3626 cm −1 due to the stretching of the cations and hydroxyls groups from the octahedral sheet .
2855 cm −1 , which appeared in the IR signal of the S-MMT nanofiller, indicate the existence of organic surfactant that related to intermolecular attractions between the adjacent alkyl chain (dimethyl dialkyl amine) in the S-MMT inter-galleries, while the peak at
1464 cm −1 was attributed to the quaternary ammonium salt that produced the vibration through the –CH2 bending mode. This indicates the intercalation of the organic surfactant molecules between the silicate layers in the S-MMT nanofiller. However, these three peaks (
1464 cm −1 ) were absent in the spectra peak of Bent (Figure 1b,c). Hence, this proved that the Bent nanofiller did not undergo surface modification with any organic compound. The bands at
1646 cm −1 (S-MMT) and
1636 cm −1 (Bent) were due to the bending in-plane vibration of the hydroxyl group. For Bent, a broad band also appeared at
3389 cm −1 due to hydroxyl stretching vibration assigned to the adsorption of the water molecules on the clay surfaces. Furthermore, the presence of water molecules could also be confirmed by the deformation peak at
1636 cm −1 (Figure 1d) [32,33]. These peaks were more intense in the IR signal of Bent when benchmarked with those of S-MMT. This was due to the hydrophilic characteristics of the Bent nanoclay.
1001 cm −1 , was associated with the stretching vibrations of the Si-O group, located in tetrahedral silica sheets. The bands at
880 cm −1 could be attributed to Al-Al-OH and Al-Fe-OH of bending vibration, respectively , while the IR bands at
698 cm −1 represented the quartz admixtures present in the sample. A more intense band at
793 cm −1 for Bent was attributed to a platy form of disordered tridymite, while a strong band at
Immobilised enzymes, the pros and cons of their use in large industrial processes are reviewed.
Parameters for economically viable biocatalytic processes: recyclability, enzyme selectivity and reaction turnover are discussed.
Large-scale applications of immobilized enzymes in the food, chemical, pharmaceutical, cosmetic and medical device industries are reported.
The use of immobilized enzymes in the industrial manufacture of foodstuffs, chiral API’s and specialty chemicals is described.
The use of immobilized urease and lipase in medical devices is described, enzymatic biosensors being also included.
The use of immobilized enzymes is now a routine process for the manufacture of many industrial products in the pharmaceutical, chemical and food industry. Some enzymes, such as lipases, are naturally robust and efficient, can be used for the production of many different molecules and have a wide range of industrial applications thanks to their broad selectivity. As an example, lipase from Candida antarctica (CalB) has been used by BASF to produce chiral compounds, such as the herbicide Dimethenamide-P, which was previously made chemically. The use of the immobilized enzyme has provided significant advantages over a chemical process, such as the possibility to use equimolar concentration of substrates, obtain an enantiomeric excess > 99%, use relatively low temperatures (< 60 °C) in organic solvent, obtain a single enantiomer instead of the racemate as in the chemical process and use a column configuration that allows dramatic increases in productivity. This process would not have been possible without the use of an immobilized enzyme, since it runs in organic solvent .
Some more specific enzymes, like transaminases, have required protein engineering to become suitable for applications in production of APIs (Active Pharmaceutical Ingredients) in conditions which are extreme for a wild type enzyme. The process developed by Merck for sitagliptin manufacture is a good example of challenging enzyme engineering applied to API manufacture. The previous process of sitagliptin involved hydrogenation of enamine at high pressure using a rhodium-based chiral catalyst. By developing an engineered transaminase, the enzymatic process was able to convert 200 g/l of prositagliptin in the final product, with e.e. >99.5% and using an immobilized enzyme in the presence of DMSO as a cosolvent .
For all enzymes, the possibility to be immobilized and used in a heterogeneous form brings important industrial and environmental advantages, such as simplified downstream processing or continuous process operations. Here, we present a series of large-scale applications of immobilized enzymes with benefits for the food, chemical, pharmaceutical, cosmetics and medical device industries, some of which have been scarcely reported on previously.
In general, all enzymatic reactions can benefit from the immobilization, however, the final choice to use them in immobilized form depends on the economic evaluation of costs associated with their use versus benefits obtained in the process. It can be concluded that the benefits are rather significant, since the use of immobilized enzymes in industry is increasing.