Reversible switching of structural and plasmonic properties of liquid-crystalline gold nanoparticle assemblies.

Hybrid materials built of spherical gold nanoparticles with three different sizes covered with (pro)mesogenic molecules have been prepared. Small-angle X-ray diffraction studies showed that after thermal annealing most of the obtained materials formed long-range ordered assemblies. Variation of the (pro)mesogenic ligand architecture enabled us to achieve a switchable material, which could be reversibly reconfigured between 3D long-range ordered structures with tetragonal and face centred cubic symmetries. This structural reconfiguration induces changes to the plasmonic response of the material. This work demonstrates that it is possible to use LC-based self-assembling phenomena to prepare dynamic materials with structural properties important for the development of active plasmonic metamaterials.

1D, 2D and 3D liquid crystalline phases formed by bent-core mesogens.

The type of the mesophase is altered by a small change in the molecular architecture, i.e. increasing the number of alkyl chains attached to the mesogenic core at terminal positions. Lamellar (1D) and columnar (2D) phases are formed for molecules with one and three terminal chains, respectively. For those with two chains 3D phases are observed with either cubic or triclinic symmetry structure.

Thermotropic cubic and tetragonal phases made of rod-like molecules.

Systematic studies on three dimensionally ordered liquid crystalline phases of different cubic and tetragonal symmetries are presented. The structures of the phases are determined by reconstruction of the electron density distribution from the X-ray diffraction patterns. The known models for electron densities in cubic structures were used whereas a new theoretical model for the structure of the tetragonal phase, which shows good agreement with the experimentally obtained electron densities, was proposed. For the first time a continuous phase transition between three dimensional phases with tetragonal and monoclinic symmetries was observed for an optically pure compound.

Control of sample alignment mode for hybrid lamellar systems based on gold nanoparticles.

New hybrid materials made of gold nanoparticles functionalized by mesogenic ligands form laminated smectic phases. Mechanical shearing produces macro size domains with uniformly oriented layers with the layer normal either perpendicular (perpendicular mode) or parallel (transverse mode) to the shearing direction. This is in contrast to low weight and polymer liquid crystals which usually show parallel mode of orientation.

'2+1' Tricarbonyltechnetium(I) and -rhenium(I) mixed-ligand complexes with N-methylpyridine-2-carboxyamide and isocyanide or imidazole ligands-potential precursors of radiopharmaceuticals.

Complexes of tricarbonyltechnetium(I)-99m and rhenium(I)-188, of '2+1' type: with N-methylpyridine-2-carboxyamide as a neutral bidentate ligand and either tert-butyl 3-isocyanopropionate or imidazole as a monodentate ligand, have been obtained on n.c.a. level. The complexes exhibit moderate lipophilicity and rather high stability in neutral aqueous solutions. The latter has been evidenced from the tests on histidine/cysteine challenge and on protein binding in rat serum. The rhenium complexes studied are much more stable than their technetium analogues. The isocyanopropionate complex may be considered promising model for radiopharmaceutical precursors.

Bent-core liquid crystals forming two- and three-dimensional modulated structures.

Two columnar phases of bent-core molecules have been observed, with a two-dimensional (2D) structure modulated in the plane perpendicular to the direction of the spontaneous polarization vector. The phases are switchable under an applied electric field, contrary to the commonly observed 2D modulated B1 phase. These new phases are built from broken smectic layers with orthogonal or tilted molecules. The evidence for a 3D structure in which the density modulations along and perpendicular to the spontaneous polarization vector co-exists is also given.

Enhanced chirality by adding achiral molecules into the chiral system.

It is generally accepted that the doping of chiral materials with achiral molecules diminishes the chirality of the system. Here we report the opposite phenomenon. It was found that the structural chirality of smectic phases made of rodlike molecules, Sm-C(*) or Sm-C(*)(A) phases, measured as the reverse length of the helical pitch, is enhanced by adding small amount of achiral bent-shaped molecules. The effect is due to the chirality transfer between host and guest systems. Achiral bent-shaped molecules become structurally chiral due to the interactions with the chiral host that induces tilt and polar order of bent-shaped molecules. This induced chirality is then transferred back to the host.

Reentrant ferroelectricity in liquid crystals.

