DFT study on the enantiotropy of amphoteric His molecule in water-liquid phase environment
The title reaction was performed using the M06-2X and MN15 methods of DFT combined with the Slovation Model Density(SMD)model method based on self-consistent reaction field theory.The results showed that,His molecule can be transferred when the carbonyl O atom as the only bridge of α-H proton,and α-H transfers with amino group N and carbonyl O atom as bridges after the proton of protonated amino group N transfers to carbonyl O atom,respectively;Also,α-H achieves enantiotropy in five channels using amino group N and carbonyl group O as bridges after the proton transfers from the protonated amino group N to the N of the imidazole ring,respectively.Investigation on the potential energy surface showed that the free energy barriers of rate-determining step for each of the five channels are 245.6,238.1,297.3,270.9 and 257.7 kJ/mol under the effect of recessive solvent;the energy barriers are reduced to about 139.9,120.7,161.7,142.7 and 157.3 kJ/mol under the effect of dominant solvent.The results show that His can racemize with a small amount in the water-liquid environment,and it is relatively safe to be used to supply His for life.
histidineenantiotropydensity functional theorytransition stateGibbs free energy
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