Factors affecting catalytic performance in yadh-catalyzed reductions in non-conventional media

The effects of parameters including water content, the amount of celite and the co-factor regeneration system on reduction of benzaldehyde to benzyl alcohol by yeast alcohol dehydrogenase (YADH) immobilized on celite in non-conventional media were investigated. Kinetic parameters (apparent) such as Vmax, Km, and kcar for different organic solvents used (butyl acetate, hexane, heptane and i-octane) were determined. Km values for benzaldehyde increased as the solvent was varied in the following manner: butyl acetate < hexane < i-octane < heptane. The highest Km value (20.26 mmol/L) was noted in heptane and the lowest (3.24 mmol/L) in butyl acetate. The Vmax value in heptane was more than an order of magnitude higher than that in butyl acetate. Catalytic efficiencies (as expressed by kcar/Km) ranged from 0.703 × 10−4 L/mol · s for hexane to 0.171 × 10−4 L/mol · s for butyl acetate. In general, linear relationships were observed between kcar/Km and the following solvent physico-chemical constants: dielectric constant logarithm of the saturated molar solubility of water in the organic solvents, log Sw/o, logarithm of partition coefficient of organic solvent in water/octanol two-phase system, log P, Hildebrand solubility parameter, δ, and solvatochromism of pyridinium-N-phenoxide betaine dye, ET(30).