To develop an alternative
to ferrous complexes, which easily lose
nitric oxide (NO) binding ability as a result of oxidation by O2 in the complexing absorption process, experiments about the
NO absorption characteristics of cobalt complexes were performed.
First, a screening experiment was conducted, and cobalt(II)–histidine
(CoHis) manifested to be the most potent absorbent to both NO and
O2 in neutral conditions among industrially available cobalt
complexes. Then, the concentration of the cobalt nitrosyl complex,
i.e., CoHis–NO, in the NO absorption liquid was measured by
the NO transfer reaction with ferrous ethylenediaminetetraacetate
[Fe(II)EDTA], thereby the standard curve for CoHis–NO quantification
by spectrophotometry was plotted. At last, as implied by NO absorption
experiments, the absorption of NO can be promoted by reducing the
absorbent temperature, increasing the CoHis concentration, or increasing
the absorbent pH appropriately. Furthermore, it was found that CoHis
could not promote NO disproportionation.