Binding of polyanions by biogenic amines. II. Formation and stability of protonated putrescine and cadaverine complexes with carboxylic ligands

The formation and stability of protonated diamines-carboxylic ligand complexes was studied potentiometrically (H(+)-glass electrode). Species formed are ALH(r) (A=cadaverine, putrescine, L=acetate, malate, tartrate, malonate, citrate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate and glutamate; r=1...m+1, where m is the maximum degree of protonation of the carboxylic ligand), and their stability is a function of charges involved in the formation reaction. For the equilibrium H(i)A(i+)+H(j)L((j-z))=ALH((i+j-z))(i+j) the following linear relationships can be written: logK(1j)=-0.25+0.75 |j-z|, logK(2j)=0.50+0.90 |j-z| (by also considering some ethylenediamine and 1,2-diaminopropane complexes). Medium effects were considered. Comparison was made with analogous inorganic polyanion complexes. The simplest relationships -DeltaG(0)=6.5+/-0.3 and -DeltaG(0)=7.9+/-0.6 kJ mol(-1)n(-1) (n=number of possible salt bridges) were found for carboxylic and inorganic anions, respectively.     

Binding of polyanions by biogenic amines. III. Formation and stability of protonated spermidine and spermine complexes with carboxylic ligands

The formation and stability of protonated spermidine and spermine-carboxylic ligand complexes (seven systems) were studied potentiometrically (H(+)-glass electrode). ALH(r) species are formed (A=spermidine, spermine, L(z-)=acetate, malonate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate; r=1...m+n-1, where m and n are the maximum degree of protonation of the amine and of the carboxylic ligand, respectively), and their stability is a function of charges involved in the formation reaction. For the equilibrium H(i)A(i+)+H(j)L((j-z))=ALH(i+j)((i+j-z)) the linear relationship logK(ij)=0.46 zeta (zeta=mid R:i(z-j)mid R:) was found. By means of this simple equation a mean free energy value can be obtained per salt bridge (n), namely -DeltaG degrees =5.25+/-0.15 kJ mol(-1)n(-1). Species formed by the highest charged ligands are quite stable (K>10(3) mol(-1) dm(3)) and potentially play an important role in the speciation of biofluids, as shown by speciation diagrams and simulated experiments.     

Polarographic study of mixed ligand complexes of Pb(II) with carboxylate ions and imidazole

Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart^2?), malonate (mal^2?) and citrate (citr^3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO₃) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β₁₁ = 4.19; with mal^2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)₂] and [Pb(mal)₂(im)]^2? with stability constants log β₁₁ = 4.3, log β₁₂ = 7.3 and log β₂₁ = 5.5 respectively are formed. With citr^3? and im a single mixed species, [Pb(citr)(im)]^? with stability constant log β₁₁ = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed.     

Ternary complexes between cationic GdIII chelates and anionic metabolites in aqueous solution: an NMR relaxometric study

The (1)H and (17)O NMR relaxometric properties of two cationic complexes formed by Gd(III) with a macrocyclic heptadentate triamide ligand, L(1), and its Nmethylated analogue, L(2), have been investigated in aqueous media as a function of pH, temperature and magnetic field strength. The complexes possess two water molecules in their inner coordination sphere for which the rate of exchange has been found to be sensibly faster for the Nmethylated derivative and explained in terms of electronic effects (decrease of the charge density at the metal center) and perturbation of the network of hydrogen-bonded water molecules in the outer hydration sphere. The proton relaxivity shows a marked dependence from pH and decreases of about six units in the pH range 6.5 to 9.0. This has been accounted for by the displacement of the two water molecules by dissolved carbonate which acts as a chelating anion. The formation of ternary complexes with lactate, malonate, citrate, acetate, fluoride and hydrogenphosphate has been monitored by (1)H NMR relaxometric titrations at 20 MHz and pH 6.3 and the value of the affinity constant, K, and of the relaxivity of the adducts could be obtained. Lactate, malonate and citrate interact strongly with the complexes (log K > or =3.7) and coordinate in a bidendate mode by displacing both water molecules. Larger affinity constants have been measured for GdL(2). Acetate, fluoride and hydrogenphosphate form monoaqua ternary complexes which were investigated in detail with regard to their relaxometric properties. The NMR dispersion (NMRD) profiles indicate a large contribution to the relaxivity of the adducts from water molecules belonging to the second hydration shell of the complexes and hydrogen-bonded to the anion. A VT (17)O NMR study has shown a marked increase of the rate of water exchange upon binding which is explained by coordination of the anion in an equatorial site, thus leaving the water molecule in an apical position, more accessible for interactions with the solvent molecules of the second hydration shell which facilitate the exchange process.     

