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.     

Surface hydrophobicity modulates the operation of actomyosin-based dynamic nanodevices

We studied the impact of surface hydrophobicity on the motility of actin filaments moving on heavy-meromyosin (HMM)-coated surfaces. Apart from nitrocellulose (NC), which is the current standard for motility assays, all materials tested are good candidates for microfabrication: hydrophilic and hydrophobic glass, poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBuMA), and a copolymer of O-acryloyl acetophenone oxime with a 4-acryloyloxybenzophenone (AAPO). The most hydrophilic (hydrophilic glass, contact angle 35 degrees) and the most hydrophobic (PtBuMA, contact angle 78 degrees) surfaces do not maintain the motility of actin filaments, presumably because of the low density of adsorbed HMM protein or its high levels of denaturation, respectively. The velocity of actin filaments presents higher values in the middle of this "surface hydrophobicity motility window" (NC, PMMA), and a bimodal distribution, which is more apparent at the edges of this motility window (hydrophobic glass and AAPO). A molecular surface analysis of HMM and its S1 units suggests that the two very different, temporally separated conformations of the HMM heads could exacerbate the surface-modulated protein behavior, which is common to all microdevices using surface-immobilized proteins. An explanation for the above behavior proposes that the motility of actin filaments on HMM-functionalized surfaces is the result of the action of three populations of motors, each in a different surface-protein conformation, that is, HMM with both heads working (high velocities), working with one head (low velocities), and fully denatured HMM (no motility). It is also proposed that the molecularly dynamic nature of polymer surfaces amplifies the impact of surface hydrophobicity on protein behavior. The study demonstrates that PMMA is a good candidate for the fabrication of future actomyosin-driven dynamic nanodevices because it induces the smoothest motility of individual nano-objects with velocities comparable with those obtained on NC.     

Immobilization of anti-CD31 antibody on electrospun poly(ɛ-caprolactone) scaffolds through hydrophobins for specific adhesion of endothelial cells

Hydrophilicity improvement and bioactive surface design of poly(?-caprolactone) (PCL) grafts are of key importance for their application in tissue engineering. Herein, we develop a convenient approach for achieving stable hydrophilic surfaces by modifying electrospun PCL grafts with a class II hydrophobin (HFBI) coating. Static water contact angles (WCA) demonstrated the conversion of the PCL grafts from hydrophobic to hydrophilic after the introduction of amphiphilic HFBI. ATR-FTIR and XPS confirmed the presence of self-assembled HFBI films on the surface of the PCL nanofibers. The biocompatibility of the HFBI-modified PCL grafts was evaluated by cell proliferation in vitro, and by arteriovenous shunt (AV shunt) experiments ex vivo. Anti-CD31 antibody, which is specific for endothelial cells (ECs), was subsequently immobilized on the HFBI-coated PCL scaffolds through protein-protein interactions. This bioactive PCL graft was found to promote the attachment and retention of endothelial cells. These results suggest that this stepwise strategy for introducing cell-specific binding molecules into PCL scaffolds may have potential for development of vascular grafts that can endothelialize rapidly in vivo.     

Fibronectin displacement at polymer surfaces

The interactions of fibronectin with thin polymer films are studied in displacement experiments using human serum albumin. Fibronectin adsorption and exchange on two different maleic anhydride copolymer surfaces differing in hydrophobicity and surface charge density have been analyzed by quartz crystal microbalance and laser scanning microscopy with respect to adsorbed amounts, viscoelastic properties, and conformation. Fibronectin is concluded to become attached onto hydrophilic surfaces as a "softer", less rigid protein layer, in contrast to the more rigid, densely packed layer on hydrophobic surfaces. As a result, the fibronectin conformation is more distorted on the hydrophobic substrates together with remarkably different displacement characteristics in dependence on the adsorbed fibronectin surface concentration and the displacing albumin solution concentration. While the displacement kinetic remains constant for the strongly interacting surface, an acceleration in fibronectin exchange is observed for the weakly interacting surface with increasing fibronectin coverage. For displaced amounts, no change is determined for the hydrophobic substrate, in contrast to the hydrophilic substrate with a decrease of fibronectin exchange with decreasing coverage leading finally to a constant nondisplaceable amount of adsorbed proteins. Furthermore, the variation of the albumin exchange concentration reveals a stronger dependence of the kinetic for the weakly interacting substrate with higher rates at higher albumin concentrations.     

