Akinori Takasu

Determination of the Degree of Acetylation of Chitin/Chitosan by Pyrolysis-Gas Chromatography in the Presence of Oxalic Acid

A new method to determine directly and rapidly the degree of acetylation of chitin/chitosan was developed based on reactive pyrolysis-gas chromatography in the presence of an oxalic acid aqueous solution. The degree of acetylation was precisely evaluated on the basis of peak intensities of the characteristic products such as acetonitrile, acetic acid, and acetamide originating from the N-acetyl group of N-acetyl-d-glucosamine units of chitin/chitosan. The observed values were in good agreement with those obtained by (1)H NMR and the other methods. Moreover, the proposed technique was applicable to any kinds of chitin/chitosan samples over the whole range of acetylation including insoluble chitin/chitosan and perfectly acetylated artificial chitin having higher crystallinity to which (1)H NMR had been inapplicable.

New chitin‐based polymer hybrids, 3. Miscibility of chitin‐graft‐poly(2‐ethyl‐2‐oxazoline) with poly(vinyl alcohol)

The miscibility of blends of poly(vinyl alcohol) (PVA) with chitin-graft-poly(2-ethyl-2-oxazoline) (1) and poly(2-ethyl-2-oxazoline) homopolymer (PEtOZO) was investigated. Calorimetric results showed a single glass transition temperature (T g ) in the entire range of compositions for both blend systems, which indicated that PVA is miscible with both the graft copolymer 1 and PEtOZO. The T g of PVA is also shifted to lower temperature upon blending with the graft copolymer 1. IR analysis revealed the existence of specific interactions via hydrogen bonding between the hydroxyl groups in PVA and the carbonyl groups in the poly(2-ethyl-2-oxazoline) side chain of graft copolymer 1. The results show that the interaction of graft copolymer 1 with PVA is increased by introduction of longer poly(2-ethyl-2-oxazoline) side chains. Thermal decomposition (TG) measurements supported the compatibility of PVA with graft copolymer 1 and with PEtOZO, and showed that the thermal stability of PVA is improved upon blending with 1 or PEtOZO.

Accelerated biodegradation of poly(vinyl alcohol) by a glycosidation of the hydroxyl groups

Abstract Biodegradability of N-acetyl- d -glucosamine (GlcNAc)-substituted poly(vinyl alcohol) (PVA) (1) in a soil suspension (pH 6.5) was investigated at 25°C for 40 days. Biochemical oxygen demand (BOD) of 1 with degree of substitution of 0.2–0.3 (DP=430–480) was higher than that of PVA under the degradation condition. Size exclusion chromatography (SEC), 1H NMR, and FT-IR measurements of the recovered sample indicated that biodegradation of PVA main chain was accelerated by partial glycosidation of hydroxyl groups in PVA.

Facile fabrication method for p∕n-type and ambipolar transport polyphenylenevinylene-based thin-film field-effect transistors by blending C60 fullerene

We have demonstrated the solution-processed p- and n-type transports including ambipolar transport organic thin-film transistors (OTFTs), required for complementary thin-film integrated circuit technology, by a facile method of blending the n-type C60 and the p-type [poly(2-methoxy-5-[2’-ethyl-hexyloxy]-1,4-phenylene vinylene] (MEH-PPV). The carrier transport of PPV-based thin-film field-effect transistors with various C60 compositions are investigated by using the field-effect gated structure. One of the important findings is that tunable electronic properties of OTFTs are achieved by controlling C60 composition using a simple and an inexpensive spin-cast technology. The mobility increases with increase in the C60 composition in both n- and p-type OTFTs. Temperature measurements on n-type OTFTs revealed that transport follows a thermally activated hopping transport model with small activation energy.

DNA-based polymer hybrids Part 1. Compatibility and physical properties of poly(vinyl alcohol)/DNA sodium salt blend

Transparent blend films of poly(vinyl alcohol) (PVA) and deoxyribonucleic acid (DNA) sodium salt from salmon testes were prepared by the solvent cast method from a homogeneous aqueous solution; as a new class of biopolymer-based hybrid materials. Differential scanning calorimetric (DSC), dynamic mechanical, thermogravimetric, and scanning electron microscopic analyses indicated that PVA and DNA are compatible in a wide range of compositions. As the DNA content increases, a melting peak of PVA reduces in intensity with a lower temperature shift, appearing at 203°C in the PVA/DNA (50 wt%) blend by DSC. Physical properties of the blend films were evaluated by tensile strength and contact angle measurements. The tensile strength values of PVA/DNA (10 wt%) and PVA/DNA (30 wt%) blend films were 56 and 48 MPa, respectively. The surface free energy of PVA/DNA (30 wt%) blend film was 46 dyn/cm, which is identical to that of PVA, while the pure DNA film was revealed to show hydrophobicity (surface free energy 32 dyn/cm; water contact angle 104°).

