Identification and Role of a 6‐Deoxy‐4‐Keto‐Hexosamine in the Lipopolysaccharide Outer Core of Yersinia enterocolitica Serotype O:3

The outer core (OC) region of Yersinia enterocolitica serotype O:3 lipopolysaccharide is a hexasaccharide essential for the integrity of the outer membrane. It is involved in resistance against cationic antimicrobial peptides and plays a role in virulence during early phases of infection. We show here that the proximal residue of the OC hexasaccharide is a rarely encountered 4‐keto‐hexosamine, 2‐acetamido‐2,6‐dideoxy‐D ‐xylo‐hex‐4‐ulopyranose (Sugp) and that WbcP is a UDP‐GlcNAc‐4,6‐dehydratase enzyme responsible for the biosynthesis of the nucleotide‐activated form of this rare sugar converting UDP‐2‐acetamido‐2‐deoxy‐D ‐glucopyranose (UDP‐D ‐GlcpNAc) to UDP‐2‐acetamido‐2,6‐dideoxy‐D ‐xylo‐hex‐4‐ulopyranose (UDP‐ Sugp). In an aqueous environment, the 4‐keto group of this sugar was present in the 4‐dihydroxy form, due to hydration. Furthermore, evidence is provided that the axial 4‐hydroxy group of this dihydroxy function was crucial for the biological role of the OC, that is, in the bacteriophage and enterocoliticin receptor structure and in the epitope of a monoclonal antibody.     

On the choice and influence of the number of boosting steps for high-dimensional linear Cox-models

In biomedical research, boosting-based regression approaches have gained much attention in the last decade. Their intrinsic variable selection procedure and ability to shrink the estimates of the regression coefficients toward 0 make these techniques appropriate to fit prediction models in the case of high-dimensional data, e.g. gene expressions. Their prediction performance, however, highly depends on specific tuning parameters, in particular on the number of boosting iterations to perform. This crucial parameter is usually selected via cross-validation. The cross-validation procedure may highly depend on a completely random component, namely the considered fold partition. We empirically study how much this randomness affects the results of the boosting techniques, in terms of selected predictors and prediction ability of the related models. We use four publicly available data sets related to four different diseases. In these studies, the goal is to predict survival end-points when a large number of continuous candidate predictors are available. We focus on two well known boosting approaches implemented in the R-packages CoxBoost and mboost, assuming the validity of the proportional hazards assumption and the linearity of the effects of the predictors. We show that the variability in selected predictors and prediction ability of the model is reduced by averaging over several repetitions of cross-validation in the selection of the tuning parameters.     

Lamellar gels and spontaneous vesicles in catanionic surfactant mixtures

Caillé analysis of the small-angle X-ray line shape of the lamellar phase of 7:3 wt/wt cetyltrimethylammonium tosylate (CTAT)/sodium dodecylbenzene sulfonate (SDBS) bilayers shows that the bending elastic constant is kappa = (0.62 +/- 0.09)k(B)T. From this and previous results, the Gaussian curvature constant is kappa = (-0.9 +/- 0.2)k(B)T. For 13:7 wt/wt CTAT/SDBS bilayers, the measured bending elasticity decreases with increasing water dilution, in good agreement with predictions based on renormalization theory, giving kappa(o) = 0.28k(B)T. These results show that surfactant mixing is sufficient to make kappa approximately k(B)T, which promotes strong, Helfrich-type repulsion between bilayers that can dominate the van der Waals attraction. These are necessary conditions for spontaneous vesicles to be equilibrium structures. The measurements of the bending elasticity are confirmed by the transition of the lamellar phase of CTAT/SDBS from a turbid, viscoelastic gel to a translucent fluid as the water fraction is decreased below 40 wt %. Freeze-fracture electron microscopy shows that the gel is characterized by spherulite defects made possible by spontaneous bilayer curvature and low bending elasticity. This lamellar gel phase is common to a number of catanionic surfactant mixtures, suggesting that low bending elasticity and spontaneous curvature are typical of these mixtures that form spontaneous vesicles.     

Scientists and Science Educators Mentoring Secondary Science Teachers

This paper examines secondary science teachers' perspectives of the role that mentoring by a scientist and science educator pair played in their professional development. Multiple data sources from three years of a professional development project, including interviews, participant reflections, and a focus group, were used to examine the benefits, supporting characteristics, and challenges of the mentoring relationship. Results indicated that primary benefits of the mentoring included assistance in translating science content and inquiry‐based pedagogy from the professional development into practice and breaking the isolation felt by secondary science teachers. Specific characteristics that were found to support the teachers in the mentoring relationship included: (1) mentors who were seen as objective, outside observers; (2) a sustained relationship with the mentors; and (3) accountability. Challenges included matching scientists' and science educators' content expertise with teachers' curriculum and the negotiation of roles and expectations between the teachers and mentors.     

Conductance Photoswitching of Metal–Organic Frameworks with Embedded Spiropyran

Conductive metal–organic frameworks (MOFs) as well as smart, stimuli‐responsive MOF materials have attracted considerable attention with respect to advanced applications in energy harvesting and storage as well as in signal processing. Here, the conductance of MOF films of type UiO‐67 with embedded photoswitchable nitro‐substituted spiropyrans was investigated. Under UV irradiation, the spiropyran (SP) reversibly isomerizes to the open merocyanine (MC) form, a zwitterionic molecule with an extended conjugated π‐system. The light‐induced SP–MC isomerization allows for remote control over the conductance of the SP@UiO‐67 MOF film, and the conductance can be increased by one order of magnitude. This research has the potential to contribute to the development of a new generation of photoelectronic devices based on smart hybrid materials.