A new application of the Mitsunobu reaction in the synthesis of phosphonium salts

The condensation of methanol or primary alcohols with triphenylphosphonium tetrafluoroborate in the presence of ethyl azodicarboxylate and triphenylphosphine in THF at room temperature gives the respective alkyltriphenylphosphonium salts in good yields. The reaction also worked for the conversion of N-acyl-2-hydroxyglycinates into N-acyl-2-triphenylphosphonioglycinates.     

The 1993 ISO Guide to the Expression of Uncertainty in Measurement Applied to NAA

Principles of the expression of uncertainty in measurements are briefly reviewed and special aspects of the uncertainty quantification in NAA are discussed in detail regarding the relative and k ₀-standardization in both modes of the technique, i.e., INAA and RNAA. A survey of uncertainty sources is presented and calculation of the combined uncertainty is demonstrated by an example of manganese determination in biological material by RNAA.     

Preparation and dielectric properties of polyimide/silica nanocomposite films prepared from sol–gel and blending process

Using poly(amic acid) (PAA) as a precursor followed by thermal imidization, the polyimide/silica nanocomposite films were prepared via an improved sol–gel process and a blending process, respectively. FT‐IR, TEM and TGA measurements were used to characterize the structure and properties of the obtained films. The results confirmed that the introduction of silica did not yield negative effects on the conversion of the PAA precursor to the polyimide. With the increase of silica content, the aggregation of silica appeared in the polyimide matrix, and the thermal stability decreased slightly for both kinds of films. The dielectric constant (ε) of both films increased slowly with the increase of the silica concentration. The dielectric constant of the obtained polyimide/silica nanocomposite films displayed good stability within a wide range of temperatures or frequency. Based on modeling relation between ε and silica content, the difference in dielectric properties for two kinds of nanocomposites are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Determination of As,Cd, Cu,Hg, Mo,Sb, and Se in biological reference materials by radiochemical neutron activation analysis

The elements As, Cd, Cu, Hg, Mo, Sb, and Se were determined in the biological reference materials (RMs) Bowen's Kale, NIST SRM-1577 Bovine Liver, NIST SRM-1549 Milk Powder, and Versieck's 2nd Generation Biological RM Human Serum using two newly developed radiochemical neutron activation analysis (RNAA) procedures. The first is based on sample decomposition in a mixutre of H₂SO₄+HNO₃+H₂O₂ and simultaneous extraction of the elements As, Cd–In, Cu, Mo, and Sb by 0.025M Zn(DDC)₂ in chloroform from 2–4M H₂SO₄ in the presence of 0.01M KI. The second consists of sample decomposition in HNO₃ in teflon bombs heated at 150°C, Hg extraction by 0.01M Ni(DDC)₂ in chloroform from about 1M HNO₃, and Se precipitation by ascorbic acid from about 1M HClO₄. The RNAA procedures were also used for intercomparison analyses of A and P NIST Leaf Materials (NIST candidate SRM-1515 Apple Leaves and NIST SRM-1547 Peach Leaves, respectively), and CZIM Bovine Liver 12-02-01 RM. Very good agreement of results with certified and/or literature values proved the high accuracy of these determinations by the proposed RNAA procedures, even at the sub-ng/g levels.     

Amperometric Tyrosinase Biosensor Based on Carbon Nanotube–Titania–Nafion Composite Film

A highly sensitive and stable amperometric tyrosinase biosensor has been developed based on multiwalled carbon nanotube (MWCNT) dispersed in mesoporous composite films of sol–gel‐derived titania and perfluorosulfonated ionomer (Nafion). Tyrosinase was immobilized within a thin film of MWCNT–titania–Nafion composite film coated on a glassy carbon electrode. Phenolic compounds were determined by the direct reduction of biocatalytically‐liberated quinone species at ?100 mV versus Ag/AgCl (3 M NaCl) without a mediator. The present tyrosinase biosensor showed good analytical performances in terms of response time, sensitivity, and stability compared to those obtained with other biosensors based on different sol–gel matrices. Due to the large pore size of the MWCNT–titania–Nafion composite, the present biosensor showed remarkably fast response time with less than 3 s. The present biosensor responds linearly to phenol from 1.0×10^?7 M to 5.0×10^?5 M with an excellent sensitivity of 417 mA/M and a detection limit of 9.5×10^?8 M (S/N=3). The enzyme electrode retained 89% of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

