Strain-Induced “Band Flips” in Cyclodecaamylose and Higher Homologues

The cavity of the larger molecule has less space for guests! Unlike the structure of the smaller annular cyclodextrins, that of the higher homologues of cycloamyloses (CAs) with more than ten glucose units contains a 90° kink between adjacent glucose residues within one half of the molecule and a 180° band flip between adjacent units in different halves (see depicted section of the CA14 structure) to yield butterfly-shaped structures with narrow, groovelike cavities.     

A Fullerene/Lipid Electrode Device: Reversible Electron Transfer Reaction of C60 Embedded in a Cast Film of an Artificial Ammonium Lipid on an Electrode in Aqueous Solution

Two reversible one-electron transfers are observed for an electrode device made from C₆₀ and an artificial lipid (see schematic drawing). Cyclic voltammetric studies reveal that the redox couples are unchanged even after 50 cycles, thus indicating that the C₆₀ radical monoanion and the C₆₀ dianion generated in aqueous solution are very stable.     

Synthesis and reactions of a poly(methacrylate) from an optically active amino alcohol

Synthesis and radical polymerization of a novel optically active methacrylate, (S)–2–tert–butoxycarbonylamino–3–phenylpropyl methacrylate (MA–F–BOC), were examined. MA–F–BOC was synthesized from methacrylic acid and N–protected (L)–phenylalaninol. Radical polymerization of MA–F–BOC quantitatively afforded the corresponding polymethacrylate with a relatively high molecular weight. Radical copolymerizations of MA–F–BOC were carried out with styrene and acrylamide to afford the copolymers. Radical polymerization of MA–F–BOC in the presence of n–butanethiol afforded the oligomers, whose degrees of polymerizations were 3.3–8.0. The BOC group was completely cloven with HBr to afford the corresponding optically active polymeric amine quantitatively. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 1981–1986, 1998     

Novel lipase-catalyzed ring-opening copolymerization of oxiranes and succinic anhydride forming polyesters bearing functional groups

Oxiranes, such as glycidyl phenyl ether (GPE) and benzyl glycidate (BG), were copolymerized with succinic anhydride (SA) by lipase at a temperature between 60 and 80°C to yield the corresponding polyesters bearing carboxyl or phenyl groups. Bulk polymerization, especially at the temperature of 80°C, and preferably using porcine pancreatic lipase gave biodegradable polyesters with a molecular weight greater than 5000.     

Cationic polymerization of glycidyl phenyl ether initiated by various arylsulfonium salts as new thermal latent cationic initiators

The cationic initiation activity of derivatives of S-methylsulfonium salts has been evaluated in the cationic polymerization of glycidyl phenyl ether ( 1 ). These initiators are soluble in 1 and capable of initiating the cationic polymerization of 1 on heating, except for methyltetrahydrothiophenium tetrafluoroborate ( 6 ) (r.t. −160°C). Among them, methyldiphenylsulfonium tetrafluoroborate ( 4 ) shows moderate thermal latency, that is the polymerization of 1 occurs efficiently at 160°C but not below 80°C.     

Asymmetric oxidation and determination of the configurations of an optically pure sulfoxide and an I-menthoxysulfonium salt of 1,9-bis(methylthio)dibenzothiophene by x-ray crystallographic analysis

1,9-Bis(methylthio)dibenzothiophene (1a) was treated with one equivalent of bromine and pyridine in the presence of l-menthol and then with aqueous sodium hydroxide to give optically active 1-(methylsulfinyl)-9-(methylthio)dibenzothiophene (2a) enriched by the S isomer (ee: 57%). The configuration of optically pure sulfoxide (2a) was determined by X-ray crystallographic analysis to be the S configuration at the sulfinyl sulfur atom. On the other hand, 1-(methyl-l-menthoxysulfonio)-9-(methylthio)dibenzothiophene tetrafluoroborate (4a) was isolated as an intermediate of this asymmetric oxidation in an optically pure form, as yellow crystals. The absolute configuration of this sulfonium salt (4a) was verified by X-ray crystallographic analysis as the R configuration. Optically pure sulfonium salt (4a) also gave partially optically active sulfoxide (2a) with net inversion on its hydrolysis. It was suggested that the hydrolysis reaction of the sulfonium salt (4a) accordingly proceeds, not only via a sulfurane having a simple S_N2 type of geometry but also by a front side attack ofhydroxide anion, with respect to the l-menthoxy group, on sulfur, and the sequential elimination of the l-menthoxy group from the tetracoordinated intermediate. © 1996 John Wiley & Sons, Inc.     

Dynamic and electrophoretic light scattering of poly(dimethyldiallylammonium chloride) in salt-free solutions

Dynamic and electrophoretic light scattering were used to study the diffusion and electrophoretic mobility of poly(dimethyldiallylammonium chloride) as a function of polymer molecular weight in salt-free solutions. Two relaxation modes characterized as fast diffusion (D_f) and slow diffusion (D_s) were obtained from dynamic light scattering. Although the slow diffusion coefficient D_s strongly depends on molecular weight (M_w), the fast diffusion coefficient D_f was found to be independent of M_w over the range in the study. The fast diffusion was considered as the diffusion of a part of the polymer chain; the slow diffusion was interpreted by multichain diffusion. Electrophoretic light scattering results in the salt-free solution show that the electrophoretic mobility of the polymer is independent of M_w. © 1996 John Wiley & Sons, Inc.     

A novel group transfer polymerization of 1-trimethylsiloxy-benzocyclobutene via hetero Diels-Alder reaction

A novel group transfer polymerization via hetero-Diels-Alder reaction is described. When 1-trimethylsiloxybenzocyclobutene ( 1 ) was treated with a catalytic amount of p-anisaldehyde (4-methoxybenzaldehyde) and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilanide) at room temperature for 0.5 h, poly[1,2-phenylene-1-(trimethylsiloxy)ethylene] was obtained quantitatively. The number-average molecular weight of the polymer was M̄_n = 2000 and the molecular weight distribution was narrow (ratio of weight-to number-average molecular weights M̄_w/M̄_n = 1.18). Structural characteristics suggested a polymerization mechanism involving isomerization of 1 to o-quinodimethane and successive hetero-Diels-Alder reaction leading to poly[1,2-phenylene-1-trimethylsiloxy ethylene]. The living-like nature of the polymerization was supported by a monomer addition experiment in which the molecular weight increased according to the increase of the added monomer.     

Living ring-opening polymerization of cyclic thiocarbonate

This work deals with the cationic ring-opening polymerization of a cyclic thiocarbonate, 5,5-dimethyl-1,3-dioxane-2-thione (1). The polymerization was carried out with 2 mol% of trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as an initiator to afford the polythiocarbonate with the narrow molecular weight distribution (M_n = 11200-31000, M_w/M_n = 1.04-1.15). The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after quantitative consumption of 1 in the first stage, supporting that the cationic ring-opening polymerization of 1 proceeded via a living process.