Specific Ion Effects of Trivalent Cations on the Structure and Charging State of $\beta$-Lactoglobulin Adsorption Layers
Langmuir (2019), 35, 11299-11307 In this work, we addressed the effects of Y$^{3+}$ and Nd$^{3+}$ cations on the adsorption of the whey protein $\beta$-lactoglobulin (BLG) at air-water interfaces as a function of electrolyte concentration. Both cations caused very similar but dramatic changes at the...
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Main Authors | , , |
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Format | Journal Article |
Language | English |
Published |
15.07.2020
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Online Access | Get full text |
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Summary: | Langmuir (2019), 35, 11299-11307 In this work, we addressed the effects of Y$^{3+}$ and Nd$^{3+}$ cations on
the adsorption of the whey protein $\beta$-lactoglobulin (BLG) at air-water
interfaces as a function of electrolyte concentration. Both cations caused very
similar but dramatic changes at the interface and in the bulk solution. Here,
measurements of the electropho-retic mobility and vibrational sum-frequency
generation spectroscopy (SFG) were applied and consistently showed a reversal
of the BLG net charge at remarkably low ion concentrations of 30 (bulk) and 40
(interface) $\mu$M of Y$^{3+}$ or Nd$^{3+}$ for a BLG concentration of 15
$\mu$M. SFG spectra of carboxylate stretching vibrations from Asp or Glu
residues of interfacial BLG showed significant changes in the carboxylate
stretching frequency, which we associate to specific and efficient bind-ing of
Y$^{3+}$ or Nd$^{3+}$ ions to the proteins carboxylate groups. Characteristic
reentrant condensation for BLG moieties with bound trivalent ions was found in
a broad concentration range around the point of zero net charge. The highest
colloidal stability of BLG was found for ion concentrations <20$\mu$M and
>50$\mu$M. Investigations on macroscopic foams from BLG solutions, revealed the
existence of structure-property relations between the interfacial charging
state and the foam stability. In fact, a minimum in foam stability at 20$\mu$M
ion concentration was found when the interfacial net charge was negligible. Our
results provide new information on the charge reversal at the liquid-gas
interface of protein/ion dispersions. Therefore, we see our findings as an
important step in the clarification of reentrant con-densation effects at
interfaces and their relevance to foam stability. |
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DOI: | 10.48550/arxiv.2007.07784 |