Molecular tweezer and clip in aqueous solution: unexpected self-assembly, powerful host-guest complex formation, quantum chemical 1H NMR shift calculation.
The newly prepared water-soluble naphthalene tweezer 2a and anthracene clip 4a (substituted both with lithium methanephosphonate groups in the central spacer unit) undergo an unexpected self-assembly in aqueous solution. The highly ordered intertwined structures of the self-assembled dimers [2a]2 and [4a]2 were elucidated by quantum chemical 1H NMR shift calculations. 2a and 4a form extremely stable host-guest complexes with N-methylnicotinamide 8 in methanol and water as well. According to the thermodynamic parameters determined by 1H NMR titration experiments at various temperatures the self-assembly of 2a and 4a and their strong binding to NMNA 8 observed in aqueous solution are enthalpy driven (DeltaH << 0); the enthalpic driving force is partially compensated by an unfavorable entropy (TDeltaS < 0). Self-assembly and the host-guest binding are therefore beautiful examples of the nonclassical hydrophobic effect.
Klärner
Frank-Gerrit
FG
Institut für Organische Chemie der Universität Duisburg-Essen, 45117 Essen, Germany. frank.klaerner@uni-essen.de
Kahlert
Björn
B
Nellesen
Anke
A
Zienau
Jan
J
Ochsenfeld
Christian
C
Schrader
Thomas
T