Study of solid-state catalytic isotope exchange of hydrogen in L-hydroxyproline under the action of spillover tritium

Reaction of high-temperature solid-state catalytic isotope exchange (HSCIE) of hydrogen in L-hydroxyproline was studied by ab initio quantum-chemical calculations. A one-center synchronous mechanism of isotope exchange between the amino acid and the H3O+ model acidic center was considered. The structures of transition states of the reaction and the activation energies were determined. Relative reactivity of the C-H bonds in the hydroxyproline molecule under conditions of HSCIE was studied. The results obtained are in agreement with experimental data on the stereoselectivity and regioselectivity of the HSCIE reaction, viz., the lower the calculated activation energy of isotope exchange, the larger the portion of hydrogen substituted by tritium in a given position of the amino acid molecule. The enhancement of the reactivity under conditions of solid-state isotope exchange can be associated with additional interaction between the exchanging I-I atoms and the electron-donor O and N atoms of the amino acid molecule in transition state.