Linear hydrogen‐bonded molecular tapes in the cocrystals of squaric acid with 4,4′‐dipyridylacetylene and 1,2‐bis(4‐pyridyl)ethylene

The title compounds, 4,4′‐(ethyne‐1,2‐diyl)­dipyridinium bis(squarate), C₁₂H₁₀N₂²⁺·2C₄HO₄^?, and 4,4′‐(ethene‐1,2‐diyl)­dipyridinium bis­(squarate), C₁₂H₁₂N₂²⁺·2C₄HO₄^?, are isomorphous and crystallize in space group P. The cocrystals contain linear hydrogen‐bonded molecular tape structures along the [120] direction. The squarate monoanions form a ten‐membered dimer linked by two intermolecular O—H?O hydrogen bonds. Each component mol­ecule forms a segregated stack along the c axis. The bond lengths of the squarate monoanion indicate delocalization of the enolate anion.     

A synchrotron X‐ray study of triclinic LiCa2Nb3O10 with perovskite‐type slabs

The triclinic superstructure of a small crystal of LiCa₂Nb₃O₁₀, lithium dicalcium triniobium decaoxide, has been investigated by synchrotron X‐ray diffraction. The unit cell is an almost rectangular parallelepiped, although there is a 0.245° offset from orthogonality for β. The structure essentially belongs to a homologous series of Li[Na_n?3Ca₂Nb_nO_3n+1] with n = 3, where the moiety in square brackets has a perovskite‐type slab structure. The superstructure has a doubled unit‐cell volume with respect to the tetragonal aristotype. The NbO₆ octahedra are rotated about axes parallel to [110] by approximately 10°. Adjacent slabs are connected by Li atoms and are geo­metrically related by 4₂ pseudosymmetry lying parallel to c . There are twice as many sites as Li atoms, providing a variation of population at these Li sites.     

Chiral zirconium catalysts using multidentate BINOL derivatives for catalytic enantioselective Mannich-type reactions; ligand optimization and approaches to elucidation of the catalyst structure

Catalytic enantioselective Mannich-type reactions of silicon enolates with aldimines were investigated using chiral zirconium catalysts prepared from Zr(O(t)Bu)(4), N-methylimidazole, and newly designed multidentate BINOL derivatives. These new multidentate BINOL ligands were designed on the basis of an assumed transition state structure of a chiral zirconium catalyst derived from two molecules of (R)-6,6'-Br(2)-BINOL. Not only tetradentate BINOL 4 but also tridentate BINOL derivatives were found to be effective, and high enantioselectivities were attained. In a structural study of the most effective zirconium complex prepared from tridentate ligand 6e, several NMR experiments and DFT calculations were carried out. Consequently, the structure of an active catalyst and plausible mechanism of asymmetric induction were elucidated.     

Incoherent quasielastic neutron scattering study on the polymorphism of tristearin: dynamical properties of hydrocarbon chains

Dynamical properties of acyl chains in the three polymorphic phases alpha, beta', and beta of tristearin [C(3)H(5)(OCOC(17)H(35))3] have been studied by means of incoherent quasielastic neutron scattering (IQNS) using selectively deuterated samples. The mean square displacement of hydrogen atoms, , was estimated from the scattering vector Q dependence of the elastic scattering component under the harmonic approximation. It was shown that the temperature dependence of was significantly different between the three phases. There was no marked difference in between these phases up to 193 K, and the value increased linearly with temperature. Although the beta phase remained linear up to 293 K, the alpha and beta' phases started to show a nonlinear increase around 200 K, suggesting an anharmonic nature of molecular motions. The alpha phase exhibited the most conspicuous temperature dependence. These characteristics were ascribable to the difference in the lateral packing of acyl chains. Compared with the beta phase which has a tightly packed T// subcell, the beta' and alpha phases have looser O perpendicular and H subcells, respectively. The molecular motion in the alpha phase was analyzed using the model of uniaxial rotational diffusion in a onefold cosine potential. It has been clarified that the rotational fluctuation about the chain axis in the alpha phase is rather restricted compared with that in the rotator phase of n-alkanes.     

An efficient novel synthesis of beta-(azuleno[1,2-b]benzothienyl)- and beta-(azuleno[2,1-b]benzothienyl)-alpha,beta-unsaturated ketones by the tropylium ion-mediated intramolecular furan ring-opening reaction and X-ray investigation of methyl ketone derivative

Intramolecular reaction of 2-tropylio-3-(5-substituted 2-furyl)benzothiophenes (3), prepared from the corresponding 2-cycloheptatrienyl-3-(5-substituted 2-furyl)benzothiophenes (2), afforded the beta-(azuleno[1,2-b]benzothienyl)-alpha,beta-unsaturated ketones (4), which are otherwise difficult to obtain, in moderate yields. The reaction involves a ring-opening process of the furan ring by intramolecular attack of the tropylium ion onto the 2-position of the furan ring. Similarly, beta-(azuleno[2,1-b]benzothienyl)-alpha,beta-unsaturated ketones (8) were obtained from the corresponding 3-tropylio-2-(5-substituted 2-furyl)benzothiophenes (7) albeit in lower yields. The molecular and crystal structures of the methyl ketone derivative, 8a, are discussed on the basis of X-ray structure analysis.     

