Precise determination of dissolved silica in seawater by ion-exclusion chromatography isotope dilution inductively coupled plasma mass spectrometry

Ion exclusion chromatograph (IEC) isotope dilution (ID) inductively coupled plasma mass spectrometry (ICP–MS) (IEC–ID–ICP–MS) was developed for measurement of dissolved silica in seawater, which was applied to production of certified reference materials (CRMs) of three concentration levels of nutrients (high, medium and low levels). IEC–ICP–MS has been employed to separate dissolved silica from seawater matrix. In the present study, in order to solve substantial problems due to spectral interference in ICP–MS and to improve the accuracy of IEC–ICP–MS beyond standard addition or conventional calibration methods, ID method was coupled with ICP-sector field mass spectrometry (operated under medium resolution,i.e., m/Δm = 4000). In addition, effects of various operating parameters in ICP–MS on a silicon background level were also investigated to obtain lower background equivalent concentration (BEC). As a result, 3 ng g⁻¹ of the BEC and 0.5 % of relative standard uncertainties were achieved in the analyses of dissolved silica in seawater samples at concentration levels from 4.0 mg kg ^-1 to 0.8 mg kg⁻¹ as silicon. The developed method was successfully validated by analyses of an artificial seawater containing a known amount of silicate and the seawater certified reference material MOOS-2 produced by the National Research Council Canada.     

Catalytic asymmetric synthesis of stable oxetenes via Lewis acid-promoted [2+2] cycloaddition

A highly enantioselective and atom-economical [2 + 2] cycloaddition of various alkynes with trifluoropyruvate using a dicationic (S)-BINAP-Pd catalyst has been established. This is the first enantioselective synthesis of stable oxetene derivatives, whose structure has been clarified by X-ray analysis. This catalytic process offers a practical synthetic method for oxetene derivatives (catalyst loading: up to 0.1 mol %), which can serve as novel chiral building blocks for pharmaceuticals and agrochemicals and can also be transformed into a variety of enantiomerically enriched CF(3)-substituted compounds with high stereoselectivity.     

Transmembrane nanopores from porphyrin supramolecules

A porphyrin-based nanopore was constructed through a bilayer lipid membrane (BLM). The macrocyclic porphyrin (the inner diameter = ca. 2.1 nm) having six carboxylic acid groups directed up and down was synthesized by self-assembly of three trisporphyrins, metathesis linking, and subsequent hydrolysis. The porphyrin was incorporated into soybean lecithin based BLM, and the ion currents through the nanopore were observed under 500 mM KCl, LiCl, CaCl2, and tetraalkylammonium chloride solutions, indicating formation of a large pore through BLM. Blocking of the ion current was achieved by addition of the polycationic fourth-generation PAMAM dendrimer.     

Two new sesquiterpenoids and two new prenylated phenylpropanoids from Illicium fargesii, and neuroprotective activity of macranthol

Two new seco-prezizaane-type sesquiterpenoids 1, 2 and two new prenylated phenylpropanoids 4, 5 were isolated along with 15 known compounds from Illicium fargesii. The structures of 1, 2 were elucidated as 10-O-(E)- and 10-O-(Z)-cinnamoyl-2-oxo-6-deoxyneoanisatin by analysis of spectroscopic data and by comparison of their NMR data with those of previously reported 2-oxo-6-deoxyneoanisatin (3), respectively, whereas the structures of 4, 5 were identified as 4-allyl-2-(3-methylbut-2-en-1-yl)phenol and 4-allyl-2-(2-methylbut-3-en-2-yl)phenol, respectively, on the basis of spectroscopic data. Among the isolated compounds, macranthol (7) was found to have neuroprotective activity at 5--10 microM in rat cortical neurons cultured in DMEM/N2 medium.     

Eight new clerodane diterpenoids from the bark of Ptychopetalum olacoides

Eight new clerodane type diterpenoids, named 7-oxo-kolavelool (1), 7alpha-hydroxykolavelool (2), 6alpha,7alpha-dihydroxykolavenol (3), 12-oxo-hardwickiic acid (4), ptycholide I (5), ptycholide II (6), ptycholide III (7), and ptycholide IV (8) were isolated from the MeOH extract of the bark of a Brazilian medicinal plant, Ptychopetalum olacoides. The structures of 1-8 were elucidated by analyzing spectroscopic data and by comparing their NMR data with those of the previously reported compounds kolavelool (la), kolavenol (3a), hardwickiic acid (4a), and ptychonolide (5a). Compounds 5 and 6 existed as a 1:1 mixture of inseparable epimers at C-15.     

