Squarate complexes of some lanthanide ions in aqueous solution

The squarate complexes of Eu³⁺, Tb³⁺ and Tm³⁺ in aqueous solutions of 0.05M, 0.075M and 0.1M ionic strength are studied using the solvent extraction method. Effects of changes in the ionic strength on the stability constants of the complexes formed are discussed.     

Rare earth element complexation by fluoride ions in aqueous solution

Rare earth fluoride stability constants for Ce, Eu, Gd, Tb and Yb at 25°C have been determined by examining the influence of fluoride ions on the distribution of rare earths between tributyl phosphate (TBP) and 0.68M NaClO₄. Our results indicate that rare earth mono and difluoro complexation constants show a steady increase as a function of atomic number from La to Tb but remain relatively constant after Dy. This behavior is similar to that which has been observed for dicarboxylic acids. Stepwise stability constant ratios, K₂/K₁, obtained in our work (where K₁=[MF²⁺][M³⁺]^–1[F^–]^–1 and K₂=[MF ₂ ⁺ ]^–1[MF²⁺]^–1[F^–]^–1) indicated that, for all rare earths, K₂/K₁=0.09±0.03.     

Complexation of polymethacrylopiperidide with transition metal ions in aqueous solution

The interactions of polymethacrylopiperidide with Cu²⁺, Ni²⁺, Co²⁺ and Fe³⁺ ions have been investigated by potentiometric and conductometric titration, ESR and u.v. spectroscopy, viscometry and sedimentation. The average number of ligands coordinating with the central metal ions and the stability constants of polymeric metal complexes were determined. It is assumed that the polymethacrylopiperidide interacts with transition metal ions through the nitrogen atoms. The influence of spatial arrangement of donor atoms on the coordination ability of polyligand is discussed.     

The acidobasic and complexation properties of humic acids Study of complexation of Czech humic acids with metal ions

The acid-base and complexation properties of humic acids (HAs) extracted from bohemian brown coals were studied. The acid-base behavior corresponds with the model of HA as a mixture of mono- and diprotic acids. This model was also verified on commercial HA substances (Aldrich and Fluka). HA binds strongly with heavy metal ions and the highest stability constant of HA-metal ion complexes was observed for copper(II). Stability constant values were found to decrease in the order: Cu(2+)>Ba(2+)>Pb(2+)>Cd(2+)>Ca(2+). Both acidobasic models for HA alone and those for HA-metal ion interactions were proposed and the computational methodology for polyelectrolyte equilibria studies demonstrated.     

Thermodynamics of mixed-ligand complexation of gadolinium ethylenediaminetetraacetate with amino acids in aqueous solution

Mixed-ligand complexation of GdEdta⁻ with glycinate, L-glutamate, DL-aspartate, iminodiacetate, and nitrilotriacetate anions in aqueous solutions at 298.15 K and the ionic strength I = 0.5 (KNO₃) was studied. The thermodynamic parameters (logK, Δ _r G, Δ _r H, Δ _r S) of these reactions were determined from calorimetric and pH-metric data. The most probable way of coordination of the amino acids in the heteroleptic complexes is discussed.     

Changes in hydration of lanthanide ions on binding to DNA in aqueous solution

The interaction of the trivalent lanthanides Ce(III), Eu(III), and Tb(III) with sodium deoxyribonucleic acid (DNA) in aqueous solution has been studied using their luminescence spectra and decays. Complexation with DNA is indicated by changes in luminescence intensity. In the system terbium(III)-DNA, changes in luminescence with pH are suggested to be due to the protonation of phosphate groups. The degree of hydration of Tb(III) on binding to DNA is followed by luminescence lifetime measurements in water and deuterium oxide solutions, and it is found that the lanthanide ion loses at least one hydration water on binding to long double stranded DNA at pH 4.7 and pH 7. Rather different behavior is observed on binding to long or short single stranded DNA, where six water molecules are lost, independent of pH. It is suggested that in this case the lanthanide probably binds to the bases of the DNA backbone. The DNA conformation seems to be an important factor in the binding. In addition, the isotopic effect on terbium luminescence lifetime may provide a useful method to distinguish between single and double stranded DNA. DSC results are consistent with cleavage of the double helix of DNA at pH 9 in the presence of terbium.     

