Light scattering study of the “pseudo-layer” compression elastic constant in a twist-bend nematic liquid crystal

The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or “pseudo-layers”, each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining “layer” compression and bending ought to be characterized by an effective layer compression elastic constant Beff and average director splay constant Keff1. The magnitude of Keff1 is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, Beff could differ substantially from the typical value of ∼10⁶ Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the “pseudo-layer” structure of the TB phase with Beff in the range 10³–10⁴ Pa. We show additionally that the temperature dependence of Beff at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director

Select Metal and Metalloid Surveillance of Free-ranging Eastern Box Turtles from Illinois and Tennessee

The Eastern box turtle has been proposed as a biomonitor because it is long lived, relies on the environment for food and water, and has a small home range. To establish this designation, ISTC partnered with the Illinois Natural History Survey, the College of Veterinary Medicine at the University of Illinois, and the Clinch River Environmental Studies Organization. Plasma samples from 273 free-range box turtles were collected in 2011 and 2012 in Tennessee and Illinois. Full results reported in Allender, Matthew C., et al (2015). "Select metal and metalloid surveillance of free-ranging Eastern box turtles from Illinois and Tennessee (Terrapene carolina carolina)." Ecotoxicology 24, 1269–1278. https://doi.org/10.1007/s10646-015-1498-5Ope

The role of growth directors in controlling the morphology of hematite nanorods

The control of the growth of hematite nanoparticles from iron chloride solutions under hydrothermal conditions in the presence of two different structure promoters has been studied using a range of both structural and spectroscopic techniques including the first report of photo induced force microscopy (PiFM) to map the topographic distribution of the structure-directing agents on the developing nanoparticles. We show that the shape of the nanoparticles can be controlled using the concentration of phosphate ions up to a limit determined to be ~6 × 10−3 mol. Akaganéite (β-FeOOH) is a major component of the nanoparticles formed in the absence of structure directors but only present in the very early stages (< 8 h) of particle growth when phosphate is present. The PiFM data suggest a correlation between the areas in which phosphate ions are adsorbed and areas where akaganéite persists on the surface. In contrast, goethite (α-FeOOH) is a directly observed precursor of the hematite nanorods when 1,2-diamino propane is present. The PiFM data shows goethite in the center of the developing particles consistent with a mechanism in which the iron hydroxide re-dissolves and precipitates at the nanorod ends as hematite

The Genetic and Molecular Basis of O-Antigenic Diversity in Burkholderia pseudomallei Lipopolysaccharide

Lipopolysaccharide (LPS) is one of the most important virulence and antigenic components of Burkholderia pseudomallei, the causative agent of melioidosis. LPS diversity in B. pseudomallei has been described as typical, atypical or rough, based upon banding patterns on SDS-PAGE. Here, we studied the genetic and molecular basis of these phenotypic differences. Bioinformatics was used to determine the diversity of genes known or predicted to be involved in biosynthesis of the O-antigenic moiety of LPS in B. pseudomallei and its near-relative species. Multiplex-PCR assays were developed to target diversity of the O-antigen biosynthesis gene patterns or LPS genotypes in B. pseudomallei populations. We found that the typical LPS genotype (LPS genotype A) was highly prevalent in strains from Thailand and other countries in Southeast Asia, whereas the atypical LPS genotype (LPS genotype B) was most often detected in Australian strains (∼13.8%). In addition, we report a novel LPS ladder pattern, a derivative of the atypical LPS phenotype, associated with an uncommon O-antigen biosynthesis gene cluster that is found in only a small B. pseudomallei sub-population. This new LPS group was designated as genotype B2. We also report natural mutations in the O-antigen biosynthesis genes that potentially cause the rough LPS phenotype. We postulate that the diversity of LPS may correlate with differential immunopathogenicity and virulence among B. pseudomallei strains

Anthrax: Evolutionary approaches for genetic-based investigative tools

A TaqMan-minor groove binding assay designed around a nonsense mutation in the plcR gene was used to genotype Bacillus anthracis, B. cereus, and B. thuringiensis isolates. The assay differentiated B. anthracis from these genetic near-neighbors and determined that the nonsense mutation is ubiquitous across 89 globally and genetically diverse B. anthracis strains

