Immobilization of Burkholderia cepacia on Pristine or Functionalized Multi‑Walled Carbon Nanotubes and Application on Enzymatic Resolution of (RS)‑1‑Phenylethanol

Abstract

The immobilization of Burkholderia cepacia lipase (BCL) on pristine or functionalized multiwalled carbon nanotubes (MWCNTs) was studied in the resolution of (RS)-1-phenylethanol. For the functionalization, three treatments were used, these being in H 2 SO 4 /HNO 3 (acid, MWCNTs-A), KOH (basic, MWCNTs-B) or in H 2 O 2 (oxidizing agent, MWCNTs-O). It was found that the pristine or functionalized BCL/MWCNTs resulted in a 3-fold improvement in the conversion and in a 5-fold improvement in ee s (enantiomeric excess of the substrate), when compared with free BCL under the same reaction conditions. This pristine or functionalized BCL/MWCNTs system could be reused for up to 8 times without significant decrease in the catalytic efficiency. Under the optimum conditions (pH of immobilization 6.0, 45 ºC and 25 mg/5 mg pristine or functionalized BCL/MWCNTs), the best results were obtained using BCL immobilized on MWCNTs-A. The simple process of physical adsorption of BCL onto MWCNTs-A has improved the catalytic efficiency when compared with free BCL and an increase in the stability was confirmed by thermogravimetric analysis (TGA).

Biocatalytic asymmetric synthesis of secondary allylic alcohols using Burkholderia cepacia lipase immobilized on multiwalled carbon nanotubes

“…Pristine MWCNTs (20 mg) were dispersed in 20 mL of H 2 SO 4 /HNO 3 (3.0 mol L −1 ) (1:1); then the mixture was refluxed for 6 h. The solution was centrifugated (3000 rpm) and washed with a solution of water/ethanol (1:1 v/v) until pH 7.0. Subsequently, the functionalized nanotubes (MWCNTs‐COOH) were dried overnight in an oven at 50°C 19 …”

“…( R,S )‐( E )‐4‐Phenyl‐3‐buten‐2‐yl acetate ( 6 ) was synthesized using the methodology described by Dias et al 19 Acetic anhydride (0.92 mL, 10 mmol), ( R,S )‐( E )‐4‐phenyl‐3‐buten‐2‐ol ( 4 ) (0.74 mL, 5 mmol), and sulfuric acid (1%) were dissolved in dichloromethane (30 mL). This solution was refluxed for 24 h. The reaction mixture was cooled to room temperature and washed with sodium bicarbonate (1 mol L −1 ) (40 mL) and then with water (40 mL).…”

“…Additionally, lipases are generally used in EKR in their immobilized form, which improves their performance, stability, and resistance to a wide range of pH, temperature, and organic solvents. Moreover, through immobilization, the enzyme can be easily recovered and used in successive catalytic cycles, making the process less expensive and environmentally friendly 19–25 …”

“…The functionalization of the defective sites can be done using oxidizing acids (a mixture of nitric and sulfuric acid), perchloric acid, or sodium hydroxide to generate the surface oxygencontaining functional groups, like carboxylic groups (ÀCOOH) or hydroxyl groups (ÀOH). 19,26,27,37,38 Another underexplored method of functionalization of MWCNTs is the insertion of amine groups [ÀNH 2 -(CH 2 ) 3 -SiÀ] through silanization using 3-aminopropyltriethoxysilane. The advantage of this method is that 3-aminopropyltriethoxysilane readily reacts with the hydroxyl groups on the nanotube surface and improves the compatibility of the support with the enzyme.…”

“…The functionalization generally occurs via oxidation in defective sites of MWCNTs, which are produced naturally during their synthesis and contain disordered structures and noncrystalline carbon and are present on their walls, tips, and surfaces. The functionalization of the defective sites can be done using oxidizing acids (a mixture of nitric and sulfuric acid), perchloric acid, or sodium hydroxide to generate the surface oxygen‐containing functional groups, like carboxylic groups (−COOH) or hydroxyl groups (−OH) 19,26,27,37,38 …”