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.