The change of the state of an endohedral fullerene by encapsulation into SWCNT: a Raman spectroelectrochemical study of Dy3N@C80 peapods

Raman and in situ Raman spectroelectrochemical studies of Dy3N@C80@SWCNT peapods have been carried out for the first time. The formation of peapods by the encapsulation of gaseous Dy3N@C80 has been confirmed by HR-TEM microscopy and by the successful transformation of Dy3N@C80@SWCNT into double-walled carbon nanotubes. The Raman spectra of the endohedral fullerene cluster changed dramatically in the interior of the single-walled carbon nanotube (SWCNT). The electrochemical charging of the peapod indicates a slight reversible attenuation of the Raman intensities of fullerene features during anodic doping. The results support the assignment of Raman bands to the Dy3N@C80 moiety inside a SWCNT.     

Various columnar phases formed by bent-core mesogens

Two new compounds containing bent-core mesogens are presented in which a flexible central methyleneoxycarbonyl unit acts as the bent fragment. The compounds form different two-dimensional columnar (‘B₁’) phases both with a rectangular lattice but different in the angle of the director of the molecules with respect to the a-axis of the lattice. Based on X-ray diffraction measurements structural models are proposed which cannot be described with the common model of p2mg symmetry for B₁ phases of bent-shaped molecules. The new models are of layer group symmetry (p11n and pm2₁ n) and are discussed as a new common model for two-dimensional columnar phases of bent-shaped mesogens.     

The binary system composed of a bent-core compound forming a B7 phase and a nematogenic calamitic compound

The isobaric phase diagram for a binary system of liquid crystals is presented. One mixing component is a bent-core mesogen forming a B₇ phase and the other one is a nematogenic calamitic compound. The occurring mesophases have been identified by their optical textures as well as by X-ray investigations. The B₇ phase exists down to about 60 mol% of the bent-core compound A / 40 mol% of the calamitic compound B. Two additional mesophases are induced in the mixed phase region. At medium concentrations (around 50 mol%) an oblique columnar phase appears which shows a similar X-ray pattern to the B₇ phase but an utterly different nucleation on cooling the isotropic liquid and a completely dissimilar texture. At concentrations below 35 mol% A, a further phase is induced which possesses an irregularly modulated layer structure. This phase can be regarded as an intermediate state between the regularly modulated Col_r (B₁) phase and the intercalated B₆ phase. It transforms on cooling into the phase with a regularly modulated structure.     

Development of a multipurpose ion source for LC-MS and GC-API MS

Over the past decade, multimode ion sources operating at atmospheric pressure (i.e., more than one ionization method is operative in the ion source enclosure) have received considerable interest. Simultaneous operation of different ionization methods targeting different compound classes within one analysis run has several advantages, including enhanced sample throughput and thus significant laboratory cost reductions. Potential drawbacks are enhanced ion suppression and other undesirable effects of the simultaneous operation of ionization methods. In this contribution we present an alternative approach-the development and characterization of a widely applicable, multipurpose ion source operating at atmospheric pressure. The optimized source geometry allows rapid changing from LC-API methods (ESI, APCI, APLI) to GC-API methods (APCI, APLI, DA-APLI) along with the appropriate coupling of chromatographic equipment required. In addition, true multimode operation of the source is demonstrated for LC-ESI/APLI and LC-APCI/APLI.     

The distribution of ion acceptance in atmospheric pressure ion sources: Spatially resolved APLI measurements

It is demonstrated that spatially resolved mass selected analysis using atmospheric pressure laser ionization mass spectrometry (APLI MS) represents a new powerful tool for mechanistic studies of ion-molecule chemistry occurring within atmospheric pressure (AP) ion sources as well as for evaluation and optimization of ion source performance. A focused low-energy UV laser beam is positioned computer controlled orthogonally on a two-dimensional grid in the ion source enclosure. Resonance enhanced multiphoton ionization (REMPI) of selected analytes occurs only within the confined volume of the laser beam. Depending on the experimental conditions and the reactivity of the primary photo-generated ions, specific signal patterns become visible after data treatment, as visualized in, e.g., contour or pseudo-color plots. The resulting spatial dependence of sensitivity is defined in this context as the distribution of ion acceptance (DIA) of the source/analyzer combination. This approach provides a much more detailed analysis of the diverse processes occurring in AP ion sources compared with conventional bulk signal response measurements.     

