Synthesis and photoinduced isomerization ofansa{·5,·5′-[1,1′-(1-silacyclopent-3-ene-1,1-diyl)bis(indenyl)]} dichlorozirconium The crystal structure of itsmeso form

ansa{·⁵,·⁵′-[1,1′-(1-silacyclopent-3-ene-1,1-diyl)bis(indenyl)]} dichlorozirconium (1a,b) was synthesized. The crystal structure ofmeso-[(1,4-CH₂CH=CHCH₂)Si(C₉H₆)₂ZrCl₂] (1b) was established by X-ray diffraction analysis. Photoinduced interconversion of the racemic (1a) andmeso forms was studied under various conditions. The photostationary state (rac: meso=55∶45) was established rapidly when solutions ofansa-zirconocene were irradiated with visible light. Deceased Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2351–2356, November, 1998.     

Revisiting catechol derivatives as robust chromogenic hydrogen donors working in alkaline media for peroxidase mimetics

Colloidal noble metal-based nanoparticles are able to catalyze oxidation of chromogenic substrates by H₂O_2, similarly to peroxidases, even in basic media. However, lack of robust chromogens, which work in high pH impedes their real applications. Herein we demonstrate the applicability of selected catechol derivatives: bromopyrogallol red (BPR) and pyrogallol (PG) as chromogenic substrates for peroxidase-like activity assays, which are capable of working over wide range of pH, covering also basic values. Hyperbranched polyglycidol-stabilized gold nanoparticles (HBPG@AuNPs) were used as model enzyme mimetics. Efficiency of several methods of improving stability of substrates in alkaline media by means of selective suppression of their autoxidation by molecular oxygen was evaluated. In a framework of presented studies the impact of borate anion, applied as complexing agent for PG and BPR, on their stability and reactivity towards oxidation mediated by catalytic AuNPs was investigated. The key role of high concentration of hydrogen peroxide in elimination of non-catalytic oxidation of PG and improvement of optical properties of BPR in alkaline media containing borate was underlined. Described methods of peroxidase-like activity characterization with the use of BPR and PG can become universal tools for characterization of nanozymes, which gain various applications, among others, they are used as catalytic labels in bioassays and biosensors.     

Development of hollow fiber‐supported liquid‐phase microextraction and HPLC‐DAD method for the determination of pyrethroid metabolites in human and rat urine

A simple hollow fiber liquid‐phase microextraction method for the determination of synthetic pyrethroid metabolites, 3‐phenoxybenzoic acid and 4‐hydroxy‐3‐phenoxybenzoic acid, in human and rat urine was developed and validated. A polypropylene hollow fiber tightly fitted onto a Nylon rod and impregnated with organic solvent served as a disposable extraction device. Desorption of analytes was carried out in NaOH solution, analyzed further by gradient HPLC and diode array detection method. Important factors were identified using Taguchi OA16 (4⁵) orthogonal array design and further optimized using univariate approach. The optimum method performance was observed when 1 mL of urine hydrolyzed with 0.2 mL of concentrated HCl was further supplemented with 100 mg of NaCl and extracted for 120 min into dihexyl ether immobilized in the pores of the hollow fiber. Metabolites were desorbed into 0.1 mL of 0.1 M NaOH for another 120 min. Limits of detection and quantitation of 15 and 50 ng/mL were obtained for both analytes. Relative standard deviations of 1.6–12.6% over the linear range (50–10,000 ng/mL, r > 0.9906) were observed. Intra‐ and inter‐day accuracies of the method ranged from 98.3 to 109.5% and from 93.3 to 110.9%, respectively. The optimized method was applied to the analysis of real urine samples collected from rats exposed orally to cypermethrin. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and evaluation of the catalytic properties of semicarbazides derived from N-triphenylmethyl-aziridine-2-carbohydrazides

A straightforward synthesis of a series of new catalysts derived from N-triphenylmethyl-aziridine-2-carbohydrazides is described. The new compounds have been tested for the enantioselective addition of diethyl- and phenylethynylzinc to aryl and alkyl aldehydes, which afforded the corresponding chiral alcohols in high chemical yields (up to 92%) and with excellent ee’s of approximately 90%.     

Non-singular space-times with a negative cosmological constant: V. Boson stars

We prove existence of large families of solutions of Einstein-complex scalar field equations with a negative cosmological constant, with a stationary or static metric and a time-periodic complex scalar field.     

Alkylation of Potassium 1-(N-Benzyloxycarbonylamino)alkylphosphonates and Phosphinates in the Presence of 18-Crown-6

During past several years we have been engaged in the synthesis of phosphono peptides, peptide analogues with phosphonic acid replacing C-terminal or N-terminal carboxylate moiety. These compounds are of interest not only because of their promise of direct practical applications^1,2 but also as a source of information about mechanisms of enzymatic reactions. ^1,3–5 Esters of N-blocked 1 -aminoalkylphosphonic and phosphinic acids are popularly used as starting substrates in multistep syntheses of phosphono peptides.^6–9 Although several methods for their preparation have been described ^6,10–13 the search for the new and useful methods of their synthesis is still in progress. In this paper we report that the use of complexes of potassium 1-(N- benzyloxycarbonylamiuo)alkylphosphonates and phosphates with 18-crown-6 as nucleophiles in the reaction with alkyl halides afforded the desired esters in good yields.