Mixed ligand palladium(II) complexes of oxalate and malonate with vitamin-B6 molecules: synthesis,crystal structure and kinetics

The synthesis of six mononuclear palladium complexes of general formula [Pd(ox)/(mal)L₂] and [Pd(ox)/(mal)L] (ox = oxalate, mal = malonate, both L and L are vitamin-B₆ molecules (I), L = pyridoxine, pyridoxal and L = pyridoxamine) has been achieved. The structures of these compounds were established by elemental analysis, i.r. and ¹³C-n.m.r. [Pd(oxalate)(pyridoxine)₂] was analyzed by single crystal X-ray diffraction. It exhibits square planar coordination with bond lengths 2.015 (2) Å for Pd—N and 2.010 (2) Å for Pd—O. The interaction of [Pd(ox)₂]^2– and [Pd(mal)₂]^2– with L has been followed kinetically in order to look into the nature of products and the mechanism of formation under the conditions [Pd^II-chelate] [L] and [L].     

Ion-selective electrode measurements for the determination of formation constants of alkali and alkaline earth metals with low-molecular-weight ligands

Formation constants of acetate, hydrogencarbonate, malonate, citrate and 1,2,3-propanetricarboxylate complexes with Na⁺, K⁺ and Ca²⁺ were determined potentiometrically using sodium, potassium and calcium selective electrodes, at 25 °C and at different ionic strengths, in the range 0 < I ≤ 1 M. Formation constants obtained by ion-selective electrode (ISE) measurements were compared with those obtained by different techniques. It has been found that the use of ISEs gives reliable results in the study of weak complexes, also under non-constant ionic strength conditions.     

Acetate and malonate complexes of cobalt(II), nickel(II) and zinc(II) with hydrazinium cation

The hydrazinium(1+) metal acetates and malonate dihydrates of the molecular formula [(N₂H₅)₂M(CH₃COO)₄] and (N₂H₅)₂[M(OOCCH₂COO)₂(H₂O)₂] respectively, whereM=Co, Ni or Zn, have been prepared and characterized by chemical analyses, conductance, magnetic, spectral, thermal and X-ray powder diffraction studies. The magnetic moments and electronic spectra indicate that these complexes are of high-spin octahedral variety. The infrared spectra show that the hydrazinium ions are coordinated in the case of acetate complexes, whereas in the malonate complexes the hydrazinium ions are out side the coordination sphere. These complexes undergo exothermic decomposition in the temperature range 150–450°C to give the respective metal oxide as the final residue. The X-ray powder diffraction patterns of the malonate complexes indicate isomorphism among them.     

Interaction of alkyltin(IV) compounds with ligands of interest in the speciation of natural fluids: carboxylate and hydroxycarboxylate complexes of monomethyltin(IV) trichloride

The formation and stability of some carboxylate and hydroxycarboxylate (acetate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate, malate and citrate) complexes of monomethyltin trichloride was studied potentiometrically at 25 degrees C and at different ionic strengths in NaNO3 aqueous solution. The following quite stable species are formed in the different systems (M = CH3Sn3+): ML(OH)+, ML2(OH)0, ML(OH)2(0) and M2L(OH)5(0) for acetate; MLH+, ML0, ML(OH)- and ML(OH)2(2-) for propanetricarboxylate; MLH2+, MLH0, ML-, ML(OH)2- and ML(OH)2(3-) for butanetetracarboxylate; ML(OH)0, ML(OH)2- and ML(OH)3(2-) for malate; ML0, ML(OH)-, ML(OH)2(2-) and ML(OH)3(3-) for citrate. Hydroxycarboxylate complexes are significantly stronger than simple carboxylate ones and this is likely to be due to the interaction of the -OH group in citrate and malate with monomethyltin(IV), whose strength was also quantified. It was found that the stability of these complexes can be roughly expressed by the simple relationship log K = a zeta, where zeta is the product of the charges of reactants and log K is the equilibrium constant. For simple carboxylic ligands we have a = 1.8 +/- 0.4 and, for hydroxycarboxylic ligands, a = 3.7 +/- 0.9. Other useful empirical relationships are reported. Moreover, hydroxycarboxylic complexes also play a prominent role in the speciation of monomethyltin(IV) under the pH conditions of interest for natural fluids.     

