Physical and structural properties of [Cu(BOT1)Cl]Cl, a fluorescent imaging probe for HNO

Massachusetts Institute of Technology, Department of Chemistry, Cambridge, MA 02139, USA.
Journal of inorganic biochemistry (Impact Factor: 3.44). 10/2012; 118. DOI: 10.1016/j.jinorgbio.2012.08.025
Source: PubMed


Nitroxyl, or HNO, is involved in a number of important physiological processes, such as vascular relaxation and neuroregulation. Effective imaging tools are required in order to gain a deeper understanding of the in vivo mechanisms of these processes and to identify the endogenous sources of HNO. Here, we further investigate the physical properties of our previously reported fluorescent nitroxyl sensor, [Cu(BOT1)Cl]Cl (J. Am. Chem. Soc.2010, 132, 5536; BOT1=BODIPY·triazole, a tetradentate ligand). A new high-yielding synthetic procedure for BOT1 is reported. The X-ray crystal structures of two Cu(II) complexes of BOT1 are described. These structural studies show that the BOT1 ligand can form Cu(II) coordination complexes of both square-pyramidal and trigonal-bipyramidal geometries. Cyclic voltammograms of [Cu(BOT1)Cl]Cl were acquired, revealing the presence of a quasi-reversible feature at 130mV (vs the ferrocene/ferrocenium couple) in MeCN and at -40mV (vs Ag/AgCl) in aqueous buffer, which is assigned to the Cu(II)/Cu(I) couple. The reactivity of [Cu(BOT1)Cl]Cl with Angeli's salt, a stable source of HNO, was further investigated. A 1000-fold excess of Angeli's salt elicits an immediate 10-fold emission turn-on response of the sensor, consistent with our previous report. A new observation, reported here, is that the intensity of this turn-on emission diminishes at longer incubation times. Fluorescent imaging of nitroxyl by [Cu(BOT1)Cl]Cl in HeLa cells was carried out. Upon treatment of the cells with Angeli's salt, there was a modest 2-fold intracellular turn-on in emission intensity.

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    ABSTRACT: A new family of benzoresorufin-based copper complexes for fluorescence detection of NO and HNO is reported. The copper complexes, CuBRNO1-3, elicit 1.5-4.8-fold emission enhancement in response to NO and HNO. The three sensors differ in the nature of the metal-binding site. The photophysical properties of these sensors are investigated with assistance from density functional theory calculations. The fluorescence turn-on observed upon reaction with HNO is an unexpected result that is discussed in detail. The utility of the new sensors for detecting HNO and NO in HeLa cells and RAW 264.7 macrophages is demonstrated.
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