Total Synthesis of Tri-, Hexa- and Heptasaccharidic Substructures of the O-Polysaccharide of Providencia rustigianii O34

A general and efficient strategy for synthesis of tri-, hexa- and heptasaccharidic substructures of the lipopolysaccharide of Providencia rustigianii O34 is described. For the heptasaccharide seven different building blocks were employed. Special features of the structures are an α-linked galactosamine and the two embedded α-fucose units, which are either branched at positions-3 and -4 or further linked at their 2-position. Convergent strategies focused on [4+3], [3+4], and [4+2+1] couplings. Whereas the [4+3] and [3+4] coupling strategies failed the [4+2+1] strategy was successful. As monosaccharidic building blocks trichloroacetimidates and phosphates were employed. Global deprotection of the fully protected structures was achieved by Birch reaction.     

Study of structural changes and mesomorphic transitions of oriented poly(ethylene therephthalate) fibers in supercritical CO2

Supercritical carbon dioxide (scCO₂), an environmentally friendly solvent, can change the fine structure of fibers depending on treatment temperature and pressure. Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn below the glass transition temperature (T_g) and then exposed to scCO₂ under tension to induce morphological changes in them. The effects of draw ratio and scCO₂ exposure on the structural changes and mesomorphic transitions were evaluated. For this purpose, thermal characteristics of the structure, especially the rearrangement of polymer chains in the amorphous phase induced by cold-drawing and exposure to scCO₂, were evaluated by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The orientation factor of the fibers was measured using a polarizing microscope. The paracrystalline portion and the crystallite sizes of exposed samples were estimated by wide-angle X-ray diffraction. To evaluate the solubility of CO₂ molecules in the samples, density and fractional free volumes were also measured. A good correlation was obtained between the results obtained from various measurement techniques. Results showed that cold-drawing of PET fibers leads to a strain-induced crystallization and that exposure to scCO₂ changes the structure of the oriented PET samples. To investigate mesophase transitions, percentage of extended chains in the amorphous regions was calculated by analyzing the results of DSC and FTIR. Results showed that the amount of extended chains developing during cold-drawing in the amorphous regions decreased when exposed to scCO₂.     

Green synthesis and biological activity investigation of new derivatives of spiroisatins

In this research, the synthesis of novel derivatives of spiroisatins in high yields was investigated. These new compounds were synthesized using a multicomponent reaction (MCR) of isatin, malononitrile, acetophenone derivatives, diethyl oxalate, primary amines, and Et₃N in aqueous media. Under similar conditions, spiropyrroloisatins were prepared using MCRs of synthesized spiroistins. The antioxidant activity of newly synthesized spiroisatins is due to having an NH group which was evaluated by two procedures. Also, the antimicrobial activity of newly generated spiroisatins was evaluated by a disk distribution process utilizing two kinds of Gram-negative bacteria and Gram-positive bacteria and bacterial growth was stopped using these compounds. The advantages of this method are short reaction times, high yields of products, and the easy separation of catalyst and product using simple procedures.     

\hbox {Ph}_{3}\hbox {P/CCl}_{4} as a highly efficient reagent for one-pot N-alkylation of sulfonamides from alcohols: a rapid route to N-alkyl sulfonamides synthesis

A mild, efficient, and selective protocol for the one-pot $N$ -alkylation of sulfonamides with alcohols using triphenylphosphine and carbon tetrachloride is described. In this method, treatment of alcohols with a mixture of triphenylphosphine, carbon tetrachloride, and potassium sulfonylamide salts in refluxing anhydrous DMF furnishes the corresponding $N$ -alkyl sulfonamides in good to excellent yields. This protocol is highly efficient for various structurally diverse alcohols and potassium sulfonylamide salts. In this paper the influence of solvents and various reagents as sources for electrophilic-halogen instead of carbon tetrachloride in combination with triphenylphosphine have been examined. This protocol demonstrates the selectivity between primary and secondary alcohols. A plausible mechanism for this protocol has been described.     

In situ formation deposited ZnO nanoparticles on silk fabrics under ultrasound irradiation

Deposition of zinc(II) oxide (ZnO) nanoparticles on the surface of silk fabrics was prepared by sequential dipping steps in alternating bath of potassium hydroxide and zinc nitrate under ultrasound irradiation. This coating involves in situ generation and deposition of ZnO in a one step. The effects of ultrasound irradiation, concentration and sequential dipping steps on growth of the ZnO nanoparticles have been studied. Results show a decrease in the particles size as increasing power of ultrasound irradiation. Also, increasing of the concentration and sequential dipping steps increase particle size. The physicochemical properties of the nanoparticles were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and wavelength dispersive X-ray (WDX).     

