Allosteric coextraction of sodium and metal ions with calix[4]arene derivatives 1

Solvent extraction of three alkali metal ions with p-t-octylcalix[6]arene hexacarboxylic acid, p-t-octylcalix[4]arene tetracarboxylic acid, corresponding linear trimeric and monomeric analogs was investigated. Cyclic tetramer selectively extracts sodium ion among alkali ions at extremely low pH, while the corresponding cyclic hexamer, the trimer, and the monomer exhibited only poor extraction ability for all alkali metals examined. The detailed extractive investigation of sodium ions with the cyclic tetramer was carried out. It was found that two sodium ions are simultaneously extracted by a single molecule of calix[4]arene derivative and that the second sodium extraction is facilitated by the uptake of the first sodium. The self-coextraction mechanism of sodium ions proposed in the present paper also strongly supports allosteric coextraction of sodium and other metal ions. In the competitive extraction of four alkali metal ions, potassium ion was slightly extracted as the second ion at low pH region, whereas it was hardly extracted in the individual extraction system. The result also supports the coextraction mechanism and role of the first-extracted sodium ion as an allosteric trigger. The extraction equilibrium constants of the cyclic tetramer and two sodium ions, K _ex1 and K _ex2, were estimated.     

Preparation of calix[4]arene methylene crosslinked resins with 2-pyridyl pendant group and their adsorption behavior towards silver ion

Three different resins namely 1:5 MC-resin, 1:3 MC-resin and 1:1 MC-resin have been synthesized by methylene crosslinking of 2-pyridylcalix[4]arene. Adsorption behavior of these resins towards the metal ions existing in photographic waste was investigated. The resins show absolute efficiency for adsorption of silver ion with no affinity for other coexisting ions. First two resins form 1:1 complex whereas the third one forms 2:1 complex with silver ion. Maximum loading capacity of silver ion on the present resins was found to be 1.15, 1.29 and 0.69 mol kg^?1, respectively. Column chromatographic separation of silver ion in presence of excess of sodium ions was also carried out with 1:5 MC-resin. Selective adsorption of silver ions over excess of sodium ions was achieved.     

The effect of phenoxy oxygen atoms on extremely high extraction ability and less separation efficiency of trivalent rare earth elements with tetraphosphonic acid derivative of calix[4]arene

A cone confomational p-t-octylcalix[4]arene with four methylenephosphonic acids at the lower rim as well as its monomeric analog have been synthesized as a new extraction reagent to investigate the extraction behavior of the nine trivalent rare earth elements: Y, La, Pr, Nd, Sm, Eu, Gd, Ho and Er. The new calix[4]arene exhibited significantly higher extraction capacity than not only the monomeric derivative and the commercial extraction reagent, 2-ethylhexyl hydrogen 2-ethylhexylphosphonate, but also the cone conformational calix[4]arene extractants employed in our previous work, composed of a tetrapropylenephosphonic acid with a longer spacer, a tetraphosphonic acid at the upper rim, and tetraacetic acid at the lower rim. A dependence on the pH was observed for the new extractant in the highly acidic region, and the extraction took place via a simple ion-exchange mechanism. Using slope analysis, the stoichiometries of tetrameric and monomeric extractants to rare earth metal ions were determined to be 2:1 and 3:1, respectively. Using the proposed extraction equations, extraction equilibrium constants and separation factors were estimated. The extremely high extraction ability and moderate separation efficiency were attributed to the chelating effect of the phosphonic acid and the phenoxy oxygen atom. The effect of the phenoxy oxygen atom on extraction ability and separation efficiency of calix[4]arene derivatives was found to be significant.     

Mid-infrared emissions from Ho3+ in Ga2S3-GeS2-Sb2S3 glass

Emission properties were investigated in the infrared region for Ga₂S₃-GeS₂-Sb₂S₃ glasses doped with Ho³⁺. We performed Judd–Ofelt analysis and lifetime measurements of the ⁵I₄, ⁵I₅, and ⁵I₆ levels, which are the initial levels of the mid-infrared emissions between 3 to 5 μm of Ho³⁺. The quantum efficiencies reached approximately 18%, 64%, and ～100% for the ⁵I₄, ⁵I₅, and ⁵I₆, respectively. Population analyses were carried out from the relative intensities of the emissions in the near-infrared region. We investigated the dependences on the Ho³⁺ ion concentration of the population ratio of the initial levels to the final levels, [initial]/[final], of the mid-infrared emissions. The population ratio of [⁵I₅]/[⁵I₆] decreased with increase of the Ho³⁺ concentration while those of [⁵I₄]/[⁵I₅] and [⁵I₆]/[⁵I₇] increased. Particularly, the former, [⁵I₄]/[⁵I₅], rapidly increased because of the strong concentration quenching of the ⁵I₅ level through cross relaxation. It was found that the population inversion for the 4.8 μm emission due to the transition, ⁵I₄→⁵I₅, was achieved at high Ho³⁺ concentration in the present experiments.     

Effects of pressure and temperature on the solubility of monosodium L-glutamate monohydrate in water

Abstract

The solubility of monosodium L-glutamate monohydrate (MSG.H₂O) in water was measured at pressures in the range of 0.10-300MPa and 298.15K. The density of MSG solution at high concentrations and heat of solution at saturated concentration were also measured at atmospheric pressure. The solubility, m_s, increased with increasing pressure and the pressure coefficient, Θ_p, [?(? In m_s,? p)_T] at 0.10 MPa was (2.0 ± 0.1) × 10-¹⁰Pa-1. It agrees well with (2.1 ±0.2)× 10-¹⁰ Pa-¹ thermodynamically estimated using the partial molar volume, the activity coefficient of the solute in solution, and the molar volume of the crystal. The excellent agreement at 0.10MPa gives us confidence in the solubility data at higher pressures. The heat of solution data and other pertinent values were used to calculate the temperature coefficient of solubility, Θ_T [? (? In m_s/?(1/T))_p], by a thermodynamic equality. The resulting Θ_T compares well with the data directly measured by Ogawa.     

A quotient curve of the Fermat curve of degree twenty-three attaining the Serre bound

The curve in the title is a non-maximal curve of genus 11, which has a defining equation analogous to the Klein quartic's. We study its properties and show how to apply it to coding theory.     

Metal-assisted stabilization and probing of collagenous triple helices

Collagen model peptides that contain 2,2'-bipyridyl (bpy) ligands were designed and synthesized. The thermal stability of the collagenous triple helix was increased by forming an Fe(II)(bpy-peptide)(3) complex. The chirality of the metal center was shifted to form right-handed Delta-isomers induced by the supercoiling of the peptide moiety. Moreover, the refolding rate of the triple helix was increased in the presence of Fe(II). This metal-coordinating system possesses potential to be used to stabilize the triple-helical conformation as well as to probe the folding status of collagen model peptides.