title: Surface activity of lysozyme and dipalmitoyl phosphatidylcholine vesicles at compressed and supercritical fluid interfaces.
abstract: The surface activities of lysozyme and dipalmitoyl phosphatidylcholine (DPPC) vesicles at aqueous/compressed fluid interfaces are examined via high-pressure interfacial tension measurements using the pendant drop technique. The density and interfacial tension in compressible fluid systems vary significantly with pressure, providing a versatile medium for elucidating interactions between biomolecules and fluid interfaces and a method to elicit pressure-dependent interfacial morphological responses. The effects of lysozyme concentration (0.0008, 0.01, and 1 mg/mL) and pressure (> or = 7 MPa) on the dynamic surface response in the presence of ethane, propane, N2, and CO2 at 298 K were examined. Interfacial lysozyme adsorption reduced the induction phase and quickly led to interfacial tensions consistent with protein conformational changes and monolayer saturation at the compressed fluid interfaces. Protein adsorption, as indicated by surface pressure, correlated with calculated Hamaker constants for the compressed gases, denoting the importance of dispersion interactions. For DPPC at aqueous/compressed or aqueous/supercritical CO2 interfaces (1.8-20.7 MPa, 308 K), 2-3-fold reductions in interfacial tension were observed relative to the pure binary fluid system. The resulting surface pressures infer pressure-dependent morphological changes within the DPPC monolayer.
authors.affiliation: NSF-STC Environmentally Responsible Solvents and Processes, Department of Mechanical and Chemical Engineering, North Carolina A&T State University, Greensboro, North Carolina 27411, USA.
authors.forename: Geoffrey D
authors.initials: GD
authors.lastname: Bothun
authors.forename: Yeh Wei
authors.initials: YW
authors.lastname: Kho
authors.forename: Jason A
authors.initials: JA
authors.lastname: Berberich
authors.forename: Justin P
authors.initials: JP
authors.lastname: Shofner
authors.forename: Tracy
authors.initials: T
authors.lastname: Robertson
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Tatum
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Knutson
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D008567:Membranes, Artificial; D009113:Muramidase / Q000737:chemistry*; D011312:Pressure; D013500:Surface Tension; D014867:Water / Q000737:chemistry
chemical_list: D005740:Gases; D008567:Membranes, Artificial; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D009113:Muramidase