Compact poly(ethylene oxide) structures adsorbed at the ethylammonium nitrate-silica interface

The adsorption of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) onto silica from ethylammonium nitrate (a protic ionic liquid) has been investigated using colloid probe AFM force curve measurements. Steric repulsive forces were measured for PEO, confirming that PEO can compete with the ethylammonium cation and adsorb onto silica. The range of the repulsion increases with polymer molecular weight (e.g., from 1.4 nm for 0.01 wt % 10 kDa PEO to 40 nm for 0.01 wt % 300 kDa PEO) and with concentration (e.g., from 16 nm at 0.001 wt % to 78 nm at 0.4 wt % for 300 kDa PEO). Fits to the force curve data could not be obtained using standard models for a polymer brush, but excellent fits were obtained using the mushroom model, suggesting the adsorbed polymer films are compressed and relatively poorly solvated. No evidence for adsorption of 3.5 kDa PPO could be detected up to its solubility limit.     

Electrospun Nanofibers Sorbents for Pre-Concentration of 1,1-dichloro-2,2 bis-(4-chlorophenyl)ethylene with Subsequent Desorption by Pressurized Hot Water Extraction

Electrospun polystyrene (PS) nanofibers (130–500 nm) incorporating a potassium salt of imidazole-1-carbodithioate were evaluated as potential sorbents for the pre-concentration of a model organochlorine pesticide; 1,1-dichloro-2,2bis-(4-chlorophenyl)ethylene (DDE). The efficiencies of DDE (0.25–1.0 μg L^?1) adsorption by the nanofiber sorbent followed by desorption employing pressurized hot water extraction (PHWE) were investigated and monitored using gas chromatography with electron capture detection (GC-ECD). Parameters such as time, temperature and pressure of extraction, sample volume, DDE concentration and sorbent mass were optimized. The maximum adsorption of DDE (0.50 μg L^?1) on electrospun PS and carbodithioate incorporated PS nanofibers was at 43.7 and 94.6%, respectively, in 20 min. Incorporation of carbodithiote doubled the adsorption efficiency of PS and achieved LOD of 0.000234 μg L^?1 for DDE. The optimal DDE desorption on the PHWE system was 93.8% in 10 min. It would seem that the use of electrospun nanofibers as sorbent material with subsequent desorption by PHWE has great potential and thus warrants further investigations. This approach as it uses water as an extraction solvent for an organochlorine pesticide provides an opportunity to eliminate organic solvents, especially for procedures aimed at monitoring organic pollutants in the environment.     

A conformationally constrained fused tricyclic nisin AB-ring system mimic toward an improved pyrophosphate binder of lipid II

The bacteria-specific membrane component lipid II is essential for bacterial cell wall synthesis. A tricyclic nisin mimic was designed and synthesized in which both thioether moieties were mimicked by an alkane-bridge, as well as the introduction of a third conformational constraint consisting of a macrocyclic lactam-bridge between the N-terminus and the B-ring. The newly designed tricyclic AB-ring mimic was found to bind lipid II since it was able to inhibit nisin-induced membrane leakage in a dose-dependent manner. These results imply that the tricyclic AB-ring mimic may form a novel class of lead structures for the development of nisin-based peptide antibiotics.     

The distribution of nickel ions among octahedral and tetrahedral sites in NiAl2O4MgAl2O4 solid solutions

The cation distribution in NiAl₂O₄ and in the solid solutions Ni_xMg_1?xAl₂O₄ with x ranging from 0.01 to 0.55 has been studied by X-ray analysis, magnetic susceptibility and reflectance spectroscopy.The relative X-ray intensities of various reflections for each compound were measured and compared with intensities calculated for various models of cation distribution. Lattice parameters, magnetic moments of Ni²⁺, and the position of nickel absorption bands have also been measured. The results show that all specimens have a predominantly octahedral distribution for their nickel ions, and that there is a small change towards a random distribution when the quenching temperature is increased from 1273 to 1673°K.Both X-ray and magnetic results show that the fraction, α, of Ni²⁺ ions on tetrahedral sites varies with nickel content. For samples quenched from 1273°K, NiAl₂O₄ is 78% inverse, but between x = 1.0 and x = 0.25 the value of α decreases from 0.22 towards 0.1. Thus, the fraction of nickel on octahedral sites in the solid solutions is higher than in NiAl₂O₄. The effect is linked with an increase in Dq for the Ni²⁺ ion. Below x = 0.25, there is tentative evidence that α may increase. In nickel-dilute solutions the matrix as a whole is nearly normal, and it is suggested that Madelung energy may then be more effective in counteracting the octahedral stabilization of nickel. The same trend is observed in the specimens quenched from 1673°K.     

