Stabilité des carboxylates de terres rares,II. Bis-hydroxyméthyl-2,2-propionates

The stability constants of 2, 2-bis-hydroxymethyl-propionates of rare earths have been determined at ionic strength 0,100 (NaClO₄) at 25.0°C by a potentiometric method. The ligand forms 1 : 1 and 1 : 2 complexes with all the rare earths and weak 1 : 3 complexes with light rare earths only. In these last complexes, it binds in a unidentate way. The dissociation constant of the acid has also been measured.     

Etude par RMN. de polyaminocarboxylates de terres rares,III. Hydroxyéthyliminodiacétates de praséodyme

¹H—NMR. has been used to study the chemistry of the hydroxyethyliminodiacetate complexes of praseodymium in aqueous solution. The ligand exchanges by spontaneous dissociation of the metal-bis-hydroxyethyliminodiacetate (1:2 complex) and of the metal-bis-hydroxyethyliminodiacetate hydroxocomplex, by acid catalysed dissociation of the 1:2 complex, and by a bimolecular process involving the free ligand and the 1:2 complex or the ternary hydroxo-complex. The ligand exchange rate constants are given and the mechanisms discussed.     

Stabilité des carboxylates de terres rares,IV N-acétylglycinates

The stability constants of N-acetylgycinates of some rare earths in aqueous solution have been determined by a potentiometric method, and by a solvent extraction technique. The ligand forms 1:1 complexes which are stabilized by relatively large positive entropies of formation, the corresponding enthalpies being endothermic. This backs up the assumption that a conjugate base of an amino acid forms innersphere complexes and acts as a unidentate ligand towards a rare earth cation, like a simple carboxylate.     

Etude par RMN. de polyaminocarboxylates de terres rares,II. Nitrilotriacétates de scandium,yttrium, lanthane et lutécium

Proton nuclear magnetic resonance has been used to study the chemistry of the diamagnetic nitrilotriacetate complexes of scandium, yttrium, lanthanum and lutecium in aqueous solution. Complexes with ligand-to-metal ratios of 1 and 2 are present depending of the solution conditions. The ligand exchanges by spontaneous and by acid catalysed dissociation of the metal-bis-nitrilotriacetate, and also by a bimolecular process involving the free ligand and the complex. The ligand exchange rate constants decrease with the ionic radii:lanthanum > yttrium > lutecium > scandium.     

Stabilité des carboxylates de terres rares I Furanne- et thiophène-carboxylates-2

The stability constants of 2-furanecarboxylates and 2-thiophencarboxylates of some rare earths have been determined at ionic strength 0.100 (NaClO₄) at 25.0°C by a potentiometric method. The ligands form 1 : 1 complexes similar to the rare earths propionates.     

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.     

A Spectrophotometric Investigation of the Interaction of Iodine with Dibenzyldiaza‐18‐crown‐6, Aza‐15‐crown‐5 and N‐phenylaza‐15‐crown‐5 in Chloroform Solution

The complex formation reactions between iodine and DBzDA18C6, A15C5 and N‐phenylA15C5 have been studied spectrophotometrically in chloroform solution. In the case of DBzDA18C6 is the resulting 1:2 (ligand…I⁺)I₃^?, while, in the case of A15C5 and N‐phenylA15C5 a 2:2 molecular complex of [(ligand)₂…I⁺]I₃^? type was formed. The spectrophotometric results indicate that gradual release of triiodide ion from its contact ion paired form in the molecular complex into the solution is the rate‐determining step of the reaction. The kinetic rate constants for the complexation reactions were determined at different temperatures, and activation parameters were calculated from Arrhenius and Eyring equations.     

Electrode Kinetics and Ternary Complex Formation of Cd2+‐Antibiotics‐Vitamin‐B5 System. A Polarographic Study

Cd²⁺ complexes with antibiotics viz. neomycin, chlortetracycline, oxytetracycline, tetracycline, penicillin‐V and penicillin‐G as primary ligands and vitamin‐B₅ as secondary ligand have been reported at pH = 7.30 ± 0.01 and μ = 1.0 M KNO₃ at 298 K by polarographic technique.¹ Cd²⁺ formed 1:1:1, 1:1:2, and 1:2:1 complexes with a stability constants trend of neomycin < chlortetracycline < oxytetracycline < tetracycline < penicillin‐V < penicillin‐G can be explained on the basis of the nature of ligands, bonding, and steric hindrance of these drugs. The nature of electrode processes were reversible and diffusion controlled. The values of stability constants showed that these drugs can be used to reduce the toxicity of Cd.     

