Magnetic Bistability of Individual Single‐Molecule Magnets Grafted on Single‐Wall Carbon Nanotubes

A POM to remember : Hexanuclear Fe^III polyoxometalate (POM) single‐molecule magnets (see structure) can be noncovalently assembled on the surface of single‐wall carbon nanotubes. Complementary characterization techniques (see TEM image and magnetic hysteresis loops) demonstrate the integrity and bistability of the individual molecules, which could be used to construct single‐molecule memory devices.

     

Influence of surface tension on damping of the oscillations of a viscous incompressible fluid in a cylindrical channel

A numerical calculation is made of small oscillations of a viscous incompressible fluid that fills half of a horizontal cylindrical channel. The calculation is made with and without allowance for surface tension. The results of the calculation show that allowance for surface tension increases the damping of the oscillations. The general properties of problems of the normal oscillations of a heavy and capillary viscous incompressible fluid were studied in [1–3], in which the possibility of applying the Bubnov-Galerkin method to these problems was pointed out. A method for calculating the oscillations of a viscous incompressible fluid that partly fills an arbitrary vessel at large Reynolds numbers was developed in [3–5].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 128–132, May–June, 1980.     

Single-enzyme-based amperometric assay for phosphate ion

An amperometric assay for phosphate ion, using a single enzymatic process, has been developed. The enzyme used was pyruvate oxidase, which catalyzes the oxidation of pyruvate in the presence of oxygen and phosphate ion. The products of the enzymatic reaction are acetyl phosphate, carbon dioxide, and hydrogen peroxide. The latter was monitored by means of a hydrogen peroxide electrode and an oxidase meter. Phosphate ion in the concentration range of 50–500 μM can be measured within 4 min. Anions, such as pyrophosphate, sulfate, nitrate, nitrite, and acetate, gave only marginal responses.     

Ultrasensitive chromogen system for Horseradish Peroxidase Using 3-Methyl-2-benzothiazolinone Hydrazone andN-Phenyldiethanolamine

An ultrasensitive chromogenic system for horseradish peroxidase (HRP) is described. The chromogenic substrate system consists of 3-methyl-2-benzothiazolinone hydrazone (MBTH) andN-phenyldiethanolamine (PDEA). The oxidative coupling of MBTH and PDEA using H₂O₂ and HRP, respectively, as the oxidant and catalyst, yields a blue chromophore that most likely is an indamine dye. The chromophore has a rather broad absorption band, with an absorption maximum at 602 nm. In 0.1M phosphate, 0.1M citrate buffer, pH 7.5, the optimal concentrations of MBTH, PDEA, and H₂O₂ are, respectively, 0.5, 25, and 8 mM. Using this assay system, HRP can be determined in lower picomolar levels by either a rate or fixed-time method.     

A note on quasi-Frobenius rings

It is shown that a semiperfect ring is quasi-Frobenius if and only if every closed submodule of is non-small, where denotes the direct sum of copies of the right -module and is the first infinite ordinal.

     

Laser-induced breakdown detection combined with asymmetrical flow field-flow fractionation: application to iron oxi/hydroxide colloid characterization

The combination of asymmetrical flow field-flow fractionation (AsFlFFF) with the laser-induced breakdown detection (LIBD) is presented as a powerful tool for the determination of colloid size distribution at trace particle concentrations. Detection limits (D1) of 1, 4, and 20 microg/L have been determined for a mixture of polystyrene reference particles with 20, 50, and 100 nm in size, respectively. This corresponds to injected masses of 1, 4, and 20 pg, which is lower than found in a previous study with the symmetrical FlFFF (SyFlFFF). The improvement is mainly due to the lower colloid background discharged from the AsFlFFF channel. The combined method of AsFlFFF-LIBD is then applied to the analysis of iron oxi/hydroxide colloids being considered as potential carriers for the radionuclide migration from a nuclear waste repository. Our LIBD arrangement is less sensitive for iron colloid detection as compared to reference polystyrene particles which results in a detection limit of approximately 240 microg/L FeOOH for the AsFlFFF-LIBD analysis. This is superior to the detection via UV-Vis absorbance and comparable to ICP-MS detection. Size information (mean size 11-18 nm) for different iron oxi/hydroxide colloids supplied by the present method is comparable to that obtained by sequential ultrafiltration and dynamic light scattering. A combined on-line ICP-MS detection is used to gain insight into the colloid-borne main and trace elements.     

Carrier-mediated transport of rare earth elements through liquid membranes

Transport of tervalent REEs — Sc, Y, Ce, Eu, Gd, Tm, Yb — from nitrate medium through a liquid membrane containing TBP in n-dodecane, impregnated on a flat-sheet nucleoporous support, has been studied as a function of time and initial metal concentration, salting-out agent concentration and pH of the feed phase. Influences of various complexing agents dissolved in the strip phase was investigated, too. Adding a suitable amount of EDTA into the feed phase, separation of binary mixtures of REEs was experimentally achieved.     

Asymmetric construction of quaternary carbon stereocenters: high stereoselection in Mukaiyama aldol reactions of 2-siloxyindoles with chiral aldehydes

[reaction: see text] A new synthesis of enantiopure 3,3-disubstituted oxindoles by stereoselective Mukaiyama aldol reaction of 3-substituted 2-siloxyindoles and chiral, enantiopure aldehydes having nitrogen or oxygen substituents at the alpha carbon is described. When the C3 substituent of the prochiral nucleophile is aryl or heteroaryl, stereoselectivity is high (10-80:1).     

Separation-free amperometric enzyme immunoassay

A new technique for conducting a separation-free amperometric enzyme immunoassay is described using DNP-aminocaproic acid as the analyte. The technique is based on the combined use of a recently described separation-free enzyme immunoassay (19) and an electrode system that senses H₂O₂. Oxidation of glucose to gluconate and H₂O₂ by the enzyme reconstituted from DNP-conjugate apoglucose oxidase (DPN-CAGO) and FAD was continuously measured amperometrically. The reconstitution was inhibited by preincubation with anti-DNP antibody before adding FAD. This antibody-induced inhibition of the reconstituting of the holoenzyme was reversed by adding DNP-amino caproic acid to DNP-CAGO before adding the antibody to DNP-CAGO. Based on (a) the antibody-induced inhibition of holoenzyme reconstitution, (b) a specific ligand-induced reversal of the inhibition, and (c) an electrochemical system that measures H₂O₂, we developed a separation-free (homogeneous) amperometric enzyme immunoassay.     

Some criteria for Buchsbaum modules

The paper gives a criterion for Buchsbaum modules over a local ringR which depends only on a finite system of elements ofR.