Kikujiro Ujimoto

Mechanism of separation of aliphatic alcohols in aqueous dextran gel systems

Abstract The gel chromatographic behaviour of aliphatic alcohols on Sephadex G-10 and G-15 in aqueous systems was elucidated primarily in terms of hydrophobic interactions by use of the thermodynamic functions for dissolution in water and for partition in gel chromatography; the former was obtained from the literauture and the latter from the temperaure dependence of the distribution coefficient (Kd). From an enthalpy—entropy compensation test for partitioning processes of solutes between the mobile and stationary phases of gel columns, it was found that methanol, ethanol,2-propanol and 2-methyl-2-propanol behaved in a different manner to the primary n-alkanols containing more than two carbon atoms in the molecule did. The salting-out effect of the alcohols from the bulk to the gel phase and the effect of addition of methanol to water as the eluent are discussed.

The effect of second-sphere coordination—II. Adduct formation between [Ru(NH3)5L](PF6)n (n = 2 and 3) and 18-crown-6 ether in solution and the effect on redox behaviour☆

Abstract The adduct formation of [Ru(NH3)5L](PF6)n (n = 2 for L = isonicotinamide and pyrazine; n = 3 for L = 4-aminopyridine and 4-dimethylaminopyridine) with 18-crown-6 ether (18C6) was investigated spectrophotometrically and electrochemically in non-aqueous solution. The adduct formation gave a red shift of the MLCT band for [Ru(NH3)5L](PF6)2 and a blue shift of the LMCT band for [Ru(NH3)5L](PF6)3. The magnitude of the shifts is linearly dependent on the reciprocal of the dielectric constant of the solvents examined. The adduct formation was interpreted in terms of the hydrogen bonding between the ammine coordinating to ruthenium and the ether oxygen of 18C6. The stoichiometry of the adducts in non-aqueous solution was determined to be 1 : 1 (complex: 18C6) for [Ru(NH3)5L](PF6)2 and 1 : 2 for [Ru(NH3)5L](PF6)3. The potential of a ruthenium(III)/ruthenium(II) redox couple in acetonitrile solution was measured at various concentrations of 18C6 by cyclic voltammetry. The redox couples shifted to more negative potentials with an increasing 18C6 concentration, where no additional redox peak appeared. The shift of redox potentials was about − 130 mV at 0.10 mol dm−3 18C6 concentration, irrespective of the nature of L. Thus, it becomes possible to tune the redox potential of the ruthenium complexes by second-sphere coordination with 18C6.

The effect of second-sphere coordination of 18-crown-6 ether on electronic spectra and electrochemical properties of [Ru(NH3)5L](PF6)3 and [Ru(NH3)5L](PF6)2

Abstract Ruthenium(III) complexes [Ru(NH3)5L](PF6)3 (L = 4-aminopyridine or 4-dimethylaminopyridine) and ruthenium(II) complexes [Ru(NH3)5L](PF6)2 (L = isonicotinamide or pyrazine) form adducts with 18-crown-6 ether in acetonitrile giving a blue shift of the LMCT band for the ruthenium(III) complex, a red shift of the MLCT band for the ruthenium(II) complex and a negative shift of the ruthenium(III)/ruthenium(II) redox potential for all the complexes.

pH Dependence of the distribution coefficients of monomeric oxo anions of phosphorus in gel chromatography with tightly cross-linked gels

Abstract Sodium phosphinate, sodium phosphonate and potassium dihydrogen orthophosphate were chromatographed on a Sephadex G-10, G-15 or G-25 column with six kinds of eluents containing different alkali metal halides at various pH values. The distribution coefficient ( K d ) on a tightly cross-linked gel column varies significantly depending on the pH of the eluent and is effectively insensitive to the kind of the eluent used. The pH profile of the K d value is characteristic of the corresponding oxo acid of phosphorus and resembles closely its pH titration curve. The pH dependence of the K d value of the oxo anion is discussed in terms of the distribution of the species in different dissociation states, which depends on the pH of the eluent.

