Catalytic Properties of rPichia/lip Lipase Adsorbed on Carbon Nanotubes in the Low-Temperature Synthesis of Esters

The recombinant r Pichia /lip lipase was immobilized by adsorbing the enzyme on aggregated carbon nanotubes (CNTs), unmodified, or doped with nitrogen (N-CNTs). Heterogeneous biocatalysts prepared in this way were investigated in the reaction of the low-temperature synthesis of esters proceeding in organic solvents at room temperature. We studied the effect of the texture and morphology of the CNTs, as well as the nitrogen concentration in doped N-CNTs, on the catalytic properties of immobilized lipase, such as activity, specificity, and stability. The activity of biocatalysts and the specific activity of the adsorbed enzyme increased by 1.5–1.6 times with an increase in the concentration of nitrogen introduced into the CNTs (2 and 5 wt % of nitrogen). When studying the specificity of the esterification of saturated fatty acids (heptanoic, stearic) with aliphatic alcohols ( n -butanol, n -hexadecanol), the maximum rate was observed in the synthesis of n -butyl heptanoate. The prepared biocatalysts were highly stable in the batch process of the low-temperature synthesis of esters, while retaining at least 80–85% of the activity of the conditioned biocatalysts for 36 reaction cycles (720 h).