Figure 4.

Boltzmann weighted average free energy surface for solvated uracil along the Z_x and Z_y sugar pucker coordinates (see 1). Two minima are observed roughly corresponding to C3′-endo and C2′-endo pucker states (black diamonds, also marking saddle points). An apparently periodic transition between these states along the pseudorotation angle $(P_{\theta }=\text{arctan}\frac{Z_y}{Z_x}$ is also observed (white dots). Energies are in kcal/mol and axes are in degrees.