Designed Single-Step Synthesis, Structure, and Derivative Textural Properties of Well-Ordered Layered Penta-coordinate Silicon Alcoholate Complexes

The controllable synthesis of well-ordered layered materials with specific nanoarchitecture poses a grand challenge in materials chemistry. Here the solvothermal synthesis of two structurally analogous 5-coordinate organosilicate complexes through a novel transesterification mechanism is reported. Since the polycrystalline nature of the intrinsic hypervalent Si complex thwarts the endeavor in determining its structure, a novel strategy concerning the elegant addition of a small fraction of B species as an effective crystal growth mediator and a sacrificial agent is proposed to directly prepare diffraction-quality single crystals without disrupting the intrinsic elemental type. In the determined crystal structure, two monomeric primary building units (PBUs) self-assemble into a dimeric asymmetric secondary BU via strong Na+[BOND]O2− ionic bonds. The designed one-pot synthesis is straightforward, robust, and efficient, leading to a well-ordered (10ī)-parallel layered Si complex with its principal interlayers intercalated with extensive van der Waals gaps in spite of the presence of substantial Na+ counter-ions as a result of unique atomic arrangement in its structure. However, upon fast pyrolysis, followed by acid leaching, both complexes are converted into two SiO2 composites bearing BET surface areas of 163.3 and 254.7 m2 g−1 for the pyrolyzed intrinsic and B-assisted Si complexes, respectively. The transesterification methodology merely involving alcoholysis but without any hydrolysis side reaction is designed to have generalized applicability for use in synthesizing new layered metal–organic compounds with tailored PBUs and corresponding metal oxide particles with hierarchical porosity.United States. Defense Advanced Research Projects Agency (control No. 0471-1627)National Institute for Biomedical Imaging and Bioengineering (U.S.) (award No. EB-001960)National Institutes of Health (U.S.) (NIBIB award No. EB-002026)National Science Foundation (U.S.) (Grant No. CHE-0946721

Structural and functional characterization of a cross-reactive dengue virus neutralizing antibody that recognizes a cryptic epitope

Understanding the molecular basis of the neutralizing antibody response to dengue virus (DENV) is an essential component in the design and development of effective vaccines and immunotherapeutics. Here we present the structure of a cross-reactive, neutralizing antibody, 3E31, in complex with domain III (DIII) of the DENV envelope (E) protein and reveal a conserved, temperature-sensitive, cryptic epitope on DIII that is not available in any of the known conformations of E on the dengue virion. We observed that 3E31 inhibits E-mediated membrane fusion, suggesting that the antibody is able to neutralize virus through binding an as-yet uncharacterized intermediate conformation of DENV E and sterically block trimer formation. Finally, we show that, unlike cross-reactive fusion peptide-specific antibodies, 3E31 does not promote antibody-dependent enhancement of infection at sub-neutralizing concentrations. Our results highlight the 3E31 epitope on the E protein DIII as a promising target for immunotherapeutics or vaccine design

Apatite and titanite from the Karrat Group, Greenland; implications for charting the thermal evolution of crust from the U-Pb geochronology of common Pb bearing phases

Titanite and apatite have Pb closure temperatures of ~700 °C and 450–550 °C, respectively, allowing different points on a cooling trajectory to be determined. However, both phases typically accommodate moderate to significant quantities of common Pb. Understanding the thermal diffusivity of a specific isotopic system in different minerals along with their apparent U-Pb age allows modelling of regional cooling trends. Such cooling trends may provide key evidence for correct interpretation of the measured geochronometer. Specifically, thermal history reconstruction may address questions related to the interpretation of an isotopic date as the time of crystallization versus cooling, or alternatively, as a resetting age. In this work, a case study from metavolcanic rocks of the Karrat Group, West Greenland, is used to inform the U-Pb geochronology of common Pb bearing phases, thermal modelling, and also the regional geology. Magmatic apatite yields a reset U-Pb age of 1826 ± 9 Ma, whereas titanite yields a mean U-Pb age of 1768 ± 8 Ma. The apatite age is interpreted as the time of total resetting during a > 485 °C event. In contrast, the titanite age is interpreted as the time of metamorphic crystallization, consistent with its REE chemistry. Thermal modelling indicates this metamorphic event did not exceed 452 °C. The resetting of the U-Pb system in magmatic apatite is interpreted as a response to the collision between the Rae Craton and the Superior Craton during the Trans-Hudson Orogeny. However, subsequent metamorphic titanite growth is interpreted as distal evidence of an event shared with the Nagssugtoqidian Orogen. The modelled thermal history implies over 100 million years of communal tectonic history between the Nagssugtoqidian and Rinkian Orogens. Of great significance is the fact that both apatite and titanite show distinctly different common Pb compositions. Apatite retains common Pb with a composition similar to ancient common Pb, whereas titanite retains common Pb with a lower 207 Pb/ 206 Pb ratio implying it was influenced also by Pb from recrystallized precursor U bearing minerals. The common Pb signature in minerals may assist in interpretation of the growth mechanism of the dated phase