Recognition of achiral and chiral ammonium salts by neutral ditopic receptors based on chiral salen-UO2 macrocycles.
A mononuclear (M20) and a dinuclear (M40) uranyl chiral macrocyclic complex, incorporating both a salen unit containing two phenyl rings linked to a chiral diimine bridge and the (R)-BINOL unit, behaves as an efficient ditopic receptor for achiral and chiral quaternary ammonium salts. Binding affinities in chloroform solution have been measured for 1:1 complexes of many quaternary salts encompassing tetramethylammonium (TMA), tetraethylammonium (TEA), tetrabutylammonium (TBA), and acetylcholine (ACh), as well as trimethylanilinium (TriMAn), benzyltrimethylammonium (BnTriMA), (alpha-methylbenzyl)trimethylammonium and pyrrolidinium cations. The anion of the salt is bound by the hard Lewis acidic uranyl site, with an increasing binding efficiency on increasing the anion hardness (I(-) < Br(-) < Cl(-)), whereas CH-pi or pi-pi attractions by binapthyl moiety, or the salicylaldehyde unit, or the phenyl rings of diimine bridge ensure the recognition of the cation partner. Optimized structures of receptor-anion-cation ternary complexes obtained by MM calculations are supported by 2D-ROESY NMR measurements.
Dipartimento Scienze Chimiche, University of Catania, viale A. Doria 6, 95125 Catania, Italy.
Maria E
ME
Amato
Francesco P
FP
Ballistreri
Salvatore
S
Gentile
Andrea
A
Pappalardo
Gaetano A
GA
Tomaselli
Rosa M
RM
Toscano
D000447:Aldehydes / Q000737:chemistry; D001952:Bridged-Ring Compounds / Q000737:chemistry; D047028:Macrocyclic Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012996:Solutions; D014501:Uranium / Q000737:chemistry*
D000447:Aldehydes; D001952:Bridged-Ring Compounds; D047028:Macrocyclic Compounds; D000644:Quaternary Ammonium Compounds; D012996:Solutions; C013243:salicylaldehyde; D014501:Uranium; C009405:tetrabutylammonium; C027917:tetramethylammonium