Shizunobu Hashimoto

Three-Component Complexes of Cyclodextrins. Exciplex Formation in Cyclodextrin Cavity

The fluorescence quenching of naphthalene, 1-methylnaphthalene, and acenaphthene by trimethylamine (TMA) was studied in aqueous β-cyclodextrin (β-CD) solutions to know the structural requirements for guest molecules to form three-component complexes. The apparent rates for the fluorescence quenching of the naphthalene derivatives by TMA markedly increased in the presence of β-CD. The fluorescence quenching of 1-methylnaphthalene and acenaphthene by TMA was accelerated by β-CD more efficently than that of naphthalene. These results suggest the structures of the three-component complexes as the arene-capped β-CD including TMA in its cavity.

Binding forces in complexation ofp-alkylphenols withβ-cyclodextrin and methylatedβ-cyclodextrins

Abstract.Fluorescence spectroscopy has been used to determine the binding constants (K) for inclusion complexes of six kinds ofp-Akyphenols withβ-cyclodextrin (β-CDx), heptakis(2,6-di-O-methyl)-β-CDx (DMe-β-CDxg), and heptakis(2,3,6-tri-O-methyl)-β-CDx (TMe-β-CDx). The stability of the inclusion complex of each cyclodextrin increases with increasing alkyl chain length of thep-alkylphenol. TheK values decrease in the order of DMe-β-CDx,β-CDx, and TMe-β-CDx for each guest. In complexation of 3-(p-hydroxyphenyl)-1-propanol (3) withβ-CDx as well as with DMe-β-CDx, negative enthalpy (ΔH) and positive entropy changes (ΔS) have been obtained, suggesting both van der Waals and hydrophobic interactions as binding forces. The inclusion of 3 by TMe-β-CDx, however, is an enthalpically favorable but entropically unfavorable process. The van der Waals interactions may be the main binding forces for complexing3 with TMe-β-CDx.

Porphyrinatoiron-catalysed reduction of styrene with sodium borohydride: proposed σ-alkyliron(III) complex as an intermediate

5,10,15,20-Tetrakis(para-substituted phenyl)porphyrinatoiron(III) chloride complexes catalyse the reduction of styrene with NaBH4 to ethylbenzene and 2,3-diphenylbutane and the precursor is assumed to be the σ-alkyl complex (Xtpp)FeIII–PhCHMe.

Chiral recognition of binaphthyls by permethylated β-cyclodextrin

The (S)-enantiomers of binaphthyl derivatives such as 1,1′-bi-2-naphthol, 2,2′-dimethoxy-1,1′-binaphthyl, and 1,1′-binapthyl-2,2′-diyl hydrogen phosphate are more preferable guests for permethylated β-cyclodextrin compared with the (R)-enantiomers.

A facile method of transesterification using phosphorus ylid

Abstract The transesterification of carboxylic esters catalyzed with phosphorus ylid under neutral and mild conditions has been investigated. The reactions of esters having an electron withdrawing group with methanol proceeded rapidly and with high yield, whereas the reverse reactions proceeded slowly or not at all.

Synthesis and Properties of Phosphorus-Containing Aromatic Polyethers

Abstract The phosphorus-containing aromatic polyethers were prepared from bis(p-chlorophenyl)phenylphosphine oxide (BCPO) with the sodium salt of several bisphenols by high temperature solution polycondensation. The best result (yield 84%, n sp /c = 0.15) was obtained from BCPO with bisphenol A (BPA) in dimethyl sulfoxide. However, the polymerization in the solvents such as N, N′-dimethyl-2-pyrrolidone, hexamethylphosphoramide, and N,N′-dimethylformamide, and the polymerization with the other bisphenols HO-C6H4-X-C6H4−OH, where X = CO, S02, CH3P(O), C6H5P(O) in place of BPA gave gumlike polymers. The polymer prepared from BCPO and BPA did not decompose up to ca. 300°C under air or nitrogen atmosphere, but it decomposed slowly at 300–520°C, and decomposed rapidly at 520–540°C. The activation energy (δE) for the maximum rate of weight loss was 47.8 kcal/mole.

Chiral recognition by cyclic oligosaccharides. Enantioselective complexation of bilirubin with β-cyclodextrin through hydrogen bonding in water

The mechanism for enantioselective complexation of bilirubin (BR) with β-cyclodextrin (β-CDx) in water (pH 10.8) has been studied by means of CD spectroscopy. The (–) to (+) bisignate CD signals observed for BR bound to β-cyclodextrin are enhanced upon addition of co-existing guests such as cyclohexanol and cyclooctanol which are completely included in the β-CDx cavity. Non-cyclic oligosaccharides such as maltoheptaose also induce the bisignate CD signals of BR. These results clearly indicate that a lipophilic cavity of β-CDx does not play an important role for enantioselective complexation of BR with β-CDx. The CD signals disappear in water at pH 13.0 where an electrostatic repulsion is expected between BR and β-CDx because either the carboxy groups of BR or the secondary hydroxy group of β-CDx are dissociated under these conditions. BR complexed with heptakis(6-deoxy)-β-CDx also shows the (–) to (+) bisignate CD Cotton effect. On the basis of these results, it has been concluded that optically active BR is bound to the rim of the β-CDx cavity and hydrogen bonding between the carboxylate ions of BR and the secondary hydroxy groups of β-CDx participates in the enantioselective complexation of BR with β-CDx.

Enantioselective complexation of bilirubin with cyclodextrins and non-cyclic oligosaccharides

Circular dichroism spectra indicate that intermolecular hydrogen bonding plays an essential role in enantioselective binding of bilirubin to cyclodextrins and non-cyclic oligosaccharides.

Ring-Opening Polymerization of 1-Benzylazetidine

Abstract The ring-opening polymerization of 1-benzylazetidine (BA) was investigated in bulk and in acetonitrile. The bulk polymerization of BA proceeded with cationic initiators, such as methyl tosylate and 3-hydroxy-1-propanesulfonic acid sultone (PS), at 60°C, and a white, powdery polymer was obtained. The polymer structure was confirmed by elemental analysis and NMR spectroscopy. The polymerization of BA with PS was assumed to proceed via a zwitterion formed by the addition reaction of BA and PS. The polymerization rate was studied in acetonitrile as a solvent. The enthalpy of activation ΔH∗ and the entropy of activation ΔS∗ for the propagation were determined.

Kinetic Study of 1-Substituted Aziridines for Ring-Opening Polymerization Initiated with 3-Hydroxy-1-propane Sulfonic Acid Sultone

Abstract Kinetics of the cationic polymerization of 1-substituted aziridines, such as 1-methoxycarbonylmethyl aziridine, 1-methoxycarbonylethyl aziridine, and 1-benzyl aziridine, initiated with 3-hydroxy-1-propane sulfonic acid sultone have been investigated, and the results are compared with the results of the polymerization of 1-β-cyanoethyl aziridine. The course of polymerization of 1-methoxycarbonylmethyl aziridine involved a termination reaction due to the reaction between the growing endgroup and the imino group in the polymer chain. On the other hand, the polymerizations of 1-methoxycarbonylethyl aziridine and 1-benzyl aziridine were terminated by a backbiting reaction with the formation of a piper-adinium ring on the polymer end. The propagation and termination constants were obtained at different temperatures, and the enthalpies of activation (ΔH∗) and the entropies of activation (ΔS∗) for this polymerization were calculated.