Preliminary mu SR studies on the incorporation of steroidal drug molecules into liposomes

Muon spin relaxation of two liposome samples consisting of 100% DPPC (dipaimitoylphosphatidyleholine) and 50:50mole% DPPC: Cholesterol at a final lipid concentration of 100mg/mL are compared. The observation of a significant loss in the muonium fraction from 11% to 6% when cholesterol is present is compatible with radical formation in the second sample. Also reported are measurements on pure solid cholesterol where a clear T-1 minimum at ca 100K, corresponding to a dynamic process with activation energy of ca. 1.89 kJmol(-1) and an attempt frequency of 5.89 x 10(10) s(-1), is observed. An estimate of a hyperfine interaction of 255.4 MHz for this radical predicts a Delta M= 1 ALC transition at 0.94 T. (c) 2005 Elsevier B.V. All rights reserved.