The first catalytic enantioselective total synthesis of riccardiphenol B, a sesquiterpene derivative isolated from a Japanese collection of the liverwort Riccardia crassa, has been achieved. A copper‐catalyzed asymmetric conjugate addition of trimethylaluminum was used at an early stage to generate the quaternary stereogenic center with high enantiomeric excess. The corresponding sterically encumbered aluminum enolate was directly trapped with an α‐amino ether, allowing after oxidation, the release of a key intermediate in the total synthesis of the target natural product.
Organic–inorganic hybrids offer great promise as solution-processable thermoelectric materials. However, they have struggled to surpass the performance of their rigid inorganic counterparts due, in part, to a lack of synthetic control and limited understanding of how inorganic nanostructure dimensions impact overall charge transport. While it has been hypothesized that length, diameter, and aspect ratio (AR) all impact electronic transport in hybrid nanowires, the field lacks clarity on the relative role of each. In this study, the experimental parameter of ligand molecular weight (MW) is investigated as a synthetic knob for modulating nanowire dimensions, as well as the deconvolution of nanowire length versus diameter impacts on electron transport. By increasing ligand MW, larger nanowire AR dispersions occur and an optimal power factor of ≈130 μWm−1 K−2 is achieved for a modest AR of 73. Power factors of this magnitude are thought to only be achievable in ultrahigh AR systems; representing a 183% increase in performance over literature reports with similar AR. Additionally, nanowire diameter is demonstrated to be a far more sensitive parameter for enhancing performance than modulating length. This study provides improved fundamental insight into rational synthetic design avenues for future enhancements in the performance of hybrid materials. 相似文献
Bacteriophages have a well-defined nanoscale size, shape, and surface chemistry, making them promising candidates for creating advanced biomaterials for applications including biocatalysis, drug delivery, and biosensing. This study demonstrates the self-assembly of the ≈29 nm diameter bacteriophage Qbeta (Qubevirus durum) with the synthetic polycation, poly [2-(methacryloyloxy)ethyl] trimethylammonium chloride (pMETAC), into compartmentalized colloidal crystals. The pH and the polymer chain length tune their self-assembly and the resulting structure, with the potential for further chemical modification or loading with bioactive molecules. Small angle X-ray scattering (SAXS), multi-angle dynamic light scattering (DLS), and atomic force microscopy (AFM) are used for studying the Qbeta self-assembly into the geometrically ordered aggregates. The suprastructures form at pH > 7.0 and disassemble at pH < 7.0. Zeta potential measurements and X-ray photoelectron spectroscopy (XPS) show pMETAC adsorption onto the negatively charged Qbeta surface. The colloidal crystal formation is achieved without chemically modifying the Qbeta surface. Additionally, the Qbeta/pMETAC suprastructures can be easily separated from the suspension as macroscopic aggregate, maintaining their activity. Their simple preparation allows for large-scale production of advanced materials in food and health science applications and nanotechnology. The insights from this study will further advance the tailored design and production of novel colloidal materials. 相似文献
The oxidation of roquefortine C to the nitrone roquefortine L was investigated using a number of different electrophilic oxidizing reagents. mCPBA and Oxone were shown to be the most effective in achieving this transformation, while unfavorable steric interactions precluded oxidation by bulky reagents such as Davis oxaziridine. Finally, each of the oxidants was shown to promote aromatic hydroxylation following the synthesis of the nitrone functionality. 相似文献
