Hematin
is a hydroxyl group linked heme site (hydroxyl heme) of
the natural enzymes/proteins like hemoglobin, cytochrome c, catalase,
and horseradish peroxidase, and it has an important role in the physiological
function. Because of problems like poor electron-transfer functionality
(on solid electrodes), poor solubility, and molecular aggregation
in aqueous solution, limited electrochemical studies have been reported
in the literature. A new electrode modification method for hematin
using graphitized mesoporous carbon nanomaterial and chitosan for
enhanced redox-active and efficient electrocatalytic reductions of
hydrogen peroxide and dissolved oxygen in neutral pH was demonstrated
in this work. The hematin-modified electrode showed a highly stable
redox peak at E°′ = −0.390 V versus
Ag/AgCl with a heterogeneous rate constant value of 1.34 s–1. Calculated hematin-active loading concentration
(Γhemat = 126 × 10–10 mol
cm–2) is ∼20 times higher than the reported
values. Physicochemical and electrochemical characterizations revealed
trapping of the hematin via axial bond coordination and intermolecular
hydrogen bonding with amino functional groups of chitosan and π–π
interactions with the graphitic site of mesoporous carbon within the
matrix. The new hematin electrode showed ∼400 mV reduction
in the overpotential with current sensitivity/detection range of 570
nA μM–1/100–900 μM and 6.7 μA
ppm–1/1–10 ppm, respectively, for H2O2 and dissolved oxygen reduction reactions in pH 7 phosphate
buffer solution. Michaelis–Menten kinetics were applied for
the H2O2 reduction reaction and estimated the
rate constant values as K
M = 0.78 mM and k
s = 1.15 s–1. No marked interference
was noticed with common biochemicals such as nitrite, nitrate, glucose,
uric acid, ascorbic acid, xanthine, hypoxanthine, cysteine, and dopamine
on amperometric i–t detection
of H2O2 indicating the activity similar to the
heme-based proteins/enzymes.