A lead-filled G-quadruplex:: Insight into the G-quartet's selectivity for Pb2+ over K+

GRAPHICS The lipophilic nucleoside, G 1, extracts Pb2+ picrate from water into organic solvents to give structures based on the hydrogen-bonded G-quartet. Crystal structures indicate important differences between (G 1)(8)-Pb2+ and (G 1)(8)-K+. The divalent Pb2+ templates a smaller G(8) cage than does K+, as judged by the M-O6 bond length, O6-O6 diagonal distance, and inter-tetramer separation. The more compact Pb2+ octamer correlates with NMR data indicating that N2-N7 hydrogen bonds in (G 1)(8)-Pb2+ are kinetically more stable than in (G I)(8)-K+.