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. 2023 Dec 22;29(1):82.
doi: 10.3390/molecules29010082.

pH-Dependent HEWL-AuNPs Interactions: Optical Study

Elena A Molkova  1 , Vladimir I Pustovoy  1 , Evgenia V Stepanova  1 , Irina V Gorudko  2 , Maxim E Astashev  1 , Alexander V Simakin  1 , Ruslan M Sarimov  1 , Sergey V Gudkov  1
Affiliations

pH-Dependent HEWL-AuNPs Interactions: Optical Study

Elena A Molkova et al. Molecules. .

Abstract

Optical methods (spectroscopy, spectrofluorometry, dynamic light scattering, and refractometry) were used to study the change in the state of hen egg-white lysozyme (HEWL), protein molecules, and gold nanoparticles (AuNPs) in aqueous colloids with changes in pH, and the interaction of protein molecules with nanoparticles was also studied. It was shown that changing pH may be the easiest way to control the protein corona on gold nanoparticles. In a colloid of nanoparticles, both in the presence and absence of protein, aggregation-deaggregation, and in a protein colloid, monomerization-dimerization-aggregation are the main processes when pH is changed. A specific point at pH 7.5, where a transition of the colloidal system from one state to another is observed, has been found using all the optical methods mentioned. It has been shown that gold nanoparticles can stabilize HEWL protein molecules at alkaline pH while maintaining enzymatic activity, which can be used in practice. The data obtained in this manuscript allow for the state of HEWL colloids and gold nanoparticles to be monitored using one or two simple and accessible optical methods.

Keywords: aggregation; hen egg-white lysozyme; nano-sized gold; nanoparticles; pH; protein.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure A1
Figure A1
Effect of pH on the polydispersity index in colloids HEWL (7 × 104 nM), AuNPs (2.2 nM), and HEWL (7 × 104 nM) + AuNPs (2.2 nM).
Figure A2
Figure A2
Autocorrelation functions of colloids: (a) HEWL, (7 × 104 nM); (b) AuNPs (2.2 nM); (c) HEWL (7 × 104 nM) + AuNPs (2.2 nM) at different pH values. The color of the lines has only an artistic component.
Figure 1
Figure 1
Physical characteristics of gold nanoparticles: (a) Size distribution of nanoparticles in an aqueous colloid; (b) Concentration of individual nanoparticles and their aggregates in the colloid; (c) TEM micrograph of gold nanoparticles; (d) Absorption spectrum of an aqueous colloid of gold nanoparticles.
Figure 1
Figure 1
Physical characteristics of gold nanoparticles: (a) Size distribution of nanoparticles in an aqueous colloid; (b) Concentration of individual nanoparticles and their aggregates in the colloid; (c) TEM micrograph of gold nanoparticles; (d) Absorption spectrum of an aqueous colloid of gold nanoparticles.
Figure 2
Figure 2
Effect of pH on the size distribution of objects in colloids: (a) HEWL, (7 × 104 nM); (b) AuNPs (2.2 nM); (c) HEWL (7 × 104 nM) + AuNPs (2.2 nM); (d) Dependence of the hydrodynamic diameter of objects in colloids HEWL (7 × 104 nM), AuNPs (2.2 nM), and HEWL (7 × 104 nM) + AuNPs (2.2 nM) on pH.
Figure 3
Figure 3
Effect of pH on the optical absorption of solutions: (a) HEWL (7 × 104 nM); (b) AuNPs (2.2 nM); (c) HEWL (7 × 104 nM) + AuNPs (2.2 nM); (d) Dependence of λmax absorption on pH for colloids HEWL (7 × 104 nM) + AuNPs (2.2 nM), HEWL (7 × 104 nM), AuNPs (2.2 nM); (e) Dependence of optical density in maximum on pH for colloids HEWL (7 × 104 nM) + AuNPs (2.2 nM), HEWL (7 × 104 nM), and AuNPs (2.2 nM).
Figure 3
Figure 3
Effect of pH on the optical absorption of solutions: (a) HEWL (7 × 104 nM); (b) AuNPs (2.2 nM); (c) HEWL (7 × 104 nM) + AuNPs (2.2 nM); (d) Dependence of λmax absorption on pH for colloids HEWL (7 × 104 nM) + AuNPs (2.2 nM), HEWL (7 × 104 nM), AuNPs (2.2 nM); (e) Dependence of optical density in maximum on pH for colloids HEWL (7 × 104 nM) + AuNPs (2.2 nM), HEWL (7 × 104 nM), and AuNPs (2.2 nM).
Figure 4
Figure 4
Effect of pH on the fluorescence of solutions: (a) HEWL (7 × 104 nM) (The color of the lines reflects only the spectral range); (b) HEWL (7 × 104 nM) + AuNPs (2.2 nM) (The color of the lines reflects only the spectral range); (c) Dependence of fluorescence intensity on pH of colloids HEWL (7 × 104 nM) and HEWL (7 × 104 nM) + AuNPs (2.2 nM); (d) Dependence of λmax of fluorescence on pH of colloids HEWL (7 × 104 nM) and HEWL (7 × 104 nM) + AuNPs (2.2 nM).
Figure 5
Figure 5
Effect of pH on the dispersion curve of circular dichroism in colloids HEWL (7 × 104 nM) and HEWL (7 × 104 nM) + AuNPs (2.2 nM).
Figure 6
Figure 6
Effect of pH on the refractive index in colloids HEWL, (7 × 104 nM), AuNPs (2.2 nm), HEWL (7 × 104 nM) + AuNPs (2.2 nM), measured at three wavelengths: (a) 435.8 nm; (b) 589.3 nm; (c) 632.9 nm. Dependence of electrical conductivity (d), redox potential (e), ζ-potential (f) of colloids HEWL, (7 × 104 nM), AuNPs (2.2 nM), and HEWL (7 × 104 nM) + AuNPs (2.2 nM) from pH.
Figure 7
Figure 7
The effect of pH on the enzymatic activity of colloids HEWL (7 × 104 nM) and HEWL (7 × 104 nM) + AuNPs (2.2 nM).
Figure 8
Figure 8
Effect of pH on colloids HEWL (7 × 104 nM), AuNPs (2.2 nM), and HEWL (7 × 104 nM) + AuNPs (2.2 nM).
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