Comparative selectivities of immobilized lipases from Pseudomonas cepacia and Candida antarctica (fraction B) for esterification reactions with glycerol and glycerol analogues in organic media

Esterification reaction selectivity in homogeneous organic media was evaluated for Candida antarctica B and Pseudomonas cepacia lipases toward members of an homologous series of even carbon number, saturated n-fatty acids (FAs) of 4–16 carbons (C4–C16), glycerol, and glycerol analogues ( n-propanol, isopropanol, 1,2-, and 1,3-propanediols). Dual FA optima were observed in almost all reaction mixtures, with C. antarctica and P. cepacia lipases generally favoring C10/C6 and C8/C16, respectively. Several explanations are offered to account for multiple FA optima. Reaction selectivity toward FAs was more influenced by steric than electronic features of FA substrates. Relative selectivity and discriminatory power among the series of FAs was modulated by the specific alcohol acceptor used. This may be founded on partial sharing of binding pockets by alcohol and FA co-substrates. Evidence was obtained that implicates the sn-2 alcohol functional group as being a determinant of FA selectivity and lipase discriminatory power.