Carbon dots (CDs), as new type of carbon-based nanoparticles, are considered to be an aggregate with irreversible polymerization. Achieving the reversible tunability of CDs luminescence based on their reversible polymerization is a challenging subject. Herein, we, for the first time, design and construct the blue-emitting CDs with reversible polymerization by a room-temperature Schiff base reaction between tannic acid and ethylenediamine. The formation of CDs is proven to be due to the crosslinking polymerization of precursors caused by imine bond. As a dynamic covalent bond, imine bond endows CDs with controllable structural transformation properties, and the prepared CDs can be depolymerized and polymerized reversibly by pH-controlled imine bond cleavage and re-formation. These properties of reversible fluorescence photoswitching make the CDs have a good application prospect in reversible information encryption.
Eight new gelsedine-type oxindole alkaloids and ten known analogues were isolated from the stems and leaves of Gelsemium elegans . Gelseansdine A ( 1 ) was an N 4 -deficient Gelsemium alkaloid, while gelseansdines E–H ( 12 , 14 , 16 – 17 ) represented a class of alkaloids polymerized with iridoid. Their structures were elucidated based on UV, HRESIMS, NMR spectroscopy, and electronic circular dichroism (ECD) data analyses. Additionally, the isolated compounds were screened for their inhibitory activity on macrophage M2 polarization.
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