4-(4′-Diamino-di-phenyl)-sulfone supported on hollow magnetic mesoporous Fe3O4@SiO2 NPs: As a reusable and efficient catalyst for the synthesis of ethyl 2-amino-5,10-dihydro-5,10-dioxo-4-phenyl-4H benzo[g]chromene-3-carboxylates

4-(4′-diamino-di-phenyl)-sulfone supported on hollow magnetic mesoporous (HMMS) Fe₃O₄@SiO₂ NPs has been used as a novel and efficient catalyst in the preparation of ethyl 2-amino-5,10-dihydro-5,10-dioxo-4-phenyl-4H benzo[g]chromene-3-carboxylates by a simple one-pot three-component reaction of aldehydes, ethyl cyanoacetate and 2-hydroxynaphthalene-1,4-dione under reflux conditions in ethanol. Wide range of products, excellent yields in short times, reusability of the catalyst, low catalyst loading and environmental benignity are some of the important features of this protocol.     

KAl(SO4)2 · 12H2O (alum) a reusable catalyst for the synthesis of some 4-substituted coumarins via Pechmann reaction under solvent-free conditions

A simple, efficient, and practical procedure for the Pechmann condensation using KAl(SO₄)₂ · 12H₂O (alum) as a non-toxic, reusable, inexpensive, and easily available catalyst is described under solvent-free condition at 65°C. These improved reaction conditions allow the preparation of a wide variety of some new substituted coumarins in high yields (86–96%) and purity under mild reaction conditions. Compared to the classical Pechmann condensation, this new method consistently has the advantage of high yields. Correspondence: Ali A. Mohammadi, Department of Chemistry, Shahid Beheshti University, P.O. Box 19839-4716, Tehran, Iran.     

Biginelli reaction for synthesis of novel trifluoromethyl derivatives of bis(tetrahydropyrimidinone)benzenes

A facile one-pot three-component condensation of terephthalic aldehyde with urea and fluorinated 1,3-dicarbonyl derivatives is developed using catalytic quantities of chlorotrimethylsilane at ambient temperature. As a consequence, efficient synthesis of novel trifluoromethyl derivatives of bis(tetrahydropyrimidinone)benzenes is observed within short time periods. The procedure is shown to be equally efficient when urea is replaced with thiourea or guanidine.     

Structural,theoretical and multinuclear NMR study of mercury(II) complexes of phosphorus ylides: Mono and binuclear complexes

Reaction of phosphorus ylide Ph₃PCHC(O)C₆H₄Cl (Y₁) with HgX₂ (X = Cl, Br and I) and ylide (p-tolyl)₃PCHC(O)CH₃ (Y₂) with HgI₂ in equimolar ratios using methanol as solvent leads to binuclear products. The bridge-splitting reaction of binuclear complex [(Y₁) · HgCl₂]₂ by DMSO yields a mononuclear complex containing DMSO as ligand. O-coordination of DMSO is revealed by single crystal X-ray analysis in mononuclear complex of [(Y₁) · HgCl₂ · DMSO]. C-coordination of ylides is confirmed by X-ray structure of binuclear complex [(Y₂) · HgI₂]₂. Characterization of the obtained compounds was also performed by elemental analysis, IR, ¹H, ³¹P, and ¹³C NMR. Theoretical studies on mercury(II) complexes of Y₁ show that formation of mononuclear complexes in DMSO solution in which DMSO acts as a ligand, energetically is more favorable than that of binuclear complexes.     

Succinimidinium N-sulfonic acid hydrogen sulfate as an efficient ionic liquid catalyst for the synthesis of 5-arylmethylene-pyrimidine-2,4,6-trione and pyrano[2,3-d]pyrimidinone derivatives

Research on Chemical Intermediates - Succinimidinium N-sulfonic acid hydrogen sulfate ([SuSA-H]HSO4) as a new ionic liquid is prepared and characterized using a variety of techniques, including...     

Development of a Reversed-Phase Liquid Chromatographic Assay for the Quantification of Total Persipeptides in Fermentation Broth

The emergence and prevalence of multi-drug-resistant bacterial strains increase the potential for outbreaks of incurable infections. The discovery of novel antibiotics and pharmacological preparations requires the identification of novel bioactive small molecules. A specific, sensitive, and reliable quantification method using high-performance liquid chromatography (HPLC) with UV detection was developed for the determination of total persipeptides (A and B), which are cyclic pentapeptides found in the fermentation broth of Streptomyces zagrosensis UTMC 1154 that exhibit bioactivity against methicillin-resistant Staphylococcus aureus (MRSA). A simple liquid–liquid extraction (LLE) method using butanol was employed to extract persipeptides from the fermentation broth prior to HPLC analysis. The chromatographic separation of persipeptides and the internal standard, virginiamycin, was achieved with a gradient of acetonitrile and water on a C18 reversed-phase analytical column in a 25-min analytical run utilizing a flow rate of 0.8 mL min⁻¹ and detection at 210 nm. The whole assay was validated, and the method presented a linear response range with a regression coefficient of determination R ² of 0.9996 for the quantification of persipeptides in the concentration range of 3.9–250.0 µg mL⁻¹, as well as extraction recoveries ranging from 54.78 ± 9.83 % to 56.45 ± 16.33 %. The bias and the precision of the proposed method were <10 %. The detection and quantification limits for the persipeptides were 27 and 83 µg L⁻¹, respectively.