Synthesis,spectral, thermal,potentiometric and antimicrobial studies of transition metal complexes of tridentate ligand

A series of metal complexes of Cu(II), Ni(II), Co(II), Fe(III) and Mn(II) have been synthesized with newly synthesized biologically active tridentate ligand. The ligand was synthesized by condensation of dehydroacetic acid (3-acetyl-6-methyl-(2H) pyran-2,4(3H)-dione or DHA), o-phenylene diamine and fluoro benzaldehyde and characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, ¹H-NMR, UV–Vis spectroscopy and mass spectra. From the analytical data, the stoichiometry of the complexes was found to be 1:2 (metal:ligand) with octahedral geometry. The molar conductance values suggest the non-electrolyte nature of metal complexes. The IR spectral data suggest that the ligand behaves as a dibasic tridentate ligand with ONN donor atoms sequence towards central metal ion. Thermal behaviour (TG/DTA) and kinetic parameters calculated by the Coats–Redfern and Horowitz–Metzger method suggest more ordered activated state in complex formation. To investigate the relationship between stability constants of metal complexes and antimicrobial activity, the dissociation constants of Schiff bases and stability constants of their binary metal complexes have been determined potentiometrically in THF–water (60:40%) solution at 25 ± 1 °C and at 0.1 M NaClO₄ ionic strength. The potentiometric study suggests 1:1 and 1:2 complexation. Antibacterial and antifungal activities in vitro were performed against Staphylococcus aureus, Escherichia coli and Aspergillus niger, Trichoderma, respectively. The stability constants of the metal complexes were calculated by the Irving–Rosotti method. A relation between the stability constant and antimicrobial activity of complexes has been discussed. It is observed that the activity enhances upon complexation and the order of antifungal activity is in accordance with stability order of metal ions.     

9Be and 31P NMR analyses on the influence of imino groups on Be2+ complex stabilities of a series of cyclo‐μ‐imido triphosphate anions

The complexation behaviors of Be²⁺ with cyclo‐μ‐imido triphosphate anions, cP₃O_9?n(NH)_n^3? (n = 1, 2), have been investigated by both ⁹Be and ³¹P NMR techniques at ?2.3 °C in order to clarify the coordination structures of the complexes. The spectra showed that cP₃O_9?n(NH)_n (n = 1, 2) ligands form ML, ML₂, and M₂L complexes with Be²⁺ ions, and the formation of complexes coordinating with nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. These complexation trends are very similar to those of Be²⁺‐cP₃O₆(NH)₃^3? system, which has been reported by us. The peak deconvolution of ⁹Be NMR spectra made these beryllium complexes amenable to stability constant determinations. The stability constants of the complexes increase with an increase in the protonation constants of the ligands as the number of imino groups, which constitute the ligand molecules, is ascended. This increase is primarily attributable to the lower electronegativity of nitrogen atoms than oxygen atoms, which are directly bonded to central phosphorus atoms; moreover, tautomerism equilibrium in the entire of the imidopolyphosphate molecule is also responsible to the higher basicity. ³¹P NMR spectra measured concurrently have verified the formation of the complexes estimated by the ⁹Be NMR measurement. Intrinsic ³¹P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be²⁺ cations have been determined. Not only the protonation constants but also the stability constants of all Be²⁺ complexes increase approximately linearly with an increase in the number of imino groups. Copyright © 2013 John Wiley & Sons, Ltd.     

Étude thermodynamique de la complexation des lanthanides trivalents avec l'acide hydroxyethyl-ethylenediaminetriacetique et d'autres acides aminoacetiques: III. Détermination des Constantes de Formation des Complexes Mixtes par Titrage Potentiométrique

A thermodyrmmic study of the complex formation of trivaient lanthanides with hydroxyethylethyienediaminetriacetic acid and other aminoacetic acids. Part III. The determination of the formation constants of mixed complexes by potentiometric titration.The partial stability constants of the mixed and 1:2 complexes Ln—HEDTA—L (where Ln = La, Ce,... and L = glycine, IMDA, NTA, HEDTA and EDTA) have been determined by potentiometric titration at 25°C and at a constant ionic strength of 1 (KCl). The changes in stability of the complexes studied (1:1, 1:2, mixed, protonated and unprotonated) vs. atomic number of the lanthanide are discussed. The changes observed in the trends of the partial and overall stability constants across the lanthanide series are attributed to the decrease in the number of water molecules in the 1:1 LnHEDTA ·xH₂O from x = 3 for light lanthanides to x = 2 for heavy ones. However, in this 1:1 complex, HEDTA seems to be a hexadeutate ligand in the La—Sm range of the series and a pentadentate ligand in the Gd—Lu range. Significant differences have been found between the complexes containing four nitrogen atoms, i.e. L = HEDTA, EDTA, and those with three nitrogen atoms i.e. L = glycine, IMDA, NTA.     

