Yoshinobu Miyazaki

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.

11B NMR studies on complexation of borate with linear and crosslinked polysaccharides

11 B NMR spectroscopy has been employed to elucidate the nature of the complexation of borate with crosslinked Dextran–containing glucopyranoside residues, and with linear Dextran and the monomer derivative, α-methyl-D-glucopyranoside. Well resolved 11B NMR spectra for Sephadex gel as well as for a solution of Dextran or α-methyl-D-glucopyranoside were observed. Four borate complexes with α,β-diols and α,γ-diols of glucopyranoside residues were present. The characteristic 11B chemical shift values were at δ–13 to –14 for the 1:1 complex with α,β-diol and at δca.–10 for the 1:2 complex with α,β-diols, and at δca.–18 for the 1:1 and 1:2 complexes with α,γ-diols, irrespective of the linear or crosslinked structure of the polysaccharide. The 1:1 complexes with the α,β-diols of Dextran and Sephadex gels have higher stability compared with those with α,γ-diols, whereas the complex with α,γ-diols is predominant for the α-methyl-D-glucopyranoside system. This indicates that the glucopyranoside residues of Dextran and Sephadex gels prefer the C1 conformation and the interconversion between the C1 and 1C conformers is restricted owing to the hydrodynamic and steric hindrance of the linear or crosslinked polymer in aqueous media. The formation of 1:1 complexes with α,γ-diol of the Dextran and Sephadex gels induces the conformational changes of the glucopyranoside residues from the C1 to 1C conformation in a part of the Dextran strands to create a domain of high local concentration of the α,γ-diol moiety, so that the α,γ-diols are located at a suitable position for 1:2 complexation.

Anion exchanger as a reaction/separation medium-absorptiometric determination of trace amounts of boron in waters by on-line complexation with chromotropic acid presorbed on the anion-exchange column.

A novel method of on-line absorptiometric determination for trace amounts of boron was developed based on the complexation with chromotropic acid presorbed on an anion-exchange column. On-line reaction and separation were achieved by controlling pH conditions in solutions to accelerate the 1:2 complex formation in the concentration process at pH 3 and to stabilize the complex in the separation process at pH 8. About 75% of the boron introduced into the stream was kinetically collected as the 1:2 complex on the column under the experimental conditions. The 1:2 complex was satisfactorily separated from excess reagent and matrix components by changing the concentration of NaClO4 in the eluent and its peak height on the chromatogram monitored at 350 nm was used for calibration. The sensitivity could be enhanced by increasing the sample amount introduced and the detection limits (3sigma) were 162 ng dm(-3) and 45 ng dm(-3) of boron, when 5.0 cm3 and 13.4 cm3 of the samples were used, respectively. The method has been successfully applied to the determination of boron in samples of river water, tap water and ion-exchanged water.

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.

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.

NMR studies on the complexation of aluminium ion with inorganic ligands in crosslinked polysaccharide gel

Abstract Complexation equilibria of aluminium ion with phosphinate, thiocyanate and sulphate anions in uncharged polysaccharide gels with different degrees of crosslinking have been investigated by using 27 Al NMR spectroscopy. Stability constants of these 1 : 1 complexes in the gel phase were compared with those in an aqueous solution. The constants for Al 3+ −PH 2 O 2 − and −SO 4 2− systems increased in the order : aqueous solution 3+ −SO 4 2− system. On the other hand, the order for AlSCN 2+ was reversed. These results are interpreted in terms of a low dielectric constant in the gel phase and a “hydrophobic interaction” between the anions and the gel matrix.

Systematic interpretation of the anion-exchange behaviour of polyphosphate oligomers

Abstract Anion-exchange distribution ratio of some linear and cyclo -polyphosphate oligomers were measured in tetramethylammonium chloride solution using Dowex 1-X4 anion-exchange resin. The selectivity coefficient K Cl P , of the exchange reaction was evaluated from the log D vs. log ([ Cl − ]/ [ Cl − ] ) plot for each polyphosphate anion. The dependence of selectivity coefficient on the charge of the anion is interpreted in terms of the structure of the phosphate species. Differences in selectivity coefficients between the linear and cyclo -polyphosphate series are also discussed.

ADDITIONAL REACTIONS OF INORGANIC CONDENSED PHOSPHATE OLIGOMERS DURING THEIR DEGRADATION REACTIONS IN THE PRESENCE OF ALUMINUM(III) IONS

Abstract When linear di-, tri-, or tetraphosphate was degraded in the presence of Al 3+ , in addition to the usual degradation products, phosphates formed which possessed one more PO 4 group than the parent phosphates. This was confirmed by using HPLC. Tetraphosphate produced from the hydrolysis of triphosphate in the presence of Al 3+ was isolated with the use of an anion-exchange column, and its structure was ascertained by 31 P-NMR measurement. Moreover, linear tetra-, penta-and hexaphosphates resulted from the six-membered cyclo -triphosphate in the presence of Al 3+ ions. The yield of the unusual hydrolysis products of the phosphates became maximum when an equimolar amount of Al 3+ ion was used.

Protonation and ion exchange equilibria of weak base anion-exchange resins.

Protonation and ion exchange equilibria of weak base anion-exchange resins, in which tertiary amine moieties were introduced as a functional group, were investigated by applying NMR spectroscopy to species adsorbed into the resins. (31)P NMR signals of the phosphinate ion in the resin phases shifted to a lower field due to the influence of protonation of the tertiary amine groups of the resins in the pH range of 4-10. Protonation constants of the tertiary amine groups in styrene-divinylbenzene (DVB)-based resins were estimated to be K(H)=10(6.4) for Amberlite IRA96 and 10(6.5) for DIAION WA30 by the (31)P NMR method using the phosphinate ion as a probe species. In addition to the low field shift caused by the protonation of the tertiary amine moieties, another low field shift was observed for the phosphinate ion in acrylic acid-DVB-based resins at a rather high pH. This shift should be due to an unexpected deprotonation in the acrylic resin: a tautomerism accompanying the proton release from the amide form to the imide one in the functional group, thus, the resin could exhibit a cation exchange property at the high pH. Protonation constants of the tertiary amine moieties in the acrylic resins were estimated to be 10(8.8) for DIAION WA10, 10(9.0) for Amberlite IRA67 and 10(9.3) for Bio-Rad AG 4-X4 on the basis of the Henderson-Hasselbalch equation using the resin phase pH estimated by the (133)Cs and (1)H NMR signal intensities.