摘要
Electron beam irradiation can cause damage to biological and organic samples,as determined via transmission electron microscopy(TEM).Cryo-electron microscopy(cryo-EM)significantly reduces such damage by quickly freezing the environmental water around organic molecules.However,there are multiple hypotheses about the mechanismof cryo-protection in cryo-EM.A lower temperature can cause less molecular dissociation in the first stage,or frozen water can have a“cage”effect by preventing the dissociated fragments from flying away.In this work,we use real-time time-dependent density functional theory molecular dynamics(rt-TDDFT-MD)simulations to study the related dynamics.We use our recently developed natural orbital branching(NOB)algorithm to describe the molecular dissociation process after the molecule is ionized.We find that despite the difference in surrounding water molecules at different temperatures,the initial dissociation process is similar.On the other hand,the dissociated fragments fly away at room temperature,while they remain in the same cage when frozen water is used.Our results provide direct support for the cage effect mechanism.
基金
supported by the National Natural Science Foundation of China under Grant Nos.T2293700 and T2293702
the Science and Technology Innovation Program of Hunan Province under Grant No.2021RC4026
the Postgraduate Technology Innovation Program of Hunan Province under Grant No.CX20220070.
