PB-23 Hydrogen Bonding Catalyzed Excited-State Double Proton Transfer Reaction between 2-aminopyridine and Acetic Acid

Phototautomerization process involving a double proton-transfer reaction has been a hot topic in biochemistry and photochemistry in recent years. We have investigated the photo-induced tautomerization of 2-aminopyridine (2AP) to 2(1H)-pyridineimine(1H2PI) by experimental and theoretical methods. In solution 2AP and acetic acid could form a complex connected by intermolecular hydrogen bonding. With photo excitation intermolecular proton transfer reaction would happen along hydrogen bonding. The reaction mechanism is complex and still need to investigate. During the process of protons transferring, the hydrogen bonding plays an important role. The intermolecular hydrogen bonding in the electronically excited states has been strengthened significantly which induces the proton transferring. The reaction mechanism is determined by the unsymmetrical molecular structure and the strength of hydrogen bonding. The acetic acid acts as a catalyst, providing proton first and accepting proton later. The C=O dual bond has a shift from one side to the other side in the acid molecular, which accompanies the catalysis in the intermolecular double proton transfer reaction