Synthesis of Gold Nanoparticles Using Cucurbitacin E-Glycoside and Methyl Gallate Isolated from Citrullus colocynthis L. Fruit and Evaluation of their Antibacterial and Antibiofilm Activities

Introduction: Metal nanoparticles have received much attention due to their unique physical dynamics, chemical reactivity, and promising biological applications. Green synthesis using natural compounds is an alternative to traditional chemical methods for the synthesis of nanoparticles.

Materials and methods: Herein, two secondary metabolites were isolated from different fractions of methanolic extract of Citrullus colocynthis (bitter apple) Schard. and identified as cucurbitacin Eglycoside (1) and methyl gallate (2). Both compounds were used in the green nanoformulation of gold nanoparticles. Mass spectrometry and NMR spectroscopy were used for structure elucidation of compound 1 and compound 2. UV-vis spectroscopy, FTIR, and AFM were performed to confirm the formation of AuNPs.

Result and discussions: The spectra of UV-Vis showed a characteristic peak at 519 nm and 548 nm for compounds 1 and 2, respectively. AuNPs ranged mostly between 1 and 50 nm measured using AFM. The FTIR analysis confirmed the presence of phytochemicals on the surface of AuNPs. The synthesized AuNPs showed good antibacterial activity against Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa.

Conclusion: The synthesized AuNPs demonstrated good antibiofilm activity against Streptococcus mutans. Thus, the green synthesized AuNPs can combat the pathogenicity of several human pathogens.