An experimental and computational study of calamitic and bimesogenic liquid crystals incorporating an optically active [2,2]-paracyclophane

Two liquid-crystalline materials containing an optically active (R)-4-hydroxy-[2,2]-paracyclophane group were prepared, one in which the chiral group is a bulky terminal unit and one in which it forms part of a terphenyl-like mesogenic unit. Both materials exhibit monotropic chiral nematic phases. Partial phase diagrams were constructed for mixtures of both materials with 5CB, allowing us to extrapolate pitch lengths and helical twisting power values (HTP) for each material. The HTP value of the material with a ‘locked’ paracyclophane is 70% higher than that of a ‘free’ paracyclophane and this is rationalised as being due to the reduction in conformational freedom of the former material relative to the later

Agenesis of the corpus callosum is associated with developmental delay and intellectual disability

A critical appraisal and clinical application of Romaniello R, Marelli S, Giorda R, et al. Clinical characterization, genetics, and long-term follow-up of a large cohort of patients with agenesis of the corpus callosum. Journal of Child Neurology, 2016;32(1):60-71. doi: 10.1177/0883073816664668

Nutrition labelling: a review of research on consumer and industry response in the global South

KIMBACKGROUND: To identify peer-reviewed research on consumers' usage and attitudes towards the nutrition label and the food industry's response to labelling regulations outside Europe, North America, and Australia and to determine knowledge gaps for future research. DESIGN: Narrative review. RESULTS: This review identified nutrition labelling research from 20 countries in Asia, Africa, the Middle East, and Latin America. Consumers prefer that pre-packaged food include nutrition information, although there is a disparity between rates of use and comprehension. Consumer preference is for front-of-pack labelling and for information that shows per serving or portion as a reference unit, and label formats with graphics or symbols. Research on the food and beverage industry's response is more limited but shows that industry plays an active role in influencing legislation and regulation. CONCLUSIONS: Consumers around the world share preferences with consumers in higher income countries with respect to labelling. However, this may reflect the research study populations, who are often better educated than the general population. Investigation is required into how nutrition labels are received in emerging economies especially among the urban and rural poor, in order to assess the effectiveness of labelling policies. Further research into the outlook of the food and beverage industry, and also on expanded labelling regulations is a priority. Sharing context-specific research regarding labelling between countries in the global South could be mutually beneficial in evaluating obesity prevention policies and strategies

Developments in liquid-crystalline dimers and oligomers

Liquid-crystalline dimers and bimesogens have attracted much attention due to their propensity to exhibit the spontaneously chiral twist-bend mesophase (NTB), most often by dimers with methylene spacers. Despite their relative ease of synthesis, the number of ether-linked twist-bend materials significantly lags behind those of methylene-linked compounds. In this work, we have prepared and studied a range of ether-linked bimesogens homologous in structure to the FFO9OCB; as with methylene-linked systems, it appears that it is molecular topology and the gross molecular shape that are the primary drivers for the formation of this phase of matter. Dimers and bimesogens are well studied within the context of the twist-bend phase; however, present understanding of this mesophase in oligomeric systems lags far behind. We report our recent efforts to prepare further examples of oligomeric twist-bend nematogens, including further examples of our ‘n+1’ methodology, which may allow the synthesis of high-purity, monodisperse materials of any given length to be prepared. We have observed that there is a tendency for these materials to exhibit highly ordered soft-crystalline mesophases as opposed to the twist-bend phase

Investigating the Cusp between the Nano- and Macro-sciences in Supermolecular Liquid-Crystalline Twist-Bend Nematogens

In this article we report the first known linear liquid-crystalline hexamer and in doing so demonstrate that higher oligomers and main chain polymers, with chemical structures based upon dimers and bimesogens, can exhibit the topical twist-bend ‘nematic’ mesophase. In doing so we find that there is continuation of properties and structures across the spectrum from dimer to polymer and possibly to macroscale objects such as helical flagella. This finding highlights the cross over from nanoscience based mainly on electrostatics and other non-covalent interactions to macroscience based mainly on molecular topology, density of packing, and minimisation of the free energy

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

The twist-bend phase (NTB) 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 NTB 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 NTB 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 NTB phase

Structural variants of RM734 in the design of splay nematic materials

The recent discovery of the splay nematic phase, a new nematic polymorph that has been found to be both polar and ferroelectric, is the lead paragraph in an entirely new chapter in the history of liquid crystals. The potential for transformative applications utilising this state of matter–such as photonics, non-linear optics, memory applications and so on–can only be met with significant improvements in the temperature range of existing materials such as 4-(4-nitrophenoxycarbonyl)phenyl 4-methoxy-2-methoxybenzoate (RM734). Herein we present several families of materials which are structurally related to the archetypal new nematic material, RM734, including the first non-rod-like materials within the context of the splay nematic phase. We find that the incidence (or absence) of this new nematic variant in a designer material cannot be easily rationalised in terms of molecular dipole moment or polarisability. However, mixture formulation shows promise for the engineering of materials with improved working temperature ranges

Guest-host systems containing anthraquinone dyes with multiple visible transitions giving positive and negative dichroic order parameters : an assessment of principal molecular axes and computational methods

Three 1,4-disubstituted anthraquinone dyes with bis(4-n-butylphenyl) substituents connected via amine or amide linking groups have been studied as guest molecules dissolved in the nematic host E7. UV-visible absorption spectroscopy has shown each of the dyes to exhibit multiple absorption bands in the visible region, and dichroic order parameters obtained from polarised spectra of aligned guest–host samples were shown to differ significantly between the bands for each dye, and between the dyes. Time-dependent density functional theory calculations indicated that each dye exhibits several transitions, giving transition dipole moment vectors with a range of orientations, and fully atomistic molecular dynamics simulations of the guest–host mixtures showed differences in the calculated molecular alignments of the dyes. Combining the results from these two sets of calculations enabled a comparison of molecular alignment models based on the moments of inertia and the surface tensors of the dyes. The match between calculated and experimental values was improved significantly when using the surface tensor rather than the moment of inertia model, indicating that the shapes of the molecular surfaces of these dyes are crucial to their alignment. A novel method of calculating polarised UV-visible absorption spectra of dyes in liquid crystal hosts is also presented

Conclusions about Niche Expansion in Introduced Impatiens walleriana Populations Depend on Method of Analysis

Determining the degree to which climate niches are conserved across plant species' native and introduced ranges is valuable to developing successful strategies to limit the introduction and spread of invasive plants, and also has important ecological and evolutionary implications. Here, we test whether climate niches differ between native and introduced populations of Impatiens walleriana, globally one of the most popular horticultural species. We use approaches based on both raw climate data associated with occurrence points and ecological niche models (ENMs) developed with Maxent. We include comparisons of climate niche breadth in both geographic and environmental spaces, taking into account differences in available habitats between the distributional areas. We find significant differences in climate envelopes between native and introduced populations when comparing raw climate variables, with introduced populations appearing to expand into wetter and cooler climates. However, analyses controlling for differences in available habitat in each region do not indicate expansion of climate niches. We therefore cannot reject the hypothesis that observed differences in climate envelopes reflect only the limited environments available within the species' native range in East Africa. Our results suggest that models built from only native range occurrence data will not provide an accurate prediction of the potential for invasiveness if applied to areas containing a greater range of environmental combinations, and that tests of niche expansion may overestimate shifts in climate niches if they do not control carefully for environmental differences between distributional areas