ABSTRACT
Associating copolymers self-assemble during their passage through a liquid chromatography (LC) column, and the elution differs from that of common non-associating polymers. This computational study aims at elucidating the mechanism of their unique and intricate chromatographic behavior. We focused on amphiphilic diblock copolymers in selective solvents, performed the Monte Carlo (MC) simulations of their partitioning between a bulk solvent (mobile phase) and a cylindrical pore (stationary phase), and investigated the concentration dependences of the partition coefficient and of other functions describing the phase behavior. The observed abruptly changing concentration dependences of the effective partition coefficient demonstrate the significant impact of the association of copolymers with their partitioning between the two phases. The performed simulations reveal the intricate interplay of the entropy-driven and the enthalpy-driven processes, elucidate at the molecular level how the self-assembly affects the chromatographic behavior, and provide useful hints for the analysis of experimental elution curves of associating polymers.
ABSTRACT
The transport of a photosensitizer to target biological structures followed by the release of singlet oxygen is a critical step in photodynamic therapy. We compared the (photo)physical properties of polystyrene nanoparticles (TPP@PS) of different sizes and self-assembled poly(ethylene glycol)-b-poly(ε-caprolactone) core/shell nanoparticles (TPP@PEG-PCL) with different lengths of copolymer blocks, both suitable for the transport of the tetraphenylporphyrin (TPP) photosensitizer. The singlet oxygen was formed inside both nanoparticles after irradiation with visible light. Its kinetics was controlled by the size of TPP@PS; its lifetime (τΔ) increased with increasing nanoparticle size (from 6.5 to 16 µs) because of hindered diffusion into the external aqueous environment, where it was quickly deactivated. Accordingly, the prolongation of the singlet oxygen-sensitized delayed fluorescence kinetics was found for TPP@PS of high size. The TPP@PEG-PCL self-assemblies allowed for enhanced oxygen diffusion, and the estimated low values of τΔ ≈ 3.7 µs were independent of the size of building blocks. The delayed fluorescence in oxygen-free conditions originating from triplet-triplet annihilation indicated a high mobility of TPP in the PCL core in comparison with fixed molecules in the PS matrix. Photooxidation of uric acid revealed the highest efficacy for TPP@PS of small sizes, whereas the largest TPP@PS exhibited the lowest activity, and the efficacy of TPP@PEG-PCL remained independent of the sizes of the building blocks.
