B. Kieran Hodnett

Characteristics of a mesoporous silicate immobilized trypsin bioreactor in organic media

Mesoporous silicates (MPS) materials are attractive materials for immobilizing proteins/enzymes because of their well ordered structures, large surface areas (up to 1000 m2 g−1), narrow pore size distributions, large pore diameters, and pore volumes. MPS with average pore diameters ranging from 28 to 300 Å were prepared using cationic and nonionic surfactants. The influence of water content, pH, storage, and thermal treatment on the activity of trypsin immobilized onto MPS was investigated. In a range of solvents, the amidolytic activity of immobilized trypsin was higher than that of the lyophilized preparation. Significant increases in kcat/KM occurred in propanol, ethanol, methanol, and formamide of 90, 62, 45 and 26, respectively. The observed increases were primarily a result of substantial increases in kcat.

Oxidation of ABTS by silicate-immobilized cytochrome c in nonaqueous solutions

Cytochrome c can be readily adsorbed onto mesoporous silicates at high loadings of up to 10 mmol g‐1 of silicate. The adsorbed protein retains its peroxidative activity, with no diffusional limitations being observed. The protein can be adsorbed onto the external surface of the silicate or, provided that the pore diameter is sufficiently large, into the channels. In aqueous buffer, the catalytic activity of the adsorbed protein (for the oxidation of ABTS) decreased with increasing temperature, with the decrease being less marked for cytochrome c held within the silicate channels. Similar results were obtained in 95% methanol. Analysis of kinetic data showed that significant increases in kcat/KM occurred in methanol, ethanol, and formamide, with slight decreases occurring in 1‐methoxy‐2‐propanol. The observed increases were primarily a result of substantial increases in kcat, while the results in 1‐methoxy‐2‐propanol can be ascribed to increases in KM. Resonance Raman spectroscopy indicated that the structure of the heme environment of the adsorbed protein was essentially unchanged, in aqueous buffer and in the nonaqueous solvents, methanol, 1‐methoxy‐2‐propanol, and ethanol. In addition, Raman spectra of the lyophilized protein indicated that there were no apparent changes in the heme structure.

Epitaxial growth of polymorphic systems: The case of sulfathiazole

The creation of composite crystals formed by the epitaxial interaction between differing polymorphs of sulfathiazole (forms II and IV) has been reported through the experimental growth from ethanol. The intermolecular interaction between the crystal phases was calculated by application of the differential evolution global optimisation algorithm. This indicates that the interaction between form IV and form II is greater than that between form IV and itself, but less than that between form II and itself. Thus from the initial nucleation of form IV the creation of form II through mismatching of the growth units would be favoured leading the growth of form II. This mechanism explains the structure of the observed crystals with an inner layer of form IV surrounded by a shell of form II.