Thermodynamic and Kinetic Elucidation of the Biogenic Capping Mechanism: Evidence of Ordered Self-assembly in Gongronema latifolium-Silver Nanoparticles

Abstract

While our previous research successfully established the exceptional in vivo safety profile (LD50 > 5000 mg/kg) and the potent antimalarial efficacy of silver nanoparticles synthesized using Gongronema latifolium, and subsequently identified both Sarsasapogenin and Cinchonidine as the primary molecular stabilizers through Density Functional Theory (DFT) modelling, the precise, intricate physical chemistry governing the formation of this protective “Safety Shield” remained largely unexplored. This current study actively bridges that critical gap by systematically investigating the underlying energetic mechanisms and complex molecular interactions involved. As the third study in this series, it experimentally elucidates the intricate energy landscape and the specific self-assembly mechanism of these biogenic caps. We meticulously monitored the reduction of silver ions under pseudo-first-order conditions across a temperature range of 303–333 K. Kinetic analysis revealed a surface-controlled process, while Eyring analysis yielded significantly negative entropy of activation. This thermodynamic signature offers compelling physical evidence for an associative mechanism, suggesting that the critical, rate-determining step involves the assembly of a highly ordered and sterically constrained "biopolymer cage" around the silver nuclei. These experimental findings provide crucial validation for the "Safety Shield" model for biocompatible nanotherapeutics, which was originally proposed in our previous density functional theory (DFT) studies, confirming its real-world efficacy. Graphical Abstract