Radiation patterns of electric dipole antenna in the presence of a biisotropic sphere

Analytic expressions of the dyadic Green's function of an arbitrary electric current source embedded in a general biisotropic sphere are presented at first, and the radiation characteristics of an electric dipole antenna placed on the surface of a biisotropic sphere lens are examined. The effects of the electric-and the magnetic-coefficients ( _e and _m ) of biisotropic medium on the radiation patterns of electric dipole antenna are investigated in detail.     

Determination of hexamethylene-based isocyanates in spray-painting operations. Part 1. Evaluation of a polyurethane foam sponge sampler

A polyurethane foam (PUF) sponge was mounted in a cassette sampler and evaluated as a sorbent for the collection of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. Recovery studies indicated 112 +/- 34% average recovery of HDI monomer and 92 +/- 9% and 97 +/- 25% average recovery of HDI-based oligomers when using impregnated PUF sponges. The PUF sponge was also evaluated during actual spray-painting operations. In a series of side-by-side sampling events, an impinger filled with 1-(2-methoxyphenyl)piperazine (MOP) in toluene was compared directly with a cassette sampler containing a PUF sponge impregnated with MOP or 1-(9-anthracenylmethyl)piperazine (MAP) in dimethyl sulfoxide (DMSO). For the analysis of HDI-based oligomer, there is no significant difference (p < 0.05, n = 7) in the air concentration when sampling with either the PUF sponge cassette or the impinger. The results are significant because they indicate that a PUF sponge, which is more convenient than an impinger, may be used for the collection of HDI-based oligomer generated during spray-painting operations.     

A practical synthetic route to 4′-alkylaristeromycin derivatives: 4′-methylaristeromycin

(−)-(1S,4R)-4-Hydroxy-2-cyclopenten-1-yl acetate provided a convenient entry point for a 16-step chiral preparation of 4′-methylaristeromycin. This procedure is adaptable to a number of carbocyclic nucleosides with a diversity of substitution at C-4′ and C-5′ and a variety of heterocyclic bases.     

Design and Synthesis of 1-Benzyl-3-(a-hydroxy-(un)substituted benzylidene)pyrrolidine-2,4-diones as Potential Herbicides

The inhibitors of 4-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) are an new kind of herbicides.[1]Generally, in structure, potent herbicides of this kind must possess: (1) a tricarbonyl methane structure and one of the three carbonyl groups must be a subustituted benzoyl group; (2) the compound must be able to enolise so that the enolate is capable of inhibiting HPPD enzyme by competitive combination with Fe2+, the reaction center of HPPD enzyme.[2]Recently, we noticed that the 3-acyltetramic acids form an expanding group of antibiotics and pigments from micro-organisms,[3] they display a range of biological activities[4] and all of this kind compounds possess all of the characters mentioned above. Tests of their antimicrobial activities indicated that the structure of the acyl substituent at the 3-position was important to many typical antibiotics.[4～6] These characters stimulated us to study this kind of compounds so as to discover new herbicides. In this report, we synthesized a series of compounds 3 and tested their herbicidal activities to investigate their structure-activity relationships.     

THE STRUCTURAL BASIS OF THE POOR FIBRIN SPECIFICITY OF UROKINASE(Ⅰ)——KNOWLEDGE-BASED PREDICTION OF KRINGLE STRUCTURES OF UROKINASE AND ITS RELATED PROTEINS

The Kringle-1 structure of plasminogen (PGK-1), the Kringle-2 structure of tissue plasminogen activator (PAK-2) and the Kringle structure of prourokinase (UKK) has been modeled on the basis of the three-dimensional structure of Kringle-1 of prothrombin (PTK-1) at 2.8 resolution. The predicted three-dimensional structure of these Kringles shows that the binding site of PGK-1 is characterized by an apparent dipolar site, the polar parts of which are separated by a hydrophobic region. PAK-2 possesses the anionic center but has not a cationic binding center which might be provided by a guanidinium group from Arg-69 located adjacent to the Arg-71 position. UKK possesses neither the anionic binding center nor the cationic center which are probably the main reason for the poor fibrin specificity of urokinase.     

Lysine peroxycarbamates: free radical-promoted peptide cleavage

Strategies are reported that combine in one step a predictable chemical-based protein digestion with mass spectrometry. Lysine residue amino groups in peptides and proteins are modified by reaction with a peroxycarbonate derived from p-nitrophenol, and tert-butyl hydroperoxide. The peroxycarbonate reacts with lysine residues in peptides and proteins, and the resulting lysine peroxycarbamates undergo homolytic fragmentation under conditions of low-energy collision-induced dissociation (CID). Observed fragmentation of the peptides involves apparent free radical processes including Hofmann-L?ffler-type rearrangements that lead to peptide chain fragmentation. Strategies for directed cleavage of peptides by free radical promoted processes are feasible, and such strategies may well simplify schemes for protein analysis.     

Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Speciation of arsenic in environmental samples gains increasingly importance, as the toxic effects of arsenic are related to its oxidation state. A method was developed for the determination of trace amounts of arsenic (III) and total arsenic by flow injection hydride generation coupled with an in-house made non-dispersive AAS device. The total arsenic is determined after prereduction of arsenic (V) to arsenic (III) with L-cysteine in a low concentration of hydrochloric, acetic or nitric acid. The conditions for the prereduction, hydride generation and atomization were systematically investigated. A quartz tube temperature of 800 degrees C was found to be optimum in view of peak shape and baseline stability. Pb(II), Ni(II), Fe(III), Cu(II), Ag(I), Al(III), Ga(II), Se(IV), Bi(III) were checked for interfering with the 2 microg/L As(V) signal. A serious signal depression was only observed for Se(IV) and Bi(III) at a 150-fold excess. With the above system, arsenic was determined at a sampling frequency of about 1/min with a detection limit (3sigma) of 0.01 microg/L using a 0.5 mL sample. The reagent blank was 0.001+/-0.0003 absorbance units and the standard deviation of 10 measurements of the 2 microg/l As signal was found to be 1.2%. Results obtained for standard reference materials and water samples are in good agreement with the certified values and those obtained by ICP-MS     

Analysis of Equilibrium and Kinetics of Chromium-Fluoride Complexation from Spectroscopic Data via Chemometrics Methods

IntroductionStudies on reversible kinetic systems are consi-dered as a hotspot of chemical and biochemical kineticresearches[1,2]. Of late, some researches have been fo-cused on the simultaneous optimization of the obverseand reverse rate constants[3,4].H…     

Effect of electric field on liquid chromatographic separation of peptide digests. Combining capillary separation techniques

A system is described which allows operation of a range of capillary based liquid phase separations including capillary electrophoresis, isocratic and gradient capillary electrochromatography, isocratic and gradient capillary liquid chromatography and electrically assisted gradient capillary liquid chromatography. The system was coupled to electrospray ionization mass spectrometry in the electrically assisted capillary liquid chromatography mode to investigate the effect of applied voltage on the selectivity in peptide mapping separations. Analyses were performed on tryptic digests of recombinant human growth hormone and tissue plasminogen activator. The results show a small but useful effect on selectivity that can be used to fine tune specific separations.