Improved enzymatic two-phase biotransformation for (R)-phenylacetylcarbinol: Effect of dipropylene glycol and modes of pH control

An octanol/aqueous two-phase process for the enzymatic production of (R)-phenylacetylcarbinol (PAC) has been investigated further with regard to optimal pH control and replacement of 2.5?M MOPS buffer by a low cost solute. The specific rate of PAC production in the 2.5?M MOPS system controlled at pH?7 was 0.60?mg?U^-1?h^-1 (reaction completed at 34?h), a 1.6 times improvement over the same 2.5?M MOPS system without pH control (0.39?mg?U^-1?h^-1 at 49?h). An improved stability of PDC was evident at the end of biotransformation for the pH-controlled system with 84% residual carboligase activity, while 23% of enzyme activity remained in the absence of pH control. Lowering the MOPS concentration to 20?mM resulted in a lower benzaldehyde concentration in the aqueous phase with a major increase in the formation of by-product acetoin and three times decreased PAC production (0.21?mg?U^-1?h^-1). Biotransformation with 20?mM MOPS and 2.5?M DPG as inexpensive replacement of high MOPS concentrations provided similar aqueous phase benzaldehyde concentrations compared to 2.5?M MOPS and resulted in a comparable PAC concentration (92.1?g?L^-1 in the total reaction volume in 47?h) with modest formation of acetoin.