Fibre diffraction in the analysis of filamentous virus structure

In many plant and bacterial viruses, a filamentous nucleocapsid makes up the entire virus particle. These viruses usually form fibres naturally, but they do not crystallize. Fibre diffraction has therefore been the method of choice for structural studies, aided in recent years by cryo-electron microscopy (EM) and solid state nuclear magnetic resonance (ssNMR). Filamentous viruses, particularly tobacco mosaic virus (TMV), have been important in developing fibre diffraction methods, and fibre diffraction allowed TMV to be among the first virus structures determined. Structures of several viruses related to TMV and several filamentous bacterial viruses have been determined at resolutions of 3?Å or better, and lower resolution structures have been determined by fibre diffraction, sometimes in conjunction with other methods, for many other, unrelated, filamentous viruses.     

Assessing the Antimicrobial Activity of Polyisoprene Based Surfaces

There has been an intense research effort in the last decades in the field of biofouling prevention as it concerns many aspects of everyday life and causes problems to devices, the environment, and human health. Many different antifouling and antimicrobial materials have been developed to struggle against bacteria and other micro- and macro-organism attachment to different surfaces. However the “miracle solution” has still to be found. The research presented here concerns the synthesis of bio-based polymeric materials and the biological tests that showed their antifouling and, at the same time, antibacterial activity. The raw material used for the coating synthesis was natural rubber. The polyisoprene chains were fragmented to obtain oligomers, which had reactive chemical groups at their chain ends, therefore they could be modified to insert polymerizable and biocidal groups. Films were obtained by radical photopolymerization of the natural rubber derived oligomers and their structure was altered, in order to understand the mechanism of attachment inhibition and to increase the efficiency of the anti-biofouling action. The adhesion of three species of pathogenic bacteria and six strains of marine bacteria was studied. The coatings were able to inhibit bacterial attachment by contact, as it was verified that no detectable leaching of toxic molecules occurred.     

Physical gelation of crystallizing metallocene and Ziegler-Natta ethylene-hexene copolymers

The effect of molecular architecture on the evolution of viscoelastic properties during crystallization was investigated using ethylene-hexene copolymers manufactured via metallocene (M-LLDPE) and Ziegler-Natta (ZN-LLDPE) processes. Differences in branching distribution were shown to have a drastic effect on the viscoelastic properties near the gel point. It is shown that the branching distribution rather than branch content is the determining parameter for the evolution of the rheological properties during isothermal and non-isothermal crystallization, and for the width of the solidification interval. We developed a partial melting technique for the preparation of stable critical gels of LLDPE whose viscoelastic properties correspond to the intermediate state between melt and solid. Local molecular conformation and crystallinity in these gels were characterized by Raman spectroscopy, which shows that the transition from melt-like to solid-like rheological behavior (physical gelation) in LLDPE occurs at a very low overall crystallinity of less than 5%.     

Adhesion between oppositely charged polyelectrolytes

The adhesion between a grafted polyelectrolyte layer (brush) and a gel of an oppositely charged polyelectrolyte has been measured as a function of applied pressure, and the interface has been traced using neutron reflectometry. The interface (in aqueous medium at pH 6) between the (polycationic) brush and the (polyanionic) gel has a limited pressure dependence, with a small amount of deformation of the interface at the brush–gel contact. Brushes with a dry thickness of up to 13 nm exhibit weak adhesion (measured using a mechanical force tester) with an adhesive failure when the gel is detached. Thicker brushes result in the gel exhibiting cohesive failure. Reversing the geometry, whereby a polycationic brush is replaced with a polyanion and the polyanionic gel is replaced with a polycation, reveals that the pH dependence of the adhesion is moderately symmetric about pH 6, but that the maximum force required to separate the polycation gel from the polyanion brush over the range of pH is greater than that for the polycation brush and polyanion gel. The polyanion used is poly(methacrylic acid) (PMAA) and polycations of poly[2-(diethylamino)ethyl methacrylate] (PDEAEMA) and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) were used.     

Threshold Levels for Bromate Formation In Drinking Water

Ozone is a sufficiently strong oxidant to cause the oxidation of bromide ion and formation of bromate ion. In this study, bromate ion formation in a wide variety of drinking water sources was analyzed, with bromate ion formed in all sources under drinking water treatment conditions. Threshold levels for pH, bromide ion concentration, and ozone dose were found to be source-specific. Two non-linear empirical models were developed to predict bromate ion formation; these models are easy to use and require only several water quality and treatment variables. The models were tested against several literature data and a good simulation was found in other bench-scale tests, whereas the model tended to under-predict bromate ion formation in pilot-scale and full-scale programs.     

