Shingo Matsukawa

Effects of droplet size on the oxidative stability of oil-in-water emulsions.

The effects of droplet size and emulsifiers on oxidative stability of polyunsaturated TAG in oil-in-water (o/w) emulsions with droplet sizes of 0.806±0.0690, 3.28±0.0660, or 10.7±0.106 μm (mean ± SD) were investigated. Hydroperoxide contents in the emulsion with a mean droplet size of 0.831 μm were significantly lower than those in the emulsion with a mean droplet size of 12.8 μm for up to 120 h of oxidation time. Residual oxygen contents in the headspace air of the vials containing an o/w emulsion with a mean droplet size of 0.831 μm were lower compared with those of the emulsion with a mean droplet size of 12.8 μm. Hexanal developed from soybean oil TAG o/w emulsions with smaller droplet size showed significantly lower residual oxygen contents than those of the larger droplet size emulsions. Consequently, oxidative stability of TAG in o/w emulsions could be controlled by the size of oil droplet even though the origins of TAG were different. Spin-spin relaxation time of protons of acyl residues on TAG in o/w emulsions measured by 1H NMR suggested that motional frequency of some acyl residues was shorter in o/w emulsions with a smaller droplet size. The effect of the wedge associated with hydrophobic acyl residues of emulsifiers was proposed as a possible mechanism to explain differences in oxidative stability between o/w emulsions with different droplet sizes.

A study on dynamics of water in crosslinked poly (N-isopropylacrylamide) gel by n.m.r. spectroscopy

Abstract The dynamics of crosslinked poly ( N -isopropylacrylamide) gel have been studied by means of pulsed-gradient spin-echo (PGSE) 1 H nuclear magnetic resonance (n.m.r.), pulse 1 H n.m.r. and 1 H n.m.r. imaging. The self-diffusion coefficients of HDO ( D HDO ) in D 2 O (containing a small amount of HDO) in the gels with various degree of swellings were determined by the PGSE 1 H n.m.r. method. From these experimental results, it was found that the D HDO is decreased as the degree of swelling is decreased, and D HDO in the gels with a constant degree of swelling in going from 20 to 45°C is transitionally decreased at about 32°C, which corresponds to the phase transition temperature. From the detailed analysis of proton spin-spin relaxation time T 2 determined by the pulse 1 H n.m.r. method, the process of the volume phase transition of the gel has been elucidated. Furthermore, spatial information about the molecular motion of water in the gel sample was obtained by T 2 enhanced 1 H n.m.r. imaging.

Hydrogen-bonding behavior of gellan in solution during structural change observed by 1H NMR and circular dichroism methods

1H NMR relaxation times for water and the circular dichroism for gellan solutions were measured in order to elucidate the hydrogen-bonding behavior and the structural change of the gellan molecule. From the results of the temperature dependence, it was found that 1H T2 for water significantly changes with the conformational change of gellan, such as the random coil-double helix transition or the formation of aggregates of gellan molecules, which alters the proton-exchange rate between a water molecule and the hydroxyl groups of gellan. From results for gellan solutions with various concentrations of K+, it is suggested that the hydrogen bonding between gellan molecules is accelerated by the shielding effect of K+ ions and reinforces the double-helix structure and the aggregates of double helices, and that an aggregate even among the random coils is induced at high concentrations of K+. For a solution with Ca2+, it is suggested that ionic bonds are formed between carboxylic acids of gellan and Ca2+, and these reinforce the aggregates of double helices.

Hydration structure and dynamics in pullulan aqueous solution based on 1H NMR relaxation time

Abstract Dynamic properties of water and polymer chain proton in pullulan/H2O systems in aqueous solutions and in frozen states were analyzed based on T2 relaxation times in 1H-NMR and DSC. Two relaxing species with different T2 detected in the CPMG pulse sequence were assigned to inert polymer protons with the shorter T2 and to water protons with the longer T2 by using deuterated pullulan solutions in D2O. It has been proved that hydration water and free water undergoes rapid exchange in pullulan aqueous solutions. In the frozen state at −11°C, protons in ice crystals (T 2 ∼17 μs ), protons in mobile water (T2>ms) and inert and labile protons in polymer chains (T 2 ∼0.1 ms ) were distinguished in FID curves measured by using the solid echo pulse sequence. With increase in temperature, the inert protons and the labile protons show different mobility, and the inert protons are separately observable from the labile protons in the Carr–Percell–Meiboom–Gill (CPMG) method at temperatures higher than 0°C and the labile protons become mixed with water protons by rapid chemical exchange. These findings indicate the extremely high flexibility of the pullulan chain in aqueous solution.

