Investigation of changes in the arrangement of water molecules and salt ions surrounding different atoms of the DNA molecule during the melting process: a molecular dynamics simulation study

A molecular dynamics simulation was performed on a B-DNA duplex (CGCGAATTGCGC) at different temperatures. The DNA was immerged in a saltwater medium with 1 mol/L NaCl concentration. The arrangements of water molecules and cations around the different atoms of DNA on the melting pathway were investigated. Almost for all atoms of the DNA by double helix -> single-stranded transition, the water molecules released from the DNA duplex and cations were close to single-stranded DNA, but this behavior was not clearly seen at melting temperatures. Therefore, release of water molecules and cations approaching the DNA by the increase of temperature does not have any effect on the sharpness of the transition curve. Most of the water molecules and cations were found to be around the negatively charged phosphate oxygen atoms. The number of water molecules released from the first shell hydration upon melting in the minor groove was higher than in the major groove, and intrusion of cations into the minor groove after melting was higher than into the major groove. The hydrations of imino protons were different from each other and were dependent on DNA bases.