A novel access to pyrido[4,3-d]pyrimidine scaffold via Staudinger/intramolecular aza-Wittig reaction of 5-acyl-4-(β-azidoalkyl)-1,2,3,4-tetrahydropyrimidin-2-ones

A general four-step approach to 1,2,3,7,8,8a-hexahydropyrido[4,3-d]pyrimidin-2-ones via Staudinger/intramolecular aza-Wittig reaction of 5-acyl-4-(β-azidoalkyl)-1,2,3,4-tetrahydropyrimidin-2-ones promoted by PPh₃ was developed. Synthesis of the starting pyrimidinones included preparation of 3-azidoaldehydes by the addition of hydrazoic acid to α,β-unsaturated aldehydes, transformation of 3-azidoaldehydes into N-[(3-azido-1-tosyl)alkyl]ureas followed by the reaction with enolates of dibenzoylmethane, benzoylacetone, acetylacetone, or ethyl 2,4-dioxo-4-phenylbutanoate and dehydration of the resulting products under acidic conditions.     

Efficiency of Pt and Ir modifiers for the simultaneous determination of As, Se and In in a sodium sulphate matrix by electrothermal atomic absorption spectrometry

The effect of pre-reduced Pt and Ir modifiers towards simultaneous determination of As, Se and In in a sodium sulphate matrix was investigated. In spite of application of very isothermal THGA atomizer, negative influence of the matrix is pronounced. The efficiency of iridium modifier is somewhat higher than that of platinum modifier. However compared to palladium modifier both are significantly less effective in sulphate media. Taking into account our previous data, effectiveness of platinum group metal (PGM) modifiers in the determination of As, Se and In in the presence of sodium sulphate increases in the order Ru<Rh≈Pt<Ir<Pd. This order is opposite to the data on enthalpy of formation of PGM sulphides. This supports our hypothesis that effectiveness of PGM modifiers in the presence of sulphate matrix is determined mainly by stability of the corresponding sulphides. Efforts to enhance the effectiveness of Pt modifier mixing it with small (10-20%) amounts of Pd, Rh or Ir were not successful. Although mixture containing equal amounts of Pd, Pt, Rh and Ru is relatively effective, pure pre-reduced Pd is the best modifier for the simultaneous determination of As, Se and In in a sulphate media.     

Investigations into the catalytic activity of rhodium(III) in red-ox reactions by capillary zone electrophoresis

Speciation of rhodium(III) in different acidic media has been studied by capillary zone electrophoresis (CZE). Depending on the nature of the acid, rhodium was shown to occur in the form of positive, neutral and/or negatively charged complexes. The relationship between the distribution of rhodium forms and its catalytic action on the oxidation of N-methyldiphenylamine-4-sulfonic acid by periodate ions has been investigated. It was found that only positively charged complexes of rhodium, such as those dominating in perchloric acid solutions, catalyzed a given reaction to form a colored oxidation product. The rate of the catalyzed reaction was optimized with respect to the pH, reagent and oxidant concentration levels, ionic strength, concentration of the catalyst, as well as the presence of interfering ions. The developed kinetic spectrophotometric method features rather high sensitivity (limit of determination 10 μg l⁻¹) and tolerance for most platinum metals and was applied to a complex industrial sample of a platinum concentrate.     

Secondary structure of DNA is recognized by slightly cross-linked cationic hydrogel

Interaction of salmon sperm DNA (300-500 bp) and ultrahigh molecular mass DNA (166 kbp) from bacteriophage T4dC with linear poly(N-diallyl-N-dimethylammonium chloride) (PDADMAC) and slightly cross-linked (#) PDADMAC (#PDADMAC) hydrogel in water has been studied by means of UV-spectroscopy, ultracentrifugation, atomic force, and fluorescence microscopy (FM). It is found that the linear polycation induced compaction of either native (double-stranded) or denatured (single-stranded) DNA by forming PDADMAC-DNA interpolyelectrolyte complexes (IPEC)s. At the same time, #PDADMAC hydrogel is able to distinguish between native and denatured DNA. Native DNA is adsorbed and captured in the hydrogel surface layer, while denatured DNA diffuses to the hydrogel interior until the whole hydrogel sample is transformed into the cross-linked IPEC. Both native and denatured DNA can be completely released from the hydrogel in appropriate conditions with no degradation by adding a low molecular salt. The data observed using conventional physicochemical methods with respect to DNA of a moderate molecular mass remarkably correlate with the pictures directly observed for ultrahigh molecular mass DNA in dynamics by using FM.     

