Etsuo Kokufuta

Ciliary motion actuator using self-oscillating gel

A ciliary motion actuator made of self-oscillating polymer gel has been demonstrated. The actuator was made of polymer gel and a micro projection array was formed on the surface. It was fabricated by moving mask deep X-ray lithography (M/sup 2/DXL) technique and micro molding technique. The polymer gel exhibited spontaneous swelling-deswelling oscillations and dynamic rhythm was created in the array structure. It was demonstrated that this oscillation propagated in the gel with projection array.

Small angle neutron scattering studies on structural inhomogeneities in polymer gels: irradiation cross-linked gels vs chemically cross-linked gels

A comparison of network structure in a solvent was made for two types of poly(N-isopropylacrylamide) gels cross-linked by chemical reaction with N,N 0 -methylenebisacrylamide (BIS) (chemical gels) and by g-ray irradiation (g-ray gels). The cross-linking density dependence for these gels was examined by small angle neutron scattering (SANS). The SANS results indicated an increase of frozen inhomogeneities with an introduction of cross-links for both chemical and g-ray gels. However, it was found that the effect of cross-linking is much stronger in the chemical gels than in the g-ray gels. The differences in the structure were successfully interpreted by a statisticalmechanical theory of gels proposed by Panyukov– Rabin (Phys. Rep. 269 (1996) 1). The degree of polymerization between cross-links, N, was a decreasing function of cross-linking content for both types of gels, while that for the g-ray gels was a weak function of irradiation dose. Quantitative analyses on BIS concentration and g-ray dose dependence led to an experimental evidence of the existence of cross-linking saturation threshold. q 2002 Elsevier Science Ltd. All rights reserved.

On the intermolecular crosslinking of PVA chains in an aqueous solution by γ-ray irradiation

Abstract We studied how the polymer chains of poly(vinyl alcohol)(PVA) are crosslinked in its O 2 -free aqueous solution by γ -rays. The static–dynamic laser light scattering method was employed for determining the molecular weight ( M w ), hydrodynamic radius ( R h ) and radius of gyration ( R g ) for the original PVA ( M w =1.0×10 5 ) and its radiation products. The γ -ray irradiation from Co 60 to the PVA solutions with different concentrations was performed at different dose levels. It was found that both molar mass and size (i.e., R g and R h ) of the radiation products increased with a dose increase. The magnitude of these increases was enhanced by decreasing the polymer concentration ( C p ). In particular, at C p C p using the dose curves of M w . It became apparent that, regardless of C p , the intermolecular crosslinking reactions were dominant in the initial stage of irradiation. The radiation yield of intermolecular crosslinking was found to increase linearly when increasing C p , and at C p > the overlap concentration it asymptotically approached a limiting value estimated from the dimerization of pentane-2,4-diol as a model compound of PVA.

The influence of polymer concentration on the radiation-chemical yield of intermolecular crosslinking of poly(vinyl alcohol) by γ-rays in deoxygenated aqueous solution

Abstract The effect of polymer concentration on G value of intermolecular crosslinking of poly(vinyl alcohol) (PVA) during γ-ray irradiation is reported here. The G value, determined by the measurement of weight average molecular weight (Mw) from static light scattering, increased initially due to the polymer concentration and approached a maximum value of 0.5 × 10−7 mol J−1. It then markedly decreased for the more concentrated water-swollen PVA film (polymer concentration Cp>300 g dm−3). Our results suggest that polymer concentration plays an important role in the crosslinking and degradation reactions of PVA during γ-ray irradiation.

Coimmobilization of Nitrosomonas europaea and Paracoccus denitrificans cells using polyelectrolyte complex-stabilized calcium alginate gel

Calcium alginate gel (CAG) that withstands phosphate ions in the medium was prepared by reinforcing a network structure of the gel with a polyelectrolyte complex (PEC) consisting of potassium poly(vinyl alcohol) sulfate and trimethylammonium glycol chitosan iodide. The PEC-stabilized CAG beads were used as a supporting matrix for the coimmobilization of Nitrosomonas europaea ATCC 25978 cells and Paracoccus denitrificans IFO 12442 cells. The coimmobilized cells were aerobically cultured on a medium containing 3 mM of phosphate ions, using (NH4)2SO4 as a substrate and ethanol as a carbon source. Ammonia was consumed without forming nitrite, indicating the concurrence of nitrification and denitrification in the same system. No breakage of the gel beads was observed during the cultivation. Repeated aerobic cultivation using a column packed with beads of coimmobilized cells had stable initial activity for at least one month.

