Cross-chiral examinations of molecular enantioselective recognition by fast atom bombardment mass spectrometry: Host–guest complexations between chiral crown ethers and chiral organic ammonium ions

Using fast atom bombardment (FAB) mass spectrometry (MS), cross-chiral relationships were confirmed for the first time for the diasteromeric host-guest complexations between the chiral crown ether host (1) and the chiral organic ammonium ion guest (2) on the basis of the relative peak intensities (RPI). Both host–guest combinations (R, R, R, R) – 1, (R) – 2 and (S, S, S, S) – 1, (S) – 2 obviously provided larger RPI values than the combination of both (R, R, R, R) – 1, (S) – 2 and (S, S, S, S) – 1, (R) – 2 by a factor of 1.6 as an averaged value: 1.87 (n = 4)/1.16 (n = 4) = 1.6. These results are consistent with the expected stabilities of the host-guest complexations by CPK model examinations. Successfully observed cross-chiral examinations strongly suggest a potentially useful FABMS/RPI methodology for rapidly searching newly designed and synthesized crown ether-like host compounds with a higher degree of enantioselectivity.     

Photopolymerization mechanisms of acrylates in poly(methyl methacrylate) films

Photoinitiation processes for photopolymer coating layers have been investigated with respect to quenching rates by a laser flash photolysis using a total reflection cell, as well as to the decomposition‐quantum yield of a sensitizer dye and a radical‐generating reagent by a gel permeative chromatographic analysis (GPC); the sensitizer dye,2‐[p‐(diethylamino)styryl]naphtho[1,2‐d]‐thiazole (DNT) and the radical‐generating reagent, 2,2′‐bis(2‐chlorophenyl)‐4,4′,5,5′‐tetraphenyl‐1,1′‐bi‐1H‐imidazole (BI). From experiments using flash photolysis, strong fluorescence was observed at excitation of 355 nm laser pulse, though no transient absorption was observed. The fluorescence was statically quenched by BI with a quenching distance, R = 11 Å. From the experiments using GPC, the high‐quantum yield of decomposition (Φ) was obtained as Φ (DNT) = 3 and Φ (BI) = 9 for DNT and BI in the presence of acrylate monomers, trimethyrolpropanetri‐acrylate (TMPTA), at 488 nm exposure of 3.36 mJ cm which was required to form a photo‐hardened image, however no decomposition of DNT and BI was detected in the absence of TMPTA. The results imply that the photoinitiator system undergoes efficient static‐dye sensitization and efficient polymerization of the acrylate monomers accompanied with the chain decomposition of DNT and BI. Copyright © 1999 John Wiley & Sons, Ltd.     

Gas chromatographic determination of lower fatty acids in gaseous samples via conventional in situ derivatization of the strontium salts catalysed by poly(crow ether)

Poly(crown ether)-catalysed derivatization of lower fatty acids with p-bromophenacyl bromide or pentafluorobenzyl bromide has been used for their determination in gaseous samples by gas chromatography (employing either flame-ionization or electron-capture detection). Stontium hydroxide was employed as a base for the derivatization, taking advantage of the fact that a column packed with strontium hydroxide-coated glass beads is very suitable for preconcentration of the fatty acids from ambient air. In situ derivatization of lower fatty acids, preconcentrated on the glass beads as their strontium salts, proceeded nearly quantitatively in acetonitrile. Traces of lower fatty acids in artificial sample gases could be determined successfully using this conventional derivatization followd by direct injection of the reaction mixture into a gas chromatograph.     

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One‐Handed Double Helices

New types of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12‐dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left‐ and right‐handed double helical structures were constructed via chemoselective Sonogashira–Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.     

The influence of magnetic field swept rate on the ultrasonic propagation velocity of magnetorheological fluids

Structure of magnetorheological (MR) fluids depends on the strength of the magnetic field applied and on the mode of its application. The ultrasonic wave propagation velocity changes under the effect of an external magnetic field as a result of formation of clusters arranged along the direction of the field in the MR fluids. Therefore, we propose a qualitative analysis of these clustering structures by measuring properties of ultrasonic propagation. Since the MR fluids are opaque, the non-contact inspection using this ultrasonic technique can be very useful. In this study, we measured ultrasonic propagation velocity in MR fluid influenced by an external magnetic field for different swept rate precisely. With increasing magnetic field intensity, the changes of the ultrasonic wave velocity are more pronounced. Sedimentation effect takes place in certain time for different swept rate due to magnetic particle size and it follows linear relationship in log scale. Significant differences of the ultrasonic wave velocity are established between the case when the field is swept at a constant rate and the case when it is stepped up.     

Preparation and applications of novel fluoroalkyl end‐capped vinyltrimethoxysilane oligomer/hydroxyapatite nanocomposites

Novel fluoroalkyl end‐capped vinyltrimethoxysilane oligomer/hydroxyapatite (HAp) nanocomposites were prepared by the reaction of calcium nitrate tetrahydrate and phosphoric acid in the presence of the corresponding oligomer. These fluorinated oligomer/HAp composites thus obtained are nanometer size‐controlled fine particles (83–173 nm), and were found to exhibit good dispersibility in methanol, ethanol, and isopropyl alcohol. These fluorinated HAp nanocomposites were applied to the surface modification of glass and poly(methyl methacrylate) (PMMA) to exhibit good hydro‐ and oleophobic characteristics imparted by fluorine on their surface. In addition, the surface structural changes of the modified polyethylene terephtalate and PMMA films treated with these fluorinated nanocomposites before and after soaking in a simulated body fluid (SBF) were analyzed by using SEM, XRD, and EDX to observe the formation of spherical HAp deposits on the surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Chlorogenic Acid UVA–UVB Photostability

Chlorogenic acid is a natural potent antioxidant. It can be used in cosmetics formulations, but for this purpose its photochemical stability should be determined to ensure that the compound will not be degraded after UV radiation exposure. To evaluate this possibility, the concentration of a chlorogenic acid solution was determined by HPLC before and after UVA and UVB irradiation. The results indicate that chlorogenic acid is not degraded under UVA or UVB irradiation.