Porous poly(bismaleimide-co-divinylbenzene) microspheres as dispersive solid-phase extraction adsorbent coupled to high-performance liquid chromatography for the determination of triazine herbicide residues in vegetable samples.

In this work, monodisperse and nano-porous poly(bismaleimide-co-divinylbenzene) microspheres with large specific surface area (427.6 m2 /g) and rich pore structure were prepared by one-pot self-stable precipitation polymerization of 2,2'-bis[4-(4-maleimidophenoxy) phenyl] propane and divinylbenzene. The prepared poly(bismaleimide-co-divinylbenzene) microspheres were employed as dispersive solid-phase extraction (DSPE) adsorbent for the extraction of triazine herbicides. Under optimized conditions, good linearities were obtained between the peak area and the concentration of triazine herbicides in the range of 1-400 µg/L (R2 ≥ 0.9987) with the limits of detection of 0.12-0.31 µg/L. Triazine herbicides were detected using the described approach in vegetable samples (i.e., cucumber, tomato, and maize) with recoveries of 93.6%-117.3% and relative standard deviations of 0.4%-3.5%. In addition, the recoveries of triazine herbicides remained above 80.7% after being used for nine DSPE cycles, showing excellent reusability of poly(bismaleimide-co-divinylbenzene) microspheres. The adsorption of poly(bismaleimide-co-divinylbenzene) microspheres toward triazine herbicides was a monolayer and chemical adsorption. The adsorption mechanism between triazine herbicides and adsorbents might be a combination of hydrogen bonding, electrostatic interaction, and π-π conjugation. The results confirmed the potential use of the poly(bismaleimide-co-divinylbenzene) microspheres-based DSPE coupled to the high-performance liquid chromatography method for the detection of triazine herbicide residues in vegetable samples.

Bioinspired Two-Phase Synthesis of Gibbosterol A.

The disecosteroid natural product gibbosterol A-which has a 14/5-bicyclic framework, a high oxidation state, and a twisted trans-9,11-epoxy motif-is the first water-soluble 5,10:8,9-disecosteroid. Herein, we report a bioinspired two-phase synthesis of this natural product in only 15 steps from inexpensive ergosterol. In the first (isomerase) phase, the core bicyclic framework is rapidly installed by the skeletal reorganization of ergosterol endoperoxide via a ruthenium-catalyzed dual C-C bond fragmentation. In the second (oxidase) phase, chemoselective, regioselective, and stereoselective redox transformations precisely introduce the requisite oxygenated functional groups. This work demonstrates that the ingenious two-phase synthesis logic that has been applied to terpenes is also a powerful strategy for steroid synthesis.

ß-cyclodextrin-functionalized magnetic graphene oxide for the efficient enrichment of bisphenols in milk and milk packaging.

In this work, ß-cyclodextrin-functionalized magnetic graphene oxide (NiFe2O4@GO@ß-CD) was synthesized and employed as magnetic solid-phase extraction adsorbent for the extraction of bisphenols before high performance liquid chromatography analysis. The modification of ß-cyclodextrin could enhance the adsorption performance of NiFe2O4@GO@ß-CD towards bisphenols through the host-guest interaction and hydrogen-bond interaction. Under the optimal conditions, good linearities between peak area and concentration of bisphenols (1 - 300 µg L-1, r ≥ 0.9989) were obtained with the limits of detection (S/N = 3) in the range of 0.050 - 0.10 µg L-1. The recoveries of bisphenols in milk and milk packaging ranged from 78.0% to 101.6%. Moreover, NiFe2O4@GO@ß-CD showed stable chemical properties and good reusability with the recoveries of bisphenols remained above 80.0% after 12 MSPE cycles. The adsorption characteristics of NiFe2O4@GO@ß-CD towards bisphenols fitted well with the pseudo-second-order kinetic model and Langmuir model. The hydrogen-bond interaction, π-π interaction, host-guest interaction and electrostatic interaction between sorbent and bisphenols played important role during the adsorption process. The developed method showed potential applications for the analysis of trace bisphenols in milk and milk packaging.

Facile room temperature synthesis of a NiFe2O4-based magnetic covalent organic framework for the extraction of tetracycline residues in environmental water samples prior to HPLC.

In this study, a functionalized magnetic covalent organic framework (NiFe2O4@TAPB-TPA) was fabricated with NiFe2O4 nanoparticles as the magnetic core, and 1,3,5-tris(4-aminophenyl)benzene (TAPB) and terephthalaldehyde (TPA) as building blocks by a facile room temperature strategy. Benefitting from the π-π stacking and hydrogen bond interaction, NiFe2O4@TAPB-TPA showed great potential as a magnetic adsorbent for the extraction of tetracyclines (TCs). Under optimal conditions, good linearities (R2 > 0.9990) were obtained between the peak area and TC concentration in the range of 1-500 µg L-1 with limits of detection ranging from 0.09 to 0.26 µg L-1. The intra-day and inter-day relative standard deviations were less than 2.2% and 4.7%, respectively. The established method was successfully applied for the determination of TCs in diverse environmental water samples with satisfactory recoveries in the range of 91.6-102.7%. In addition, NiFe2O4@TAPB-TPA showed good reusability with the recoveries for TCs higher than 73.1% after nine recycles, indicating potential application of NiFe2O4@TAPB-TPA as an ideal adsorbent for the enrichment of TCs.

