Hirofumi Sakashita

Complexation of boric acid with the N-methyl-D-glucamine group in solution and in crosslinked polymer

N-Methylglucamine resin has been shown to be a good adsorbent for borate or boric acid. Above ca. pH 6, the boron adsorbability of this resin increased with a maximum around pH 9. The maximum distribution ratio was higher than 106, however, further increase in pH resulted in a decrease in the distribution ratio. The combination of distribution and 11B MAS NMR measurements revealed the formation of a 1:1 tetradentate complex of B(OH)4- with the N-methylglucamine group. The calculated pH-dependence of boron adsorption agreed well with the experimental results with respect to the -log [H+] values in the resin phase (not in the external solution) estimated by 31P NMR measurements. The maximum adsorption around pH 9 of the equilibrated solution is due to the fact that the pH in the resin phase remains higher than that in the external solution. Therefore, B(OH)3/B(OH)4- is selectively concentrated into the resin phase and by the dehydration condensation B(OH)4- forms the 1:1 tetradentate complex with the anchor group. The overall formation constant of the complex was estimated to be 104.0±0.1, which was almost the same magnitude as that of the 1:1 monochelate complex with an α,β-diol site of N-methyl-D-glucamine (which is an analogue of the functional group of the resin) in aqueous solutions of pH 5.1–7.4. However, the binding structures of each 1:1 complex with the N-methyl-D-glucamine group are quite different in the aqueous solution and in the crosslinked polymer.

11B NMR investigation of the complexation behavior of borate with polysaccharides in aqueous solution

Abstract The complexation of borate with linear dextrans consisting of pyranoside residues and their monomer derivatives (α-methyl- d -glucopyranoside and α-methyl- d -mannopyranoside) was investigated in detail by using 11 B NMR spectroscopy. For the monomer systems five kinds of borate complexes with α,β-diols and α,γ-diols of the pyranosides were present: that is, (α,β)-monochelate, (α,γ)-monochelate, (α,β)(α,β)-bischelate, (α,γ)(α,γ)-bischelate and (α,β)(α,γ)-bischelate complexes. Borate reacts with dextran to form inter-chain (α,β)(α,β)- and (α,β)(α,γ)-bischelate complexes in the 1:2-complexation in addition to the (α,β)- and (α,γ)-monochelate complexes. The formation of intra-chain bischelate complexes can be negligible for a rather stiff polymer as dextran. Formation constants of the (α,γ)-monochelate complex are almost constant among dextrans with different chain lengths except Dextran 3000 which is the shortest polymer examined. On the other hand, the stability of (α,β)-monochelate complexes decreases with an increase in the chain length. The complexation behavior for polysaccharides with various chain lengths was discussed in correlation with hydrodynamic and steric hindrance of the polymer ligands.

Diffuse X-Ray Scattering in Random Mixture of Ferroelectric and Antiferroelectric: Rb1-x(NH4)xH2PO4

The measurement of the diffuse X-ray scattering in a random mixture of ferroelectric RbH 2 PO 4 (RDP) and antiferroelectric NH 4 H 2 PO 4 (ADP), (RDP) 1- x (ADP) x , has been carefully carried out. The equi-intensity contours of the diffuse scattering observed in glassy (RDP) 0.3 (ADP) 0.7 is similar to that in antiferroelectric (RDP) 0.15 (ADP) 0.85 near the Neel temperature, implying that there are small antiferroelectric clusters in the glassy phase of the antiferroelectric side. But the temperature dependence of the scattering intensity in the glassy phase is distinctly different from that in the antiferroelectric phase.

HYDROLYSIS OF CONDENSED PHOSPHATES IN AN ANION-EXCHANGE RESIN

The alkaline hydrolysis of diphosphate, triphosphate and cyclo-triphosphate sorbed into anion-exchange resins has been investigated using 31P NMR spectroscopy. Well resolved 31P NMR spectra of the sample species and their hydrolysis products within the resin phase were observed. For diphosphate and triphosphate systems, the rate constant and activation parameters for each hydrolysis reaction are quite similar, both in the resin phase and in a basic solution. For the cyclo-triphosphate system, however, the hydrolysis is significantly retarded compared to that in a solution of tetramethylammonium hydroxide. This retardation is shown to be entirely due to a much more unfavourable ΔH‡ for the reaction in the resin phase. The relationship between mechanisms and reactivities of the hydrolysis in the resin phase is discussed.