Some algebraic properties of hypergraphs

We consider Stanley-Reisner rings k[x ₁, …, x _n ]/I(H) where I(H) is the edge ideal associated to some particular classes of hypergraphs. For instance, we consider hypergraphs that are natural generalizations of graphs that are lines and cycles, and for these we compute the Betti numbers. We also generalize some known results about chordal graphs and study a weak form of shellability.     

UV-prepared salep-based nanoporous hydrogel for controlled release of tetracycline hydrochloride in colon

A highly swelling nanoporous hydrogel (NPH) was synthesized via UV-irradiation graft copolymerization of acrylic acid (AA) onto salep backbone and its application as a carrier matrix for colonic delivery of tetracycline hydrochloride (TH) was investigated. Optimized synthesis of the hydrogel was performed by the classic method. The swelling behavior of optimum hydrogel was measured in different media. The hydrogel formation was confirmed by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA/DTG/DTA). The study of the surface morphology of hydrogels using SEM showed a nanoporous (average pore size: about 350nm) structure for the sample obtained under optimized conditions. The drug delivery results demonstrated that this NPH could successfully deliver a drug to the colon without losing the drug in the stomach, and could be a good candidate as an orally administrated drug delivery system.     

Regularized robust optimization: the optimal portfolio execution case

An uncertainty set is a crucial component in robust optimization. Unfortunately, it is often unclear how to specify it precisely. Thus it is important to study sensitivity of the robust solution to variations in the uncertainty set, and to develop a method which improves stability of the robust solution. In this paper, to address these issues, we focus on uncertainty in the price impact parameters in an optimal portfolio execution problem. We first illustrate that a small variation in the uncertainty set may result in a large change in the robust solution. We then propose a regularized robust optimization formulation which yields a solution with a better stability property than the classical robust solution. In this approach, the uncertainty set is regularized through a regularization constraint, defined by a linear matrix inequality using the Hessian of the objective function and a regularization parameter. The regularized robust solution is then more stable with respect to variation in the uncertainty set specification, in addition to being more robust to estimation errors in the price impact parameters. The regularized robust optimal execution strategy can be computed by an efficient method based on convex optimization. Improvement in the stability of the robust solution is analyzed. We also study implications of the regularization on the optimal execution strategy and its corresponding execution cost. Through the regularization parameter, one can adjust the level of conservatism of the robust solution.     

Electro-optical properties of zigzag and armchair boron nitride nanotubes under a transverse electric field: Tight binding calculations

The electro-optical properties of zigzag and armchair BNNTs in a uniform transverse electric field are investigated within tight binding approximation. It is found that the electric field modifies the band structure and splits band degeneracy where these effects reflect in the DOS and JDOS spectra. A decrease in the band gap, as a function of the electric field, is observed. This gap reduction increases with the diameter and it is independent of chirality. An analytic function to estimate the electric field needed for band gap closing is proposed which is in good agreement with DFT results. In additional, we show that the larger diameter tubes are more sensitive than small ones. Number and position of peaks in DOS and JDOS spectra for armchair and zigzag tubes with similar radius are dependent on electric field strength.     

Organic Electrosynthesis as a New Facile and Green Method for One‐pot Synthesis of Nanosized Particles of Octahydro‐imidazo[1,2‐a]quinolin‐6‐one Derivatives via a Multicomponent Reaction

Organic electrosynthesis as a new facile and green method was applied for one‐pot synthesis of octahydro‐imidazo[1,2‐a]quinolin‐6‐one derivatives, via a three component condensation of a dimedone, an aldehyde and 2‐(nitromethylene)imidazolidine in propanol in an undivided cell in the presence of sodium bromide as an electrolyte at room temperature. In this study, the anion of dimedone that was produced on the cathode reacted with aromatic aldehydes through the Knoevenagel reaction and then the product condensed with 2‐(nitromethylene)imidazolidine that resulted in a highly efficient formation of octahydro‐imidazo[1,2‐a]quinolin‐6‐one with 50–96% substance yields.