Photoelectron energy analysis in a strong magnetic field: The role of elastic scattering

A new photoelectron spectroscopic method is described directed towards the measurement of the photoelectron spectra of trapped ions. An electrostatic retarding field electron energy analyser incorporating a channel plate is included with an ion trap in a strong magnetic field. The form of photoelectron spectrum is shown to be strongly influenced by a elastic scattering effects which can be enhanced by using an electron trapping potential well. The resultant spectra then have a particularly simple and useful form.     

SYNTHESIS AND CONFORMATIONAL STUDIES OF A NUMBER OF SATURATED BICYCLIC SIX-MEMBERED RING PHOSPHITES

Abstract

An ¹H NMR study of the conformation of the dioxaphosphorinane ring of a number of diastereoisomeric bicyclic saturated six-membered ring phosphites (3ab-10ab) has been performed. The dioxaphosphorinane ring of these phosphites is transannelated with a tetrahydrofuran, cyclopen-tane, tetrahydropyran or cyclohexane ring. The substituent on the phosphorus atom is a methoxy or phenoxy group. It is shown that the cis isomers 3a-10a prefer a chair conformation of the dioxaphosphorinane ring, independent of the substituent on the phosphorus atom and of the nature of the transannelated ring. In contrast, for the trans isomers 3b-10b a twist rather than a chair conformation of the dioxaphosphorinane ring is preferred. The fraction of the twist conformer in the trans isomers is mainly determined by the substituent on phosphorus. The size and composition of the transannelated ring are relatively unimportant in this respect. For both cis and trans isomers the preferred geometry is solvent-independent. The measured ^3JPOCH couplings of the cis isomers 3a-10a are used to formulate an expression for the dependence of such couplings upon dihedral angles in bicyclic phosphites.     

Enantiospecific synthesis of annulated nicotine analogues from D-glutamic acid. 7-Azabicyclo[2.2.1]heptano[2.3-c]pyridines

The conformationally restricted nicotinoid (1S,4S)-7-methyl-7-azabicyclo[2.2.1]heptano[2,3-c]pyridine dihydrochloride has been prepared enantiospecifically from D-glutamic acid. The method involved a lithium cis-2,6-dimethylpiperidide-mediated intramolecular anionic cyclization of (2S,5R)-N-(tert-butyloxycarbonyl)-5-[3-(4-N-chloropyridinyl]proline methyl ester in tandem with a standard decarboxylation sequence. Reductive amination afforded the desired N-methylated [2.2.1]bicyclonicotinoid. Cyclization of the corresponding iodopyridinylproline methyl ester, obtained via ultrasound-facilitated chloro-iodo exchange, was also effected.     

Pressurized hot ethanol extraction of carotenoids from carrot by-products

Carotenoids are known for their antioxidant activity and health promoting effects. One of the richest sources of carotenoids are carrots. However, about 25% of the annual production is regarded as by-products due to strict market policies. The aim of this study was to extract carotenoids from those by-products. Conventional carotenoid extraction methods require the use of organic solvents, which are costly, environmentally hazardous, and require expensive disposal procedures. Pressurized liquid extraction (PLE) utilizes conventional solvents at elevated temperatures and pressure, and it requires less solvent and shorter extraction times. The extraction solvent of choice in this study was ethanol, which is a solvent generally recognized as safe (GRAS). The extraction procedure was optimized by varying the extraction time (2-10 min) and the temperature (60-180 °C). β-Carotene was used as an indicator for carotenoids content in the carrots. The results showed that time and temperatures of extraction have significant effect on the yield of carotenoids. Increasing the flush volume during extraction did not improve the extractability of carotenoids, indicating that the extrication method was mainly desorption/diffusion controlled. Use of a dispersing agent that absorbs the moisture content was important for the efficiency of extraction. Analysing the content of β-carotene at the different length of extraction cycles showed that about 80% was recovered after around 20 min of extraction.