Publications [#64950] of Sidney A Simon

Papers Published

1. Simon, S.A. and Fink, C.A. and Kenworthy, A.K. and McIntosh, T.J., The hydration pressure between lipid bilayers. Comparison of measurements using X-ray diffraction and calorimetry, Biophys. J. (USA), vol. 59 no. 3 (1991), pp. 538 - 46
   (last updated on 2007/04/15)

   Abstract:
   The hydration pressure between dipalmitoyl phosphatidyl-N,N-dimethylethanolamine (DPPE-Me₂) bilayers has been analyzed by both X-ray diffraction measurements of osmotically stressed liposomes and by differential scanning calorimetry. By the X-ray method, the authors obtain a magnitude (P₀) and decay length (λ) for the hydration pressure which are both quite similar to those found for bilayers of other zwitterionic lipids, such as phosphatidylcholines. The is, X-ray analysis of DPPE-Me₂ in the gel phase gives λ=1.3 Å, the same as the previously measured for the analogous gel phase lipid dipalmitoylphosphatidylcholine (DPPC), and P₀=3.9×10⁹ dyn/cm², which is in excellent agreement with the value of 3.6×10⁹ dyn/cm² calculated from the measured Volta potential of DPPE-Me₂ monolayers in equilibrium with liposomes. These results indicate that the removal of one methyl group to convert DPPC to DPPE-Me₂ does not markedly alter the range or magnitude of the hydration pressure. Calorimetry shows that the main gel to liquid-crystalline phase transition temperature of DPPE-Me₂ is approximately constant for water contents ranging from 80 to 10 water molecules per lipid molecule, but increases monotonically with decreasing water content below 10 waters per lipid. A theoretical fit to these temperature vs. water content data predicts λ=6.7 Å

   Keywords:
   biomechanics;biothermics;lipid bilayers;X-ray diffraction examination of materials;