Azeotropic-like (congruent melting) phenomena of lamellar liquid crystals

The binary system of water and didecyldimethylammonium bromide (DDeAB), having a double hydrocarbon chain, was found to exhibit exhibit an azeotropic-like phase transition from lamellar liquid crystal to micellar solution. That is, the maximum limiting value of temperatures where the present system is allowed to exist in a lamellar liquid crystal corresponds to the socalled azeotropic point (AZP) or congruent melting point. At this temperature, the compositions of the liquid crystal and micellar solution phases become identical. Upon addition of a small amount of NaBr, the AZP shifts to a high temperature, but the point disappears above 0.375 wt% NaBr in water. The AZP is also increased by adding cholesterol. On the other hand, the transition enthalpies at AZPs are extremely small and almost constant, even if NaBr and cholesterol are added. The sharp DSC peak is observed in the presence of salt, whereas it is broad in the presence of cholesterol. It is considered that salt induces a closely packed state of the liquid crystal phase. Although cholesterol also has an ordering effect on the surfactant aggregates its hydrophobic property increases the phase transition temperature. The phase transition occurs due to a packing change of the hydrocarbon chains of DDeAB molecule from the lamellar to micellar states. The correlation between the movement of AZP and the phase behavior in the presence of salt is also discussed.     

A family of low-molecular-weight hydrogelators based on L-lysine derivatives with a positively charged terminal group

A family of L-lysine-based low-molecular-weight compounds with various positively charged terminals (pyridinium and imidazolium derivatives) was synthesized and its gelation behavior in water was investigated. Most of the compounds can be very easily synthesized in high yields (total yields >90 %), and they function as excellent hydrogelators that form hydrogels below 1 wt %; particularly, N(epsilon)-lauroyl-N(alpha)-[11-(4-tert-butylpyridinium)undecanoyl]-L-lysine ethyl ester (2 c) and N(epsilon)-lauroyl-N(alpha)-[11-(4-phenylpyridinium)undecanoyl]-L-lysine ethyl ester (2 d), which are able to gel water at concentration of only 0.2 wt %. This corresponds to a gelator molecule that entraps more than 20 000 water molecules. All hydrogels are very stable and maintain the gel state for at least 9 months. TEM observations demonstrated that these hydrogelators self-assemble into a nanoscaled fibrous structure; a three-dimensional network is then formed by the entanglement of the nanofibers. An FTIR study in [D(6)]DMSO/D(2)O and in CHCl(3) revealed the existence of intermolecular hydrogen bonding between the amide groups. This was further supported by a (1)H NMR study in [D(6)]DMSO/H(2)O. A luminescence study, in which ANS (1-anilino-8-naphtharenesulfonic acid) was used as a probe, indicated that the hydrogelators self-assemble into nanostructures possessing hydrophobic pockets at a very low concentration. Consequently, it was found that the driving forces for self-assembly into a nanofiber are hydrogel bonding and hydrophobic interactions.     

Fairly marked enantioselectivity for the hydrolysis of amino acid esters by chemically modified enzymes

The hydrolysis (deacylation) of enantiomeric substrates by the chemically modified enzymes decanoyl-alpha-chymotrypsin and decanoyl-trypsin was studied. Reaction activity for decanoyl-alpha-chymotrypsin was lower than that for the native enzyme, although intriguingly the enantioselectivity was markedly enhanced as compared with the native enzyme. In particular, the apparently complete enantioselective catalysis was attained for the hydrolytic cleavage of p-nitrophenyl N-dodecanoyl-D(L)-phenylalaninates. The enhancement of enantioselectivity, however, was not observed for decanoyl-trypsin. These results suggest that the chemically modified alpha-chymotrypsin by addition of hydrophobic groups has promoted enantioselectivity for the hydrolysis of hydrophobic esters.     

New High-Performance Catalysts Developed at Mitsui Chemicals for Polyolefins and Organic Synthesis

This contribution reports Mitsui's R&D activities in the field of catalysis technology focusing on molecular catalysts. Examples of the high-performance molecular catalysts developed at Mitsui include bis(phenoxy-imine) group 4 transition metal complex catalysts (FI Catalysts), phosphazene catalysts (PZN catalysts) and b(beta)-ketoiminato Co(II) complex catalysts. Many of the materials stemming from these catalysts were either difficult or impossible to prepare using conventional catalysts.     

