Amide functionalized DWCNT nanocomposite membranes for chiral separation of the racemic DOPA

In view of the demand for enantiopure compounds of drug molecules, a new strategy was developed to improve the enantioseparation performance of a racemic mixture of 3,4-dihydroxyphenylalanine (DOPA) with the help of a functionalized Double-walled Carbon Nanotube (DWCNT) membrane. With the aid of covalent oxidation followed by an amidation reaction, chiral selectors, namely L-tryptophan and L-DOPA were incorporated separately into the DWCNT solution phase. The corresponding hybrid dispersions were assembled into two nanocomposite membranes (ML-tryp and ML-DOPA) via vacuum-assisted filtration. The enantioselective performance of each membrane was evaluated by conducting permeation experiments. The time-dependent membrane permeation results have shown an enantiomeric excess value of up to 99% for the ML-DOPA and 98% for the ML-tryp membrane. Due to the self-linkage across the amide layer grafted on the FDWCNT surface, the L-isomer from the racemic mixture of DOPA was preferentially adsorbed onto the membrane, which has also been established by considering three-point interaction model. In contrast, the D-isomer was permeated through the nanoporous membrane. This tradeoff in permeation results in a high flux value for D-isomer (37.44 mmol.m(-2).h(-1)) with concomitant lowering of the flux value for L-isomer (0.35 mmol.m(-2).h(-1)) at an applied pressure of 5 bar was observed. The peclet number for both the membranes was found to be similar to 500, which can be attributed to the higher convective velocity of the fluid through bulk transport phenomena in a continuous manner.