title: Effect of colloidal carriers on ascorbyl palmitate stability.
abstract: Active compounds can be protected against degradation by incorporation into colloidal carrier systems. The stabilizing effect of carrier systems for ascorbyl palmitate (AP) was investigated using microemulsions (ME), liposomes and solid lipid nanoparticles (SLN). Analysis of chemical stability by HPLC showed that AP is most resistant against oxidation in non-hydrogenated soybean lecithin liposomes, followed by SLN, w/o and o/w ME, and hydrogenated soybean lecithin liposomes. The molecular environment of the AP-like nitroxide probe (C(16)-Tempo) in colloidal carriers was characterized using electron paramagnetic resonance (EPR) spectroscopy. We have found that the nitroxide groups are located in environments with different polarity and mobility. The hydrophilic part of AP is the reactive moiety, and high stability is obtained in systems in which this part is exposed to a less polar environment. Additionally, the determined accessibility of nitroxide groups to reduction correlated well with the chemical stability of AP. It is more deeply immersed in the interface when entrapped in a liquid-state carrier than when applied in gel-state particles. Encapsulation of AP in SLN core leads to greater stability. We conclude that the location of the sensitive group of the drug-molecule in a carrier system is crucial for its stability.
authors.affiliation: Faculty of Pharmacy, University of Ljubljana, Askerceva 7, 1000 Ljubljana, Slovenia.
authors.forename: Julijana
authors.initials: J
authors.lastname: Kristl
authors.forename: Breda
authors.initials: B
authors.lastname: Volk
authors.forename: Mirjana
authors.initials: M
authors.lastname: Gasperlin
authors.forename: Marjeta
authors.initials: M
authors.lastname: Sentjurc
authors.forename: Polona
authors.initials: P
authors.lastname: Jurkovic
mesh_terms: D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003102:Colloids; D004337:Drug Carriers / Q000737:chemistry*; D004355:Drug Stability; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008081:Liposomes / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D013997:Time Factors
chemical_list: D003102:Colloids; D004337:Drug Carriers; D008081:Liposomes; D001205:Ascorbic Acid; C031226:6-O-palmitoylascorbic acid