publications by Sidney A Simon.


Papers Published

  1. Kenworthy, A.K. and Simon, S.A. and McIntosh, T.J., Structure and phase behavior of lipid suspensions containing phospholipids with covalently attached poly(ethylene glycol), Biophys. J. (USA), vol. 68 no. 5 (1995), pp. 1903 - 20 .
    (last updated on 2007/04/15)

    Abstract:
    Liposomes containing phospholipids with covalently attached poly(ethylene glycol) (PEG-lipids) are being developed for in vivo drug delivery. In this paper we determine the structure and phase behavior of fully hydrated distearoylphosphatidylcholine (DSPC) suspensions containing PEG-lipids composed of distearoylphosphatidylethanolamine with attached PEGs of molecular weights ranging from 350 to 5000. For DSPC:PEG-lipid suspensions containing 0-60 mol% PEG-lipid, differential scanning calorimetry shows main endothermic transitions ranging from 55 to 64°C, depending on the size of the PEG and concentration of PEG-lipid. The enthalpy of this main transition remains constant for all PEG-350 concentrations but decreases with increasing amounts of PEG-750, PEG-2000, or PEG-5000, ultimately disappearing at PEG-lipid concentrations greater than about 60 mol%. Low-angle and wide-angle X-ray diffraction show that tilted gel (Lβ') phase bilayers are formed for all PEG-lipid molecular weights at concentrations of about 10 mol% or less, with the distance between bilayers depending on PEG molecular weight and PEG-lipid concentration. At PEG-lipid concentrations greater than 10 mol%, the lipid structure depends on the size of the PEG moiety. X-ray diffraction analysis shows that untilted interdigitated (Lβl) gel phase bilayers form with the incorporation of 40-100 mol% PEG-35D or 20-70 mol% PEG-750, and untilted gel (Lβ) phase bilayers are formed in the presence of about 20-60 mol% PEG-2000 and PEG-5000. Light microscopy, turbidity measurements, X-ray diffraction, and 1H-NMR indicate that a pure micellar phase forms in the presence of greater than about 60% PEG-750, PEG-2000, or PEG-5000

    Keywords:
    biothermics;enthalpy;lipid bilayers;molecular biophysics;molecular weight;optical microscopy;phase equilibrium;suspensions;thermal analysis;X-ray diffraction;