粉状白钨酸的研究——ⅩⅫ.六聚钨酸二甲基亚砜加合物的制备

1968年,Fuchs等首次用控制水解法从WO(CH_3)_4中获得了六聚钨酸盐,它的阴离子W_6O_(19)~(2-)结构也已被测定。迄今六钨酸盐主要还是局限于几个多碳有机胺盐。以粉状白钨酸为原料,在二甲基亚砜(DMSO)中制得了一系列DMSO配位的多价金属的六钨酸盐晶体,并测定了其中部分盐类的晶体结构。但六聚钨酸仍未     

Radiation stability tests of the SMELS materials in the LVR-15 experimental reactor at Řež

Radiation stability of a set of three synthetic multielement standards (SMELS) designed for validation of k ₀-standardization in neutron activation analysis was tested by monitoring mass and element content changes following irradiation at a high neutron fluence rate (up to 9^.10¹³ n^.cm^-2.s^-1) for stepwise increased periods of time. No mass changes were detected and for all the 26 elements investigated only a chlorine content loss was observed. Thus, radiation stability of the SMELS materials for the given purpose and their suitability for use also in high-power reactors was demonstrated.     

PHOTOCONTROL OF ANTHOCYANIN SYNTHESIS: PHYTOCHROME,CHLOROPHYLL AND ANTHOCYANIN SYNTHESIS*

Abstract —Anthocyanin synthesis in cabbage and mustard seedlings depends upon duration and irradiance of the light treatment. The relative effectiveness of radiation in various spectral regions depends upon the length of the irradiation and decreases with increasing dose. In intermittent light treatments, far-red light can reverse the promoting action of red light if the dark interval between successive irradiations is longer than one hour. If the length of the dark interval is less than one hour, far-red applied immediately after each red irradiation, enhances anthocyanin accumulation. Anthocyanin accumulation under various light treatments seems to correlate, to some extent, with the rate of phytochrome decay, but not with chlorophyll production. Anthocyanin accumulation is inhibited by 2,4-dinitrophenol and by the ammonium ion, but not by DCMU. The ammonium ion inhibits anthocyanin accumulation induced by a single, short red irradiation. This suggest that the ammonium ion may have a wider spectrum of action in vivo than in chloroplast preparations where it acts as a specific uncoupler of photophosphorylation. Streptomycin inhibits chlorophyll synthesis and enhances anthocyanin accumulation. These results suggest that there is very little, if any, interaction between photosynthesis and ‘high-irradiance-reaction’ anthocyanin synthesis in cabbage and mustard seedlings.     

Aligned inclusion of hemicyanine dyes into silica zeolite films for second harmonic generation

Silicalite-1 films (thickness = 400 nm) supported on both sides of glass plates (SL/G) were prepared, and hemicyanine dyes (HC-n) with different alkyl chain lengths (n, n = 3, 6, 9, 12, 15, 18, 22, and 24) were included into the silicalite-1 films by dipping SL/Gs into each methanol solution of HC-n (1 mM) for 1 d. The included numbers of HC-n per channel (N(C)) generally decreased with increasing n; that is, they were 6.4, 23.1, 15.4, 8.2, 5.7, 3.5, 0.9, and 1.2 molecules per channel, respectively. The d(33) value gradually increased with increasing n but decreased when n > 18; that is, they were 1.12, 0.50, 2.25, 3.59, 4.99, 5.30, 1.71, and 2.57 pm V(-1), respectively. However, d(33)/N(C) progressively increased with increasing n. The d(31) values were approximately 100 times smaller than the corresponding d(33) values, and the average d(33)/d(31) ratio was 109, which is higher than those of Langmuir-Blodgett (LB) films and poled polymers of nonlinear optical (NLO) dyes, by approximately 2-5 and approximately 30-50 times, respectively. The estimated average tilted angle of the dyes with respect to the channel direction was 7.7 degrees, and the calculated average order parameter was 0.97, which is approximately 480 times higher than the values observed from poled polymers. The degree of uniform alignment (DUA) generally increased with increasing n. The progressive increase of both DUA and d(33)/N(C) with n is attributed to the increase in the tendency of HC-n to enter hydrophobic silicalite-1 channels with the hydrophobic alkyl chain first. A more than 134-fold increase in DUA was observed upon increasing n from 6 to 24. The DUA of HC-24 in the silicalite-1 film reached close to 1. Although the observed d(33) values were lower than those of the LB films of NLO dyes due to very small dye densities of the silicalite films, this methodology bears a great potential to be developed into the methods for preparing practically viable NLO films.