Solid-state tailored silver nanocomposites from chitosan: Synthesis, antimicrobial evaluation and molecular docking

This study thoroughly explores the synthesis, characterization, and antimicrobial efficacy of three α-aminophosphonate-chitosan (α-AP-Cs) compounds and their nano‑silver functionalized organic hybrids. α-AP-Cs derivatives (CU, CT and CSC) were synthesized via an in-situ, one-pot reaction using chitosan and triphenyl-phosphite, with different carbamide-glutaraldehyde crosslinkers; urea-glutaraldehyde, thiourea-glutaraldehyde and semicarbazide-glutaraldehyde, respectively. Subsequently, their corresponding α-AP-Cs‑silver nanocomposites (CU-Ag⁰NPs, CT-Ag⁰NPs and CSC-Ag⁰NPs) were synthesized via solid-state approach. Their physicochemical and morphological profiles were fully characterized and compared against chitosan-Ag⁰NPs (Cs-Ag⁰NPs) and their bare organic-cores via CHNS/P/O, FT-IR, XRD, TEM, EDX, XPS and UV-visible analysis. The synthesis procedure, including phosphonation and carbamide-glutaraldehyde crosslinking, was confirmed through spectroscopic and elemental analyses. XPS and XRD affirmed the metallic silver with FCC structure. The UV-visible absorption peak was ⁓399 nm with averaging TEM size of the semi-spherical Ag⁰NPs around 30.4 nm. Thereafter, antimicrobial properties were systematically explored and optimized by evaluating minimum inhibition concentration, dose-killing, growth kinetics curves, protein leakage, and antibiofilm activity against bacterial strains (Streptococcus mutans and Pseudomonas aeruginosa) and fungal strains (Candida albicans and Rhizopus oryzae). Notably, incorporating α-aminophosphonate and Ag⁰NPs into chitosan-backbone markedly enhanced its antimicrobial efficacy against bacterial and fungal biofilms. Finally, a detailed structure-activity relationship study was conducted to elucidate the antimicrobial mechanisms.