Effect of surface hydrophobicity/hydrophilicity of mesoporous supports on the activity of immobilized lipase

Taking advantage of the virtue of hydrophilic surface, lipase was firstly immobilized on SBA-15 as a support. Then the surface of the SBA-15 with enzyme entrapped inside the channels was modified by grafting with organic moieties. It has been found that the silylation with n-decyltrimethoxysilane (DE) and 3-(trimethoxysilyl)propyl methacrylate (MA) following the lipase immobilization increases the surface hydrophobicity. But the surface modified by MA shows more hydrophilicity than that modified by DE. The activity assay indicates that the hydrolytic activity for the hydrolysis of insoluble or partly soluble substrates increases with enhanced surface hydrophobicity.     

The Flo11p-deficient Saccharomyces cerevisiae strain background S288c can adhere to plastic surfaces

The effects of four types of plastic surfaces and four pre-incubation media, containing high/low glucose and +/- amino acids, on adhesion of Saccharomyces cerevisiae BY4742 wild type and Deltaflo11 mutant (strain background S288c) were investigated. No difference in adhesive ability between the two yeast strains was observed in any of our experiments, thus confirming that FLO11 is not operational in the S. cerevisiae S288c strain background. The adhesive abilities of both yeast strains depended on the plastic type and pre-incubation conditions. The poorest adhesion was observed on hydrophilic polystyrene, whereas hydrophobic polystyrene resulted in moderate adhesion. The best adhesion of both yeast strains was observed on polystyrene surfaces with combined hydrophilic/hydrophobic domains. When amino acids were present in the pre-incubation media, lack of glucose increased the cell surface hydrophobicity and enhanced the adhesion to all four types of polystyrene. Lack of amino acids in the pre-incubation media increased the cell surface hydrophobicity and enhanced the adhesion especially to polystyrene surfaces with combined hydrophilic/hydrophobic domains. Our results suggest that glucose and amino acid starvation induces other genes than FLO11 in S. cerevisiae S288c coding for hydrophobic cell surface constituents with adhesive properties to especially moderately hydrophobic plastic surfaces.     

Catalytic activity of lipase immobilized onto ultrathin films of cellulose esters

Ultrathin (approximately 2.0 nm) films of cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) supported on Si wafers have been prepared by adsorption and characterized by means of ellipsometry, atomic force microscopy (AFM), and contact angle measurements. CA, CAP, and CAB ultrathin films were characterized in air just after their formation and after annealing under reduced pressure at temperature higher than the corresponding melt temperature. Upon annealing, CA, CAP, and CAB ultrathin films became smoother and more hydrophobic, evidencing molecular reorientation at the solid-air interface. CA, CAP, and CAB films were used as supports for the immobilization of lipase. The adsorption of lipase onto annealed films was more pronounced than that onto untreated films, showing the strong affinity of lipase for the more hydrophobic substrates. Enzymatic activity was evaluated by a standard procedure, namely, (spectrophotometric) measurement of p-nitrophenol, the product formed from the hydrolysis of p-nitrophenyl dodecanoate (p-NPD). Lipase immobilized onto hydrophobic films exhibited higher activity than that of free lipase and could be recycled three times while retaining relatively high activity (loss of ca. 30% of original enzymatic activity). The effect of storing time on the activity of immobilized lipase was studied. Compared with free lipase, that immobilized onto more hydrophobic films retained 70% activity after 1 month. More importantly, the latter level of activity is similar to that of free lipase. However, lipase immobilized onto more hydrophilic films retained 50% and 30% activity after 20 and 30 days, respectively. These results are explained in terms of surface wettability and the contribution of the interactions between the polar residues of lipase and the glucopyranosyl moieties of cellulose ester to maintain the natural conformation of immobilized enzyme.     

