A Surface Effect Allows HNO/NO Discrimination by a Cobalt Porphyrin Bound to Gold

SEBASTIAN A. SUAREZ; MARIANO FONTICELLI; ALDO A. RUBERT; E. DE LA LLAVE; DAMIAN A SCHERLIS; ROBERTO SALVAREZZA; MARCELO MARTI; FABIO DOCTOROVICH

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Año: 2010 vol. 49 p. 6955 - 6966

0020-1669

Nitroxyl (HNO) is a small short-lived molecule for which it has been suggested that it could be produced, under certaincofactors conditions, by nitric oxide (NO) synthases. Biologically relevant targets of HNO are heme proteins, thiols,molecular oxygen, NO, and HNO itself. Given the overlap of the targets and reactivity between NO and HNO, it is verydifficult to discriminate their physiopathological role conclusively, and accurate discrimination between them still remainscritical for interpretation of the ongoing research in this field. The high reactivity and stability of cobalt(II) porphyrins towardNO and the easy and efficient way of covalently joining porphyrins to electrodes through S-Au bonds prompted us to testcobalt(II) 5,10,15,20-tetrakis[3-(p-acetylthiopropoxy)phenyl]porphyrin [Co(P)], as a possible candidate for the electro-chemical discrimination of both species. For this purpose, first, we studied the reaction between NO, NO donors, andcommonly used HNO donors, with CoII(P) and CoIII(P). Second, we covalently attached CoII(P) to gold electrodes andcharacterized its redox and structural properties by electrochemical techniques as well as scanning tunneling microscopy,X-ray photoelectron spectroscopy, and solid-state density functional theory calculations. Finally, we studied electro-chemically the NO and HNO donor reactions with the electrode-bound Co(P). Our results show that Co(P) is positionedover the gold surface in a lying-down configuration, and a surface effect is observed that decreases the CoIII(P)(but not CoIII(P)NO-) redox potential by 0.4 V. Using this information and when the potential is fixed to values thatoxidize CoIII(P)NO- (0.8 V vs SCE), HNO can be detected by amperometric techniques. Under these conditions, Co(P) isable to discriminate between HNO and NO donors, reacting with the former in a fast, efficient, and selective manner withconcomitant formation of the CoIII(P)NO- complex, while it is inert or reacts very slowly with NO donors.