SELECTION OF SURPLUS PLUTONIUM MATERIALS FOR DISPOSITION TO WIPP

The U.S. Department of Energy (DOE) is preparing a Surplus Plutonium Disposition (SPD) Supplemental Environmental Impact Statement (SEIS). Included in the evaluation are up to 6 metric tons (MT) of plutonium in the form of impure oxides and metals for which a disposition plan has not been decided, among options that include preparation as feed for the Mixed Oxide Fuel Fabrication Facility; disposing to high-level waste through the Savannah River Site (SRS) HB Line and H Canyon; can-in-canister disposal using the SRS Defense Waste Processing Facility; and preparation for disposal at the Waste Isolation Pilot Plant (WIPP). DOE and SRS have identified at least 0.5 MT of plutonium that, because of high levels of chemical and isotopic impurities, is impractical for disposition by methods other than the WIPP pathway. Characteristics of these items and the disposition strategy are discussed

From 3D to 2D: A review of the molecular imprinting of proteins

Molecular imprinting is a generic technology that allows for the introduction of sites of specific molecular affinity into otherwise homogeneous polymeric matrices. Commonly this technique has been shown to be effective when targeting small molecules of molecular weight <1500, while extending the technique to larger molecules such as proteins has proven difficult. A number of key inherent problems in protein imprinting have been identified, including permanent entrapment, poor mass transfer, denaturation, and heterogeneity in binding pocket affinity, which have been addressed using a variety of approaches. This review focuses on protein imprinting in its various forms, ranging from conventional bulk techniques to novel thin film and monolayer surface imprinting approaches

Concentration dependent atrazine-atrazine complex formation promotes selectivity in atrazine imprinted polymers

An atrazine (ATR) molecularly imprinted polymer (MIP) was prepared using a non-covalent strategy. The affinity and selectivity of the polymer was initially evaluated under non-equilibrium conditions and the polymer was shown to possess good template selectivity. The selectivity of the polymer was further investigated under equilibrium conditions and over a range of concentrations using Scatchard plots and Hill plots and by assessing distribution coefficients and normalised selectivity values. It was observed that both selectivity and affinity were dependent on the concentration of the ligand and that unusually selectivity and affinity were better at higher atrazine concentrations. It was concluded that this phenomenon resulted from the formation of atrazine-atrazine complexes during the pre-polymerisation stage and during rebinding and that the polymer demonstrated improved atrazine affinity when the conditions favoured complex formation

Novel biphasic separations utilising highly selective molecularly imprinted polymers as biorecognition solvent extraction agents

Molecularly imprinted polymers (MIPs) represent a class of artificial receptors that promise an environmentally robust alternative to naturally occurring biorecognition elements of biosensing devices and systems. However, in general, the performance of conventional MIPs in aqueous environments is poor. In the study reported here, this limitation has been addressed by the novel application of MIPs as a solvent extraction solid phase in a biphasic solvent system. This paper describes a previously unreported use of MIPs as solvent extraction reagents, their successful application to aqueous sample media and the opportunities for utilisation of this unique system in novel biosensing and separation procedures. This study demonstrates the development of a novel biphasic solvent system utilising MIP in the extracting phase to enhance both efficiency and selectivity of a simple two phase liquid extraction. Monodisperse propranolol imprinted polymer microspheres [p(divinylbenzene-co-methacrylic acid)] were prepared by precipitation polymerisation. Initially, the affinity of the polymers for (R,S)-propranolol was assessed by established techniques whereby the MIP demonstrated greater affinity for the template than did the non-imprinted control polymer (NIP). Importantly, MIP performance was also assessed using the novel dual solvent system. The depletion of (R,S)-propranolol from the aqueous phase into the polymer containing organic phase was determined. When compared to control extractions containing no polymer the presence of MIP in the extracting solvent phase resulted in an increased extraction of (R,S)-propranolol from the aqueous phase. Importantly, this extraction was significantly greater in the presence of MIP when compared to NIP. This unique principle generates opportunities for MIP based extractions and chemical enrichments in industrial applications, offering commercial, ecological and practical advantages to traditional solvent extraction techniques. The technique is readily transferable to analytical microsystems utilising MIP recognition elements generating promising opportunities for MIP based sensing of aqueous sample media