FACTORS AFFECTING CATALYTIC PERFORMANCE IN YADH-CATALYZED REDUCTIONS IN NONCONVENTIONAL MEDIA

The effects of parameters including water content, the amount of celit e and the co-factor regeneration system on reduction of benzaldehyde t o benzyl alcohol by yeast alcohol dehydrogenase (YADH) immobilized on celite in nonconventional media were investigated. Kinetic parameters (apparent) such as V-max, K-m, and k(cat) for different organic solven ts used (butyl acetate, hexane, heptane and i-octane) were determined. K,values for benzaldehyde increased as the solvent was varied in the following manner: butyl acetate < hexane < i-octane < heptane. The hig hest k(m) value (20.26 mmol/L) was noted in heptane and the lowest (3. 24 mmol/L) in butyl acetate. The V-max value in heptane was more than an order of magnitude higher than that in butyl acetate. Catalytic eff iciencies (as expressed by k(cat)/K-m) ranged from 0.703 x 10(-4) L/mo l . s for hexane to 0.171 x 10-4 L/mol . s for butyl acetate. In gener al, linear relationships were observed between k(cat)/K-m and the foll owing solvent physico-chemical constants: dielectric constant, epsilon , logarithm of the saturated molar solubility of water in the organic solvents, log S-w/o, logarithm of partition coefficient of organic sol vent in water/octanol two-phase system, log P, Hildebrand solubility p arameter, delta, and solvatochromism of pyridinium-N-phenoxide betaine dye, ET(30).