[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.