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    Impact of sphingomyelin acyl chain (16:0 vs 24:1) on the interfacial properties of Langmuir monolayers: A PM-IRRAS study

    Year: 2019

    Journal: Colloid Surf. B-Biointerfaces, Volume 173, 1-Jan, page 549–556

    Authors: Vazquez, Romina F.; Daza Millone, Antonieta; Pavinatto, Felippe J.; Fanani, Maria L.; Oliveira, Osvaldo N., Jr.; Vela, Maria E.; Mate, Sabina M.

    Organizations: Agencia Nacional de Promocion Cientifica y TecnologicaANPCyT [PICT 2657/2013, 1627/2014, 0679/2016]; Consejo Nacional de Investigaciones Cientificas y TecnicasConsejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) [PIP 0671]; Comision de Investigaciones Cientificas de la Provincia de Buenos Aires (CICBA); Universidad Nacional de La PlataNational University of La Plata [M11/181, M11/191, 11/X760]; FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2013/14262-7]; CNPq (Brazil)National Council for Scientific and Technological Development (CNPq); Universidad Nacional de Cordoba (SECyT_UNC)Secretaria de Ciencia y Tecnologia (SECYT)

    Keywords: Membrane rafts; Cholesterol-sphingomyelin interactions; Langmuir monolayers; PM-IRRAS

    Membrane structure is a key factor for the cell's physiology, pathology, and therapy. Evaluating the importance of lipid species such as N-nervonoyl sphingomyelin (24:1-SM) -able to prevent phase separation- to membrane structuring remains a formidable challenge. This is the first report in which polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) is applied to investigate the lipid-lipid interactions in 16:0 vs 24:1-SM monolayers and their mixtures with 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol (Chol) (DOPC/SM/Chol 2:1:1). From the results we inferred that the cis double bond (Delta 15) 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 in DOPC/16:0-SM/Chol monolayers (a two-phase [Lo/Le] system), whereas an extremely low intensity of the C=0 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.
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