title: Rheological properties of regular insulin and aspart insulin Langmuir monolayers at the air/water interface: condensing effect of Zn2+ in the subphase.
abstract: The interfacial behavior of regular insulin (Reg-insulin) and aspart insulin (Asp-insulin) was critically affected by the presence of Zn(2+) in the subphase. This cation induced a condensed-like behavior in the compression isotherms, especially apparent for Reg-insulin films when observed by Brewster angle microscopy. Immediately after spreading, Reg-insulin, but not Asp-insulin, showed bright patches that moved in a gaseous-like state. Moreover, Zn(2+) caused marked variations of the surface electrostatics of both insulin monolayers and considerable hysteresis of their molecular organization. By oscillatory compression-expansion cycles, we observed in all cases the development of a dilatational response to the surface perturbation, and both monolayers exhibited well-defined shear moduli in the presence of Zn(2+), which was higher for Reg-insulin. Development of a shear modulus indicates behavior resembling a nominal solid, more apparent for Reg-insulin than for Asp-insulin, suggesting the presence of viscoelastic networks at the surface.
authors.affiliation: Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC-CONICET), Dpto. de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Pabellón Argentina, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
authors.forename: E J
authors.initials: EJ
authors.lastname: Grasso
authors.affiliation: Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC-CONICET), Dpto. de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Pabellón Argentina, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
authors.forename: R G
authors.initials: RG
authors.lastname: Oliveira
authors.affiliation: Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC-CONICET), Dpto. de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Pabellón Argentina, Ciudad Universitaria, X5000HUA Córdoba, Argentina. Electronic address: bmaggio@fcq.unc.edu.ar.
authors.forename: B
authors.initials: B
authors.lastname: Maggio
mesh_terms: D000388:Air; D019245:Compressive Strength; D055119:Elastic Modulus; D006801:Humans; D007328:Insulin / Q000737:chemistry*; D061267:Insulin Aspart / Q000737:chemistry*; D011312:Pressure; D012212:Rheology; D013499:Surface Properties; D013816:Thermodynamics; D014783:Viscosity; D014867:Water / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D007328:Insulin; D014867:Water; D061267:Insulin Aspart; D015032:Zinc
keywords: Aspart insulin; Langmuir monolayer; Regular insulin; Surface behavior; Surface rheology