A series of highly active organoboron catalysts for the coupling of CO2 and epoxides with the advantages of scalable preparation, thermostability, and recyclability is reported. The metal‐free ...catalysts show high reactivity towards a wide scope of cyclic carbonates (14 examples) and can withstand a high temperature up to 150 °C. Compared with the current metal‐free catalytic systems that use mol % catalyst loading, the catalytic capacity of the catalyst described herein can be enhanced by three orders of magnitude (epoxide/cat.=200 000/1, mole ratio) in the presence of a cocatalyst. This feature greatly narrows the gap between metal‐free catalysts and state‐of‐the‐art metallic systems. An intramolecular cooperative mechanism is proposed and certified on the basis of investigations on crystal structures, structure–performance relationships, kinetic studies, and key reaction intermediates.
A highly active bifunctional organoboron catalyst with the advantages of scalable preparation, thermostability, and recyclability was reported for the cyclization of CO2 and epoxides. An intramolecular cooperative mechanism was substantiated by investigations into the crystal structure of the catalysts, structure– performance relationships, kinetic studies, and the key reaction intermediates.
Producing polyesters with high molecular weight (Mn) through ring‐opening copolymerization (ROCOP) of epoxides with cyclic anhydrides remains a major challenge. Herein, we communicate a metal‐free, ...highly active, and high thermoresistance system for the ROCOP of epoxides with cyclic anhydrides to prepare polyesters (13 examples). The organoboron catalysts can endure a reaction temperature as high as 180 °C for the ROCOP of cyclohexane oxide (CHO) with phthalic anhydride (PA) without the observation of any side reactions. The average Mn of the produced poly(CHO‐alt‐PA) climbed to 94.5 kDa with low polydispersity (Ð=1.19). Furthermore, an unprecedented turnover number of 9900, equivalent to an efficiency of 7.4 kg of polyester/g of catalyst, was achieved at a feed ratio of CHO/PA/catalyst=20000:10000:1 at 150 °C. Kinetic studies, crystal structure analysis, 11B NMR spectra, and DFT calculations provided mechanistic justification for the effectiveness of the catalyst system.
Ring‐opening copolymerization of epoxides and cyclic anhydrides by organoboron catalysts is presented. In view of their facile preparation and unprecedented performance (thermostability, reactivity, and productivity), the catalysts provided here hold promise in pushing ROCOP of epoxides with cyclic anhydrides to the industry line.
This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring‐opening polymerization (ROP) of epoxides under mild conditions. ...The bifunctional catalyst incorporates two 9‐borabicyclo3.3.1nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>106 g mol−1). Based on the investigations on crystal structure of catalyst, MALDI‐TOF, and 11B NMR spectroscopy, an intramolecular ammonium cation assisted SN2 mechanism is proposed and verified by DFT calculations.
A new organocatalyst that has unprecedented reactivity for ring‐opening polymerization of epoxides follows a novel intramolecular ammonium cation assisted mechanism. The bifunctional catalyst incorporates two 9‐borabicyclo3.3.1nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site.
To determine distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards in Wuhan, China, we tested air and surface samples. Contamination was greater in intensive care units ...than general wards. Virus was widely distributed on floors, computer mice, trash cans, and sickbed handrails and was detected in air ≈4 m from patients.
Recent deep learning based approaches have achieved great success on handwriting recognition. Chinese characters are among the most widely adopted writing systems in the world. Previous research has ...mainly focused on recognizing handwritten Chinese characters. However, recognition is only one aspect for understanding a language, another challenging and interesting task is to teach a machine to automatically write (pictographic) Chinese characters. In this paper, we propose a framework by using the recurrent neural network (RNN) as both a discriminative model for recognizing Chinese characters and a generative model for drawing (generating) Chinese characters. To recognize Chinese characters, previous methods usually adopt the convolutional neural network (CNN) models which require transforming the online handwriting trajectory into image-like representations. Instead, our RNN based approach is an end-to-end system which directly deals with the sequential structure and does not require any domain-specific knowledge. With the RNN system (combining an LSTM and GRU), state-of-the-art performance can be achieved on the ICDAR-2013 competition database. Furthermore, under the RNN framework, a conditional generative model with character embedding is proposed for automatically drawing recognizable Chinese characters. The generated characters (in vector format) are human-readable and also can be recognized by the discriminative RNN model with high accuracy. Experimental results verify the effectiveness of using RNNs as both generative and discriminative models for the tasks of drawing and recognizing Chinese characters.
Poly(cyclopentene carbonate) (PCPC) produced by copolymerization of CO2 and cyclopentene oxide (CPO) is a promising but challenging chemical recyclable polymer that has high potential in minimizing ...plastic pollution and maximizing CO2 utilization. Currently, problems remain to be solved, include low reactivity of toxic metal catalysts, inevitable byproducts, and especially the ambiguous mechanism understanding. Herein, we present the first metal‐free access to PCPC by using a series of modular dinuclear organoboron catalysts. PCPC was afforded in an unprecedented catalytic efficiency of 1.0 kg of PCPC/g of catalyst; while the depolymerization of PCPC abides by a combination pathway of random chain scission and chain unzipping, returning CPO in near‐quantitative yield (>99 %). The preparation and depolymerization of PCPC along with in depth understanding of related mechanisms would be helpful for further development of advanced catalysts and recyclable plastics.