Molecular explanation for why talc surfaces can be both hydrophilic and hydrophobic

While individual water molecules adsorb strongly on a talc surface (hydrophilic behavior), a droplet of water beads up on the same surface (hydrophobic behavior). To rationalize this dichotomy, we investigated the influence of the microscopic structure of the surface and the strength of adhesive (surface-water) interactions on surface hydrophobicity. We have shown that at low relative humidity, the competition between adhesion and the favorable entropy of being in the vapor phase determines the surface coverage. However, at saturation, it is the competition between adhesion and cohesion (water-water interactions) that determines the surface hydrophobicity. The adhesive interactions in talc are strong enough to overcome the unfavorable entropy, and water adsorbs strongly on talc surfaces. However, they are too weak to overcome the cohesive interactions, and water thus beads up on talc surfaces. Surprisingly, even talc-like surfaces that are highly adhesive do not fully wet at saturation. Instead, a water droplet forms on top of a strongly adsorbed monolayer of water. Our results imply that the interior of hydrophobic zeolites suspended in water may contain adsorbed water molecules at pressures much lower than the intrusion pressure.     

Adsorption and activity of Thermomyces lanuginosus lipase on hydrophobic and hydrophilic surfaces measured with dual polarization interferometry (DPI) and confocal microscopy

The adsorption and activity of Thermomyces lanuginosus lipase (TLL) was measured with dual polarization interferometry (DPI) and confocal microscopy at a hydrophilic and hydrophobic surface. In the adsorption isotherms, it was evident that TLL both had higher affinity for the hydrophobic surface and adsorbed to a higher adsorbed amount (1.90 mg/m²) compared to the hydrophilic surface (1.40–1.50 mg/m²). The thickness of the adsorbed layer was constant (3.5 nm) on both surfaces at an adsorbed amount >1.0 mg/m², but decreased on the hydrophilic surface at lower surface coverage, which might be explained by partially unfolding of the TLL structure. However, a linear dependence of the refractive index of the adsorbed layer on adsorbed amount of TLL on C18 surfaces indicated that the structure of TLL was similar at low and high surface coverage. The activity of adsorbed TLL was measured towards carboxyfluorescein diacetate (CFDA) in solution, which upon lipase activity formed a fluorescent product. The surface fluorescence intensity increase was measured in a confocal microscope as a function of time after lipase adsorption. It was evident that TLL was more active on the hydrophilic surface, which suggested that a larger fraction of adsorbed TLL molecules were oriented with the active site facing the solution compared to the hydrophobic surface. Moreover, most of the activity remained when the TLL surface coverage decreased. Earlier reports on TLL surface mobility on the same surfaces have found that the lateral diffusion was highest on hydrophilic surfaces and at low surface coverage of TLL. Hence, a high lateral mobility might lead to a longer exposure time of the active site towards solution, thereby increasing the activity against a water-soluble substrate.     

Lipase-catalyzed reactions at different surfaces

Starting from gold chips, we have tailor-made three surfaces by the self-assembly monolayer technique: one entirely hydrophobic, one hydrophobic with dispersed carboxyl groups, and one hydrophilic, containing hydroxyl groups. Rhizomucor miehei lipase has been adsorbed to the hydrophobic and the hydrophilic surfaces and covalently bound to the surface containing carboxyl groups. The adsorption of two substrates-capric acid (decanoic acid) and monocaprin-on the lipase-covered surfaces was monitored by the surface plasmon resonance (SPR) technique. Biocatalysis was also performed in the SPR instrument by circulating a solution of the substrate, dissolved in an 85:15 water-glycerol mixture at a(w) = 0.81, through the instrument, thus exposing the capric acid or the monocaprin to the lipase-covered surfaces. The product composition was found to depend on the type of surface used. Lipase adsorbed at the hydrophilic surface favored hydrolysis, and capric acid was the main product formed when monocaprin was used as substrate. Lipase adsorbed at a hydrophobic surface and, in particular, lipase covalently bound to a hydrophobic surface favored condensation. More dicaprin than capric acid was formed in experiments with monocaprin as the substrate. Reactions performed outside the SPR instrument showed that small amounts of triglyceride were also formed under these conditions. We believe that this work constitutes the first example of the SPR instrument being used for in-situ biotransformation.     

