Efficient and selective extraction of azamethiphos and chlorpyrifos residues from mineral water and grape samples using magnetic mesoporous molecularly imprinted polymer.

A magnetic mesoporous molecularly imprinted polymers was synthesized on the surface of magnetic nanoparticles silanized with 3-(trimethoxysilyl) propyl methacrylate to introduce reactive methacrylate groups. Subsequently, methacrylic acid monomers were grafted onto the surface of this adsorbent functionalized via polymerization by precipitation. Magnetic mesoporous molecularly imprinted polymer was properly characterized by different techniques and applied as adsorbent in magnetic solid phase extraction for selective determination of two organophosphorus pesticides, azamethiphos and chlorpyrifos, in mineral water and grape samples. After sample preparation optimization, recoveries of 99.56% and 98.86% were obtained for azamethiphos and chlorpyrifos, respectively. The magnetic solid phase extraction coupled to HPLC-UV presented limit of quantification of 5 ng mL-1, linearity ranged of 5 to 1000 ng mL-1, in addition to adequate accuracy, precision and robustness. The pesticides showed stability in the matrix and were satisfactorily quantified in real mineral water and grape samples.

Molecularly imprinted solid-phase extraction coupled with LC-APCI-MS-MS for the selective determination of serum cholesterol.

The assessment of selective molecularly imprinted solid-phase extraction (MISPE) for clean-up and extraction of cholesterol (CHO) from bovine and human serum samples was evaluated. Two molecular imprinted polymers (MIP) based on organic and inorganic/organic (hybrid) materials were obtained and compared regarding recovery and selectivity toward CHO. Optimum chromatographic separation between the CHO and its isobaric compound lathosterol (LATHO) has been achieved within 15 min using an Agilent Poroshell 120 EC-C18 column (120 mm × 3.0 mm, 2.7 µM) and mobile phase consisting of acetonitrile:methanol (8:2, v/v) at a flow rate of 0.6 mL min-1 . Mass spectrometry detection was operated in atmospheric pressure chemical ionization (APCI) (+) mode and the SIM transitions [M - H2 O + H]+ for CHO and LATHO were 364.1 → 161.2 → 95.2 and 364.1 → 95.1 → 81.1 m/z, respectively. The sample preparation could be accomplished within 1 h, and the matrix effect on the MS signal after sample pretreatment did not interfere in the analyses. The method provided a good linear range (0.013-312 µM.) with coefficients of determination of R2  > 0.99, substantial sensitivity (limits of detection of 6.5 nM), good recovery (∼90%), high reproducibility (intraday and interday relative standard deviations less than 15%) and satisfactory accuracy (relative error ranged from -13.46% to 11.54%). The organic MIP showed superior performance compared with the hybrid. Finally, the MISPE procedure followed by LC-APCI-MS-MS analysis showed their suitable applicability to examine CHO and LATHO in serum samples.

Computational contribution to the electrophoretic enantiomer separation mechanism and migration order using modified ß-cyclodextrins.

Capillary electrophoresis (CE) is an extremely effective technique in many kinds of separations, including separation of enantiomers. Some additional techniques may be necessary to determine the enantiomer migration order (EMO) and also the mechanism involved in chiral recognition. This paper reports the development and optimization of a CE method for enantioseparation of racemic mixture of both R- and S-stereoisomers of tramadol (TRM) with a computational contribution for the EMO determination and the responsible mechanisms for chiral distinction. Parameters such as composition and concentration of background electrolyte (BGE) and type and concentration of cyclodextrins (CD) were evaluated. For calculations, a sequential methodology was used, resorting to semiempirical Parametric Model 3 (PM3) followed by calculations accomplished using density functional theory. The best results were obtained with sulfated-ß-CD (s-ß-CD) and carboxymethyl-ß-cyclodextrin (cm-ß-CD) as chiral selector. Calculations show that the inclusion of TRM is not a probable process due to the shape of the TRM molecule and the size CDs cavities. Therefore, the chiral recognition process occurs by the formation of association complexes between modified ß-CD and groups of TRM molecules. The structural analysis of the fragments of complexes at a pH of 10 and a thermodynamic analysis of the complexes' formation process allows determining the EMO. Comparing results obtained experimentally and computationally, it seems that the developed method is adequate for separation of TRM enantiomers and the computational methodology is also adequate to get a sense of the system at a molecular level.

A shared biosynthetic pathway for botcinins and botrylactones revealed through gene deletions.

Isotopic labelling experiments and the study of mutants with disrupted genes encoding botcinic acid have revealed a common link in the biosynthesis of the polyketide toxins excreted by Botrytis cinerea: botcinins and botrylactones. Furthermore, the results reported here shed light on the origin of the starter unit, thereby solving a long-standing mystery in the biosynthesis of botcinins.