有机酸与无机阴离子的梯度离子色谱法分析研究

研究了用离子色谱法梯度洗脱抑制电导检测器分析有机酸与无机阴离子的色谱条件,建立了最佳梯度程序。用阴离子交换分离,选用去离子水、氢氧化钠和甲醇作淋洗液,分别对５种二元有机酸和３种无机阴离子做二元梯度淋洗,对１０种多元有机酸和３种无机阴离子做三元梯度淋洗。方法用于果汁饮料与柠檬酸发酵液的测定,结果令人满意。     

Binding of 1,2,4-benzenetricarboxylate by open chain polyammonium cations

The interaction of some open chain polyammonium cations with 1,2,4-benzenetricarboxylate was studied potentiometrically, at 25 degrees C. For all the investigated systems, the species ALHr(r-3) (r = 1,2 ... n + 2; n = number of aminogroups; A = amine; L = carboxylate) are formed. The stability of these complexes depends on charges in the polyammonium cation and in the carboxylic ligand, and for the reaction HiAi+ + HjL(j - 3) = ALHi + j(i + j - 3) we found a mean free energy contribution for salt bridge -delta G0 = 6.5 +/- 0.3 kJ mol-1 n-1 (n = number of possible salt bridges). The results of this investigation are compared with those of similar systems. By considering also the tricarboxylic ligands citrate and 1,2,3-propanetricarboxylate, we found for their complexes with polyammonium cations a fairly close stability. Calculations performed including complexes formed with these two ligands give -delta G0 = 6.6 +/- 0.4 kJ mol-1 n-1.     

Mixed complex formation of copper(II) with 2,2′, 2″-terpyridine and some tridentate ligands in aqueous solution

Summary The formation of copper(II) ternary complexes [Cu(tpy)(L)] (tpy = 2,2,2-terpyridine; L = oxydiacetate, thiodiacetate, iminodiacetate or dipicolinate) has been studied by potentiometric measurements in aqueous solution at 25° and I = 0.1 mol dm^–3 (NaNO₃ or NaClO₄). All the systems investigated also form protonated species of the [Cu(tpy)(L)H]⁺ type. The effect of the different heteroatoms (donor atoms) in the ligands L (i.e. O, S or N), other than oxygens of the carboxylic groups, on the stability of the mixed complexes has been evaluated and compared with the trends observed for the analogous complexes of copper(II) with 2,2-bipyridine (bpy).The stabilization of ternary complexes of copper(II) with respect to the different coordination levels is also discussed.     

Interaction of methyltin(IV) compounds with carboxylate ligands. Part 2: formation thermodynamic parameters,predictive relationships and sequestering ability

Thermodynamic data of mono‐, di‐ and tri‐methyltin(IV)‐carboxylate complexes (acetate, malonate, succinate, oxydiacetate, diethylenetrioxydiacetate, malate, citrate, 1,2,3‐tricarballylate, 1,2,3,4‐butanetetracarboxylate, 1,2,3,4,5,6‐benzenehexacarboxylate) in aqueous solution are reported at t = 25 °C and I = 0 mol l⁻¹. Thermodynamic parameters obtained were analysed to formulate empirical predictive relationships as a function of different parameters, such as the number of carboxylate groups of the ligand and the charge of the alkyltin(IV) cation. Sequestration diagrams of citrate and 1,2,3‐tricarballylate towards alkyltin(IV) cations at different pH values are also reported and discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

FEATURES OF A FLEXIBLE BACKBONE IN THE COORDINATION COMPOUNDS OF A DIOXIME LIGAND: THE CHARACTERIZATION OF SUPRAMOLECULAR AND DINUCLEAR METAL COMPLEXES

