Search

The goal of the work reported here was to amplify the fluorescent properties of 4-aryliden-5(4 H )-oxazolones by suppression of the hula-twist non-radiative deactivation pathway. This aim was achieved by simultaneous bonding of a Pd center to the N atom of the heterocycle and the ortho carbon of the arylidene ring. Two different 4-(( Z )-arylidene)-2-(( E )-styryl)-5(4 H )-oxazolones, the structures of which are closely related to the chromophore of the Kaede protein and substituted at the 2- and 4-positions of the arylidene ring ( 1a OMe; 1b F), were used as starting materials. Oxazolones 1a and 1b were reacted with Pd(OAc) 2 to give the corresponding dinuclear orthometalated palladium derivates 2a and 2b by regioselective C-H activation of the ortho -position of the arylidene ring. Reaction of 2a ( 2b ) with LiCl promoted the metathesis of the bridging carboxylate by chloride ligands to afford dinuclear 3a ( 3b ). Mononuclear complexes containing the orthopalladated oxazolone and a variety of ancillary ligands (acetylacetonate ( 4a , 4b ), hydroxyquinolinate ( 5a ), aminoquinoline ( 6a ), bipyridine ( 7a ), phenanthroline ( 8a )) were prepared from 3a or 3b through metathesis of anionic ligands or substitution of neutral weakly bonded ligands. All species were fully characterized and the X-ray determination of the molecular structure of 7a was carried out. This structure has strongly distorted ligands due to intramolecular interactions. Fluorescence measurements showed an increase in the quantum yield (QY) by up to one order of magnitude on comparing the free oxazolone (QY < 1%) with the palladated oxazolone (QY = 12% for 6a ). This fact shows that the coordination of the oxazolone to the palladium efficiently suppresses the hula-twist deactivation pathway.

Electrochemistry and confocal fluorescence microscopy were successfully combined to selectively bleach and monitor the fluorescence of NBD (7-nitrobenz-2-oxa-1,3-diazole)-labeled phospholipids of giant liposomes. Three types of giant unilamellar vesicles have been investigated, the fluorescent phospholipids being localized either mainly on their outer-, inner-, or both inner/outer leaflets. We established that only the fluorescent lipids incorporated in the outer leaflet of the vesicles underwent electrochemical bleaching upon reduction. The relative fluorescence intensity decay was quantified all along the electrochemical extinction through an original fluorescence loss in electrobleaching (FLIE) assay. As expected, the reorganization of the fluorescent phospholipids followed diffusion-driven dynamics. This was also evidenced by comparison with fluorescence loss in photobleaching (FLIP) and the corresponding numerical model. The value of the lateral diffusion coefficient of phospholipids was found to be similar to that obtained by other methods reported in the literature. This versatile and selective bleaching procedure appears reliable to explore important biological and pharmacological issues., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)