Structural characterization of linear isomalto-/malto-oligomer products synthesized by the novel GTFB 4,6-α-glucanotransferase enzyme from Lactobacillus reuteri 121

Recently, a novel glucansucrase (GS)-like gene (gtfB) was isolated from the probiotic bacterium Lactobacillus reuteri 121 and expressed in Escherichia coli. The purified recombinant GTFB enzyme was characterized and turned out to be inactive with sucrose, the natural GS substrate. Instead, GTFB acted on malto-oligosaccharides (MOSs), thereby yielding elongated gluco-oligomers/polymers containing besides (α1→4) also (α1→6) glycosidic linkages, and it was classified as a 4,6-α-glucanotransferase. To gain more insight into its reaction specificity, incubations of the GTFB enzyme with a series of MOSs and their corresponding alditols [degree of polymerization, DP2(-ol)–DP7 (-ol)] were carried out, and (purified) products were structurally analyzed with matrix-assisted laser desorption ionization time-of-flight mass spectrometry and one-/two-dimensional 1H and 13C nuclear magnetic resonance spectroscopy. With each of the tested malto-oligomers, the GTFB enzyme yielded series of novel linear isomalto-/malto-oligomers, in the case of DP7 up to DP >35.

Volatile aldehydes in libraries and archives

Volatile aldehydes are produced during degradation of paper-based materials. This may result in their accumulation in archival and library repositories. However, no systematic study has been performed so far. In the frame of this study, passive sampling was carried out at ten locations in four libraries and archives. Despite the very variable sampling locations, no major differences were found, although air-filtered repositories were found to have lower concentrations while a non-ventilated newspaper repository exhibited the highest concentrations of volatile aldehydes (formaldehyde, acetaldehyde, furfural and hexanal). Five employees in one institution were also provided with personal passive samplers to investigate employees’ exposure to volatile aldehydes. All values were lower than the presently valid exposure limits. The concentration of volatile aldehydes, acetic acid, and volatile organic compounds (VOCs) in general was also compared with that of outdoor-generated pollutants. It was evident that inside the repository and particularly inside archival boxes, the concentration of VOCs and acetic acid was much higher than the concentration of outdoor-generated pollutants, which are otherwise more routinely studied in connection with heritage materials. This indicates that further work on the pro-degradative effect of VOCs on heritage materials is necessary and that monitoring of VOCs in heritage institutions should become more widespread

Patient-reported outcomes following flexible sigmoidoscopy screening for colorectal cancer in a demonstration screening programme in the UK

<p>OBJECTIVES: Flexible sigmoidoscopy (FS) screening for colorectal cancer will be introduced into the National Cancer Screening Programmes in England in 2013. Patient-reported outcome measures (PROMs) from trial participants indicate high acceptability and no adverse physical or psychological consequences, but this may not generalize to routine screening in the community. This study examined PROMs in a community-based FS screening programme.</p> <p>METHODS: Eligible adults aged 58-59 (n = 2016) registered at 34 London general practices were mailed a National Health Service-endorsed invitation to attend FS screening. Pain and side-effects were assessed in a 'morning-after' questionnaire, and satisfaction was assessed in a three-month follow-up questionnaire. Anxiety, self-rated health and colorectal symptoms were assessed at prescreening and follow-up.</p> <p>RESULTS: In total, 1020 people attended screening and were included in the current analyses, of whom 913 (90%) returned the morning-after questionnaire, and 674 (66%) the follow-up questionnaire. The prescreening questionnaire had been completed by 751 (74%) of those who attended. The majority (87%) of respondents reported no pain or mild pain, and the most frequent side-effect (wind) was only experienced more than mildly by 16%. Satisfaction was extremely high, with 98% glad they had the test; 97% would encourage a friend to have it. From prescreening to follow-up there were no changes in anxiety or self-rated health, and the number of colorectal symptoms declined. Satisfaction and changes in wellbeing were not moderated by gender, deprivation, ethnicity or screening outcome.</p> <p>CONCLUSIONS: PROMs indicate high acceptability of FS screening in 58-59 year olds, with no adverse effects on colorectal symptoms, health status or psychological wellbeing.</p&gt

Machine learning-assisted non-destructive plasticizer identification and quantification in historical PVC objects based on IR spectroscopy