Enzyme Entrapped in Polymer‐Modified Nanopores: The Effects of Macromolecular Crowding and Surface Hydrophobicity

Macromolecular crowding is an ubiquitous phenomenon in living cells that significantly affects the function of enzymes in vivo. However, this effect has not been paid much attention in the research of the immobilization of enzymes onto mesoporous silica. Herein, we report the combined effects of macromolecular crowding and surface hydrophobicity on the performance of an immobilized enzyme by accommodating lipase molecules into a series of mesoporous silicas with different amounts of inert poly(methacrylate) (PMA) covalently anchored inside the nanopores. The incorporation of the PMA polymer into the nanopores of mesoporous silica enables the fabrication of a crowded and hydrophobic microenvironment for the immobilized enzyme and the variation in polymer content facilitates an adjustment of the degree of crowding and surface properties of this environment. Based on this system, the catalytic features of immobilized lipase were investigated as a function of polymer content in nanopores and the results indicated that the catalytic efficiency, thermostability, and reusability of immobilized lipase could all be improved by taking advantage of the macromolecular crowding effect and surface hydrophobicity. These findings provide insight into the possible functions of the macromolecular crowding effect, which should be considered and integrated into the fabrication of suitable mesoporous silicas to improve enzyme immobilization.     

How to make the Cassie wetting state stable?

Wetting of rough hydrophilic and hydrophobic surfaces is discussed. The stability of the Cassie state, with air trapped in relief details under the droplet, is necessary for the design of true superhydrophobic surfaces. The potential barrier separating the Cassie state and the Wenzel state, for which the substrate is completely wetted, is calculated for both hydrophobic and hydrophilic surfaces. When the surface is hydrophobic, the multiscaled roughness of pillars constituting the surface increases the potential barrier separating the Cassie and Wenzel states. When water fills the hydrophilic pore, the energy gain due to the wetting of the pore hydrophilic wall is overcompensated by the energy increase because of the growth of the high-energetic liquid-air interface. The potential barrier separating the Cassie and Wenzel states is calculated for various topographies of surfaces. Structural features of reliefs favoring enhanced hydrophobicity are elucidated.     

In situ conformational analysis of fibrinogen adsorbed on Si surfaces

Fibrinogen is a major plasma protein. Previous investigations of structural changes of fibrinogen due to adsorption are mostly based on indirect evidence after its desorption, whereas our measurements were performed on fibrinogen in its adsorbed state. Specific enzyme-linked immunosorption experiments showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. Atomic force microscopy (AFM) investigations revealed the trinodular shape of fibrinogen molecules adsorbed on hydrophilic surfaces, whereas all of the molecules appeared globular on hydrophobic surfaces. The distribution of secondary structures in adsorbed fibrinogen was quantified by in situ Fourier-transform infrared (FTIR) analysis. Substrates of identical chemical bulk composition but different surface hydrophobicity permit direct comparison among them. Adsorption properties of fibrinogen are different for each degree of hydrophobicity. Although there is some increase of turn structure and decrease of β-sheet structure, the secondary structure of adsorbed fibrinogen on hydrophilic surface turned out to be rather similar to that of the protein in solution phase with a major -helix content. Hydrophilic surfaces exhibit superior blood compatibility as required for medical applications.     