pH-Metrische Untersuchungen über einige Komplexe von Seltenen Erden mit gemischten Liganden

The biligand systems, Ln(III)-Aminopolycarboxylic acid₁-Aminopolycarboxylic acid₂ — have been studied pH-metrically and the analysis of the titration curves has shown the formation of 1 : 1 : 1 mixed ligand complexes. Their formation constants have been calculated at 30±1°C and the value of log K follows the order La(III)     

Experimental and calculated complex formation curves for mixed, dynamic and semi-dynamic, metal–ligand systems.: A differential pulse polarographic study of Cu–sarcosine–OH and Cd–MIDA–OH systems at a fixed ligand to metal ratio and varied pH

The Cu–sarcosine–OH and Cd–MIDA–OH systems have been studied by differential pulse polarography (DPP) at a fixed total ligand to total metal concentration ratio and varied pH at 298 K and μ=0.5 mol dm⁻³ in the background of NaNO₃. Both the metal–ligand systems show initially dynamic (labile), followed by semi-dynamic behaviour on the DPP time scale. It has been shown that the experimental and calculated DPP complex formation curves used previously only for labile metal–ligand systems can be employed for the modelling of all species formed in a solution and optimisation of their stability constants. The stability constants of ML and ML₂ complexes as log β were estimated for Cu^II and Cd^II as 7.75±0.02, 14.49±0.01 and 6.67 ±0.02, 12.00±0.02, respectively (all known hydroxide species of copper and cadmium, including polynuclear species, were incorporated into the metal–ligand–OH systems). The formation of the complex CuL₂(OH) is suggested also and its stability constant as log β has been estimated to be 16.2±0.2. Results reported here seem to be reasonable when compared with the literature data reported at 298 K and different ionic strengths.     

Déplacements Chimiques du Carbone 13, Constantes de Couplage 1J(CH) et 3J(CH) dans une série de dérivés trisubstitués du benzène

¹³C chemical shifts, 1-bond and 3-bond (meta) ¹³C? H coupling constants have been determined in a series of trisubstituted benzene; the substituents are Cl, NH₂, N(C₂H₅)₂, N(iC₃H₇)₂, N(C₂H₄)₂O. Chemical shifts are only in moderate agreement with the usual additivity rules. Additivity rules relative to the above mentioned coupling constants are proposed. With few exceptions, the difference between predicted and observed values is less than 10%.     

Lanthanide complexes of D-penicillamine: formation constants,spectral and thermal properties

The complex-formation of lanthanide(III) elements with D-penicillamine have been investigated in acidic and neutral media. The macroscopic protonation constants of the ligand and the formation constants of [Ln.Pen]⁺, [Ln.Pen₂]^?, [Ln.Pen.OH] and [Ln.Pen.(OH)₂]^? complexes were determined from pH-metric data using the BEST computer program. Elemental analyses of the solid complexes indicate formation of 1?:?1 metal?:?ligand species. The binding sites in the complexes with the possible role of –COO^?, –NH₂ and –SH groups in the coordination have been discussed using infrared data. The complexes decompose in four steps as shown by their t.g. and d.t.a. analyses. A mechanism of decomposition is proposed which is supported by mass spectral data.     

Détermination de constantes de stabilité de chélates par résonance magnétique nucléaire du proton

In a solution containing an excess of two metal ions in regard to a ligand (e.g. NTA) a competitive equilibrium is established. The measure, by proton NMR. spectroscopy, of the individual concentrations of both chelates, and eventually of the free ligand, allows to determine the ratio of the stability constants of the two complexes. As an illustration the ratios of the stability constant of the 1:1 nitrilotriacetate chelates of Pb and Zn, respectively Mo and W, were determined.     

