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

[Display omitted] •We examined impact of the ceramide (Cer) and its dihydo-analog (DHCer) on the sphingomyelin bilayers.•Both of Cer and DHCer form the Cer-rich and DHCer-rich domains, respectively, in sphingomyelin bilayers.•DHCer are more condensed in the DHCer-rich domains than Cer in the Cer-rich domains.•DHCer forms larger crystallites than Cer due to stronger intermolecular interaction of DHCer than that of Cer. 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.