The Chemistry and Biology of Nitroxyl (HNO)

MIGUEL ANGEL MORALES VÁSQUEZ; MARIANA HAMER; FABIO DOCTOROVICH

The Chemistry and Biology of Nitroxyl (HNO)

Elsevier

Lugar: Amsterdam; Año: 2016; p. 1 - 8

In this chapter, we will briefly describe the fundamental chemistry of HNO and3NO- making a comparison with NO reactivity. Rate constants for the reactionsmentioned below are summarized in Table 1.1.Despite being a three atoms molecule, the chemical characteristics/properties of HNO are complex and less straightforward as compared to NO. One of the intriguing properties of HNO involves its acidbase chemistry. HNO is a weak acid with an accepted pKa of 11.4 and a singlet ground state.However, the deprotonation of HNO generates the corresponding anion 3NO-,which has a triplet ground state, analogous to the isoelectronic O2 molecule.Consequently, the loss of a proton from HNO is not a simple acid/base equilibrium but a spin-forbidden slow deprotonation (Table 1.1, Eq. 1.1): HNO + OH- ---- 3NO- + H2O (1.1)Thus, as HNO acidbase equilibrium species have different electronic spin states,both deprotonation of HNO (Table 1.1, Eq. 1.1) and reprotonation of 3NO-(Table 1.1; Eq. 1.1) are very slow. Taking this into account, in biological media (pH = 7.4) HNO is likely to be the exclusive species present. And in case that 3NO2 is produced, it may have a long enough lifetime to be chemically relevant (milliseconds), even under acidic conditions, since the protonation rate for this anion is slow.