Molecular tweezers and clips as synthetic receptors. Molecular recognition and dynamics in receptor-substrate complexes.
The molecular tweezers (1, 2) and clips (3-7) containing naphthalene and benzene spacer units can be synthesized via repetitive Diels-Alder reactions by the use of a molecular "Lego" set consisting of bisdienophiles (8, 9, 14) and dienes (10, 13). The new receptors selectively bind electron-deficient neutral and cationic substrates in solution. Only the benzene-spaced tweezers form complexes with aliphatic substrates, whereas the other receptors bind aromatic substrates preferentially. HPLC studies with 1 and 2 chemically bonded to stationary phases give similar results for the heterogeneous systems. The formation of stable complexes between the water-soluble clip 5g and N-alkylpyridinium cations, such as N-methylnicotinamide and NAD(+), in aqueous solution illustrates the importance of the hydrophobic effect for arene-arene interactions. The dynamics of the complex formation and substrate mobility were investigated by the use of temperature-dependent liquid- and solid-state NMR spectroscopy. The electrostatic potential surface (EPS) of 1-7 is calculated to be surprisingly negative on the concave side of each molecule and, hence, complementary to the EPS of the electron-deficient substrates, suggesting that the attractive receptor-substrate interaction is here of predominantly electrostatic nature.
Klärner
Frank-Gerrit
FG
Institut für Organische Chemie, Universität Duisburg-Essen, 45117 Essen, Germany. frank.klaerner@uni-essen.de
Kahlert
Björn
B
D001554:Benzene / Q000737:chemistry; D001555:Benzene Derivatives / Q000138:chemical synthesis* / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics
D001555:Benzene Derivatives; D009281:Naphthalenes; D012996:Solutions; D012997:Solvents; C031721:naphthalene; D001554:Benzene