Residues and dissipation of guadipyr in rice ecological system

A modified QuEChERs method with liquid chromatography-tandem mass spectrometry for analysis of guadipyr residue and dissipation in rice matrices, paddy soil and paddy water was developed and validated. Mean recoveries and relative standard deviations in paddy soil, paddy water, rice plant, rice straw, rice hull and husked rice matrices at three spiking levels were 83.1–116.5% and 1.6–9.5%, respectively. The half-life of guadipyr was determined in 2 years at three different field sites in China via a dissipation experiment. The half-lives of guadipyr in paddy water were 0.22–0.37 days, 0.24–3.33 days in paddy soil and 0.44–1.90 days in rice plant. The terminal residues of guadipyr ranged from ND (concentrations of guadipyr were below limit of detection) to 50 μg kg^?1 in paddy soil, 10–470 μg kg^?1 in rice hull, ND70 μg kg^?1 in husked rice and ND to 110 μg kg^?1 in rice straw. The results would be helpful in fixing maximum residue limit of guadipyr, a new insecticide, in rice.     

Existence and regularity of positive solutions of a degenerate elliptic problem

Existence and regularity of positive solutions of a degenerate elliptic Dirichlet problem of the form in Ω, on , where Ω is a bounded smooth domain in , , are obtained via new embeddings of some weighted Sobolev spaces with singular weights and . It is seen that and admit many singular points in Ω. The main embedding results in this paper provide some generalizations of the well‐known Caffarelli–Kohn–Nirenberg inequality.     

Trifluoromethyl Derivatives of Elusive Fullerene C98

Data concerning the isomeric composition of C₉₈ and the chemistry of C₉₈ derivatives are scarce due to very low abundance of C₉₈ in the fullerene soot. Trifluoromethylation of C₉₈-containing mixtures followed by HPLC separation of CF₃ derivatives and single crystal X-ray diffraction study resulted in structural characterization of four compounds C₉₈(248)(CF₃)_18/20, C₉₈(116)(CF₃)₁₈, and C₉₈(120)(CF₃)₂₀. To date, these compounds represent the largest fullerenes isolated as CF₃ derivatives with experimentally determined molecular structures. The addition patterns of C₉₈(CF₃)_18/20 are discussed in detail revealing the stabilizing factors, such as isolated double C=C bonds and benzenoid rings on C₉₈ fullerene cages. A detailed comparison with the addition patterns of the known C₉₈Cl_n allowed us to contribute to the better understanding the chemistry of elusive C₉₈ fullerene.     

Visible-light-mediated selective thiocyanation/ipso-cyclization/oxidation cascade for the synthesis of thiocyanato-containing azaspirotrienediones

A visible-light-mediated metal-free thiocyanate radical addition/ipso-cyclization/oxidation cascade reaction for the synthesis of thiocyanato-containing azaspirotrienediones from N-phenylpropynamides is described. Cheap and readily available ammonium thiocyanate was used as a precursor to the thiocyanate free radical, which undergoes a radical addition reaction with the alkyne, followed by selective ipso-cyclization and oxidation to afford the dearomatized products. No product of ortho-cyclization was detected. The reaction completes the synthesis of C–S, C–C, and CO bonds in one pot, with abundant and renewable air oxygen as the sole sacrificial reagent and oxygen source.