Elucidation of gelation mechanism and molecular interactions of agarose in solution by 1H NMR

Many biopolymers assume ordered structure in solution due to specific intermolecular interactions, and subsequently aggregate to form fibrous network structures, which play important structural and functional roles both in biomedical tissues and in biopolymeric applied materials. In this study, the pulsed-field-gradient stimulated echo (PGSTE) (1)H NMR method was utilized to elucidate the gelation mechanism and to determine the network structure of agarose. The echo signal intensity of agarose decreased with the formation of aggregated bundles, and therefore, it was used to determine the concentration of the solute agarose (c(sol)) in the gel. The diffusion coefficient of a dendrimer, added to the gel as a probe molecule, increased concomitantly with the formation of the network of aggregated bundles, suggesting apparent dilution of solute agarose in the network interspaces. The hydrodynamic mesh size (ξ) of the network was estimated from the degree of retardation of the diffusion. The dependence of ξ on c(sol) was interpreted using a simple model, where the hydrodynamic interaction of the probe molecule with a solute chain or an aggregated bundle of chains is same. Our theoretically predicted lines fitted well on the experimentally obtained plots, thus validating the use of this model.

Diffusional behavior of n alkanes in the rotator phase as studied by pulse field-gradient spin-echo 1H NMR method

Self-diffusion coefficients, D, of n-C21H44, n-C23H48, n-C24H50, n-C28H58, n-C32H66, and n-C34H70 were measured in the rotator phase and the liquid phase over a wide range of temperatures by using pulse field-gradient spin–echo 1H NMR method, in order to clarify diffusional behavior of the n-alkanes in the rotator phase. From these experimental results it was found that the self-diffusion coefficients of these n-alkanes in the rotator phase and the liquid phase are decreased with a decrease in temperature with different slopes, and at the transition temperature in going from the liquid phase to the rotator phase do not change with a transitionally large decrease. From the Arrhenius plot of diffusion coefficient against temperature, the activation energies for diffusion of n-C24H50, n-C32H66, and n-C34H70 in the rotator phase were obtained to be 19.9, 33.9, and 35.9 kcal/mol, respectively, and on the other hand those in the liquid phase to be 4.8, 4.8, and 5.1 kcal/mol, respectively. Further, the correspon...

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.

Influence of pH and temperature on the ultraviolet-absorbing properties of porphyra-334

Mycosporine-like amino acids (MAA) are a class of small, water-soluble ultraviolet (UV)-absorbing compounds composed of aminocyclohexenone or aminocycloheximine rings with nitrogen or imino alcohol substitutes. Their absorption maxima are from 310 to 360 nm. They have been reported in green, red and brown algae from torrid zones, temperate zones and polar regions. Approximately 20 MAA have been identified in marine organisms since the 1960s. As natural UV-absorbing compounds with high molar extinction coefficients, MAAs have potential commercial applications in suncare products, such as cosmetics for skin protection, and in the protection of non-biological materials, such as photostabilizing additives in the plastic, paint and varnish industries. Porphyra-334 is one kind of MAA widely distributed among marine algae. It has a maximum absorption at 334 nm (ε = 4.23 × 10). Porphyra334 has potential commercial applications. Most of the studies on MAA are concerned with environmental control (mainly light, salinity and temperature) of production of MAA and their physiological roles. There are few reports on the stability of MAA in different conditions. The lack of basic studies limits the use of MAA. The present study investigates the stability of porphyra-334 solution using the UV absorption spectra under various environments of pH and temperature. Commercial products of Porphyra yezoensis harvested from the Ariake Sea in Saga Prefecture, Japan were used. Dried nori was stored at −20°C until used. Porphyra-334 was extracted and purified based on Takano et al. Porphyra-334 was identified by comparing the absorption spectrum and retention time reported by Klisch and Häder. pH of purified porphyra-334 aqueous solution was adjusted with 0.1 M HCl and 0.1 M NaOH to give pH values of 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 9.0, 10.0, 11.0, 12.0 and 13.0. After pH adjustment, the porphyra-334 solutions were sealed in airtight containers with N2 and maintained at room temperature or in 40, 60 and 80°C water baths in darkness. The absorption spectra of porphyra-334 solutions were measured every 2 or 4 h in the range 200– 400 nm using a spectrophotometer (Hitachi, U-

