Zinc sensors based on 2,3-dipicolylamine (DPA) and quinoline have been synthesized. They fluoresced in the presence of Zn(2+) and remained fluorescent when other metal ions were present. Fluorescence enhancement of the sensors was not seen for most other metal ions. In vitro studies with fibroblasts showed fluorescence when sensor and Zn(2+) were present. As seen by single crystal X-ray analysis, four nitrogens from the sensor bind to Zn(2+). These new sensors have lower binding constants than the pentadentate sensors based on 2,2-DPA.

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A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl(2)][Et(4)N] (1; H(2)bpc = 4,5-dichloro-1,2-bis(2-pyridine-2-carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X-ray crystallography. This nonheme Co(III) complex catalyzes olefin epoxidation upon treatment with meta-chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O-O bond to afford Co(V)=O (3) and Co(IV)=O (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical-type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co-OOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O-O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O-O bond of the Co-OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co(V) O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co(V)=O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.

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