Novel fluorescein- and pyridine-conjugated schiff base probes for the recyclable real-time determination of Ce3+ and F.

The effect of aminopyridines substituted at different positions on the fluorescence properties deserves to be studied. Since 2-aminopyridyl-based probes have been reported, the effects of 3-aminopyridine and 4-aminopyridine on the performance of fluorescein probes were discussed in here. Two Schiff base fluorescein probes FN-1, FN-2 were designed and synthesized. Among them, since the ligand shows a highly selective and sensitive response to metal charge transfer (LMCT), the fluorescence of FN-1 can be quenched by Ce3+ ions in PBS buffer. At the same time, a specific precipitation reaction between Ce3+ and F- releases the free probe to restore the fluorescence of FN-1. Therefore, FN-1 can be used for the recyclable 'ON-OFF-ON' detection of Ce3+and F-. The detection limits for Ce3+and F- are 4.48 µM and 11.58 µM in concentration range of 0-50 µM and 0-150 µM. However, due to the para position of N and amino groups on 4-aminopyridine, the spatial structure of FN-2 cannot be complexed with ions, resulting in poor selectivity. Polyvinylidene fluoride (PVDF) membrane containing FN-1 were prepared for the real-time qualitative detection of Ce3+and F- in real water samples. FN-1 exhibits high water solubility and biocompatibility and has been successfully applied to biological imaging in vascular smooth muscle cells (VSMCs).

Synthesis and spectral analysis of fluorescent probes for Ce4+ and OCl- ions based on fluorescein Schiff base with amino or hydrazine structure: Application in actual water samples and biological imaging.

Two Schiff base fluorescein probes (FDA, FDH) based on fluorescein-aldehyde and nitroaniline derivatives were synthesized. The effects of amino and hydrazine substituents in fluorescein backbones were examined via fluorescence and absorbance spectra. In the presence of Ce4+, the fluorescence of FDA was quenched due to the ligand to metal charge transfer (LMCT). Hypochloric acid can react with the CN bond, and blocking the photo induced electron transfer (PET) of FDH leads to enhancement of the fluorescence. FDA showed detection limits for Ce4+ and OCl- as low as 63 nM in concentration range of 0-4 µM. FDH showed detection limits for OCl- as low as 0.8 µM in concentration rang 0-100 µM. Polyvinylidene fluoride (PVDF) membrane containing the probes was prepared for the real-time qualitative detection of Ce4+ and OCl- in real water samples. The probes were successfully applied to biological imaging in vascular smooth muscle cells (VSMCs) and are expected to find applications in biosensing.

Crystal structure of AlpK: An essential monooxygenase involved in the biosynthesis of kinamycin.

AlpK is an essential monooxygenase involved in the biosynthesis of kinamycin. It catalyzes the C5-hyfroxylattion of the crucial benzo[b]-fluorence intermediate in kinamycin synthesis. However, the structure and mechanism of AlpK is unclear. Here, we report the first structure of AlpK in complex with FAD. Our structure sheds light on the catalytic mechanism of AlpK.

Fluorescent probes for detecting cysteine.

Cysteine plays a crucial role in physiological processes. Therefore, it is necessary to develop a method for detecting cysteine. Fluorimetry has the advantages of convenient detection, short response time, high sensitivity and good selectivity. In this review, fluorescent probes that detect cysteine over the past three years are summarized based on structural features of fluorophores such as coumarin, BODIPY, rhodamine, fluorescein, CDs, QDs, etc and reaction groups including acrylate, aldehyde, halogen, 7-nitrobenzofurazan, etc. Then, effects of different combinations between fluorophores and response groups on probe properties and detection performances are discussed.