New chitin-based polymer hybrids, 4: soil burial degradation behavior of poly(vinyl alcohol)/chitin derivative miscible blends

Soil burial degradation behavior of miscible blend systems of poly(vinyl alcohol) (PVA)/partially deacetylated chitin (1), PVA/chitin-graft-poly(2-methyl-2-oxazoline) (2), and PVA/chitin-graft-poly(2-ethyl-2-oxazoline) (3) was investigated in comparison with the case of a pure PVA film. The degradation of the blend films was followed by the weight changes, scanning electron microscopic observation, Fourier transform infrared spectroscopy, 1H-NMR, and size exclusion chromatography analyses. The rate of weight decrease in these PVA/chitin derivative hybrids was higher than that of control PVA in the soil burial test. Fourier transform infrared spectra of the recovered samples of the blends showed an apparent increase of the absorption intensity due to β-diketone structure in PVA, which reflects the progress of biodegradation of PVA by PVA-oxidizing enzymes. Scanning electron microscopic observation revealed that these blend films were degraded by bacteria and actinomycetes. The triad tacticity and number-average molecular weight of PVA in the hybrids after soil burial determined by 1H-NMR and size exclusion chromatography, respectively, were almost the same as those before soil burial. These results suggested that enzymatic degradation of the hybrid films occurred mainly on the surface and that degradation of the PVA-based samples in the soil was accelerated by blending the chitin derivatives.

Site-Specific Bioconjugation of a Murine Dihydrofolate Reductase Enzyme by Copper(I)-Catalyzed Azide-Alkyne Cycloaddition with Retained Activity

Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is an efficient reaction linking an azido and an alkynyl group in the presence of copper catalyst. Incorporation of a non-natural amino acid (NAA) containing either an azido or an alkynyl group into a protein allows site-specific bioconjugation in mild conditions via CuAAC. Despite its great potential, bioconjugation of an enzyme has been hampered by several issues including low yield, poor solubility of a ligand, and protein structural/functional perturbation by CuAAC components. In the present study, we incorporated an alkyne-bearing NAA into an enzyme, murine dihydrofolate reductase (mDHFR), in high cell density cultivation of Escherichia coli, and performed CuAAC conjugation with fluorescent azide dyes to evaluate enzyme compatibility of various CuAAC conditions comprising combination of commercially available Cu(I)-chelating ligands and reductants. The condensed culture improves the protein yield 19-fold based on the same amount of non-natural amino acid, and the enzyme incubation under the optimized reaction condition did not lead to any activity loss but allowed a fast and high-yield bioconjugation. Using the established conditions, a biotin-azide spacer was efficiently conjugated to mDHFR with retained activity leading to the site-specific immobilization of the biotin-conjugated mDHFR on a streptavidin-coated plate. These results demonstrate that the combination of reactive non-natural amino acid incorporation and the optimized CuAAC can be used to bioconjugate enzymes with retained enzymatic activity.

NEW MEASUREMENT OF HYDROGEN GAS AND ACETONE VAPOR IN GASES EMANATING FROM HUMAN SKIN

ABSTRACT We have found that hydrogen gas and acetone vapor emanate from human skin. Emanation gases from human skin were collected for 5–10 min from arm, palm, or forefinger with a homemade probe and bags. The trapped gases were analyzed by gas chromatography, and hydrogen gas and acetone vapor were found to exist in all subjects. The probe (44 mm outer diameter, 6 mm height and inner volume of 3.8 mL) directly covered a 9.4 cm2—flat skin surface of the arm, and a modified Tedlar bag or aluminum bag could cover a finger or the whole palm. The average rates of acetone vapor and hydrogen gas released from human skin (15 subjects) is 80–800 and 5–50 pg cm−2 min−1, respectively. There is a good linear relationship between the emanation rate and the concentration of those gases in human breath. Correlation factors for acetone vapor and hydrogen gas are 0.81 and 0.66, respectively. The proposed non-invasive clinical technique imposes only very minor physical stress on a subject during sampling.

Chemical modification of hydroxyl groups of poly(vinyl alcohol) by a glycosidation reaction

A new procedure for chemical modification of poly(vinyl alcohol) (PVA) was established by a glycosidation reaction of hydroxyl groups in PVA with triacetylated sugar oxazoline 1. 1 H and 13 C NMR analyses indicated that triacetylated N-acetyl-D-glucosamine (GlcNAc) was introduced onto a PVA backbone selectively via a β-O-glycoside linkage. Deacetylation of triacetylated GlcNAc-substituted PVA 2 resulted in GlcNAc-substituted PVA 3 in good yield. These modified PVAs 2 and 3 exhibited solubilities and thermal properties different from the original PVA.

Synthesis and assembly of novel chitin derivatives having amphiphilic polyoxazoline block copolymer as a side chain

The first synthesis of chitin derivatives with well-defined block copolymer side chains, i. e., chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazoline)] (5), chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-butyl-2-oxazoline)] (6), and chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-tert-butyl-2-oxazoline)] (7), was achieved by the reaction of partially deacetylated chitin (1) with living polyoxazoline block copolymers 2–4. The graft copolymers 5–7 are associated into micelles above the critical micelle concentration (CMC). CMCs of 5 (0.01–0.02 wt.-%) are smaller than those (0.32–0.50 wt.-%) of ω-hydroxyl-terminated poly(2-phenyl-2-oxazoline)-block-poly(2-methyl-2-oxazoline) (2-OH), which is a model block copolymer of the side chain segment of 5. The self-aggregates of 5–7 are capable of forming a complex with hydrophobic low molecular weight substances such as pyrene and magnesium 1-anilinonaphthalene-8-sulfonate (ANS). Cryo-transmission electron microscopy showed that the graft copolymer 5 forms globular particles (diameter: 40 nm) and larger cylindrical aggregates (diameter: 40 nm, length: 80–200 nm). The average radius of gyration of the particles of 5 from the SANS analysis is 36 nm.