Synthesis of nanosized (Li,La){Ti,Nb,Ta}O3 particles using the sol-gel method

Nanoparticles of lithium titanate, niobate, and tantalate with the structure of defect perovskite were synthesized using the Pechini method. The formation of single-phase lithium lanthanum titanate was shown to occur at 700°C. The average particle size was d ～ 15 nm. For niobate and tantalate, the formation of the perovskite phase started at 900°C; the average particle size in this case was 50–100 nm.     

Solid-phase spectrophotometric iodometric determination of nitrite and selenium(IV) using a polymethacrylate matrix

Procedures for the iodometric solid-phase spectrophotometric determination of nitrite and selenium( IV) using a polymethacrylate matrix are proposed. The procedures are based on the reaction of nitrite and selenium(IV) with iodine in an acidic medium with the release of free iodine in amounts equivalent to those of the substances to be determined, extraction of the iodine formed with a polymethacrylate matrix, and measurement of absorbance of the matrix at 370 nm. The developed procedures ensure the determination of 0.01–0.12 mg/L of nitrite and 0.05–0.40 mg/L of selenium(IV) with limits of detection of 0.005 and 0.03 mg/L, respectively. It was shown that the proposed procedures can be applied to the determination of selenium(IV) in mineral water and nitrites in vegetables and soil.     

Stability of reinforced cylindrical shells under combined loading

A new approach to solving buckling problems for ribbed cylindrical shells subject to longitudinal force and pressure is proposed. Results for shells reinforced with stringers and rings are presented     

Polymerization of isoprene with cobalt catalysts

The polymerization of isoprene with catalytic systems efficient for the cis polymerization of butadiene, i.e., cobalt 2-ethyl hexanoate-diethylaluminum chloride and cobalt 2-ethyl hexanoate-ethylaluminum sesquichloride, is studied. The catalysts are obtained via in situ mixing of the components or at a reduced temperature (0–5°C) in the presence of a small amount of the monomer. In situ polymerization proceeds with an induction period, whose duration depends on the polymerization conditions, or without this period if a preformed catalyst is used. In each case, the resulting polymer is characterized by a mixed microstructure with a predominant content of cis-1,4 units and 3,4 units.     

Third Generation Buchwald Precatalysts with XPhos and RuPhos: Multigram Scale Synthesis,Solvent-Dependent Isomerization of XPhos Pd G3 and Quality Control by 1H- and 31P-NMR Spectroscopy

The third generation Buchwald precatalysts Pd(ABP)(Phos)(OMs) (also known as Phos Pd G3)) with XPhos and RuPhos were prepared in multigram scale by a modified procedure (ABP = fragment of C-deprotonated 2-aminobiphenyl, XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl, RuPhos = 2-dicyclohexylphosphino-2′,6′-diisopropoxybiphenyl, OMs⁻ = CH₃SO₃⁻). The ¹H- and ³¹P-NMR spectra of the title complexes and some impurities, measured by various 1D and 2D techniques, were analyzed in detail. The solvent-dependent isomerization of Pd(ABP)(XPhos)(OMs) was studied by NMR, and the X-ray structures of two isomers were determined. The impurities in precatalysts, such as Pd(ABP)(HABP)(OMs) (HABP—neutral 2-aminobiphenyl coordinated to Pd²⁺ in N-monodentate mode) and PdCl₂(XPhos)₂, were identified and characterized by single crystal X-ray diffraction. A simple method for the quick quality control (QC) of the precatalysts, suitable for routine use, was proposed. The method was based on the assessment of the impurity content on the basis of the ¹H-NMR spectra analysis.