Oxygen Adsorption-Desorption Behavior and Superconducting Properties of High-Tc Bi(Pb)-Sr-Ca-Cu-O

Temperature-programmed desorption (TPD) chromatograms revealed that a small amount of oxygen was desorbed from high-Tc Bi(Pb)-Sr-Ca-Cu-O (BPSCCO) in the temperature range from ca. 350 to ca. 650°C prior to a steep increase of oxygen desorption in the higher temperature range. The Tc of BPSCCO was significantly lowered with the progress of oxygen desorption especially in the former temperature range, and was restored to the original level when the desorbed oxygen was recovered. With no corresponding changes in X-ray powder diffraction pattern being detected, the oxygen desorbed below ca. 650°C was concluded to have strong relevance to the superconductivity of BPSCCO.

Temperature and Concentration Dependence of Lattice Constants in a Rondom Mixture of Ferroelectric and Antiferroelectric; Rb1-x(NH4)xH2PO4

The measurements of thermal expansion in a random mixture of ferroelectric RbH 2 PO 4 (RDP) and antiferroelectric NH 4 H 2 PO 4 (ADP), (RDP) 1- x (ADP) x , were made by X-ray diffraction. Anomalous expansion of lattice constants was observed in glassy (RDP) 1- x (ADP) x (0.22< x <0.75) at low temperatures, while the crystal symmetry was still tetragonal. Temperature dependence of the anomalous expansion can be related to the idea of cluster condensation. The NH 4 -concentration dependence of the anomalous expansion implies that the glass is the mixture of two kinds of local strains at low temperatures.

Effects of Oxygen Sorption-Desorption on Superconductivity of High-Tc Bi(Pb)-Sr-Ca-Cu-O

Abstract Temperature-programmed desorption (TPD) chromatograms revealed that a small amount of oxygen (2.5 × 10−5 mol/g) was desorbed from high-Tc Bi(Pb)-Sr-Ca-Cu-O (BPSCCO) in the temperature range from ca. 350 to ca 600 °C. The Tc of BPSCCO lowered by 15 K from 111 K to 96 K with the above oxygen desorption below 600 °C, and was restored to the original level when the desorbed oxygen was recovered. As revealed by a temperature-programmed oxidation (TPO) technique, the desorbed oxygen was sorbed reversibly at ca 100–350 °C in a O2(5%)-He atmosphere, accompanied with an increase in Tc by 12 K. In these oxygen sorption- desorption processes, no corresponding changes in X-ray powder diffraction pattern were observed.

Lattice distortions in GaAs-AIAs and GaAs-InAs superlattices

Abstract Measurements of X-ray diffraction profiles in GaAs-AlAs and GaAs-InAs superlattices and quantitative analyses of the diffraction patterns have been carried out. The strain field plavs an important role in the superlattices. Especially, the tetragonality in strained GaAs-InAs superlattices, which increases with decreasing GaAs layer size, is well explained by a simple model.

Study of ion exchange selectivity of organic ions by using 31P NMR spectroscopy

Ion exchange distribution of the phenylphosphoric acid has been studied on various types of chloride form strong base resins as a function of pH at 25 degrees C, at 0.1 M ionic strength. Equilibrium measurements were supplemented by the study of pH dependence of the (31)P NMR spectra of the resin-phase phenylphosphate species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the chemical shift of the resin-phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the resin-phase (31)P chemical shifts of the mono- and divalent ions have been calculated. Comparison of distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. A well-defined correlation between the ion exchange selectivity and the resin-phase (31)P NMR chemical shift data has been pointed out.

Randomly Mixed Ferroelectric and Antiferroelectric; Cs1-xTlxH2PO4

X-ray diffraction and dielectric constant measurements have been carried out in a one-dimensional ferro- and antiferroelectric mixed crystal Cs1-xTlxH2PO4 with a concentration range from x=0 to x=1. In the Cs rich region (0≤x<0.15), the crystals undergo a paraelectric to a ferroelectric phase transition, while a paraelectric to an antiferroelectric phase transition occurs in the Tl rich region (0.3<x≤1). A new phase is found to appear in the intermediate concentration region (0.15<x<0.3). It becomes evident that the transitions are diffusive.