Stereoselective cycloaddition of 1,3-cyclohexadiene on Si(100): a simple algorithm for product identification based on secondary orbital interactions

We consider the reaction of 1,3-cyclohexadiene (1,3-CHD) on Si(100) and show that the observed reactivity and stereoselectivity cannot be explained on the basis of thermodynamics. We postulate the existence of secondary orbital interactions (SOIs) and introduce a simple algorithm that examines all possible secondary interactions between the frontier orbitals of the molecule and the surface. We demonstrate using an orbital symmetry-based algorithm supported by DFT calculations that SOIs favor a particular molecular configuration, consistent with the experimental observations. The potential role of SOIs in controlling surface chemical reactions is discussed.     

Expression, Purification, Crystallization and Molecular Replacement Studies of TorI, an Inhibition Protein of Tor System

TorI, a Tor system inhibitor acting through protein-protein interaction with the TorR response regulator, is an excisionase that interacts with the integrase and DNA during prophage excision. It has been crystallized by the vapor-diffusion method using polyethylene glycol 3350 as a precipitant at pH 8.5. The X-ray diffraction data sets from the TorI crystal was collected at a resolution of 2.1 , using a synchrotron source. The crystal belongs to primitive monoclinic lattice with cell parameters of 46.210 × 53.992 × 73.561     

Non-dominant hand movement facilitates the frontal N30 somatosensory evoked potential

Background  

Previous literature has shown that the frontal N30 is increased during movement of the hand contralateral to median nerve stimulation. This finding was a result of non-dominant left hand movement in right-handed participants. It is unclear however if the effect depends upon non-dominant hand movement or if this is a generalized phenomenon across the upper-limbs. This study tests the effect of dominant and non-dominant hand movement upon contralateral frontal and parietal somatosensory evoked potentials (SEPs) and further tests if this relationship persists in left hand dominant participants. Median nerve SEPs were elicited from the wrist contralateral to movement in both right hand and left hand dominant participants alternating the movement hand in separate blocks. Participants were required to volitionally squeeze (~ 20% of a maximal voluntary contraction) a pressure-sensitive bulb every ~3 seconds with the hand contralateral to median nerve stimulation. SEPs were continuously collected during the task and individual traces were grouped into time bins relative to movement according to the timing of components of the Bereitschaftspotential. SEPs were then averaged and quantified from both FCZ and CP3/4 scalp electrode sites during both the squeeze task and at rest.     

The effect of γ-irradiation and polymer composition on the stability of PLG polymer and microspheres

The effects of lactide:glycolide ratio and γ-irradiation on the stability characteristics of poly(d,l-lactide-co-glycolide) (dl-PLG) co-polymer and microspheres were studied. Samples containing 50:50, 65:35, 75:25, 85:15 and 95:5 lactide:glycolide were studied as both the raw polymer and microspheres. The samples were characterised and degradation was monitored using a variety of spectroscopic, chromatographic, thermal and particle analysis techniques. The lactide:glycolide ratio was shown to be an important parameter in controlling the degradation of PLG co-polymer, especially in the microspheres, and the raw polymer samples were observed to be less stable than the microspheres. γ-Irradiation was shown to reduce the molecular weight of the PLG samples without significantly affecting the polydispersity, suggesting a random chain scission degradation mechanism. The detrimental effects of γ-irradiation were shown to continue on storage of the samples for 4 weeks in the solid state at ambient and accelerated conditions.     

The structure of tri(cyclohexyl)tin chloride between 108 and 298 K: a compound in which molecular dimensions vary with temperature

Care is necessary when relating physical data obtained at one temperature on compounds showing significant intermolecular interactions to X-ray data obtained at other temperatures. This is revealed by the determination of the structure of tri(cyclohexyl)tin chloride at nine different temperatures between 108 and 298 K. In the crystal, the molecules pack in chains parallel to the c axis with the Sn and Cl atoms close to the plane, with y = 0.25. At low temperature, successive molecules in the chain are related by the glide plane in space group P2(1)/c, and there is significant intermolecular interaction. As the temperature is raised, the Cy(3)SnCl.Sn interactions weaken and the intramolecular Sn-Cl bonds strengthen. At about 248 K, there is an order-disorder transition to space group P2(1)/m with the c axis halved, and at room temperature the structure is best described as comprising discrete molecules, as previously reported. Thus, some of the molecular dimensions, in particular the Sn-Cl bond lengths, are not constant but are functions of temperature.     

A new FeII quaterpyridyl M4L6 tetrahedron exhibiting selective anion binding

A rigid linear bis-bidentate quaterpyridine undergoes metal directed self-assembly with iron(ii) salts yielding M(4)L(6) host-guest complexes; selective anion binding for PF(6)(-) over BF(4)(-) is observed.     

Live lectures or online videos: students’ resource choices in a first-year university mathematics module

In Maths for Business, a mathematics module for non-mathematics specialists, students are given the choice of completing the module content via short online videos, live lectures or a combination of both. In this study, we identify students’ specific usage patterns with both of these resources and discuss their reasons for the preferences they exhibit. In 2015–2016, we collected quantitative data on each student's resource usage (attendance at live lectures and access of online videos) for the entire class of 522 students and employed model-based clustering which identified four distinct resource usage patterns with lectures and/or videos. We also collected qualitative data on students’ perceptions of resource usage through a survey administered at the end of the semester, to which 161 students responded. The 161 survey responses were linked to each cluster and analysed using thematic analysis. Perceived benefits of videos include flexibility of scheduling and pace, and avoidance of large, long lectures. In contrast, the main perceived advantages of lectures are the ability to engage in group tasks, to ask questions, and to learn ‘gradually’. Students in the two clusters with high lecture attendance achieved, on average, higher marks in the module.