Hidekazu Yasunaga

Molecular characteristics and gelling properties of the carrageenan family, 1: Preparation of novel carrageenans and their dilute solution properties

The carrageenans are a family of sulfated polysaccharides extracted from red seaweed, and are conventionally classified into three major groups as κ-, ι- and λ-carrageenan according to the maximum number (1, 2 and 3, respectively) of sulfate groups per disaccharide repeating unit in corresponding ideal structures. β- and θ- carrageenan (not available in nature) possessing none and two sulfate groups per repeating unit, respectively, were prepared from κ- and λ-carrageenan by desulfonation. Here the aqueous solutions of κ-, ι-, β- and θ-carrageenans undergo the thermoreversible gelation by lowering temperature, whereas the aqueous solution of λ-carrageenan forms no gel.Light scattering and small-angle X-ray scattering were observed from the aqueous solution of κ-, ι-, λ-, β- and θ-carrageenans, and the results were analyzed conventionally and by adapting the molecular model in order to elucidate the effect of sulfate groups and anhydrous residue on the conformational characteristics of carrageenans.

Dynamic behavior of water in hydro-swollen crosslinked polymer gel as studied by PGSE 1H NMR and pulse 1H NMR

Abstract 1H NMR measurements on spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) were carried out on hydro-swollen crosslinked poly(methacrylic acid) (PMAA) gel to elucidate molecular motion of water molecules contained in the gel as a function of the degree of crosslinking. From these experimental results, it was found that 1H T1 and T2 decrease with an increase of the degree of crosslinking. This shows that molecular motion of water molecules is strongly restrained owing to crosslinking. Further, pulsed-field-gradient spin-echo 1H NMR measurements were carried out to determine the self-diffusion coefficient of water molecules (DH2O contained in the PMAA gel at 300 K as a function of the degree of crosslinking. From these experimental results, it was found that the DH2O value decreases with an increase of the degree of crosslinking. This shows that translational molecular motion of water molecules is restrained by crosslinking.

Structures and Dynamics of Polymer Gel Systems Viewed Using NMR Spectroscopy

Recent fundamental research on hydro-polymer gel systems by means of NMR techniques such as pulse NMR, pulsed field-gradient spin-echo NMR, solid-state high-resolution NMR and NMR imaging methods have been reviewed. Such NMR techniques have elucidated structures and dynamics of gel systems as a function of the degree of crosslinking and their response process by an application of stimulus such as change in temperature, stress and electric field. It has been demonstrated that NMR techniques are powerful means of determining micro- and macroscopic structures and dynamics of more complicated systems with mobile components such as gel systems.

A 13C PST/MAS NMR study of the structure and molecular motion of a crosslinked polymer in the gel phase

Abstract 13 C pulse saturation transfer/magic angle spinning NMR spectra and 13 C spin-lattice relaxation times ( T 1 ) of poly(methacrylic acid) (PMAA)/water gel were measured as functions of the degree of swelling and the degree of crosslinking. From these results, it was found that the segmental motion of the side chains of the network polymer is faster than that of the main chain, and that an increase in the degree of crosslinking in the PMAA gel leads to an increase in restraint of the segmental motion of the network polymer even when the water content in the gel is constant.

Effect of cross-linking on the molecular motion of water in polymer gel as studied by pulse 1H NMR and PGSE 1H NMR

Abstract 1 H NMR measurements on the spin-spin relaxation time ( T 2 ) and self-diffusion coefficient ( D H 2 O) of water in a poly(metacrylic acid) gel were carried out to clarify the molecular motion of water molecules as a function of the degree of cross-linking under a constant amount of water contained in the gel. From experimental results, it was found that 1 H T 2 and D H 2 O decrease with an increase in the degree of cross-linking in the gel. It can therefore be said that an increase in cross-linking leads to a restraint of molecular motion of the water molecules in the gel.

Spatial information on a polymer gel as studied by 1H-NMR imaging: 4. Shrinkage by the application of an alternating electric field to a polymer gel

Abstract We have measured the spatial distribution of 1 H spin density and 1 H spin–spin relaxation time, T 2 , of water molecules in a crosslinked poly(methacrylic acid) (PMAA) gel under an alternating current (AC) electric field by means of proton nuclear magnetic resonance imaging. The experimental results show that a cylindrical gel shrinks to a cylindrical shape at long elapsed time after the application of an AC electric field, and that the 1 H spin densities on both electrode sides of the gel are high and the mobilities are low. The translational behavior of water molecules in the gel during shrinkage processes under an AC electric field is discussed at the molecular level.

Hydrogen-bonded structure of water in crosslinked polymer gel as studied by 1H NMR chemical shift data

Abstract The structure of water in poly(methacrylic acid) (PMAA) gel as a function of the degree of crosslinking of the PMAA gel was investigated by experimentally observed and theoretically calculated 1 H NMR chemical shifts. On the basis of these results, the hydrogen-bonded structure of water in the gel was elucidated.

Effect of reaction pH and CuSO4 addition on the formation of catechinone due to oxidation of (+)-catechin

A novel hair dyeing technique being milder and safer for a human body is desired. The oxidation product of (+)‐catechin, catechinone, was invented as a safer dyestuff for hair colouring under such the situation. The preparation of catechinone by a chemical oxidation is a practical way and the objective of the study is clarify the effect of the solution pH and in the presence or absence of Cu2+ on the formation rate and yield of catechinone in order to improve the efficiency of the dye formation. The catechinone formation was monitored by ultraviolet‐visible spectroscopy. Catechinone was prepared chemically from (+)‐catechin in aqueous solution with O2 gas introduced over a pH range of 7.1–11.7. The rate and amount of the dye formation increase with increasing pH. Dissociation of the hydroxyl group of the catechol part of (+)‐catechin is significant for the oxidation of (+)‐catechin and promotes the dye production. This is because the deprotonated (+)‐catechin has a higher reactivity with O2. The production of catechinone is accelerated by the addition of CuSO4 and the production rate reaches the maximum at pH = 8.8. (+)‐Catechin ‐ Cu2+ complexes are formed and the formation promotes the oxidation of the catechol part of (+)‐catechin at pH ≤ 8.8. On the other hand, the complex becomes too stable to proceed for the oxidation reaction at pH > 8.8.

Dynamic behaviour of water in hydrogel containing hydrophobic side chains as studied by pulse 1H NMR

Abstract 1 H NMR measurements on spin–lattice relaxation time ( T 1 ) and spin–spin relaxation time ( T 2 ) were carried out on water contained in water-swollen copolymer gels prepared from hydrophilic methacrylic acid and hydrophobic stearyl methacrylate (SMA) or lauryl methacrylate (LMA). The degree of swelling of the copolymer gels decreases drastically with increasing component of hydrophobic monomers. 1 H T 1 and T 2 of water show linear relationship with the cube root of the degree of swelling. Motion of water is restrained with the decreasing network size and the amount of hydrophobic groups in the network. T 1 measurements with temperature change revealed that the hydrogen bondings in water are decreased by introducing hydrophobic groups into the hydro gel..

Preparation of amylose gel and probe diffusion through the gel membranes

Hydro-swollen amylose gels were prepared by chemical crosslinking with a polyethylene glycol diglycidyl ether. The degree of swelling of the amylose gel (qw) increases with increasing the amount of crosslinker in the preparation, which is a result contrary to other cases of chemically crosslinked polymer gels. The diffusion coefficient of a fluorescein and a fluorescein-dextran conjugate in the gel membranes was determined by the time lag method and increases as qw of the gels increases.