Research On The Influence Of Salt In Nano-confined Solution On Solute Correlation Behavior

Solute association phenomenon is widely spread in various physical and biological processes,such as nucleation of colloid particles,self-assembly or biomineralization of macromolecules,and ensures the normal progress of these processes.At the nanoscale,solute molecules often exhibit different behaviors that are different from the dispersion state or aggregation state at the macroscale,such as incomplete dissolution of methanol in water and the"reversible" state of 1-pentanol.The association behavior of solutes is influenced by many factors such as ions,temperature or pH value,as ions exist widely in the cell fluid of organisms,they play a role in stabilizing RNA structure,promoting self-assembly of collagen and phospholipid molecules in cell membrane.Therefore,it is important to study the effects of ions on solute association behaviors.In this paper,we use molecular dynamic simulations to study the ionic effects on the solute association behaviors in nanoconfined aqueous solutions,including the solute association states,critical aggregation number,the size distribution of the clusters and the structure of the largest cluster,the interactions of solutes,the distribution of ions around solutes.The results show that the solute molecules tend to form larger clusters after the addition of ions in the nanoconfined aqueous solutions,and the critical aggregation number of solute molecules also decreases.For the intermediate solute concentration,the addition of salts will change the solute association state.Further analyses show that when the solute concentration is relatively low,there is insufficient solute molecules to form nuclei for the growth of clusters.The solute association state is independent of the ionic concentration and solute molecules remain in the dispersion state.When the solute concentration is relatively high,the solute molecules are almost exhausted and form relatively stable clusters.This aggregation state are almost unaffected by the ionic concentration,except for the slight change in the stacking order of the largest cluster with the increase of ions concentration.For the intermediate solute concentration,ions will interact with the surrounding water molecules,resulting in the reduction of the number of free water molecules in nanoconfined space and leading to the formation of clusters and precipitation of solute molecules,which eventually leads to the change of the solute aggregation state.In summary,the "reversible state" still exists in the nanoconfined aqueous solutions after adding ions.For the intermediate solute concentration,ions can change the association state of the solute molecules from dispersion state to reversible state or from reversible state to aggregation state.Because the electrostatic interaction between ions and water molecules affects the number of free water molecules in nanoconfined aqueous solutions,and promotes the aggregation of solutes.These results can enlighten us in understanding the ionic effects in cellular life activities such as metabolism of substances,and replication of genetic material,it also provides the theoretical basis for the study of ionic effects in nanoconfined environment.