摘要
Dynamics of ammonium and ammonia in solutions is closely related to the metabolism of arnrnoniac compounds, therefore plays an important role in various biological processes. NMR measurements indicated that the reorientation dynamics of NH4＋ is faster in its aqueous solution than in rnethanol, which deviates from the Stokes-Einstein-Debye rule since water has higher viscosity than methanol. To address this intriguing issue, we herein study the reorientation dynamics of ammonium ion in both solutions using numerical simulation and an extended cyclic Markov chain model. An evident decoupling between translation and ro- tation of methanol is observed in simulation, which results in the deviation of reorientation from the Stokes-Einstein-Debye rule. Slower hydrogen bond （HB） switchings of ammonium with rnethanol comparing to that with water, due to the steric effect of the rnethyl group, remarkably retards the jump rotation of ammonium. The observations herein provide useful insights into the dynamic behavior of ammonium in the heterogeneous environments including the protein surface or protein channels.
基金
supported by the National Key Research and Development Program of China(2017YFA0206801)
the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB20000000 and XDB10040304)
the National Natural Science Foundation of China(No.21373201and No.21433014)