Molecular dynamics simulation study of xyloglucan adsorption on cellulose surfaces: effects of surface hydrophobicity and side-chain variation

The effect of surface hydrophobicity and side-chain variation on xyloglucan adsorption onto cellulose microfibrils (CMF) is investigated via molecular dynamics simulations. A molecular model of CMF with (100), (010), (1–10), (110) and (200) crystal faces was built. We considered xylogluco-oligosaccharides (XGO) with three repeating units, namely (XXXG)_3, (XXLG)₃, and (XXFG)₃ (where each (1,4)-β-d-glucosyl residue in the backbone is given a one-letter code according to its substituents: G = β-d-Glc; X = α-d-Xyl-(1,6)-β-d-Glc; L = β-d-Gal-(1,2)-α-d-Xyl-(1,6)-β-d-Glc; F = α-l-Fuc-(1,2)-β-d-Gal-(1,2)-α-d-Xyl-(1,6)-β-d-Glc). Our work shows that (XXXG)₃ binds more favorably to the CMF (100) and (200) hydrophobic surfaces than to the (110), (010) and (1–10) hydrophilic surfaces. The origin of this behavior is attributed to the topography of hydrophobic CMF surface, which stabilizes (XXXG)₃ in flat conformation. In contrast, on the rough hydrophilic CMF surface (XXXG)₃ adopts a less favorable random-coil conformation to facilitate more hydrogen bonds with the surface. Extending the xyloglucan side chains from (XXXG)₃ to (XXLG)₃ hinders their stacking on the CMF hydrophobic surface. For (XXFG)₃, the interaction with the hydrophobic surface is as strong as (XXXG)₃. All three XGOs have similar binding to the hydrophilic surface. Steered molecular dynamics simulation was performed on an adhesive model where (XXXG)₃ was sandwiched between two CMF hydrophobic surfaces. Our analysis suggests that this sandwich structure might help provide mechanical strength for plant cell walls. Our study relates to a recently revised model of primary cell walls in which extensibility is largely determined by xyloglucan located in limited regions of tight contact between CMFs.     

Flow-focusing generation of monodisperse water droplets wrapped by ionic liquid on microfluidic chips: from plug to sphere

Generating droplets via microfluidic chips is a promising technology in microanalysis and microsynthesis. To realize room-temperature ionic liquid (IL)-water two-phase studies in microscale, a water-immiscible IL was employed as the continuous phase for the first time to wrap water droplets (either plugs or spheres) on flow-focusing microfluidic chips. The IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), could wet both hydrophilic and hydrophobic channel surfaces because of its dual role of hydrophilicity/hydrophobicity and extremely high viscosity, thus offering the possibility of wrapping water droplets in totally hydrophilic (THI), moderately hydrophilic (MHI), and hydrophobic (HO) channels. The droplet shape could be tuned from plug to sphere, with the volume from 6.3 nL to 65 pL, by adding an orifice in the focusing region, rendering the hydrophilic channel surface hydrophobic, and suppressing the Uw/UIL ratio below 1.0. Three different breakup processes were defined and clarified, in which the sub-steady breakup and steady breakup were essential for the formation of plugs and spheric droplets, respectively. The influences of channel hydrophilicity/hydrophobicity on droplet formation were carefully studied by evaluating the wetting abilities of water and IL on different surfaces. The superiority of IL over water in wetting hydrophobic surface led to the tendency of forming small, spheric aqueous droplets in the hydrophobic channel. This IL-favored droplet-based system represented a high efficiency in water/IL extraction, in which rhodamine 6G was extracted from aqueous droplets to [BMIM][PF6] in the hydrophobic orifice-included (HO-OI) channel in 0.51 s.     

柱状假丝酵母脂肪酶同工酶的一种高效液相色谱分离新方法

建立一种“疏水界面亲和色谱”分离柱状假丝酵母脂肪酶同工酶的高效液相色谱新方法。将商品化的CRL经离子交换色谱分离为两个同工酶组分 (CRLA和CRLB) ,在极低离子强度下 ,根据同工酶活性中心周围处于“开放”构象的疏水腔具亲疏水界面的特性 ,用疏水界面亲和色谱在NucleosilC4 (10 μ ,3 0 0 ,2 5 0× 4.60mm)柱上将CRLA和CRLB都分离为 4种同工酶组分。疏水界面亲和色谱非常适用于分离这种结构差异轻微的同工酶组分     

Immobilized Lipase from Candida sp. 99–125 on Hydrophobic Silicate: Characterization and Applications

