New gem-dicyanocyclobutane-containing hydroxyesters

Six new gem-dicyanocyclobutanes containing carbomethoxy and hydroxyl/acetoxy functions were synthesized by cycloaddition of the appropriate vinyl ethers or alkoxystyrenes to methyl β,β-dicyanoacrylate. They proved to be too thermally labile to allow polycondensation to potentially piezoelectric linear polyesters.     

Stereoselective synthesis of procyanidin B3-3-O-gallate and 3,3″-di-O-gallate, and their abilities as antioxidant and DNA polymerase inhibitor

A simple method for the synthesis of procyanidin B3 substituted with a galloyl group at the 3 and 3″ position is described. Condensation of a benzylated catechin-3-O-gallate electrophile with a nucleophile, catechin and catechin-3-O-gallate, proceeded smoothly and stereoselectively to afford the corresponding dimer gallates, procyanidin B3-3-O-gallate and procyanidin B3-3,3″-di-O-gallate, in good yields. Further, their antioxidant activities on UV-induced lipid peroxide formation, DPPH radical scavenging activity and inhibitory activity of DNA polymerase were also investigated. Among three procyanidin B3 congeners (procyanidin B3, 3-O-gallate and 3,3″-di-O-gallate), the 3,3″-di-O-gallate derivative showed the strongest antioxidant and radical scavenging activity. Interestingly, the 3-O-gallate derivative was the strongest inhibitor of mammalian DNA polymerase with IC₅₀ value of 0.26 μM, although it showed the weakest antioxidant and radical scavenging activity. It became apparent that the presence of a galloyl group at the C-3 position in the proanthocyanidin oligomer was very important for biological activity, however, the antioxidant activity of these compounds was not parallel to the DNA polymerase inhibitory activity.     

Synthesis of Ultrafine SiC Powders from Carbon-Silica Hybridized Precursors with Carbothermic Reduction

Inorganic-organic hybrid gels were prepared by simultaneous condensation of the liquid mixture of ethyl silicate, ethyl borate and water soluble phenol resin with low molecular weight. The liquid mixtures were changed into lightly colored transparent gels after a catalyst addition and stirring. The obtained gels were crushed, dried and fired in controlled conditions to yield the inorganic precursors. Since the tailored inorganic precursors mainly consisted of SiO2 and carbon, silicon carbide was formed with the heat treatments in an Ar atmosphere beyond 1773 K with carbothermic reduction. The properties and morphology of the formed silicon carbide powders in terms of the starting precursor compositions and the conditions of the carbothermic reduction were investigated with SEM, XRD and TG-DTA analysis.     

Effect of pressure on the thermotropic phase behavior of surfactant assemblies in water

The temperature (T)—pressure (P) phase diagrams of aqueous solutions of a homologous series of cationic surfactants, tetradecyl- (C14TAB), hexadecyl- (C16TAB), and octadecyltrimethylammonium bromide (C18TAB), have been determined by observing the sudden change of the transmittance accompanying the phase transition under high pressure up to 160 MPa. Regarding three kinds of phase transitions which have been previously assigned by the differential scanning calorimetry (DSC) (S. Kaneshina and M. Yamanaka, J. Colloid Interface Sci.131, 493, 1989), all the transition temperatures were linearly elevated by applying pressure. The volume changes associated with the transitions were estimated from the Clapeyron—Clausius equation by using the values of the T—P slopes on the phase diagrams and of the transition entropies taken from the DSC study. A chemical potential vs pressure profile, of which slope reflects the partial molar volume, among the states of surfactant assemblies, i.e., micelle, gel, and coagel, was drawn schematically on the basis of the transition volumes. The phase boundary between the coagel phase and the micellar solution should be the critical solution line of the surfactant, representing the pressure dependence on the Krafft temperature. In the C18TAB-water system, the phase boundary line between the metastable gel and the supercooled micelle had a break point at 45 MPa, suggesting the existence of a new pressure-induced mesophase above 45 MPa. The metastable gel phase of C14TAB disappeared in the pressure range up to 160 MPa.     

