Layer-by-layer films of hemoglobin or myoglobin assembled with zeolite particles: Electrochemistry and electrocatalysis

Positively charged hemoglobin (Hb) or myoglobin (Mb) at pH 5.0 in solutions and negatively charged zeolite particles in dispersions were alternately adsorbed onto solid surfaces forming {zeolite/protein}n layer-by-layer films, which was confirmed by quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The protein films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV peaks at about − 0.35 V vs. SCE at pH 7.0, characteristic of the heme Fe(III)/Fe(II) redox couples. Hydrogen peroxide (H2O2) and nitrite (NO2−) in solution were catalytically reduced at {zeolite/protein}7 film modified electrodes, and could be quantitatively determined by CV and amperometry. The shape and position of infrared amide I and II bands of Hb or Mb in {zeolite/protein}7 films suggest that the proteins retain their near-native structure in the films. The penetration experiments of Fe(CN)63− as the electroactive probe into these films and scanning electron microscopy (SEM) results indicate that the films possess a great amount of pores or channels. The porous structure of {zeolite/protein}n films is beneficial to counterion transport, which is crucial for protein electrochemistry in films controlled by the charge-hopping mechanism, and is also helpful for the diffusion of catalysis substrates into the films. The proteins with negatively charged net surface charges at pH 9.0 were also successfully assembled with like-charged zeolite particles into layer-by-layer films, although the adsorption amount was less than that assembled at pH 5.0. The possible reasons for this were discussed, and the driving forces were explored.