13C NMR study of D-pantothenic acid complexes with heavy lanthanide ions in aqueous solution

The ¹³C NMR study of the interaction between the trivalent lanthanide ions (from Dy to Lu) and D-pantothenic acid in aqueous solution was presented. The unambiguous resonance assignments were made on the basis of pH dependence and the analysis of molecular geometry. ¹³C paramagnetic shifts were separated into the contact and dipolar components by Reilley's method. The complex stability constant is 12.0 L / mol for the 1:1 ytterbium complex. An analysis of the shift data shows that heavy lanthanide ions form isostructural complexes with the substrate and the hyperfine coupling constant is independent of the ions used in the study. D-pantothenic acid is coordinated to the metal via the two oxygens of the carboxyl group with 2.25Å of Ln—O distances. The electron spin density distribution and the structural details of the complex were elucidated from the shift data. It is stated that contact contributions, while small for nuclei of several bonds away from the metal, should not be dismissed a priori.     

Complexation of citric and tartaric acids with Na and K ions in aqueous solution

The formation of MTar^–, MCit^2– and M₂Cit^– complexes (M is Na⁺ or K⁺) was established in reactions of aqueous solutions of citric and tartaric acids with sodium or potassium chloride solutions; their stability constants were determined by potentiometric titration in aqueous solution at 298.15 K and ionic strength 0.1 and 0.3 mol/l with tetraethylammonium chloride (TEACl) as a supporting electrolyte. Heat effects of reactions between citric acid solutions and sodium or potassium chlorides were measured by calorimetric method at 288.15, 298.15, and 308.15 K and at the ionic strength 0.1, 0.2, and 0.3 M TEACl. The increasing ionic strength was found to decrease exothermic effect of complex formation processes, while the temperature produced the opposite effect. Extrapolation to zero ionic strength was used to find thermodynamic stability constants and standard heat effects of complex formation reactions in solutions of oxyacids. The changes in entropy and heat capacity were calculated as well as standard enthalpies of formation of Na and K complexes of the indicated oxyacids in aqueous solution at 298.15 K.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 253–261.Original Russian Text Copyright © 2005 by Zelenina, Zelenin.     

Co-operative effect of Lewis acids with transition metals for organic synthesis

Transition metal-mediated or -catalyzed carbon-carbon bond or carbon-heteroatom bond forming reactions are among the most powerful tools in organic synthesis. In addition, Lewis acid-mediated or -catalyzed organic transformations are widely used. In this context, an effective combination of these two powerful protocols or an efficient cooperation of transition metals with Lewis acids should open a new era in synthetic chemistry. This tutorial review summarizes representative synthetic methodologies developed in the past decades employing this co-operative effect.     

New lariat ether carboxylic and hydroxamic acids: Synthesis and lanthanide ion complexation

Twenty-six new lariat ether carboxylic and hydroxamic acids based upon dibenzo-13-crown-4, dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 ring systems are synthesized and the solid-state structure for a dibenzo-19-crown-6 lariat ether hydroxamic acid is determined. The efficiency and selectivity for lanthanide ion extraction into chloroform by these proton-ionizable lariat ethers is strongly influenced by the crown ether ring size, lipophilic group attachment site and identity of the acidic function. In general, the lariat ether hydroxamic acids were more efficient and selective lanthanide ion extractants than the corresponding lariat ether carboxylic acids. The ¹H nmr and ir binding studies indicate that both the macrocyclic polyether unit and the proton-ionizable group are involved in lanthanide ion complexation.     

Redox-dependent complexation ability of flavin-hosts in aqueous solution

The synthesis of the novel macrocyclic host 1 incorporating an isoalloxazine moiety as model for active sites of flavoenzymes is described. The complexation between oxidized and reduced flavin-host and aromatic guests is analyzed in aqueous solution.     

