RESUMEN
The photophysical behavior of a ß-blocker drug propranolol (PPL) in micellar environments, formed by alkyltrimethylammonium bromide surfactants viz.; Cetyltrimethylammonium bromide (CTAB), Tetradecyltrimethylammonium bromide (TTAB), and Dodecyltrimethylammonium bromide (DTAB), has been investigated through fluorescence and UV-visible spectroscopic techniques at pH levels of 3.5, 7.4, and 10.4. The impact of pH on the critical micelle concentration (cmc) and micropolarity of micelles were assessed using pyrene as a photophysical probe. The cmc values were found to be lower at pH 10.4 compared to pH 7.4 and pH 3.5. Fluorescence emission intensities of PPL at 323 nm, 338 nm, and 352 nm were significantly influenced by pH, hydrophobic alkyl chain length of surfactants, and their concentrations. Quenching experiments with Cetylpyridinium chloride (CpCl) indicated the localization of charged and uncharged forms of PPL within micelles, with quenching constant (Ksv) values dependent on alkyl chain length and pH. At pH < pKa, PPL is positioned near the Stern layer, whereas at pH 10.4, its naphthalene moiety resides near the hydrophobic micellar core. UV spectroscopy showed that the charged form of PPL interacted with micelles only above cmc, while the neutral form interacted even below the cmc. Density Functional Theory (DFT) reveals the HOMO of the surfactants to be localized on the hydrocarbon chains, and the LUMO localized around the quaternary ammonium unit. Upon complexation with PPL, both HOMO and LUMO shifted to the drug, thereby decreasing energy levels. The findings are explained based on weak noncovalent interactions, further supported and analyzed through Reduced Density Gradient (RDG) and Noncovalent Interaction (NCI) methods, confirming synergistic non-covalent interactions in surfactant-PPL complexes.
RESUMEN
Interaction of neutral and charged lipophilic beta-blocker drug, propranolol (PPL) with biomimicking nanocavities formed by micelles bearing same and opposite charges namely, cationic cetyltrimethylammonium bromide (CTAB), a surface-active ionic liquid 1-hexadecyl-3-methylimidazolium chloride (HDMIC) and anionic sodium dodecyl sulphate (SDS) have been investigated using fluorescence and absorption spectroscopic techniques. Binding of PPL to SDS at pH < pKa is characterised by biphasic interactions with decrease in fluorescence intensity at lower concentrations and subsequent increase post micellization. All the surfactants show significant interactions with the neutral drug molecule at pH > pKa, which is evident from the strongest binding constant ([Formula: see text]) values at pH 10.4. Results of quenching studies indicate that the location of drug molecule is determined by its charge, which is influenced by both pH and charge on micelle surface. For PPL-CTAB and PPL-HDMIC systems, quenching was strongest at pH 10.4, moderate at pH 7.4 and was absent at pH 3.5. However, the PPL-SDS system displayed similar [Formula: see text] values at all pH conditions, suggesting that the probe is at the same position regardless of pH. Non-covalent interactions, which play crucial role in biological systems, are similarly the primary driving force governing the interaction between PPL and surfactant micelles.