Immobilization of Paracoccus denitrificans cells with polyelectrolyte complex and denitrifying activity of the immobilized cells

Abstract Whole cells from Paracoccus denitrificans IFO 12442 were immobilized with a polyelectrolyte complex composed of potassium poly(vinyl alcohol) sulfate (KPVS) and poly(diallyldimethylammonium chloride) (PDDA) by the following procedures: An excess of PDDA was first mixed with a cell suspension to aggregate cells, then KPVS was added to form a complex with excess PDDA and to entrap the aggregated cells. Electron microscopic analysis showed that the aggregated cells were entrapped or surrounded by an amorphous complex support. The rate of nitrate reduction or carbon consumption by the immobilized cells was almost the same as that by the free cells, as determined by anaerobic incubation using a non-growth medium containing KNO 3 as a substrate and potassium aspartate as a carbon source. The immobilized cells exhibited activity at pH 4, at which the free cells lost their activity. The initial activity of the immobilized cells remained stable for at least one month in a phosphate buffer with gentle stirring.

Light scattering, CD, and ligand binding studies of ferrihemoglobin-polyelectrolyte complexes.

Quasi-elastic light scattering (QELS), electrophoretic light scattering (ELS), CD spectroscopy, and azide binding titrations were used to study the complexation at pH 6.8 between ferrihemoglobin and three polyelectrolytes that varied in charge density and sign. Both QELS and ELS show that the structure of the soluble complex formed between ferrihemoglobin and poly(diallyldimethylammonium chloride) [PDADMAC] varies with protein concentration. At fixed 1.0 mg/mL polyelectrolyte concentration, protein addition increases complex size and decreases complex mobility in a tightly correlated manner. At 1.0 mg/mL of greater protein concentration, a stable complex is formed between one polyelectrolyte chain and many protein molecules (i.e., an intrapolymer complex) with apparent diameter approximately 2.5 times that of the protein-free polyelectrolyte. Under conditions of excess polyelectrolyte, each of the three ferrihemoglobin-polyelectrolyte solutions exhibits a single diffusion mode in QELS, which indicates that all protein molecules are complexed. CD spectra suggest little or no structural disruption of ferrihemoglobin upon complexation. Azide binding to the ferrihemoglobin-poly(2-acrylamide-2-methylpropanesulfonate) [PAMPS] complex is substantially altered relative to the polyelectrolyte-free protein, but minimal change in induced by complexation with an AMPS-based copolymer of reduced linear charge density. The change in azide binding induced by PDADMAC is intermediate between that of PAMPS and its copolymer.

Stoichiometric complexation of bovine trypsin with potassium poly(vinyl alcohol sulphate) and enzymatic activity of the complex

Abstract The complexation of bovine trypsin with potassium poly(vinyl alcohol sulphate) (KPVS) was investigated at different pHs by means of colloid titration. The number of moles of the basic (amino, imidazolyl, and guanidyl) groups in 1 g of trypsin, which were bound to the sulphate groups in KPVS by salt linkages, was evaluated from the titration data. From a comparison of the results obtained with the number of basic groups counted from the amino acid sequence already reported, it was found that the complexation follows a stoichiometric relationship in the range pH Nα- benzoyl- dl -arginine -p- nitroanilide and casein as substrates. The complexed enzyme showed appreciable retention of activity, not only towards the low molecular weight substrate but also towards the polymeric substrate. Therefore, it became apparent that the stoichiometric complexation of trypsin with KPVS does not have a large influence on conditions for the active site of the enzyme, because the salt linkages for maintaining the structure of the complex are very loose.

Stoichiometry and the Mechanism of Complex Formation in Protein-Polyelectrolyte Coacervation

Abstract The complexation and coacervation of bovine serum albumin (BSA) with poly(dimethyldiallylammonium chloride) (PDMDAAC) in pH 7.86 buffer solutions, at various ionic strengths (I), was investigated by turbidimetric titration, quasi-elastic light scattering, and electrophoretic light scattering. The results obtained support the following mechanism. Upon addition of PDMDAAC to BSA at I = 0.01 M, a stoichiometric complex is initially formed. Subsequent addition of polymer causes this complex to form a coacervate with concomitant charge neutralization. At higher ionic strengths (0.05 and 0.10 M), the initial complex is nonstoichiometric, and coacervates are formed by the aggregation of the complex. These coacervates are observed to be ∼ 700 nm by optical microscopy.

Continuous column denitrfication using polyelectrolyte complex-entrapped Paracoccus denitrificans cells

Abstract Whole cells from Paracoccus denitrificans IFO 12442 were immobilized with a polyelectrolyte complex consisting of poly(vinyl alcohol) sulfate and poly(diallyldimethylammonium chloride). Continuous denitrification using a column packed with the immobilized cells was carried out as follows: A non-growth medium containing KNO3 as a substrate and potassium aspartate as a carbon source was passed through the column under anaerobic conditions for about three months. It was found that the immobilized system remained stable during a period of more than two months, without the loss of activity or the leakage of the cells from the support.