Simultaneous determination of arsenite and arsenate in arsenic trioxide injection by dual detection ion chromatography

This paper describes a rapid method to determine arsenite assay and arsenate impurity in Arsenic Trioxide Injection using a single conductivity detector. The arsenite assay was determined in a non-suppressed conductivity detection mode and arsenate impurity was quantified in a suppressed conductivity detection mode. Dual-conductivity detections were enabled by valve switching and time programming. The method was validated with respect to specificity, linearity, precision, accuracy, stability, and limit of quantification. The limit of detection and quantification for arsenite were 0.855 mg/L and 2.593 mg/L, and 0.044 mg/L and 0.133 mg/L for arsenate, respectively.     

Bromenium‐Catalysed Tandem Ring Opening/Cyclisation of Vinylcyclopropanes and Vinylcyclobutanes: A Metal‐Free [3+2+1]/[4+2+1] Cascade for the Synthesis of Chiral Amidines and Computational Investigation

We present a detailed study of a [3+2+1] cascade cyclisation of vinylcyclopropanes (VCP) catalysed by a bromenium species (Br^δ+? X^δ?) generated in situ, which results in the synthesis of chiral bicyclic amidines in a tandem one‐pot operation. The formation of amidines involves the ring‐opening of VCPs with Br? X, followed by a Ritter‐type reaction with chloramine‐T and a tandem cyclisation. The reaction has been further extended to vinylcyclobutane systems and involves a [4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo[4.3.0]‐, ‐[4.3.1]‐ and ‐[4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has been put forth to account for the formation of the products and the observed stereoselectivity. We propose the existence of a π‐stabilised homoallylic carbocation at the cyclopropane carbon as the reason for high stereoselectivity. DFT studies at B3LYP/6‐311+G** and M06‐2X/6‐31+G* levels of theory in gas‐phase calculations suggest the ring‐opening of VCP is initiated at the π‐complex stage (between the double bond and Br? X). This can be clearly perceived from the solution‐phase (acetonitrile) calculations using the polarisable continuum model (PCM) solvation model, from which the extent of the ring opening of VCP was found to be noticeably high. Studies also show that the formation of zero‐bridge bicyclic amidines is favoured over other bridged bicyclic amidines. The energetics of competing reaction pathways is compared to explain the product selectivity.     

Computational prediction of ionic liquid 1-octanol/water partition coefficients

Wet 1-octanol/water partition coefficients (log?K(ow)) predicted for imidazolium-based ionic liquids using adaptive bias force-molecular dynamics (ABF-MD) simulations lie in excellent agreement with experimental values. These encouraging results suggest prospects for this computational tool in the a priori prediction of log?K(ow) values of ionic liquids broadly with possible screening implications as well (e.g., prediction of CO(2)-philic ionic liquids).     

In silico free energy predictions for ionic liquid-assisted exfoliation of a graphene bilayer into individual graphene nanosheets

Free energies for graphene exfoliation from bilayer graphene using ionic liquids based on various cations paired with the bis(trifluoromethylsulfonyl)imide anion were determined from adaptive bias force-molecular dynamics (ABF-MD) simulation and fall in excellent qualitative agreement with experiment. This method has notable potential as an a priori screening tool for performance based rank order prediction of novel ionic liquids for the dispersion and exfoliation of various nanocarbons and inorganic graphene analogues.     

Synthesis of optically pure 2,3,4-trisubstituted tetrahydrofurans via a two-step sequential Michael-Evans aldol cyclization strategy: total synthesis of (+)-magnolone

Synthesis of optically pure 2,3,4-trisubstituted tetrahydrofurans is described employing a two-step Michael-Evans aldol cyclization strategy. The approach is successfully applied for the total synthesis of furano lignan natural product (+)-magnolone.     

2,2‐Bis(ethoxycarbonyl)vinyl (BECV) as a Versatile Amine Protecting Group for Selective Functional‐Group Transformations

A 2,2‐Bis(ethoxycarbonyl) vinyl‐ (BECV) group was used for the selective protection of amines at room temperature in the presence of potentially interfering functional groups such as OH, SH, COOH as well as other NH₂ groups. Several functional group transformations such as esterification, O‐alkylation, O‐acylation, N‐alkylation, N‐acylation, S‐alkylation can selectively be carried out in the presence of the BECV group. The selective deprotection of the BECV group was achieved in a short time using ethylenediamine at room temperature while several other functional groups such as benzoate, aliphatic esters, amides and ethers remain intact. The BECV group shows orthogonal stability against the common protecting groups such as Fmoc, Cbz and Boc.     

Catalyst-free one-pot synthesis of 2,4,5-tri- and 1,2,4,5-tetrasubstituted imidazoles

The present work emphasizes catalyst-free 2,4,5-tri- and 1,2,4,5-tetra substituted imidazole synthesis using diversified aldehydes with benzil, ammonium acetate, or amines. Ammonium acetate plays a vital role as a reactant catalyst by dissociating into acetic acid to afford imine and diamine formation to ascertain the 2,4,5-tri- and 1,2,4,5-tetra substituted imidazoles. The key advantages of the current approach are efficient, greener, eco-friendly, and facile, with moderate to excellent yield in shorter reaction time at the temperature of 80°C. Ethanol:water as a solvent makes the reaction process eco-friendly. Overall, the described approach offers a promising route for the efficient and sustainable synthesis of substituted imidazoles, which have a wide range of applications in various fields, including pharmaceuticals, agrochemicals, and materials science.     

Investigation on mechanical properties of some thiourea complex crystals: Important nonlinear optical materials

In this work the authors have grown good quality single crystals of zinc thiourea sulphate, bis thiourea cadmium acetate, bis zinc thiourea acetate and bis thiourea zinc chloride were grown from slow evaporation solution growth method at ambient temperature and studied their mechanical properties. The crystal system and lattice parameters were confirmed by powder X-ray diffraction analysis. Vickers microhardness of the grown crystals was investigated by using Leitz-Wetzlar (Miniload 2) hardness tester up to an applied load of 120 g. It was observed that, upto 40 g applied load the hardness of the grown crystals increases with increasing the load and thereafter it is practically independent of the indentation load. Meyer's law and Hays–Kendall's law fail to explain the observed load variations. But the variation could be satisfactorily explained by PSR model proposed by Li and Bradt. Classification of cracks and their transition from Palmqvist to median types is explained. The average value of fracture toughness, brittleness index, Young's modulus and yield strength were calculated using expressions for Palmqvist and median types of cracks. Anisotropic nature of the grown crystals was studied using Knoop indentation technique.