Eigen kinetics in surface complexation of aqueous metal ions

The mechanism of chemisorption of aqueous metal ions at surfaces has long been a topical issue in such fields as soil chemistry and bioenvironmental science. Here it is quantitatively demonstrated for the first time that release of water from the inner hydration shell is the rate-limiting step in inner-sphere surface complexation. The reactive intermediate is an outer-sphere complex between metal ion and surface site, with an electrostatically controlled stability defined by Boltzmann statistics. Using tabulated dehydration rate constants for metal ions, the resulting scheme allows for prediction of rates of sorption of aqueous metal ions at any type of complexing surface.     

Study of triglycine complexation with Cu<Subscript>2+</Subscript> ions in aqueous solution

Composition and stability of triglycine complexes with Cu(II) ions in a wide range of concentration ratios at T = 298.15 K and I = 0.2 (KNO₃) have been determined by potentiometric method. Existence of CuHL²⁺, CuHL₂₊, CuH₂L^{2+ 2}, CuL⁺, CuH_–1L, CuH_–2L–, CuH_–3L^2–, CuL₂, CuH_-1L^- ₂, and CuH_–2L^2- ₂, species has been established.     

Luminescence kinetics and association equilibria of lanthanide ions in aqueous solutions

Luminescence life time measurement can be used under certain conditions to determine the thermodynamic constants of complex formation between the luminescent (central ion) and ligand. The basic equations correlating the life time and the equilibria constants were derived for two cases: the time for establishing the thermodynamic equilibrium is much shorter than the life time of the excited state of the central ion; and the time for establishing the equilibrium and the life time are of the same order of magnitude.     

Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor

A novel fluorescent peptide sensor containing tryptophan (donor) and dansyl fluorophore (acceptor) was synthesized for monitoring heavy and transition metal (HTM) ions on the basis of metal ion binding motif (Cys-X-X-X-Cys). The peptide probe successfully exhibited a turn on and ratiometric response for several heavy metal ions such as Hg²⁺, Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ in aqueous solution. The enhancements of emission intensity were achieved in the presence of the HTM ions by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The detection limits of the sensor for Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ were lower than the EPA's drinking water maximum contaminant levels (MCL). We described the fluorescent enhancement, binding affinity, and detection limit of the peptide probe for HTM ions.     

Solubilization of lanthanide ions by cyclodextrins in basic aqueous solutions

Cyclodextrins form complexes with lanthanide ions in basic aqueous solutions. This complex formation in basic solution dramatically enhances the solubility of lanthanide ions, which are otherwise insoluble due to the formation of hydroxide gels. Solutions of the -cyclodextrin-Ce³⁺ complex effectively hydrolyze 2-deoxyadenosine-5-monophosphate to 2-deoxyadenosine.     

Features of the complexation of octadecane-2,4-dione and lanthanide ions in Langmuir monolayers

Monolayers of octadecane-2,4-dione on the surfaces of EuCl₃ and TbCl₃ solutions in the concentration range of 1 × 10^–4 to 5 × 10^–3 M at pH 5.8 are studied. It is found that the limiting area of octadecane-2,4-dione molecule in a monolayer dependence on Eu³⁺ and Tb³⁺ concentration is of extreme nature. The formation of complex compounds in the ligand monolayer is postulated, and structures are proposed for these compounds at different concentrations of metal ions.     

Theoretical insight to the complexation of some transition metals with cryptand

The most practicable complexes formed between Cryptand[2.2.2] and hydrated Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) cations (denoted as [ML]⁺²) were modeled using computational chemistry methods. The energies of complexation reactions were calculated in both gas phase and solution at B3LYP/6-31+G(d) and B3LYP/6-311++G(3df,2pd) levels of theory. The accuracy of selected computational methods was confirmed with comparison between available X-ray data and computational results. The results suggested that [CuL]⁺² and [CoL]⁺² structures could be the most and the least stable systems, respectively. The nature of metal-ligand interactions based on quantum theory of atoms in molecule (QTAIM) was discussed for all the complexes. This analysis confirmed the ionic nature of metal-ligand interactions due to electron density values for M-O bonds and M-N interactions. Natural bond orbital (NBO) and natural energy decomposition analysis (NEDA) were utilized to explain more details of interaction between divalent cations and donor atoms of the ligand.