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 betwee n the amino acid and the H3O+ model acidic center was considered. The struc tures of transition states of the reaction and the activation energies were determined. Relative reactivity of the C-H bonds in the hydroxyproline mol ecule under conditions of HSCIE was studied. The results obtained are in ag reement with experimental data on the stereoselectivity and regioselectivit y of the HSCIE reaction, viz., the lower the calculated activation energy o f isotope exchange, the larger the portion of hydrogen substituted by triti um in a given position of the amino acid molecule. The enhancement of the r eactivity under conditions of solid-state isotope exchange can be associate d with additional interaction between the exchanging I-I atoms and the elec tron-donor O and N atoms of the amino acid molecule in transition state.