Triazine-based porous organic polymer as pipette tip solid-phase extraction adsorbent coupled with HPLC for the determination of sulfonamide residues in food samples.

In this work, triazine-based porous organic polymer (TAPT-BPDA) synthesized by simple solvothermal method with stable chemical properties was employed as pipette tip solid-phase extraction (PT-SPE) adsorbent for the extraction of sulfonamides for the first time. Under the optimal conditions, good linearities (1-300 µg L-1, R2 ≥ 0.9987) and low limits of detection (0.10-0.28 µg L-1) were obtained. The recoveries of sulfonamides in meat, egg and milk samples were in the range of 76.1-114.0 %. The prepared TAPT-BPDA showed good reusability with the recoveries of sulfonamides remained above 80.0 % after eight recycles. The adsorption mechanism between SAs and adsorbent might be the combined effects of electrostatic interactions, hydrogen bonding and π-π interactions. The results demonstrated potential applications of a TAPT-BPDA-based PT-SPE-HPLC method for the analysis of trace sulfonamide residues in food samples.

Determination of sulfonamides in milk and egg samples by HPLC with mesoporous polymelamine-formaldehyde as magnetic solid-phase extraction adsorbent.

In this work, magnetic mesoporous polymelamine-formaldehyde composites were synthesized via a facile Schiff base reaction. The magnetic mesoporous polymelamine-formaldehyde composites combined both the properties of mesoporous polymelamine-formaldehyde and the magnetism of NH2 -SiO2 @Fe3 O4 nanoparticles, possessing high specific surface area (150.66 m2 g-1 ) and good magnetism (24.50 emu g-1 ). The magnetic mesoporous polymelamine-formaldehyde composites were employed as magnetic adsorbent for the extraction of sulfonamides. Under optimal conditions, good linearities with correlation coefficients higher than 0.9984 were obtained between peak area and sulfonamides concentration (2-200 µg L-1 ) with limits of detection in the range of 0.33-0.58 µg L-1 . The established method was successfully applied for the determination of sulfonamides in egg and milk samples. The adsorption mechanisms demonstrated that the adsorption of magnetic mesoporous polymelamine-formaldehyde composites toward sulfonamides was a multilayer process, and adsorption kinetics followed the pseudo-second-order model.

Covalent organic framework-LZU1@PEI@Fe3O4-based magnetic dispersive micro-solid phase extraction of tetracyclines from environmental water prior to HPLC analysis.

In this work, COF-LZU1@PEI@Fe3O4 was synthesized by immobilization of COF-LZU1 onto the surface of polyethyleneimine-functionalized Fe3O4 nanoparticles (PEI@Fe3O4) and employed as an adsorbent for magnetic dispersive micro-solid phase extraction of tetracyclines (TCs). COF-LZU1@PEI@Fe3O4 was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and nitrogen adsorption-desorption isotherms analysis. The optimal extraction and desorption conditions were as follows: 15.00 mL sample solution (pH 7.0) extracted with 5.0 mg of adsorbent for 30 min at 30 °C, and then desorbed with 1.50 mL methanol/acetonitrile/0.02 mol L-1 oxalic acid solution (v/v, 1 : 2 : 7). Good linearities were obtained between the peak area and TC concentration ranging from 5-500 µg L-1 with correlation coefficients (R2) higher than 0.9992 and limits of detection lower than 0.51 µg L-1. The relative standard deviations (RSDs) of intra-day and inter-day were less than 5.7% and 7.4%, respectively. The developed method was successfully applied to the determination of TCs in environmental water samples with recoveries in the range of 87.0-113.8% and RSDs less than 5.1%, suggesting great potential of COF-LZU1@PEI@Fe3O4 for efficient extraction and analysis of trace TCs in water samples.

Biogenesis-Guided Synthesis and Structural Revision of Sarocladione Enabled by Ruthenium-Catalyzed Endoperoxide Fragmentation.

Sarocladione is the first 5,10:8,9-diseco-steroid with a 14-membered macrocyclic diketone framework to have been isolated from a natural source. Herein we report a biomimetic synthesis of sarocladione in only two or seven steps from inexpensive, commercially available ergosterol. The key feature of this synthesis was a novel ruthenium-catalyzed endoperoxide fragmentation, which transformed various saturated endoperoxides into olefinic diketones by cleavage of two C-C bonds. This synthesis allowed us to unambiguously determine the structure of sarocladione and provided experimental support for its revised biosynthetic origin. This work also vividly demonstrates that consideration of the biogenesis is a powerful tool for elucidating the structures of natural products.

Divergent Synthesis of Antiviral Diterpenes Wickerols A and B.

Wickerols A and B are diterpene natural products that have a novel fused 6-5-6-6 ring framework and exhibit potent antiviral activity against the H1N1 type A influenza virus. Herein, we report a divergent synthesis of wickerols A and B in 16 and 15 steps, respectively, from commercial sitolactone. The key reactions of the synthesis are a SmI2-mediated intramolecular ketone-allylic acetate reductive cyclization, a Claisen rearrangement, and an intramolecular alkylation/aldol reaction that rapidly assembled the compact tetracyclic core framework in a stereocontrolled manner. The work described herein allowed us to confirm the absolute configurations of wickerols A and B.