title: Cholesterol-Induced Structural Changes in Saturated Phospholipid Model Membranes Revealed through X-ray Scattering Technique.
abstract: Lateral and out-of-plane organization of cholesterol and its effect on regulating the physicochemical properties of zwitterionic phospholipid model membranes have been investigated by a pressure-area isotherm study from the Langmuir monolayer, atomic force microscopy (AFM), and X-ray reflectivity (XRR) measurements from supported binary monolayer films. The systematic isotherm studies on the Langmuir monolayer of phospholipids and the subsequent extraction of excess Gibbs free energy (ΔGexc) revealed the mechanism of cholesterol interaction and the molecular cooperativeness for different arrangements in the phospholipid model membranes. We have found a critical cholesterol molar concentration (χc) up to which the lipid-cholesterol miscibility gradually increases and then further increase in the concentration leads to an inhomogeneous structure formation similar to raft structures. The thickening in the lipid acyl chain and the subsequent lowering of the lipid head group thickness up to χcare also evident from the XRR study. Beyond χc, large-sized domains are observed in the AFM images from the deposited monolayer. χchas also been observed to depend on the phase of the monolayer, in particular, ∼25 molar % in the gel phase and ∼40 molar % in the fluid phase, wherein a regular distribution has been found with the highest separation between the cholesterol molecules. The extracted isothermal compressibility coefficient (CS) and ΔGexcfrom the monolayer isotherms indicate that the molecular arrangement at χcare the most stable configurations of the monolayer. Our study provides direct evidence into cholesterol-induced evolution in phase behavior and the consequent model on the structure at different phases in the phospholipid Langmuir monolayers.
authors.affiliation: Saha Institute of Nuclear Physics, HBNI , 1/AF, Bidhannagar, Kolkata 700064, India.
authors.forename: Rajendra P
authors.initials: RP
authors.lastname: Giri
authors.affiliation: Saha Institute of Nuclear Physics, HBNI , 1/AF, Bidhannagar, Kolkata 700064, India.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Chakrabarti
authors.affiliation: Saha Institute of Nuclear Physics, HBNI , 1/AF, Bidhannagar, Kolkata 700064, India.
authors.forename: Mrinmay K
authors.identifier: 0000-0001-8050-8661
authors.initials: MK
authors.lastname: Mukhopadhyay
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D010743:Phospholipids / Q000737:chemistry*; D013499:Surface Properties; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D008567:Membranes, Artificial; D010743:Phospholipids; D002784:Cholesterol