Aminotroponiminates as Ligands for Potential Metal-Based Nitric Oxide Sensors

Abstract

A family of new fluorescently labeled ligands, HRDATI, was prepared to develop transition-metal-based NO sensing strategies. The ligands are composed of aminotroponiminates (ATIs) with a dansyl fluorophore on one of the imine nitrogen atoms and an alkyl substituent, either i-Pr (8), t-Bu (9), or Bz (10), on the other. Bis(chelate) Co2+ ([Co(i-PrDATI)2] (12), [Co(t-BuDATI)2] (14), [Co(BzDATI)2] (15)) and Zn2+ ([Zn(i-PrDATI)2] (13)) complexes were prepared and characterized by X-ray crystallography. The bis(ATI) complex [Co(i-Pr2ATI)2] (11) was also prepared and its X-ray crystal structure determined. Cyclic voltammetry reveals reversible redox waves at -2.57 and -0.045 V (vs Cp2Fe/Cp2Fe+) in THF for the Co2+/Co+ and Co3+/Co2+ couples, respectively, of 11. Only a Co2+/Co+ wave at -2.09 V is observed for 12. When excited at 350 nm, the HRDATI ligands and the diamagnetic Zn2+ complex 13 fluoresce around 500 nm, whereas the paramagnetic Co2+ complexes quench the fluorescence. These air-stable cobalt compounds react with nitric oxide to dissociate a DATI ligand and form neutral dinitrosyl complexes, [Co(NO)2(RDATI)]. The release of the fluorophore-containing ligand is accompanied by an increase in fluorescence intensity, thus providing a strategy for fluorescent NO sensing. Linking two DATI moieties via a tetramethylene chain affords the ligand H2DATI-4 (18). The Co2+ complex [Co(DATI-4)] (19) reacts more readily with NO than the bis(DATI) compounds and also displays an increase in fluorescence intensity upon NO binding.

Metal-Based NO Sensing by Selective Ligand Dissociation

“…[14] In the newly designed ligand H 2 DATI-4 (1), each aminotroponiminate (ATI) ring is modified with a dansyl fluorophore on one of the imine nitrogen atoms and linked through the other nitrogen by a 4-methylene chain to a second such chelating unit. [15] The yellow ligand 1 is rather insolved by direct methods with SHELXS-86 and refined with SHELXL-93. [12] The program XPMA was used for the graphical processing of the data.…”

“…Related [Co( R DATI) 2 ] where R DATI alkyldansylaminotroponiminate, complexes that exhibit similar fluorescence responses to NO do not exhibit such p ± p interactions in the solid state. [15,21] The ability of a sensor to report only the desired analyte while ignoring competitors is crucial. Although NO rapidly reacts with O 2 to yield NO 2 , the reaction is second order with respect to NO.…”

Meeting of the minds: Metalloneurochemistry

“…6). In addition to Zn 2ϩ sensors, we have ongoing efforts to develop NO sensors, and have had some initial success (88,89). Access to both Zn 2ϩ and NO sensors would be useful for studying such problems as the transformation of NO signals to Zn 2ϩ ones by MTs as well as other questions in metalloneurochemistry.…”

A FRET-based biosensor for NO detection

“…Currently available technologies to monitor NO levels are based among others on chemiluminescent instrumentation [9], amperometry [10], EPR spectroscopy [11], colorimetric assays or porphyrin based fluorescent compounds [12]. While each technique has its own advantages [8,13,14] there remains a need for simple to implement, cheap NO sensors that can be used repeatedly [15].…”