In this work,steered molecular dynamics simulations were performed to study the process of Na＋,K＋ and Cl-traversing through（6,6）,（7,7）,（8,8）,（9,9） and（10,10） carbon nanotubes（CNTs）.The potential of mean forces（PMF） of ions passing through CNTs were calculated with the umbrella sampling method.Ion hydration in CNTs and in bulk solution was analyzed and compared.Simulation results show that ions are hindered from entering narrow CNTs at the entrance;however,it is easy for ions to leave narrow CNTs into bulk solution at the exit.There is almost no hindrance for ions to translocate through wide CNTs.The free energy barriers for ions translocating through CNTs decrease sharply with the increase of diameter.Different free energy barriers of Na＋,K＋ and Cl-entering CNTs indicate that CNTs have an inherent ion selectivity.When ions traverse through CNTs,coordination numbers and preferential orientation of water molecules in coordination shells of ions are different from those in bulk,which determine the dehydration energies of ions and affect free energy barriers of ions traversing CNTs and the ion selectivity of CNTs.Studies on ions traversing through the hydrophobic pores of CNTs assist in understanding the function of hydrophobic regions of ion-channel proteins and provide guidance for the design of CNT-based nanofluidic devices.%采用拉伸分子动力学模拟研究了Na＋,K＋和Cl-通过（6,6）,（7,7）,（8,8）,（9,9）和（10,10）碳纳米管的过程,利用伞形取样法计算了离子通过碳管的平均力势能,并对离子在管中和本体相中的水化作了比较.结果表明,离子通过管径较窄的碳管时,在入口处遇到较大的阻力,从出口进入本体相较容易;而通过管径相对较宽的碳管则几乎无阻碍.离子通过碳管的能垒随管径的增大而降低,不同离子的能垒各不相同,表明碳管具有固有的离子选择性;离子通过碳管时,不仅其配位数改变了,而且配位层中水分子的取向也有所改变,这两者共同决定了离子进入碳管时的去水化能,进而影响离子通过碳管的能垒和碳管的离子选择性.本工作将有助于理解离子通道蛋白中疏水区域的功能作用,并可以为基于碳纳米管的纳流控系统的设计提供指导.
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