Fullerene- and pyromellitdiimide-appended tripodal ligands embedded in light-harvesting porphyrin macrorings

Three new tripyridyl tripodal ligands appended with either fullerene or pyromellitdiimide moieties, named C(60)-s-Tripod, C(60)-l-Tripod, and PI-Tripod, were synthesized and introduced into a porphyrin macroring N-(1-Zn)(3) (where 1-Zn = trisporphyrinatozinc(II)). From UV-vis absorption and fluorescence titration data, the binding constants of C(60)-s-Tripod, C(60)-l-Tripod, and PI-Tripod with N-(1-Zn)(3) in benzonitrile were estimated to be 3 × 10(8), 1 × 10(7), and 2 × 10(7) M(-1), respectively. These large binding constants denote multiple interactions of the ligands to N-(1-Zn)(3). The binding constants of the longer ligand (C(60)-l-Tripod) and the pyromellitdiimide ligand (PI-Tripod) are almost the same as those without the fullerene or pyromellitdiimide groups, indicating that they interact via three pyridyl groups to the porphyrinatozinc(II) coordination. In contrast, the larger binding constants and the almost complete fluorescence quenching in the case of the shorter ligand (C(60)-s-Tripod) indicate that the interaction with N-(1-Zn)(3) is via two pyridyl groups to the porphyrinatozinc(II) coordination and a π-π interaction of the fullerene to the porphyrin(s). The fluorescence of N-(1-Zn)(3) was quenched by up to 80% by the interaction of C(60)-l-Tripod. The nanosecond transient absorption spectra showed only the excited triplet peak of the fullerene on selective excitation of the macrocyclic porphyrins, indicating that energy transfer from the excited N-(1-Zn)(3) group to the fullerenyl moiety occurs in the C(60)-l-Tripod/N-(1-Zn)(3) composite. In the case of PI-Tripod, the fluorescence of N-(1-Zn)(3) was quenched by 45%. It seems that the fluorescence quenching probably originates from electron transfer from the excited N-(1-Zn)(3) group to the pyromellitdiimide moiety.     

Synthesis of biantennary complex-type nonasaccharyl asn building blocks for solid-phase glycopeptide synthesis

The biantennary complex-type N-glycans bearing LacNAc and LacdiNAc as the nonreducing end motif were synthesized in a protected form suitable to use in the Fmoc solid-phase peptide synthesis studies. Two approaches for the nonasaccharide synthesis were examined by taking advantage of the highly β-selective glycosylation with GlcNTCA (N-phenyl)trifluoroacetimidate. An earlier approach, which involved the reaction of the trisaccharide donor (Gal-GlcNTCA-Man) and trisaccharide acceptor (Man-GlcNPhth(2)-N(3)), produced a mixture of nonasaccharide isomers. On the other hand, mannosylation of the trisaccharide acceptor (Man-GlcNPhth(2)-N(3)) stereoselectively afforded the known pentasaccharide (Man(3)-GlcNPhth(2)-N(3)), which was reacted with the disaccharyl glycosyl donor (Gal-GlcNTCA or GalNTCA-GlcNTCA) to produce the desired nonasaccharide as a single stereoisomer. Selective dephthaloylation followed by N-acetylation furnished the GlcNAc(2) functionality. The resulting nonasaccharyl azides were condensed with Fmoc-Asp(OPfp)-OBu(t) or Fmoc-Asp(OPfp)-OPac in the presence of Ph(CH(3))(2)P and HOOBt. Finally, the Zn reduction and cleavage of the tert-butyl ester or Zn reduction alone produced the targeted nonasaccharyl Asn building blocks.     

Search for anomalous top–gluon couplings at LHC revisited

Through top-quark pair productions at LHC, we study possible effects of nonstandard top–gluon couplings yielded by SU(3)×SU(2)×U(1) invariant dimension-6 effective operators. We calculate the total cross section and also some distributions for $pp\to t\bar{t}X$ as functions of two anomalous-coupling parameters, i.e., the chromoelectric and chromomagnetic moments of the top, which are constrained by the total cross section $\sigma(p\bar{p}\to t\bar{t}X)$ measured at Tevatron. We find that LHC might give us some chances to observe sizable effects induced by those new couplings.     

Solid-phase synthesis of benzazoles,quinazolines, and quinazolinones using an alkoxyamine linker

An alkoxyamine linker was applied for the solid-phase synthesis of benzazoles, quinazolines, and quinazolinones. Aromatic aldehydes were anchored by aldoxime linkage. After some reactions on a solid support, the products were cleaved with paraformaldehyde under the acidic conditions to afford the corresponding aldehydes, which were subsequently subjected to oxidative coupling with 2-substituted anilines under air atmosphere to give the desired compounds.