Mesoporous enzyme-immobilized material

One of the most promising applications of enzyme-immobilized mesoporous materials is as microscopic reactors. Galameau et al. investigated the effect of mesoporous silica structures and their surface natures on the activity of immobilized lipases [199]. Too hydrophilic (pure silica) or too hydrophobic (butyl-grafted silica) supports are not appropriate for the development of high activity for lipases. An adequate hydrophobic/hydrophilic balance of the support, such as a supported-micelle, provides the best route to enhance lipase activity. They also encapsulated the lipases in sponge mesoporous silicates, a new procedure based on the addition of a mixture of lecithin and amines to a sol-gel synthesis to provide pore-size control. 

Porous polymer materials, especially in particulate form, are of interest in a diverse range of applications, including controlled drug delivery, enzyme immobilization, molecular separation technology, and as hosts for chemical synthesis [101-104]. MS materials have been used as hosts for the template synthesis of nanoporous polymer replicas through in situ polymerization of monomers in the mesopores [105-108]. 

Relatively little attention has been paid to enzyme immobilization in connection with ionic liquids, and only one systematic study of this subject has appeared [78]. Itoh et al. studied the effects of the carrier material on PcL in [BMIm][PF6] [79]. The activity of PsL on ceramic Toyonite carriers varied by a factor of 1000 between Toyonite 200M and Toyonite 200A. PsL adsorbed on a methacryloxypropyl-modified mesoporous silica also had a relatively high activity [78]. 

Since the discovery of ordered mesoporous materials, researchers have explored many possible applications that can take advantage of the unique compositional or structural features of mesoporous materials. In addition to apphcations in traditional areas such as catalysis, separation, and ion exchange, new applications that might involve mesoporous materials include stationary phases in HPLC, bio and macromolecular separations, low dielectric constant materials, enzyme immobilization, optical host materials, templates for fabrication of porous carbons, and reactions in confined enviromnents. 

Z. Zhou, M. Hartmann, Progress in enzyme immobilization in ordered mesoporous materials and related applications, Chem. Soc. Rev. 42 (2013) 3894-3912. 

Since Diaz and Balkus first attempted to immobilize enzymes on mesoporous MCM-41 [101], several research groups have investigated the influence of various physical factors such as pore size, ambient pH, and ionic strength, on the adsorption efficiency of proteins [102-118]. This research revealed the general tendencies of protein adsorption behavior and outlines for successful immobilization of proteins onto mesoporous materials. As one of the representative examples, systematic... 

For application of protein-immobilized porous materials to sensor fields, use of an electroactive substance as the framework material is important. DeLouise and Miller demonstrated the immobilization of glutathione-S-transferase in electrochemically etched porous silicon films [134], which are attractive materials for the construction of biosensors and may also have utility for the production of immobilized enzyme bioreactors. Not limited to this case, practical applications of nanohybrids from biomolecules and mesoporous materials have been paid much attention. Examples of the application of such hybrids are summarized in a later section of this chapter. 

Addition of third components to nanohybrids of proteins and mesoporous materials sometimes brings advantages in their functions. Kim, Hyeon, and coworkers immobilized enzyme molecules together with magnetite (Fe304) nanoparticles in hierarchically ordered, mesocellular, mesoporous silica (HMMS) (Figure 4.25)... 

In this communication a study of the catalytic behavior of the immobilized Rhizomucor miehei lipase in the transesterification reaction to biodiesel production has been reported. The main drawbacks associated to the current biodiesel production by basic homogeneous catalysis could be overcome by using immobilized lipases. Immobilization by adsorption and entrapment have been used as methods to prepare the heterogeneous biocatalyst. Zeolites and related materials have been used as inorganic lipase supports. To promote the enzyme adsorption, the surface of the supports have been functionalized by synthesis procedures or by post-treatments. While, the enzyme entrapping procedure has been carried out by sol-gel method in order to obtain the biocatalyst protected by a mesoporous matrix and to reduce its leaching after several catalytic uses. 

Immobilized CPO on SB A-16 mesoporous materials The Cs+-doped material incremented the CPO load and its catalytic activity. The Cs+-doped and CPO covalent bonded materials showed a higher enzyme activity compared to physical random immobilization [7]... 

Immobilized CPO in the mesoporous silicate material, mesocellular foam The optimal pH at which the maximum amount of enzyme is immobilized was determined to be pH 3.4, slightly below the isoelectric point of the enzyme [12]... 

In the first report about immobilization of peroxidases on mesoporous materials, Takahashi and coworkers shed light on different parameters that affect the process. Using horseradish peroxidase (HRP) as a model, the authors reported that higher stability to temperature and organic solvent, important variables on industrial processes, were obtained when the size of the pore match the size of the enzyme, in such a way that the encapsulated enzyme was located in a restricted space that slowed down its free movement, preventing its denaturation [4],... 

Several studies have demonstrated the improved stability of peroxidases when they were subjected to immobilization. Akhtar and Husain observed that bitter gourd peroxidase (BGP) was able to remove higher percentage of phenols over a wider range of pH when immobilized on a bioaffinity support [37]. Sasaki et al. highlighted an improvement of thermal stability of MnP immobilized on FSM-16 mesoporous material [59]. Furthermore, some other studies demonstrated a protective effect of peroxidase immobilization against inactivation by H202 [7, 20]. The different behavior of immobilized peroxidases with respect to soluble ones points out the necessity of an optimization of the process conditions when immobilized enzyme is used. Nevertheless, the possible improvement in stability should balance the usual decrease in kinetic rates, due to substrate transfer limitations to reach the enzyme inside the support. 

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