Electrostatic discharge sensitivity and electrical conductivity of composite energetic materials

Composite energetic material response to electrical stimuli was investigated and a correlation between electrical conductivity and ignition sensitivity was examined. The composites consisted of micrometer particle aluminum combined with another metal, metal oxide, or fluoropolymer. Of the nine tested mixtures, aluminum (Al) with copper oxide (CuO) was the only mixture to ignite by electrostatic discharge. Under the loose powder conditions of these experiments, the Al–CuO minimum ignition energy (MIE) is 25 mJ and exhibited an electrical conductivity two orders of magnitude higher than the next composite. This study showed a similar trend in MIE for ignition triggered by a discharged spark compared with a thermal hot wire source.     

DANGLE: A Bayesian inferential method for predicting protein backbone dihedral angles and secondary structure

This paper introduces DANGLE, a new algorithm that employs Bayesian inference to estimate the likelihood of all possible values of the backbone dihedral angles ? and ψ for each residue in a query protein, based on observed chemical shifts and the conformational preferences of each amino acid type. The method provides robust estimates of ? and ψ within realistic boundary ranges, an indication of the degeneracy in the relationship between shift measurements and conformation at each site, and faithful secondary structure state assignments. When a simple degeneracy-based filtering procedure is applied, DANGLE offers an ideal compromise between accuracy and coverage when compared with other shift-based dihedral angle prediction methods. In addition, per residue analysis of shift/structure degeneracy has potential to be a useful new approach for studying the properties of unfolded proteins, with sufficient sensitivity to identify regions of residual structure in the acid denatured state of apomyoglobin.     

A Review of Surface Functionalized Amine Terminated Dendrimers for Application in Biological and Molecular Sensing

Dendrimers are three dimensional nanosized synthetic molecules that have internal cavities and numerous surface groups. In recent times they have received increased attention in sensing applications. For dendrimers to be used as sensors, they most commonly require functionalization at their surface. This is because the surface is generally the first point of contact between the dendrimer and the outside world, hence surface functionalization serves to selectively home in on the target analyte. Further, sensor signals may be transmitted through surface functionalities e.g. fluorochromic molecules. It is therefore important to document surface functionalization approaches. Dendrimers with amine surface groups have the advantage of being able to be conjugated to other molecules via an amide linkage, which is one of the most fundamental and widespread chemical bonds in nature. In this paper we demonstrate the properties of dendrimers that make them so applicable to sensing. We review several methods for functionalizing dendrimers via an amide linkage, as well as present a review of surface functionalized polyamidoamine, polyamine, and polypeptide dendrimers that have been employed for biological, chemical and molecular sensing.     

Mixed electrolytes in hydrophobic interaction chromatography†

An essential part of the modulation of protein‐binding capacity in hydrophobic interaction chromatography is the buffer‐salt system. Besides using “single” electrolytes, multicomponent electrolyte mixtures may be used as an additional tool. Both the protein solubility and the binding capacity depend on the position of a salt in the so‐called Hofmeister series. Specific interactions are observed for an individual protein‐salt combination. For salt mixtures, selectivity, recovery, and binding capacity do not behave like for the single salts that are positioned in between the two mixed components in the Hofmeister series, as the continuous correlation would suggest. Thus, finding strategies for mixed salts could potentially lead to improved capacities in hydrophobic interaction chromatography. Mixtures of ammonium sulfate, sodium citrate, sodium sulfate, sodium chloride, sodium acetate, and glycine were used to investigate the binding capacities for lysozyme and a monoclonal antibody on various hydrophobic resins. Resin capacity for two investigated proteins increases when mixtures consisting of a chaotropic and a kosmotropic salt are applied. It seems to be related to the rather basic isoelectric points of the proteins.     

Synthesis of Benzopyran Derivatives,XIV: New Procedure for the Preparation of 2,2-Dimethyl-2H-chromenes

2,2-Dimethyl-4-methoxychromans (1–12) have been converted into 2,2-dimethyl-2H-chromenes (13–24) in acidic media.     

Identification of polyimide materials using quantitative CE with UV and QTOF‐MS detection

Polyimides (PIs) are a group of widely used synthetic materials that service a variety of different purposes including microelectronics, insulating films and aerospace applications. Depending on the requirements (defined by the particular final product), the actual composition of PIs may show substantial chemical variation. To study this variation in chemical structure, CE‐MS can be employed for the determination of PI composition following chemical degradation of the polymer sample. PI is chemically decomposed to corresponding aromatic diamine and carboxylic acid components using an alkali fusion reaction. Solid polymer samples are fused in a potassium hydroxide melt yielding reaction products that are diluted in acid and can be immediately analysed by CE coupled to a Q/TOF‐MS with quantification performed using conventional UV detection. This approach involves a simple and rapid sample preparation yielding both qualitative and quantitative information regarding the chemical composition of the polymer. Application of the CE‐MS approach is shown for a range of commercially available PI and poly(amide–imide) materials and the results are used to infer the respective chemical compositions.     

Comprehensive two-dimensional liquid chromatography coupled to the ABTS radical scavenging assay: a powerful method for the analysis of phenolic antioxidants

The on-line combination of comprehensive two-dimensional liquid chromatography (LC?×?LC) with the 2,2′-azino-bis(3-ethylbenzothiazoline)-6 sulphonic acid (ABTS) radical scavenging assay was investigated as a powerful method to determine the free radical scavenging activities of individual phenolics in natural products. The combination of hydrophilic interaction chromatography (HILIC) separation according to polarity and reversed-phase liquid chromatography (RP-LC) separation according to hydrophobicity is shown to provide much higher resolving power than one-dimensional separations, which, combined with on-line ABTS detection, allows the detailed characterisation of antioxidants in complex samples. Careful optimisation of the ABTS reaction conditions was required to maintain the chromatographic separation in the antioxidant detection process. Both on-line and off-line HILIC?×?RP-LC–ABTS methods were developed, with the former offering higher throughput and the latter higher resolution. Even for the fast analyses used in the second dimension of on-line HILIC?×?RP-LC, good performance for the ABTS assay was obtained. The combination of LC?×?LC separation with an on-line radical scavenging assay increases the likelihood of identifying individual radical scavenging species compared to conventional LC–ABTS assays. The applicability of the approach was demonstrated for cocoa, red grape seed and green tea phenolics.