Use of solid-phase extraction, reverse osmosis and vacuum distillation for recovery of aromatic sulfonic acids from aquatic environment followed by their determination using liquid chromatography-electrospray ionization tandem mass spectrometry

Three different sample preparation techniques (i) solid-phase extraction, (ii) reverse osmosis and (iii) vacuum distillation have been investigated and the recoveries were compared for determination of highly water-soluble benzene and stilbene sulfonic acids in aqueous environment by liquid chromatography with photodiode array (PDA) and electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The recoveries were quite high using vacuum distillation (>90%) compared to solid phase extraction and reverse osmosis. The negative ion ESI mass spectra containing the peaks of quasimolecular ion [M-H]- allow the molecular mass determination of unknown compounds whereas the structures were proposed using fragments obtained from MS/MS analysis of [M-H]- ions. At lower fragmentation voltages only the quasimolecular ion [M-H]- was observed and as fragmentation voltages increased, it led to the formation of fragment ions corresponding to [M-H-SO3]-, [M-H-SO2]-, and SO3-. The detection limits were 1-28 microg/L with LC-ESI-MS. The sample collected from wastewater treatment plant was found to contain 21.1, 13.3, 12.1, 41.8 and 9.9 microg/L of cis-4,4(l)-diaminostilbene-2,2(l)-disulfonic acid (cis-DASDA), trans-4,4(l)-diaminostilbene-2,2(l)-disulfonic acid (trans-DASDA), 3-amino acetanilide-4-sulfonic acid (3-AASA), 4-chloroaniline-2-sulfonic acid (4-CASA), 2-chloroaniline-5-sulfonic acid (2-CASA), respectively.     

Synthesis of beta-hydroxysulfides from alkenes under supramolecular catalysis in the presence of beta-cyclodextrin in water

An environmentally benign and highly efficient procedure has been developed for the direct one-pot synthesis of beta-hydroxysulfides in good yields under neutral conditions from alkenes and thiophenols in the presence of aerial oxygen using beta-cyclodextrin in water. This protocol tolerates a wide variety of functional groups or substrates and does not require the use of either acid or base catalysts. beta-Cyclodextrin can be recovered and reused for a number of runs without any loss of activity.     

The empirical performance of a polynomial algorithm for constrained nonlinear optimization

In [6], a polynomial algorithm based on successive piecewise linear approximation was described. The algorithm is polynomial for constrained nonlinear (convex or concave) optimization, when the constraint matrix has a polynomial size subdeterminant. We propose here a practical adaptation of that algorithm with the idea of successive piecewise linear approximation of the objective on refined grids, and the testing of the gap between lower and upper bounds. The implementation uses the primal affine interior point method at each approximation step. We develop special features to speed up each step and to evaluate the gap. Empirical study of problems of size up to 198 variables and 99 constraints indicates that the procedure is very efficient and all problems tested were terminated after 171 interior point iterations. The procedure used in the implementation is proved to converge when the objective is strongly convex.Supported in part by the Office of Naval Research under Grant No. N00014-88-K-0377 and Grant No. ONR N00014-91-J-1241.     

A facile and stereoselective synthesis of the C-2 epimer of (+)-deacetylanisomycin

A short, simple and efficient synthesis of the C-2 epimer of (+)-deacetylanisomycin starting from d-mannitol, utilizing an epoxide opening with a Grignard reagent and acid catalysed unusual intramolecular 5-endo-tet cyclization as key steps has been reported.     

Stereoselective synthesis of (−)-tetrahydrolipstatin via a radical cyclization based strategy

An efficient and flexible approach for the total synthesis of (−)-tetrahydrolipstatin is described. The main features of the synthetic strategy are a stereocontrolled radical cyclization and the successful utilization of commercially available S-malic acid.     

Design,Synthesis, and Biological Evaluation of 2‐(4‐Aminophenyl)benzothiazole Analogues as Antiproliferative Agents

A series of 28 novel 2‐(4‐aminophenyl)benzothiazole analogues have been synthesized and characterized using various analytical techniques like ¹H NMR, ¹³C NMR, electrospray ionization mass spectrometry, and IR and bioevaluated for their antiproliferative activity over a group of three human cancer cell lines, namely, lung cancer (A549), cervical cancer (HeLa), and breast cancer (MDA‐MB‐231), using sulforhodamine B assay method. Few synthesized molecules ( 5a , 5c , 5d , 5f , 7b , and 7j ) displayed effective growth inhibition (GI₅₀) activity against the tested human cancer cell lines at lower micromolar concentration (GI₅₀) values in the range 0.2–1.7 μM. Noticeably, compound 7b exhibited reasonable activity in all three cancer cell lines in the GI₅₀ range 0.55–1.2 μM. Further, when 7b was screened for tubulin polymerization inhibition, it exhibited more than 55% inhibition at concentration of 5.0 μM. The molecular docking simulations supported the molecular interactions of the derivatives with the targeted receptor. These derivatives may serve as lead structures for development of potential anticancer drug candidates, and 7b might act as a potential microtubule polymerization inhibitor.     

The COVID19-NMR Consortium: A Public Report on the Impact of this New Global Collaboration

The outbreak of COVID-19 in December 2019 required the formation of international consortia for a coordinated scientific effort to understand and combat the virus. In this Viewpoint Article, we discuss how the NMR community has gathered to investigate the genome and proteome of SARS-CoV-2 and tested them for binding to low-molecular-weight binders. External factors including extended lockdowns due to the global pandemic character of the viral infection triggered the transition from locally focused collaborative research conducted within individual research groups to digital exchange formats for immediate discussion of unpublished results and data analysis, sample sharing, and coordinated research between more than 50 groups from 18 countries simultaneously. We discuss key lessons that might pertain after the end of the pandemic and challenges that we need to address.     

Isolation of Homo-/Mixed-Valence Ag12, Ag29, and Ag8 Clusters Stabilized by Cyclic Alkyl(amino) Carbene-Anchored Monoanionic Phosphorus Ligand

Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag₁₂Cl₃, Ag₂₉, and Ag₈ cores [((cAAC)P)₆Ag₁₂Cl₃](OTf)₃ ( 1 ), [((cAAC)P)₆Ag₂₉] ( 2 ), and [((cAAC)P)₄Ag₈] ( 3 ) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP⁻) as the π-accepting stabilizing ligand. The average diameters of Ag NCs 1 , and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P⁻) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P−B(NⁱPr₂)₂ through cleavage of the P−B bond with the help of a triflate anion (OTf⁻) as a weak nucleophile. Equivalent number of the (cAAC)P⁻ anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)₂P₂ leading to the generation of Ag⁰ ions in solution for the formation of the unprecedented mixed-valence Ag NC 2 . Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf₂. The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1 – 3 , further providing a three- ( 1 , 2 )/two- ( 3 ) fold stand. The Ag₁₂Cl₃ NC ( 1 ) with a tricationic core [Ag^I₁₂Cl₃] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag₂₉ ( 2 ) and Ag₈ ( 3 ) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag⁰ at room temperature.