Preparation and certification of tea leaves reference material

Summary Tea leaves reference material was prepared and certified for elemental composition. Japanese green tea leaves were ground, sieved to pass a 80-mesh screen, blended and bottled. The prepared material satisfied the homogeneity criteria for a reference material. Trace element analysis of the material was carried out by flame and graphite furnace atomic absorption and inductively coupled plasma atomic emission spectrometry.Certification of the material was performed using the data obtained by various analytical techniques and certified values are provided for Al, Ca, Cd, Cu, K, Mg, Mn, Na, Ni, Pb and Zn. The elemental composition of the tea leaves reference material is considered typical of Japanese green tea leaves.     

Alkylation of benzyl,cyclopropylmethyl and allyl acetates with trialkylaluminum. A stereochemical study

The title reaction is found synthetically useful and the stereochemical sudy has revealed that carbocationic intermediates are involved in the reaction of endo-2-acetoxy-norcarane, its epimer, and acetates of cis- and trans-carveol with trimethylaluminum.     

Hydride Reduction by a Sodium Hydride–Iodide Composite

Sodium hydride (NaH) is widely used as a Brønsted base in chemical synthesis and reacts with various Brønsted acids, whereas it rarely behaves as a reducing reagent through delivery of the hydride to polar π electrophiles. This study presents a series of reduction reactions of nitriles, amides, and imines as enabled by NaH in the presence of LiI or NaI. This remarkably simple protocol endows NaH with unprecedented and unique hydride‐donor chemical reactivity.     

Luminescent Europium(III) Coordination Zippers Linked with Thiophene‐Based Bridges

Novel Eu^III coordination polymers [Eu(hfa)₃(dpt)]_n (dpt: 2,5‐bis(diphenylphosphoryl)thiophene) and [Eu(hfa)₃(dpedot)]_n (dpedot: 2,5‐bis(diphenylphosphoryl)ethylenedioxythiophene) with hydrogen‐bonded zipper structures are reported. The coordination polymers are composed of Eu^III ions, hexafluoroacetylacetonato ligands, and thiophene‐based phosphine oxide bridges. The zig‐zag orientation of single polymer chains induced the formation of densely packed coordination structures with multiple intermolecular interactions, resulting in thermal stability above 300 °C. They exhibit a high intrinsic emission quantum yield (ca. 80 %) due to their asymmetrical and low‐vibrational coordination structures around Eu^III ions. Furthermore, the characteristic alternative orientation of substituents also contributes to the dramatically high ligand‐to‐metal energy transfer efficiencies of up to 80 % in the solid state.     

Characterization of cross-linking structure in terephthalate polyesters formed through material recycling process by pyrolysis-gas chromatography in the presence of organic alkali

Typical terephthalate polyesters such as poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were characterized by pyrolysis-gas chromatography (Py-GC) in the presence of tetramethylammonium hydroxide in terms of the cross-linking structure formed during their material recycling. In the pyrograms of PBT and PET thermally treated at 270 °C for 1 h, which were prepared as model polymers containing cross-linking structures, an additional peak was commonly observed as well as the main reactive pyrolysis products for the original polyesters such as dimethyl terephthalate. Based on the observed spectra obtained by Py-GC/mass spectrometry and Py-GC/Fourier transform infrared spectrometry measurements, this peak was assigned to the product reflecting a biphenyl-type cross-linking structure. Furthermore, in the pyrograms of kneaded PBT and PET samples also at 270 °C for a total of 1 h, which were prepared to simulate material recycling, the same peak for the cross-linking structure was also observed, although its intensity was slightly lower than that in the samples thermally treated in air. This fact verified that the biphenyl-type cross-linking structure would be considerably formed during the recycling of PBT and PET, which might in turn contribute to the deteriorated properties of the recycled materials from waste polyesters. Moreover, difference in the formation of the cross-linking between PBT and PET is discussed on the basis of the observed results.     

