Regiodirected Synthesis and Stereochemistry of 2,4,8‐Trialkyl‐3‐thia‐1,5‐diazabicyclo[3.2.1]octanes and α,ω‐Bis(2,4,6‐trialkyl‐1,3,5‐dithiazinane‐5‐yl)alkanes

2,4,8‐Trialkyl‐3‐thia‐1,5‐diazabicyclo[3.2.1]octanes have been obtained by the regioselective and stereoselective cyclocondensation of 1,2‐ethanediamine with aldehydes RCHO (R═Me, Et, Prⁿ, Buⁿ, Pentⁿ) and H₂S at molar ratio 1:3:2 at 0°C. The increase in molar ratio of thiomethylation mixture RCHO–H₂S (6:4) at 40°C resulted in selective formation of bis‐(2,4,6‐trialkyl‐1,3,5‐dithiazinane‐5‐yl)ethanes. Cyclothiomethylation of aliphatic α,ω‐diamines with aldehydes RCHO (R═Me, Et) and H₂S at molar ratio 1:6:4 and at 40°С led to α,ω‐bis(2,4,6‐trialkyl‐1,3,5‐dithiazinane‐5‐yl)alkanes. Stereochemistry of 2,4,8‐trialkyl‐3‐thia‐1,5‐diazabicyclo[3.2.1]octanes have been determined by means of ¹H and ¹³С NMR spectroscopy and further supported by DFT calculations at the B3LYP/6‐31G(d,p) level. The structure of α,ω‐bis(2,4,6‐trialkyl‐1,3,5‐dithiazinane‐5‐yl)alkanes was confirmed by single‐crystal X‐ray diffraction study.     

Reversible intramolecular Dieckmann-type condensation of 2-(2-hydroxymethyl-5,5,6-trimethoxytetrahydropyran-3-ylcarbonyl)-cyclopentanone: an alternative access to medium-sized lactones

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Evidence for the role of the monB genes in polyether ring formation during monensin biosynthesis

Ionophoric polyethers are produced by the exquisitely stereoselective oxidative cyclization of a linear polyketide, probably via a triepoxide intermediate. We report here that deletion of either or both of the monBI and monBII genes from the monensin biosynthetic gene cluster gave strains that produced, in place of monensins A and B, a mixture of C-3-demethylmonensins and a number of minor components, including C-9-epi-monensin A. All the minor components were efficiently converted into monensins by subsequent acid treatment. These data strongly suggest that epoxide ring opening and concomitant polyether ring formation are catalyzed by the MonB enzymes, rather than by the enzyme MonCII as previously thought. Consistent with this, homology modeling shows that the structure of MonB-type enzymes closely resembles the recently determined structure of limonene-1,2-epoxide hydrolase from Rhodococcus erythropolis.     

Optimum design for maximum wavelength resolution for an edge filter-based ratiometric system

This paper provides a straightforward design method for achieving a maximum wavelength resolution for an edge filter-based ratiometric system. An analysis of the influence of a range of factors on the resolution of the ratiometric wavelength measurement system was carried out. The investigation shows that, for a given input optical signal and when the working wavelength range is known, it is relatively straightforward to select an optimum slope for the edge filter that will yield a maximum resolution for the system. An experimental verification is carried out using a tunable laser and three macrobending fibre edge filters, with a good match between experimental and simulation results.     

Novel Galvanic Nanostructures of Ag and Pd for Efficient Laser Desorption/Ionization of Low Molecular Weight Compounds

A simple approach for synthesis of palladium and silver nanostructures with readily adjustable morphologies was developed using galvanic electrochemical deposition, for application to surface-assisted laser desorption/ionization (SALDI) of small biological molecules. A range of fatty acids, triglycerides, carbohydrates, and antibiotics were investigated to assess the performance of the new materials. Intense analyte cations were generated from the galvanic surfaces upon UV laser irradiation such as potassium adducts for a film thickness <100 nm (originating from impurities of the electrolyte solution) and Pd and Ag cluster ions for films with a thickness >120 nm. Possible laser desorption/ionization mechanisms of these galvanic structures are discussed. The films exhibited self-organizing abilities and adjustable morphologies by changing electrochemical parameters. They did not require any stabilizing agents and were inexpensive and very easy to produce. SALDI analysis showed that the materials were stable under ambient conditions and analytical results with excellent measurement reproducibility and detection sensitivity similar to MALDI were obtained. Finally, we applied the galvanic surfaces to fast screening of natural oils with minimum sample preparation.

Measurement of mercury species in human blood using triple spike isotope dilution with SPME-GC-ICP-DRC-MS

The measurement of different mercury compounds in human blood can provide valuable information about the type of mercury exposure. To this end, our laboratory developed a biomonitoring method for the quantification of inorganic (iHg), methyl (MeHg), and ethyl (EtHg) mercury in whole blood using a triple-spike isotope dilution (TSID) quantification method employing capillary gas chromatography (GC) and inductively coupled dynamic reaction cell mass spectrometry (ICP-DRC-MS). We used a robotic CombiPAL® sample handling station featuring twin fiber-based solid-phase microextraction (SPME) injector heads. The use of two SPME fibers significantly reduces sample analysis cycle times making this method very suitable for high sample throughput, which is a requirement for large public health biomonitoring studies. Our sample preparation procedure involved solubilization of blood samples with tetramethylammonium hydroxide (TMAH) followed by the derivatization with sodium tetra(n-propyl)borate (NaBPr₄) to promote volatility of mercury species. We thoroughly investigated mercury species stability in the blood matrix during the course of sample treatment and analysis. The method accuracy for quantifying iHg, MeHg, and EtHg was validated using NIST standard reference materials (SRM 955c level 3) and the Centre de Toxicologie du Québec (CTQ) proficiency testing (PT) samples. The limit of detection (LOD) for iHg, MeHg, and EtHg in human blood was determined to be 0.27, 0.12, and 0.16 μg/L, respectively.

Preconditioned iterative methods for diffusion problems with high‐contrast inclusions

This paper is concerned with robust numerical treatment of an elliptic PDE with high‐contrast coefficients, for which classical finite‐element discretizations yield ill‐conditioned linear systems. This paper introduces a procedure by which the discrete system obtained from a linear finite element discretization of the given continuum problem is converted into an equivalent linear system of the saddle‐point type. Three preconditioned iterative procedures—preconditioned Uzawa, preconditioned Lanczos, and preconditioned conjugate gradient for the square of the matrix—are discussed for a special type of the application, namely, highly conducting particles distributed in the domain. Robust preconditioners for solving the derived saddle‐point problem are proposed and investigated. Robustness with respect to the contrast parameter and the discretization scale is also justified. Numerical examples support theoretical results and demonstrate independence of the number of iterations of the proposed iterative schemes on the contrast in parameters of the problem and the mesh size.     

Synthesis and antiviral activity of novel 3-substituted pyrazolinium salts

Chemistry of Heterocyclic Compounds - For the first time, convenient methods for the preparation of pyrazoline N-alkylidene salts based on terpene (camphor, camphorquinone, carvone) ketones, cage...     

Electrocatalytic cascade approach to the synthesis of dihydro-2'H,3H-spiro[1-benzofuran-2,5'-pyrimidines]

Chemistry of Heterocyclic Compounds - Electrocatalytic cascade assembly of benzylidenebarbiturates and cyclohexane-1,3-diones in methanol in the presence of sodium bromide as mediator in an...