Synthetic studies on chartelline C: stereoselective construction of the core skeleton

What a core-ker! The title synthesis was achieved using a route featuring an intramolecular Mitsunobu reaction of a nosyl amide, stereoselective construction of the β-lactam, and formation of an enamide moiety by selenoxide elimination. The stereochemistry of the alkylation for the formation of the β-lactam was controlled by a secondary hydroxy group on the ten-membered ring. SEM=2-(trimethylsilyl)ethoxymethyl; TBS=tert-butyldimethylsilyl.     

Size-controlled deposition of Ag nanoparticles on alumina with the assistance of a photo-induced chromic reaction, and study of their catalytic properties

This paper describes a promising method to synthesize supported metal catalysts based on a photochromic reaction. Highly dispersed Ag nanoparticles (NPs) with a mean diameter of ca. 10 nm stabilized by 3-mercaptopropionic acid (3-MPA) were prepared as a colloidal precursor solution. The zeta electric potential was found to be negatively charged in the region of pH higher than 5 due to the presence of dissociated carboxylate ions (-COO(-)), which led to electric repulsion between Ag NPs and kept the solution in a highly dispersed colloidal state. In the presence of photochromic molecules, trans-2-hydroxychalcone, the photo-irradiation gradually decreased the electric charge on the nanoparticles owing to the formation of flavylium cations, which induced the assembly of Ag NPs. Such photo-induced assembly-dispersion control of Ag NPs enables size selective deposition on a catalyst support, which is controlled by varying the photo-irradiation time.     

Stereochemistry and mechanism of catalytic hydrogenation of substituted cyclohexanones

Substituted alkylcyclohexanones were hydrogenated over several transition metal catalysts. The hydrogenation with freshly prepared Raney Ni gave predominantly the axial alcohols but catalyst to which sodium hydroxide was added or aged catalyst increased the stereoselectivity. In contrast to the PtO₂ hydrogenation in which the equatorial alcohols were favoured, more axial alcohols were obtained than the equatorial counterparts on Pt-black. On Pd catalyst the isomeric ratios of the cyclohexanols changed as the reaction progressed. This may be due to a decrease in the amount of hydrogen available caused by the strong adsorption of ketones on the catalyst. Rh catalyst gave more of the axial alcohols than any other catalyst used in the present study.     

Theory of diffusion-controlled reaction between non-simple molecules. I

A new vibrational principle is presented for reaction rates of diffusion-controlled chemical reaction. The variational principle is obtained by a modification of the closure approximation of Wilemski and Fixman. The closure approximation is found to correspond to a special choice of the trial function in this formation and to yield a lower bound of the reaction rate. This formulation is found to be especially useful for the analysis of reaction between non-simple molecules, such as macromolecules.     

Efficient photocleavage of DNA by cationic porphyrin-acridine hybrids with the effective length of diamino alkyl linkage

Positively charged porphyrins bearing an acridine with various lengths of diamino alkyl linkage, 5-[4-[(6-chloro-2-methoxy-9-acridyl)aminoalkylaminocarbonyl]phenyl]-10,15,20-tris(4-N-methylpyridiniumyl)porphine triiodide, alkyl=ethyl, butyl, hexyl, or octyl, were synthesized. They exhibited more enhanced photocleavage activity of pUC18 plasmid DNA than TMPyP, meso-tetrakis(4-N-methylpyridiniumyl)porphine, which is well known to bind to DNA tightly and to cleave DNA effectively; the hybrid linked with the hexamethylene chain showed particularly high activity. An equilibrium dialysis experiment demonstrated that the binding ability of the hybrids to calf thymus (CT) DNA correlated quantitatively with the photocleavage activity. The lack of the substantial red-shift of the Soret maxima of the hybrids through the titration with CTDNA denied the intercalative binding of the porphyrin part. In their circular dichroism (CD) spectral change on binding to CTDNA, two negative peaks appeared at 275 nm and at 285-290 nm in the UV range. The latter negative peak was observed for hybrids, but not for TMPyP, and thus we assigned it to induced CD (ICD) derived from intercalation of acridine chromophore. In the visible range, the hybrids showed only a positive peak around their Soret maxima, and this feature suggested the porphyrin moiety lay in the DNA groove. In addition, the length of the linker markedly influenced the ellipticity of their visible ICD, suggesting that the proximity of the porphyrin moiety to DNA was greatly affected by the linker.