The ferroelectric (Sm C*)-antiferroelectric (Sm C*A)-reentrant ferroelectric (re Sm C*) phase temperature sequence was observed for systems with competing synclinic-anticlinic interactions. The basic properties of this system are as follows: (i) the Sm C* phase is metastable in the temperature range of the Sm C*A; (ii) the helix handedness inverts at both Sm C*-Sm C*A and Sm C*A-re-Sm C* phase transitions; (iii) the threshold electric field that is necessary to induce synclinic ordering in the Sm C*A phase decreases near both Sm C*A-Sm C* and Sm C*A-re-Sm C* phase boundaries. All these properties are properly described by a simple Landau model that accounts for nearest neighboring layer steric interactions and quadrupolar ordering only.

Behavior of frustrated phase in ferroelectric and antiferroelectric liquid crystalline mixtures.

Binary mixtures of two successive homologues from a series of 4-(4(')-alkoxy-biphenyl-4-yloxymethyl)benzoic acid 2-octanol esters exhibit a polar phase that differs from both ferroelectric (FE) and antiferroelectric (AF) phases, which exist in the pure compounds. When the concentration of the FE component is increased, this phase gradually changes its polar character from AF-like to FE-like, which is confirmed by the study of dielectric properties. Sample boundaries as well as the dc electric field introduce the FE phase, which remains stable after the field is switched off. Dielectric study confirms that this phase is composed of FE and AF clusters. The clusters arise due to frustration of FE and AF molecular order, which occurs as a result of the lowering of interlayer interactions.

Induced antiferroelectric smectic- C(*)(A) phase by doping ferroelectric- C* phase with bent-shaped molecules

Doping of the ferroelectric Sm-C(*) phase with bent-shaped molecules induces the antiferroelectric Sm-C(*)(A) phase. The effect was observed by means of electro-optic and dielectric measurements in systems with weak interlayer interactions in which the relative strength of anticlinic-synclinic order between molecules in adjacent layers is easily controlled by external factors. Fourier-transform infrared spectroscopy studies suggest that the bent-shaped molecules are not flat. They reorient upon the electric field-induced antiferroelectric-ferroelectric transition to adopt a position in which the average direction of the carbonyl groups is in the smectic plane and a bending tip along the C2 symmetry axis.

Carbonate ion selective electrodes with trifluoroacetophenone derivatives in potentiometric clinical analyser.

Properties of six derivatives of 1-trifluoroacetylbenzene: [4-(n-butyl)- (1), 4-(n-hexadecyl)- (2), 4-dodecyloxy- (3), 4-(n-dodecylsulfonyl)- (4), N,N-dioctyl-4-trifluoroacetylbenzamide (5), octyl-p-trifluoroacetylbenzoate (6)] as neutral carriers for carbonate ion were examined and compared. The sensitivity towards carbonate ion was for (3) pH dependent. This eliminates (3) from practical applications in clinical analysis. When measuring CO(3)(2-) within the physiological range of human blood using as carriers compounds 1 and 2 the interference of chloride must be taken into account. In the case of carriers 4, 5, 6 this effect is negligible. Electrodes with membranes containing as carriers 2, 4, 5 and 6 were tested in an automatic potentiometric clinical analyser Microlyte 6, KONE. To avoid contamination by atmospheric CO(2) of three aqueous standards (TES, NaCl, NaHCO(3)), pH was adjusted by coulomeric generation of H(+) or OH(-) in a system devoid of carbon dioxide. Recovery of HCO(3)(-) calculated from measured CO(3)(2-) and pH, was investigated in a series of aqueous solutions and spiked bovine serum samples. The correlation between added and recovered concentration of HCO(3)(-) was linear with the intercept close to 0 and slope equal to 1 in aqueous solutions for all ligands and in bovine serum samples only in the case of ligand (2).

Total synthesis of hexuronic acids.

Six stereoisomeric hexuronic acids (tert-butyl esters of methyl pyranosides) having the altro, manno, gluco, gulo, galacto, and talo configurations were obtained from cis,trans-tert-butyl 2-methoxy-5,6-dihydro-2H-pyran-6-carboxylate (5). The synthesis involved the following successive steps: epoxidation of the double bond in 5, opening of the epoxides with dimethylamine, Cope degradation of the dimethyl-amino derivatives, and hydroxylation of the double bond in the tert-butyl hex-3-enuronates. All compounds were obtained as pure diastereoisomers in racemic form.