Wetting the lock and key enthalpically favours polyelectrolyte binding.

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry
• Computational Chemistry

Background:

• Understanding molecular recognition in aqueous solutions is crucial for various chemical and biological processes.
• Traditional models like the lock-and-key concept often fail to fully explain binding selectivities in complex systems.
• Polyanionic macrocycles and alkylammonium guests represent a model system for studying host-guest interactions in water.

Purpose of the Study:

• To investigate the driving forces behind the association between polyanionic dyn[4]arene and a series of α,ω-alkyldiammonium ions.
• To determine the factors governing selectivity in host-guest complexation in aqueous media.
• To elucidate the roles of desolvation and solvation enthalpies in molecular recognition.

Main Methods:

• Employed a combination of experimental and computational techniques in water.
• Systematically varied the chain length of α,ω-alkyldiammonium guests.
• Analyzed energetic and structural contributions to binding affinity and selectivity.

Main Results:

• The lock-and-key concept was insufficient to explain the observed binding selectivities.
• Binding was primarily governed by solvent-related phenomena: decreased guest desolvation enthalpy and increased complex solvation enthalpy.
• An unexpected increase in favorable enthalpy of complex solvation was observed with increasing guest chain length.

Conclusions:

• Solvent effects, particularly the enthalpy of complex solvation, play a decisive role in the binding of polyelectrolytes via inclusion.
• This study highlights the importance of considering solvent contributions beyond simple molecular complementarity in host-guest chemistry.
• Findings offer insights into molecular recognition in water, potentially contributing to a broader understanding of such processes.