Sodium alginate-derived hydrophilic Gel@CuO microspheres: a green nanocatalyst for diverse Petasis transformations with antibacterial activity

Abstract

A sustainable heterogeneous catalytic system based on sodium alginate-derived Gel@CuO microspheres has been developed for Petasis multicomponent reactions under environmentally benign conditions. CuO nanoparticles synthesized via a biogenic route using Buchanania lanzan Spreng leaf extract were immobilized within a calcium-crosslinked alginate matrix to afford a mechanically robust and hydrophilic microsphere nanocatalyst. Comprehensive characterization by FT-IR, XRD, SEM-EDX, XPS, TGA-DTA, and contact angle analysis confirmed successful CuO entrapment, uniform elemental distribution, strong metal–polymer interactions, and high thermal stability. The Gel@CuO nanocatalyst enabled the synthesis of 27 structurally diverse Petasis products, delivering isolated yields of 86–99% within 7–90 min in an aqueous sodium p-toluenesulfonate (NaPTS) hydrotropic medium under mild conditions. Quantitative green metrics revealed low total PMI values (9.2–14.1 g g⁻¹) and high Reaction Mass Efficiency (RME = 77–85%) for alkylaminophenol derivatives, while more complex substrates showed moderately higher PMI yet retained excellent yields. The catalyst exhibited excellent recyclability over multiple cycles with negligible activity loss. In addition, the Gel@CuO microspheres displayed notable antibacterial activity against both Gram-positive (Staphylococcus aureus, Bacillus cereus) and Gram-negative (Salmonella typhimurium, Proteus vulgaris) bacteria. Overall, this work presents a biopolymer-based, recyclable nanocatalyst offering a sustainable platform for organic transformation.