title: Surface interactions, thermodynamics and topography of binary monolayers of Insulin with dipalmitoylphosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylcholine at the air/water interface.
abstract: The molecular packing, thermodynamics and surface topography of binary Langmuir monolayers of Insulin and DPPC (dipalmitoylphosphatidylcholine) or POCP (1-palmitoyl-2-oleoylphosphatidylcholine) at the air/water interface on Zn(2+) containing solutions were studied. Miscibility and interactions were ascertained by the variation of surface pressure-mean molecular area isotherms, surface compressional modulus and surface (dipole) potential with the film composition. Brewster Angle Microscopy was used to visualize the surface topography of the monolayers. Below 20mN/m Insulin forms stable homogenous films with DPPC and POPC at all mole fractions studied (except for films with XINS=0.05 at 10mN/m where domain coexistence was observed). Above 20mN/m, a segregation process between mixed phases occurred in all monolayers without squeezing out of individual components. Under compression the films exhibit formation of a viscoelastic or kinetically trapped organization leading to considerable composition-dependent hysteresis under expansion that occurs with entropic-enthalpic compensation. The spontaneously unfavorable interactions of Insulin with DPPC are driven by favorable enthalpy that is overcome by unfavorable entropic ordering; in films with POPC both the enthalpic and entropic effects are unfavorable. The surface topography reveals domain coexistence at relatively high pressure showing a striped appearance. The interactions of Insulin with two major membrane phospholipids induces composition-dependent and long-range changes of the surface organization that ought to be considered in the context of the information-transducing capabilities of the hormone for cell functioning.
authors.affiliation: CIQUIBIC, Universidad Nacional de Córdoba-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina. Electronic address: ejgrasso@conicet.gov.ar.
authors.forename: E J
authors.initials: EJ
authors.lastname: Grasso
authors.affiliation: CIQUIBIC, Universidad Nacional de Córdoba-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
authors.forename: R G
authors.initials: RG
authors.lastname: Oliveira
authors.affiliation: CIQUIBIC, Universidad Nacional de Córdoba-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
authors.forename: B
authors.initials: B
authors.lastname: Maggio
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000388:Air; D007328:Insulin / Q000737:chemistry*; D010316:Particle Size; D010713:Phosphatidylcholines / Q000737:chemistry*; D013499:Surface Properties; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D007328:Insulin; D010713:Phosphatidylcholines; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine
keywords: 1-Palmitoyl-2-oleoylphosphatidylcholine (POPC); Binary monolayers; Dipalmitoylphosphatidylcholine (DPPC); Hysteresis; Insulin; Insulin surface behavior; Langmuir monolayers