Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling

Table 2 Optimization of the Ca-alginate/chitosan hybrid immobilization

Immobilization conditions^a	Values	v₀(μ mol/min)^b	Specific activity (μ mol/min/g dw cells)^c	Specific activity (μ mol/min/g ww catalyst)^c	Reuse cycles^d	*e.e.*(%)
Alginate concentration	1.5	0.96	24.10	0.45	6	>99%
(% w/v)	2.0	0.97	24.18	0.26	8	>99%
	3.0	0.95	23.80	0.18	8	>99%
	4.0	0.95	23.68	0.17	8	>99%
Chitosan pH	3.0	0.00	0.00	0.00	0	>99%
	3.5	0.00	0.00	0.00	0	>99%
	4.0	0.98	24.53	0.25	8	>99%
	4.5	1.32	33.10	0.32	14	>99%
	5.0	1.37	34.30	0.33	14	>99%
Chitosan concentration	0	1.39	34.78	0.31	10	>99%
(% w/v)	0.3	1.39	34.65	0.32	12	>99%
	0.6	1.38	34.38	0.32	14	>99%
	0.9	1.38	34.47	0.33	14	>99%
	1.2	1.36	34.03	0.33	14	>99%
	1.5	1.36	34.10	0.33	14	>99%
Coating time	5	1.38	34.53	0.32	10	>99%
(min)	10	1.38	34.38	0.33	14	>99%
	15	1.37	34.20	0.34	14	>99%
	20	1.36	33.73	0.35	14	>99%
	30	1.34	34.30	0.37	14	>99%
Cell loading	6.90	1.10	33.24	0.23	12	>99%
(mg-dw cells/	10.34	1.62	33.46	0.35	16	>99%
g-ww catalyst)	13.79	2.18	33.56	0.46	21	>99%
	17.24	2.79	34.66	0.60	25	>99%
	20.69	3.05	32.04	0.66	25	>99%

Conditions: 8 mL TEA-HCl buffer (100 mmol/L, pH 5.0) containing 130 mmol/L of isopropanol and 5.0 mmol/L of 4′-chloroacetophenone, 2.76 g immobilized beads, T = 30°C, 160 rpm.
^a Immobilization perameters were initially: chitosan pH, 3.89; chitosan concentration 1.0% w/v; coating time 15 min; cell loading 8.82 (mg-dw cells/g-ww cat). Individual immobilization perameters were then optimized in the order shown in the table. As each parameter was optimized, it was fixed at the optimal value indicate during optimization of subsequent parameters. Values chosen as optimal are shown in bold in the table. During optimization of alginate concentration it appeared that the best performance was between 2 and 3% wt/v alginate and so a concentration of 2.5% was chosen as optimal.
^b The reaction rate during the first cycle.
^c The specific activity during the first cycle.
^d The number of cycles achieved whilst maintaining the yield at 120 min reaction time at ≥50%.

ISSN: 1475-2859