Free energy calculations were performed with Gromacs 5.0 and molecular dynamics simulations to calculate other observables were performed with AMBER 14 . All systems were assembled using the built-in tools of the software package used to perform the simulations. A summary of the most relevant parameters used during the production runs is given in SI Table . Simulations used a time-step of 2 fs and constraints (LINCS in Gromacs, SHAKE in Amber) were applied to all bonds involving hydrogen atoms. Integration of the equations of motion was done using a leap-frog Langevin algorithm. Van der Waals interactions were shifted to zero between 1.0 and 1.2 nm, and long-range dispersion corrections were applied to both pressure and energy. Long-range electrostatics were treated with the PME scheme with a 1.2 nm cutoff, a grid spacing of 0.1 nm (AMBER) or 0.12 nm (Gromacs) and a 4th (AMBER) or 6th (Gromacs) order interpolation. Production runs were done in the NpT ensemble. The Monte Carlo (AMBER) or Berendsen (Gromacs) barostats were used with a relaxation time of 1 ps for an isotropic coupling of system pressure to 1 bar; temperature coupling was handled by the leap-frog Langevin integrator with a collision frequency of 1 ps 1 and a target temperature of 298 K.