Jean Juillard

Interactions between metal cations and the ionophore lasalocid. Part 1.—Complexation of alkaline-earth-metal cations by lasalocid, bromolasalocid and salicylic acid in methanol

Interactions of the ionophore lasalocid (X-547 A), 5-bromolasalocid and model compounds, salicylic acid and o-methoxybenzoic acid with alkaline-earth-metal cations (Mg2+, Ca2+, Sr2+ and Ba2+) have been studied in methanol using a potentiometric method. For all the acids (AH) investigated, successive complexes AM+ and A2M are formed with M2+ cations, but the strength of complexation is stronger for the AM+ complexes. Gibbs energies of interaction of ionophore anions with alkaline-earth-metal cations are very close for lasalocid and its bromo-derivative. Comparison between these and model acids shows that the salicylic group is the leading site of ligation for these cations and possibly the sole site for Mg2+. As the size of the cation increases, other oxygen sites participate in complexation.

Interactions solutès-solvants dans les mèlanges eau-alcool tert.-butylique: V. enthalpie de dissolution des chlorures de sodium, potassium, rubidium et cesium☆

Abstract By using a calorimetric method, solution enthalpies of sodium, potassium, rubidium and cesium chlorides in mixtures containing from 0 to 45% by weight of alcohol are obtained. Standard enthalpies and transfer enthalpies are estimated. From previous data concerning Gibbs energies of transfer from water to the same solvent mixtures, transfer entropies are calculated. Enthalpies and entropies exhibit a maximum for molar fractions of about 0.07 of organic solvent. Results are discussed in terms of enhancement of the structuration of the aqueous network.

Solute–solvent interactions in water + t-butyl alcohol mixtures. Part 12.—Single-ion enthalpies of transfer using the tetraphenylarsonium tetraphenylborate assumption

Heats of solution of tetraphenylarsonium chloride (ϕ4AsCl) and sodium tetraphenylboride (NaBϕ4) in water and water + t-butyl alcohol mixtures (from 0 to 40% by weight) have been measured. From these data and the previous values for NaCl, enthalpies of transfer of tetraphenylarsonium tetraphenylboride are estimated. Using the classical assumption of equivalent change of solvation with solvent media of the two tetra-aryl ions, ionic enthalpies of transfer are estimated for various cations and anions. This reveals a completely distinct behaviour for the two types of ions. These results are discussed in terms of the structure of the water + t-butyl alcohol mixtures.

Interactions between metal cations and the ionophore lasalocid. Part 7.—Heat capacities and volumes of complexation of lasalocid with alkali-metal and alkaline-earth-metal cations in methanol

Volume changes and heat-capacity changes for the formation in methanol of the 1–1 complexes of the ionophore lasalocid anion with either the alkali-metal cations or the alkaline-earth-metal cations have been obtained from density and calorimetric measurements. The data obtained are discussed in relation to what is known about the structure of these various complexes in solution. The peculiar behaviour of lithium and magnesium ions with respect to the other cations in each series is stressed, heat capacity–entropy correlations being particularly significant. In agreement with the structural features, this could be due to the fact that in these particular complexes, the ligand has more degrees of freedom and that the cation and possibly the carboxylate group of the ligand remain more solvated. Complexation volumes and heat capacities of the other cations vary more or less regularly depending on the size and charge of the cation.

Solute–solvent interactions in water–t-butyl alcohol mixtures. Part 14.—ΔG⊖, ΔH⊖ and ΔS⊖ of transfer for alkaline-earth-metal cations

Solubility products of alkaline-earth-metal fluorides and enthalpies of solution of alkaline-earth-metal chlorides have been determined in water and water–t-butyl alcohol mixtures containing up to 40 wt % of alcohol. Using the classical assumption of an equivalent change of solvation with the solvent media of tetraphenylarsonium and tetraphenylboride ions, it was, from these data and data obtained previously, possible to estimate ionic enthalpies, entropies and Gibbs free energies of transfer of alkaline-earth-metal cations from water to the mixtures. The results are discussed in terms of the structure of the water–t-butyl alcohol mixtures.

Interactions between metal cations and the ionophore lasalocid. Part 2.—Gibbs functions, enthalpies and entropies for complexation of alkali-metal cations by lasalocid and bromolasalocid

The nature and stability of the complexes formed in methanol through interaction of the ionophore lasalocid, and its 5-bromo-derivative, with alkali-metal cations were studied by a potentiometric method. The involvement of the salicylate group of the ionophore in the complexation process is discussed in the light of u.v.–visible spectra and of literature data. Enthalpies and (from the Gibbs functions) entropies for anionic 1 : 1 metal–ionophore complexes were obtained from calorimetric measurements. The results are discussed in terms of competition between complexation and solvation of the ions. It is shown that the variations observed with different metal cations are a fairly regular function of the size of the cation, suggesting a progressive adaptation of the ionophore with no conspicuous selectivity for any particular cation.

Interactions between metal cations and the ionophore lasalocid. Part 5.—A potentiometric, polarographic and electron spin resonance study of copper(II)–lasalocid equilibria in methanol

The complexation of Cu2+ by lasalocid and the model compound salicylic acid, AH, has been studied in methanol. The stability constants of species ACu+ and A2Cu were obtained from potentiometric measurements using a pH glass electrode and a copper-selective electrode, and by polarographic determinations. The stability of these copper(II) complexes was shown to be higher than that of the analogous complexes of the other transition-metal cations of the first row and very similar for lasalocid and salicylic acid. The e.s.r. spectra suggest that the structures of the species formed with the two ligands differ; the oxygen of the backbone probably participates in complexation with lasalocid. In addition, other complexes possibly involving the methoxide ion, formed in more basic media, were characterised.

Neutral and charged complexes of aklali metal cations with the ionophore nigericin in methanol. A thermodynamic study

Interactions between the ionophore nigericin AH and alkali metal cations M+ were studied using both potentiometry and calorimetry. Two types of complexes are formed: AHM+ and AM. Formation constants as well as ΔG, ΔH, and ΔS of formation are reported. These results are discussed in terms of the ‘open’ and ‘closed’ structure of various forms of nigericin (AH, A−, AM, AHM+).

Interactions between metal cations and the ionophore lasalocid. Part 11.—Equilibria of lasalocid alkali-metal salts in water and water–chloroform systems

Alkali-metal complex salts of the ionophore lasalocid are shown to be slightly soluble in pure water and aqueous phases. Both the ionic solubility products and the solubilities of the neutral undissociated forms of these salts are obtained. Their association constants in water are thus calculated and their partition constant between water and chloroform estimated. These various results are discussed in terms of solvation and structure of the species involved. Relevant biological functional aspects are also considered.

Interactions between metal cations and the ionophore lasalocid. Part 3.—Interactions of lasalocid with Mn2+, Fe2+, Co2+, Ni2+ and Zn2+ in methanol

The stability of complexes formed in methanol between the bacterial ionophore lasalocid and first-row transition-metal cations has been studied using potentiometry and, for manganese, electron spin resonance. Both AM+ and A2M complexes were obtained from the ionophore AH and the metal cation M2+. Comparison of the stability of the analogous salicylic acid complexes in the same medium suggests that the salicylic moiety in lasalocid is the main site of complexation for the cations studied here.