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.     

Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

By exploring lithium–bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium–bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium–bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et₂O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et₂O yielded almost double the conversion of cyclic products than in THF.     

Bismuth(III) Flavonolates: The Impact of Structural Diversity on Antibacterial Activity,Mammalian Cell Viability and Cellular Uptake

A series of homoleptic and heteroleptic bismuth(III) flavonolate complexes derived from six flavonols of varying substitution have been synthesised and structurally characterised. The complexes were evaluated for antibacterial activity towards several problematic Gram-positive (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE)) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The cell viability of COS-7 (monkey kidney) cells treated with the bismuth flavonolates was also studied to determine the effect of the complexes on mammalian cells. The heteroleptic complexes [BiPh(L)₂] (in which L=flavonolate) showed good antibacterial activity towards all of the bacteria but reduced COS-7 cell viability in a concentration-dependent manner. The homoleptic complexes [Bi(L)₃] exhibited activity towards the Gram-positive bacteria and showed low toxicity towards the mammalian cell line. Bismuth uptake studies in VRE and COS-7 cells treated with the bismuth flavonolate complexes indicated that Bi accumulation is influenced by both the substitution of the flavonolate ligands and the degree of substitution at the bismuth centre.     

Decontamination of radionuclides on construction materials

A wide variety of materials can become contaminated by radionuclides, either from a terrorist attack or an industrial or nuclear accident. The final disposition of these materials depends, in large part, on the effectiveness of decontamination measures. This study reports on investigations into the decontamination of a selection of building materials. The aim has been to find an effective, easy-to-use and inexpensive decontamination system for radionuclides of cesium and cobalt, considering both the chemical and physical nature of these potential contaminants. The basic method investigated was surface washing, due to its ease and simplicity. In the present study, a basic decontamination formulation was modified by adding isotope-specific sequestering agents, to enhance the removal of cesium(I) and cobalt(II) from such construction materials as concrete, marble, aluminum and painted steel. Spiking solutions contained ¹³⁴Cs or ⁶⁰Co, which were prepared by neutron activation in the SLOWPOKE-2 nuclear reactor facility at the Royal Military College of Canada. Gamma spectroscopy was used to determine the decontamination efficiency. The results showed that the addition of sequestering agents generally improved the radiological decontamination. Although the washing of both cesium and cobalt from non-porous materials, such as aluminum and painted steel, achieved a 90–95 % removal, the decontamination of concrete and marble was more challenging, due to the porous nature of the materials. Nevertheless, the removal efficiency from 6-year-old concrete increased from 10 % to approximately 50 % for cobalt(II), and from 18 to 55 % for cesium(I), with the use of isotope binding agents, as opposed to a simple water wash.     

Synthesis and Characterisation of Bismuth(III) Aminoarenesulfonate Complexes and Their Powerful Bactericidal Activity against Helicobacter pylori

The synthesis and characterisation of nine new tris‐substituted bismuth(III) aminoarenesulfonates of the general formula [Bi(O₃S‐R^N)₃] (R^N=o‐aminophenyl 1 , m‐aminophenyl 2 , 6‐amino‐3‐methoxyphenyl 3 , p‐aminophenyl 4 , 2‐pyridyl 5 , o‐aminonaphthyl 6 , 5‐aminonaphthyl 7 , 4‐amino‐3‐hydroxynaphthyl 8 and 5‐isoquinolinyl 9 ) is described. Two synthetic strategies, using Ag₂O and [Bi(OtBu)₃], were explored and compared. The possibility to access heteroleptic bismuth(III) complexes with the new silver(I) metathesis reaction is demonstrated with the synthesis of the heteroleptic bismuth(III) aminoarenesulfonate complexes [PhBi(O₃S‐P2)₂(dmso)] 10 , [Ph₂Bi(O₃S‐P2)]_∞ 11 and [PhBi(O₃S‐P2)₂]_∞ 12 , of which the solid state structures 10 and 12 are presented (2P‐SO₃^?=2‐pyridinesulfonate). These complexes offer remarkable in‐vitro activity against three standard laboratory strains of Helicobacter pylori (H. pylori) as demonstrated by their exceptionally low minimum inhibitory concentration (MIC) values of 0.049 μg mL^?1 for the strains 251 and B128, which places most MIC values in the nano‐molar region. These results demonstrate the importance of the amino functionality in addition to the sulfonate group on the bactericidal properties against H. pylori.     

Matrix Infrared Spectroscopy and Quantum‐Chemical Calculations for the Coinage‐Metal Fluorides: Comparisons of Ar?AuF,Ne?AuF,and Molecules MF2 and MF3

The reactions of laser‐ablated Au, Ag, and Cu atoms with F₂ in excess argon and neon gave new absorptions in the M? F stretching region of their IR spectra, which were assigned to metal‐fluoride species. For gold, a Ng? AuF bond was identified in mixed neon/argon samples. However, this bonding was much weaker with AgF and CuF. Molecules MF₂ and MF₃ (M=Au, Ag, Cu) were identified from the isotopic distribution of the Cu and Ag atoms, comparison of the frequencies for three metal fluorides, and theoretical frequency calculations. The AuF₅ molecule was characterized by its strongest stretching mode and theoretical frequency calculations. Additional evidence was observed for the formation of the Au₂F₆ molecule.     

Electrochemical hydrogen storage in porous carbons with acidic electrolytes: Uncovering the potential

Electrochemical hydrogen storage in porous carbon materials is emerging as a cost-effective hydrogen storage and transport technology with competitive power and energy densities. The merits of electrochemical hydrogen storage using porous conductive carbon-based electrodes are reviewed. The employment of acidic electrolytes in such storage systems is compared with alkaline electrolytes. The recent innovations of a proton battery for smaller-scale electricity storage, and a proton flow reactor system for larger (grid)-scale storage and bulk export of hydrogen produced from renewable energy, are briefly described. It is argued that such systems, along with variants proposed by others, all of which rely on electrochemical hydrogen storage in porous carbons, can contribute to the search for energy storage technologies essential for the transition to a zero-emission global economy.     

Inter-particle interaction induced by broadband radiation

The recent fabrication of optical traps using super-continuum light impresses the need for a theory of inter-particle interactions under such conditions. Development of the theory provides a basis for calculation of the observations expected under experimental conditions. An expression for the inter-particle potential energy induced by continuum states of light is first derived using quantum electrodynamics. This energy expression is cast as a function of the spectral irradiance of the light, and the electric susceptibility of the interacting particles. Specific results are derived for light with a Lorentzian spectrum. It is shown that by filtering part of the spectrum, it is possible to exert control over the length of linear particle chains organized along the Poynting vector. The results exhibit scope for the optical fabrication of moldable structures using broadband light.