Stereoselective synthesis of steroid side chain and CD-rings. A route to (±)-de-ab-cholesta-8(14),22-dien-9-one

The stereoselective synthesis of (±)-de-AB-cholesta-8(14),22-dien-9-one from(±)-erythro-6-benzyloxy-5-hydroxy-8-methyl-l-tetrahydropyranyloxy-3(Z)-nonene by two Claisen rearrangements as a precursor of vitamin D₃ is presented.     

The reaction of vinyl ethers with acridine

The reaction of vinyl ethers with acridine gives new acridine derivatives in the presence of an organic ammonium salt and alcohol. An organic ammonium salt such as acridinium chloride affect this reaction. All of the addition products were obtained as dihydroacridinyl derivatives. Moreover, in the reaction of ketene silyl acetal with acridine, the addition products were also obtained as the dihydroacridine derivatives.     

Palladium-catalyzed [3 + 2] cycloaddition reaction of vinylcyclopropanes with α,β-unsaturated esters or ketones

Reaction of vinylcyclopropanes having two electron-withdrawing groups with α,β-unsaturated esters or ketones in the presence of Pd₂(dba)₃.CHC1₃-1,2- bis(diphenylphosphino)ethane (dppe) or tributylphosphine catalyst gave vinyl- cyclopentanes in good yields.     

Crystal structure of a NIR‐Emitting DNA‐Stabilized Ag16 Nanocluster

DNA has been used as a scaffold to stabilize small, atomically monodisperse silver nanoclusters, which have attracted attention due to their intriguing photophysical properties. Herein, we describe the X‐ray crystal structure of a DNA‐encapsulated, near‐infrared emitting Ag₁₆ nanocluster (DNA–Ag₁₆NC). The asymmetric unit of the crystal contains two DNA–Ag₁₆NCs and the crystal packing between the DNA–Ag₁₆NCs is promoted by several interactions, such as two silver‐mediated base pairs between 3′‐terminal adenines, two phosphate–Ca²⁺–phosphate interactions, and π‐stacking between two neighboring thymines. Each Ag₁₆NC is confined by two DNA decamers that take on a horse‐shoe‐like conformation and is almost fully shielded from the solvent environment. This structural insight will aid in the determination of the structure/photophysical property relationship for this class of emitters and opens up new research opportunities in fluorescence imaging and sensing using noble‐metal clusters.     

Critical condition of inner cylinder radius for sustaining rotating detonation waves in rotating detonation engine thruster

We describe the critical condition necessary for the inner cylinder radius of a rotating detonation engine (RDE) used for in-space rocket propulsion to sustain adequate thruster performance. Using gaseous C₂H₄ and O₂ as the propellant, we measured thrust and impulse of the RDE experimentally, varying in the inner cylinder radius r_i from 31 mm (typical annular configuration) to 0 (no-inner-cylinder configuration), while keeping the outer cylinder radius (r_o = 39 mm) and propellant injector position (r_inj = 35 mm) constant. In the experiments, we also performed high-speed imaging of self-luminescence in the combustion chamber and engine plume. In the case of relatively large inner cylinder radii (r_i = 23 and 31 mm), rotating detonation waves in the combustion chamber attached to the inner cylinder surface, whereas for relatively small inner cylinder radii (r_i = 0, 9, and 15 mm), rotating detonation waves were observed to detach from the inner cylinder surface. In these small inner radii cases, strong chemical luminescence was observed in the plume, probably due to the existence of soot. On the other hand, for cases where r_i = 15, 23, and 31 mm, the specific impulses were greater than 80% of the ideal value at correct expansion. Meanwhile, for cases r_i = 0 and 9 mm, the specific impulses were below 80% of the ideal expansion value. This was considered to be due to the imperfect detonation combustion (deflagration combustion) observed in small inner cylinder radius cases. Our results suggest that in our experimental conditions, r_i = 15 mm was close to the critical condition for sustaining rotating detonation in a suitable state for efficient thrust generation. This condition in the inner cylinder radius corresponds to a condition in the reduced unburned layer height of 4.5–6.5.     

