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Cited by 279

The DOI matches its Crossref record; 34 of the 34 references it cites were found in a registry or an index.

Measurements and Theoretical Interpretation of Points of Zero Charge/Potential of BSA Protein

Salis, Andrea, Boström, Mathias, Medda, Luca, Cugia, Francesca, Barse, Brajesh, Parsons, Drew F., Ninham, Barry W., Monduzzi, Maura·2011·Langmuir

Abstract

The points of zero charge/potential of proteins depend not only on pH but also on how they are measured. They depend also on background salt solution type and concentration. The protein isoelectric point (IEP) is determined by electrokinetical measurements, whereas the isoionic point (IIP) is determined by potentiometric titrations. Here we use potentiometric titration and zeta potential (ζ) measurements at different NaCl concentrations to study systematically the effect of ionic strength on the IEP and IIP of bovine serum albumin (BSA) aqueous solutions. It is found that high ionic strengths produce a shift of both points toward lower (IEP) and higher (IIP) pH values. This result was already reported more than 60 years ago. At that time, the only available theory was the purely electrostatic Debye-Hückel theory. It was not able to predict the opposite trends of IIP and IEP with ionic strength increase. Here, we extend that theory to admit both electrostatic and nonelectrostatic (NES) dispersion interactions. The use of a modified Poisson-Boltzmann equation for a simple model system (a charge regulated spherical colloidal particle in NaCl salt solutions), that includes these ion specific interactions, allows us to explain the opposite trends observed for isoelectric point (zero zeta potential) and isoionic point (zero protein charge) of BSA. At higher concentrations, an excess of the anion (with stronger NES interactions than the cation) is adsorbed at the surface due to an attractive ionic NES potential. This makes the potential relatively more negative. Consequently, the IEP is pushed toward lower pH. But the charge regulation condition means that the surface charge becomes relatively more positive as the surface potential becomes more negative. Consequently, the IIP (measuring charge) shifts toward higher pH as concentration increases, in the opposite direction from the IEP (measuring potential).

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Crossref · 10.1021/la2024605

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Metadata

Authors
Salis, A., Boström, M., Medda, L., Cugia, F., Barse, B., Parsons, D. F., Ninham, B. W., & Monduzzi, M.
Venue
Langmuir
Published
2011-08-23
Volume
27
Issue
18
Pages
11597-11604
ISSN
  • 0743-7463 (ISSN-L)
  • 1520-5827
OpenAlex
W1969259546
Cited by
279
References
34
FWCI
8.81
Type
journal article
Language
en
Open access
closed

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