Bilayer-by-bilayer antiferroelectric ordering in freely suspended films of an achiral polymer-monomer liquid crystal mixture

Thin freely suspended films of a mixture of an achiral side-chain liquid crystal polymer and its monomer have been studied with depolarized reflected light microscopy. We observe that regions with an odd number of bilayers exhibit a net spontaneous polarization in the tilt plane of the molecules, while regions with an even number of bilayers have no net polarization. These odd-even effects are direct evidence that the tilted smectic bilayers are anticlinic at the polymer backbone and synclinic at bilayer interface and confirm that the phase is bilayer-by-bilayer antiferroelectric.     

Molecular motion of a nickel-bis(dithiolato) complex in solution

The molecular motion of the planar bis(maleonitriledithiolato)nickel anion, Ni(mnt)(2)(-), has been studied as a function of temperature using electron spin resonance (ESR) in several polar solvents; they are ethyl alcohol, eugenol, dimethyl phthalate, tri-n-butyl phosphate, tris(2-ethyl-hexyl)phosphate, diglyme, and a dimethylformamide-chloroform mixed solvent. Calculated spectra in agreement with the experimental X-band spectra are obtained using axially symmetric reorientation when the long in-plane axis is the unique (parallel) axis of the rotational diffusion tensor with D parallel/D perpendicular = 3.0-4.0; D parallel and D perpendicular are the diffusion constants for reorientation about the parallel and perpendicular axes, respectively. The reorientational model required for the simulations is either in or close to the Brownian rotational diffusion limit. In the slow motional (low temperature) region, the spectra can be simulated using the glassy g values. As the temperature increases, however, agreement is obtained only if the intermediate g factor, g(y), for the non-axially symmetric Zeeman interaction increases while g(x), g(z), and the motional model remain unchanged; this scheme and others for which gx and g(z) are possibly temperature-dependent are discussed. The values of D perpendicular from the simulations are in general agreement with those from earlier analyses of the width of the central spectral feature. The simulations and width analyses indicate (as do electrochemical, conductivity, and vapor-phase osmometry data) that the paramagnetic species reorienting in solution has a shape similar to that of the Ni(mnt)(2)(-) ion.     

Catalytic asymmetric approaches towards enantiomerically enriched diarylmethanols and diarylmethylamines

Enantiopure diarylmethanols and diarylmethylamines are important intermediates for the synthesis of pharmaceutically relevant products with antihistaminic, antiarrhythmic, diuretic, antidepressive, laxative, local-anesthetic and anticholinergic properties. Furthermore, they have been used as precursors for 1,1-diarylalkyl moieties, which occur in other antidepressants as well as in antimuscarinics and endothelin antagonists. In this critical review catalytic strategies towards enantioenriched diarylmethanols and diarylmethylamines are discussed, including methods for asymmetric carbon-carbon bond formations by aryl transfer reactions to aldehydes and arylimines, respectively, and enantioselective reductions of diarylketones.     

A new hybrid target concept for multi-keV X-ray sources

A novel concept for using hybrid targets to create multi-keV X-ray sources was tested on the GEKKO XII facility of the OSAKA University and on the OMEGA facility of the University of Rochester. The sources were made via laser irradiation of a titanium foil placed at the end of a plastic cylinder, filled with a very low-density (2 and 5 mg/cm³) silicon-dioxide aerogel that was designed to control the longitudinal expansion of the titanium plasma. Preliminary calculations were used to determine optimal conditions for the aerogel density, cylinder diameter and length that maximize multi-keV X-ray emission. The X-ray emission power was measured on OMEGA using absolutely calibrated broad-band, diode-based CEA diagnostics, in addition to high resolution crystal spectrometers. On GEKKO XII, the heat wave propagation velocity in the aerogel was also measured with an X-ray framing camera. The advantage of using the thermal wave generated in the aerogel to heat a solid material to increase the conversion efficiency has not been fully demonstrated in these experiments. However, it was shown that a 5 mg/cm³ aerogel placed in front of a titanium foil can improve the x-ray conversion efficiency with respect to the case of 2 mg/cm³ for some target diameter and length.     

Reactions of O−. with methyl benzoate: A negative ion chemical ionization and Fourier transform ion cyclotron resonance study

The reactions of O*- with methyl benzoate have been examined by the measurement of negative ion chemical ionization (NICI) mass spectra using a CI source, with confirmatory studies carried out on a Fourier transform ion cyclotron resonance mass spectrometer. Reaction mechanisms have been elucidated using isotopically labeled esters. Nucleophilic attack at the carbonyl carbon and the aromatic ring were important reaction pathways. Nucleophilic attack at the carbonyl carbon was followed by the production of products (C6HsCO2- and CH3OCO2-) characteristic of radical, beta-fragmentation. Using 18O-labeled methyl benzoate, the SN2 reaction was found to account for a smaller percentage, 21(+/-1)%, of the benzoate product. Aromatic ring attack resulted in formation of [M + O - H]- and [M - 2H]*- ions. Although aryl hydrogens accounted for most H2*+ abstracted by O*-, evidence for abstraction of HarylH*+alkyl and HalkylH*+alkyl was also found. Although present at much lower abundance, dehydrobenzoate, dehydrophenoxy, and C7H6*- ([M - 2H - CO2]*-) radical anions were also observed. An Haryl/Halkyl exchange associated with formation of the benzoate anion was attributed to an Halkyl abstraction that occurred within the methanol/dehydrobenzoate ion-dipole complex. The [M - 2H]*-, dehydrobenzoate, dehydrophenoxy, and [M - 2H - CO2]*- ion signals were quenched by reaction with O2. Conditions required for production of O*- spectra under NICI conditions were also examined.