Structures of LiCaAlF6 and LiSrAlF6 at 120 and 300 K by synchrotron X-ray single-crystal diffraction

The low-temperature structures of the colquiriite-type fluorides LiCaAlF₆ and LiSrAlF₆ have been investigated by single crystal X-ray diffraction. Molecular orbital calculations were also carried out using cluster models based on the obtained structures. The crystallographic c-axis at 120 K in LiSrAlF₆ became slightly elongated with respect to the 300 K lattice and the structure became more distorted. In contrast, there was uniform lattice parameter contraction in LiCaAlF₆ and the structure changed minimally between 300 and 120 K. These structural variations support other studies of temperature dependent optical properties reported in the literature.     

Two‐Photon Absorption Properties of Dehydrobenzo[12]annulenes and Hexakis(phenylethynyl)benzenes: Effect of Edge‐Linkage

Two‐photon absorption (TPA) properties of two trefoil‐shaped compounds with different edge linkages—tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)—and three asterisk‐shaped compounds having no edge‐linkage—hexakis(phenylethynyl)benzenes—are investigated experimentally by the open‐aperture Z‐scan and TPA‐induced fluorescence methods with wavelength tuneable femtosecond pulses. The compound with ethynylene edge‐linkage exhibits the most intense TPA (the maximal TPA cross section is 1300±170 GM at 572 nm where 1 GM=10^?50 cm⁴ s molecule^?1 photon^?1). The TPA activity of the compounds is primarily explained in terms of the planarity of the molecules in relation with the type of edge‐linkage.     

Enantiospecific total synthesis of (-)-megaphone by a highly controlled consecutive 1,4- and 1,3-asymmetric induction

Enantiospecific total synthesis of (-)-megaphone (1) is reported. The key synthetic tactic is the use of (4$\text{S}$)-2$\text{Z}$-ethylidene-4-trityloxymethyl-butan-4-olide (6) to both establish the relative and absolute stereochemistry of the contiguous tertiary and quaternary carbon centers by a highly controlled 1,4- and 1,3-asymmetric induction and construct the 4-methoxy-6,6-dialkyl-cyclohexenone portion of 1.     

Permeation and separation characteristics for benzene/cyclohexane mixtures through tosylcellulose membranes in pervaporation

Tosylcelluloses (TosCells) with different degrees of tosylation were synthesized as membrane materials for the separation of benzene/cyclohexane (Bz/Chx) mixtures. TosCell membranes showed a high benzenepermselectivity for the Bz/Chx mixtures in pervaporation (PV). An increase in the benzene concentration in the feed mixtures increased permeation rate but decreased the benzenepermselectivity of the TosCell membranes. The increase in the permeation rate was attributed to the increase of the degree of swelling of the TosCell membranes by the feed mixtures and the decrease in the benzenepermselectivity was mainly caused by the decrease of sorption selectivity. With low benzene concentrations in the Bz/Chx mixtures, the permeation rate of a TosCell membrane with a higher degree of tosylation was greater than that with a lower degree of tosylation, but was vice versa with a high benzene concentration. The benzenepermselectivity of the former TosCell membrane was higher than that of the latter membrane. Differences of the permeation rate and benzenepermselectivity with changes in the benzene concentration in the feed mixture and degree of tosylation of the TosCell membrane were significantly influenced by the degree of swelling of the TosCell membrane and the benzene concentration sorbed into the TosCell membrane. Mechanism of separation for the Bz/Chx mixtures through the TosCell membranes is discussed by the solution–diffusion model.     

Short-step synthesis of optically and biologically active exo-brevicomin

Optically and biologically active (IR,5S,7R)-(+)-exo-brevicomin was synthesized in the six-step sequence starting from diethyl (S,S)-(−)-tartrate.     

Syntheses of (5E)-PGE2 and New 6-Functionalized Derivatives by the Use of Palladium-Catalyzed Decarboxylative Allylic Alkylation

(5 )-Prostaglandin E₂ (7) was synthesized fron ( )-4- -butyldimethylsilyloxy-2-cyclopentenone (1) by 2-alkenyloxycarbonylatlon of the organocopper conjugate-addition adduct (3) followed by intramolecular palladium-catalyzed decarboxylative allylic alkylation. The (5 )-prostaglandin E₂ skeleton was also obtained from the β-keto allylic ester (11) by a similar decarboxylative allylic alkylation. The decarboxylative allylic alkylation of another type of the three-component coupling product (12) gave new 6-methyleneprostaglandin E1 skeleton (15a), which was converted into new 6-methylprosta-glandin I methyl ester (20) 6-methyleneprostaglandin F₁ derivative (16) by two different ways. The stereochemistry of this intramolecular decarboxylative allylic alkylation was discussed in the reaction of 2-[( )- or ( )-2-butenyloxy-carbonyl] cyclopentanone systems.