Photo-Orientation of Liquid Crystals on Azo Dye-Containing Polymers

In this communication, we summarise our results related to light-induced orientational phenomena at liquid crystal–polymer interfaces. We investigated photoalignment for various nematics at the interface with the photosensitive polymer layer polymethyl methacrilate functionalised with azo dye Disperse Red 1. It was found that the efficiency of photoalignment exhibits marked differences depending on the structure of the rigid core of the liquid crystal molecules. It was demonstrated that the photo-orientation process is also significantly affected by the type of mesophase in which irradiation is carried out. The observations highlight the importance of the mutual influence of the polymer and the liquid crystal in light-induced processes.

Simultaneous description of wobbling and chiral properties in even-odd triaxial nuclei

A particle-triaxial rigid core Hamiltonian is semi-classically treated. The coupling term corresponds to a particle rigidly coupled to the triaxial core, along a direction that does not belong to any principal plane of the inertia ellipsoid.The equations of motion for the angular momentum components provide a sixth-order algebraic equation for one component and subsequently equations for the other two. Linearizing the equations of motion, a dispersion equation for the wobbling frequency is obtained. The equations of motion are also considered in the reduced space of generalized phase space coordinates. Choosing successively the three axes as quantization axis will lead to analytical solutions for the wobbling frequency, respectively. The same analysis is performed for the chirally transformed Hamiltonian. With an illustrative example one identified wobbling states whose frequencies are mirror image to one another. Changing the total angular momentum I, a pair of twin bands emerged. Note that the present formalism conciliates between the two signatures of triaxial nuclei, i.e., they could coexist for a single nucleus.

Controlling the Phase Behaviour and Photophysical Properties of Metallomesogens Through Structural Modification

<p>Metallomesogens (metal-containing liquid crystals) have been of interest to chemists since the early 1980s. Since this period, many of the studies published on metallomesogens have focussed on the synthesis of novel metallomesogens, and studies of their phase behaviour. As a result there is a substantial body of knowledge of their synthesis and phase behaviour, however many of these studies have overlooked the interesting physical properties that transition metals or lanthanides may impart to the mesophase (liquid crystal state). The studies that have been carried out suggest that the optical and photophysical properties resulting from their self assembly are very different to those observed in the crystalline or isotropic liquid phases, and are highly dependent on the structure of the mesophase. A series of salicylaldimine-based ligands and copper(II) complexes with a variety of structural modifications were synthesised and characterised. The structure, phase behaviour and phase relaxation kinetics of these compounds in the crystalline state were studied using differential scanning calorimetry (DSC), single crystal X-ray crystallography and variable temperature powder X-ray diffraction. The mesomorphism of the compounds was studied using small angle X-ray scattering (SAXS) and polarised optical microscopy (POM). The photophysical properties of the complexes and ligands were studied in the solution phase using ultraviolet-visible (UV-vis) spectroscopy. It was found that the smallest complexes (copper(II) N-alkyl,4-alkoxysalicylaldimine complexes) were not metallomesogens, but did exhibit multiple crystalline phases that formed as a result of changes in the conformation of the N-alkyl chains. The transition temperatures of these crystalline phase changes were strongly dependent on the length of the alkyl chains due to kinetic phenomena. The extension of the rigid core of the complex via synthesis of an N-(4-butylphenyl) derivative was successful in inducing mesomorphism in both the complex and the ligand. The ligand formed an enantiotropic nematic mesophase, while the complex formed a monotropic smectic A mesophase. The structural differences between the non-mesomorphic complexes, the mesomorphic ligand and the mesomorphic complex indicate that the determining factor in the formation of mesophases is the magnitude of lateral interactions between the molecules, which is governed by the size and shape of the rigid core. Further attempts at inducing mesomorphism by formation of bimetallic copper complexes were unsuccessful due to chemical instability. The photophysical properties of the compounds showed that the salicylaldimine ligands exist in solution in a tautomeric equilibrium, which can be influenced by the hydrogen-bonding character of the solvent. The ligands also show evidence of photochromism, while the complexes exhibit LMCT bands, both features which could affect and be affected by self assembly. It was also determined from their UV-vis spectra and DFT studies that the ligands bind to the metal centre in a manner which is intermediate to the two tautomeric forms, but close to the higher energy keto-amine tautomer. These results demonstrate that structural modification can be used to control both the phase behaviour and physical properties of salicylaldimine complexes. The compounds studied here also show potential to exhibit a variety of self assembly-dependent photophysical properties in the mesophase and would be good candidates for future research in this area.</p>

Controlling the Phase Behaviour and Photophysical Properties of Metallomesogens Through Structural Modification

