Maki Horikawa

Preparation and characterization of dispersible chitosan particles with borate crosslinking and their antimicrobial and antifungal activity

We synthesized new dispersive chitosan particles at circumneutral pH. Particles composed of a chitosan-borate complex were synthesized by a method consisting of two simple steps: mixture and dialysis. As this method does not employ reagents such as organic solvents or surface-active agents and does not require heat treatment, it has a minimal negative impact on the environment. Crosslinking of the reaction of glucose and boric acid at ordinary temperature and pressure led to the formation of composite particles. Stereoscopic microscopy and investigation of the particle size distribution by dynamic light scattering (DLS) revealed that particles ranging in size from submicrons to several microns with high dispersibility in water were obtained. Even after heat treatment at 80°C for 12h, the particles maintained their composite formation, indicating that they have high thermal stability. Chitosan powders demonstrated inadequate antimicrobial properties at circumneutral pH, but the particles of the chitosan-borate complex had antimicrobial properties against the gram-negative bacterium, Escherichia coli, and the gram-positive bacterium, Staphylococcus aureus, as well as the fungi Aspergillus niger and Fusarium solani. These results indicated that the particles of the chitosan-borate complex had a broad antimicrobial spectrum at circumneutral pH.

Cellulose/boron nitride core–shell microbeads providing high thermal conductivity for thermally conductive composite sheets

We fabricated sheets with high thermal conductivity in a way that required less filler. Our approach is as follows: (1) we used core–shell spherical microbeads as the thermally conductive filler; (2) we developed cellulose/h-boron nitride (BN) core–shell spherical microbeads using phase separation of a cellulose xanthate aqueous solution (viscose); (3) we hybridized the cellulose/h-BN core–shell microbeads with epoxy resin using compression molding. This process reduced the amount of h-BN required because the microbeads efficiently formed thermally conductive pathways among the shells in the insulating resin. The thermal conductivities of the resulting sheet in the thickness and in-plane directions were 10.6 and 15.6 W m−1 K−1, respectively, using only 48.5 vol% h-BN. In contrast, the thermal conductivities of the composite sheet with 75 vol% of naked h-BN particles were 6.31 and 22.9 W m−1 K−1 in the thickness and in-plane directions, respectively. This large difference resulted from the anisotropic structure of h-BN. The changes in thermal conductivity with h-BN content were inconsistent with percolation theory, when using the cellulose/h-BN core–shell microbeads as a filler. The thermally conductive sheets fabricated with microbeads exhibited thermal conductivities several times greater than that of sheets fabricated with naked h-BN. This indicated that thermally conductive pathways had formed in the insulating resin.

The development of a highly conductive PEDOT system by doping with partially crystalline sulfated cellulose and its electric conductivity

Using direct sulfation of cellulose, we prepared sulfated cellulose (CS) with various degrees of substitution of sulfate groups (DS), which we used as dopants for PEDOT. PEDOT/CS were prepared via in situ chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) in an aqueous CS solution. Films of the obtained PEDOT/CS were formed using spin-coating. As a reference, a PEDOT/PSS film was also formed. The electrical conductivity of the PEDOT/CS film with a DS of 1.03 was 0.576 S m−1. In contrast, the electrical conductivity of the PEDOT/PSS film was 0.0153 S cm−1. Using Raman spectroscopy, we found that the 1400 and 1500 cm−1 bands correspond to the CαCβ vibrations in the five-member PEDOT ring. Compared with the band of the PEDOT/PSS film, the band of the PEDOT/CS film red-shifted from 1437 to 1433 cm−1 and narrowed. We attributed the increased electrical conductivity of the PEDOT/CS film to a greater proportion of the quinoid structure than in PEDOT contained in PEDOT/PSS.

Synthesis of a series of malonic diester-introduced fullerene derivatives

Abstract A facile preparation method for derivatization of fullerene through the Bingel reaction was introduced. A series of fullerene derivatives, to which malonic diester with different substituents were introduced, were systematically synthesized by Bingel reaction. Malonic diester could be added to fullerene at room temperature in the presence of iodine and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and various substituents such as phenyl, hexyl, thienyl, and pyrenyl were introduced into both sides of the malonic diester. As a result, 17 systematic variations were synthesized. The solubility parameters of the obtained fullerene derivatives calculated by the method reported by Fedors were in the range of 33 to 43 (J cm−3)1/2. [Supplementary materials are available for this article. Go to the publishers online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] GRAPHICAL ABSTRACT