The role of pristine carbon nanotubes as nanocarriers of 7,8-dihydroxyflavone

Flavonoids are secondary plant metabolites with a wide range of pharmacological effects. Among others, their antioxidant, anti-inflammatory and vasoprotective actions are noteworthy. However, the low bioavailability of flavonoids limits their direct clinical use. Nanoencapsulation of flavonoids is an effective tool to improve their biopharmaceutical characteristics, as the drug is protected inside the nanocarrier and specifically released into the therapeutic target. Bearing this in mind, pristine single- and multi-walled carbon nanotubes have been studied in this work as nanocarriers of 7,8-dihydroxyflavone, 7,8-DHF. Flavone encapsulation is optimized according to the influence of pH, the type of CNTs and their concentration on the association process. The equilibrium binding constants of 7,8-DHF to the CNTs are determined by measuring the variation observed in the flavone absorbance when the concentration of carbon nanotubes increases. CNTs/flavone complexes are characterized by particle size distribution and Z-potential measurements, as well as Transmission Electron Microscopy. The antioxidant capacity of free 7,8-DHF and the CNTs/7,8-DHF complexes are estimated by using the DPPH⋅, 2,2-diphenyl-1-picrylhydrazyl radical scavenging method. The results show that the encapsulation of the flavone in the CNTs results in a preservation of its pharmacological properties and provides stability to the encapsulated drug. • Pristine carbon nanotubes, MWCNTs and SWCNTs, are suitable nanocarriers for the controlled delivery of 7,8-DHF. • The adsorption of 7,8-DHF onto pristine CNTs improves the biodistribution and bioavailability of the drug. • 7,8-DHF encapsulated in both types of CNTs maintains its antioxidant activity unchanged and is preserved over time. • The encapsulation (adsorption) of 7,8-DHF on CNTs walls is produced via π−π and hydrophobic interactions. • SWCNTs have a higher flavone adsorption capacity than MWCNTs: K SWCNT/7,8-DHF > K MWCNT/7,8-DHF for all the pHs studied.