Triplet Diradical-Cation Salts Consisting of the Phenothiazine Radical Cation and a Nitronyl Nitroxide

The spin–spin and magnetic properties of two (nitronyl nitroxide)-(di-p-anisylamine-phenothiazine) diradical cation salts, ( DAA-PTZ ) ⁺ -NN⋅ MBr₄⁻ (M=Ga, Fe), have been investigated. These diradical-cation species were prepared by the cross-coupling of iodophenothiazine DAA-PTZ-I with NN-AuPPh₃ followed by oxidation with the thianthrenium radical cation ( TA⁺⋅ MBr₄⁻). These salts were found to be highly stable under aerobic conditions. For the GaBr₄ salt, large ferromagnetic intramolecular and small antiferromagnetic intermolecular interactions (J₁/k_B=+320 K and J₂/k_B=−2 K, respectively) were observed. The magnetic property of the Fe³⁺ salt was analyzed by using a six-spin model assuming identical intramolecular exchange interaction (J₃/k_B=+320 K) and the other exchange interactions (J₄/k_B=−7 K and J₅/k_B=−4 K). A significant color change was observed in the UV/Vis/NIR absorption spectra upon electrochemical oxidation of the doublet DAA-PTZ-NN to the triplet ( DAA-PTZ ) ⁺ -NN .     

Effect of calcination temperature during preparation of Ru?Sn-alumina catalysts on the hydrogenation of carboxylic acid

The conversion of a carboxylic acid was increased to 90% with 100% selectivity to the corresponding alcohol by calcination of the catalyst precursor, Sn/alumina, of Ru–Sn/alumina in the hydrogenation of the carboxylic acid.     

The first synthesis of peptide thioester carrying N-linked core pentasaccharide through modified Fmoc thioester preparation: synthesis of an N-glycosylated Ig domain of emmprin

Peptide thioester carrying N-linked core pentasaccharide was prepared by the Fmoc solid-phase method with a combination of the benzyl-protection strategy at the carbohydrate portion. The obtained peptide thioester was successfully used for the synthesis of the first Ig domain of emmprin composed of 61 amino acid residues.     

The degeneration of the two dimensional garnier system and the polynomial Hamiltonian structure

Summary We study the theory of isomonodromic deformation for the second order linear differential equations on the Riemann sphere and show that the deformation equations are written in the form of Hamiltonian system completely integrable in the sense of Frobenius. We also obtain from them the Hamiltonian systems with the polynomials Hamiltonians.     

Entropic Repulsion for Two Dimensional Multi-Layered Harmonic Crystals

We consider two dimensional lattice free fields (harmonic crystals) and study the asymptotic behavior of the fields under the constraint that each field lies above a hard-wall and is forced to be piled on top of another. This problem is the so-called entropic repulsion and our result extends that of ref. 2 which studied the higher dimensional case.     

Synthesis,structure, and aromaticity of a hoop-shaped cyclic benzenoid [10]cyclophenacene

The first hoop-shaped cyclic benzenoid compounds, [10]cyclophenacene derivatives that contain 40 pi electrons, have been synthesized in three or four steps from [60]fullerene by rationally designed chemical modification. The compounds thus synthesized are chemically stable, yellow-colored, luminescent, and EPR-silent. X-ray crystallographic analysis provided high precision structural data sets. On the basis of these results and theoretical investigations, the new cyclic benzenoid molecules were proven to be aromatic.     

Phase behavior and surface tensions of amphiphilic fluorinated random copolymer aqueous solutions

Phase behavior and surface tension of aqueous solutions of fluorinated random copolymers [perfluoroalkylacrylate]–[poly(ethyleneoxide)methacrylate], [C_mRf-acrylate]-[EO_n-methacrylate] with fluroalkyl carbon number m = 8, 6, 4, 2 and number of ethyleneoxide unit, n = 9 and 4.5 were investigated as a function of composition and different combinations of m and n. Isotropic solutions are formed at lower temperatures over wide concentration range of copolymer but at higher temperature phase separation occurs. The cloud point of copolymer decreases with decreasing n as well as m, and also with decreasing the number of poly(ethyleneoxide)methacrylate chain per perfluorinatedalkylacrylate chain, suggesting that the copolymers become more hydrophobic on decreasing m and n. Equilibrium and dynamic surface tension measurements show that copolymers become increasingly surface active as m as well as n decrease but the adsorption at the air–water interface is very slow due to bulkiness of the molecules. No clear evidence of the formation of micellar aggregates could be obtained from surface tension–composition curves.     

