Template enhanced activity of lipase accommodated in siliceous mesocellular foams

Review of large-pore mesostructured cellular foam (MCF) silica and its applications

The unique properties of mesostructured cellular foam (MCF) silica such as, large pore size, continuous three-dimensional (3D) pore system and hydrothermal robust materialallow favorable conditions for incorporating active sites to produce modified MCF silica as catalysts, biocatalysts and adsorbents. Recently, the modified MCF silicas were reported to be efficient catalysts for the hydrogenation of phenylacetylene, heck coupling reaction of arylboronic acid, etc. Biocatalysts derived from modified MCF silicas were found to be a potential to convert glucose to gluconic acid, hydrolysis of N-benzoyl-DLarginine-p-nitroanilide (BAPNA) and casein, transesterification of racemic 1 phenyl- ethanol and hydrolytic, etc. Several separation processes such as CO2 capture and adsorption of L-tryptophan, lysozyme and bovine serum were sucessfully conducted using adsorbents derived from modified MCF silicas. This paper reviews the synthesis of the MCF silica material and the incorporation of active sites or immobilization of enzymes in the MCF silica material. Additionally, a detailed understanding of the characterization of the modified MCF silicas, which includes pore size, active sites/enzymes sizes, amount of active sites/enzymes bound with the MCF silica, was also discussed to obtain their potentialities as catalysts, biocatalysts and adsorbents. The review also describes recent progress on the applications of the MCF silica.

Towards efficient chemical synthesis via engineering enzyme catalysis in biomimetic nanoreactors

Biocatalysis with immobilized enzymes as catalysts holds enormous promise in developing more efficient and sustainable processes for the synthesis of fine chemicals, chiral pharmaceuticals and biomass feedstocks. Despite the appealing potentials, nowadays the industrial-scale application of biocatalysts is still quite modest in comparison with that of traditional chemical catalysts. A critical issue is that the catalytic performance of enzymes, the sophisticated and vulnerable catalytic machineries, strongly depends on their intracellular working environment; however the working circumstances provided by the support matrix are radically different from those in cells. This often leads to various adverse consequences on enzyme conformation and dynamic properties, consequently decreasing the overall performance of immobilized enzymes with regard to their activity, selectivity and stability. Engineering enzyme catalysis in support nanopores by mimicking the physiological milieu of enzymes in vivo and investigating how the interior microenvironment of nanopores imposes an influence on enzyme behaviors in vitro are of paramount significance to modify and improve the catalytic functions of immobilized enzymes. In this feature article, we have summarized the recent advances in mimicking the working environment and working patterns of intracellular enzymes in nanopores of mesoporous silica-based supports. Especially, we have demonstrated that incorporation of polymers into silica nanopores could be a valuable approach to create the biomimetic microenvironment for enzymes in the immobilized state.

Improved catalytic performance of lipase accommodated in the mesoporous silicas with polymer-modified microenvironment

The highly ordered mesoporous silicas with elaborately controlled microenvironment were synthesized via covalent incorporation of long-chain polymers (M(w) = 2000 g mol(-1)) bearing specific hydrophilic/hydrophobic balance. The microenvironment (hydrophilicity/hydrophobicity) of the mesoporous silicas was quantitatively determined by gas adsorption experiments and investigated by lysozyme (LYZ) adsorption. The relative activity of lipase from Pseudomonas cepacia (PCL) encapsulated in the mesoporous silica with moderate hydrophobic microenvironment (hereafter denoted as MHM) reaches up to 281% compared with the free PCL, notably higher than that of PCL accommodated in the mesoporous silicas with hydrophilic or strong hydrophobic microenvironment (20.7-26.2% relative to the free PCL). Moreover, PCL entrapped in the nanochannels with MHM affords the highest initial rate in the kinetic resolution of (R,S)-1-phenylethanol relative to other immobilized PCL. The above results suggest that the MHM could render the active center of PCL entirely exposed to the substrates without interrupting its native conformation in the "interfacial activation". In addition, the nanochannels with MHM could markedly improve the thermal stability of PCL (preserving nearly 60% of the initial activity after the incubation at 70 °C for 2 h) and facilitate the recycling of the immobilized PCL in both aqueous and organic media. Our work demonstrates that the subtle modulation of the microenvironment of mesoporous silicas for enzyme immobilization designates a very promising strategy to fabricate the highly active and stable heterogeneous biocatalysts for industrial application.

Hydrophobic surface induced activation of Pseudomonas cepacia lipase immobilized into mesoporous silica

Lipase from Pseudomonas cepacia (PCL) was successfully immobilized into siliceous mesocellular foams (MCFs) with various hydrophobic/hydrophilic surfaces. The catalytic performances of immobilized PCL were investigated using the transesterification reaction and hydrolytic reaction as model reactions. The specific activity of immobilized PCL greatly increased with enhanced surface hydrophobicity of MCFs, mainly because of lipase activation via hydrophobic interaction between alkyl groups in MCFs and the surface loop (so-called "lid") of PCL. Conformational changes of immobilized PCL were further investigated using time-resolved fluorescence spectroscopy with Trp as an intrinsic probe. When the immobilized PCL was suspended in phosphate buffer, short-lived τ(1) shortened and the fractional contribution of τ(1) significantly increased with the increasing level of surface hydrophobicity of MCFs. These results revealed that Trp(s) of the immobilized PCL were surrounded by a hydrophilic microenvironment because of the fact that the opened "lid" permitted the diffusion of water to the active site cleft. However, for the immobilized PCL suspended in n-hexane, long-lived τ(3) increased with the increase of surface hydrophobicity of MCFs. The reduced interaction between Trp(s) and the surrounding protein matrix was due to intercalation of n-hexane into the active site cleft when the lipase was in open conformation. The above results demonstrated that PCL immobilized into MCF with hydrophobic surfaces were in an activated open conformation.

Amylase-functionalized mesoporous silica thin films as robust biocatalyst platforms

A robust biocatalyst was produced by immobilization of alpha-amylase into mesoporous silica thin films with local order pore structure and 11 nm pore diameter, supported on glass stripes. The activity of this novel catalyst was evaluated for direct starch degradation. The catalyst films show excellent activity, and enhanced stability with respect to free enzyme at extreme conditions of pH and temperature. In addition, they can be easily separated from the reaction media and reused several times.

Improved enzymatic activity of Thermomyces lanuginosus lipase immobilized in a hydrophobic particulate mesoporous carrier

Lipase from Thermomyces lanuginosus has been immobilized within particulate mesoporous silica carriers, with either hydrophilic or hydrophobic supporting surfaces, produced by the newly developed emulsion and solvent evaporation (ESE) method. The Michaelis-Menten model was used to calculate the parameters related to the enzymatic activity of lipase i.e. the turnover number, k(cat), and the specific activity. The specific activity was improved by immobilization of lipase onto the hydrophobic support, compared to lipase immobilized onto the hydrophilic support and lipase free in solution. The enhanced enzymatic activity of lipase onto a hydrophobic support was attributed to interfacial activation of the Thermomyces lanuginosus lipase when it is attached to a hydrophobic surface and a reduced denaturation. Confocal scanning laser microscopy (CLSM) studies, of fluorescently tagged lipase, showed that leakage of the lipase from the mesoporous particles was limited to an initial period of only a few hours. Both the rate and the amount of lipase leached were reduced when the lipase was immobilized onto the hydrophobic support.