Potentiometric flow injection determination of manganese(II) by using a hexacyanoferrate(III)-hexacyanoferrate(II) potential buffer

A highly sensitive potentiometric flow injection analysis method for the determination of manganese(II), utilizing a redox reaction with hexacyanoferrate(III) in near neutral media containing ammonium citrate is described. The analytical method is based on the detection of the change in potential of a flow-through type redox electrode detector, resulting from the composition change of an [Fe(CN)₆]³⁻-[Fe(CN)₆]⁴⁻ potential buffer solution. A linear relationship between the potential change (peak height) and the concentration of manganese(II) was found. Manganese(II) in a wide concentration range from 10⁻⁴ to 10⁻⁷ M could be determined by appropriately altering the concentration of the potential buffer from 10⁻³ to 10⁻⁵ M. The lower detection limit of manganese(II) was determined to be 1×10⁻⁷ M. The sampling rate and relative standard deviation were 20 h⁻¹ and 1.9% (n=8) for 6×10⁻⁶ M manganese(II), respectively. The proposed method was successfully applied to the determination of manganese(II) in actual soil samples obtained from tea fields. Analytical results obtained by the proposed method were in good agreement with those obtained by an atomic absorption spectrophotometric method.     

Silychristin derivatives conjugated with coniferylalcohols from silymarin and their pancreatic α-amylase inhibitory activity

Abstract

Silymarin is a mixture of flavonolignans extracted from the fruit of Silybum marianum (milk thistle). The latter is used as a medicinal plant to treat liver and gallbladder disorders. Recently, silymarin has been investigated for its effects against diabetes mellitus, and shown to reduce serum levels of glucose in model animals and in clinical trials. This effect can be explained mainly by the protective effect of silymarin against pancreatic beta-cells, but the involvement of other mechanisms is possible. We demonstrated the α-amylase inhibitory activity of silymarin and investigated the components responsible for this effect. Two major flavonolignans, silibinin and silychristin, did not show inhibition against α-amylase, but two novel silychristin derivatives conjugated with dehydrodiconiferyl alcohol were isolated as the mildly inhibiting components of silymarin. Further analyses indicated the presence of various silychristin derivatives in silymarin that may act synergistically to show α-amylase inhibitory activity.

     

Optimization of tether length in nonglycosidically linked bivalent ligands that target sites 2 and 1 of a Shiga-like toxin

A series of bivalent ligands for a Shiga-like toxin have been synthesized, their experimentally determined inhibitory activities were compared with a simplified thermodynamic model, and computer simulations were used to predict the optimal tether length in bivalent ligands. The design of the inhibitors exploits the proximity of the C-2' hydroxyl groups of two P(k)-trisaccharides when bound to two different, neighboring carbohydrate recognizing binding sites located on the surface of Shiga-like toxin. NMR studies of the complex between the toxin and bivalent ligands show that site 2 and site 1 of a single B subunit are simultaneously occupied by a tethered P(k)-trisaccharide dimer. A simplified thermodynamic treatment provides the intrinsic affinities and binding energies for the intermolecular and intramolecular association events and permits the deconvolution of the contributions to the relative binding energies for the set of bivalent ligands. Conformational analysis based on MD simulations for bivalent galabioside dimers containing different tethers demonstrated that the calculated local concentrations of the pendant ligand at the second binding site correlate with the experimentally determined relative affinity values of the respective bivalent ligands, thereby providing a predictive method to optimize tether length.     

Measurement of neutron emission from a SiO2−D2 system

As a new fact, the neutron emission from the d-d nuclear fusion reaction in a SiO₂–D₂ system has been confirmed as well as that in the Ti–D₂ system. By using a liquid scintillation detector, the neutron emissions from 8 sample materials consisted of SiO₂, in which a small amount of deuterium was adsorbed chemically on the surface layer, were measured in the range of temperature between liquid nitrogen temperature and 400 °C. As a result, it was demonstrated that the neutron-emission reactions take place predominantly on the surface layer of sample material.     

Line tension and wetting behavior of an air/hexadecane/aqueous surfactant system

The line tension of an air/hexadecane/aqueous solution of an dodecyltrimethylammonium bromide (DTAB) system was measured as a function of the molality of DTAB at 298.15 K by means of a newly constructed apparatus. It was estimated to be on the order of 10(-10)-10(-12) N, which is comparable to the theoretical estimation. Furthermore, its sign was reversed from positive to negative in the vicinity of the wetting transition concentration. The reversal of the sign was examined on the basis of our experimental findings on the wetting transition and the theory of Indekeu.     

