CHEMICAL-REACTIVITY WITHIN A SMECTIC-B LIQUID-CRYSTALLINE PHASE - A MODEL OF ENZYME CATALYSIS

The rearrangement of allyl p-dimethylaminobenzenesulphonate (ASE) to f orm a zwitterionic product has already been recognized as an effective probe for the study of reactivity within the smectic B phase [4,5,19] . We have used deuterium NMR, linear dichroism and X-ray diffraction t echniques to investigate the phase diagram of the ASE-OS35 reaction sy stem. The partitioning of the reactant molecules between coexisting sm ectic, nematic and/or isotropic phases and the structural organization of the smectic catalytic host at different temperatures and reactant guest concentrations have been characterized. On the basis of these me asurements, a model of ASE reactivity in smectic solvents has been dev eloped. The reaction takes place provided that coexisting isotropic or nematic phases are present to act as a reservoir for the ASE reactant molecules prior to their entering the smectic phase; they then react and leave the smectic phase as a zwitterionic product. The analogy bet ween this model of reactivity within smectic phases and the Michaelis- Menten enzyme processes is discussed. This relationship opens up the i ntriguing possibility of designing new experiments with which to inves tigate further liquid crystalline models of enzyme catalysis.