Grotthus-type and diffusive proton transfer in 7-hydroxyquinoline.(NH(3))(n) clusters.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Proton transfer is fundamental in chemical and biological systems.
• Ammonia clusters serve as model systems for studying proton dynamics in hydrogen-bonded networks.
• 7-hydroxyquinoline (7-HQ) provides a molecular platform for initiating and observing proton translocation.

Purpose of the Study:

• To investigate proton translocation along ammonia wires in 7-hydroxyquinoline.(NH(3))(n) clusters.
• To model finite-size systems for proton transfer along hydrogen-bonded solvent chains.
• To characterize the energetics and mechanisms of proton transfer events.

Main Methods:

• Experimental investigation using laser spectroscopy.
• Theoretical calculations employing Hartree-Fock and Density Functional Theory (DFT).
• Characterization of stable zwitterionic clusters and transition states.

Main Results:

• Proton translocation and reprotonation of 7-HQ were observed, forming the keto tautomer.
• Exoergic proton transfer to form a zwitterion occurs at a threshold cluster size of n=5 or 6.
• Grotthus-type proton hopping mechanisms with low barriers were identified for most transfer steps.
• One step exhibits a high barrier due to structural reorganization and diffusive motions.

Conclusions:

• Ammonia wires facilitate proton translocation in 7-hydroxyquinoline clusters.
• The study elucidates the mechanisms and energetics of proton transfer in these model systems.
• DFT and experimental methods provide complementary insights into complex proton dynamics.