Artificial water channels—deconvolution of natural Aquaporins through synthetic design

Abstract

Artificial Water Channels (AWCs) have been developed during the last decade with the hope to construct artificial analogues of Aquaporin (AQP) proteins. Their osmotic water permeability are in the range of natural transporters, making them suitable candidates that can potentially transport water at lower energy and operating cost. Compared to AQPs, AWCs would have several potential advantages, such as improved stability, simple and scalable fabrication and higher functional density when confined in 2D membrane arrays. The first knowledge gap between AWCs and AQPs is in the mimicry of the complete set of functionality, in terms of obtaining systems capable of simultaneous water permeation and salt rejection, while not forfeiting the advantage of simplicity. Despite incipient developments, major problems still remain unsolved, such as their up-scaling preparation procedures from laboratory studies to square meters needed for large industrial membrane applications. However, the flow of structural information from molecular level through nanoscale dimensions, towards highly ordered ultradense macroscopic arrays of AWCs is conceptually possible. Successfully transitioning from synthetic molecules to functional channels and materials could lead to a new generation of membranes for water purification. Moving AWCs into products in the commercial arena is now the main objective of research in this newborn field.

Porous organic cages as synthetic water channels

“…Bioinspired synthetic water channels commonly have water permeable central apertures surrounded by hydrophobic outer shells for stabilizing within the hydrophobic core of lipid bilayer systems 14 . The two general synthetic strategies are unimolecular tubular architectures 5 – 9 , 13 and bottom-up assemblies 10 – 12 .…”

Bola-amphiphile-imidazole embedded GO membrane with enhanced solvent dehydration properties

“…In the application of AQP biological membranes, main challenges might include: i) difficulty in controlling stable structure and scaling-up because of insufficient stability of AQP proteins in high saline and operational pressure; ii) fragile lipid bilayers show poor compatibility with the practical applications; iii) high fabrication cost compared with synthetic counterparts [11,12] . Therefore, researchers attempt to mimic the structure of AQP [13] and synthesize artificial simpler molecules with similar structural and thus water transport properties, namely artificial water channels, first reported by Barboiu et al [14] Common artificial water channels such as carbon nanotubes [15][16][17] (CNTs), imidazole-quartet water channel [14,18,19] (IQWC) and peptide-appended pillar [5]arene [20][21][22] (PAP) have been explored during the last decades. Noy et al [17] indicated that water permeability in 0.8-nanometer-diameter CNTs, which confined water down to a single-file chain, exceeded that AQP.…”

Biomimetic Nanomembranes: An Overview

“…This was the reason synthetic alternatives were sought for. The synthetic structures serving a function analogous to natural aquaporins are called artificial water channels [152,153].…”