[Figure 2]
Selection of Ionic Exchange
Resins
The efficiency and selectivity of ion exchange resins is specifically
controlled by their chemical structure. Noteworthy, the choice of
operating conditions has a substantial directional effect on the overall
process using such ion exchange resins, incl. its respective
productivity, and should always be investigated in detail. This is
particularly relevant for an imine reductase-catalyzed reaction, as
significant differences between the substrates (imines/primary amines)
and the final product (secondary amines) are found. Unfortunately, to
date, no effective ion exchange resin-based recovery method has been
reported for imine reductase-catalyzed reaction in the scientific
literature. Most reports involve classical extraction and distillation
steps, which require an additional effort during the DSP.
Thus, different commercially available cation- and anion- exchange
resins were screened for their ability to remove the reactant’s product
(S )-2-MPN and the possibly remaining substrate 2-MP from the
reaction solution. Therefore, test solutions containing
100 mmol·L-1 of the product and the substrate together
with 500 mmol·L‑1 d‑glucose in
100 mmol·L-1 NaPi buffer pH 7.5 were
prepared and three different doses (0.02 g, 0.1 g and 0.2 g per mL test
solution, respectively) were analyzed. The residual concentration in
solution was measured via GC and the results are shown in Figure 3.
Figure 3A presents the remaining concentration after 30 min and
Figure 3B after 24 h. For all entries, equilibrium concentrations are
almost achieved after 30 minutes, but a longer adsorption time should be
executed to improve yields. Values greater than 100% were the result of
the swelling degree of the polymeric material. Here, the resins soak up
the solvent water and consequently this increases the residual
concentration in solution.