Structural change of polymer chains of gellan monitored by circular dichroism

The random-coil-to-helix transition of gellan gum with various counter monocations, such as Li+, Na+, K+, Rb+, Cs+ and tetramethyl ammonium (TMA+) in aqueous solution has been studied by circular dichroism (CD) and NMR methods in the absence of any additional salts. CD data show a sharp decrease in the molar ellipticity at 202 nm at the transition point, the temperature of which is defined as T CD, i.e., the transition temperature determined by CD. T CD depends on the concentration of gellan and on the countercation, for example, from 0.65 to 21.2 °C for 0.1–0.92% of Na-type gellan solution and from 6.7 to 26.1 °C for 0.13–1.0% Rb-type gellan solution. The molar ellipticity changes reversibly over the whole temperature range investigated for 1% Na, Rb, and TMA-type gellan solutions, while it shows a temperature delay in the recovery to random coil for 1% Li- and K-type gellan solutions. This phenomenon becomes more remarkable in higher concentration solutions. The water proton spin-spin relaxation time, T 2, drastically decreases around the transition temperature. The temperature at which the decrease of T 2 begins, however, is higher than T CD in some cases. This observation indicates that a change in the state of water (mobility, hydrogen bonding, hydration structure and so on) may occur preceding the helix formation of the polymer chain. The T 2 value shows the irreversibility of the transition in 1 % Li, K, and TMA gellan solutions. In comparison to the result obtained from CD, the aggregate formed at low temperature still remains as an aggregation of random coils at higher temperatures in the heating process.

Molecular mobility and microscopic structure changes in κ-carrageenan solutions studied by gradient NMR.

Changes in the molecular mobility of κ-carrageenan were observed by the pulsed field gradient stimulated echo (PGSTE) and Carr-Purcell-Meiboom-Gill (CPMG) methods for elucidating the molecular aspect of the sol-to-gel transition. The echo signal intensity of κ-carrageenan without a gradient, Ikap(0), decreased steeply near the sol-to-gel temperature (Tsg), suggesting that κ-carrageenan chains formed aggregates and a network structure. Below Tsg, the spin-spin relaxation time T2 and the diffusion coefficient of κ-carrageenan (Dkap) increased with decreasing temperature, indicating that the solute κ-carrageenan chains have a lower molecular weight Mw than chains involved in the aggregation. The diffusion coefficient of pullulan (Dpul) added as a probe molecule in κ-carrageenan solutions was measured, and the characteristic hydrodynamic screening length, ξ, was then estimated from the degree of diffusion restriction. Below a certain temperature, Dkap reached a higher value than that of Dpul, suggesting that the Mw of solute κ-carrageenan became lower than that of pullulan. GPC measurements confirmed the presence of κ-carrageenan chains with a lower Mw than that of pullulan. A simple physical model of the structural change in κ-carrageenan solution was proposed with a bimodal distribution of κ-carrageenan with higher and lower Mw than the pullulan probe. The higher Mw chains form the gel network restricting the probes diffusion, and the lower Mw chains increase the effective viscosity. The concentration of the high Mw solute κ-carrageenan chains in 1%, 2% and 4% κ-carrageenan solutions was estimated from Ikap(0) and the total κ-carrageenan concentration, and the relation with pullulan diffusion was studied.