Abstract

The grinding of a 2: 1 molar ratio mixture of isonitrosoacetylacetone and 1,3-diaminopropan-2-ol led to formation of the tribasic ligand (H₃L), (1) with two oxime groups and a flexible alcoholic backbone. The 1:2 molar ratio reaction of (1) with CuX₂ produced the planar dinuclear complexes LCu₂(X) nH₂O; × = acetate (2), phenylacetate (3), formate (4), monochloroacetate (5), dichloroacetate (6), trichloroacetate (7), benzoate (8), and p-hydroxybenzoate (9); n = 1 for (2) and (8); n = 2 for (3)-(7); and n = 4 for (9). The copper(II) ions are bridged by the carbox-ylate and the alcoholic oxygen. The strong antiferromagnetic interactions in (2)-(9) are impeded in (5)-(7) by the chloroacetate bridge withdrawing electron density from the carboxylate. The latter bridge is replaced by picrate in the 1:1 molar ratio reaction of (2) with picric acid (10). The 1:1 molar ratio reaction of (1) with copper(II) acetate produced the tetranuclear [HLCu]₂[LCu₂(OAc)] 5H₂O (11), whereas the 2:1 molar ratio reaction, similar to the reaction which led to (8), produced HLCu (12). The latter complex reacted (1:1 molar ratio) with either copper(ll) acetate or nickel(II) acetate to produce complexes (2) and the heterodinuclear LNi-Cu(OAc) 2H₂O (13), respectively. Similar reactions with (11) gave the same complexes (2) and (13). The acid adducts of (9) with p-hydroxybenzoic acid (14) and LCu₂(X)-HX (15); × = p-aminobenzoic acid were isolated. The cobalt(II) analogue of the mononuclear (12), HLCo 2H₂O (16) was obtained from the 1:1 molar reaction of (1) with cobalt(II) acetate. The supramolecular structure of (11), (12) and (16) took place via intermolecular hydrogen bonding of the alcoholic proton with the oximato oxygen of the adjacent molecule which mediated electron density and allowed for a magnetic exchange interaction. The suggested structures of the ligand and metal complexes are in accordance with analytical, spectral and magnetic moment data.     

Kinetics of Ga(NOTA) formation from weak Ga-citrate complexes

Gallium complexes are gaining increasing importance in biomedical imaging thanks to the practical advantages of the (68)Ga isotope in Positron Emission Tomography (PET) applications. (68)Ga has a short half-time (t(1/2) = 68 min); thus the (68)Ga complexes have to be prepared in a limited time frame. The acceleration of the formation reaction of gallium complexes with macrocyclic ligands for application in PET imaging represents a significant coordination chemistry challenge. Here we report a detailed kinetic study of the formation reaction of the highly stable Ga(NOTA) from the weak citrate complex (H(3)NOTA = 1,4,7-triazacyclononane-1,4,7- triacetic acid). The transmetalation has been studied using (71)Ga NMR over a large pH range (pH = 2.01-6.00). The formation of Ga(NOTA) is a two-step process. First, a monoprotonated intermediate containing coordinated citrate, GaHNOTA(citrate)*, forms in a rapid equilibrium step. The rate-determining step of the reaction is the deprotonation and slow rearrangement of the intermediate accompanied by the citrate release. The observed reaction rate shows an unusual pH dependency with a minimum at pH 5.17. In contrast to the typical formation reactions of poly(amino carboxylate) complexes, the Ga(NOTA) formation from the weak citrate complex becomes considerably faster with increasing proton concentration below pH 5.17. We explain this unexpected tendency by the role of protons in the decomposition of the GaHNOTA(citrate)* intermediate which proceeds via the protonation of the coordinated citrate ion and its subsequent decoordination to yield the final product Ga(NOTA). The stability constant of this intermediate, log K(GaHNOTA(citrate)*) = 15.6, is remarkably high compared to the corresponding values reported for the formation of macrocyclic lanthanide(III)-poly(amino carboxylates). These kinetic data do not only give mechanistic insight into the formation reaction of Ga(NOTA), but might also contribute to establish optimal experimental conditions for the rapid preparation of Ga(NOTA)-based radiopharmaceuticals for PET applications.     

Thermodynamic Studies of the Complexation between Neodymium and Acetate at Elevated Temperatures

Complexation of neodymium (III) with acetate in 2.2 mol-kg^-1 NaClO₄ solution was studied at elevated temperatures (45 and 70°C) by potentiometry, calorimetry, and optical spectroscopy. The formation constants of the consecutive complexes, Nd(OOCCH₃),²⁺ Nd(OOCCH₃) ₂ ⁺ , and Nd(OOCCH₃)₃, and the molar enthalpies of complexation at these temperatures were determined. The stability of the three complexes increases with increased temperatures, because of increased positive entropy change at higher temperatures, which exceeds the increased values of the positive (endothermic) enthalpy. The molar heat capacity changes of complexation C_p,m(MLj) (J-K^-1-mol^-1) for Nd(OOCCH₃) _j ^(3-j)+ in the temperature range from 25 to 70°C were calculated to be: 102 ± 13 (j = 1); 122 ± 19 (j = 2); and 239 ± 27 (j = 3). The effect of temperature on the complexation is discussed in terms of the electrostatic model.     

