Inclusion complexation of diquat and paraquat by the hosts cucurbit[7]uril and cucurbit[8]uril.
The binding interactions in aqueous solution between the dicationic guest diquat (DQ(2+)) and the cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) hosts were investigated by (1)H NMR, UV/Vis, and fluorescence spectroscopy; mass spectrometry; single-crystal X-ray diffraction; and electrochemical techniques. The binding data were compared with previously reported results for the related paraquat guest (PQ(2+)). DQ(2+) was found to bind poorly (K=350 m(-1)) inside CB7 and more effectively (K=4.8 x 10(4) m(-1)) inside CB8. One-electron reduction led to increased binding affinity with both hosts (K(r)=1 x 10(4) m(-1) with CB7 and K(r)=6 x 10(5) m(-1) for CB8). While (1)H NMR spectroscopic data revealed that DQ(2+) is not fully included by CB7, the crystal structure of the CB8DQ(2+) complex-obtained from single-crystal X-ray diffraction-clearly establishes its inclusion nature. Overall, both diquat and its one-electron reduced radical cation are bound more effectively by CB8 than by CB7. In contrast to this, paraquat exhibits selectivity for CB7, but its radical cation forms a highly stable dimer inside CB8. These differences highlight the pronounced sensitivity of cucurbit[n]uril hosts to guest features such as charge, charge distribution and shape.
Ling
Yonghua
Y
Center for Supramolecular Science and Department of Chemistry, University of Miami, Coral Gables, FL 33124-0431, USA.
Mague
Joel T
JT
Kaifer
Angel E
AE
D001952:Bridged-Ring Compounds / Q000737:chemistry*; D004178:Diquat / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010269:Paraquat / Q000737:chemistry*; D012996:Solutions; D014867:Water; D014961:X-Ray Diffraction; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
D001952:Bridged-Ring Compounds; D004178:Diquat; D007093:Imidazoles; D010269:Paraquat; D012996:Solutions; D014867:Water; C456276:cucurbit(7)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils; C507198:cucurbit(8)uril