Influence of Glucose on the Self-Assembly and Photophysical Properties of Hydrophilic Pluronic F98

This study investigates the effect of glucose, a kosmotropic osmolyte, on the micellization and hydration dynamics of the highly hydrophilic triblock copolymer (BCP), Pluronic F98. The outcomes obtained from the physicochemical studies are described. Clouding behavior demonstrated that increasing glucose concentration decreases the CP, highlighting a sugaring-out effect. Surface tension (γ) measurements revealed that glucose enhances hydrophobic interactions at the air-liquid interface, promoting micellization. The relative viscosity (η_rel) increases, suggesting the dehydration of the poly(ethylene oxide) (PEO) blocks of F98. The sugaring-out effect of the PEO and PPO blocks of F98 in the presence of glucose was evaluated by monitoring changes in bond stretching using Fourier-transform infrared (FT-IR) spectroscopy, which was further corroborated through two-dimensional Nuclear Overhauser Effect Spectroscopy (2D-NOESY) analysis that inferred glucose to remain in the PEO hydrated shell. These spectroscopic findings were further validated through the evaluation of optimum descriptors using computational simulations performed with the DFT/B3LYP method within the 3-21G basis set framework, utilizing the Gaussian 5.0.9 software. Fluorescence spectroscopy, using pyrene as a probe, confirmed a glucose-induced decrease in the I₁/I₃ ratio, suggesting increased hydrophobicity and a lower critical micelle temperature (CMT). Photophysical studies employing fluorescein sodium salt (FLU) dye demonstrated that glucose concentration and temperature modulate the microenvironment that has not been explored in prior studies, emphasizing the novelty and originality of this work, leading to a blue shift at lower glucose concentrations and a red shift at 1.0 M glucose as a function of temperature. Despite spectral shifts, the fluorescence lifetime (∼3.5 ns) remains unchanged. Fluorescence quenching of FLU-loaded F98 micelles with potassium iodide (KI) confirmed dynamic quenching at the micelle-water interface. Dynamic light scattering (DLS) inferred a temperature-dependent variation in micelle size attributed to hydrogen bonding and hydrophilic interactions, while small-angle neutron scattering (SANS) analysis, using a core-shell spherical model, detailed the micellar structural changes.