The current study presents for the first time the synthesis of a new 2:1-[α/aza]-pseudopeptide series possessing charged amino acid (i.e., lysine) and aims at studying the influences of chirality, backbone length, and 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 compared with the hetero-analogue. 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 case of short trimer sequences, while the chirality and the backbone length exerted more distortion on the β-turn adopted by the longer hexamer sequences. The large disturbance in hexamers from classical β-turn was attributed to increasing the flexibility and the possibility of molecules to adopt 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 decreases the high steric hindrance between the lysine side chains, as in the homo analogue, 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 additive, with an increase in both ideal selectivity αCO2/N2 (from 42.8 to 47.6) and CO2 permeability (from 132 to 148 Barrer) compared to the virgin Pebax® 1074 membrane.