p‐TSA Catalyzed Synthesis of 2,4,5‐Triarylimidazoles from Ammonium Heptamolybdate Tetrahydrate in TBAI

A one‐pot synthesis of 2,4,5‐trisubstituted imidazoles from 1,2‐diketone or α‐hydroxy ketone, aldehyde and ammonium heptamolybdate tetrahydrate in an inexpensive and readily available ionic liquid, tetrabutylammonium iodide (TBAI) in molten state using catalytic amounts of p‐TSA has been described.     

Highly efficient polymer‐stabilized palladium heterogeneous catalyst: Synthesis,characterization and application for Suzuki–Miyaura and Mizoroki–Heck coupling reactions

A suitable approach to stabilize palladium nanoparticles (Pd NPs), with an average diameter of 3–4 nm, on magnetic polymer is described. A new magnetic polymer containing 4′‐(4‐hydroxyphenyl)‐2,2′:6′,2″‐terpyridine (HPTPy) ligand was prepared by the polymerization of itaconic acid (ITC) as a monomer and trimethylolpropane triacrylate (TMPTA) as a cross‐linker and fully characterized. Pd NPs embedded on the magnetic polymer were successfully applied in Suzuki–Miyaura and Mizoroki–Heck coupling reactions under low palladium loading conditions, and provided the corresponding products with excellent yields (up to 98%) and high catalytic activities (TOF up to 257 hr^?1). Also, the catalyst can be easily separated and reused for at least consecutive five times with a small drop in catalytic activity.     

A new strategy to design a graphene oxide supported palladium complex as a new heterogeneous nanocatalyst and application in carbon–carbon and carbon‐heteroatom cross‐coupling reactions

The palladium nanoparticles were successfully stabilized with an average diameter of 6–7 nm through the coordination of palladium and terpyridine‐based ligands grafted on graphene oxide surface. The graphene oxide supported palladium nanoparticles were thoroughly characterized and applied as an efficient heterogeneous catalyst in carbon–carbon (Suzuki‐Miyaura, Mizoroki‐Heck coupling reactions) and carbon–heteroatom (C‐N and C‐O) bond‐forming reactions. The catalyst was simply recycled from the reaction mixture and was reused consecutive four times with small drop in catalytic activity.     

Exploring and modeling the ion mobility spectrometry of perindopril: Example of protonation-dissociation reactions in large molecules

The current research is constructed for considering the chemical ionization and dissociation of perindopril in the positive mode of corona discharge ion mobility spectrometry. Four product ion peaks are observed in the ion mobility spectrum of perindopril erbumine at the cell temperature of 473 K. These peaks are assigned through the obtained intensity variation analysis in the ion mobility spectra over the elapsed time accompanied by the calculations backed by the validated density functional theory (DFT). In this regard, the most stable ionic species associated with each peak and the corresponding reliable generation pathways are found by the well-confirmed meta hybrid density functional method, M06-2X. The peaks are assigned to the protonated perindopril and its dissociation products, including counter ion and the related fragment ions. However, the structures of the neutral perindopril in the gas phase are thoroughly assessed to find a more stable one. The predicted chemical ionization products by the theory are in excellent agreement with our presented experiment here. Theoretical evaluations demonstrated that the production of a fragment by dissociation process occurs when perindopril gets a proton from the ionization region. Also, without protons, there is no dissociation process. Therefore, our mechanism investigated here is the proton transfer one. All possible sites of perindopril are considered theoretically for protonation along with their possible reactions. In addition to the computed PES, the assigned ions for obtained spectra are confirmed by the computed equilibrium constants and rate constants. Our theoretical results show that the peak of the main fragment is for M-CH₃CH₂OH produced by a reaction pathway involving no barrier. This study opens new perspectives in interpreting large molecules spectra for future studies.     