<p>Metallomesogens (metal-containing liquid crystals) have been of interest to chemists since the early 1980s. Since this period, many of the studies published on metallomesogens have focussed on the synthesis of novel metallomesogens, and studies of their phase behaviour. As a result there is a substantial body of knowledge of their synthesis and phase behaviour, however many of these studies have overlooked the interesting physical properties that transition metals or lanthanides may impart to the mesophase (liquid crystal state). The studies that have been carried out suggest that the optical and photophysical properties resulting from their self assembly are very different to those observed in the crystalline or isotropic liquid phases, and are highly dependent on the structure of the mesophase. A series of salicylaldimine-based ligands and copper(II) complexes with a variety of structural modifications were synthesised and characterised. The structure, phase behaviour and phase relaxation kinetics of these compounds in the crystalline state were studied using differential scanning calorimetry (DSC), single crystal X-ray crystallography and variable temperature powder X-ray diffraction. The mesomorphism of the compounds was studied using small angle X-ray scattering (SAXS) and polarised optical microscopy (POM). The photophysical properties of the complexes and ligands were studied in the solution phase using ultraviolet-visible (UV-vis) spectroscopy. It was found that the smallest complexes (copper(II) N-alkyl,4-alkoxysalicylaldimine complexes) were not metallomesogens, but did exhibit multiple crystalline phases that formed as a result of changes in the conformation of the N-alkyl chains. The transition temperatures of these crystalline phase changes were strongly dependent on the length of the alkyl chains due to kinetic phenomena. The extension of the rigid core of the complex via synthesis of an N-(4-butylphenyl) derivative was successful in inducing mesomorphism in both the complex and the ligand. The ligand formed an enantiotropic nematic mesophase, while the complex formed a monotropic smectic A mesophase. The structural differences between the non-mesomorphic complexes, the mesomorphic ligand and the mesomorphic complex indicate that the determining factor in the formation of mesophases is the magnitude of lateral interactions between the molecules, which is governed by the size and shape of the rigid core. Further attempts at inducing mesomorphism by formation of bimetallic copper complexes were unsuccessful due to chemical instability. The photophysical properties of the compounds showed that the salicylaldimine ligands exist in solution in a tautomeric equilibrium, which can be influenced by the hydrogen-bonding character of the solvent. The ligands also show evidence of photochromism, while the complexes exhibit LMCT bands, both features which could affect and be affected by self assembly. It was also determined from their UV-vis spectra and DFT studies that the ligands bind to the metal centre in a manner which is intermediate to the two tautomeric forms, but close to the higher energy keto-amine tautomer. These results demonstrate that structural modification can be used to control both the phase behaviour and physical properties of salicylaldimine complexes. The compounds studied here also show potential to exhibit a variety of self assembly-dependent photophysical properties in the mesophase and would be good candidates for future research in this area.</p>

Structural characterization of a Thorarchaeota profilin indicates eukaryotic-like features but with an extended N-terminus

The emergence of the first eukaryotic cell was preceded by evolutionary events which are still highly debatable. Recently, comprehensive metagenomics analysis has uncovered that the Asgard super-phylum is the closest yet known archaea host of eukaryotes. However, it remains to be established if a large number of eukaryotic signature proteins predicated to be encoded by the Asgard super-phylum are functional at least, in the context of a eukaryotic cell. Here, we determined the three-dimensional structure of profilin from Thorarchaeota by nuclear magnetic resonance spectroscopy and show that this profilin has a rigid core with a flexible N-terminus which was previously implicated in polyproline binding. In addition, we also show that thorProfilin co-localizes with eukaryotic actin in cultured HeLa cells. This finding reaffirm the notion that Asgardean encoded proteins possess eukaryotic-like characteristics and strengthen likely existence of a complex cytoskeleton already in a last eukaryotic common ancestor

Co-factor-free aggregation of tau into seeding-competent RNA-sequestering amyloid fibrils

Pathological aggregation of the protein tau into insoluble aggregates is a hallmark of neurodegenerative diseases. The emergence of disease-specific tau aggregate structures termed tau strains, however, remains elusive. Here we show that full-length tau protein can be aggregated in the absence of co-factors into seeding-competent amyloid fibrils that sequester RNA. Using a combination of solid-state NMR spectroscopy and biochemical experiments we demonstrate that the co-factor-free amyloid fibrils of tau have a rigid core that is similar in size and location to the rigid core of tau fibrils purified from the brain of patients with corticobasal degeneration. In addition, we demonstrate that the N-terminal 30 residues of tau are immobilized during fibril formation, in agreement with the presence of an N-terminal epitope that is specifically detected by antibodies in pathological tau. Experiments in vitro and in biosensor cells further established that co-factor-free tau fibrils efficiently seed tau aggregation, while binding studies with different RNAs show that the co-factor-free tau fibrils strongly sequester RNA. Taken together the study provides a critical advance to reveal the molecular factors that guide aggregation towards disease-specific tau strains.

Identification of the Rigid Core for Aged Liquid Droplets of the TDP-43 Low Complexity Domain

The biomolecular condensation of proteins with low complexity sequences plays a functional role in RNA metabolism and a pathogenic role in neurodegenerative diseases. The formation of dynamic liquid droplets brings biomolecules together to achieve complex cellular functions. The rigidification of liquid droplets into β-strand-rich hydrogel structures composed of protein fibrils is thought to be purely pathological in nature. However, low complexity sequences often harbor multiple fibril-prone regions with delicately balanced functional and pathological interactions. Here, we investigate the maturation of liquid droplets formed by the low complexity domain of the TAR DNA-binding protein 43 (TDP-43). Solid state nuclear magnetic resonance measurements on the aged liquid droplets identify a structured core region distinct from the region thought to be most important for pathological fibril formation and aggregation. The results of this study show that multiple segments of this low complexity domain are prone to form fibrils, and that stabilization of β-strand-rich structure in one segment precludes the other region from adopting rigid fibril structure.Table of Contents Graphic