Validation of the RNA force field -Slippage phenomena in r(G4C2) exp . Our previous studies as well as those completed by others report that depending on the salt properties r(G4C2) exp prefers either a hairpin structure with repeating 1×1 G/G internal loops in syn-anti orientations (Figure ) or a G-quadruplex structure . Moreover, a small molecule, CB253, (Figure ) revealed formation of a minor and highly dynamic RNA structure, where the repeating 1×1 G/G loops transformed to 2×2 GG/GG due to strand slippage, which was detected by NMR spectroscopy . Before investigating the structural properties of 2×2 GG/GG internal loops using T-REMD, we validated the RNA force field.