     

Automated hollow‐fiber liquid‐phase microextraction followed by liquid chromatography with mass spectrometry for the determination of benzodiazepine drugs in biological samples

In this study, two‐phase hollow‐fiber liquid‐phase microextraction and three‐phase hollow‐fiber liquid‐phase microextraction based on two immiscible organic solvents were compared for extraction of oxazepam and Lorazepam. Separations were performed on a liquid chromatography with mass spectrometry instrument. Under optimal conditions, three‐phase hollow‐fiber liquid‐phase microextraction based on two immiscible organic solvents has a better extraction efficiency. In a urine sample, for three‐phase hollow fiber liquid‐phase microextraction based on two immiscible organic solvents, the calibration curves were found to be linear in the range of 0.6–200 and 0.9–200 μg L^?1 and the limits of detection were 0.2 and 0.3 μg L^?1 for oxazepam and lorazepam, respectively. For two‐phase hollow fiber liquid‐phase microextraction, the calibration curves were found to be linear in the range of 1–200 and 1.5–200 μg L^?1 and the limits of detection were 0.3 and 0.5 μg L^?1 for oxazepam and lorazepam, respectively. In a urine sample, for three‐phase hollow‐fiber‐based liquid‐phase microextraction based on two immiscible organic solvents, relative standard deviations in the range of 4.2–4.5% and preconcentration factors in the range of 70–180 were obtained for oxazepam and lorazepam, respectively. Also for the two‐phase hollow‐fiber liquid‐phase microextraction, preconcentration factors in the range of 101–257 were obtained for oxazepam and lorazepam, respectively.     

Density functional theory study of the regio‐ and stereoselectivity of 1,3-dipolar cycloaddition reactions between 2-ethylthio-4-phenyl-1-azetin and some substituted nitrile oxides

The mechanism (regio- and stereoselectivity) of 1,3-dipolar cycloaddition (1,3-DC) of 2-ethylthio-4-phenyl-1-azetin 1 with benzonitrile oxide 2a, 2-aminobenzonitrile oxide 2b and 2-azidobenzonitrile oxide 2c has been investigated by density functional theory-based reactivity indices and activation energy calculations at B3LYP/6-31G(d,p) level of theory in the gas and solvent phase. Thermodynamic and kinetic parameters of the possible ortho/meta regioisomeric and endo/exo stereoisomeric pathways have been determined. In order to rationalize complete endo selective fashion provided by these 1,3-DC cycloadditions, a natural steric analysis between NLMOs i,j for TS1ox and TS1on and also a second-order interaction energy, E ², analysis between the donor–acceptor orbitals in these TSs were carried out. In all cases, the ortho pathways are more favorable compared to the meta alternatives and it is found that the endo pathway is preferred. Our results show that these cycloadditions follow an asynchronous one-step mechanism with a nonpolar character. Theoretical data are in good agreement with the experimental results.     

Dispersion-corrected DFT study on the carbon monoxide sensing by B<Subscript>2</Subscript>C nanotubes: effects of dopant and interferences

Electrical sensitivity of a boron carbon nanotube (B₂CNT) was examined toward carbon monoxide (CO) molecule by using dispersion-corrected density functional theory calculations. It was found that CO is weakly adsorbed on the tube, releasing energy of 3.5–4.1 kcal/mol, and electronic properties of the tube are not significantly changed. To overcome this problem, boron and carbon atoms of the tube were substituted by aluminum and silicon atoms, respectively. Although both Al and Si doping make the tube more reactive and sensitive to CO, Si doping seems to be a better strategy to manufacture CO chemical sensors due to the higher sensitivity without deformation of nanotube structure after adsorption procedure. Moreover, it was shown that some interference molecules such as H₂O, H₂S and NH₃ cannot significantly change the electronic properties of B₂CNT. Therefore, the Si-doped tube might convert the presence of CO molecules to electrical signal.     

Constructive Approximation in de Branges–Rovnyak Spaces

In most classical holomorphic function spaces on the unit disk in which the polynomials are dense, a function f can be approximated in norm by its dilates \(f_r(z):=f(rz)~(r<1)\). We show that this is not the case for the de Branges–Rovnyak spaces \(\mathcal{H}(b)\). More precisely, we exhibit a space \(\mathcal{H}(b)\) in which the polynomials are dense and a function \(f\in \mathcal{H}(b)\) such that \(\lim _{r\rightarrow 1^-}\Vert f_r\Vert _{\mathcal{H}(b)}=\infty \). On the positive side, we prove the following approximation theorem for Toeplitz operators on general de Branges–Rovnyak spaces \(\mathcal{H}(b)\). If \((h_n)\) is a sequence in \(H^\infty \) such that \(\Vert h_n\Vert _{H^\infty }\le 1\) and \(h_n(0)\rightarrow 1\), then \(\Vert T_{\overline{h}_n}f-f\Vert _{\mathcal{H}(b)}\rightarrow 0\) for all \(f\in \mathcal{H}(b)\). Using this result, we give the first constructive proof that, if b is a nonextreme point of the unit ball of \(H^\infty \), then the polynomials are dense in \(\mathcal{H}(b)\).