Superabsorbent hydrogel composites

A new cost‐effective approach to enhance gel strength of superabsorbent hydrogels was invented. Superabsorbent hydrogel composites (SHCs) were prepared through an optimized rapid solution polymerization of concentrated partially neutralized acrylic acid in the presence of a crosslinking agent under normal atmospheric conditions. Kaolin was used as an inorganic component in the polymerization process to strengthen the hydrogel products. FT‐IR spectroscopy was used to confirm grafting of acrylic chains on to the surface of kaolin particles. Morphology of the products was studied by scanning electron microscopy (SEM). Compared with the kaolin‐free hydrogel (control), kaolin caused a reduced equilibrium swelling and swelling rate as low as 17–31% and 19–29%, respectively. Kaolin, however, resulted in enhanced gel strength as high as 21–35% compared to the control. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study thermal properties of the composites. The SHCs exhibited higher thermal stability than the control. Meanwhile, changes in certain thermal transitions reconfirmed the chemical interaction of the acrylic chain with kaolin. These thermostabilized strengthened superabsorbent hydrogels may be considered as good candidates for agricultural application to retain more water under soil pressure. Copyright © 2003 John Wiley & Sons, Ltd.     

SOLVENT-FREE CONVERSION OF OXIRANES TO THIIRANES WITH THIOUREA

A simple and efficient method for the conversion of various oxiranes to the corresponding thiiranes using thiourea under solvent free conditions is described.     

Synthesis and characterization of polymer linked copper(I) bis(N‐heterocyclic carbene) mechanocatalysts

In this paper, the synthesis and characterization of a series of latent polymeric bis(N‐heterocyclic carbene) (NHC) copper(I) complexes is reported, which can be activated for the copper(I)‐catalyzed azide/alkyne cycloaddition (CuAAC) via ultrasound. To prove the influence of chain length and nature of the polymer towards the activation, poly(isobutylene) (PIB), poly(styrene) (PS) and poly(tetrahydrofuran) (PTHF) are synthesized via living polymerization techniques (LCCP, ATRP, CROP) obtaining different chain lengths (from 2500 to 9000 g/mol), followed by quaternization with N‐methylimidazole, generating the corresponding N‐methylimidazolium‐telechelic polymers. The deprotonation of these macroligands via strong bases like sodium tert‐butoxide (NaO^tBu) or potassium hexamethyldisilazide (KHMDS) yields the free N‐heterocyclic carbenes (NHCs), which are used to coordinate to tetrakis(acetonitrile)copper(I) hexafluorophosphate, forming the final polymer‐based mono‐ and bis(N‐methylimidazole‐2‐ylidene) copper(I)X complexes. The structural proof of these complexes is accomplished via ¹H‐NMR spectroscopy, MALDI‐TOF‐MS and GPC‐techniques. The activation of the copper(I) biscarbene catalysts by ultrasound is studied by GPC, revealing the cleavage of one shielding NHC‐ligand. The initial catalytic latency and the via ultrasound introduced catalytic activation is successfully demonstrated monitoring a CuAAC “click” reaction of benzyl azide and phenylacetylene by in situ ¹H‐NMR spectroscopy introducing thus “click” conversions up to 97%. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3893–3907     

Winkelverteilungen elastisch an Edelgas-Atomstrahlen gestreuter Elektronen; Spinpolarisation eines an Argon gestreuten 40 eV-Elektronenstrahls

Various non-leptonic decay modes of baryons are calculated in a simple quark model. Form factors for various matrix elements are taken both from experiment and the quark model. Additionally theK→2π andK→3π decay modes are computed in the same model. The theory has theΔ I=1/2 rule and static SU⁶ built-in. A relation between the∑ ⁺→N ⁺ π ⁺ decay, not calculable in the model, and theK→3π decay is given via an effective six quark interaction. Agreement with experiment is order of magnitude for the baryonic decays and worse for theK decays.     

Color screening and deconfinement for bound states of heavy quarks

We study the binding and deconfinement of heavy quarks in a thermal environment, using a non-relativistic confinement potential model with color screening. As a result, we obtain the dependence of the dissociation energies, the binding radii and the masses of heavy quark resonances (charmonium and bottonium states) on the color screening lengthr _D of the medium, and we determine for the different resonances those values ofr _D below which no more binding is possible. Finally, we consider the implication of our results on resonance suppression as signal for deconfinement.     

