Phosphonic Acid Ligands Research Articles

Dynamic NMR Study of Ligand Exchange Reactions in U(VI)−Phosphonic Acid Systems

The rates of hydrogen ion exchange on phosphonic acid ligands and that of phosphonate ligand exchange on selected uranyl−phosphonate complexes have been investigated by dynamic NMR spectroscopy. The spin−spin relaxation time (ln(1/T2)) for H+ exchange on the free ligands exhibits a parabolic dependence on reciprocal temperature (1/T (K-1)). The empirical fit parameters are correlated with the activation parameters (ΔH*, ΔS*, ΔCp*) by adapting the statistical mechanical framework developed by Braibanti et al. to the Eyring activated complex theory. The correlation of the apparent activation enthalpy with temperature indicates that 6−11 water molecules participate in the transition from reactants to activated complex for ligand proton exchange reactions, depending on the ligand. Mechanistic details of ligand exchange reactions of phosphonic acid complexants onto the corresponding uranium(VI) complexes are not fully developed, but the negative values for ΔS* imply increased order in the transition to the activated complex. Though ΔH* for ligand exchange covers a range of 15 kJ/mol, the free energy of activation (ΔG*) is nearly constant for the series of ligands, implying substantial entropy compensation in the activation process. Application of the Marcus relationship defines a correlation between ΔG* and the thermodynamic stability (ΔG°) for the 1:2 uranyl complexes with methanediphosphonic acid and 1-hydroxyethane-1,1-diphosphonic acid.

A MECHANISM FOR ENHANCING IONIC ACCESSIBILITY INTO SELECTIVE ION EXCHANGE RESINS

ABSTRACT A bifunctional monophosphonic/sulfonic acid ion exchange resin with high capacity has been synthesized. Metal ion studies have been carried out with europium, americium, and ferric nitrate in solutions of varying acidity, with and without sodium nitrate added. The bifunctional resin complexes far higher levels of Eu(III) from 0.5 and 1 N nitric acid than the monofunctional phosphonic acid resin. It is postulated that the sulfonic acid ligand provides an access mechanism for the metal ions into the polymer matrix by hydrating the matrix and preventing its collapse in high ionic strength solutions thus allowing for rapid ionic complexation by the selective phosphonic acid ligands. The bifunctional monophosphonic/sulfonic acid resin has both ligands bound to a polystyrene support. It complexes higher levels of metal ions than a comparable resin differing only by having the monophosphonic acid ligand directly bound to the C-C backbone. Results are compared to a diphosphonic / sulfonic acid resin.

Solid‐state 31P NMR characterization of bifunctional ion‐exchange resins

AbstractNMR was used to provide evidence of site—site interactions in bifunctional polymers. A series of polymer‐supported phosphonic acid and phosphonate ester ligands was examined by solid‐state 31P NMR spectroscopy. Interaction between phosphonate monoethyl ester sites was demonstrated and disruption of this interaction by the addition of diethyl ester groups was shown. The effect of the synthesis conditions on the bifunctionality of resins containing both phosphonic acid and quaternary amine groups was examined. The spectra indicated that the phosphonic acid groups exists as phosphonate ions in the bifunctional amine/acid polymers and are capable of displacing chloride as the counterion on the amine sites.

Actinide phosphonate complexes in aqueous solutions

Complexes formed by actinides with carboxylic acids, polycarboxylic acids, and aminopolycarboxylic acids play a central role in both the basic and the process chemistry of the actinides. Recent studies of f element complexes with phosphonic acid ligands indicate that new ligands incorporating doubly ionizable phosphonate groups (PO 3H 2) have many properties which are unique chemically, and promise more efficient separation processes for waste clean-up and environmental restoration. Simple diphosphonate ligands form much stronger complexes than isostructural carboxylates, often exhibiting higher solubility as well. In this manuscript recent studies of the thermodynamics and kinetics of f element complexation by 1,1- and 1,2-diphosphonic acid ligands are described.

Synthesis of bifunctional ion‐exchange resins through the Arbusov reaction: Effect on selectivity and kinetics

AbstractBifunctional ion‐exchange resins are synthesized from vinylbenzyl chloride—styrne copolymers. The two types of functional groups are introduced by an Arbusov reaction followed by sulfonation. The effect of ligand ratios, macroporosity, and matrix rigidity on the complexation of Eu (III) from solutions of low pH is quantified. It is found that ion complexation kinetics and selectivity are maximized with resins having both sulfonic and phosphonic acid ligands. Maximum metal ion complexation rates depend on a balance between chemical interactions (i.e., a bifunctional network interacting with a given substrate through an access and a recognition mechanism) and physical parameters (i.e., matrix porosity and rigidity). Structural integrity must be maintained through an appropriate crosslink level in order for the advantage of bifunctionality to be maintained in low‐pH solutions. © 1994 John Wiley & Sons, Inc.