Effect of second-sphere coordination.: 10. Contribution of π-electron acceptability of ancillary ligand to stability of 18-crown-6 ether adduct of ruthenium complex

Abstract Redox potentials of rutheniumpentaammine complexes, [Ru(NH 3 ) 5 (pz)](PF 6 ) 2 and [Ru(NH 3 ) 5 (pzMe)](PF 6 ) 3 {pz=pyrazine, pzMe= N -methylpyrazinium}, were measured in acetonitrile solution in the presence of 18-crown-6 ether. Stability constants of 18-crown-6 ether adducts were evaluated from the dependence of redox potentials on the concentrations of 18-crown-6 ether. The stability constants were also evaluated from the dependences of diffusion coefficient of the complexes determined by chronocoulometry and the chemical shift of the ammine protons of the complexes determined by 1 H NMR spectroscopy on the concentrations of 18-crown-6 ether. The factors contributing to stability of the 18-crown-6 ether adducts were discussed on the basis of these stability constants obtained.

Gel chromatographic behaviour of eluent ions on sephadex G-10 and evidence for electroneutrality in the gel phase

Abstract Methods for determining the distribution coefficient, K d , of sodium, hydrogen, chloride and hydroxide ions in the eluent were examined by using refractometric and potentiometric detection and a radiotracer method on Sephadex G-10 with a 0.1 M sodium chloride eluent at several pH values. The K d values of sodium and chloride ions obtained by using their radiotracers were considerably different from those by both refractometry and potentiometry. It was demonstrated by the use of the K d values of sodium and chloride ions (radiotracer method) and that of hydrogen ion (refractometry) that electroneutrality for the eluent ions holds in the gel phase over the range pH 1.5–3.

Gel chromatographic behaviour of tetraalkylammonium ions on sephadex G-10

Abstract The gel chromatographic abehaviour of tetraaklkylammonium (TAA) ions on Sephadex G-10 was studied chiefly by a thermodynamic and an extra-thermodynamic approach. The pH dependence of the distribution coefficients of TAA ions was observed, and compared with those of alkali metal and halide ions. The extra-thermodynamic approach showed that no enthalpy-compensation was operative in the partitioning of TAA ions between the mobile and the gel phase. Examination of the effects of eluent concentration, organic eluent and temperature suggested that hydrophobic interaction and sieving effects contribute to various extents to the separation mechanism of individual TAA ions in the temperature range studied.

Effect of second-sphere coordination 6. Adduct formation of monoammine-, diammine-, triammine- and tetraamineruthenium(II) complexes with 18-crown-6 ether

Abstract Adduct formation was spectrophotometrically and electrochemically investigated for monoammine-, diammine-, triammine- and tetraamineruthenium(II) complexes. It was found that an adduct was formed through hydrogen bonding between the coordinating ammonia ligands to the ruthenium(II) and the ether oxygens of 18-crown-6 ether. The stoichiometry of adduct formation was determined to be a 1:1 ratio of complex to 18-crown-6 ether. The electrochemical results offer the evidence that the increased electron density around the metal center by formation of the hydrogen bond is redistributed over the whole complex through pπ-dπ back donation. The electrochemical behavior in the presence of 18-crown-6 ether revealed the concurrent electrode reactions for the ruthenium(II)-ammine complexes with fewer ammine ligands.

Evaluation of hydrophobicity of gels by use of some 1-alkanols as pilot solutes

Abstract 1-Propanol, -butanol, -pentanol and -hexanol were employed as pilot solutes for evaluating the hydrophobicity of gels. By using both the thermodymamic functions on transfer of the solute from the mobile phase to the gel phase and the specific volume of the gel matrix, the hydrophobicity of gels was evaluated and was found not to be affected adversely by their porosity and particle size. The hydrophobicity of the gels examined increased in the order Bio-Gel P-2

Effect of second-sphere coordination. 11. Selectivity in adduct formation of polypyridineruthenium(II) complexes with crown ethers

Adduct formation of polypyridineruthenium(II) complexes involving a different type of protic ligand was investigated for a series of crown ethers with different ring size. Changes in redox potential and in absorption spectra of the complex were measured on addition of crown ether to the complex solution. The magnitude of the change in both properties is dependent on the ring size of crown ethers. Chemical shifts of protic ligand of the complexes were measured at various concentrations of crown ethers. The stability constants of crown ether adduct were determined from the dependences of the chemical shift on crown ether concentration. It is found from their stability constants that the individual complex shows the different selectivity in adduct formation with crown ethers.