Effects of concentrated NaCl and KCl solutions on the behaviour of aqueous peptide bond environment: Single-particle dynamics and H-bond structural relaxation

Abstract

The effects of salt concentrations on the structure, dynamics and hydrogen bond structural relaxation properties of ?1.10 M aqueous N-methylacetamide (NMA) solution at 308 K are studied by classical molecular dynamics simulations. We have considered the concentration range of salts solution from 0.222 to 3.756 M to investigate the behaviour of aqueous environment of peptide bonds in the presence of concentrated NaCl and KCl solution. It is found that the addition of salt solution facilitates the structural breaking of aqueous NMA hydrogen bonds, as a result the number of hydrogen bonds per NMA molecule and their stability decreases. The water and NMA molecule shows slower translational and rotational dynamics with increasing salt concentrations due to additional ion atmospheric friction. Our result shows that the cation-ONMA radial distribution function decreases whereas the Cl- - H NMA radial distribution function increases with ion concentration. On the other hand, the cation-Owater and Cl- - H water radial distribution function shows very negligible change with respect to ion concentration. We have also calculated NMA-water and water-water hydrogen bond structural relaxation times. It is observed that the hydrogen bond structural relaxation of ONMA - Hwater is comparatively slower than the HNMA - Owater hydrogen bond, which can be attributed to higher number and greater stability of the former hydrogen bond than the latter. The change of the dynamical quantities observed here is more prominent in addition of NaCl rather than the KCl solution. � 2013 Taylor & Francis.