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β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH

Gochev, Georgi G. ; Kovalchuk, Volodymyr I. ; Aksenenko, Eugene V. ; Fainerman, Valentin B. ; Miller, Reinhard (2022):
β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH. (Publisher's Version)
In: Colloids and Interfaces, 5 (1), MDPI, e-ISSN 2504-5377,
DOI: 10.26083/tuprints-00019601,
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Item Type: Article
Origin: Secondary publication DeepGreen
Status: Publisher's Version
Title: β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH
Language: English
Abstract:

The theoretical description of the adsorption of proteins at liquid/fluid interfaces suffers from the inapplicability of classical formalisms, which soundly calls for the development of more complicated adsorption models. A Frumkin-type thermodynamic 2-D solution model that accounts for nonidealities of interface enthalpy and entropy was proposed about two decades ago and has been continuously developed in the course of comparisons with experimental data. In a previous paper we investigated the adsorption of the globular protein β-lactoglobulin at the water/air interface and used such a model to analyze the experimental isotherms of the surface pressure, Π(c), and the frequency-, f-, dependent surface dilational viscoelasticity modulus, E(c)f , in a wide range of protein concentrations, c, and at pH 7. However, the best fit between theory and experiment proposed in that paper appeared incompatible with new data on the surface excess, Γ, obtained from direct measurements with neutron reflectometry. Therefore, in this work, the same model is simultaneously applied to a larger set of experimental dependences, e.g., Π(c), Γ(c), E(Π)f , etc., with E-values measured strictly in the linear viscoelasticity regime. Despite this ambitious complication, a best global fit was elaborated using a single set of parameter values, which well describes all experimental dependencies, thus corroborating the validity of the chosen thermodynamic model. Furthermore, we applied the model in the same manner to experimental results obtained at pH 3 and pH 5 in order to explain the well-pronounced effect of pH on the interfacial behavior of β-lactoglobulin. The results revealed that the propensity of β-lactoglobulin globules to unfold upon adsorption and stretch at the interface decreases in the order pH 3 > pH 7 > pH 5, i.e., with decreasing protein net charge. Finally, we discuss advantages and limitations in the current state of the model

Journal or Publication Title: Colloids and Interfaces
Journal volume: 5
Issue Number: 1
Publisher: MDPI
Collation: 26 Seiten
Uncontrolled Keywords: β-lactoglobulin, pH effect, adsorption layer, monolayer, secondary layer, adsorption isotherm, surface pressure isotherm, equation of state, surface dilational modulus, protein unfolding
Classification DDC: 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften
500 Naturwissenschaften und Mathematik > 530 Physik
500 Naturwissenschaften und Mathematik > 540 Chemie
Divisions: 05 Department of Physics > Institute for Condensed Matter Physics
Date Deposited: 02 Feb 2022 13:30
Last Modified: 02 May 2022 12:07
DOI: 10.26083/tuprints-00019601
Corresponding Links:
URN: urn:nbn:de:tuda-tuprints-196018
SWORD Depositor: Deep Green
URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/19601
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