In situ and real-time vibrational spectroscopic characterizations of the photodegradation of nitrite in the presence of methanediol.

Nitrite (NO2-) is one of the common salts in aqueous aerosols, and its photolytic products, nitric oxide (NO) and hydroxyl radical (OH), have potential for use in the oxidation of organic matter, such as dissolved formaldehyde, methanediol (CH2(OH)2), which is regarded as the precursor of atmospheric formic acid. In this work, the simulation of UVA irradiation in an aqueous mixture of NaNO2/CH2(OH)2 was carried out via continuous exposure with a 365 nm LED lamp, and the reaction evolutions were probed by in situ and real-time infrared and Raman spectroscopy, which provided multiplexity in the identification of the relevant species and the corresponding reaction evolution. Although performing infrared absorption measurements in aqueous solution seemed impracticable due to the strong interference of water, the multiplexity of the vibrational bands of parents and products in the non-interfered infrared regimes and the conjunction with Raman spectroscopy still make it possible to perform in situ and real-time characterization of the photolytic reaction in the aqueous phase, supplementary to chromatographic approaches. During the 365 nm irradiation, NO2- and CH2(OH)2 gradually decreased, concomitant with the formation of nitrous oxide (N2O) and formate (HCOO-) in the early period and carbonate (CO32-) in the late period, as revealed by the vibrational spectra. The losses or the gains of the aforementioned species increased with increases in the concentration of CH2(OH)2 and the irradiation flux of the 365 nm UV light. The ionic product HCOO- was also confirmed by ion chromatography, but oxalate (C2O42-) was absent in the vibrational spectra and ion chromatogram. The reaction mechanism is reasonably proposed on the basis of the evolutions of the aforementioned species and the predicted thermodynamic favorableness.

Fluorescence sensing of heparin and heparin-like glycosaminoglycans by stabilizing intramolecular charge transfer state of dansyl acid-labeled AG73 peptides with glutathione-capped gold nanoclusters.

Sensors that can specifically and accurately detect glycosaminoglycans are rare. Here, a dual-mode platform for fluorescence intensity and lifetime sensing of plasma heparin and fluorescence imaging of heparan sulfate proteoglycan-expressed cancer cells was developed by stabilizing the intramolecular charge transfer (ICT) state of dansyl acid-labeling AG73 (DA-AG73) peptide with glutathione-capped gold nanoclusters (GSH-AuNCs). DA-AG73 peptides, including an electron-donor dimethylamino group and an electron-withdrawing sulfonamide moiety in the labeled DA molecules, emitted weak fluorescence due to the formation of the twisted ICT excited state. The complexation of heparin with DA-AG73 peptides followed by interacting with the GSH-AuNCs could restrict the rotation of the dimethylamino groups of the labeled DA molecules, triggering the transition from their twisted ICT state to ICT excited state. As a result, the fluorescence intensity and lifetime of the labeled DA molecules in DA-AG73 peptides were gradually enhanced with increasing the heparin concentration. The proposed platform provided excellent selectivity toward heparin and heparan sulfate and exhibited two linear calibration curves for quantifying 20-800 nM and 20-1000 nM heparin in the fluorescence intensity and lifetime modes, respectively. The proposed platform was practically applied for the fluorescence intensity and lifetime determination of plasma heparin and for the selective imaging of heparan sulfate proteoglycan-expressed cells.