CONICET | Buscador de Institutos y Recursos Humanos

Sphingomyelin (SM) and related sphingolipids are believed to have important functional roles on membrane domain formation, e.g. for the Cholesterol (Chol)-rich liquid-ordered (Lo) phase. Notwithstanding, N-nervonoyl-SM (24:1-SM) the most common unsaturated SM natural species, is able to prevent phase segregation. In this study, Polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) was applied to investigate the conformational properties and intermolecular interactions in 16:0 vs 24:1-SM monolayers and their mixtures with 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Chol (DOPC/SM/Chol 2:1:1). From the results we inferred that the cis double bond (Δ15) in 24:1-SM molecule diminishes intermolecular H-bonding and chain packing density compared to that of 16:0-SM. In ternary mixtures containing 16:0-SM, the relative intensity of the two components of the Amide I band reflected changes in the H-bonding network due to SM-Chol interactions. In contrast, the contribution of the main components of the Amide I band in DOPC/24:1-SM/Chol remained as in 24:1-SM monolayers, with a larger contribution of the non-H-bonded component. The most interesting feature in these ternary films is that the C=O stretching mode of DOPC appeared with an intensity similar to that of SM Amide I band inDOPC/16:0-SM/Chol monolayers (a two-phase [Lo/Le] system), whereas an extremely low intensity of the C=O band was detected in DOPC/24:1-SM/Chol monolayers (single Le phase). This is evidence that the unsaturation in 24:1-SM affected not only the conformational properties of acyl chains but also the orientation of the chemical groups at the air/water interface. The physical properties and overall H-bonding ability conferred by 24:1-SM may have implications in cell signaling and binding of biomolecules.