A theoretical investigation on intramolecular hydrogen-atom transfer in curcumin

Intramolecular H-atom-transfers (IHTs) in curcumin (enol) and its mimic, 1,6-heptadiene-3,5-dione (enol), in ground state and excited state were investigated by ab initio and CIS methods in this paper. It is revealed that double ortho-methoxy-phenolic rings have little effect on the IHT barrier of curcumin, and the IHT barrier of curcumin in ground state is much lower than those of other IHT models, such as 9-hydroxyphenalen-1-one and perylenequinonoid pigments. More interestingly, the IHT barrier of 1,6-heptadiene-3,5-dione (enol) in the singlet excited state is nearly 25kJ/mol higher than that in the ground state, which is very unique in IHT phenomenon. The unexpected IHT behavior of 1,6-heptadiene-3,5-dione (enol) is explained in terms of O–O distance, charge variation of H-atom, and flexibility of the structure. [Copyright &y& Elsevier]