Massenspektren der von Aminosäuren bzw. Peptiden abgeleiteten Triazin-Derivate

A mass spectrometric study of about 30 triazine derivatives from amino acids and peptides is reported. These derivatives incorporated the C-terminal of amino acids and peptides in the ring. In contrast to the mass spectra of amino acids and peptide esters reported previously, they always showed characteristic fragments, denoting the presence of the terminal triazine ring. By using this peak as a marker, it is easy to estimate the C-terminal of peptides. In dipeptides, the N-terminal and C-terminal are determined simultaneously.     

Ru3(CO)12-catalyzed silylation of benzylic C-H bonds in arylpyridines and arylpyrazoles with hydrosilanes via C-H bond cleavage

Ruthenium-catalyzed silylation of sp3 C-H bonds at a benzylic position with hydrosilanes gave benzylsilanes. For this silylation reaction, Ru3(CO)12 complex showed high catalytic activity. This silylation proceeded at the methyl C-H bond selectively. For this silylation reaction, pyridyl and pyrazolyl groups, and the imino group in hydrazones, can function as a directing group. Several hydrosilanes involving triethyl-, dimethylphenyl-, tert-butyldimethyl-, and triphenylsilanes can be used as a silylating reagent. Coordination of an sp2 nitrogen atom to the ruthenium complex is important for achieving this silylation reaction.     

Conformation-dependent change in antitumor activity of linear and branched (1----3)-beta-D-glucans on the basis of conformational elucidation by carbon-13 nuclear magnetic resonance spectroscopy.

The antitumor activity of (1----3)-beta-D-glucans was tested in order to clarify its conformation-dependent response together with conformational elucidation by carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy. It was shown that the following three conformations, single chain, single helix and triple helix, are readily distinguished by the high-resolution solid-state 13C-NMR method. It turned out that preparations of linear (1----3)-beta-D-glucans of a triple helical conformation were ineffective in the inhibition of tumor growth. These linear (1----3)-beta-D-glucans were converted to an effective form in the inhibition of tumor growth when they were lyophilized from dimethyl sulfoxide (DMSO) solutions as a result of a conformational change from the triple helical to the single chain forms. They were not effective, however, when assayed in DMSO solution. In contrast, it was found that a branched (1----3)-beta-D-glucan is effective not only in either saline solutions of the triple helical sample or the lyophilized sample from DMSO, but also in DMSO solution. The aforementioned drastic change in antitumor activity was interpreted in terms of resulting conformational changes as analyzed by the 13C-NMR method.     

Selective Formation of Spinel Iron Oxide in Thin Films by Complexing Agent-Assisted Sol-Gel Processing

The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α-Fe₂O₃ with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one mole of iron nitrate and the calcination temperatures were below 400°C, ψ-Fe₂O₃ with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α-Fe₂O₃ appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in thin films. Thus, a transparent magnetic film composed of γ-Fe₂O₃ could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz and calcining the gel film at 350°C.     

Artificial model for cystathionine β-synthase: efficient β-replacement reaction with thiols employing a novel pyridoxal model compound having an imidazole function

As a second-generation pyridoxal model compound for cystathionine β-synthase, we designed a novel model compound having an ionophore function and an imidazole function, application of which to the β-replacement reaction with various thiols smoothly took place to give S-substituted cysteines. Peptides having a serine-O-carbonate residue at the N-terminal position were also converted to the corresponding peptides having an S-substituted cysteine residue under the catalytic conditions of the novel pyridoxal model compound.     

Supramolecular Templating of Mesopores in Phase-Separating Silica Sol-Gels Incorporated with Cationic Surfactant

Silica gels with hierarchical macropores and mesopores have been prepared by inducing phase separation in the alkoxide-based sol-gel system with an addition of alkyltrimethylammonium salt. Narrowly distributed mesopores were observed in the heat-treated gel samples possibly as a result of supramolecular templating of silica oligomers in the reacting solution. The ionic attractive interaction and hydrophobicity of the attached alkyl group cooperatively determined the phase separation tendency. No indication of long-range order of the mesopores was obtained.     

