Regensburg 2016 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 43: Poster: The Physics of Water Interactions with Biological Matter

CPP 43.6: Poster

Mittwoch, 9. März 2016, 18:15–21:00, Poster B2

Specific Effects of Ca²⁺ Ions and Molecular Structure of β-Lactoglobulin Interfacial Layers at Air/Water Interfaces — •Felix Schulze-Zachau and Björn Braunschweig — Institute of Particle Technology (LFG), Friedrich-Alexander University of Erlangen-Nürnberg (FAU), Cauerstrasse 4, 91058 Erlangen, Germany

β-lactoglobulin (BLG) adsorbate layers at air-water interfaces were studied on a molecular level with vibrational sum-frequency generation (SFG), tensiometry and ellipsometry and on a macroscopic level by foam property measurements as a function of bulk Ca²⁺ concentrations (C). For C <10 mM, a strong decrease in SFG intensity of O-H stretching bands from interfacial water molecules is observed. This decrease is indicative of charge screening and presumably also of specific ion interactions. Support for the latter comes from a change in polarity of C-H stretching modes from aromatic amino acid residues such as Trp, accompanied by an abrupt increase in layer thickness from 5 to 10 nm. Such a polarity change was previously observed in a pH dependent study where the isoelectric point of BLG was crossed and is likely to be associated with interfacial charge compensation and overcharging due to the presence of Ca²⁺. Macroscopic foam stability, however, is decreased once the interfacial charges become fully screened which is in line with previous studies of thin foam films. Once the negative net charge of BLG is overcharged by Ca²⁺ at high C, agglomerates at the interface start to form which increase the layer thickness and interfacial elasticity and decrease the viscosity of the interfacial layer which leads to much higher foam stabilities and smaller bubble sizes.