Preparation and properties of a mitomycin C-albumin conjugate

Mitomycin C, an anti-neoplastic agent, was covalently attached to bovine serum albumin through various kinds of spacers such as glutaryl, succinyl, trans-aconityl, methylsuccinyl and the trimellityl group. The prior acylation of albumin not only prevented protein polymerization in the presence of carbodiimide, but also increased the extent of conjugation of the drug. The conjugate of mitomycin C-glutarylated albumin showed the best properties among the conjugates prepared in meeting the requirements for a high yield of nonpolymerized product with an adequately high mitomycin C content and stability as a macromolecular prodrug.     

Functionalization of chitosan with 3-nitro-4-amino benzoic acid moiety and its application to the collection/concentration of molybdenum in environmental water samples

A chitosan resin functionalized with 3-nitro-4-amino benzoic acid moiety (CCTS-NABA resin) was newly synthesized for the collection/concentration of trace molybdenum by using cross-linked chitosan (CCTS) as base material. The carboxyl group of the moiety was chemically attached to amino group of cross-linked chitosan through amide bond formation. The adsorption behavior of molybdenum as well as other 60 elements on the resin was examined by passing the sample solutions through a mini-column packed with the resin. After the elution of the elements collected on the resin with 1 M HNO₃, the eluates were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and atomic emission spectrometry (ICP-AES).

The CCTS-NABA resin can adsorb several metal ions, such as vanadium, gallium, arsenic, selenium, silver, bismuth, thorium, tungsten, tin, tellurium, copper, and molybdenum at appropriate pHs. Among these metal ions, only molybdenum could be adsorbed almost completely on the resin at acidic regions. An excellent selectivity toward molybdenum could be obtained at pH 3–4. The adsorption capacity of CCTS-NABA resin for Mo(VI) was 380 mg g⁻¹ resin. Through the column pretreatment, alkali and alkaline earth metals in river water and seawater samples were successfully removed.

The CCTS-NABA resin was applied to the adsorption/collection of molybdenum in river water and seawater samples. The concentrations of molybdenum in river water samples were found in the range of 0.84 and 0.95 ppb (ng g⁻¹), whereas molybdenum in seawater was about 9 ppb. The validation of the proposed method was carried out by determining molybdenum in the certified reference materials of SLRS-4, CASS-4, and NASS-5 after passing through the CCTS-NABA resin; the results showed good agreement with the certified values.     

o-Diketonedioxime compounds as analytical reagents for the spectrophotometric determination of nickel

Sixteen dioxime compounds, including six new compounds, were synthesized and their reactions with nickel, cobalt, iron(II, III) and copper ions were examined. The nickel chelates of the glyoxime derivatives show hardly any absorption in the visible region, and are therefore unsuitable as color reagents. The nickel chelates of the benzildioxime derivatives can be extracted into organic solvents and provide a selective color reaction, so that useful extraction-spectrophotometric methods are possible. The metal complexes of quinonedioximes are extracted into some organic solvents, and the complexes have relatively large molar absorptivities in the visible region, but the reagents are not selective. However, the molar absorptivity of the ternary complex, Ni²⁺-reagent-zephiramine, with 1,2-naphthoquinonedioxime-4-sulfonic acid was 2.03·10⁴ at 480 nm, and that of the nickel complex of 9,10-phenanthrenequinonedioxime was 2.49·10⁴at 456 nm. The compositions of the nickel-dioxime complexes were examined spectrophotometrically.     

On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry

On-line preconcentration system for the selective, sensitive and simultaneous determination of chromium species was investigated. Dual mini-columns containing chelating resin were utilized for the speciation and preconcentration of Cr(III) and Cr(VI) in water samples. In this system, Cr(III) was collected on first column packed with iminodiacetate resin. Cr(VI) in the effluent from the first column was reduced to Cr(III), which was collected on the second column packed with iminodiacetate resin. Hydroxyammonium chloride was examined as a potential reducing agent for Cr(VI) to Cr(III).The effects of pH, sample flow rate, column length, and interfering ions on the recoveries of Cr(III) were carefully studied. Five millilitres of a sample solution was introduced into the system. The collected species were then sequentially washed by 1 M ammonium acetate, eluted by 2 M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15 μg l⁻¹, respectively. The total analysis time was about 9.4 min.The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results.