Jacob T. Cohen

Mapping of Molecular Docking of Organic Cations on Negatively Charged Polymers by Picosecond Time Resolved Fluorescence Spectroscopy.

Picosecond time resolved spectroscopy is used to probe the binding between positively charged diaminostilbene derivatives and negatively charged polyions. Several binding modes of roughly equal stability but of different polarity and enviromnent were found; implying a compensation mechanism between the hydrophobic and electrostatic interactions.

Demonstration of structure-selective binding of organic cations to anionic polyelectrolytes

The binding of diprotonated trans-4,4 0 -diaminostilbene (DASH2 2C ) to poly (styrenesulfonate) (PSS) and poly(vinylsulfonate) (PVS) in aqueous solution have been studied by following the changes in the absorption, fluorescence and polarization emission spectra of the complexed chromophors. It was found that in the DASH2 2C ‐PSS complex most of the DASH2 2C molecules are bound in their trans-isomer form, while in the DASH2 2C ‐PVS complex, which is less stable and lack p‐p interactions, the DASH2 2C molecules are bound in the electrostatically preferred cis conformation. The higher stability of the DASH2 2C ‐PSS complex is due to structural fitting between trans-DASH2 2C and p-styrene sulfonic units. This structural fitting allows formation of p‐p bonds between aromatic moieties in combination with electrostatic attraction between the protonated amine and sulfonate charged groups. Our findings demonstrate the delicate interplay between electrostatic and non-polar interactions which controls the binding of relatively large molecules to high-molecular weight receptors, and may be used to model a binding site in biological systems. These findings are corroborated by molecular mechanics simulation of the complexes.