Carbon monoliths enzyme

Table 3 shows the textural characteristics of three carbon monoliths, two of which were produced by dipcoating a cordierite monolith with a solution of sucrose or PFA and one of which was produced by a CVD process resulting in a CNF coating. These are referred to as Cord-SUC, Cord-PFA, and Cord-CNF, respectively. From a texture analysis, it was concluded that the sucrose-derived carbon is highly porous, with pore diameters in a favorable range (t)q5ically, 11 nm). The PFA-derived carbon was microporous and, as a consequence, not suitable for adsorption of large species, such as enzymes. 

Figure 32 includes results illustrating the performance of lipase/car-bon monolith systems in an acylation reaction. For comparison, the free lipase and a commercial immobilized lipase (Novozyme) were also tested. As expected, in all cases the specific activity of immobilized lipase was foimd to be lower than that of the free enzyme. Such a difference is usually ascribed to conformational changes of the enzyme, steric effects, or denaturation. For the monolithic biocatalysts, the activity of the immobilized catalyst relative to that of the pure enzyme was found to be 30-35%, and for the Novozyme catalyst about 80% in the first rim. However, the Novozyme catalyst underwent significant deactivation, in contrast to the carbon monolith-supported catalysts. The deactivation of the Novozyme catalyst in consecutive runs is probably a consequence of the instability of the support matrix under reaction conditions (101,102). 

Carbon monolith Carbon loading (wt%) Lipase adsorption (mg/gcarbon) Enzyme activity (mmol/s/genzyrne) Overall activity of monolith (pmol/gmonolith )... 

In this example, lipase is immobilized on different carbon monoliths and applied in a transesterification reaction in toluene. The biocatalysts are compared in terms of carrier preparation, enzyme immobilization, and performance. A commercially available immobilized lipase is used as a comparison. A convenient tool to compare monolithic biocatalysts is the monolithic stirrer reactor (MSR), consisting of two monoliths that have the catalyst immobilized on the wall of their channels. These monoliths work as stirrer blades that can easily be removed from the reaction medium, thereby eliminating the need for a filtration step after reaction [37]. 

Several monolithic enzyme biocatalysts were prepared and characterized with carbon coatings consisting of carbonized sucrose, carbonized polyfurfuryl alcohol, and carbon nanofibers. The coated carbon monoliths were also compared with an integral (composite) carbon monolith. A lipase from Candida antarctica was adsorbed on the monolithic supports. Adsorption on carbon coatings can be very effective, depending on the carbon microstructure. For a high lipase loading. 

The use of a monolithic stirred reactor for carrying out enzyme-catalyzed reactions is presented. Enzyme-loaded monoliths were employed as stirrer blades. The ceramic monoliths were functionalized with conventional carrier materials carbon, chitosan, and polyethylenimine (PEI). The different nature of the carriers with respect to porosity and surface chemistry allows tuning of the support for different enzymes and for use under specific conditions. The model reactions performed in this study demonstrate the benefits of tuning the carrier material to both enzyme and reaction conditions. This is a must to successfully intensify biocatalytic processes. The results show that the monolithic stirrer reactor can be effectively employed in both mass transfer limited and kinetically limited regimes. 

A wide range of polymeric materials can be prepared from HIPEs. Polymerisation of the continuous phase yields highly porous cellular polymers with a monolithic structure. These are known as PolyHIPE polymers, and possess a number of unique properties including, in most cases, an interconnected cellular structure and a very low dry-bulk density. Their very high porosity favours their use as supports for catalytic species, precursors for porous carbons and inert matrices for the immobilisation of enzymes and micro-organisms. 

The bulk polymeric format, characterised by highly cross-linked monolithic materials, is still widely used for the preparation of enzyme mimic despite some of its evident drawbacks. This polymerisation method is well known and described in detail in the literature and has often be considered the first choice when developing molecular imprinted catalysts for new reactions. The bulk polymer section is presented in three subsections related to the main topics covered hydrolytic reactions, carbon-carbon bond forming reactions and functional groups interconversion. 

Extensive investigations were performed to determine the potential of carbon-coated monoliths as supports for enzymes. The enzymes were adsorbed on the functionalized supports under ambient conditions, in a recycle reactor in which the liquid was recycled over the support under upflow conditions. A 50 mM phosphate buffer with pH 7 was used as a medium. The protein concentration was determined by using UV-VIS... 

The first report, in 1991, describes the immobilization of carbonic anhydrase. Interestingly, an increase in enzyme activity with the increase of flow rate through the bioreactor was observed. Recently, the immobilization of trypsin was reported. Contrary to the previous work, increased flow rate diminished the extent of protein degradation. In contrast to the previously mentioned experiments, where the immobilized enzyme was used for substrate degradation, the synthesis of polyriboadenylate from ADP was studied by polynucleotide phosphorylase immobilized on a monolithic disk. 

Lozano, P., Garcia-Verdugo, E., Piamtongkam, R., Karbass, N., De Diego, T., Burguete, M.I., Luis, S.V., and Iborra, J.L. (2007) Bioreactors based on monolith-supported ionic liquid phase for enzyme catalysis in supercritical carbon dioxide. Adv. Synth. Catal., 349 (7), 1077-1084. 

Using the reaction rate observed (in moFs m ataiyst) in experiments performed at 150 rpm, the Wheeler-Weisz modulus was calculated for aU monoUths by estimating the layer thickness (L) from the carbon yield. inside the carbon layers was estimated to be 1 to 3 x 10 ° m /s inside the varions carbons. The valnes for are presented in Table 11.5. For 1-Al, consisting mainly of macroporons carbon, it is likely that internal diffusion limitations are present inside the carbon walls (where the lipase is located). This was also indicated by the decreased activity per gram of enzyme for these monoliths (Table 11.5). For ceramic monoliths, all adsorbed enzyme is used effectively (a constant tnmover freqnency for all carbon types), as confirmed by the low valnes for... 

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