One-pot synthesis of novel (E)-3-(3,8a-dihydro-2H-oxazolo[3,2-a]pyridin-2-ylidene)chroman-2-one derivatives

An efficient synthetic procedure for the preparation of novel (E)-3-(3,8a-dihydro-2H-oxazolo[3,2-a]pyridin-2-ylidene)chroman-2-one derivatives was developed. A sequential one-pot, two-step tandem reaction starting from 3-(2-bromoacetyl)-2H-chromen-2-one derivatives synthesized, pyridine, and naphthols in the presence of triethylamine proceeded smoothly in acetonitrile under reflux conditions. In this process, 2-oxo-2H-chromen-3-yl)ethyl)pyridinium bromide derivatives as intermediate produced in situ, followed by Michael addition of naphthoxide anion and intramolecular cylization, resulted the corresponding products in good to high yields. All of the compounds were obtained in high purity without any use of more purification.     

Negishi coupling: an easy progress for C–C bond construction in total synthesis

Negishi cross-coupling reactions were used extensively in total synthesis. The expansion of substrate scope, the development of mild reaction conditions, the advancement of the methods to improve the stereo- and regio-selectivity of carbon–carbon bond formation, the maturity of a large number of sequential processes, and the development of non-toxic reactions signify the importance of Negishi coupling. The following review illustrates a strategic role of this reaction in constructing carbon–carbon bonds in the recent total synthesis of natural products.     

Electromagnetic fields with 217 Hz and 0.2 mT as hazardous factors for tubulin structure and assembly (in vitro study)

Nowadays exposure to extremely low frequency electromagnetic fields (ELF-EMFs) is an unavoidable fact in human societies. In spite of destructive effects of ELF-EMF such as impression on short-term memory and cognitive performances, neuroprotective and neurogeneration effects of ELF-EMF have been reported. On the other hand, microtubule (MT) proteins, the dynamic cytoskeleton proteins that are mostly located in axons, are able to produce local EMFs and possess key role in memory formation and consciousness. Therefore, MTs have strong potential to be affected by exogenous ELF-EMFs. In the present study, decline of MT polymerization was shown by transmission electron microscopy images and turbidimetry method after exposure to ELF-EMFs with 50, 100, and 217 Hz frequencies at 0.2 mT intensity. Circular dichroism and 8-anilino-1-naphthalenesulfonate (ANS) fluorometry were used to demonstrate the MT secondary and third structural changes. Decrement of MT polymerization through disruption of tubulin native structure, and increasing the β-sheets and random coils were observed in all exposure conditions. Therefore, ELF-EMFs with 50, 100, and specially 217 Hz frequencies at 0.2 mT could lead to disruption of MT functions in the neural cells.     

Mathematical modeling and validation of mass transfer phenomenon in homogeneous charge compression ignition engines based on a thermodynamic multi zone model

The main purpose of the current study is mathematical modelling and validation of mass transfer phenomenon in homogeneous charge compression ignition engines. A validated multi-zone model coupled to a semi-detailed chemical kinetics is used to predict homogeneous charge compression ignition combustion and emissions. Heat and Mass transfer submodels are linked to the multi-zone model. Bulk flow and diffusion mass transfer between zones are considered. The results indicate that the diffusion mass transfer is negligible in homogeneous charge compression ignition engines. Bulk flow mass transfer plays a critical role in homogeneous charge compression ignition simulation and applying it in the multi-zone model leads to accurate prediction of the start of combustion, peak pressure and exhaust emissions. The results show that the maximum error changes from 90% to 5% in carbon monoxide prediction and from 98% to 14% in unburned hydrocarbons prediction, using the mass transfer submodel.     

Theoretical investigations on electronics structure and chemical bonding on iridathiabenzene and iridaoxabenzene

The electronic structure and properties of the iridathiabenzene and iridaoxabenzene isomers have been investigated using the hybrid density functional mpw1pw91 theory. The energetic aspect shows that trans-ortho-isomer is the most stable isomer. This is compatible with principles of minimum energy and minimum polarizability. Molecular orbital analysis shows a linear correlation between hardness and anisotropic polarizability values for Iridathiabenzene and iridaoxabenzene isomers. The structural and natural bond analysis (NBO) results illustrate electronic delocalization in these rings. Also, the study of non linear optical properties of these molecules indicate a good correlation between β_tot and E(HOMO) for iridathiabenzene. The results from natural bond orbital (NBO) analysis have provided insights into Ir—ligand, P—H_apical and P—H_basal bonding.     

