Molecular mechanism of phytochemical cinnamic acid/cinnamaldehyde from the spice cinnamon binding to bovine haemoglobin

Cinnamic acid (CA) and cinnamaldehyde (CMA) are essential components of the spice cinnamon, a commonly used food oxidizer and preservative. In this work, the binding mechanism and structural information of CA/CMA to bovine haemoglobin (BHb) were investigated through multi-spectroscopic and molecular simulation experiments focusing on assessing the effect of phytochemicals in spices on BHb. Fluorescence and isothermal titration calorimetry experiments showed that CA possessed a binding constant of 10 5  L/mol and an electrostatic interaction with BHb resulting in the formation of stable complexes compared to CMA-BHb. Spectroscopic results (UV–Vis, CD and synchrotron fluorescence experiments) demonstrated that the addition of CA/CMA differently altered or affected the polarity of the BHb microenvironment, slightly perturbing the secondary structure of BHb. Thermodynamic analyses and molecular docking data were analyzed to confirm the dominance of van der Waals and hydrogen bonding forces in the energy contribution of the CMA-BHb system, and molecular dynamics simulations demonstrated that CA/CMA was relatively stable in the hydrophobic pocket of the protein (BHb). These findings will provide a basis for applying phytochemicals in spices in meat processing.