Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes

The relative sensitivity of structurally related Eu(III) complexes to quenching by electron and energy transfer processes has been compared. In two sets of 9-coordinate complexes based on 1,4,7-triazacyclonane, the Eu...

Bioorthogonal red and far-red fluorogenic probes for wash-free live-cell and super-resolution microscopy

Small-molecule fluorophores enable the observation of biomolecules in their native context with fluorescence microscopy. Specific labelling via bioorthogonal tetrazine chemistry confers minimal label size and rapid labelling kinetics. At the same time, fluorogenic tetrazine-dye conjugates exhibit efficient quenching of dyes prior to target binding. However, live-cell compatible long-wavelength fluorophores with strong fluorogenicity have been difficult to realize. Here, we report close proximity tetrazine-dye conjugates with minimal distance between tetrazine and fluorophore. Two synthetic routes give access to a series of cell permeable and impermeable dyes including highly fluorogenic far-red emitting derivatives with electron exchange as dominant excited state quenching mechanism. We demonstrate their potential for live-cell imaging in combination with unnatural amino acids, wash-free multi-colour and super-resolution STED and SOFI imaging. These dyes pave the way for advanced fluorescence imaging of biomolecules with minimal label size.

Free Radical Mediated Oxidative Degradation of Carotenes and Xanthophylls

This article reviews the excited-state quenching, pro-vitamin A activity and anticarcinogenicity of carotenes and xanthophylls in relation to their chemical structures. Excited-state quenching improved with the length of the conjugated chain structure. Pro-vitamin A activity was dependent on the presence of at least one beta-ionyl ring structure. The effectiveness of carotenoids as antioxidants depended on their ability to trap peroxyl radicals with production of resonance-stabilized carotenyl radicals. The products identified from oxidations of carotenes and xanthophylls with molecular oxygen and other oxidizing agents are presented. The free radical-mediated mechanisms that have been proposed to account for the different classes of products are reviewed.