A lead-filled G-quadruplex: insight into the G-Quartet's selectivity for Pb(2+) over K(+)

The lipophilic nucleoside, G 1, extracts Pb(2+) 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)-Pb(2+) and (G 1)(8)-K(+). The divalent Pb(2+) 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 Pb(2+) octamer correlates with NMR data indicating that N2-N7 hydrogen bonds in (G 1)(8)-Pb(2+) are kinetically more stable than in (G 1)(8)-K(+).