Tetrameric,trititanium(IV)-substituted polyoxotungstates with an alpha-Dawson substructure as soluble metal-oxide analogues: molecular structure of the giant "tetrapod" [(alpha-1,2,3-P2W15Ti3O62)4[mu3-Ti(OH)3]4Cl]45-

The preparation and structural characterization of the novel polyoxoanion [(alpha-1,2,3-P(2)W(15)Ti(3)O(62))(4)[mu(3)-Ti(OH)(3)](4)Cl](45-) (1 a; abbreviated to [TiO(6)](16); FW approximately 16 000) which consists of four tri-Ti(IV)-1,2,3-substituted alpha-Dawson substructures, four Ti(OH)(3) bridging groups, and one encapsulated Cl(-) ion, are described. A water-soluble, all-inorganic composition compound of the tetrameric Ti-O-Ti-bridged anhydride form, Na(x)H(45-x)[1 a].y H(2)O (1; x=16-19, y=60-70), which was afforded by the reaction of the tri-lacunary Dawson polyoxotungstate Na(12)[B-alpha-P(2)W(15)O(56)].19 H(2)O with an excess of TiCl(4) in aqueous solution, was obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analysis revealed that 1 a was an inorganic, giant "tetrapod"-shaped molecule (inscribed to a sphere with a diameter of approximately 32 A) with approximately T(d) symmetry, in which the 16 edge- and/or corner-shared TiO(6) octahedra were contained. This number of TiO(6) octahedra was larger than that found in other titanium(IV)-substituted polyoxotungstates. Complex 1 was characterized by complete elemental analysis, TG/DTA, FTIR, UV/Vis absorption, and solution ((31)P and (183)W) NMR spectroscopy. The longest wavelength band in the UV/Vis absorption spectra of 1 in water was attributed to the O-->Ti(IV) ligand-to-metal charge-transfer (LMCT) transition: the wavelength of the LMCT band increased linearly as the number of TiO(6) octahedra contained in the Keggin and Dawson polyoxoanions increased. The Ti(n) chromophores formed in the Keggin and Dawson polyoxotungstates are water-soluble analogues of solid TiO(2) or SrTiO(3) as light-semiconductors and photocatalysts.     

Determination of paraquat and diquat in human body fluids by high-performance liquid chromatography/tandem mass spectrometry

Paraquat (PQ) and diquat (DQ) in human whole blood and urine were analyzed by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) with positive ion electrospray ionization (ESI). The compounds were extracted with Sep-Pak C18 cartridges from whole blood and urine samples containing ethyl paraquat as an internal standard. The separation of PQ and DQ was carried out using ion-pair chromatography with heptafluorobutyric acid in 20 mM ammonium acetate and acetonitrile gradient elution for successful coupling with MS. Both compounds formed base peaks due to [M-H]+ ions by HPLC/ESI-MS and the product ions produced from each [M-H]+ ion by HPLC/MS/MS. Selective reaction monitoring (SRM) showed much higher sensitivity for both body fluids. Therefore, a detailed procedure for the detection of compounds by SRM with HPLC/MS/MS was established and carefully validated. The recoveries of PQ and DQ were 80.8-95.4% for whole blood and 84.2-96.7% for urine. The calibration curves for PQ and DQ showed excellent linearity in the range of 25-400 ng ml(-1) of whole blood and urine. The detection limits were 10 ng ml(-1) for PQ and 5 ng ml(-1) for DQ in both body fluids. The intra- and inter-day precision for both compounds in whole blood and urine samples were not greater than 13.0%. The data obtained from the determination of PQ and DQ in rat blood after oral administration of the compounds are also presented.     

A catalytic asymmetric strecker-type reaction promoted by Lewis acid-Lewis base bifunctional catalyst

