To test if the increase in sampling efficiency observed in protein dynamics extends to other biomolecules, we prepared systems of the polyribonucleotides Ade 2 and Ade 4 with both water models. In contrast to polypeptides, where backbone dynamics can be characterized by the two Ramachandran dihedrals, nucleic acids have six different torsion angles shared between consecutive residues. Here, we only analyzed the phosphate α and ζ dihedrals of the central residues, together with the distance between the O5' and the O3' atoms of terminal ribonucleotides (d O5 ′ -O3 ′ ). Figure shows the structures and variables used for the polyribonucleotides.