title: Selective 226Ra2+ ionophores provided by self-assembly of guanosine and isoguanosine derivatives.
abstract: The self-assembled guanosine (G 1)-based hexadecamers and isoguanosine (isoG 2)-based decamers are excellent 226Ra2+ selective ionophores even in the presence of excess alkali (Na+, K+, Rb+, and Cs+) and alkaline earth (Mg2+, Ca2+, Sr2+, and Ba2+) cations over the pH range 3-11. G 1 requires additional picrate anions to provide a neutral assembly, whereas the isoG 2 assembly extracts 226Ra2+ cations without any such additives. Both G 1-picrate and isoG 2 assemblies show 226Ra2+ extraction even at a 0.35 x 10(6) fold excess of Na+, K+, Rb+, Cs+, Mg2+, or Ca2+ (10(-2) M) to 226Ra2+ (2.9 x 10(-8) M) and at a 100-fold salt to ionophore excess. In the case of the G 1-picrate assembly, more competition was observed from Sr2+ and Ba2+, as extraction of 226Ra2+ ceased at an M2+/226Ra2+ ratio of 10(6) and 10(4), respectively. With the isoG 2 assembly, 226Ra2+ extraction also occurred at a Sr2+/226Ra2+ ratio of 10(6) but ceased at a 10(6) excess of Ba2+. The results clearly demonstrate the power of molecular self-assembly for the construction of highly selective ionophores.
authors.affiliation: Laboratory of Supramolecular Chemistry and Technology, Mesa Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Fijs W B
authors.initials: FW
authors.lastname: van Leeuwen
authors.forename: Willem
authors.initials: W
authors.lastname: Verboom
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Shi
authors.forename: Jeffery T
authors.initials: JT
authors.lastname: Davis
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
mesh_terms: D000241:Adenosine; D002413:Cations, Divalent; D011232:Chemical Precipitation; D002623:Chemistry Techniques, Analytical / Q000379:methods; D006151:Guanosine / Q000031:analogs & derivatives* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000737:chemistry*; D008673:Metals, Alkaline Earth / Q000737:chemistry; D008958:Models, Molecular; D010851:Picrates / Q000737:chemistry; D011883:Radium / Q000737:chemistry* / Q000302:isolation & purification; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; D007476:Ionophores; D008673:Metals, Alkaline Earth; D010851:Picrates; D006151:Guanosine; C008184:isoguanosine; D000241:Adenosine; D011883:Radium