Two-dimensional surface chirality control by solvent-induced helicity inversion of a helical polyacetylene on graphite

We report the direct evidence for the macromolecular helicity inversion of a helical poly(phenylacetylene) bearing l- or d-alanine pendants with a long alkyl chain in different solvents by atomic force microscopy observations of the diastereomeric helical structures. The diastereomeric helical poly(phenylacetylene)s induced in polar and nonpolar solvents self-assembled into ordered, two-dimensional helix bundles with controlled molecular packing, helical pitch, and handedness on graphite upon exposure of each solvent. The macromolecular helicity deposited on graphite from a polar solvent further inverted to the opposite handedness by exposure to a specific nonpolar solvent, and these changes in the surface chirality based on the inversion of helicity could be visualized by atomic force microscopy with molecular resolution, and the results were quantified by X-ray diffraction of the oriented liquid crystalline, diastereomeric helical polymer films.     

Nanosphere and nanonetwork formations of [60]fullerene-end-capped stereoregular poly(methyl methacrylate)s through stereocomplex formation combined with self-assembly of the fullerenes

We report a novel and versatile method for constructing a supramolecular nanosphere and nanonetwork based on isotactic and syndiotactic C60-end-capped poly(methyl methacrylate)s (it- and st-PMMA-C60's) through their stereocomplex formation combined with self-assembly of the terminal C60. The stereoregular PMMA-C60's with a precisely controlled structure including molecular weight, its distribution, tacticity, and the chain-end structure were synthesized by the stereospecific anionic living polymerizations of methyl methacrylate followed by end-capping with C60, and their structures were proven by size exclusion chromatography, NMR, UV-vis, and MALDI-TOF-MS analyses. The stereoregular PMMA-C60's self-assembled to form a core-shell aggregate with C60 as the core and the PMMA chains as the shell in H2O/CH3CN (1/9, v/v) due to the solvophobic interaction of the C60 units. These it- and st-PMMA-C60 aggregates further supramolecularly assembled through iterative stereocomplex formation into nanonetworks in which the self-assembled C60 clusters were robustly connected with two- and three-dimensional arrangements. In addition, when the it- and st-PMMA-C60's were simultaneously mixed, self-assembly of the C60 units and stereocomplex formation of the it- and st-PMMA chains took place at once, resulting in the formation of uniformly sized spherical nanoparticles with resistance to heat. Similar nanonetwork architectures can be produced using it-PMMA-C60 clusters and st-PMMA prepolymers as the binder.     

Antiproliferative constituents from umbelliferae plants. IX. New triterpenoid glycosides from the fruits of Bupleurum rotundifolium

The MeOH extract of the fruits of Bupleurum rotundifolium showed inhibitory activity against human gastric adenocarcinoma (MK-1) cell growth. Bioactivity-guided fractionation of the MeOH extract led to the isolation of four new triglycosides of 13beta,28-epoxy oleanane-type triterpenes, named rotundiosides O, Q, S and T; 12 new glycosides of oleanane-type triterpenes, named rotundiosides J-N, P, R, U-Y, and others; echinocystic acid 3-O-sulfate; and three known oleanane-type triterpene glycosides, rotundiosides A, F and G. The structures of the new isolates were determined based on chemical and spectroscopic evidence. The GI(50) of isolates against MK-1, HeLa and B16F10 cell lines are reported.     

Texture change of ice on anomalously preserved methane clathrate hydrate

We used a confocal scanning microscope to observe growth and texture change of ice due to the dissociation of methane gas clathrate hydrate (CH(4) hydrate). The experiments were done under CH(4) gas atmospheric pressure and isothermal conditions between 170 and 268 K. Above 193 K, the dissociation of CH(4) hydrate resulted in many small ice particles that covered the hydrate surface. These ice particles had roughly the same shape and density between 193 and 210 K. In contrast, above 230 K the ice particles developed into a sheet of ice that covered the hydrate surface. Moreover, the measured release of CH(4) gas decreased when the sheet of ice formed at the surface of the hydrate. These findings can explain the anomalous preservation behavior of CH(4) hydrate; that is, the known increase of storage stability of CH(4) hydrate above 240 K is likely related to the formation of the ice that we observed in the experiments.     

Electronic structure of light-induced lophyl radical derived from a novel hexaarylbiimidazole with pi-conjugated chromophore

A novel photochromic hexaarylbiimidazole with a bithienyl group as an extended pi-conjugation unit was synthesized and the light-induced lophyl radical was found to be stabilized due to the delocalization of an unpaired electron, and to strongly absorb near-infrared light.