Combustion of Mechanically Alloyed Aluminum‐Magnesium Powders in Steam

Mechanically alloyed Al ⋅ Mg powders with the mole fraction of Al varied from 0.47 to 0.9 were burned at atmospheric pressure in water vapor. The powders were carried by nitrogen through the center of a hydrogen‐oxygen diffusion flame. The particles ignited in the steam at approximately 2500 K, generated as the hydrogen‐oxygen flame product. Filtered photomultiplier tubes were used to capture the optical emission traces of individual particles as they burned. It was assumed that the measured durations of individual emission pulses are representative of individual particle burn times. Distributions of the burn times were obtained for each powder and correlated with respective particle size distributions to relate particle burn times with their sizes. Color temperatures corresponding to the particle emission signals were also obtained. It was observed that the burn times measured for alloys were more close to those of pure Al than Mg; for particles smaller than 2–3 μm, burn times for the alloys were shorter than for pure metal particles. The effect was strongest for the alloy with 50 wt‐% of Mg (Al_0.47Mg_0.54). Approximately, burn times, τ, as a function of particle size, d, could be estimated using a τ∼dⁿ law, where n increased from 0.72 to 1.05 as the mole fraction of Mg increased from 0.1 to 0.53. The particle flame temperatures varied between 2500 and 3100 K for all alloys except for Al_0.7Mg_0.3, for which the temperatures were somewhat lower. The measured flame temperatures were reasonably close to the adiabatic flame temperatures calculated for combustion of mixed elemental Al and Mg in steam.     

Computer-controlled Raman microspectroscopy (CC-Raman): A method for the rapid characterization of individual atmospheric aerosol particles

The ability of an atmospheric aerosol particle to impact climate by acting as a cloud condensation nucleus (CCN) or an ice nucleus (IN), as well as scatter and absorb solar radiation is determined by its physicochemical properties at the single particle level, specifically size, morphology, and chemical composition. The identification of the secondary species present in individual aerosol particles is important as aging, which leads to the formation of these species, can modify the climate relevant behavior of particles. Raman microspectroscopy has a great deal of promise for identifying secondary species and their mixing with primary components, as it can provide detailed information on functional groups present, morphology, and internal structure. However, as with many other detailed spectroscopic techniques, manual analysis by Raman microspectroscopy can be slow, limiting single particle statistics and the number of samples that can be analyzed. Herein, the application of computer-controlled Raman (CC-Raman) for detailed physicochemical analysis that increases throughput and minimizes user bias is described. CC-Raman applies automated mapping to increase analysis speed allowing for up to 100 particles to be analyzed in an hour. CC-Raman is applied to both laboratory and ambient samples to demonstrate its utility for the analysis of both primary and, most importantly, secondary components (sulfate, nitrate, ammonium, and organic material). Reproducibility and precision are compared to computer controlled-scanning electron microscopy (CCSEM). The greater sample throughput shows the potential for CC-Raman to improve particle statistics and advance our understanding of aerosol particle composition and mixing state, and, thus, climate-relevant properties.

© 2017 American Association for Aerosol Research     

Evaluation of Simple and Inexpensive High-Throughput Methods for Phytic Acid Determination

High‐throughput/low‐cost/low‐tech methods for phytic acid determination that are sufficiently accurate and reproducible would be of value in plant genetics, crop breeding and in the food and feed industries. Variants of two candidate methods, those described by Vaintraub and Lapteva (Anal Biochem 175:227–24, 1988 ; “VL” methods) and Huang and Lantzsch (J Sci Food Agric 34:1423–1426, 1983 ; “HL” methods), were evaluated. The primary concern with these methods is that, due to interference of matrix constituents including inorganic P, they can overestimate phytic acid and are ineffective at low levels of phytic acid. Twelve seed flours, representing lines of soybean, maize, barley and dry bean, containing a wide range of phytic acid levels, were analyzed by a minimum of eight cooperating laboratories using three variants of the VL method and two variants of the HL method. No method had consistently acceptable (?2.0”) “Horwitz ratios”, a measure of reproducibility, although some treatments approached that. For example, one variant of the VL method when used to assay a soybean flour with a “standard” level of phytic acid had a Horwitz ratio of 2.15. Some variants of the VL method were adequate for analyses of cereal grains regardless of phytic acid level but none accurately measured phytic acid when at low levels in soybean flours. One variant of the HL method in which the 0.2 N HCl extraction media is modified to contain 10% Na₂SO₄, did accurately measure phytic acid levels in both cereal and legume flours regardless of endogenous phytic acid levels or matrix constituents.     

Substrate Selection Influences Molecular Recognition in a Screen for Lymphoid Tyrosine Phosphatase Inhibitors

Assay design is an important variable that influences the outcome of an inhibitor screen. Here, we have investigated the hypothesis that protein tyrosine phosphatase inhibitors with improved biological activity could be identified from a screen by using a biologically relevant peptide substrate, rather than traditional phosphotyrosine mimetic substrates. A 2000‐member library of drugs and drug‐like compounds was screened for inhibitors of lymphoid tyrosine phosphatase (LYP) by using both a peptide substrate (Ac‐ARLIEDNE‐pCAP‐TAREG‐NH₂, peptide 1) and a small‐molecule phosphotyrosine mimetic substrate (difluoromethyl umbelliferyl phosphate, DiFMUP). The results demonstrate that compounds that inhibited enzyme activity on the peptide substrate had greater biological activity than compounds that only inhibited enzyme activity on DiFMUP. Finally, epigallocatechin‐3,5‐digallate was identified as the most potent inhibitor of lymphoid tyrosine phosphatase activity to date, with an IC₅₀ of 50 nM and significant activity in T‐cells. Molecular docking simulations provided a first model for binding of this potent inhibitor to LYP; this will constitute the platform for ongoing lead optimization efforts.