Minako Shibata

Novel method of synthesizing poly(succinimide) and its copolymeric derivatives by acid-catalysed polycondensation of L-aspartic acid

Abstract High molecular weight poly(succinimide) was quantitatively synthesized by polycondensation of l -aspartic acid using a catalytic amount of o -phosphoric acid in the mixed solvent of mesitylene and sulfolane. In addition, under similar conditions, l -aspartic acid and ω-amino acid produced an organic solvent-soluble poly(succinimide- co -ω-amino acid), which melted below the decomposition temperature.

Synthesis and phototoxic property of tetra- and octa-glycoconjugated tetraphenylchlorins

New tetraphenylchlorin derivatives having four or eight glucose molecules were synthesized. Phototoxicity against the HeLa cell, singlet oxygen producing ability, and cell permeability were examined to evaluate the activity on photodynamic therapy of the compounds.

Synthesis and characterization of poly(succinimide-co-6-aminocaproic acid) by acid-catalyzed polycondensation of L-aspartic acid and 6-aminocaproic acid

The polycondensation of L-aspartic acid (ASP) with 6-aminocaproic acid (ACA) using o-phosphoric acid produced poly(succinimide-co-6-aminocaproic acid). The yield of the MeOH-insoluble copolymer decreased from 99 to 52% and that of the MeOH-soluble one increased from 9 to 47%, with increasing molar ratio of ACA in the monomer feed. The compositions of the succinimide (SCI) unit in the MeOH-insoluble and -soluble copolymers tended to be higher than those of ASP in the monomer feed. The copolymers with the 35 mol % SCI units or above were soluble in DMSO, DMF, and conc-H2SO4, but those with the 20 and 21 mol % SCI units were soluble only in conc-H2SO4. The melting temperature appeared for the copolymers with less than 76 mol % SCI units. Poly(succinimide-co-6-aminocaproic acid) was easily hydrolyzed to yield poly(aspartic acid-co-6-aminocaproic acid), and it exhibited biodegradability toward activated sludge.

Synthesis and radical polymerization of end-methacrylated poly(succinimide) leading to poly(aspartic acid) hydrogel

The polycondensation of aspartic acid in the presence of phthalic anhydride was carried out in mesitylene/sulfolane using o-phosphoric acid as a catalyst. The polymer yields were 91–78%, when 5–20 mol-% phthalic anhydride was added into the feed. The obtained poly(succinimide) carried a phthalic imide unit and a succinic acid unit as end groups. In the MALDI-TOF mass spectrum, the peak-to-peak distances between adjacent signals were 97.07 m/z, corresponding to the calculated value (97.07) of the succinimide unit. Poly(succinimide) was reacted with 2-(methacryloxy)ethyl isocyanate to give end-methacrylated poly-(succinimide), in which the end-functionality of the methacrylate group was ca. 1. End-methacrylated poly-(succinimide) was polymerized with ethylene glycol dimethacrylate using 2,2′-azoisobutyronitrile to give poly(succinimide) gel, which could be converted into water-absorbing poly(aspartic acid) hydrogel.

Synthesis and photodynamic properties of maltohexaose-conjugated porphyrins

A series of porphyrin derivatives with one to four maltohexaose moieties in their meso positions have been synthesized. Zinc or free-base m-THPP (5,10,15,20-tetrakis(m-hydroxyphenyl)-porphyrin) was used as the porphyrin platform. The reaction of m-THPP with 3-iodopropyl nonadecaacetylmaltohexaoside afforded a mixture of all possible combinations of glycoconjugated porphyrins having one to four maltohexaose moieties; monoglycosylated (Ac-1), bisglycosylated (Ac-cis-2 and Ac-trans-2), triglycosylated (Ac-3), and tetraglycosylated (Ac-4) porphyrins were obtained in 11–26% yield. Removal of acetyl groups at maltohexaose moiety afforded highly water-soluble glycoconjugated porphyrins 1–4. Zinc derivatives were synthesized in a similar manner. These maltohexaose-linked porphyrins exhibit remarkable water-solublity (530 mg/mL for 4). The singlet oxygen production ability upon visible light irradiation is not affected by the maltohexaose substitution. Photo- and dark cytotoxicities of the maltohexaose-conjugated porphyrins 1–4 and Zn-1–4 were examined against a HeLa cell line, which showed that the mono-maltohexaosylated derivative (1 and Zn-1) was the most effective photosensitizer for PDT.

Excitation relaxation dynamics and molecular dispersion of maltohexaose-linked tetraphenylporphyrins in aqueous solution

Abstract Molecular aggregation of five types of maltohexaose-linked tetraphenylporphyrins in aqueous solution has been examined by means of a picosecond fluorescence spectroscopy. By changing the number of maltohexaosyl chains from 1 to 4 (HP1, HP2a, HP2b, HP3 and HP4), their hydrophilicity was controlled. Fluorescence spectral profile and its decay lifetime (10.5 ns) of HP4 are identical to those of monomeric H2TPP solution, while HP1 shows a multi-exponential decay even in low concentration. It was found that HP1 entirely forms more stable aggregates because of its high hydrophobicity, and that the aggregation behaviors of HP2s and HP3 are just between those of HP1 and HP4.

Cis-trans isomerization and 13C-NMR chemical shift of polyphenylacetylene

Before and after cis-trans isomerization, the observed 13C-NMR chemical shifts of poly(phenylacetylene) (PPA) in the solid state were investigated on the basis of 13C-NMR chemical shift calculations within AM1 for the cis-transoidal and deflected trans-transoidal forms. Two 13C-resonance peaks in the observed CP/MAS 13C-spectrum were assigned theoretically by the 13C chemical shifts of the main and side chains. After thermal isomerization, the 13C peak of the main chain for PPA shifted upfield by 3.5 ppm, in contrast to the downfield shift of the 13C peak for polyacetylene. This upfield shift of trans-PPA largely was attributed to the increases of the excitation energy from the ground state to the lowest φπ–π* state in the paramagnetic terms of 13C chemical shift on the main chain carbons with the increase in deflected angle τ of 0 to 80°. The ±80° deflected conformation of the trans-transoidal chain due to the cis-trans isomerization was confirmed.