ChemInform Abstract: Synthesis and Structural Studies of Selected Multifunctional Phosphonate and Phosphonic Acid Ligands.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and structural studies of selected multifunctional phosphonate and phosphonic acid ligands

The carbanion [(RO) 2P(O)][C(O)NEt 2]CH − is used to prepare several new carbamoylmethyl phosphonates of the general type [(RO) 2P(O)][C(O)NEt 2]CH(X), XCH 3, C 2H 5, (CH 2) 2CN, CH 2CH[(RO) 2P(O)][C(O)NEt 2], (CH 2) 3OH and CH 2C(O)OCH 3. In addition, an interesting intramolecular transesterification process for the molecule with X(CH 2) 3OH and novel hydrolysis chemistry that produces useful phosphonic acids are described. The molecular structure determinations of two compounds, {[(i-PrO) 2P(O)][C(O)NEt 2]CH} 2CH 2 ( 4b) and [ NH 2C(CH 3) 2CH 2C(O)CH 2C(C H 3) 2 +][(HO)PO 2CH 2C(O)NEt 2 −] (bd11) are outlined. Compound (bd4b) crystallizes in the triclinic space group P1, with a=9.0996(24), b=12.6604(31), c=16.5711(48) Å, α=68.655(20), β=78.714(22), γ=70.742(19)° and Z=2. The molecular structure confirms that two carbamoylmethyl phosphonate fragments are bonded to a central methyl group. Compound 11 crystallizes in the triclinic space group P1, with a=9.2384(21), b=9.8404(21), c=11.0702(25) Å, α=85.276(18), β=74.477(17), γ=78.644(17)° and Z=2. The molecular structure contains a 2,2,6,6-tetramethyl piperidone cation and a carbamoylmethyl phosphonic acid anion.

Mechanism of polymer-based separations: II. Targeted metal ion complexation by reactive polymers

The metal ion affinities of polystyrene-supported phosphinic and phosphonic acid ligands have been examined under a wide variety of solution conditions in order to elucidate the interaction mechanisms displayed by the two polymeric reagents for different metals. Nitrate solutions of Fe(III), Hg(II), Ag(I), and Mn(II) were contacted with the resins. Three variables studied were the pH, ionic strength, and initial metal concentration (viz., 10 −1 to 10 −5 N). It was concluded that: the phosphinic resin is more sensitive to loading effects and its phosphoryl oxygen has a lower H + affinity than the phosphonic resin under highly acidic conditions; the phosphinic resin's recognition mechanism, reduction, intervenes at Hg(II) concentrations ≥ 10 −4 N; and Ag(I) is reduced to Ag metal by the phosphinic resin only from relatively high metal ion concentrations coupled with low acid solutions. The log D / pH correlations were found to fall into one of four categories from which the relative affinities displayed by the resin for M n+ / H + / Na + could be deduced. The inherent ligand / M n+ affinity is best defined in dilute solutions (10 −5 N) and acid concentrations wherein the ratio of solution H + to polymer ligand is 1:1 or less; the relative coordinative affinity for M n+ / H + displayed by the ligand is best defined in dilute solutions and high acid concentrations (≥ 2 N HNO 3). The sensitivity of the polymer to loading effects may then be defined by increasing the initial metal concentration from 10 −5 N to 10 −1 N.

Kinetics of the removal of ferric ion from transferrin by aminoalkylphosphonic acids

The kinetics of ion removal at 25°C in 0.1 M Tris, pH 7.4 by a series of phosphonic acids have been evaluated. The initial rate of iron removal is first order in ferric-transferrin, but shows a hyperbolic dependence on the concentration of the phosphonate ligand. At high ligand concentrations the reaction is clearly biphasic, and the data are interpreted in terms of nonequivalent rate constants for iron removal from the two transferrin iron-binding sites. Rate constants for three phosphonic acid ligands are $ ̃ 0.025 min −1 and $ ̃ 0.007 min −1 for the faster and slower binding sites. The results are discussed in relation to the conformational change mechanism for iron removal from transferrin proposed by Cowart et al. [21].

Alkaline phosphatase: affinity chromatography and inhibition by phosphonic acids

Five phosphonic acid derivatives were synthesized, coupled to agarose, and tested for affinity chromatographic binding of alkaline phosphatase from bovine intestine. Agarose coupled to L-histidyldiazobenzylphosphonic acid was found to be a highly effective adsorbent. In order to understand the large differences in binding capacity observed with derivatized agaroses, inhibition of alkaline phosphatase by phosphonic acid ligands, and related phosphonic acids, was measured. The results of affinity chromatography and inhibition studies were in good agreement, demonstrating that phosphonic acids with large aromatic/hydrophobic, carboxylate substituents bind strongly and competitively to the enzyme active site.