Existence of energy maximizing vortices in a three-dimensional quasigeostrophic shear flow with bounded height

The existence of an energy maximizer relative to a class of rearrangements of a given function is proved. The maximizers are stationary and stable solutions of the quasigeostrophic equation, which governs the time evolution of large-scale three-dimensional geophysical flow in a vertically bounded domain. The background flow is unidirectional, with linear horizontal shear. The theorem proved implies the existence of a family of stationary and stable vortices that rotate in the same direction as the background shear. It extends an earlier theorem by Burton and Nycander, which is valid for a vertically unbounded domain.     

Direct conversion of thiols and disulfides into sulfonamides

The H₂O₂-ZrCl₄ reagent system is used as a new and efficient reagent for the conversion of thiols and disulfides into sulfonamides. The protocol offers several advantages such as excellent yields of products and extremely fast reactions at room temperature. The reagent system is very easy to handle and is environmentally safe and economical.     

High-resolution iterative frequency identification for NMR as a general strategy for multidimensional data collection

We describe a novel approach to the rapid collection and processing of multidimensional NMR data: "high-resolution iterative frequency identification for NMR" (HIFI-NMR). As with other reduced dimensionality approaches, HIFI-NMR collects n-dimensional data as a set of two-dimensional (2D) planes. The HIFI-NMR algorithm incorporates several innovative features. (1) Following the initial collection of two orthogonal 2D planes, tilted planes are selected adaptively, one-by-one. (2) Spectral space is analyzed in a rigorous statistical manner. (3) An online algorithm maintains a model that provides a probabilistic representation of the three-dimensional (3D) peak positions, derives the optimal angle for the next plane to be collected, and stops data collection when the addition of another plane would not improve the data model. (4) A robust statistical algorithm extracts information from the plane projections and is used to drive data collection. (5) Peak lists with associated probabilities are generated directly, without total reconstruction of the 3D spectrum; these are ready for use in subsequent assignment or structure determination steps. As a proof of principle, we have tested the approach with 3D triple-resonance experiments of the kind used to assign protein backbone and side-chain resonances. Peaks extracted automatically by HIFI-NMR, for both small and larger proteins, included approximately 98% of real peaks obtained from control experiments in which data were collected by conventional 3D methods. HIFI-NMR required about one-tenth the time for data collection and avoided subsequent data processing and peak-picking. The approach can be implemented on commercial NMR spectrometers and is extensible to higher-dimensional NMR.     

Kinetic studies and mechanism on the permanganic oxidation of L‐Glutamine in strong acid medium in the presence and absence of Silver (I)

The kinetic study and mechanism of the permanganic oxidation of L‐glutamine in sulfuric acid has been carried out both in the absence and presence of silver (I) using a spectrophotometric technique. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. The overall rate expression for the oxidation may be written as In the presence of silver (I) the rate law is The reaction appears to involve an acid catalyzed and data showed role of water molecules in the rate‐determining step is proton transfer which satisfies Bunnett's theory. A mechanism satisfying the various kinetic parameters has been proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 95–102, 1999     

Application of graphene nanoplatelets silica composite,prepared by sol–gel technology,as a novel sorbent in two microextraction techniques

In this study, the application of a novel nanomaterial composite was investigated in two microextraction techniques of solid‐phase microextraction and a needle trap device in a variety of sampling conditions. The optimum sampling temperature and relative humidity were 10°C and 20%, respectively, for both techniques with two sorbents of graphene/silica composite and polydimethyl siloxane. The two microextraction techniques with the proposed sorbent showed recoveries of 95.2 and 94.6% after 7 days. For the needle trap device the optimums desorption time and temperature were 3 min at 290°C and for SPME these measures were 1 and 1.5 min at 240–250°C for the graphene/silica composite and polydimethyl siloxane, respectively. The relative standard division obtained in inter‐ and intra‐day comparative studies were 3.3–14.3 and 5.1–25.4, respectively. For four sample the limit of detection was 0.021–0.25 ng/mL, and the limit of quantitation was 0.08–0.75 ng/mL. The results show that the graphene/silica composite is an appropriate extraction media for both techniques. Combining an appropriate sorbent with microextraction techniques, and using these in conjunction with a sensitive analytical instrument can introduce a strong method for sampling and analysis of occupational and environmental pollutants in air.