A general asymmetric Strecker-type reaction is reported, catalyzed by the Lewis acid-Lewis base bifunctional catalyst 1. The reaction of trimethylsilyl cyanide (TMSCN) with various fluorenyl imines, including n-aldimines and alpha,beta-unsaturated imines, proceeds with good to excellent enantioselectivities in the presence of a catalytic amount of phenol as additive (20 mol%) (catalytic system 1). The products were successfully converted to the corresponding amino acid derivatives in high yields without loss of enantiomeric purity. Furthermore, hydrogenation or dihydroxylation of the products from alpha,beta-unsaturated imines afforded saturated or functionalized aminonitriles also without loss of enantiomeric purity. The absolute configuration of the products and a control experiment using catalyst 2 supported the proposed dual activation of the imine and TMSCN by the Lewis acid (Al) and the Lewis base moiety (phosphine oxide) of 1. From the mechanistic studies including kinetic and NMR experiments of the catalytic species, the role of PhOH seems to be a proton source to protonate the anionic nitrogen of the intermediate. Specifically, we have found that TMSCN is more reactive than HCN in this catalytic system, probably due to the activation ability of the phosphine oxide moiety of 1 toward TMSCN. This fact prompted us to develop the novel catalytic system 2, consisting of 1 (9 mol%), TMSCN (20 mol%) and HCN (1.2 mol eq). This new system afforded comparable results with obtained by system 1 (1 (9 mol%)-TMSCN (2 mol eq)-PhOH (20 mol%)).     

Micro-flow injection system for the urinary protein assay

A urinary protein assay has been investigated, employing a micro-flow injection analysis (μFIA) combined with an adsorptive separation of protein from analyte. The adsorptive separation part of protein in the artificial urine with ceramic hydroxyapatite is integrated on the μFIA chip, since the interference of other components coexisting in urine occurs in the conventional FIA system. The typical FI peak can be obtained following the adsorption–elution process of the protein prior to the detection, and the protein concentration in artificial urine can be quantitatively determined.     

Effect of type of peroxide on cross-linking of poly(l-lactide)

Poly(l-lactide) (PLLA) was cross-linked with various types of peroxides under constant mole ratios of peroxide-derived radicals to PLLA during reactive extrusion. Peroxides were classified into three groups according to their decomposition rates (Group I: fast, Group II: moderate and Group III: slow) and comparisons were performed within each group. Cross-linking behavior was readily understood in terms of free radical efficiency and hydrogen abstraction ability of radicals. In the case of Groups II and III, the weight-average molecular weight (M_w) of cross-linked PLLA increased with overall hydrogen abstraction ability, because slow decomposition caused uniform cross-linking in molten PLLA. In Group I, M_w and gel fraction were higher than other groups despite Group I's lower hydrogen abstraction ability, leading to the conclusion that peroxide decomposition localized in solid PLLA caused partial cross-linking because of rapid decomposition. Furthermore, the efficiency of peroxide-induced cross-linking was investigated using the Charlesby-Pinner equation.     

Nanomaterial-based electrochemical biosensors for medical applications

With recent advances in nanotechnology, great progress has been made in biosensors based on nanomaterials, but there are still numerous challenges to overcome. We describe nanomaterial-based biosensors for researchers new to the field, paying particular attention to metal nanoparticles and carbon nanotube (CNT)-based label-free approaches. Label-free monitoring of biorecognition events provides a promising platform, which is simple, cost-effective, and requires no external modification to biomolecules. Using examples from recent reports, we illustrate the diversity of biological recognition events and the range of experimental techniques employed for metal-nanoparticle-based and label-free characterization.     

Metal atoms collinear with the spiro carbon of 6,6-open adducts, M2@C80(Ad) (M = La and Ce, Ad = adamantylidene)

The photochemical reaction of M2@C80 (M = La and Ce) with 2-adamantane-2,3'-[3H]-diazirine (1) affords the corresponding adducts by carbene addition. The adducts were characterized by spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for the adduct La2@C80(Ad) (2, Ad = adamantylidene) reveal that the two La atoms are collinear with the spiro carbon of the 6,6-open adduct. It is noteworthy that the La-La distance is highly elongated by the addition of carbene. Paramagnetic 13C NMR spectral analysis of the adduct Ce2@C80(Ad) (3) indicates that the two Ce atoms are also collinear with the spiro carbon at room temperature in solution. The unique metal positions were confirmed by density functional calculations.     

Prenylated Phloroglucinol Derivatives from Hypericum perforatum var. angustifolium

Two new prenylated phloroglucinol derivatives and 15 known compounds were isolated from the aerial parts of Hypericum perforatum var. angustifolium. Their structures were determined on the basis of spectroscopic evidence.     

Expanding functionality of RNA: synthesis and properties of RNA containing imidazole modified tandem G-U wobble base pairs

Imidazole modification at C-5 of uridine that is part of tandem G-U wobble base pairs causes slight reduction of thermal stability (DeltaDeltaG(0)(310) < 0.4 kcal mol(-1)) and relatively small change in hydration of short RNA helices.