Substrate discrimination by cholapod anion receptors: geometric effects and the "affinity-selectivity principle".
Cholapod anion receptors can achieve high affinities while maintaining compatibility with nonpolar media. Previously they have been shown to transport anions across cell and vesicle membranes. In the present work, the scope of the architecture is expanded and structure-selectivity relationships are investigated. Eight new receptors have been synthesized, with up to six H-bond donor centers. Using Cram's extraction method, these compounds plus five known examples have been tested for binding to seven monovalent anions (tetraethylammonium salts, wet chloroform as solvent). Association constants in excess of 10(10) M(-1) have been measured for several pairings. Selectivities vary with receptor geometry, as expected. More remarkably, they also depend on receptor strength: more powerful receptors show a wider range of binding free energies, and therefore a greater spread of Ka(X-)/Ka(Y-). This "affinity-selectivity" effect can be derived from empirical relationships for H-bond strengths, and could prove widely operative in supramolecular chemistry.
Clare
John P
JP
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
Ayling
Alan J
AJ
Joos
Jean-Baptiste
JB
Sisson
Adam L
AL
Magro
Germinal
G
Pérez-Payán
M Nieves
MN
Lambert
Timothy N
TN
Shukla
Rameshwer
R
Smith
Bradley D
BD
Davis
Anthony P
AP
D000838:Anions; D003510:Cyclohexanes / Q000737:chemistry; D006860:Hydrogen Bonding; D007700:Kinetics; D008968:Molecular Conformation; D027361:Organic Anion Transporters / Q000737:chemistry*; D011956:Receptors, Cell Surface / Q000737:chemistry*; D013329:Structure-Activity Relationship
D000838:Anions; D003510:Cyclohexanes; D027361:Organic Anion Transporters; D011956:Receptors, Cell Surface