An extensive study of lbur types of porous silica supports has been performed, with particular emphasis on their physical and morphological characteristics. These silicas were modified by reacting the surface silanol groups present with either 3-(trimethoxysilyl)propylmethacrylate or 3-glycidoxypropyltrimethoxysilane or 3-aminopropyltriethoxysilane, to produce derivatives with suitable functional groups for further utilisation in the immobilisation of biological compounds. The silicas and their derivatives used were fully characterised with regard t,~ particle size distribution (laser light scattering), specific surface area (BET method), pore size distribution (gas adsorption and mercury porosimetry), density (helium pycnometry), yield of grafting (TGA) and chemical composition (FTIR/DRIFT).

Alcalase 2T, a commercial preparation of Subtilisin Carlsberg, was covalent immobilized onto physiochemically characterized silica supports. The effect of mean pore diameter and surface chemistry on enzyme activity in the hydrolysis of casein has been examined. Two sets of chemically distinct silica supports were used presenting terminal amino (S APTES) or hydroxyl groups (S TESPM-pHEMA). The percentage of immobilized protein was smaller in S APTES (31-39%) than in S TESPM-pHEMA (62-71%), but presented higher total and specific activity. Silicas with large pores (S 1000 , 130/1200 Å) presented higher specific activities relative to those with smaller pore sizes (S 300 , 130/550 Å). The influence of glutaraldehyde concentration and the time of enzyme coupling to the S 1000 S APTES supports was examined. The apparent K m value for the S 1000 S APTES immobilized enzyme is lower than the soluble one which may be explained by the partitioning effects of the substrate. No intraparticle diffusion limitations were observed for the immobilized enzyme and therefore the substrate diffusion does not influence the observable kinetics. Finally, the optimum pH, optimum temperature, thermal stability, operational stability, and storage stability of the immobilized and freely soluble enzymes were compared.

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This work reports the results of structural analysis in novel dextran-acrylate (dexT70-VA) hydrogels generated chemoenzymatically. Porous structure as well as hydrogel surface and interior morphologies were evaluated by mercury intrusion porosimetry (MIP), nitrogen adsorption (NA), and scanning electron microscopy (SEM) analyses, as a function of the degree of substitution (DS), and initial water content used in the preparation of the hydrogel. MIP analysis showed that the overall networks were clearly macroporous with pore sizes ranging from 0.065 to 10 microm. As expected, the average pore size decreased as DS increased and as initial water content decreased. Moreover, the porosity values ranged from 75 up 90%, which shows that these hydrogels present an interconnected pore structure. Nitrogen adsorption analyses showed that the specific surface area of dexT70-VA hydrogels increased either by increasing the DS or by decreasing the initial water content of the hydrogel. SEM results revealed that the surface of hydrogels with lower DS presented either a porous structure or a polymeric "skin" covering the pores, whereas hydrogels with higher DS were totally porous. Furthermore, the interior morphology varied according to the DS and the initial water content of the hydrogels. Finally, the average pore size was also determined from the swelling of hydrogel using a theoretical model developed by Flory-Rehner. The comparison of the SEM and MIP results with the ones obtained by the equilibrium swelling theory of Flory-Rehner shows that this approach highly underestimates the average pore size.

A new process was developed which enables one to obtain surface-modified silica with a high heavy metal ion\ud complexing ability. The synthetic approach is based on grafting of vinyl-terminated macromonomers onto silica via\ud covalent bonding. A proper selection of the macromonomer structure, molecular weight, and molecular weight\ud distribution allows materials to be obtained with a range of desirable properties. The process has been tested on various\ud dispersions (ranging from 35 and 200 pm) of silica particles and two structurally related macromonomers. Native silica\ud and the resulting mixed organic-inorganic products were fully characterized by IR spectroscopy, SEM, yield of grafting\ud (elemental analysis and calcination), density (helium pycnometry), specific surface area (BET method), and pore size (gas\ud adsorption and mercury porosimetry) measurements. It was found that the corresponding polymers are effectively\ud grafted onto the surface; the density, surface area, and pore size of the silica particles decrease with polymer grafting.\ud Preliminary results on metal-ion uptake indicate that polymer-grafted silica exhibits an excellent complexing ability