The influences of driving forces on behaviors of Na+ and H2O in cyclic octa-peptide nanotube: investigated by steered molecular dynamics

Abstract

The behaviors of Na+ and H2O in cyclic peptide nanotube (CPN) under different conditions are important for their applications. In this study, a series of driving forces has been applied to Na+ and H2O constrained in the self-assembled nanotube of {cyclo[(-D-Ala-L-Ala)4-]}10, to understand the influence on the transport properties and behaviors of Na+ and H2O using steered molecular dynamics (SMD). The results show that H2O need less driving force (0.4 kcal mol−1 Å−1) to migrate in the nanotube than that of Na+ (2.3 kcal mol−1 Å−1). Under the same driving force, the transport speed of H2O is about 135 times faster than that of Na+. The instantaneous velocity curves reveal that water adopts a kind of irregular hopping transport mode which does not change with the driving force, while Na+ transports in an obvious hopping mode changing with driving force in three different types. Particularly, the instantaneous velocity curves of Na+ under the driving force of 3.2–5.2 kcal mol−1 Å are roughly similar to the pulse signal, which is of great significance to the treatment of human diseases and the detection of electrolytes. The transport resistance mainly comes from electrostatic interaction. Results in this work show that cyclic octa-peptide nanotubes have excellent performance sensitive to external driving forces and are good potential materials for drug design, biosensors, ion transmembrane transport and ion probe for the detection of Na+ in organisms.