pH-equilibration of human hair: Kinetics and pH-dependence of the partition ratios for H +  - and OH - -ions based on a Freundlich isotherm.

Autor: Wortmann FJ; Department of Materials, School of Natural Sciences, The University of Manchester, UK; F & GW - Consultants, Aachen, DE. Electronic address: franz.wortmann@manchester.ac.uk., Hardie K; Department of Materials, School of Natural Sciences, The University of Manchester, UK., Schellenberg N; Department of Materials, School of Natural Sciences, The University of Manchester, UK; Henkel AG & Co. KGaA, Hamburg, DE., Jones C; Department of Materials, School of Natural Sciences, The University of Manchester, UK., Wortmann G; Department of Materials, School of Natural Sciences, The University of Manchester, UK; F & GW - Consultants, Aachen, DE., Schulze Zur Wiesche E; Henkel AG & Co. KGaA, Hamburg, DE.
Jazyk: angličtina
Zdroj: Biophysical chemistry [Biophys Chem] 2023 Jun; Vol. 297, pp. 107010. Date of Electronic Publication: 2023 Mar 25.
DOI: 10.1016/j.bpc.2023.107010
Abstrakt: Hair is an insoluble, fibrous, α-keratinous, protein composite material, providing outer coverage, e.g., for mammals. In the context of a wider study on the effects of pH on human hair properties, we investigated the time-dependence of pH-equilibration study across the acid and the basic pH-range, using appropriate pure solutions of hydrochloric acid and sodium hydroxide. The results show that pH-equilibration follows essentially equal 1 st -order kinetics across the pH-range. The characteristic process time does not change significantly and is in the range of 2.5-5 h. The analysis enables to determine the equilibrium uptakes of H + - and OH - -ions. These follow the expected U-shaped path across the pH-range. For both acidic and alkaline conditions, data are well described by two very similar sorption isotherms of the Freundlich-type. In consequence, partition ratios for both ions are highest near neutrality (pH 7: >6000) and drop off strongly towards low and high pHs (<50). Hair is thus a very strong 'sink' for H + and OH - . This observation fundamentally challenges traditional views of limited ion uptake, namely, in the mid-pH-range due to hindered diffusion. It also does not support considerations on special roles of certain pHs, specific groups of amino acids, or morphological components. Our analysis thus suggests that established views of the interaction of hair and pH need to be reconsidered, The Freundlich isotherm approach appears to provide a versatile tool to refine our understanding of the interactions of hair and possibly other keratinous materials (horn, nail, feathers) with acids and bases.
Competing Interests: Declaration of Competing Interest FJW and GW are partners in F & GW – Consultants GbR. The company provides academic support for the hair cosmetics industry on a consultancy basis. ESzW is Head of Research & Development at Dr Kurt Wolff GmbH & Co KG. In this role he leads, e.g., hair cosmetics R&D at this company.
(Copyright © 2023. Published by Elsevier B.V.)
Databáze: MEDLINE
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