The Synthesis of 4-Decarboxy-4-phosphono-O-2-isooxacephems, -isopenams and -isooxacephems Containing Phosphorus at the 3-Position

Two new types of iso-oxacephems have been synthesized in which a phosphonate group replaces either the carboxyl group or C(3). The latter compound exists as a stable trialkoxyphosphonium ylide. Potassium thioacetate and O₂ in DMF are transformed in an autocatalytic, probably sulfur-catalyzed process to CH₃COOK and sulfur; the latter two reagents are sufficient to transform the methanesulfonate 7 to the isopenam 15 .     

N-Levulination of Guanosine

A procedure have been developed for the synthesis of the N-levulinoyl derivative of guanosine.     

Adsorption of Cu(II) and Zn(II) ions from aqueous solutions onto fine powder of Typha latifolia L. root: kinetics and isotherm studies

Fine powder of Typha latifolia L. root was used for adsorption of copper and zinc ions from buffered and nonbuffered aqueous solutions. The adsorption reached equilibrium in 60 min. During this time, more than 90 % of the adsorption process was completed. The effect of initial pH, initial concentration of metal ion, and contact time was investigated in a batch system at room temperature. The optimum adsorption performance was observed at pH 5.00 and 4.25 for nonbuffered solutions of Cu(II) and Zn(II), respectively, while for buffered solutions it occurred at pH 6.00. The total metal uptake decreased on application of ammonium acetate buffer, from 37.35 to 17.00 mg g^?1 and 28.80 to 9.90 mg g^?1 for Cu(II) and Zn(II) solutions, respectively, with 100 mg L^?1 initial concentration. The pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models were used to describe the adsorption kinetics. The experimental data followed the pseudo-second-order kinetic model. The biosorption equilibrium was well described by Langmuir and Freundlich isotherm models.     

Syntheses of Molybdenum and Tungsten Imido Alkylidene Complexes that Contain a Bidentate Oxo/Thiolato Ligand

3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl[1,1′-biphenyl]-2-ol (H₂[^tBu₄OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H₂[^tBu₄OS] to Mo(NAr)(CHCMe₂Ph)(2,5-dimethylpyrrolide)₂ led to formation of Mo(NAr)(CHCMe₂Ph)[^tBu₄OS], which was trapped with PMe₃ to give Mo(NAr)(CHCMe₂Ph)[^tBu₄OS](PMe₃) ( 1 (PMe₃)). An X-ray crystallographic study of 1 (PMe₃) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1 (PMe₃)_A and 1 (PMe₃)_B are disordered. Mo(NAd)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 2 (PMe₃); Ad=1-adamantyl) and W(NAr)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 3 (PMe₃)) were prepared using analogous approaches. 1 (PMe₃) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(^tBu₄OS)(C₂H₄) ( 4 ) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for the ethylene ligand in 4 are like those found for bisalkoxide ethylene complexes of the same general type. Complex 1 (PMe₃) in the presence of one equivalent of B(C₆F₅)₃ catalyzes the homocoupling of 1-decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature. 1 (PMe₃), 2 (PMe₃), and 3 (PMe₃) all catalyze the ROMP of rac-endo,exo-5,6-dicarbomethoxynorbornene (rac-DCMNBE) in the presence of B(C₆F₅)₃, but the polyDCMNBE that is formed has a random structure.     

Considering the effect of different arrangements of pentagons on density of states of capped carbon nanotubes

We have used a non-equilibrium surface Green's function matching formalism combined with a tight-binding Hamiltonian to consider the effect of different arrangements of pentagon rings on localization of density of states at the tip regions of semi-infinite capped carbon nanotubes. The transfer matrixes are obtained by an iterative procedure. The results demonstrate that the positions of the peaks near Fermi energy are remarkably affected by the relative locations of pentagons. It is observed that in thin nanotubes, carbon atoms belonging two neighboring pentagon rings have significant contribution in the localized states near fermi energy. From our calculations, it turns out that the metallic or semiconducting behavior of capped nanotubes in the tip regions depends on the metallic or semiconducting nature of their nanotube stems.     

Numerical simulation of dimethyl ether/natural gas blend fuel HCCI combustion to investigate the effects of operational parameters on combustion and emissions

Journal of Thermal Analysis and Calorimetry - Homogeneous charge compression ignition (HCCI) combustion phasing control is one of the most difficult challenges of operating this new concept of...     

Synthesis and characterization of PEGylated iron and graphene oxide magnetic composite for curcumin delivery

Nowadays, nanostructures have been given significant attention in medical and biological fields. Among these nanostructures, graphene oxide (GO) has been widely used in drug delivery systems, because of its unique properties, and the ability to connect to other nanostructures such as magnetic nanoparticles (NPs) as well as polymers by its functional groups. In this research, first, GO was prepared by exfoliating graphite according to the modified Hummer’s method, and then the Fe₃O₄ NPs were synthesized by a simple co-precipitation method on GO nanosheets. In the next step, with the help of the ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide coupling reagents, the polyethylene glycol (PEG) polymer was bonded to the GO-Fe₃O₄ nanocomposite. Finally, anti-cancer drug, curcumin (Cur) was loaded onto the nanocomposite and the Cur loading ratio was measured at about 8%. The samples were evaluated using Fourier transform-infrared, differential scanning calorimtery, vibrating-sample magnetometry, atomic force microscopy and dynamic light scattering techniques. The results show that the prepared nanocomposite is an appropriate candidate for biomedical applications.     

Novel marine-based gold nanocatalyst in solvent-free synthesis of polyhydroquinoline derivatives: Green and sustainable protocol

We report an ecofriendly synthetic approach for the fabrication of biogenic gold nanoparticles (AuNPs) using electron-rich sea cucumber extract as a bio-reductant and stabilizing agent in reducing gold cations into AuNPs at the optimal conditions. The produced AuNPs are spherical in shape with an average particle size of 11 ± 1.5 nm in transmission electron microscopy (TEM) and exhibited a crystal structure of face-centered cubic in X-ray diffraction (XRD) analyses. Our results indicated that bioinspired AuNPs demonstrate superior catalytic activity in the safe and facile one-pot synthesis of polyhydroquinoline derivatives under solvent-free reaction conditions. This green route encompasses multiple benefits including highly recyclable bioinspired catalyst (5 cycles), short reaction times, convenient workout, high to excellent product yields (82%–97%), and nonhazardous conditions.     

SBA-15-SO3H-assisted preparation of 4-aza-phenanthrene-3,10-dione derivatives via a one-pot,four-component reaction

Research on Chemical Intermediates - A novel four-component approach for the synthesis of 1-phenyl-1,4-dihydro-2H-9-oxa-4-aza-phenanthrene-3,10-dione derivatives has been presented via the reaction...