New hydrophobic L‐amino acid salts: maleates of L‐leucine,L‐isoleucine and L‐norvaline

Crystals of maleates of three amino acids with hydrophobic side chains [L‐leucenium hydrogen maleate, C₆H₁₄NO₂⁺·C₄H₃O₄⁻, (I), L‐isoleucenium hydrogen maleate hemihydrate, C₆H₁₄NO₂⁺·C₄H₃O₄⁻·0.5H₂O, (II), and L‐norvalinium hydrogen maleate–L‐norvaline (1/1), C₅H₁₁NO₂⁺·C₄H₃O₄⁻·C₅H₁₂NO₂, (III)], were obtained. The new structures contain C₂²(12) chains, or variants thereof, that are a common feature in the crystal structures of amino acid maleates. The L‐leucenium salt is remarkable due to a large number of symmetrically non‐equivalent units (Z′ = 3). The L‐isoleucenium salt is a hydrate despite the fact that L‐isoleucine is a nonpolar hydrophobic amino acid (previously known amino acid maleates formed hydrates only with lysine and histidine, which are polar and hydrophilic). The L‐norvalinium salt provides the first example where the dimeric cation L‐Nva...L‐NvaH⁺ was observed. All three compounds have layered noncentrosymmetric structures. Preliminary tests have shown the presence of the second harmonic generation (SGH) effect for all three compounds.     

Etude en Résonance Magnétique Nucléaire et Stéréochimie d'un Composé Cyclopropanique d'Intérět Thérapeutique. Résonance du Proton à 250 MHz avec Triple Irradiation

1-Pivaloyl-2-hydroxymethylcyclopropane is studied with nuclear magnetic resonance. The C-1? C-2 configuration is determined from the 250 MHz n.m.r. spectrum (triple irradiation experiments have been performed for this purpose). Rotational isomerism around the ring-carbonyl bond is studied from the ASIS effect. Rotational isomerism around the ring-hydroxymethyl bond is studied from vicinal coupling constants over a temperature range of ?20 to +125°C. From the J(HOCH) coupling constant (in CCl₄) rotamer populations of the hydroxyl group are examined and the overall conformational distribution can be established.     

Synthesis,characterization, potentiometry,and antimicrobial studies of transition metal complexes of a tridentate ligand

Complexes of Cu(II), Ni(II), Co(II), Mn(II), and Fe(III) with the tridentate Schiff base, 4-hydroxy-3(1-{2-(benzylideneamino)-phenylimino}-ethyl)-6-methyl-2H-pyran-2-one (HL) derived from 3-acetyl-6-methyl-(2H)-pyran-2,4(3H)-dione (dehydroacetic acid or DHA), o-phenylenediamine, and benzaldehyde were characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, ¹H-NMR, UV-Vis spectroscopy, and mass spectra. From analytical data, the stiochiometry of the complexes was found to be 1?:?2 (metal?:?ligand) with octahedral geometry. The molar conductance values suggest nonelectrolytes. X-ray diffraction data suggest monoclinic crystal systems. IR spectral data suggest that the ligand is dibasic tridentate with ONN donors. To investigate the relationship between formation constants of metal complexes and antimicrobial activity, the dissociation constants of Schiff base and stability constants of its binary metal complexes have been determined potentiometrically in THF–water (60?:?40) at 30?±?1°C and at 0.1?mol?L^?1 NaClO₄ ionic strength. The potentiometric titrations suggest 1?:?1 and 1?:?2 complexation. Antibacterial and antifungal activities in vitro were performed against Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Trichoderma with determination of minimum inhibitory concentrations of ligand and metal complexes. The structure–activity correlation based on stability constants of metal complexes is discussed. Activity enhances upon complexation and the order of activity is in accord with the stability order of metal ions.     

Studies on kinetics of complexation of lanthanide α-hydroxycarboxylates with 1,10-phenanthroline

Kinetics of the coordination reaction of lanthanide (La^III, Eu^III) α-hydroxycarboxylates [LnL₃(H₂O)₂] with 1,10-phenanthroline (phen) in methanol-water (v/v, 3:2) were studied at 25°C by calorimetric titration. A one-step reaction process in accordance with the rate law has been suggested. The reaction is found to be first order for both lanthanide α-hydroxycarboxylates and phen. We have evaluated rate constants of the reactions. It is found that a linear free energy relationship exists between the stability constants of the lanthanide-α-hydroxycarboxylate-phen ternary complex and the rate constants. It is also found that a linear free energy relationship exists between the rate constants of La-hydroxycarboxylate with phen and the acid strength of α-hydroxy-acid as primary ligand, but the linear free energy relationship does not exist in the Eu-α-hydroxycarboxylate-phen ternary complex. The influence of other factors upon the reaction rate constants was also discussed.