HighlightsAn analytical methodology based on DLLME-LIBS combination is presented. This method is aimed to improve sensitivity of LIBS in liquids analysis. DLLME-LIBS resulted more efficient than SDME-LIBS for enhancing LIBS sensitivity.
t r a c tA rapid and efficient Dispersive Liquid-Liquid Microextraction (DLLME) followed by Laser-Induced Breakdown Spectroscopy detection (LIBS) was evaluated for simultaneous determination of Cr, Cu, Mn, Ni and Zn in water samples. Metals in the samples were extracted with tetrachloromethane as pyrrolidinedithiocarbamate (APDC) complexes, using vortex agitation to achieve dispersion of the extractant solvent. Several DLLME experimental factors affecting extraction efficiency were optimized with a multivariate approach. Under optimum DLLME conditions, DLLME-LIBS method was found to be of about 4.0-5.5 times more sensitive than LIBS, achieving limits of detection of about 3.7-5.6 times lower. To assess accuracy of the proposed DLLME-LIBS procedure, a certified reference material of estuarine water was analyzed.
The thermal 1,3-dipolar cycloaddition of unactivated azomethine ylides derived from allylamine and aromatic or heteroaromatic aldehydes with maleimides and 1,1- and 1,2-bis(phenylsulfonyl)ethylene affords endo-2,5- trans cycloadducts in moderate to good yields. DFT calculations provide evidence that the diastereoselectivity observed depends on the isomerization between S- and W-ylides according to Curtin-Hammett's principle. DFT calculations also explain the different diastereomeric ratio observed for 2-pyridyl and 2-thienyl derivatives in which the isomerization is not possible due to the competitiveness between isomerization barrier and the rate-limiting step (ylide formation barrier). This methodology is applied to the diastereoselective synthesis of a tricyclic thrombin inhibitor.
Primary allylic amines with enantiomeric excesses from 97 to >99% were prepared by asymmetric transfer hydrogenation of α,β-unsaturated N-(tert-butylsulfinyl)ketimines followed by removal of the sulfinyl group. The effect caused by different substituents at the C═C bond and at the iminic carbon atom on the chemoselectivity of the reduction was studied. The desired enantiomer of the final allylic amine can be synthesized by choosing the sulfinyl group with the appropriate absolute configuration.
Structurally diverse novel 1,4-benzodiazepine analogues related to selective CCKA antagonist MK-329, and CCKB antagonists L-365,260 and YM022 are prepared via palladium-catalyzed three component domino reactions involving allenylation-carbonylation-anion capture in onepot cascade protocol in good to excellent yields.
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