The first metal‐free access to poly(cyclopentene carbonate) and its chemical recycling to monomer were achieved by using a dinuclear bifunctional organoboron catalyst, enriching the portfolio of the circular plastic economy.
This paper presents a novel asymptotic tracking controller for an underactuated quadrotor unmanned aerial vehicle using the robust integral of the signum of the error (RISE) method and an immersion ...and invariance (I&I)-based adaptive control methodology. The control system is decoupled into two parts: the inner loop for attitude control and the outer loop for position control. The RISE approach is applied in the inner loop for disturbance rejection, whereas the I&I approach is chosen for the outer loop to compensate for the parametric uncertainties. The asymptotic tracking of the time-varying 3-D position and the yaw motion reference trajectories is proven via the Lyapunov-based stability analysis and LaSalle's invariance theorem. Real-time experiment results, which are performed on a hardware-in-the-loop simulation testbed, are presented to illustrate the performance of the proposed control scheme.
Tumor hypoxia severely limits the efficacy of traditional photodynamic therapy (PDT). Here, a liposome‐based nanoparticle (designated as LipoMB/CaO2) with O2 self‐sufficient property for dual‐stage ...light‐driven PDT is demonstrated to address this problem. Through a short time irradiation, 1O2 activated by the photosensitizer methylene blue (MB) can induce lipid peroxidation to break the liposome, and enlarge the contact area of CaO2 with H2O, resulting in accelerated O2 production. Accelerated O2 level further regulates hypoxic tumor microenvironment and in turn improves 1O2 generation by MB under another long time irradiation. In vitro and in vivo experiments also demonstrate the superior competence of LipoMB/CaO2 to alleviate tumor hypoxia, suppress tumor growth and antitumor metastasis with low side‐effect. The O2 self‐sufficient LipoMB/CaO2 nanoplatform with dual‐stage light manipulation is a successful attempt for PDT against hypoxic tumor.
A liposome‐based nanoparticle (desig‐nated as LipoMB/CaO2) with O2 self‐sufficient property is developed to combat hypoxic tumor. Through dual‐stage irradiation, O2 self‐sufficient LipoMB/CaO2 can alleviate tumor hypoxia and strongly suppress tumor growth with low side‐effect.
The increasing global environmental and energy crisis has urgently motivated the advancement of sustainable materials. Significant effort has been focused on developing new materials to replace the ...fossil‐based resists in the semiconductor industry based on greener sources such as ice, dry ice, small organic molecules, and proteins. Such resist materials, however, have yet to meet the stringent requirements of high sensitivity, high resolution, reliable repeatability, and good compatibility with the current protocols. To this end, CO2‐based polycarbonates (CO2‐PCs) obtained from the copolymerization of CO2 and epoxides are demonstrated as sustainable dual‐tone (positive & negative tone) resists for electron beam lithography. By adjusting the chemical structure, developing agent, and molecular weight, the CO2‐PCs present high sensitivities to electron beam (1.3/120 µC cm−2), narrow critical dimensions (29/58 nm), and moderate line edge roughness (4.6/26.7 nm) for negative and positive resists, respectively. A deep understanding of the exposure mechanism of CO2‐PC resists is provided on the basis of the Fourier transform infrared, Raman, and electron ionization mass spectroscopy. 2D photonic crystal devices are fabricated using the negative and positive CO2‐PC resists, respectively, and both devices show distinct colors derived from their well‐defined nanostructures, indicating the great practical potential of CO2‐derived electron beam resists.
CO2‐derived polycarbonates obtained via the copolymerization of CO2 with various oxiranes are utilized as dual‐tone resists for the first time with outstanding sensitivity and resolution under electron beam exposure.
(1) Background: The novel coronavirus disease 2019 (COVID-19) is a global public health emergency that has caused worldwide concern. Vast resources have been allocated to control the pandemic and ...treat patients. However, little attention has been paid to the adverse impact on mental health or effective mitigation strategies to improve mental health. (2) Purpose: The aim of this study was to assess the adverse impact of the COVID-19 outbreak on Chinese college students' mental health, understand the underlying mechanisms, and explore feasible mitigation strategies. (3) Methods: During the peak time of the COVID-19 outbreak in China, we conducted longitudinal surveys of sixty-six college students. Structured questionnaires collected information on demographics, physical activity, negative emotions, sleep quality, and aggressiveness level. A mixed-effect model was used to evaluate associations between variables, and the mediating effect of sleep quality was further explored. A generalized additive model was used to determine the dose-response relationships between the COVID-19 death count, physical activity, and negative emotions. (4) Results: The COVID-19 death count showed a direct negative impact on general sleep quality (β = 1.37, 95% confidence interval 95% CI: 0.55, 2.19) and reduced aggressiveness (β = -6.57, 95% CI: -12.78, -0.36). In contrast, the COVID-19 death count imposed not a direct but an indirect impact on general negative emotions (indirect effect (IE) = 0.81,
= 0.012), stress (IE = 0.40,
< 0.001), and anxiety (IE = 0.27,
= 0.004) with sleep quality as a mediator. Moreover, physical activity directly alleviated general negative emotions (β = -0.12, 95% CI: -0.22, -0.01), and the maximal mitigation effect occurred when weekly physical activity was about 2500 METs. (5) Conclusions: (a) The severity of the COVID-19 outbreak has an indirect effect on negative emotions by affecting sleep quality. (b) A possible mitigation strategy for improving mental health includes taking suitable amounts of daily physical activity and sleeping well.
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