Volume 90 Issue 22 | p. 10 | News of The Week
Issue Date: May 28, 2012

Single Molecule Channels Water

Nanotechnology: Molecular tube transports water across lipid membrane
Department: Science & Technology
News Channels: Materials SCENE, JACS In C&EN
Keywords: water channels, aquaporin, membrane
[+]Enlarge
A crystal structure of a hydrazide-containing pillar[5]arene viewed through the tube (top) and from the side (bottom).
Credit: J. Am. Chem. Soc.
Two views of a crystal structure of a hydrazide-containing pillar[5]arene, from the side (left) and through the tube (right).
 
A crystal structure of a hydrazide-containing pillar[5]arene viewed through the tube (top) and from the side (bottom).
Credit: J. Am. Chem. Soc.

Chinese researchers have made the first nanoscale artificial water channels that selectively transport water across lipid membranes. Such a system could be used for applications such as water purification and desalination.

Jun-Li Hou and coworkers at Fudan University, in Shanghai, constructed the channels from single pillar[5]arene molecules with hydrazide-containing side chains (J. Am. Chem. Soc., DOI: 10.1021/ja302292c). Intramolecular hydrogen bonds between side chains turn the molecules into tubes.

Hou and coworkers inserted these tubes into vesicles to form membrane-spanning channels. The researchers induced water flow via salt concentration and osmosis. “The osmotic pressure difference prevents water inside the vesicles from coming back out,” Hou says.

Although several groups had previously reported water-trapping molecules, none had demonstrated a synthetic channel that could selectively transport water, says Huaqiang Zeng of the National University of Singapore. The new work of Hou and coworkers “represents a very important step toward realizing the full potential of water-transporting molecules for their eventual uses as nanofiltration membranes and devices for water purification,” Zeng says.

The hydrogen-bonding pattern is reminiscent of the interactions between peptides in aquaporins, proteins that transport water across cell membranes, says Peter J. Cragg of the University of Brighton, in England. Studying such synthetic molecules could help researchers better understand the workings of biological channels as well, he notes.

“Understanding how any transmembrane channel-forming molecule works is of fundamental importance, and we still know so little about how these systems select chemical species or switch their transport on and off in a process known as gating,” Cragg says. “Observing ion transport by model transmembrane channels will help to identify those chemical motifs that are responsible for selectivity and gating.”

Hou and his coworkers are working on tweaking the pillar[5]arene backbone to improve transport efficiency and to better control the process.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
Mihai Barboiu (Tue May 29 04:26:40 EDT 2012)
I read with interest the recent paper in Chemical Eng. News magazine regarding the “the first nanoscale artificial water channels that selectively transport water across lipid membranes”. The JACS paper is very nicely done.
I noticed, however, that this system “represents a very important step toward realizing the full potential of water-transporting molecules for their eventual uses as nanofiltration.
You may be interested to know that in November 2011 we published a paper “Imidazole-Quartet Water and Proton Dipolar Channels” (http://onlinelibrary.wiley.com/doi/10.1002/anie.201103312/suppinfo) showing that highly selective water channels can transport water across bilayer membranes and moreover the polarization of water wires like in aquaporins, can induce very fast proton transport.This paper has been considered Hot paper and Back Cover of Angewandte Chemie at this time.
It appears to be difficult to understand that the peoples discussing the results are not aware of this article, so it was cited (ref 9) in the JACS paper.
An other important point is that the water structure inside pillar[5]arene channels is not a continual “hydrogen-bonding pattern, reminiscent of the interactions between peptides in aquaporins, proteins that transport water across cell membranes”, thus not really the aquaporins model in which the water wires are formed. In crystal structures we can observe dimers of water which can diffuse within the hydrophobic space of the pillar. However this system can be very useful for creating synthetic pathways for water, with reduced friction within the channel.
Again, congratulations for this very important highlight. I look forward to hearing from you. Any comments welcome.
Montpellier, 29/05/2012
Mihai Barboiu
mihai.barboiu@iemm.univ-montp2.fr
Huaqiang ZENG (Thu May 31 01:43:48 EDT 2012)
Hi Mihai, Thank you for mentioning your beautiful work in Angew. The first artificial water-channel described by Hou is featured by its high discrimination against proton transporation (not to mention other cations) while allowing water moelcules to go through the membrane. In my view, this is the most valuable and significant aspect of the work, which is truely reminicent of the function by Aquaporin. Another beauty of the work lies in its unimolecular approach, making its futuristic applications more feasible and readily accomplishable. On the other hand, mimicking the Nature can be carried out via either structural or functional approaches with the latter being more important than the former (this is my personal bias). From this point of view, the work by Hou is very encouraging toward reproducing the function by aquaporins and realizing its eventual applications.

Leave A Comment

*Required to comment