A practical procedure for the synthesis of esonarimod, (R,S)-2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid,an antirheumatic agent (part 1)

An efficient and practical procedure for the synthesis of esonarimod, (R,S)-2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (1), a new antirheumatic drug, has been developed. The intermediate, 2-methylene-4-(4-methylphenyl)-4-oxobutanoic acid (2), was prepared by Friedel-Crafts acylation of toluene with itaconic anhydride (3) in the presence of aluminum trichloride and nitrobenzene in 63% yield without silica gel column purification. Compound 1 was prepared by Michael addition of 2 with thioacetic acid (4) in 74% yield. Overall, 1 was obtained in 47% yield from 3. The structures and synthetic mechanisms of by-products (five compounds) of 2 were also clarified.     

Site-directed 13C solid-state NMR studies on membrane proteins: strategy and goals toward revealing conformation and dynamics as illustrated for bacteriorhodopsin labeled with [1-13C]amino acid residues

We have so far demonstrated that well-resolved and site-specifically assigned (13)C peaks as recorded by site-directed NMR study on (13)C-labeled membrane proteins can serve as a convenient probe to reveal their local conformation and dynamics. We attempted here to clarify the extent to which (13)C NMR spectra of (13)C-labeled fully hydrated bacteriorhodopsin (bR) as a typical membrane protein are visible or well resolved in the presence of inherent fluctuation motions with frequency of 10(2)-10(8) Hz, especially at the membrane surfaces. Accordingly, we estimated the relative proportion of (13)C NMR signals from the surface areas with and without peak suppression by the accelerated transverse relaxation effect by surface-bound Mn(2+) ions, which could be effective for residues within 8.7 angstroms of the membrane surface. It turned out that the experimental findings are consistent with the predicted amount of amino acid residues under consideration located within 8.7 angstroms of the surface for [1-(13)C]Val- and Ile-labeled bR and also [3-(13)C]Ala-bR. In contrast, (13)C NMR peaks from such surfaces area are almost completely or partially suppressed for [1-(13)C]Gly-, Ala-, Leu-, Phe- and Trp-labeled bR, as a result of plausible interference of the fluctuation frequency with frequency of magic angle spinning (10(4) Hz). We further assigned several (13)C NMR signals of [1-(13)C] Val-, Trp- and Ile-labeled bR on the basis of a variety of site-directed mutants with reference to those of the wild type. Further, we recorded the (13)C NMR of bR in lipid bilayers to search for the optimal conditions to be able to obtain signals with the highest peak intensities and spectral resolution. Backbone dynamics turn out to be essential for recording (13)C NMR spectra so as to escape from motional frequencies of the order of 10(4)-10(5) Hz, either in the direction of accelerated fluctuation or slowed motions in the direction of forming the 2D array.     

A concept for controlling singlet oxygen (1 Delta g) yields using nitroxide radicals: phthalocyaninatosilicon covalently linked to nitroxide radicals

In this study, we have investigated the singlet oxygen ((1)Delta(g)) generation mechanism using phthalocyaninatosilicon (SiPc) covalently linked to nitroxide radicals (NRs), and we succeeded in increasing the singlet oxygen quantum yield (Phi(Delta)) by linking the NRs. This originates from both an increase in the triplet quantum yield and excited-state lifetimes long enough to utilize photochemical reactions. Because the electron exchange interactions with paramagnetic species were known to result only in very fast excited-state relaxation, leading to a decrease in photochemical reaction yields, this increase in Phi(Delta) is an unusual and precious example for increasing photochemical reaction yields by electron exchange interactions with paramagnetic species. In addition, our experiments and theoretical analyses show that the spin-selective energy transfer rate constant is not influenced by linking the NRs and can be evaluated by the product of spin-statistical factors and matrix elements between the initial and final states.     

Preparation of monodisperse SiO2 nanoparticles by membrane emulsification using ideally ordered anodic porous alumina

Monodisperse SiO2 particles of nanometer dimensions were fabricated by membrane emulsification using ideally ordered anodic porous alumina. For the preparation of monodisperse emulsion droplets, the dispersed phase was pressed through a porous alumina membrane into the continuous phase. After solidification treatment of the emulsion droplets, prepared spherical SiO2 nanoparticles with uniform sizes were obtained. From scanning electron microscope observation of the obtained particles, it was confirmed that the size distribution of SiO2 nanoparticles is relatively narrow.