Published papers

A porphyrin derivative effectively and selectively degraded the target transcription factor, human estrogen receptor-alpha (hER-alpha), upon visible light irradiation, in the absence of additives and under neutral conditions.

Environmentally benign processes for polymer synthesis are needed in order to establish green and sustainable polymer chemistry. From the standpoint of saving natural resources and avoiding carbon dioxide emission, the use of renewable or biomass resources is essential for the production of such polymers. The application of enzymatic reactions for the production of green polymers may act as a key role for environmentally benign processes in the next generation. Furthermore, enzymes act effectively as catalysts for the chemical recycling of the polymers. This review focuses on enzymatic processes for polyester synthesis and chemical recycling of bio-based diol-diacid type polymers, poly(butylene succinate) and poly(butylene adipate), and hydroxy-acid type polymers, poly(ricinoleic acid) and poly(12-hydroxystearic acid). High-molecular-weight diol-diacid type polyesters are produced via the ring-opening polymerization of cyclic oligomers using lipase. The produced diol-diacid type polyesters are readily depolymerized by lipases foaming repolymerizable cyclic oligomers for chemical recycling. The sustainable chemical recycling of these polymers and polymer blends using an enzyme is also discussed.

The cyclic oligomer is a key intermediate both for the lipase-catalyzed synthesis and chemical recycling of diol-diacid type polyesters, such as poly(butylene succinate) (PBS) and poly(butylene adipate) (PBA). The lipase-catalyzed ring-opening polymerization of molecularly pure cyclic oligomers with a definite oligomerization degree was analyzed with respect to the polymerization profiles, such as the molecular weight of the produced polymer and some kinetic parameters of the enzymatic reaction. The cyclic butylene adipate (BA) dimer to tetramer were polymerized faster than the cyclic BA monomer; however, the latter produced a significantly higher molecular weight PBA with an Mw 173000. Though the Kms for these cyclic oligomers were almost the same, the Vmax of the cyclic BA monomer was lower than those of the cyclic BA dimer and trimer. These results indicated that cyclic oligomers showed similar affinities with lipase, but the cyclic monomer tended to be slowly ring-opened by lipase forming the hydroxy acid type initiator. The instantaneous concentration of the hydroxy acid as an initiator was lower than that produced by the cyclic BA dimer and trimer, thus leading to the formation of a higher molecular weight polymer. Similarly, the cyclic BS dimer produced a higher molecular weight PBS with an Mw of 172000 when compared to the cyclic BS trimer.

A novel bio-based thermosetting elastomer was prepared by the lipase-catalyzed polymerization of methyl ricinoleate with subsequent vulcanization. Some mechanical properties of the cured carbon black-filled polyricinoleate compounds were evaluated as a thermosetting elastomer. It was found that the carbon black-filled polyricinoleate compounds were readily cured by sulfur curatives to produce a thermosetting elastomer that formed a rubber-like sheet with a smooth and non-sticky surface. The curing behaviors and mechanical properties were dependent on both the molecular weight of the polyricinoleate and the amount of the sulfur curatives. Cured compounds consisting of polyricinoleate with a molecular weight of 100,800 showed good mechanical properties, such as a hardness of 48 A based on the durometer A measurements, a tensile strength at break of 6.91 MPa and an elongation at break of 350 %.

The lipase-catalyzed ROP of molecularly pure cyclic oligomers with a definite degree of oligomerization is analyzed with respect to the molecular weights of the resulting polymers and certain kinetic parameters of the enzymatic reaction. Cyclic BA dimers, trimers, and tetramers polymerize faster than the equivalent monomer; however, the latter produces PBA of significantly higher molecular weight. The reason is that the ring opening of the cyclic monomer is slow, leading to a lower initiator concentration than that produced by the cyclic BA dimer and trimer. Similarly, the cyclic BS dimer produces PBS of higher molecular weight than that obtained from the cyclic BS trimer.

環境にやさしい高分子合成法の確立は持続的発展を遂げる上で必要不可欠な要素である。本稿では、発酵法や酵素触媒法など生物化学的なアプローチを中心とした高分子合成法、ケミカルリサイクル法、及び架橋やグラフトなどポリマーの修飾法について紹介する。これらバイオプロセスの活用は次世代の環境低負荷型高分子合成を担うことが期待される。

Two novel types of chemically recyclable ester-containing polyurethanes, namely, a diol-diacid-type poly(diester-urethane) (PDEU) and a hydroxy acid type poly(ester-urethane) (PEU), were prepared by a green synthetic route that avoids the use of hazardous diisocyanate. The urethane linkage was introduced by the reaction of ethylene carbonate with amino alcohols and amino acids to form urethanediol and urethane-containing hydroxy acids, respectively. The urethanediol underwent polymerization with dimethyl adipate in the presence of lipase to produce a high-molecular-weight PDEU, while PEU was prepared by the lipase-catalyzed direct polycondensation of the urethane-containing hydroxy acid monomer. The periodic introduction of ester linkages into the polyurethane chain afforded primary biodegradation points and chemically recyclable segments. Both PDEU and PEU were readily degraded in the presence of lipase into oligomers which were readily repolymerized in the presence of the same enzyme.

The authers proposed to develop a hydrogel based on a cyclic acetal unit that produces diols and propanals upon hydrolytic degradation. In particular, the fabrication of hydrogels formed by the free radical polymerization of two diacrylate monomers, 5-ethyl-5-(hydroxymethyl)-b,b-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD), a cyclic acetal having two acryl groups, and poly(ethylene glycol)diacrylate(PEGDA) were proposed. This work develops a strategy to form hydrogels with a co-monomer system, one of which is hydrophobic, and subsequently describes the properties of the resulting hydrogel. Results showed that EH–PEG hydrogel may be formed using the co-solvent system. Further results indicated that swelling degree is dependent upon initiator concentration, monomer concentration, and molar ratios of monomers, while sol fraction significantly depended on initiator concentration and monomer concentration, only. These results demonstrate the ability to fabricate hydrogels using EHD and PEGDA system as well as to control the properties of the resulting hydrophilic networks.

a designed 2-phenylquinoline-estradiol hybrid effectively and selectively degraded the target transcription factor, human estrogen receptor-alpha, which has a high affinity with the estradiol moiety, under long-wavelength UV photo-irradiation, without additives and under neutral conditions.

An innovative method for target-selective degradation of oligosaccharides induced by a light-activated hybrid molecule consisting of anthraquinone and lectin has been developed. The reaction takes place under neutral conditions, and no additives are required.

The application of an efficient glycosylation methodology using 2,3-unsaturated sugards to synthesize critical precursors required for the total synthesis of an antibiotic, Vineomycin B2, was demonstrated.

Sulfated zirconia (SO4/ZrO2) catalyzed Mannich-type reaction of ketene silyl acetals and aldimines proceeded smoothly at room temperature to afford b-amino esters in good to high yields. In addition, the heterogeneous solid acid catalyst SO4/ZrO2 was easily recovered from the reaction mixture and then reused without significant loss of effectiveness.