Immunoenzyme assay of nonylphenol: study of selectivity and detection of alkylphenolic non-ionic surfactants in water samples

Immunoenzyme assay (ELISA) is proposed and characterized for determination of alkylphenol ethoxylates, a primary class of manufactured non-ionic surfactants. The assay is based on the obtained polyclonal antibodies against nonylphenol (NP), the main stable intermediate of the decomposition of nonylphenol ethoxylates. A mixture of non-modified branched isomers of NP was applied as hapten coupled to protein carriers by Mannich reaction with the use of formaldehyde. The proposed ELISA format is based on immobilized NP-(soybean trypsin inhibitor) conjugate as a competitor of antigen molecules contained in the tested sample for binding with specific antibodies indirectly labeled via an anti-species immunoperoxidase conjugate. The developed ELISA allows to reveal NP with the limit of detection about 10 ng ml⁻¹ and NP-related compounds such as octylphenol, alkylphenoletoxylates, alkylphenolcarboxylates and their halogenated derivatives. The ELISA was applied for assaying polluted water samples, namely influents and effluents from different wastewater treatment plants (WWTP) and tap water. ELISA and chromatographic data demonstrate good correlation (r = 0.94), while ELISA gives higher values. Due to endocrine disrupting and other toxic activities of some metabolites of alkylphenolic non-ionic surfactants, the developed assay may be effectively used in ecological monitoring and sanitary control.     

Computation of the pseudorotation matrix to satisfy the Eckart axis conditions

A general solution for satisfying the Eckart axis conditions [C. Eckart, Phys. Rev. 47, 552 (1935)] is presented. The goal is to find such a pseudorotation matrix T that the vector product between the reference molecular conformation R and another transformed conformation r' is zero [ summation operator(a)m(a) r(a) 'xRa=0; r(a) '=Tr(a)]. Our solution avoids the limitations of the earlier one [H. M. Pickett and H. L. Strauss, J. Am. Chem. Soc. 92, 7281 (1970)], which fails when one of the involved intermediate matrices is singular. We also discuss how to choose among the always nonunique pseudorotation matrices T the one that represents a true rotation for situations when an alignment of the two conformations is desired.     

Synthesis and copolymerization of azidomethyl-substituted oxetanes: the morphology of statistical block copolymers

Chemistry of Heterocyclic Compounds - 3,3-Bis(azidomethyl)oxetane and 3-azidomethyl-3-methyloxetane were obtained by bromination of pentaerythritol and metriol with a mixture of hydrobromic,...     

Rapid Full-Cycle Technique to Control Adulteration of Meat Products: Integration of Accelerated Sample Preparation,Recombinase Polymerase Amplification,and Test-Strip Detection

Verifying the authenticity of food products is essential due to the recent increase in counterfeit meat-containing food products. The existing methods of detection have a number of disadvantages. Therefore, simple, cheap, and sensitive methods for detecting various types of meat are required. In this study, we propose a rapid full-cycle technique to control the chicken or pig adulteration of meat products, including 3 min of crude DNA extraction, 20 min of recombinase polymerase amplification (RPA) at 39 °C, and 10 min of lateral flow assay (LFA) detection. The cytochrome B gene was used in the developed RPA-based test for chicken and pig identification. The selected primers provided specific RPA without DNA nuclease and an additional oligonucleotide probe. As a result, RPA–LFA, based on designed fluorescein- and biotin-labeled primers, detected up to 0.2 pg total DNA per μL, which provided up to 0.001% w/w identification of the target meat component in the composite meat. The RPA–LFA of the chicken and pig meat identification was successfully applied to processed meat products and to meat after heating. The results were confirmed by real-time PCR. Ultimately, the developed analysis is specific and enables the detection of pork and chicken impurities with high accuracy in raw and processed meat mixtures. The proposed rapid full-cycle technique could be adopted for the authentication of other meat products.     

1-Substituted 5-thiotetrazoles as novel capping agents for stabilization of gold nanoparticles

Stable and nearly monodispersed gold nanoparticles with sizes of 2.8–4.7 nm are easily prepared by the reduction of tetrachloroaurate salts in a toluene-water system in the presence of 1-R-5-thiotetrazoles (R = Et, t-Bu, 1-adamatyl). The prepared gold nanoparticles were characterized by TEM, XRD, UV–Vis, FTIR and TGA.