Controllable Synthesis of Hemoglobin–Metal Phosphate Organic–Inorganic Hybrid Nanoflowers and Their Applications in Biocatalysis

In recent years, organic–inorganic hybrid nanoflower technology has become an effective method for enzyme immobilization. Here, seven hierarchical flower-like hemoglobin-phosphate organic-inorganic hybrid nanomaterials (Hb-M₃(PO₄)₂·nH₂O HNFs) were synthesized through an improved universal one-pot wet-chemical method, with Ca²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ as inorganic components. In this synthesis process, the metal cations are successively involved in the coordination reaction with Hb and the metathesis reaction to generate phosphate precipitation. The coordination ability of metal cations and the generation rate of phosphate precipitations were evaluated, then the progress of the two chemical reactions was controlled synchronously by adjusting the phosphate buffer (PB) concentration, and finally a flower-like structure conducive to substrate diffusion and transport was obtained. Due to the conformational transformation of hemoglobin and the abundant Cu²⁺/Fe³⁺ active sites, the hemoglobin-Cu₃(PO₄)₂·3H₂O nanoflowers have extremely high catalytic activity, which is ～14 times that of Hb. Importantly, this method is suitable for the monometallic-ionic, polymetallic-ionic and polyvalent metal-ion nanoflowers, which broadens the chemical composition and structural diversity of nanoflowers.