Simultaneous nitrosylation and N-nitrosation of a Ni-thiolate model complex of Ni-containing SOD

• Published in: Chemical science (Cambridge) 2018-12, Vol.9 (45), p.8567-8574
• Main Authors: Truong, Phan T, Broering, Ellen P, Dzul, Stephen P, Chakraborty, Indranil, Stemmler, Timothy L, Harrop, Todd C
• Format: Article
• Language: English
• Subjects: Anions; Crystallography; Disproportionation; Electronic structure; Nickel; Nitric oxide; Nitrosyls; Oxidation; Spectroscopy; Substrates; Superoxide dismutase; X ray spectra
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c8sc03321h

Nitric oxide (NO) is used as a substrate analogue/spectroscopic probe of metal sites that bind and activate oxygen and its derivatives. To assess the interaction of superoxide with the Ni center in Ni-containing superoxide dismutase (NiSOD), we studied the reaction of NO + and NO with the model complex, Et 4 N[Ni(nmp)(SPh- o -NH 2 - p -CF 3 )] ( 1 ; nmp 2− = dianion of N -(2-mercaptoethyl)picolinamide; − SPh- o -NH 2 - p -CF 3 = 2-amino-4-(trifluoromethyl)benzenethiolate) and its oxidized analogue 1 ox , respectively. The ultimate products of these reactions are the disulfide of − SPh- o -NH 2 - p -CF 3 and the S , S -bridged tetrameric complex [Ni 4 (nmp) 4 ], a result of S-based redox activity. However, introduction of NO to 1 affords the green dimeric {NiNO} 10 complex (Et 4 N) 2 [{Ni(κ 2 - S Ph- o-N NO- p -CF 3 )(NO)} 2 ] ( 2 ) via NO-induced loss of nmp 2− as the disulfide and N-nitrosation of the aromatic thiolate. Complex 2 was characterized by X-ray crystallography and several spectroscopies. These measurements are in-line with other tetrahedral complexes in the {NiNO} 10 classification. In contrast to the established stability of this metal-nitrosyl class, the Ni-NO bond of 2 is labile and release of NO from this unit was quantified by trapping the NO with a Co II -porphyrin (70-80% yield). In the process, the Ni ends up coordinated by two o -nitrosaminobenzenethiolato ligands to result in the structurally characterized trans -(Et 4 N) 2 [Ni( S Ph- o-N NO- p -CF 3 ) 2 ] ( 3 ), likely by a disproportionation mechanism. The isolation and characterization of 2 and 3 suggest that: (i) the strongly donating thiolates dominate the electronic structure of Ni-nitrosyls that result in less covalent Ni-NO bonds, and (ii) superoxide undergoes disproportionation via an outer-sphere mechanism in NiSOD as complexes in the {NiNO} 9/8 state have yet to be isolated. Nitric oxide reacts with a NiSOD model complex to yield a thiolate-ligated/N-nitrosated {NiNO} 10 species with unusually labile Ni-NO bonds.