Metal Ion–Enhanced Self‐Assembly Properties of Amygdalin Extracted From Bitter Almond: Characterization and Potential Antiviral Applications

Bitter almond is not only a widely used food, but also a classic tonic Chinese medicine, which mainly contains amygdalin (Amy), a bitter compound. Amy possesses multiple beneficial pharmacological activities, such as anticancer properties, blood sugar reduction, and immune enhancement. Based on previous research about the biological properties of Amy in different ion strength solutions, it was found to have certain self-assembly potential. In this study, a Ca²⁺ assisted self-assembly nanoparticle based on Amy is fabricated. The ability of metal ions to form Amy nanoparticles is explored with respect to the Amy concentrations, proportion of constituents, and temperature conditions. Dynamic light scattering (DLS) was employed for detection, revealing that the diameter of Amy-Ca²⁺ nanoparticles (ACNPs) ranges from 122 to 459 nm, with a polydispersity index (PDI) of 0.377. Subsequently, the assembly mechanism of ACNPs is investigated using ultraviolet-visible (UV-vis) spectra, Fourier transform infrared (FT-IR) spectra, and H nuclear magnetic resonance (H NMR) spectra. It is demonstrated that there is a hydrogen bonding interaction between Amy and Ca²⁺, and it is likely that the non-hydroxyl hydrogen at the position of the Amy sugar group interacts with Ca²⁺. Furthermore, the potential of ACNPs in an antivirus assay was validated by using respiratory syncytial virus (RSV) as an infection model. The results reveal that Amy exhibits anti-RSV activity to some degree, and when combined with calcium sulfate (CaSO₄), another common food additive, it significantly enhances the anti-RSV effect. The enhanced anti-RSV effect may be attributed to the self-assembly phenomenon of Amy and Ca²⁺. In addition, in vitro hemolysis assays and cytotoxicity tests have demonstrated that ACNPs are biocompatible and safe. All in all, this study reveals the potential application of natural ingredient Amy in antivirus bioaction, highlighting its dual roles as a bioactive ingredient.