Velocity statistics and flow structures observed in bypass transition using stereo PTV

It is known from smoke visualizations that in a transitional boundary layer subjected to free-stream turbulence, streaks appear and eventually break down to turbulence after wavy motions. In order to observe the streaky structures directly, a stereo particle-tracking velocimetry system using hydrogen bubbles in a water channel has been developed and validated against laser Doppler velocimetry. Mean flow statistics show good agreement with previous results. With the developed measurement system, the instantaneous spanwise distribution of the streamwise and wall-normal velocities can be measured fast enough to resolve the time development of the streaky structures. Measurements of instantaneous spanwise distributions of the streamwise and wall-normal velocity disturbances show strong negative correlation between the wall-normal and streamwise velocities in the streaks. Published online: 19 November 2002     

Transition-metal chloride mediated addition reaction of diorganomagnesium to easily enolizable ketones

An alkylation to an easily enolizable ketone, such as β-tetralone, is difficult to perform with Grignard reagent (RMgX) or with diorganomagnesium (R₂Mg), because a deprotonation to form a magnesium enolate occurs predominantly. To avoid the prior enolization, a complex reagent of a transition-metal salt and R₂Mg was examined: A combination of R₂Mg with iron(II) chloride (FeCl₂) or ytterbium(III) chloride (YbCl₃) gave a complex reagent that can realize a nucleophilic reaction to β-tetralone prior to the enolization. A combination of RMgX with these metal salts is inferior to a combination of R₂Mg with them to obtain the nucleophilic complex reagent.     

Target-selective one-way membrane fusion system based on a pH-responsive coiled coil assembly at the interface of liposomal vesicles

The coiled coil trimer structure is a common motif observed in membrane fusion processes of specific fusion proteins such as the hemagglutinin glycoprotein. The HA2 subunit in the hemagglutinin changes its conformation or geometry to be favorable to membrane fusion in response to endosomal weakly acidic pH. This pH responsiveness is indispensable to an artificial polypeptide-triggered delivery system as well as the membrane fusion reaction in biology. In this study, we have constructed an AAB-type coiled coil heteroassembled system that is sensitive to weakly acidic pH. The heterotrimer is formed from two kinds of polypeptides containing an Ala or a Trp residue at a hydrophobic a position, and it was observed that the Glu residue at the other a position induced an acidic pH-dependent conformational change. On the basis of this pH-responsive coiled coil heteroassembled system, a boronic acid coupled working polypeptide for the combination of an intervesicular complex with a sugarlike compound on the surface of the target liposome, and a supporting polypeptide for the construction of a pH-responsive heterotrimer with the working polypeptide were designed and synthesized. The process of membrane fusion was characterized by lipid-mixing, inner-leaflet lipid-mixing, and content-mixing assays. The target selective vesicle fusion is clearly observed at a weakly acidic pH, where the working polypeptides form a heterotrimeric coiled coil with the supporting polypeptides in a 1:2 binding stoichiometry and the surfaces between pilot and target vesicles come into close proximity to each other.     

A tandem reaction of organozinc reagent prepared from palladium-catalyzed umpolung method: diastereoselective formation of cyclohexene derivatives bearing three adjacent stereocenters

In the presence of a palladium catalyst, treatment of γ-acyloxy-α,β-unsaturated ketone with bis(iodozincio)methane caused umpolung of π-allylpalladium to give a zinc dienolate. Thus formed zinc species afforded a cyclohexene derivative via a self-condensation reaction. It is noteworthy that the three adjacent stereogenic centers were created in a single process with quite high diastereoselectivity.     

Nickel-catalyzed cycloaddition of anthranilic acid derivatives to alkynes

A nickel-catalyzed cycloaddition has been developed where readily available anthranilic acid derivatives react with alkynes to afford substituted indoles. The reaction involves oxidative addition of Ni(0) to an ester moiety, which allows intermolecular addition to alkynes via decarbonylation and 1,3-acyl migration.     

Decarbonylative cycloaddition of phthalic anhydrides with allenes

The decarbonylative cycloadditions of phthalic anhydrides with allenes were performed by using nickel catalyst. The asymmetric variant of the cycloaddition was also achieved by using chiral phosphine ligands to provide δ-lactones enantioselectively.     

Dehydrogenative Diels-Alder reaction

The dehydrogenative cycloaddition of dieneynes, which possess a diene in the form of a styrene moiety and a dienophile in the form of an alkyne moiety, produces naphthalene derivatives when heated. It was found that a key requirement of this process is the presence of a silyl group attached to the alkyne moiety, which forces a dehydrogenation reaction to occur.     

Development of a polar lipid profiling method by supercritical fluid chromatography/mass spectrometry

We established a high-throughput and high-resolution analytical method based on supercritical fluid chromatography (SFC) coupled with mass spectrometry (MS) for the simultaneous profiling of diverse polar lipids in a mixture. Trimethylsilyl (TMS) derivatization was used for the analysis of ten polar lipids: phosphatidylglycerol (PG), phosphatidic acid (PA), phosphatidylinositol (PI), lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), lysophosphatidylglycerol (LPG), lysophosphatidic acid (LPA), lysophosphatidylinositol (LPI), sphingomyeline (SM), and sphingosine-1-phosphate (S1P). Using the developed method, the peak tailings of PA, PI, LPA, LPI, and S1P improved, and the limit of detection of PG, PI, LPA, LPI, and S1P was enhanced by 12-, 40-, 510-, 39-, and 1490-fold, respectively. Next, in the analysis of sheep plasma, 20 minor species of PI, LPC, LPE, and SM, and 7 molecular species of LPA, LPI, and S1P were additionally analyzed. The relative ratio of the molecular species in each polar lipid was also found by quantification. Finally, the simultaneous and detail profiling of ten polar lipids was successfully performed by SFC/MS applying TMS derivatization. This developed method is particularly applicable to metabolomics, especially for targeting polar lipids.     

Direct synthesis of fluorescent 1,3a,6a-triazapentalene derivatives via click-cyclization-aromatization cascade reaction

An efficient and versatile method was established for the preparation of 1,3a,6a-triazapentalenes. The 1,3a,6a-triazapentalene skeleton without an additional fused ring system was discovered to be a compact and highly fluorescent chromophore, which exhibited various interesting fluorescent properties such as a noteworthy correlation of luminescent wavelength with the Hammett σ(p) value and a strongly positive solvatofluorochromism.