Structure of Aqueous Sodium Perchlorate Solutions

摘要

Salt solutions have been the object of study of many scientists through history,but one of the most important findings came along when the Hofmeister series were discovered.Their importance arises from the fact that they influence the relative solubility of proteins,and solubility is directly related to one of today's holy grails:protein folding.In this work we characterize one of the more-destabilizing salts in the series,sodium perchlorate,by studying it as an aqueous solution at various concentrations ranging from 0.08 to 1.60 mol/L.Molecular dynamics simulations at room temperature permitted a detailed study of the organization of solvent and cosolvent,in terms of its radial distribution functions,along with the study of the structure of hydrogen bonds in the ions'solvation shells.We found that the distribution functions have some variations in their shape as concentration changes,but the position of their peaks is mostly unaffected.Regarding water,the most salient fact is the noticeable(although small)change in the second hydration shell and even beyond,especially for g_(O_w…O_w),showing that the locality of salt effects should not be restricted to considerations of only the first solvation shell.The perturbation of the second shell also appears in the study of the HB network,where the difference between the number of HBs around a water molecule and around the Na~+ cation gets much smaller as one goes from the first to the second solvation shell,yet the difference is not negligible.Nevertheless,the effect of the ions past their first hydration shell is not enough to make a noticeable change in the global HB network.The Kirkwood-Buff theory of liquids was applied to our system,in order to calculate the activity derivative of the cosolvent.This coefficient,along with a previously calculated preferential binding,allowed us to establish that if a folded AP peptide is immersed in the studied solution,becoming the solute,then increasing the salt concentration will make the helix more stable.