Microchip analysis of plant glucosinolates

We describe a new and selective analytical method for the separation and quantitation of plant glucosinolates. The new method, which utilizes microchip CE (micro-CE) with fluorescence detection, circumvents the multistep procedures characteristic of conventional methods. Glucosinolates form charge transfer complexes with the xanthene dyes phloxine-B and eosin-B. The glucosinolates-phloxine-B complex cannot be excited at 470 nm. Thus, the decrease in peak intensity of phloxine-B after complex formation is used to quantitatively measure total glucosinolates in Arabidopsis thaliana seeds. For qualitative analysis, complex formation with eosin-B is used. The sensitivity of eosin-B detection at excitation/emission 470 nm/540 nm was low. However, sensitivity increased following complex formation with sinigrin (> or =3 microg/mL). A batch-learning, self-organizing map was applied to visualize and organize analytical data into 2-D matrix with similar and related data clustered together or near each other. This organized matrix was used to optimize electrophoretic conditions for the analysis. This study suggests potential applications of micro-CE in plant metabolomics analyses without use of labeling fluorophores.     

Morphology and size-controlled synthesis of silver nanoparticles in aqueous surfactant polymer solutions

We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies. The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter were obtained when 1 wt% aqueous starch solution of AgNO₃ precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized by NaOH reduction of AgNO₃ in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time.     

Site-specific synthesis of oxo-bridged mixed-valence binuclear complexes on mesoporous silica

We report the site-specific synthesis of mixed valence TiIV-O-FeII complexes within the pores of ordered mesoporous silica (SBA-15). By using 6-di- tert-butylpyridine as the selective activator of tripodally linked TiIV-OH groups of Ti-grafted SBA-15, the FeCl2.4H2O complexes reacted selectively with the nucleophilic TiIV-O(-) groups. The formation of Si-O-FeII byproducts, due to the reaction with the abundant Si-OH groups, was successfully restricted and the selectivity for forming the TiIV-O-FeII complexes exceeded 80%. The metal-metal interaction of TiIV-O-FeII complexes was confirmed by the appearance of TiIV/FeII --> TiIII/Fe III metal-to-metal charge transfer band, and their coordination, valency, and spin state were characterized by diffuse transmission UV-vis, Fourier transform IR, and Fe K-edge X-ray absorption fine structure measurements. It was also confirmed that the present methods can be extended to other metal combinations of TiIV-O-NiII and TiIV-O-MnII. The electron transfer processes occurring under photoinduced metal-to-metal charge transfer of oxo-bridged mixed valence complexes on silica supports have recently been proven as a new class of visible-light-sensitive redox centers. Thus, the present synthetic procedure allows the fabrication of a variety of photochemical reaction centers according to the molecular-level design.     

Near-field Raman imaging and electromagnetic field confinement in the self-assembled monolayer array of gold nanoparticles

Spatial distribution of surface enhanced Raman activity is visualized for two-dimensional (2D) nearly close-packed and well-ordered monolayer array of gold nanoparticles by using scanning near-field optical microscope. The 2D arrays exhibit highly nonuniform enhancement in Raman scattering, i.e., the regions along the edge of the 2D array are preferentially enhanced. We demonstrate that the spatial distribution of the localized electric field is also nonuniform and agrees well with that of the Raman enhancement.     

Binding of Ricinus communis agglutinin to a galactose-carrying polymer brush on a colloidal gold monolayer

A polymer with many pendent galactose residues was prepared by atom-transfer radical polymerization (ATRP) of galactose-carrying vinyl monomer, 2-lactobionamidoethyl methacrylate (LAMA), with a disulfide-carrying ATRP initiator, 2-(2'-bromoisobutyroyl)ethyl disulfide (DT-Br). The galactose-carrying polymer obtained (DT-PLAMA) was accumulated as a polymer brush via Au-S bond on a colloidal gold monolayer deposited on a cover glass. For comparison, a disulfide which carried one galactose residue at both ends (2-lactobionamidoethyl disulfide, Cys-Lac) was accumulated as a self-assembled monolayer (SAM) on the colloidal gold monolayer, too. The association and dissociation processes of galactose residues on the colloidal gold with a lectin, Ricinus communis agglutinin (RCA(120)), were observed by the increase and decrease in absorbance at 550nm corresponding to localized surface plasmon resonance (LSPR) phenomena. The Cys-Lac SAM-carrying glass chip showed a strong non-specific adsorption of the lectin, whereas the DT-PLAMA brush-carrying one reversibly associated with the lectin, indicating reusability of the latter device. The apparent association constant of the lectin with the galactose residues in the DT-PLAMA brush was much larger than the association constant for free galactose, and the detection limit of RCA(120) by the glycopolymer brush-modified device was satisfactorily low. Furthermore, a microscopic observation clearly indicated that the DT-PLAMA brush could reversibly associate with a HepG2 cell having galactose receptors, though these processes could not be observed spectrophotometrically due to a gigantic size of the cell.