Monday, May 3, 2010

Permeable membranes: Peptide


New research published in April suggests that Di-peptides have been shown to form hydrogen-bonded microporous crystals. These have interesting gas absorption properties. The researchers of Institute of Molecular and Cell Biology in Porto, led by Luís Gales have observed that dipeptide single-crystals can act as permeable membranes able to distinguish between argon, nitrogen and oxygen. It is a process for air separation. But, it is difficult to carry out because of the similarity in size between the species.

                               The permeability of three Di-peptides [L-leucyl-L-serine (LS), L-valyl-L-isoleucine (VI), and L-alanyl-L-alanine (AA)]  which crystallize into different lattices with different porosities. L-leucyl-L-serine (LS), with nanochannels that are larger than argon, nitrogen and oxygen, is permeable to all three. L-valyl-L-isoleucine (VI), whose channel size is close to that of the gas molecules, was only permeable to oxygen and nitrogen. And L-alanyl-L-alanine (AA)'s porosity consists of discrete pockets rather than channels, it was found to be permeable to oxygen.
                             The AA dipeptide retained its crystallinity after oxygen permeation, suggesting that its guest-induced flexibility is reversible. This dynamic response was also guest-dependent: AA was more permeable to oxygen than to helium — even though helium is a smaller species. This excellent selectivity suggests that dipeptide crystals hold promise for a variety of separation processes.


ReferenceAfonso, R. V., Durão, J., Mendes, A., Damas, A. M. & Gales, L. Dipeptide crystals as excellent permselective materials: sequential exclusion of argon, nitrogen, and oxygen.Angew. Chem. Int. Ed. doi:10.1002/anie.201000007 (2010). | Link

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