PEG-N2O4: An Efficient Nitrating Agent for the Selective Mono- and Dinitration of Phenols Under Mild Conditions

N₂O₄ was easily impregnated on polyethyleneglycol to give a stable reagent. The polyethyleneglycol-N₂O₄ (PEG-N₂O₄) system was used as an effective nitrating agent for the nitration of phenols. Mono- and dinitrophenols can be obtained via direct nitration of phenols in the presence of PEG-N₂O₄ at room temperature in moderate to high yields.     

Magnetic dispersive solid phase extraction using modified magnetic multi-walled carbon nanotubes combined with electrothermal atomic absorption spectrometry for the determination of selenium

A novel magnetic dispersive solid phase extraction method using magnetic multi-walled carbon nanotubes modified with 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (bismuthiol II) (MMWCNTs@Bis) as the sorbent was developed for the separation and preconcentration of inorganic selenium (IV) prior to its determination by electrothermal atomic absorption spectrometry. The prepared MMWCNTs@Bis sorbent was characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer and X-ray diffraction. Total selenium was determined after reduction of Se(VI) to Se(IV) by addition of hydrochloric acid and heating the mixture in a boiling water bath. Se(VI) concentration was determined from the difference between the amounts of total selenium and Se(IV). Under the optimised experimental conditions, an enhancement factor of 196 and a detection limit (based on 3S_b/m) of 0.003 µg L^?1 was obtained for aqueous samples. The relative standard deviation at 0.1 µg L^?1 concentration level of Se(IV) (n = 6) was found to be 5.2 and 7.7% for intra- and inter-day analysis, respectively. The method was successfully applied to the determination of inorganic selenium species in water and total selenium in food samples.     

Singlet–triplet energy differences in divalent five membered cyclic conjugated Arduengo-type carbenes XC<Subscript>2</Subscript>HN<Subscript>2</Subscript>M (M = C,Si, Ge,Sn, and Pb; X = F,Cl, Br,and I)

Singlet-triplet energy differences in Arduengo-type carbenes XC₂HN₂C compared and contrasted with their sila, germa, stana and plumba analogues; at B3LYP/6-311++G** level of theory. Free Gibbs energy differences between triplet (t) and singlet (s) states (ΔG(t–s)) change in the following order: plumbylenes > stannylenes > germylenes > silylenes > carbenes. The singlet states in XC₂HN₂C are generally more stable when the electron withdrawing groups such as–F was used at β-position. However, the singlet states in XC₂N₂HM (M = Si, Ge, Sn, and Pb) are generally more stable when the withdrawing groups such as–F was placed. The puckering energy is investigated for each the singlet and triplet states. The DFT calculations found the linear correlation to size of the group 14 divalent element (M), the ∠N–M–N angle, and the Δ(LUMO–HOMO) of XC₂HN₂M.     

Aluminum(III)-doped ZnO@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite as a magnetic sorbent for preconcentration of cadmium(II)

An Al-doped ZnO@Fe₃O₄ nanocomposite was synthesized and used as a magnetic sorbent for solid-phase extraction of Cd(II) prior to its determination by flame atomic absorption spectrometry (FAAS). The size and morphology of the nano-sorbent were characterized via X-ray diffraction analysis, scanning electron microscopy and FTIR. Following its desorption with acetic acid, cadmium was quantified by FAAS. Factors affecting the extraction of the Cd(II) were optimized. Under optimized experimental conditions, the calibration graph is linear in the 0.6 to 60 ng mL^?1 concentration range. The limit of detection is 0.17 ng mL^?1 and the pre-concentration factor is 50. The inter- and intra-day relative standard deviations for six replicate determinations at a Cd(II) level of 40 ng mL^?1 are 3.8% and 2.5%, respectively. The method was successfully applied to the trace determination of Cd(II) in spiked water samples. The accuracy of the method was confirmed by analyzing the certified reference material NIST SRM 1643e.

Open image in new window

Graphical abstract Schematic of the synthesis of an Al-doped ZnO@Fe₃O₄ nanocomposite and its application as a magnetic sorbent for solid-phase extraction of Cd(II) prior to its determination by flame atomic absorption spectrometry (FAAS).