Effect of ionic strength on the interfacial viscoelasticity and stability of silk fibroin at the oil/water interface

Abstract

The positively-charged ions significantly affect the interfacial elasticity and stability of silk fibroin layers at the oil/water interface as a result of the strong electrostatic interactions between counter-ions and the negatively-charged groups of silk fibroin. © 2016 Society of Chemical Industry.

Protein–protein interactions controlling interfacial aggregation of rhIL‐1ra are not described by simple colloid models

“…This strong empirical correlation between bulk interaction strength and interfacial gel strength suggested that the same types of PPI measured in the bulk solution (e.g., cation– π interactions) may also drive increased interactions between adsorbed proteins, leading to stronger interfacial gels. The trend observed between interfacial gel strength and ionic strength was quite distinct from observations for other proteins, in which stronger gels were formed at higher ionic strengths and were explained through the screening of double‐layer repulsive forces, although PPI were not measured . Electrostatic charge screening arises from the addition of ions in solution, which shield double‐layer repulsive forces described by DLVO theory .…”

“…However, the underlying reasons were not completely clear. In addition, the interfacial viscoelastic properties of adsorbed proteins have been measured as a function of pH, ionic strength, and interfacial packing, but were often explained in terms of simple colloid models described by electrical double‐layer theory, which could not be separated from other types of protein interactions which arose from structural or charge anisotropy . Due to the unique nature of PPI for rhIL‐1ra in bulk solution, we proposed to distinguish the role of specific PPI from electrostatic repulsive double‐layer interactions in the context of interface‐mediated aggregation.…”

“…These interfacial gels may be stabilized through protein–protein intermolecular interactions such as disulfide bridging or hydrogen bonding . The properties of protein gels at air–water and oil–water interfaces can be influenced by formulation conditions, such as pH or ionic strength . The pH and ionic strength dependence of these interfacial viscoelastic properties are often rationalized in the context of models describing uniformly charged spheres.…”

“…suggested that weaker repulsive interactions due to charge shielding could explain their observation that stronger gels of silk fibroin were formed at silicone oil–water interfaces. However, it can be difficult to differentiate interactions arising from double‐layer repulsive electrostatic forces from specific protein interactions such as dipole–dipole, π ‐interactions, and salt bridges …”

“…26 The properties of protein gels at airwater and oil-water interfaces can be influenced by formulation conditions, such as pH or ionic strength. [27][28][29][30] The pH and ionic strength dependence of these interfacial viscoelastic properties are often rationalized in the context of models describing uniformly charged spheres. For example, Tang et al 29 suggested that weaker repulsive interactions due to charge shielding could explain their observation that stronger gels of silk fibroin were formed at silicone oil-water interfaces.…”