Molecular Tweezers: Synthetic Receptors for π-Sandwich Complexation of Aromatic Substrates

The design and synthesis of a new class of synthetic “receptors” for aromatic substrates is described. Known as “molecular tweezers,” these receptors are shown to form very stable “sandwich complexes” with π-deficient aromatic substrates in organic solvents. The second π-stacking interaction plays a critical role in the complexation - analogous mono-chromophores bind only very weakly. Some of the electronic and structural features required for high complex stability have been elucidated. A molecular tweezer containing a carboxylic acid group in its binding cleft has also been synthesized. This receptor has been shown to form a very stable inclusion complex with 9- propyladenine in chloroform solution. Spectroscopic data and studies with adenine analogues suggest a complex containing two hydrogen bonds from the receptor to N-6 and N-7 of adenine and π-stacking interactions between the tweezer and the nucleotide base.