ABSTRACT
Wuhan took strict measures to prevent the spread of COVID-19 from January 26 to April 7 in 2020. The lockdown reduced the concentrations of atmospheric pollutants, except ozone (O3). To investigate the increase in O3 during the lockdown, trace gas pollutants were collected. The initial concentrations of volatile organic compounds (VOCs) were calculated based on a photochemical ratio method, and the ozone formation potential (OFP) was obtained using the initial and measured VOC concentrations. The O3 formation regime was NOX-limited based on the VOCs/NOX diurnal ratios during the lockdown period. The reduced nitric oxide (NO) concentrations and lower wind speed (WS) could explain the night-time O3 accumulation. The initial total VOCs (TVOCs) during the lockdown were 47.6 ± 2.9 ppbv, and alkenes contributed 48.1%. The photochemical loss amounts of alkenes were an order of magnitude higher than those of alkenes in the same period in 2019 and increased from 16.6 to 28.0 ppbv in the daytime. The higher initial alkene concentrations sustained higher OFP during the lockdown, reaching between 252.4 and 504.4 ppbv. The initial isoprene contributed approximately 35.0-55.0% to the total OFP and had a positive correlation with the increasing O3 concentrations. Approximately 75.5% of the temperatures were concentrated in the range of 5 and 20 °C, which were higher than those in 2019. In addition to stronger solar radiation, the higher temperatures induced higher isoprene emission rates, partially accounting for the higher isoprene concentrations. Lower isoprene-emitting trees should be considered for future urban vegetation to control O3 episodes.
ABSTRACT
The COVID-19 pandemic, instigated by the SARS-CoV-2 coronavirus, continues to plague the globe. The SARS-CoV-2 main protease, or Mpro, is a promising target for the development of novel antiviral therapeutics. Previous X-ray crystal structures of Mpro were obtained at cryogenic tem-per-ature or room tem-per-ature only. Here we report a series of high-resolution crystal structures of unliganded Mpro across multiple tem-per-atures from cryogenic to physiological, and another at high humidity. We inter-rogate these data sets with parsimonious multiconformer models, multi-copy ensemble models, and isomorphous difference density maps. Our analysis reveals a perturbation-dependent conformational landscape for Mpro, including a mobile zinc ion inter-leaved between the catalytic dyad, mercurial conformational heterogeneity at various sites including a key substrate-binding loop, and a far-reaching intra-molecular network bridging the active site and dimer inter-face. Our results may inspire new strategies for antiviral drug development to aid preparation for future coronavirus pandemics.
ABSTRACT
Owing to the pandemic of Coronavirus disease 2019 (COVID-19), the demands on ultracold-chain logistics have rapidly increased for the storage and transport of mRNA vaccines. Herein, we report a soluble luminescent thermometer based on thermally activated dual-emissions of Mn2+-alloyed 2D perovskite quantum wells (QWs). Owing to the Mn2+ alloying, the binding energy of perovskite QW exciton is reduced from 291 to 100 meV. It facilitates the dissociation of excitons into free charge carriers, which are then transferred and trapped on Mn2+. The temperature-dependent charge transfer efficiency can be tuned from 8.8% (-93 °C) to 30.6% (25 °C), leading to continuous ratiometrical modulation from exciton-dominated violet emission to Mn2+-dominated orange emission. The highest sensitivity (1.44% per K) is approximately twice that of the Mn2+-doped chalcogenide quantum dots. Taking advantage of highly reversible color switching, Mn2+-alloyed QWs provide an economical solution to monitor the ultracold-chain logistics of the COVID-19 vaccine. © 2022 American Chemical Society.