Dielectric properties of polystyrene and some polychlorostyrenes from 4°K to room temperature

Dielectric measurements of carefully purified specimens of polystyrene and poly(2,3,4 or 3,4-chlorostyrene) have been obtained at audio frequencies ranging from 0.1 to 20 kHz and at temperatures between 4 and 300°K. Each of the samples exhibits a dielectric loss maximum in the range 15–50°K. The temperature of the maximum loss decreases with the addition of a substituent which lowers the symmetry of the pendant phenyl group. The results are explained by a model which invokes a coupling mechanism between two distinct modes of side group motions. This same model also explains some results of previously reported measurements of mechanical losses in similar polymers.     

Application of the cap-pair effect in reducing the inhibition of electrode processes. The determination of zinc in the presence of tween-80

The “cap-pair” effect, which accelerates electrode processes, is shown to be useful in decreasing the effects of inhibitors on reduction processes. The determination of zinc in the presence of Tween-80 is used as an example. In the square-wave polarography of zinc at the 10^-5 M level, addition of thiourea (10 g l^-1) eliminates or greatly reduces the inhibitory action of Tween-80, thus allowing precise determinations.     

Automated structural assignment of derivatized complex N-linked oligosaccharides from tandem mass spectra

Glycoprotein function is controlled by several biological factors, one of them being the structure of carbohydrate chains (glycans) attached to specific amino acids of the protein backbone. Changes in glycan structures have been shown to modify the secondary and tertiary conformation of glycoproteins, thus their function. Powerful analytical tools are available for the characterization of sugar structures, and recently mass spectrometry (MS) has been increasingly useful for this purpose. Manual interpretation of tandem mass spectrum is possible but tedious. Automated interpretation should speed the analysis and enhance the results obtained. A new computer program for automated interpretation of tandem MS spectra of complex N-linked glycans oligosaccharides from mammals will be described. N-Linked oligosaccharides standards were derivatized with 1-phenyl-3-methyl-5-pyrazolone (PMP) and analyzed by matrix-assisted laser desorption/ionization (MALDI)-tandem MS. Simulated tandem mass spectra of other common glycans were also generated to test the algorithm. The MALDI-MS/MS spectra featured resolved isotopic distributions for the [M + H](+) and fragment ions of oligosaccharides. These isotopic distributions complicated the automated analysis of the spectra and were removed to leave only monoisotopic peaks. An algorithm was written for this purpose, yielding simplified tandem mass spectra. Another algorithm is then used to determine the structure of the oligosaccharide. A score is then given to each structure, depending on agreement with experimental results. The program successfully assigned the true structure in 24 out of the 28 cases (86%) and the true structure was among the three top scoring structures in all cases.     

Greatest common subgraphs with specified properties

A graphG without isolated vertices is a greatest common subgraph of a setG of graphs, all having the same size, ifG is a graph of maximum size that is isomorphic to a subgraph of every graph inG. A number of results concerning greatest common subgraphs are presented. For several graphical propertiesP, we discuss the problem of determining, for a given graphG with propertyP, the existence of two non-isomorphic graphsG ₁ andG ₂ of equal size, also with propertyP, such thatG is the unique greatest common subgraph ofG ₁ andG ₂. In particular, this problem is solved whenP is the property of being 2-connected and whenP is the property of having chromatic numbern.     

Dynamical instability of a doubly quantized vortex in a Bose-Einstein condensate

Doubly quantized vortices were topologically imprinted in /F=1> 23Na condensates, and their time evolution was observed using a tomographic imaging technique. The decay into two singly quantized vortices was characterized and attributed to dynamical instability. The time scale of the splitting process was found to be longer at higher atom density.     

Thermal onset chemically reactive Oldroyd-B nanofluid with immersion of microorganism in three-dimensional accelerating frame

The current research effort focuses on the employment of nanoparticles for 3-D chemically reactive flow of an Oldroyd-B nanofluid caused by a bidirectional accelerating surface. The implication of thermal radiation is also taken into account. The main characteristics of nanofluids, such as Brownian motion and thermophoresis are investigated using classic Buongiorno nanofluid design. The suitable transformation has been used to decrease the relevant equation for the defined theoretical model, for which the exact method is determined using the method of homotopic. Following that, a comprehensive graphic assessment of dimensionless velocities, concentration, and temperature distribution, as well as their physical significance, is considered. Furthermore, interesting physical quantities such as local Nusselt and Sherwood numbers are calculated and determined mathematically. The study stresses that increasing relaxation time reduces variation in both components of velocities, but the effect of continuous retardation time is exactly the reverse. For a while, larger combined convection and floating proportion parameters, the velocity distribution is said to have a rising movement in the horizontal plane. Furthermore, increasing the thermophoresis parameter improves temperature and centration distributions.     

Chalcone derived benzoheterodiazepines for medicinal applications: A Two-pot and one-pot synthetic approach

The production of effective drugs has continuously been a challenging process for researchers due to the occurrence of resistive diseases. Drugs derived from natural product-based compounds as an active scaffold have gained interest in drug development due to a wide range of biological properties. Benzoheterodiazepines, a natural product derivative of bicyclic chalcones have been widely reported with various therapeutic potentials. This review discusses current synthetic methods in the preparation of benzoheterodiazepine derivatives (i.e., homocyclic benzoheterodiazepine, heterocyclic benzoheterodiazepine, bis-benzoheterodiazepine, and fused benzoheterodiazepine) via two-pot and one-pot synthetic routes. Several reaction protocols following both synthetic routes have been developed for efficient and higher yields that offer access to different functionalization of benzoheterodiazepines are comprehensively described. This review is important in the heterocyclic chemistry of benzoheterodiazepines and pharmacological industries in drug development processes.     

Regioselective hydrothiolation of terminal acetylene catalyzed by magnetite (Fe3O4) nanoparticles

Herein, we report a new and solvent-free methodology for the preparation of vinyl thioethers from terminal alkynes and thiols, using magnetite (Fe₃O₄) nanoparticles as a recyclable catalyst. With this greener method, the desired vinyl thioethers were achieved in good yields and with good stereoselectivity. In addition, the catalyst was easily recovered using a simple external magnet and reused for further catalytic reactions without significant loss of activity up to the fifth cycle.     

Synthesis and characterization of grafted nanohydroxyapatites using functionalized surface agents

Synthetic hydroxyapatite, HA [Ca10(PO4)6(OH)2], is a bioactive material that is chemically similar to biological apatite, the mineral phase of bone (a nanocomposite material). Synthetic biocomposites, comprising a polymer and hydroxyapatite that are used for bone replacement, have limitations when loaded under fatigue in that the weak mechanical bond between the two phases can result in failure at the interface. Chemical coupling of the HA and polymer matrix may provide a means of improving the interfacial bonding between the polymer and HA phases. Herein, we report our first steps toward developing chemically coupled nano-biocomposites via a two-step process. We describe the synthesis and characterization of surface-grafted hydroxyapatite (SG-HA), which possesses a reactive C=C functional group. In future work, we will report on the second step, namely the coupling of this functional group to a polymer by a copolymerization reaction to give a chemically coupled nano-biocomposite. The SG-HA reported herein was characterized by a range of methods including 31P and 13C magic-angle spinning (MAS)-NMR, Fourier transform infrared (FTIR), and Raman spectroscopy.