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We report the surprising chemiluminescence (CL) behavior of fluorescent carbon dots in the presence of a strong alkaline solution, such as NaOH or KOH. The CL intensity was dependent on the concentration of the base and carbon dots in a certain range. A possible CL mechanism was studied by UV-Vis, fluorescence, CL, FTIR, XPS and EPR spectroscopy. Radiative recombination of the injected electrons by "chemical reduction" of carbon dots with thermally excited generated holes was proposed, which sheds new light on the characteristics of carbon dots.As a rising star of the nanocarbon family, carbon nanodots have attracted increasing attention due to their excellent luminescent properties and wide applications in many areas of fundamental and technical importance.1 Intense research still focuses on their further application and intrinsic luminescence mechanism.Luminescent properties of carbon dots are usually investigated by photoluminescence (PL) produced using photoexcitation, 2-8 and electrochemiluminescence (ECL) generated by electron injection. 9-12However, chemiluminescence (CL) generated from chemical energy excitation through a chemical reaction has been rarely used to study the optical properties of carbon dots. To the best of our knowledge, only Lin 13-15 and Cui's 16 groups have recently described the CL behavior of carbon dots when they coexist with oxidants (KMnO 4 , Ce(IV), NaIO 4 ) or an ultraweak chemiluminescence system (H 2 O 2 -NaHSO 3 , H 2 O 2 -HNO 2 ) under acidic conditions. Herein, we observed for the rst time that CL was generated when only a strongly alkaline solution was injected into the carbon dots, without the presence of any CL reagent, CL system or oxidants. Our initial purpose was to study the CL behavior of carbon dots using an alkaline solution as a reaction medium to improve the CL intensity. Surprisingly, the addition of high concentration NaOH solution to the carbon dots was accompanied by a fast CL phenomenon. This investigation provided new insight into the physical-chemical and optical properties of carbon dots.The carbon dots with a diameter of 2-4 nm (Fig. S1 in the ESI †) were synthesized by the microwave treatment described in the literature with a slight modication (see ESI †), using glucose as the carbon source and PEG 1500 as the co-reactant.9 As with the other carbon dots, the synthesized nanomaterial exhibited a UV-Vis absorption band at 280 nm, attributed to the n-p* transition of the C]O band and a p-p* transition of the conjugated C]C band.17 The uorescence (FL) emission shied as the excitation wavelength increased. When the emission reached its maximum, the peak centered at 525 nm. Interestingly, with the addition of NaOH into the carbon solution, the colour of the carbon dot aqueous solution darkened from light yellow to yellow-brown. A new absorption peak at 272 nm appeared in the UV-Vis spectrum, but no appreciable absorption peak was observed under 280 nm for the original carbon Fig. 1 The UV-Vis absorption spectra of pristine carbon dots and NaOH-treated c...

A B S T R A C TPerfluoroalkyl substances (PFASs) have been shown to cause abnormal levels of thyroid hormones (THs) in experimental animals, but the molecular mechanism is poorly understood. Here, a fluorescence displacement assay was used to determine the binding affinities of 16 PFASs with two major TH transport proteins, transthyretin (TTR) and thyroxine-binding globulin (TBG). Most of the tested PFASs bound TTR with relative potency (RP) values of 3 Â 10 À4 to 0.24 when compared with that of the natural ligand thyroxine, whereas fluorotelomer alcohols did not bind. Only perfluorotridecanoic acid and perfluorotetradecanoic acid bound TBG, with RP values of 2 Â 10 À4 when compared with that of thyroxine. Based on these results, it was estimated that displacement of T4 from TTR by perfluorooctane sulfonate and perfluorooctanoic acids would be significant for the occupationally exposed workers but not the general population. Structure-binding analysis revealed that PFASs with a medium chain length and a sulfonate acid group are optimal for TTR binding, and PFASs with lengths longer than 12 carbons are optimal for TBG binding. Three mutant proteins were prepared to examine crucial residues involved in the binding of PFASs to TH transport proteins. TTR with a K15G mutation and TBG with either a R378G or R381G mutation showed decreased binding affinity to PFASs, indicating that these residues play key roles in the interaction with the compounds. Molecular docking showed that the PFASs bind to TTR with their acid group forming a hydrogen bond with K15 and the hydrophobic chain towards the interior. PFASs were modeled to bind TBG with their acid group forming a hydrogen bond with R381 and the hydrophobic chain extending towards R378. The findings aid our understanding of the behavior and toxicity of PFASs on the thyroid hormone system.