Nanopipette dynamic microscopy unveils nano coffee ring.

Liquid-phase electron microscopy (LP-EM) imaging has revolutionized our understanding of nanosynthesis and assembly. However, the current closed geometry limits its application for open systems. The ubiquitous physical process of the coffee-ring phenomenon that underpins materials and engineering science remains elusive at the nanoscale due to the lack of experimental tools. We introduce a quartz nanopipette liquid cell with a tunable dimension that requires only standard microscopes. Depending on the imaging condition, the open geometry of the nanopipette allows the imaging of evaporation-induced pattern formation, but it can also function as an ordinary closed-geometry liquid cell where evaporation is negligible despite the nano opening. The nano coffee-ring phenomenon was observed by tracking individual nanoparticles in an evaporating nanodroplet created from a thin liquid film by interfacial instability. Nanoflows drive the assembly and disruption of a ring pattern with the absence of particle-particle correlations. With surface effects, nanoflows override thermal fluctuations at tens of nanometers, in which nanoparticles displayed a "drunken man trajectory" and performed work at a value much smaller than kBT.

Electrochemical two-electron oxygen reduction reaction (ORR) induced aerobic oxidation of α-diazoesters.

Electrochemical oxygen reduction reaction (ORR) is a powerful tool for introducing oxygen functional groups in synthetic chemistry. However, compared with the well-developed one-electron oxygen reduction process, the applications of two-electron oxygen reduction in electrochemical synthesis have been seldom studied. We present herein our recent progress in the oxidation of α-diazoesters to α-ketoesters by in situ generated hydrogen peroxide via a two-electron oxygen reduction approach. A diverse collection of valuable α-ketoester products was obtained with moderate to high yields under an exogenous-oxidant-free and metal catalyst-free electrochemical conditions.

Quantitative Chemoproteomic Profiling of Protein Cross-Links Induced by Methylglyoxal.

Methylglyoxal (MGO) is a highly reactive metabolite mainly formed as a byproduct of glycolysis. Elevated MGO has been considered as a risk factor for several diseases including diabetes and neurodegeneration. While MGO modifications on proteins were globally profiled, the cross-links between proteins induced by MGO in proteomes are unexplored to date. Here, we reported a quantitative chemoproteomic platform based on mass shifts that enables identification of events of protein cross-links induced by MGO in proteomes. A total of 66 cross-linked targets were identified from the profiling experiments when cells were treated with MGO, among which the components of functional complexes such as spliceosomes and ribosomes were enriched. We found that inosine-5'-monophosphate dehydrogenase 2 (IMPDH2) was homocross-linked by MGO and the active-site Cys331 was critical for mediating the cross-link, which in turn affected IMPDH2's activity. Our study has provided new clues for the functional impact in proteomes by MGO, and the methodology can be, in principle, applied to profile protein cross-links induced by other reactive metabolites.

Dynamics of base pairs with low stability in RNA by solid-state nuclear magnetic resonance exchange spectroscopy.

Base pairs are fundamental building blocks of RNA. The base pairs of low stability are often critical in RNA functions. Here, we develop a solid-state NMR-based water-RNA exchange spectroscopy (WaterREXSY) to characterize RNA in solid. The approach uses different chemical exchange rates between iminos and water to evaluate base pair stability; the less stable ones would exchange more frequently, leading to stronger cross-peaks on WaterREXSY. Applied to the riboA71-adenine complex (the 71nt-aptamer domain of add adenine riboswitch from Vibrio vulnificus), the U47⋅U51 base pair, which is critical in ligand binding, was found to be less stable than other base pairs. The imino-water exchange rates of U47 at different temperatures are about 500-800 s-1, indeed indicative of low stability. This implies a highly complex and plastic triad involving U47⋅U51 and that the opening of the U47⋅U51 base pair may be the early stage of ligand release.