[Lecture] Strong attractions and repulsions mediated by monovalent salts


Title: Strong attractions and repulsions mediated by monovalent salts
Speaker: Dr. Yaohua Li (Northwestern University)
Venue: Room 324, Science Park Building No.2, North Area, Wushan Campus
Time: Jan 9, Wednesday, 15:00

Controlling interactions between proteins and nanoparticles in electrolyte solutions is crucial for advancing biological sciences and biotechnology. The assembly of charged nanoparticles (NPs) and proteins in aqueous solutions can be directed by modifying the salt concentration. High concentrations of monovalent salt can induce the solubilization or crystallization of NPs and proteins. By using a multiscale coarse-grained molecular dynamics approach, we show that, due to ionic correlations in the electrolyte, NPs pairs at high monovalent salt concentrations interact via remarkably strong long-range attractions or repulsions, which can be split into three regimes depending on the surface charge densities of the NPs. NPs with zero-to-low surface charge densities interact via a long-range attraction that is stronger and has a similar range to the depletion attraction induced by polymers with radius of gyrations comparable to the NP diameter. On the other hand, moderately charged NPs with smooth surfaces as well as DNA-functionalized NPs with no possibility of hybridization between them interact via a strong repulsion of range and strength larger than the repulsion predicted by models that neglect ionic correlations, including the Derjaguin–Landau–Vervey–Overbeek (DLVO) model. Interactions between strongly charged NPs (>2 e/nm2), both types smooth and DNA-functionalized NPs, show an attractive potential well at intermediate-to-high salt concentrations, which demonstrates that electrolytes can induce aggregation of strongly charged NPs. Our work provides an improved understanding of the role of ionic correlations in NP assembly and design rules to utilize the salting-out process to crystallize NPs.

Yaohua Li obtains his bachelor’s degree of science from School of Physics, Nanjing University in 2015, with his thesis study on protein folding mechanics using single molecule force measuring technique. After his graduation from NJU, Yaohua joined the Applied Physics Program of Northwestern University, working in the group of Prof. Monica Olvera de la Cruz, who is an expert in polymer physics and soft matter. In 2017, Yaohua published his work titled Strong attractions and repulsions mediated by monovalent salts in PNAS with his advisor and co-workers. In this paper, he demonstrated that the strong ion correlations of monovalent ions at high concentrations could lead to unexpectedly strong attractive or repulsive interactions between Nano-scale objects. Since then, Yaohua has working on the self-assembly mechanism of charged proteins, as well as the role of dielectric interface on protein.

Announced by School of Materials Science and Engineering