Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid−Base Molecular Probes. III. Experimental Hydrophobicity/Hydrophilicity and Charge Distribution of MS2 Virus Surface

Abstract

MS2 bacteriophage is often used as a model for evaluating pathogenic viruses’ behaviour in aqueous solution. However, the questions of the virus surface’s hydrophilic/hydrophobic balance, the charge distribution, and the binding mechanism are open. Using dynamic light scattering method and laser Doppler electrophoresis the hydrodynamic diameter and the zeta-potential of the virus particles were measured at their concentration of 5x10^11 particles per mL and ionic strength 0.03 M. The values were found to be 30 nm and −29 or −34 mV (by Smoluchowski or Ohshima approximations) respectively. MS2 bacteriophage surface was also investigated using a series of acid-base indicator dyes of various charge type, size, and structure. Their spectral and acid-base properties (pKa) are very sensitive to microenvironment in aqueous solution including containing nano-particles. The electrostatic potential of the surface Ψ was estimated using the common formula: Ψ =59x(pKa^i − pKa) in mV at 25 °C. The Ψ values were −50 mV and +10 mV respectively, which indicate the ‘mosaic’ way of the charge distribution on the surface. These data are in good agreement with the obtained zeta-potential values and provide even more information about the virus surface. It was found that the surface of the MS2 virus is hydrophilic in solution in contrast to commonly accepted hypothesis of hydrophobicity of virus particles. No hydrophobic interactions between various molecular probes and the capsid were observed.