Common Nefafu (<i>Clerodendrum colebrookianum</i> L.)-Mediated Silver Nanoparticles for Physicochemical Insights into the Protein Corona Formation and Inhibition of Fibrillation of Human Serum Albumin

Engineering nanomaterials with products isolated from natural resources is attractive for targeted therapeutic applications. Prior to the biomedicinal applications, one significant facet of nanoparticles is the understanding of protein corona formation and its relative binding aspects. In this perspective, we have synthesized two different silver nanoparticles, one with the extract of the leaves of a traditional herb <i>Clerodendrum colebrookianum</i>, commonly known as "Nefafu", and the other with one of its major polyphenolic compounds, apigenin, and their complexations were studied with the model protein human serum albumin (HSA). The formation of the protein corona of HSA on the surface of AgNPs was revealed from the observed changes in terms of hydrodynamic size, ξ-potential, and LSPR band positions, and the gray colored layer of diameter ∼3 nm on the surface of AgNPs as visualized in the TEM micrographs. The combined multispectroscopic approaches and molecular dynamics simulation studies on the interaction process revealed the moderate binding affinities (<i>K</i>_b in the order of 10⁴ M^-1) of both the AgNPs toward HSA, where their complexations were found to be entropy driven with the involvement of hydrophobic association as the major driving force of interactions. Interestingly, both Nefafu-AgNPs and Apigenin-AgNPs could retain the secondary structural conformation of HSA. These polyphenol-capped NPs were able to significantly inhibit the fibrillation of HSA, where Nefafu-AgNPs with a higher number of polyhydroxy groups showed better inhibition than Apigenin-AgNPs, as revealed from the kinetic study with ThT assay, CR assay, ANS assay, circular dichroism, as well as from the morphological changes from amyloid-sheet structure to small globular units as visualized in fluorescence microscopic imaging.