Investigation of the different discharge mechanisms in pseudosparkdischarges

The intention of this paper is to give an overview of recent experiments explaining the development and transition of the discharge phases in a pseudospark. The reported experiments include single gap pseudospark discharges in ultra-high-vacuum systems with hydrogen as working gas, as well as multigap pseudospark discharges in argon. Temporally and spatially resolved framing photography, spectrometry, raster electron microscopy and time resolved electrical measurements are presented. The experiments comprise a current range of some hundreds of amps to 60 kA. The results are used to specify the four characteristic phases of the pseudospark: Townsend-, hollow cathode-, high current- and metal vapor arc phase     

The influence of La2O3 and TiO2 on NiO/MgO/α-Al2O3

Summary The effect of La₂O₃ and TiO₂ on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al₂O₃ catalyst were studied in a simultaneous steam and CO₂ reforming of methane to syngas. La₂O₃ and TiO₂ were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively.     

Separation and determination of closely related lantibiotics by micellar electrokinetic chromatography

A sensitive micellar electrokinetic chromatography (MEKC) method was developed for the separation and determination of four closely related lantibiotics: gallidermin, cinnamycin, duramycin and nisin. Factors affecting the separation of the lantibiotics such as pH, phosphate buffer concentration, SDS concentration and wavelength for UV detection were investigated. By optimizing these experimental conditions, successful separation was achieved between class 1A lantibiotics (nisin and gallidermin) and class 1B lantibiotics (duramycin and cinnamycin). The four lantibiotics were separated within 12 min in 50 mM phosphate buffer at pH 3.95 ± 0.1 containing 80 mM SDS with UV detection of 214 nm. The LOD (S/N = 3) were 61 ng/mL for gallidermin, 57 ng/mL for cinnamycin, 55 ng/mL for duramycin and 58 ng/mL for nisin. The method was successfully applied to real samples such as fermentation broth, bovine colostrum and predrop beer. This method yielded satisfactory results, with quantitative recoveries of spiked lantibiotics in the three samples ranging from 86.1 to 99.6%.     

Synthesis of Acyclic Nucleosides with N‐[(Benzyloxy)(aryl)methyl] Substituents as Potential HEPT,EBPU, and TNK‐651 Analogues

The syntheses of the novel acyclic nucleosides 5a – 5m , carrying different N‐[(benzyloxy)(aryl)methyl] substituents, are described (Scheme). These compounds could be prepared in medium‐to‐good yields by either direct or silyl‐assisted coupling of the electrophiles 6 with either purine or pyrimidine nucleobases, or with different imidazole derivatives. The reactivity of the positively charged electrophilic intermediates derived from 6 upon Cl^? abstraction was rationalized by ab initio HF/6‐311G quantum‐mechanic calculations. The positive charge was found to be dispersed differently, depending on the electronic properties of the aryl substituents.     

Modified chitosan III,superabsorbency, salt‐ and pH‐sensitivity of smart ampholytic hydrogels from chitosan‐g‐PAN

Polyacrylonitrile (PAN) grafted chitosan was prepared by ceric‐initiated graft polymerization of acrylonitrile onto chitosan in a homogenous medium. The copolymer chitosan‐g‐PAN product was then hydrolyzed to yield a novel smart hydrogel (H‐chitoPAN) with superabsorbing properties. The influence of add‐on values as well as temperature and time of hydrolysis of the initial chitosan‐g‐PAN on swelling behavior of the hydrogel was evaluated in water and various salt solutions. The swelling kinetics of the superabsorbing hydrogel was studied as well. The hydrogels exhibited ampholytic and pH‐sensitivity characteristics. Several sharp swelling changes were observed in lieu of pH variations in a wide range (pH 2–13). The swelling variations were explained according to swelling theory based on the hydrogel chemical structure. Superabsorbency, pH‐ and salt‐sensitivity of the chitosan‐based hydrogel was briefly compared with the classical starch‐based superabsorbent, H‐SPAN. The pH‐reversibility and on–off switching behavior of the intelligent H‐chitoPAN hydrogels makes them good candidates for considering as potential drug carries. Copyright © 2004 John Wiley & Sons, Ltd.