Synthesis of the dysiherbaine tetrahydropyran core employing a tethered aminohydroxylation reaction

A stereocontrolled and scalable synthesis of an advanced intermediate of the dysiherbaine tetrahydropyran core has been achieved in 11 steps and 27% overall yield. The key feature of this synthetic approach is the application of the Donohoe tethered aminohydroxylation reaction to install the amino diol and establish the four contiguous syn stereocenters on the tetrahydropyran ring.     

A free-energy landscape picture and Landau theory for the dynamics of disordered materials

Landau's theory of phase transitions [Nature (London) 138, 840 (1936); Statistical Physics (Pergamon, London, 1959)] is adapted to treat independently relaxing regions in complex systems using nanothermodynamics. The order parameter we use governs the thermal fluctuations, not a specific static structure. We find that the entropy term dominates the thermal behavior, as is reasonable for disordered systems. Consequently, the thermal equilibrium occurs at the internal-energy maximum, so that the potential-energy minima have negligible influence on the dynamics. The dynamics involves normal thermal fluctuations about the free-energy minimum, with a time scale that is governed by the curvature of the internal-energy maximum. The temperature dependence of the fluctuations yields Vogel-Tamman-Fulcher-type [Phys. Z. 22, 645 (1921); J. Am. Ceram. Soc. 8, 339 (1925); Z. Anorg. Allg. Chem. 156, 245 (1926)] relaxation rates and approximate time-temperature superposition, consistent with the Williams-Landell-Ferry [J. Am. Chem. Soc. 77, 3701 (1955)] procedure for analyzing the dynamics of complex fluids, while the size dependence of the fluctuations provides an explanation for the distribution of relaxation times and heterogeneity that are found in glass-forming liquids, thus providing a unified picture for several features in the dynamics of disordered materials.     

Scattering by small defects in the neighbourhood of a fluid-solid interface

The scattering of incident plane elastic waves by a varietyof different defects that lie upon a fluid-solid interface isconsidered here using matched asymptotic expansions. The expansionscheme is developed in terms of a parameter , the ratio of typicaldefect length scale to a typical wavelength of the incidentfield, taken to be small. Three different canonical situations occur and these are illustratedvia three specific examples treated here: a rigid strut, anedge crack, and a rigid strip. In each case the leading-ordermatching is performed to identify the leading-order contributionof the defect to the acoustic field in the far field. In particular,each defect is identified with a source of dipole response ininterfacial stress of displacement. It is shown in the limit as s<<s1 that in the inner problemsthe fluid and solid pieces uncouple in a particularly convenientmanner allowing analytical solutions to be deduced. These arethen matched with appropriate outer solutions.     

Activation of protein phosphatase 1 by a small molecule designed to bind to the enzyme's regulatory site

The activity of protein phosphatase 1 (PP1), a serine-threonine phosphatase that participates ubiquitously in cellular signaling, is controlled by a wide variety of regulatory proteins that interact with PP1 at an allosteric regulatory site that recognizes a "loose" consensus sequence (usually designated as RVXF) found in all such regulatory proteins. Peptides containing the regulatory consensus sequence have been found to recapitulate the binding and PP1 activity modulation of the regulatory proteins, suggesting that it might be possible to design small-molecule surrogates that activate PP1 rather than inhibiting it. This prospect constitutes a largely unexplored way of controlling signaling pathways that could be functionally complementary to the much more extensively explored stratagem of kinase inhibition. Based on these principles, we have designed a microcystin analog that activates PP1.     

Prospective Teachers' Perspectives on Mathematics Teaching and Learning: Lens for Interpreting Experiences in a Standards‐Based Mathematics Course

In a mathematics course for prospective elementary teachers, we strove to model standards‐based pedagogy. However, an end‐of‐class reflection revealed the prospective teachers were considering incorporating standards‐based strategies in their future classrooms in ways different from our intent. Thus, we drew upon the framework presented by Simon, Tzur, Heinz, Kinzel, and Smith to examine the prospective teachers' perspectives on mathematics teaching and learning and to address two research questions. What perspectives on the learning and teaching of mathematics do prospective elementary teachers hold? How do their perspectives impact their perception of standards‐based instruction in a mathematics course and their future teaching plans? Qualitative analyses of reflections from 106 prospective teachers revealed that they viewed mathematics as a logical domain representative of an objective reality. Their instructional preferences included providing firsthand opportunities for elementary students to perceive mathematics. They did not take into account the impact of a student's conceptions upon what is learned. Thus, the prospective teachers plan to incorporate standards‐based strategies to provide active experiences for their future elementary students, but they fail to base such strategies upon students' current mathematical conceptions. Throughout, the need to address prospective teachers' underlying perspectives of mathematics teaching and learning is stressed.     

In-situ imaging of the nucleation and growth of epitaxial anatase TiO2(001) films on SrTiO3(001)

The growth of TiO₂ anatase films on Nb‐doped SrTiO₃(001) molecular beam epitaxy has been studied in-situ by scanning tunneling microscopy. We show that the initial growth follows the Stranski–Krastanov mode, where islands form on top of a wetting layer consisting of two monolayers (ML) of TiO₂. The epitaxial islands subsequently nucleate and coalesce into large commonly oriented crystallites. The reconstruction observed by reflection high-energy electron diffraction (RHEED) is shown to result from the coexistence of individual (4 × 1) and (1 × 4) reconstructions present on different crystallite surfaces. The anatase grows in units of bilayers, resulting in a step height of 2 ML (~ 0.5 nm). This result explains the fact that the measured period of the RHEED specular-beam intensity oscillations corresponds to the time required for deposition of 2 ML. Ar ion sputtering and UHV annealing results in a transformation to coexisting (4 × 1) and (1 × 4) reconstructed terraces on individual crystallites, as commonly observed by ex-situ STM studies.