the stability constants values. The protonation constants values and the existence of the binuclear complexes may indicate a possible conformational change in the complexing ligand on changing the solvent from water to methanol.     

Zirconium (IV), Thorium (IV) and Dioxouranium (VI) Complexes of Dibasic Tridentate Schiff Bases

Dibasic tridentate Schiff bases obtained by the condensation of O -aminobenzoic acid with salicyldehyde and its 5-chloro and 5-bromo derivatives were synthesised and used to pracipitate Zr(IV), Th(IV) and UO₂(VI) metals as complexes. The 1:1 (metal-ligand) stoichiometry of these complexes is shown by elemental analysis, gravimetric estimations and conductometric titrations while the structures of the complexes are proved by i.r. spectra and thermogravimetric analysis. The magnetic susceptibility measurements by Gouy method show, these complexes to be monormeic and diamagnetic. The molar conductance values in nitrobenzene indicate the nonelectrolytic behaviour of the complexes. The results show that the complexes of the type Zr(OH)²L.H²O, Th(OH)²L.H²O and UO²L.H²O are formed having solvent molecule in co-ordination with metal ion.     

Spectral and thermogravimetric studies of oxohalobis(4-morpholinyldithiocarbamato)molybdenum(V) complexes

Summary Molybdenum(V) complexes [MoOX(4-Morphdtc)₂] (X=F, Cl, Br or I; 4-Morphdtc = 4-morpholinyldithiocarbamate) have been prepared from molybdenum trioxide using hydrazine hydrohalides as reducing agents. The magnetic moment values atca. 1.65 B.M. and e.p.r. studies indicated that the complexes are mononuclear and that molybdenum is in + 5 oxidation state. The i.r. spectral bands at 1500 and 960 cm^–1 suggest that the dithiocarbamate acts as a univalent bidentate ligand and the bands at 930 cm^–1 confirms the presence of a MoO³⁺ moiety in the complex. The low conductivity values for the complexes inN, N-dimethylformamide indicate that the complexes are non-ionic. The [MoOX(4-Morphdtc)₂] complexes (X=F, Cl or Br) decompose in the first step by the loss of one dithiocarbamate group, whereas in [MoOI(4-Morphdtc)₂] the iodine atom is lost in the first step. The second and third steps lead to the formation of MoS₃ and MoO₃, respectively. A six coordinate structure around Mo with an oxo, halo and two dithiocarbamate groups is proposed.     

Density functional theory insight into Eu(III) and Am(III) complexes with two 2,6-dicarboxypyridine diamide-type ligands

Extraction complexes of Eu(III) and Am(III) with two 2,6-dicarboxypyridine diamide-type ligands L–A and L–B (Fig. 1) are studied by density functional theory (DFT). At both B3LYP/6-31G(d)/RECP and MP2/6-31G(d)/RECP levels of theory, the geometrical optimizations of the structures of the complexes can achieve the same accuracy and obtain the same geometrical configuration. At the B3LYP/6-311G(d,p)/RECP level of theory Eu³⁺ and Am³⁺ prefer to form [ML]³⁺ complexes under the solvation conditions, and the Am(III) complexes with L–A are more stable than the corresponding Eu(III) complexes. In the system with the ligand L–B, both [ML]³⁺ and [ML(NO₃)₃] species are very unstable.