Stabilization of Carbon Nanotubes and Graphene by Tween-80: Mechanistic Insights from Spectroscopic and Simulation Studies.

Polyoxyethylene sorbitan monooleate is commonly used to obtain stable dispersions of nanoparticles (NPs) such as carbon nanotubes (CNTs) and graphene. However, the mechanism underlying dispersion is poorly understood. The present study aimed at investigating the mechanism of stabilization of carbon NPs (CNPs), namely, single-walled CNTs (SWCNTs), multi-walled CNTs (MWCNTs), and graphene, by Tween-80 using attenuated total internal reflection-Fourier transform infrared and nuclear magnetic resonance (NMR) spectroscopy. Molecular dynamics (MD) simulations were performed to identify, at the atomic scale, the significant interactions that underlie the adsorption and the stabilizing effect of Tween-80 on CNPs, in this way corroborating the spectroscopy results. Spectroscopic analysis revealed that the alkyl chain tether to SWCNT, MWCNT, and graphene surface, presumably through π-π interactions between the carbon-carbon double bond in the alkyl chain and the aromatic rings of CNPs. The hydrophilic polyethoxylate chains extend into the aqueous environment and stabilize the suspension by steric hindrance. MD simulations also showed that Tween-80 molecules interact with the CNP surface via the alkyl chain, thus corroborating spectroscopy results. MD simulations additionally revealed that Tween-80 aggregates on the CNP surface shifted from planar to micelle-like with increasing Tween-80 ratios, underscoring concentration-dependent changes in the nature of these interactions.

Gastric ulcer healing by chebulinic acid solid dispersion-loaded gastroretentive raft systems: preclinical evidence.

Background: Chebulinic acid (CA), a component in Terminalia chebula, exhibits antiulcer activity, but has poor aqueous solubility. Raft-forming systems incorporating solid dispersions (SDs) of CA, were developed to overcome its poor biopharmaceutical properties and to prolong the gastric residence time for maximum activity. Methods: SDs were formulated by a solvent evaporation method using Eudragit EPO. Raft formulations consisted of sodium alginate as a polymer. Results: Release of CA in the dissolution medium was 40%, whereas SDs showed 95.45% release. The CA raft system (20 mg/kg) showed curative efficacy in an alcohol-induced gastric ulcer model and increased protection when compared with omeprazole (10 mg/kg) and CA suspension (20 mg/kg). Conclusion: These studies demonstrated SD raft systems to be a promising approach for antiulcer therapy by CA.