Chemical properties and cytotoxic activity of complexes of platinum(II) and palladium(II) containing dmso and various anions; synthesis and structural characterization of [Pt(dmso)2{O2(CO)2CCH2CH2CH2}]

Treatment of cis-[Pt(dmso)₂Cl₂] with 2 mol of KBr or KI leads to the formation of the analogous dibromide or diiodide complexes. Treatment of [M(dmso)₂Cl₂] [M = Pt (cis-) or Pd (trans-)] with AgNO₃ (2 mol) in H₂O followed by 1mol of potassium oxalate, maleate, cyclobutane dicarboxylate (CBDC), malonate or 2mol of potassium cyclohexane carboxylate or pivalate leads to the formation of the corresponding Pt^II and Pd^II carboxylate complexes. The single crystal X-ray structure determination of [Pt(dmso)₂(CBDC)] has been discussed and compared with data on other related complexes. The in vitro cytotoxic activity of some of these complexes against eight tumour cell lines has been examined using the MTT-colorimetric assay.     

Salt effects on the protonation and on alkali and alkaline earth metal complex formation of 1,2,3-propanetricarboxylate in aqueous solution

The protonation of 1,2,3-propanetricarboxylate (tricarballylate, tca) was studied in LiCl, NaCl, KCl, MgCl(2), CaCl(2) and tetraethylammonium iodide (Et(4)NI) aqueous solutions, at 25 degrees C, in the ionic strength range 0 < I < 1M, using the pH-metric technique. The differences between protonation constants determined in Et(4)NI and those determined in the other background salts were interpreted in terms of complex formations. Least squares calculations are consistent with the formation of MLH(j) (j = 0,1.2), M(2)LH(i) (i = 0,1,2), M(2)L species, when M = Mg(2+), Ca(2+). Potentiometric measurements performed in mixed NaClKCl, NaClCaCl(2) and MgCl(2)CaCl(2) solutions showed the formation of mixed metal complexes NaKL, NaKHL, NaCaL and CaMgL. The dependence on ionic strength of protonation and complex formation constants was evaluated using a simple Debye-Hückel type equation.     

Two New Trinuclear MII (M = Mn,Co) Complexes Based on 2,4‐Dichlorobenzoic Acid: Synthesis,Structures and Magnetic Properties

Two new isostructural complexes, [Mn₃(L)₆(bipy)₂] ( 1 ) and [Co₃(L)₆(bipy)₂] ( 2 ) (L = 2,4‐dichlorobenzoate, bipy = 2, 2′‐bipyridine) were synthesized under the hydrothermal conditions and characterized by single‐crystal X‐ray diffraction, IR spectroscopy, EA (elemental analysis), and magnetic measurements. The two complexes are found to contain a trinuclear (M₃) unit that opens up a possibility of being magnetic materials. The magnetic measurements reveal that 1 exhibits the antiferromagnetic exchange interaction between metal ions and 2 presents a weak ferromagnetic interactions between the Co^II ions.     

Dioxouranium(VI)--carboxylate complexes. Interaction with dicarboxylic acids in aqueous solution: speciation and structure

In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.     

Interaction between ligands in ternary complexes of cadmium(II) with phenanthroline and phenylalkylmalonates in solution

The formation and stability of the ternary complexes of cadmium(II) with phenanthroline and malonate, phenylmalonate, benzylmalonate, 2-phenylethylmalonate, and 3-phenylpropylmalonate are studied by the potentiometric pH-titration technique in 40% (v/v) dioxane-water at 25°C and 0.1 mol/l ionic strength (NaNO₃). In all systems, there are stable ternary complexes. The complexes possess enhanced stability relative to their statistical values. The possible reasons that lead to these results are discussed in terms of π-electron back donation from metal ions to ligands and the intramolecular ligand-ligand aromatic ring stacking interaction. ¹H NMR measurements are used to demonstrate the aromatic ring-stacking interaction. The relative contribution of each interactions to the enhanced stability is also estimated. The results show that there are two weak interactions simultaneously observed in these ternary complexes. The interaction strength of aromatic ring stacking in the ternary complexes increases in the phenylalkylmalonate ligand order: L⁰ < L¹ < L² ≈ L³ (L⁰ = phenylmalonate, L¹ = benzylmalonate, L² = 2-phenylethylmalonate, L³ = 3-phenylpropylmalonate). The text was submitted by the autors in English.