The Influence of the Shape and the Incompatibility of Molecular Moieties on the Structure of Smectic Mesophases

For selected compounds with perfluorinated chains the structure of smectic phases was investigated by X-ray diffraction measurements. For rod-like compounds with only one terminal perfluorinated chain the incompatibility of the hydrocarbon and the fluorocarbon moieties leads to a segregation of both parts which can be considered as microphase separation. For swallow-tailed compounds the structure of smectic phases depends on the position and the length of the perfluorinated chains. If the steric interaction dominates an antiparallel packing of the molecules within the smectic layers is favoured. If the incompatibility of the hydrocarbon and fluorocarbon moieties is of importance the smectic layers are distorted and at lower temperatures the layer structure is transformed into a columnar structure.     

Induced SA phases in binary systems with EDA complexing

The phase diagrams of 13 binary systems are presented in which electron donor-acceptor (EDA) complexing is clearly detectable. In all binary systems studied the same electron donor compound was used whereas the electron acceptor compounds were members of two homologous series. It was found that the induction of smectic A phases increases with increasing length of the alkyl chain of the acceptor compound and with increasing stability of the complexes.     

X-ray Studies on the Liquid Crystalline Phases of the 4-[4-n-Heptyloxy-Benzylidene-Amino]4'-cyanobiphenyl

By means of X-ray diffraction studies of oriented and non-oriented samples the lattice parameters of the orthorhombic cell of the S_E phase as well as of the hexagonal cell of the S_B phase were determined. By packing considerations a bimolecular building unit with oppositely arranged cyano-groups was assumed in the case of the S_E phase. The S_B phase is characterized by an ABAB sequence of the smectic layers in which the molecules are hexagonal arranged. The increasing mobility of the molecules at increasing temperature offers the possibility for a part of the molecules to slide in a more stable dimerized form. In the N_R and S_A phase the existence of monomers as well as of dimers is assumed. In this way a conception of the phase transitions S_E → S_B → N_R → S_A is given on the base of a decrease by steps of the dipole-dipole repulsion.     

Structure parameters in mixed liquid crystals (I). Layer thickness of the smectic mixed phases B in the binary system of ethyl-4-(4-ethoxy-benzylidene-amino)-cinnamate and terephthylidene-bis-(4-n-butyl-aniline)

The thickness of the smectic layers in binary liquid crystalline mixed phases of the phase type B are measured in dependence on the concentration. Both components have different B-phase structures. In the part of the binary system with a smectic polymorphism BA the long molecular axes are perpendicular to the layer planes. If the polymorphism is changed by the appearance of a mixed phase of the type C, i.e. the smectic polymorphism BCA exists, there occurs a transition into the B-phase structures with tilted axes, the tilt angle of which is changed continuously with the concentration.     

Filled SA phases in binary liquid crystalline systems of terminal-nonpolar compounds (III). The role of the molecule length of the rod-like component

The phase diagrams of 8 binary systems of liquid crystals are presented whereby one component is a “biswallow tailed” compound and the second component is a member of the homologous series of 4,4′-bis-n-alkyloxy-azoxybenzenes. In all phase diagrams studied induced smectic A phases occur. X-ray investigations give evidence that in the binary systems of short-chain homologues the layer spacing d of the smectic A phase is clearly greater than the average molecular length L̄, whereas in the systems of long-chain homologoues d is found to be somewhat smaller than L̄. The results are interpreted on the basis of a simple packing model.