Design and synthesis of a trans-fused polycyclic ether skeleton as an α-helix mimetic scaffold

Inspired by the common skeletal feature of potent marine toxins, a ladder-like polycyclic ether scaffold was designed as the basis for the synthesis of structurally defined α-helix mimics. A synthetic route to trans-fused 6/6/6/6/6 pentacyclic ether skeletons is presented, involving the iterative assembly of tetrahydropyran rings via the SmI₂-mediated coupling reaction of α-sulfonyl ketones with aldehydes.     

Syntheses and reactivity of novel unsaturated cyclic compounds containing phosphorus atoms

Kinetic stabilization of compounds containing heavy main-group elements through the use of bulky substituents is of current interest. The widely used 2,4,6-tri-t-butylphenyl group (Mes*) is recognized as a powerful bulky protecting group and has enabled us to successfully prepare various types of phosphorus compounds with unusual structures. When a phosphaalkyne carrying Mes* was treated with tBuLi and then quenched with MeOH, a 1,3-diphosphacyclobutene was obtained, whereas, when MeI was used as a quencher, a 1,3-diphosphacyclobutane-2,4-diyl was formed almost quantitatively as a stable biradical compound. The reaction mechanism for the formation of both compounds can be explained by a phosphide intermediate, which can be formed via dimerization of the phosphaalkyne promoted by tBuLi. Some other diphosphacyclobutane-2,4-diyls with various substituents were prepared in a similar fashion and showed interesting reactivities including ring expansion, oxidation, isomerization and so on.     

Tough epoxy resins cured with aminimides

Aminimide compounds ( 1–4 ) thermally generating isocyanates and tertiary amines were found to be excellent curing agents for epoxy resin. Tensile behavior, glass transition temperature, and degree of curing for the combination of EPIKOTE 828 prepolymer with a series of curing agents ( 1–4 ) are reported. The resins exhibit a large elongation at breakage and a high fracture energy per unit volume. The epoxy resins (EP-AI) cured with 3 or 4 containing no hydroxyl group showed larger ultimate elongations (up to 15%) and higher fracture energies (ca. 8 J/cm³) than the resins (EP–AI_OH) cured with 1 or 2 . The curing reaction depends on the structure of aminimide (presence of hydroxyl group and generation of mono- or bisisocyanates). The origin of toughness and dependence of physical properties on the curing condition and the structure of aminimides were discussed. It was concluded that relatively slow curing at elevated temperature controlled by thermal decomposition of aminimides was a reason for the toughness.     

Synthesis in the diazasteroid group. XII Syntheses of the 10,17-diazasteroid and 10-aza-17-thiasteroid systems

Upon desulfurization with Raney Ni, the condensed heterocycles 2a,b prepared by cyclization from β-ketosulfoxides 1a,b gave β-ketones 3a,b , which were condensed with 2-carbethoxymethyl-piperidine 4 to afford the 10,17-diazasteroid 6 and the 10-aza-17-thiasteroid 7 , respectively.     

Spectroscopic studies of poly(vinyl chloride) and its deuterated derivatives

Poly(vinyl chloride) (PVC) and all its deuterated derivatives were prepared by variation of the polymerization method and polymerization temperature to study the structure of PVC and the mechanism of addition polymerization by infrared spectroscopy and high resolution NMR spectroscopy. The CH and CH₂ stretching modes of PVC were assigned completely from the infrared spectra of PVC-αd₁, PVC-β,βd₂ and PVC-d₃. The frequencies of the CCI stretching modes of the polymers depended not only on the substituents in the trans position to the Cl atom across both adjacent C? C bonds, but also on the atom attached to the C atom of the C? Cl bond. The frequency shifts were used to assign the CCl stretching modes of PVC-βd₁ and PVC-α,βd₂ and to study the opening of the double bond of VC in the addition polymerization. The differences of the chemical shifts of the α and β protons of PVC due to the tacticity were determined experimentally by PVC-β,βd₂ and PVC-αd₁ without using the spin-decoupling technique. With PVC-α,βd₂, the conception of the tetrad was required to interpret the four observed peaks whose intensities changed with the polymerization temperature and the trans–cis composition of the monomer used.