Cation effects and charge inversion contribute to the electrostatic stabilisation of protein bioconjugates in neat ionic liquids

This is the authors' abstract. We don't add key points for this paper.

-imidazol-3-ium trifluoromethane sulfonate; [MEZ][OTF]) were synthesized to study the bioconjugate dispersion. Interestingly, time-dependent polarised optical microscopy combined with transmittance measurements showed complete dispersion of all bioconjugates only in AIL. MD simulations of the PS-cCT bioconjugate were carried out in the same ILs as the experiments. The surface electrostatic potential of PS-cCT reversed from positive in PIL to negative in AIL due to overcharging by the AIL anion and lower mobility of the AIL cation. Strong screening of electrostatic potentials between two PS-cCT complexes in PIL resulted in reduced dispersion stability. Lower diffusivity of long alkyl chain [MEZ] cations of AIL leads to a depletion zone of IL ions between the two PS-cCT complexes (separation <70 Å), thus resulting in a significant negative potential between the complexes. Hence, protein bioconjugates in AIL were stabilised by a combination of surface overcharging and steric exclusion of [MEZ] cations from the space between the approaching bioconjugate complexes.