Spectroscopic-Chemometric Monitoring of Methacycline-Copper(II) Complex In-Vitro Release Kinetics from Microgel in Blood Serum: Synthesis, Bioactivities and In-Silico Validation

The controlled release monitoring of drug-metal complex in biological matrices remains a major challenge in advanced drug delivery. In this research work, the methacycline-copper(II) complex (MTC-Cu(II)) was synthesized by reflux coordination, producing a thermally (TGA/DSC) stabilized complex (M.P. 255 °C vs. 217 °C for MTC; DSC peak 351 °C). UV-Vis spectroscopy revealed a ligand-to-metal charge transfer band at 678 nm, and Job’s plot confirmed 1:1 stoichiometry. FTIR and Raman analysis demonstrated coordination through oxygen and nitrogen donor sites, while Raman-PCA showed clear spectral discrimination (PC-1 87.01% variance). PXRD and SEM-EDX confirmed structural reorganization and uniform Cu(II) incorporation (13.16 wt%). Biologically, MTC-Cu(II) exhibited enhanced antibacterial activity with inhibition zones of 29 mm (S. aureus) and 23 mm (E. coli), reduced MIC values (1.0 and 3.5 µg/mL), and improved biofilm inhibition (68% and 55%). Antioxidant activity reached 85% DPPH scavenging, while hemolysis remained below 5%, indicating good hemocompatibility. In-silico interactions revealed strong binding affinities (up to -8.5 kcal/mol) with stable conformations (RMSD < 2.0Å). Incorporation into a PNIPAM/Ag/Fe₂O₃ hybrid microgel enabled sustained release in blood serum over 36 h. SERS-PLSR quantification demonstrated excellent predictive accuracy (R² = 0.995, RMSEP = 0.106-0.154 ppm), and validated by UV-Vis spectroscopy measurement. Kinetic modeling (zero-order, first-order, Higuchi, and Korsmeyer-Peppas) revealed that the release was diffusion controlled, although slower release of the Cu(II) complex was observed because of the metal-ligand stability. This work demonstrates a synergistic platform offering a promising strategy for the next-generation antibacterial therapeutics with tunable kinetics.