La Saline fringing reef is the most important coral reef complex of La Réunion Island (southwestern Indian Ocean; 21°07′S, 55°32′E). This ecosystem is subjected to anthropogenic pressures through river inputs and submarine groundwater discharge (SGD). The goal of this study was to characterize the pool of fluorescent dissolved organic matter (FDOM) in different water bodies of La Saline fringing reef ecosystem using excitation-emission matrix (EEM) spectrofluorometry. From EEMs, we identified the different fluorophores by the peak picking technique and determined two fluorescence indices issued from the literature: the humification index (HIX) and the biological index (BIX). The main known fluorophores were present within the sample set: humic-like A, humic-like C, marine humic-like M, tryptophan-like T1 and T2, and tyrosine-like B1 and B2. In some samples, unknown fluorophores (“U”) were also detected. The surface oceanic waters located beyond the reef front displayed a typical oligotrophic marine signature, with a dominance of autochthonous/biological material (presence of peaks: T1 > B1 > A > T2 > M > C; HIX: 0.9 ± 0.4; BIX: 2.3 ± 1.1). In the reef waters, the autochthonous/biological fingerprint also dominated even though the content in humic substances was higher (same relative distribution of peaks; HIX: 1.6 ± 0.6; BIX: 1.0 ± 0.1). Sedimentary and volcanic SGD showed very different patterns with a strong terrestrial source for the former (A > T1 > C > B1 and A > C > B1; HIX: 9.8 ± 2.0; BIX: 0.8 ± 0.0) and a weak terrestrial source for the latter (A > B1 > U3 > B2 > C and A > U4 > C; HIX: 2.4 ± 0.3; BIX: 0.9 ± 0.0). In the Hermitage River, both humic substances and protein-like material were abundant (T1 > A > U5 > B1 > C > B2; HIX: 2.3; BIX: 1.4). We provide evidences for the presence of anthropogenic DOM in some of these water bodies. Some oceanic samples (presence of peaks U1 and U2) were likely contaminated by oil-derived PAHs from ships navigating around the reef front, whereas the Hermitage River was highly impacted by sewage effluents, numerous in this coastal area of La Réunion Island. We conclude that multi-dimensional fluorescence spectroscopy (EEM) coupled to the determination of HIX and BIX is a good tool for assessing the origin and distribution of DOM in the coral reef ecosystems submitted to anthropogenic impacts. 相似文献
By mapping grain orientations on parallel serial sections of a SrTiO3 ceramic, it was possible to reconstruct three-dimensional orientation maps containing more than 3000 grains. The grain boundaries were approximated by a continuous mesh of triangles and mean curvatures were determined for each triangle. The integral mean curvatures of grain faces were determined for all grains. Small grains with fewer than 16 neighbors mostly have positive mean curvatures while larger grains with more than 16 neighbors mostly have negative mean curvatures. It is also possible to correlate the mean curvature of individual triangles with the crystallographic characteristics of the grain boundary. The mean curvature is lowest for grain boundaries with (100) orientations and highest for grain boundaries with (111) orientations. This trend is inversely correlated to the relative areas of grain boundaries and directly correlated to the relative grain boundary energy. The direct correlation between the energy and curvature is consistent with the expected behavior of grain boundaries made up of singular orientations. Furthermore, because both the relative energy and curvature of grain boundaries with (100) orientations are minima in the distributions, these boundaries also have the lowest driving force for migration. 相似文献
Leaf-level microscopical symptom structure and physiological responses were investigated in seedlings experimentally exposed to ozone (O3) in indoor chambers (150 ppb, 8 h d− 1 per 7 weeks), and field trees of Manna ash (Fraxinus ornus) exposed to ambient O3 (max 93 ppb per one growing season). Ozone-induced leaf injury, including leaf reddening and stippling, was observed in both seedlings and mature trees, but the morphology of injury in the stipples differed, being hypersensitive-like (HR-like) in the chamber seedlings and accelerated cell senescence (ACS) in the field trees. In both exposure conditions, the main structural impact of O3 was on the mesophyll and especially the upper assimilating cell layers. The main physiological impact was on carbon assimilation and on stomatal sluggishness. These effects were not due to stomatal structural injury and were more severe in juvenile compared to mature trees because of environmental (water availability, light) and constitutional (gas exchange capacity) factors and differences in the cell physiology processes (HR-like vs. ACS) triggered by ozone stress. Given the plasticity of plant responses to ozone stress, dose/response relationships for tree seedlings in the indoor chambers cannot be extrapolated to mature trees unless ambient conditions are closely simulated. 相似文献
