Yoshinori Miura

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.

NMR studies on thermal stability of α-helix conformation of melittin in pure ethanol and ethanol-water mixture solvents

Thermal stability of the α‐helix conformation of melittin in pure ethanol and ethanol–water mixture solvents has been investigated by using NMR spectroscopy. With increase in water concentration of the mixture solvents (from 0 wt% to ~71.5 wt%) as well as temperature (from room temperature to 60 °C), the intramolecular hydrogen bonds formed in melittin are destabilized and the α‐helix is partially uncoiled. Further, the hydrogen bonds are found to be more thermally stable in pure ethanol than in pure methanol, suggesting that their stability is enhanced with increase in the size of the alkyl groups of alcohol molecules. Copyright

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.

Solvent isotope effect on gelation process of methylcellulose studied by NMR and DSC

The gelation process of methylcellulose (MC) in light (H2O) and heavy (D2O) waters was investigated using NMR and DSC to elucidate solvent isotope effect on the process. As temperature is raised, MC chains in both solvents undergo the aggregation and subsequent gelation; however, their onset temperatures are lower in D2O than H2O. This demonstrates that D2O enhances the hydrophobic attractive force, which is the driving force for the aggregation and gelation. We propose that the excluded volume effect of the hydrophobic segments in MC chains should play a pivotal role for the enhancement, while, prior to the above investigation, chemical shift assignments of proton and carbon resonances are performed, and six resonances are newly assigned.