Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

ABSTRACT

The twist-bend phase (N_TB) is most commonly observed in materials with a gross-bent shape: dimers; bent-cores; bent-oligomers. We had suggested previously that the bend-angle of such systems effectively dictates the relative thermal stability of the N_TB phase. However, our earlier paper relied on the use of a single energy-minimum conformer and so failed to capture any information about flexibility and conformational distribution. In the present work, we revisit our hypothesis and examine a second set of dimers with varying linking groups and spacer composition. We have improved on our earlier work by studying the conformational landscape of each material, allowing average bend-angles to be determined as well as the conformer distribution. We observe that the stability of the N_TB phase exhibits a strong dependence not only on the Boltzmann-weighted average bend-angle (rather than just a static conformer), but also on the distribution of conformers. To a lesser extent, the flexibility of the spacer appears important. Ultimately, this work satisfies both theoretical treatments and our initial experimental study and demonstrates the importance of molecular bend to the N_TB phase.     

Online induction heating for determination of isotope composition of woody stem water with laser spectrometry: a methods assessment

Application of stable isotopes of water to studies of plant–soil interactions often requires a substantial preparatory step of extracting water from samples without fractionating isotopes. Online heating is an emerging approach for this need, but is relatively untested and major questions of how to best deliver standards and assess interference by organics have not been evaluated. We examined these issues in our application of measuring woody stem xylem of sagebrush using a Picarro laser spectrometer with online induction heating. We determined (1) effects of cryogenic compared to induction-heating extraction, (2) effects of delivery of standards on filter media compared to on woody stem sections, and (3) spectral interference from organic compounds for these approaches (and developed a technique to do so). Our results suggest that matching sample and standard media improves accuracy, but that isotopic values differ with the extraction method in ways that are not due to spectral interference from organics.     

Synthesis of polyester from renewable feedstock: a comparison between microwave and conventional heating

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Controlling domain orientation of liquid crystalline block copolymer in thin films through tuning mesogenic chemical structures

Controlling the macroscopic orientation of nanoscale periodic structures of amphiphilic liquid crystalline block copolymers (LC BCPs) is important to a variety of technical applications (e.g., lithium conducting polymer electrolytes). To study LC BCP domain orientation, a series of LC BCPs containing a poly(ethylene oxide) (PEO) block as a conventional hydrophilic coil block and LC blocks containing azobenzene mesogens is designed and synthesized. LC ordering in thin films of the BCP leads to the formation of highly ordered, microphase‐separated nanostructures, with hexagonally arranged PEO cylinders. Substitution on the tail of the azobenzene mesogen is shown to control the orientation of the PEO cylinders. When the substitution on the mesogenic tails is an alkyl chain, the PEO cylinders have a perpendicular orientation to the substrate surface, provided the thin film is above a critical thickness value. In contrast, when the substitution on the mesogenic tails has an ether group the PEO cylinders assemble parallel to the substrate surface regardless of the film thickness value. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 532–541     

MgBr2 · OEt2: A Lewis Acid Catalyst for the O- and N-Boc Protection of Phenols and Amines

MgBr₂ · OEt₂ efficiently catalyzes the O- and N-tert-butoxycarbonylation of functionalized phenols and amines. The presented procedure is operationally simple and done under solvent-free conditions.     

Development and full validation of an HPLC methodology to quantify atorvastatin and curcumin after their intranasal co‐delivery to mice

There is increasing interest in atorvastatin and curcumin owing to their potential anticancer activity. A new, accurate and sensitive HPLC method was developed, for the first time, to simultaneously quantify atorvastatin and curcumin in mouse plasma and brain, liver, lung and spleen tissues following protein precipitation sample preparation. The chromatographic separation was achieved in 13 min on a C₁₈ column, at 35°C, using a mobile phase composed of acetonitrile–methanol–2% (v/v) acetic acid (37.5:2.5:60, v/v/v) at a flow rate of 1.0 mL/min. The detection of analytes and internal standard was carried out at 247, 425 and 250 nm, respectively. According to international guidelines, the method was shown to be selective, with lower limits of quantification ranging from 10 to 500 ng/mL for curcumin, and from 100 to 600 ng/mL for atorvastatin, linear over a wide concentration range (r² ≥ 0.9971) and with acceptable accuracy (bias ± 12.29%) and precision (coefficient of variation ≤13.15%). The analytes were reproducibly recovered at a percentage >81.10% and demonstrated to be stable under various experimental conditions in all biological matrices. This method can be easily applied to in vivo biodistribution studies related to the intranasal administration of atorvastatin and curcumin, separately or simultaneously.     

Transition-Metal-Mediated Modification of Biomolecules

The site-selective modification of biomolecules has grown spectacularly in recent years. The presence of a large number of functional groups in a biomolecule makes its chemo- and regioselective modification a challenging goal. In this context, transition-metal-mediated reactions are emerging as a powerful tool owing to their unique reactivity and good functional group compatibility, allowing highly efficient and selective bioconjugation reactions that operate under mild conditions. This Minireview focuses on the current state of organometallic chemistry for bioconjugation, highlighting the potential of transition metals for the development of chemoselective and site-specific methods for functionalization of peptides, proteins and nucleic acids. The importance of the selection of ligands attached to the transition metal for conferring the desired chemoselectivity will be highlighted.     

Development of a microchip capillary electrophoresis method for determination of the purity and integrity of mRNA in lipid nanoparticle vaccines

Messenger RNA (mRNA)-based vaccines are advantageous because they can be relatively quicker and more cost efficient to manufacture compared to other traditional vaccine products. Lipid nanoparticles have three common purposes: delivery, self-adjuvanting properties, and mRNA protection. Faster vaccine development requires an efficient and fast assay to monitor mRNA purity and integrity. Microchip CE is known to be a robust technology that is capable of rapid separation. Here, we describe the development and optimization of a purity and integrity assay for mRNA-based vaccines encapsulated in lipid nanoparticles using commercial microchip-based separation. The analytical parameters of the optimized assay were assessed and the method is a stability indicating assay.