A lysine-based 2:1-[α/aza]-pseudopeptide series used as additives in polymeric membranes for CO2 capture: synthesis, structural studies, and application†

The current study presents for the first time the synthesis of a new 2:1-[α/aza]-pseudopeptide series possessing charged amino acids (i.e., lysine) and aims at studying the influences of chirality, backbone length, and the nature of the lysine side chains on the conformation of the 2:1-[α/aza]-oligomers in solution using NMR, FTIR spectroscopy and molecular dynamic calculations. The spectroscopic results emphasized the conservation of the β-turn conformation adopted by the trimers regardless of the chirality which demonstrated a noticeable effect on the conformation of homochiral hexamer (8c) compared with the hetero-analogue (8d). The molecular dynamic calculations predicted that the chirality and the side chain of the lysine residues caused a little distortion from the classical β-turn conformation in the case of short trimer sequences (7c and 7d), while the chirality and the backbone length exerted more distortion on the β-turn adopted by the longer hexamer sequences (8c and 8d). The large disturbance in hexamers from classical β-turn was attributed to increasing the flexibility and the possibility of molecules to adopt a more energetically favorable conformation stabilized by non-classical β-turn intramolecular hydrogen bonds. Thus, alternating d- and l-lysine amino acids in the 2:1-[α/aza]-hexamer (8d) decreases the high steric hindrance between the lysine side chains, as in the homo analogue (8c), and the distortion is less recognized. Finally, short sequences of aza-pseudopeptides containing lysine residues improve CO₂ separation when used as additives in Pebax® 1074 membranes. The best membrane performances were obtained with a pseudopeptidic dimer as an additive (6b′; deprotected lysine side chain), with an increase in both ideal selectivity α_CO2/N2 (from 42.8 to 47.6) and CO₂ permeability (from 132 to 148 Barrer) compared to the virgin Pebax® 1074 membrane.

A new 2:1-[α/aza]-pseudopeptide series based charged lysine amino acid was synthesized. Influences of chirality, backbone length, and lysine side chains on the oligomers conformation were investigated in solution using NMR, FTIR and MD calculations.

Multiblock Copolymer Grafting for Butanol Biofuel Recovery by a Sustainable Membrane Process

Biobutanol is an attractive renewable biofuel mainly obtained by the acetone-butanol-ethanol (ABE) fermentation process. Nevertheless, the alcohol concentration has to be limited to a maximum of 2 wt % in ABE fermentation broths to avoid butanol toxicity to the microorganisms. The pervaporation (PV) membrane process is a key sustainable technology for butanol recovery in these challenging conditions. In this work, the grafting of azido-polydimethylsiloxane (PDMS-N3) onto a PDMS-based multiblock copolymer containing alkyne side groups led to a series of original membrane materials with increasing PDMS contents from 50 to 71 wt %. Their membrane properties were assessed for butanol recovery by pervaporation from a model aqueous solution containing 2 wt % of n-butanol at 50 °C. The membrane flux J50μm for a reference thickness of 50 μm strongly increased from 84 to 192 g/h m(2) with increasing PDMS content for free-standing dense membranes with thicknesses in the range of 38-95 μm. At the same time, the intrinsic butanol permeability increased from 1.47 to 4.68 kg μm/h m(2) kPa and the permeate butanol content was also strongly improved from 38 to 53 wt %, corresponding to high and very high membrane separation factors of 30 and 55, respectively. Therefore, the new grafted copolymer materials strongly overcame the common permeability/selectivity trade-off for butanol recovery by a sustainable membrane process.