path. The msesMD free energy profile for ψ G shows agreement in overall shape with the unbiased MD prediction, but differs in finding a decreased stability of G 4 by ~2 kcal mol -1 and an increase in energetic barrier for the direct and indirect G 1  G 4 routes, by 2.0 and 2.7 kcal mol respectively. As discussed above, this discrepancy between the msesMD and unbiased MD predictions is potentially due to a poor estimate of the G 4 population in the unbiased MD simulation, arising from one of the replicate trajectories becoming kinetically trapped in the higher energy G 4 well for a disproportionate amount of time. The much larger overall differences between msesMD and the umbrella sampling profile appear to be caused, as for ψ F , by a lack of sampling of the φ G rotation. Although not as obvious as in the ψ F profile, there appears to be incomplete sampling of the G 3 region by the PMF, with the path consisting primarily of a transition from G 2  G 4 (Figure ).