Organocatalytic polymerization reactions have a number of advantages over their metal-catalyzed counterparts, including environmental friendliness, ease of catalyst synthesis and storage, and alternative reaction pathways. Here we introduce an organocatalytic polymerization method called benzylic chloromethyl-coupling polymerization (BCCP). BCCP is catalyzed by organocatalysts not previously employed in polymerization processes (sulfenate anions), which are generated from bench-stable sulfoxide precatalysts. The sulfenate anion promotes an umpolung polycondensation via step-growth propagation cycles involving sulfoxide intermediates. BCCP represents an example of an organocatalyst that links monomers by C=C double bond formation and offers transition metal-free access to a wide variety of polymers that cannot be synthesized by traditional precursor routes.
Fluorescence polarization is related to the dipole orientation of chromophores, making fluorescence polarization microscopy possible to reveal structures and functions of tagged cellular organelles and biological macromolecules. Several recent super resolution techniques have been applied to fluorescence polarization microscopy, achieving dipole measurement at nanoscale. In this review, we summarize both diffraction limited and super resolution fluorescence polarization microscopy techniques, as well as their applications in biological imaging.
Adverse drug reactions (ADRs) restrict the maximum doses applicable in chemotherapy, which leads to failure in cancer treatment. Various approaches, including nano-drug and prodrug strategies aimed at reducing ADRs, have been developed, but these strategies have their own pitfalls. A renovated strategy for ADR reduction is urgently needed. Here, we employ an enzymatic supramolecular self-assembly process to accumulate a bioorthogonal decaging reaction trigger inside targeted cancer cells, enabling spatiotemporally controlled, synergistic prodrug activation. The bioorthogonally activated prodrug exhibits significantly enhanced potency against cancer cells compared with normal cells. This prodrug activation strategy further demonstrates high tumour inhibition efficacy with satisfactory biocompatibility, pharmacokinetics, and safety in vivo. We envision that integration of enzymatic and bioorthogonal reactions will serve as a general small-molecule-based strategy for alleviation of ADRs in chemotherapy.
There are more than 30,000 biomass-and fossil-fuel-burning power plants now operating worldwide, reflecting a tremendously diverse infrastructure, which ranges in capacity from less than a megawatt to more than a gigawatt. In 2010, 68.7% of electricity generated globally came from these power plants, compared with 64.2% in 1990. Although the electricity generated by this infrastructure is vital to economic activity worldwide, it also produces more CO2 and air pollutant emissions than infrastructure from any other industrial sector. Here, we assess fuel-and region-specific opportunities for reducing undesirable air pollutant emissions using a newly developed emission dataset at the level of individual generating units. For example, we find that retiring or installing emission control technologies on units representing 0.8% of the global coal-fired power plant capacity could reduce levels of PM2.5 emissions by 7.7-14.2%. In India and China, retiring coal-fired plants representing 1.8% and 0.8% of total capacity can reduce total PM2.5 emissions from coal-fired plants by 13.2% and 16.0%, respectively. Our results therefore suggest that policies targeting a relatively small number of 'super-polluting' units could substantially reduce pollutant emissions and thus the related impacts on both human health and global climate.
A terahertz (THz) Brewster vacuum window has been developed for the newly emerged ultrabroadband gyrotron application. In the simulation, the influences of the slant angle, the thickness, and the dielectric constant of the window plate on the results were systematically analyzed. In the experimental measurement, two THz high-directivity horn antennas were used to produce and collect a quasi-plane wave that travels through the window. The measurement shows that the window transmission coefficient between 0.33 and 0.50 THz is higher than -1 dB. A conventional Brewster window uses an elliptical window plate, resulting in the asymmetrical stress distribution. In this letter, a novel circular symmetrical ceramic-Kovar brazing scheme is applied to mitigate the challenging asymmetrical stress distribution. This Brewster window would promote the development of the broadband THz gyrotron and other high-power THz systems.
Recently emerged multimode gyrotron, a high-power broadband terahertz radiator, encounters the challenge of efficiently converting a series of operating whispering-gallery modes (WGMs) into free-space Gaussian beams. To this demand, we propose a frequency- and mode-insensitive antenna capable of broadband multimode converting. For a single mode, to achieve broadband operation, special reflector configuration and large-radius launcher guarantee the system high robustness to frequency-induced wave number variation. Furthermore, for a series of operating WGMs, in order to achieve multimode operation, high-order mode indices guarantees familiar field patterns and ray trajectories. In particular, high-purity Gaussian beams are simultaneously achieved in different WGMs of broad continuous bands, including 351–361 GHz for TE11,2 mode, 375–385 GHz for TE12,2 mode, and 398–410 GHz for TE13,2 mode. The results are verified by both the vector diffraction theory and the method of momentum. This kind of mode converter will promote the development of multimode gyrotrons and other antenna-feeder systems for high-power terahertz applications.
A pair of uranyl complexes incorporating tetrahydrosalen and N,N-dimethyltetrahydrosalen ligands are synthesized and studied. These new ligands, with saturated secondary and tertiary amines, exhibit higher chemostability than the prototype Schiff base (salen) structure, especially under acidic conditions. As shown by X-ray diffraction crystallography, the coordination geometry of uranium in these new complexes is a distorted pentagonal bipyramid. Interestingly, UO2([H-4]-salen), comprising the tetrahydrosalen ligand, forms a dimeric structure in the crystals, with two subunits held together by sharing one of the two phenoxy oxygen atoms from each subunit, whereas UO2([H2Me2]-salen) with the N,N-dimethyltetrahydrosalen ligand is in the monomer state, with a solvent molecule coordinated to uranium to complete the penta-coordination configuration. Moreover, as revealed by UV/Vis spectroscopy using the colorimetry method, these hydrogenated salen ligands exhibit comparable, or even higher, binding affinities toward uranyl than the prototype Schiff base salen ligand in weakly basic solution.