Non-destructive spectroscopic analysis combined with machine learning rapidly provides information on the identity and content of plasticizers in PVC objects of heritage value. For the first time, a large and diverse collection of more than 100 PVC objects in different degradation stages and of diverse chemical compositions was analysed by chromatographic and spectroscopic techniques to create a dataset used to construct classification and regression models. Accounting for this variety makes the model more robust and reliable for the analysis of objects in museum collections. Six different machine learning classification algorithms were compared to determine the algorithm with the highest classification accuracy of the most common plasticizers, based solely on the spectroscopic data. A classification model capable of the identification of di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, diisononyl phthalate, diisodecyl phthalate, a mixture of diisononyl phthalate and diisodecyl phthalate, and unplasticized PVC was constructed. Additionally, regression models for quantification of di(2-ethylhexyl) phthalate and di(2-ethylhexyl) terephthalate in PVC were built. This study of real-life objects demonstrates that classification and quantification of plasticizers in a general collection of degraded PVC objects is possible, providing valuable data to collection managers

The mechanism of caesium intercalation of graphene

Properties of many layered materials, including copper- and iron-based superconductors, topological insulators, graphite and epitaxial graphene can be manipulated by inclusion of different atomic and molecular species between the layers via a process known as intercalation. For example, intercalation in graphite can lead to superconductivity and is crucial in the working cycle of modern batteries and supercapacitors. Intercalation involves complex diffusion processes along and across the layers, but the microscopic mechanisms and dynamics of these processes are not well understood. Here we report on a novel mechanism for intercalation and entrapment of alkali-atoms under epitaxial graphene. We find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Our findings are relevant for the future design and application of graphene-based nano-structures. Similar mechanisms can also play a role for intercalation of layered materials.Comment: 8 pages, 7 figures in published form, supplementary information availabl

The Mass and Ion Kinetic Energy Spectra of Fluoro-Chloro Substituted Norbornanes and Nortricyclanes

The mass and ion kinetic energy spectra of difluoro- and fluoro- chloro-norbornanes and fluoro-chloro-nortricyclanes have been examined. In several instances the similarity of the mass spectra makes it impossible to distinguish the diastereoisomers from each other. In contrast, however, their ion kinetic energy spectra differ clearly and allow unambiguous differentiation of the stereoisomers

Al2O3-films on Ni3Al(111): a template for nanostructured cluster growth

In scanning tunnelling microscope images of thin Al2O3-films grown on Ni3Al(111) at 1000 K two super-lattices with periodicities of 2.6 and 4.5 nm, respectively, can be identified. These well-ordered nanostructures can be used as nucleation centres for metal particle growth. It can be shown that both nanostructures act as a template for the fabrication of ordered assemblies of metal clusters by mere physical vapour deposition. The degree of ordering of these nanostructures is largely dependent on the metal deposited. Here we report on the growth of Cu, Ag, Au, Mn, and V clusters on the Al2O3-films. The best results as far as ordering of the clusters is concerned was reached for V deposition at 550 K, which resulted in a nearly perfect hexagonal array of clusters with a spacing of 2.6 nm

Nematic-Wetted Colloids in the Isotropic Phase: Pairwise Interaction, Biaxiality and Defects

We calculate the interaction between two spherical colloidal particles embedded in the isotropic phase of a nematogenic liquid. The surface of the particles induces wetting nematic coronas that mediate an elastic interaction. In the weak wetting regime, we obtain exact results for the interaction energy and the texture, showing that defects and biaxiality arise, although they are not topologically required. We evidence rich behaviors, including the possibility of reversible colloidal aggregation and dispersion. Complex anisotropic self-assembled phases might be formed in dense suspensions.Comment: 4 pages, 6 figure

Interaction and flocculation of spherical colloids wetted by a surface-induced corona of paranematic order

Particles dispersed in a liquid crystal above the nematic-isotropic phase transition are wetted by a surface-induced corona of paranematic order. Such coronas give rise to pronounced two-particle interactions. In this article, we report details on the analytical and numerical study of these interactions published recently [Phys. Rev. Lett. 86, 3915 (2001)]. We especially demonstrate how for large particle separations the asymptotic form of a Yukawa potential arises. We show that the Yukawa potential is a surprisingly good description for the two-particle interactions down to distances of the order of the nematic coherence length. Based on this fact, we extend earlier studies on a temperature induced flocculation transition in electrostatically stabilized colloidal dispersions [Phys. Rev. E 61, 2831 (2000)]. We employ the Yukawa potential to establish a flocculation diagram for a much larger range of the electrostatic parameters, namely the surface charge density and the Debye screening length. As a new feature, a kinetically stabilized dispersion close to the nematic-isotropic phase transition is found.Comment: Revtex v4.0, 16 pages, 12 Postscript figures. Accepted for publication in Phys. Rev.