Physicochemical Characterization and Larvicidal Activity of a Rutin–Zn Material against Aedes aegypti

Rutin is a natural flavonoid whose larvicidal activity may be limited by its physicochemical properties. Here, a rutin–Zn material was prepared using a nominal 1:1 precursor molar ratio and evaluated against fourth-instar Aedes aegypti larvae. UV–Vis spectroscopy showed shifts of Band II from 258 to 270 nm and Band I from 361 to 439 nm. FTIR bands assigned to O–H and aromatic/conjugated vibrations shifted from 3391 to 3163 cm–1 and from 1601 to 1560 cm–1, respectively, while a new band at 694 cm–1 was tentatively associated with a Zn–O vibration. NMR revealed perturbations in several ligand environments, including an apparent C-5 shift from 157.5 to 161.6 ppm, supporting interaction between Zn2+ and oxygenated regions of rutin without defining a unique coordination site or stoichiometry. X-ray diffraction indicated limited structural reorganization and residual precursor-related crystalline features. The intensity-weighted hydrodynamic diameter increased from 226 ± 3 nm for free rutin to 1501 ± 19 nm for the rutin–Zn material, indicating the formation of larger solvated aggregates under the measurement conditions rather than an increase in primary particle size. After 48 h, LC50 decreased from 322 to 227 mg L–1 and LC90 from 701 to 420 mg L–1. These findings indicate that reaction with Zn2+ altered the physicochemical characteristics of rutin and was associated with moderately improved larvicidal activity under the tested laboratory conditions.