Yvon Pointud

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.

Selectivity of bacterial ionophore monensin for monovalent metal cations. Solvent effects in methanol and biphasic water-organic systems

Interactions of ionophore monensin with heavy metal monovalent cations, Ag+, Tl+, Hg22+, were studied in methanol and in various biphasic waterorganic solvent systems to supplement previous data on alkali-metal cations. The species formed were identified and the corresponding formation constants determined. Enthalpies of formation were also obtained in methanol for Ag+ and Tl+ from calorimetric measurements. The results for monovalent cations in general are discussed in terms of cation size and solvation, and structure of the ionophore anion.

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.

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+).

NOVEL CRYPTAND ANALOGS INCORPORATING A CHIRAL SPIRAN MOIETY

Abstract Macrobicyclic polyethers based on the cryptand model displaying a chirality due to a spiran junction were synthesized from diamines 7 and 8. Results of attempted direct macrobicyclisation varied with the length the α,ω-oligoethyleneglycol ditosylates chain used as reagent. The expected structure was obtained only for triethyleneglycol ditosylate. The complexing properties of the diaza-octaoxa ligand 11, with alkaline and ammonium cations, were measured in THF by UV-Visible spectrophotometry.

Chiral macrocyclic polyethers incorporating a tetraoxaspiro[5.5]undecane or trioxa-azaspiro[5.5]undecane moiety

Abstract New macrocyclic polyethers possessing chirality due to a spiro ring junction are prepared from 2,8-dihydroxymethylated (+)-1,4,7,10-tetraoxaspiro[5.5]undecane 1 and (+)-1,4,7-trioxa-10-azaspiro[5.5]undecane 2 , both ( E,E ). N -Functionalization of compounds derived from 2 is also examined. The complexing properties of representative ligands 3 , 4 , 5 measured by spectrophotometry in THF, for alkaline and alkaline-earth cations, indicate that these spheric positively-charged species are weakly associated.

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 4.—ΔH⊖ and ΔS⊖ for formation of 1–1 and 2–1 complexes of the lasalocid anion and salicylate with alkaline-earth metal cations in methanol

Enthalpies of formation of 1–1 and 2–1 complexes of the lasalocid anion and salicylate with alkaline-earth metal cations in methanol have been obtained from calorimetric measurements. The corresponding entropies were obtained from previously determined stability constants. Involvement in the complexation of the salicylate part of the lasalocid anion was thereby assessed. For 1–1 complexes, the results point to a transition from an extended conformation for the lasalocid anion in the magnesium complex to a folded one in the barium complex. For 2–1 complexes bonding of the second lasalocid anion may not be solely due to the salicylate moiety. Finally, the ionophoric power of lasalocid with respect to alkaline-earth metal cations is discussed.

Alkali metal and ammonium chlorides in water + urea systems ΔG, ΔH, ΔS of transfer from water to mixtures containing up to 40 % urea

Enthalpies, Gibbs free energies and entropies of transfer from water to water + urea mixtures for LiCl, NaCl, KCl, RbCl, CsCl and NH4Cl are reported. Gibbs free energies are obtained using glass electrodes sensitive to alkali cations and enthalpies of transfer are calculated from calorimetric measurements of the enthalpies of solution. Data thus obtained are discussed in terms of the various models of the water + urea mixtures. It is suggested that the properties of solutes are mainly related to the properties of water in the same mixture.

Solute–solvent interaction in water + t-butylalcohol mixtures. Part 9.—Enthalpies of transfer for KBr, KI, HBr and HI

Enthalpies of transfer of HI, HBr, KI and KBr from water to water + TBA mixtures, which have been obtained from calorimetric measurements, are reported. Gibbs free energies and entropies of transfer are calculated from previous data. The solvation of these electrolytes in water + TBA media is thus discussed in relation to the structure of the mixtures with special reference to the Atkinsons model of fluctuating cages.