Fig. 7.
Cation coordination by guanine quartets. (a) Coordination of a Sr2+ cation, shown in green, between the eight guanine O6 atoms of two G-quartets, shown in magenta. (b and c) Views of a UGGGGU octamer emphasizing the regular arrangement of O6 atoms about the central cation induced by the structure's helical twist. Coordinates are from the refinement of data set P1B.