Dipeptide Crystals as Reverse Osmosis Membranes for Water Desalination: Atomistic Simulation

Abstract

An atomistic simulation study is reported to investigate the capability of dipeptide crystals as reverse osmosis (RO) membranes for water desalination. Eight dipeptides are considered, namely, Ala-Val (AV), Val-Ala (VA), Ala-Ile (AI), Ile-Ala (IA), Val-Ile (VI), Ile-Val (IV), Val-Val (VV), and Leu-Ser (LS). It is revealed that water flux is governed by both pore size and helicity. With a relatively larger pore size, AV, AI, VV, and LS exhibit a higher water flux than VA, IA, VI, and IV. Despite similar pore size in AI and VA, a higher flux is observed in AI because of a lower helicity. On the other hand, VI, LS, IV, and IA possess higher salt rejection (>90%, and 100% for VI) than the rest (<70%). The salt rejection is determined by the electric potential difference across the membrane, induced by the staggered arrangement of −NH 3 + and −COO − groups in the dipeptides. This unique arrangement of charge groups is not observed in other types of RO membranes. A higher electric potential difference allows more ions to pass through the membrane, leading to lower salt rejection. The lifetime of hydrogen bonding of water in LS membrane is shorter than those in VI and IV, which follows the decreasing trend of the water flux. An Arrhenius relationship is found between the water flux and temperature in LS and VI, and the activation energies are predicted to be 27.72 and 33.42 kJ/mol, respectively. Furthermore, the membrane flexibility is examined; a correlation between the water flux and the position restraint force constant is obtained. This simulation study provides microscopic insights into the important structural and dynamic properties of water in dipeptide membranes and suggests their potential use as RO membranes for water desalination.

Atomistic Insights into the Anisotropic and Low Thermal Conductivity in Neopentyl Glycol Crystals: A Molecular Dynamics Study

“…Here, a hydrogen bond is counted only when the donor−acceptor distance is less than 3.5 Å and the hydrogen−donor−acceptor angle is less than 30°. 19,47 Our calculation of the average strength of hydrogen bonds in a perfect NPG crystal obtained 27.91 kJ/mol at 0 K, which is quantitatively consistent with the results of ∼25 kJ/mol computed using DFT. 41 Figure 7a depicts the average strength of intermolecular hydrogen bonds and the number of intermolecular hydrogen bonds per molecule (N HB ), which remain unchanged from 218.15 to 298.15 K. This result suggests that the orientations of NPG molecules in the crystal remain unchanged upon the temperature change.…”

“…C is the energy conversion factor, r is the distance, and ε and δ are the parameters of Lennard-Jones potential. Here, a hydrogen bond is counted only when the donor–acceptor distance is less than 3.5 Å and the hydrogen–donor–acceptor angle is less than 30°. , Our calculation of the average strength of hydrogen bonds in a perfect NPG crystal obtained 27.91 kJ/mol at 0 K, which is quantitatively consistent with the results of ∼25 kJ/mol computed using DFT …”

Antibacterial and Antibiofilm Properties of Self-Assembled Dipeptide Nanotubes

“…Peptide assemblies with channel diameters >4 Å (FF and LS) show similar antibacterial activity while the ones with narrow channels (<4 Å, IV and VI) are inactive. Zhao et al showed by atomistic simulation that IV and VI allow only relatively restricted transport of water molecules, much smaller than LS water flux [41]. FF was not investigated by the authors, but the crystal structure of this dipeptide shows that it assembles in water filled nanotubes [19].…”

“…FF was not investigated by the authors, but the crystal structure of this dipeptide shows that it assembles in water filled nanotubes [19]. LS possess high salt rejection (Na + and Cl − ) [41] which suggests that antimicrobial activity arises from a sudden increase in the membrane permeability to water. Thus, our results seem to be in agreement with the findings of Gazit and colleagues that dipeptide nanostructures may form pores in inner and outer bacterial membranes [6].…”

Novel adjustable monolayer carbon nitride membranes for high-performance saline water desalination

“…Based on the previous studies [5,47,88,89], to speed up the converging of MD simulations, high pressure was used for water desalination. However, Cohen-Tanugi and Grossman [90] have verified the system's efficiency at low pressures.…”