Characterization of Bi5Nb3O15 by refinement of neutron diffraction pattern, acid treatment and reaction of the acid-treated product with n-alkylamines

The structure of Bi₅Nb₃O₁₅ was investigated by refinement of the powder neutron diffraction pattern as well as by structural change through acid treatment and subsequent treatments of an acid-treated product with n-alkylamines. Rietveld refinement suggests that Bi₅Nb₃O₁₅ adopts a mixed-layer Aurivillius-related phase structure, [Bi₂O₂]+[NbO₄]+[Bi₂O₂]+[BiNb₂O₇] [Pnc2 (space group No. 30)] with a=2.1011(4), b=0.5473(1) and c=0.5463(1) nm. After the acid treatment of Bi₅Nb₃O₁₅ with 3 mol/L HCl, a new reflection (at 2.25 nm after drying at room temperature or at 1.89 nm after drying at 120 °C) appeared in the X-ray diffraction (XRD) pattern in addition to the reflections due to Bi₅Nb₃O₁₅. Upon acid treatment, a part of the Bi ions were lost and essentially no Nb ions were dissolved during acid treatment to give a Bi/Nb molar ratio of 1.4. The TG curves of the acid-treated product showed mass loss (ca. 4 mass%) in the range of 300-600 °C. It was also demonstrated that the particle shapes did not change upon acid treatment. The reaction of the acid-treated product (after drying at room temperature) with n-alkylamines led to a shift of the newly appearing reflection to a lower angle, and the d-value of the low-angle reflection increased linearly in accordance with the increment of the number of carbon atoms in n-alkylamines. These results indicate that the [Bi₂O₂] sheet in Bi₅Nb₃O₁₅ was partially leached by acid treatment to form a layered compound H₄BiNb₃O₁₁·xH₂O, capable of accommodating n-alkylamines in the interlayer space, and its anhydrous form, H₄BiNb₃O₁₁, upon drying. Based on the variation in the interlayer distance upon intercalation of n-alkylamines into the acid-treated product, the structure of the acid-treated product can be suggested to comprise alternately stacked protonated [BiNb₂O₇] and [NbO₄] sheets, a result consistent with the Rietveld refinement of Bi₅Nb₃O₁₅.     

Studies directed toward the synthesis of protein-bound GPI anchor

Mannobioside-linked phosphoethanolamine 10, a prototype model of the GPI anchor, was synthesized via glycosidation of the monosaccharide donor and acceptor, and subsequent phosphorylation. In order to test the reactivity of the amino group involved in 10 against the activated amino acid esters, 10 was reacted with N-protected amino acid pentafluorophenyl esters in the presence of HOBt. The reactions gave the aminoacylated products in moderate yields. When Fmoc-Ser-OPfp 12 and Fmoc-Cys(SBu^t)-OPfp 14 were reacted with 10, byproducts 19, 20 and 21 derived from N- and O-acylation were produced. In contrast, reactions of 10 and N-protected amino acid thioesters were promoted with AgNO₃, HOSu, and DIEA to afford the coupling products without the undesired O-acylation. Peptidylation of 10 with the synthesized oligopeptide thioesters 24 and 27 was also successful under the segment coupling conditions of the peptide thioester method as well as those of the native chemical ligation.     

Development of miniaturized sample preparation with fibrous extraction media

Introducing fine polymeric filaments as the extraction medium, a miniaturized sample preparation technique for micro-column liquid chromatography (micro-LC) has been developed along with the investigation of a reproducible preparation scheme of the extraction capillary. The polymeric filaments were packed longitudinally into either a fused-silica capillary or a polyether ether ketone (PEEK) capillary of appropriate dimensions, and the extraction capillary was installed to the injection valve in micro-LC system. The number of packed filaments should be precisely counted before the packing process to make sure the reproducible preparation of the extraction capillary. With conventional stationary phase materials for open-tubular gas chromatography, polymeric coating to the surface of the filaments was also studied in order to further enhance the extraction performance and selectivity. Coated with the polymeric material suitable for the extraction of particular analyte, a dramatic improvement on the extraction power was obtained. The results suggest that the future possibility of novel tailored fibrous extraction medium with an appropriate coating on it, especially for the analysis of complex sample matrices.