Catalytic Two-Electron Reductions of N₂O and N₃^- by Myoglobin in Surfactant Films

Abstract

Myoglobin (Mb), in films of dimethyldidodecylammonium bromide (ddab) on graphite electrodes, is used as a catalyst to mediate the electrochemical reduction of nitrous oxide (N2O) as well as the isoelectronic ion azide (N3-) in aqueous solutions. The electrocatalytic reductions are characterized by a rate-dependent irreversibility in cyclic voltammograms of Mb/ddab in the presence of the substrates. Bulk electrolysis shows that the reduction of 15N15NO by Mb/ddab yields 15N15N as shown by GC/MS. The catalytic reduction of azide results in almost quantitative formation of ammonia. These electrocatalytic processes are rationalized as two-electron reductions, with the catalyst cycling between the Fe(I) and Fe(III) states of Mb. To our knowledge, this is the first characterization of N2O reduction by an Fe porphyrin or heme protein.

Comparison of the direct electrochemistry of myoglobin and hemoglobin films and their bioelectrocatalytic properties

“…The formal potential of the Fe(lll)/Fe(ll) redox couple was pH dependent in basic aqueous solution for 7 < pH < 11. The cyclic voltammograms of an Mb/DDAB film showed two redox couples from the Fe(III)/Fe(II) and Fe(II)/(I) couples [20,21], with formal potentials of about À0.2, and À1.0 V, respectively. The voltammograms also showed one irreversible redox couple with a cathodic peak potential at about À0.7 V, and one irreversible redox couple with an anodic peak potential at about +0.15 V, for this film when transferred to basic aqueous solutions.…”

“…The increase in the cyclic voltammetric current shows that both have a redox couple with formal potential, E 0 0 , at about À0.1 V (vs. AgjAgCl) in acidic aqueous solution, which corresponds to the Fe(III)/Fe(II) redox couple of myoglobin and hemoglobin, respectively [18][19][20][21]. The cyclic voltammograms of Mb/DDAB and Hb/ DDAB films both showed two redox couples from the Fe(III)/Fe(II) and Fe(II)/(I) couples in aqueous solutions of pH between 7 and 13.…”

“…Farmer and co-workers have proposed the mechanisms of surfactant-immobilised myoglobin catalyzing reactions of N 2 O through a two electron reduction processes [20,21]. The electrocatalytic reduction process of N 2 O …”

Nitrogen Monoxide and Nitrous Oxide Binding and Reduction

“…Electrocatalytic N 2 O reduction mediated by heme proteins such as Mb or cytochrome P450 monooxygenase has been demonstrated in film-modified electrodes [145,212]. The authors suggest two-electron redox processes occur with the catalyst shuttling between the Fe(I) and Fe(III) states, e.g.…”

Oxidation of triphenylphosphine and norbornene by nitrous oxide in the presence of CoIILCl2 [L = 3-phenyl-5-(2-pyridylmethylidene)-2-thiohydantoin]: the first example of CoII-catalyzed alkene oxidation by N2O

“…Catalytic metal-mediated reactions of N 2 O have been found. [8][9][10][11] Recently, we have reported the syntheses of a Co II complex with 3-phenyl-5-(2-pyridilmethylidene)-2-thiohydantoin 1 ligand. 12 This complex demonstrated a capability to react reversibly with molecular oxygen 13 and to catalyze alkene epoxidation by PhIO and H 2 O 2 .…”