The influence of ceramide and its dihydro analog on the physico-chemical properties of sphingomyelin bilayers.

The influence of ceramide and its dihydro analog (Cer and DHCer, respectively; inclusively termed Cers) on sphingomyelin (SM) bilayers was examined. Fluorescent microscopy showed that SM/Cers binary bilayers undergo phase separation between Cers-rich and Cers-poor phases. Based on calorimetry, the content of Cers in the Cers-rich phase was estimated and the results show that DHCer in the DHCer-rich phase (17.5 mol%) is more condensed than Cer in the Cer-rich phase (15 mol%), likely due to a stronger intermolecular interaction of DHCer than that of Cer. Furthermore, the Cers-poor phase consists of almost pure SM. X-ray diffraction and water permeability measurements disclosed that the size of crystallites-lipid nano-clusters formed inside the Cers-rich phase-are larger for the DHCer-rich phase than those for the Cer-rich phase. Due to its stronger intermolecular interactions, DHCer could effectively suppress the inter-crystallite packing gaps to avoid the energetic disadvantage, resulting in formation of larger crystallites.
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