Measured entropy and enthalpy of hydration as a function of distance between DNA double helices

Abstract

The temperature sensitivity of hydration forces between ${\mathrm{Mn}}^{2+}$-DNA helices in ordered arrays has been used to measure the entropic part of the interaction free-energy versus helix separation. This entropy is positive, and like the hydration force itself, grows exponentially as helices move closer. Measured forces show an abrupt transition between regions of interactions with quite different characteristic decay lengths, with a discontinuous change in interhelical spacing. However, both the entropic and enthalpic components of the interaction free-energy maintain smooth single-exponential variation across this transition.