N,O6-partially acetylated chitosan nanoparticles hydrophobically-modified for controlled release of steroids and...

Diosgenin, two synthetic analogs of brassinosteroids, testosterone and dl-α-tocopherol were covalently linked to synthetic water-soluble N,O6-partially acetylated chitosan, for their controlled release. Drug linking was confirmed by FTIR spectroscopy and proton NMR. Conjugates were also characterized by differential scanning calorimetry and wide-angle X-ray diffraction. These conjugates formed self-assembled nanoparticles in aqueous solution with particle sizes ranging from 197 to 358 nm and drug contents between 11.8 and 56.4% (w/w). Spherical 30-60 nm nanoparticles were observed by scanning electron microscopy and transmission electron microscopy upon drying. In vitro release studies performed at acid pH indicated a drug release dependence on substitution degree and particle sizes. Almost constant release rates were observed during the first 6-8h. Brassinosteroids-modified nanoparticles showed good agrochemical activity in radish seeds bioassay at 10(-1) to 10(-4) mg mL(-1). Tocopheryl-modified nanoparticles exhibited radical scavenging activity in DPPH test.