Nanoporous dipeptide crystals as selective gas sorbents and polymerization nanovessels

Hydrophobic dipeptide crystals recently emerged as novel “organic zeolites” featuring tailorable pore size. In fact, seven out of nine pairwise combinations of L-isoleucine, L-valine and L-alanine amino acids crystallize according to the same charge-assisted hydrogen bond pattern, generating a family of microporous materials with right-handed 1D channels, having diameters in the sub-nanometer domain (<6Å), aliphatic environment and different degrees of helicity. The relationship between pore size and material properties was investigated with respect to gas separation, exploiting the affinity of carbon dioxide for the hydrophobic nanochannels of L-alanyl-L-valine (AV), L-isoleucyl-L-valine (IV) and L-valyl-L-isoleucine (VI). Reversible CO2 capture from an equimolar mixture of CO2 and methane, at room temperature and 1 atmosphere, was demonstrated with increasing purification performance with decrease in pore size. Dipeptide were also used as nanovessels in radical polymerizations with the aim of controlling otherwise non-specific reactions. Diene monomers (trans-1,3-pentadiene and isoprene) only yield linear 1,4-trans polymer in accordance with 1-dimensional pore geometry, while poly(acrylonitrile) (PAN) could be obtained as a stereoregular isotactic product by acrylonitrile polymerization in AV dipeptide. Finally, taking advantage of the dipeptide lability and unique thermal properties of poly(acrylonitrile), AV-PAN nanocomposites were used as a scaffold to obtain carbon replicas of the starting nanocomposite crystals (carbon micro-fibrils) showing anisotropic arrangement of the graphite domains.