A recent paper in J. Amer Chem Soc (J Kubota et al, 2001, 11115) has attempted to understand how the geometry of absorption of a chiral modifier (eg cinchonidine) on a heterogeneous catalyst can affect the ee of the product. Heterogeneous catalysts are generally preferred in industrial processes because of ease of separation of catalyst from product and for ease of recycling expensive catalysts. When chiral modifiers are added to heterogeneous catalysts (eg Pt), however, performance can be variable and unpredictable depending on small changes in structure or concentration of the modifier, particle size of the metal catalyst, nature of the solvent, or reaction conditions. Thus there are few successful examples - the asymmetric reduction of a-ketoesters is one of these. Now a study using in situ reflection absorption infrared spectroscopy (RAIRS) has shown that the initial concentration of the modifier in solution controls the absorption geometry on the Pt surface and that there is an excellent correlation between the different arrangements and the ee of the product (in the reduction of ethyl pyruvate by hydrogen). The maximum enantioselectivity occurs when cinchora alkaloid to Pt ratio is around 0.1. It is suggested that this is optimum to just cover the surface with a sufficient number of molecules to induce chirality. Any more leads to surface crowding and a change in geometry, causing loss in selectivity. Too few and the surface is not completely covered by chiral modifier.