Unravelling pH/pKa influence on pH-responsive drug carriers: Insights from ibuprofen-silica interactions and comparative analysis with carbon nanotubes, sulfasalazine, and alendronate

This study employs density functional theory to explore the interaction between ibuprofen (IBU) and silica, emphasizing the influence of the trimethylsilyl (TMS) functional group for designing pH-responsive drug carriers. The surface (S) and drug (D) molecules' neutral (0) or deprotonated (-1) states were taken into consideration during the investigation. The likelihood of these states was determined based on the pKa values and the desired pH conditions. To calculate the pH-dependent interaction energy (EintpH), four different situations have been identified: S0D0, S0D-1, S-1D0, and S-1D-1.The electrostatic component of interaction energy aligns favorably with its theoretical value in both the Debye-Hückel and Grahame models. The investigation has gathered first-hand experimental data on the drug loading and release of pH-responsive mesoporous silica nanoparticles. Effective drug loading was observed in the acidic environment of the stomach (pH 2-5), followed by a release in the slightly basic to neutral pH of the small intestine (pH 7.4), These findings align with existing literature. The results revealed horizontal drug adherence on silica surfaces, improving binding capabilities. Comparisons were made with combinations involving carboxylated carbon nanotubes and ibuprofen, silica, and sulfasalazine, and silica and alendronate, exploring drug loading/release dynamics associated with positive/negative interaction energies. The investigation, supported by experimental data, contributes valuable insights into pH-responsive mesoporous silica nanoparticles, offering new design possibilities for drug carriers.

Improved chlorine tolerance of a polyvinyl pyrrolidone-polysulfone membrane enabled by carboxylated carbon nanotubes

Chemical cleaning of membranes may be limited by the tolerance of some polymeric membranes to chlorine. In this work we show that modification of a polyvinyl pyrrolidone-polysulfone (PVP-PSF) membrane with carboxylated carbon nanotubes (CNTs) leads to greater chlorine tolerance of the membrane along with smoothing the surface roughness and improving some membrane properties including permeability, hydrophilicity and antifouling ability. In comparison with PVP-PSF membrane, incorporating carboxylated CNTs reduced the release of organic matter from the membrane and caused less decrease in hydrophilicity, permeability and BSA rejection. After chlorine treatment of a conventional PVP-PSF membrane, an infrared absorbance peak around 1670 cm^-1, representing the vibration of the amide bond in the PVP, decreased significantly and two smaller peaks at around 1725 and 1775 cm^-1 were observed. The percentage of C-Cl (2p) in the PVP-PSF membrane was about 2.8 times greater than that of the carboxylated CNT-composite PVP-PSF (CNT-PVP-PSF) membrane after chlorine exposure, suggesting greater chlorine tolerance of CNT-PVP-PSF membrane. In comparison with PVP-PSF membrane, the formation of toxic chlorinated byproducts during chlorination of organic matter released from CNT-PVP-PSF membrane was much lower. The improvement of tolerance to chlorine is attributed to stabilization of the polymer through hydrogen bonding between polymer and carboxylated CNTs.