Lipase Candida sp. 99–125 has been proved to be quite effective in catalyzing organic synthesis reactions and is much cheaper than commercial lipases. Mesoporous silicates are attractive materials for the immobilization of enzymes due to their unique structures. The present research designed a hydrophobic silicate with uniform pore size suitable for the comfort of lipase Candida sp. 99–125 for improving its activity and stability. The resulting immobilized lipase (LP@PMO) by adsorption was employed to catalyze hydrolysis, esterification, and transesterification reactions, and the performances were compared with the lipase immobilized on hydrophilic silicate (LP@PMS) and native lipase. The LP@PMO showed as high activity as that of native lipase in hydrolysis and much increased catalytic activity and reusability in the reactions for biodiesel production. Besides, LP@PMO also possessed better organic stability. Such results demonstrate that immobilization of lipase onto hydrophobic supports is a promising strategy to fabricate highly active and stable biocatalysts for applications.     

The adsorption of lysozymes: A model system

Hen egg white lysozyme was adsorbed onto clean borosilicate glass and n-pentyl silane-treated glass surfaces. Both modified (reductively methylated) and native lysozyme were studied. Variable angle X-ray photoelectron spectroscopy (VA-XPS) suggested differences in the nature of the adsorbed layer depending on substrate properties, as well as on degree of methylation of the protein. Adsorbed film thickness (as measured in the dehydrated state by XPS) ranged from 14 Å on hydrophilic glass to 25 Å on the hydrophobic surface. Degree of surface coverage ranged from 45% on the hydrophobic to 69% on the hydrophilic surface. The results suggest that lysozyme unfolds to a greater extent and covers more surface on the hydrophilic glass, possibly due to strong electrostatic interactions at the pH 7.4 conditions used in the study. An analysis of the surface structure of native hen lysozyme by molecular graphics has also been performed, suggesting that adsorption on hydrophobic surfaces should occur via the hydrophobic patch opposite the enzyme active site cleft. A comparison with human lysozyme has also been made using total internal reflection fluorescence (TIRF) spectroscopy to measure protein adsorption on model surfaces. The two proteins have significantly different interfacial properties.     

Protein immobilization on epoxy-activated thin polymer films: effect of surface wettability and enzyme loading

A series of epoxy-activated polymer films composed of poly(glycidyl methacrylate/butyl methacrylate/hydroxyethyl methacrylate) were prepared. Variation in comonomer composition allowed exploration of relationships between surface wettability and Candida antartica lipase B (CALB) binding to surfaces. By changing solvents and polymer concentrations, suitable conditions were developed for preparation by spin-coating of uniform thin films. Film roughness determined by AFM after incubation in PBS buffer for 2 days was less than 1 nm. The occurrence of single CALB molecules and CALB aggregates at surfaces was determined by AFM imaging and measurements of volume. Absolute numbers of protein monomers and multimers at surfaces were used to determine values of CALB specific activity. Increased film wettability, as the water contact angle of films increased from 420 to 550, resulted in a decreased total number of immobilized CALB molecules. With further increases in the water contact angle of films from 55 degrees to 63 degrees, there was an increased tendency of CALB molecules to form aggregates on surfaces. On all flat surfaces, two height populations, differing by more than 30%, were observed from height distribution curves. They are attributed to changes in protein conformation and/or orientation caused by protein-surface and protein-protein interactions. The fraction of molecules in these populations changed as a function of film water contact angle. The enzyme activity of immobilized films was determined by measuring CALB-catalyzed hydrolysis of p-nitrophenyl butyrate. Total enzyme specific activity decreased by decreasing film hydrophobicity.     

Intensification of lipase performance for long-term operation by immobilization on controlled pore silica in presence of polyethylene glycol

In agreement with previous studies, promising results were obtained when lipase was immobilized on controlled pore silica (CPS) in the presence of polyethylene glycol (PEG 1500). This methodology rendered immobilized derivatives with higher operational stability than those lacking PEG 1500. This article extends the scope of this approach by evaluating the combined effects of PEG concentration and lipase loading employing a multivariate statistical approach. A 2² factorial design with center point was adopted for a full understanding of these effects and their interactions. Conditions that maximize the immobilization yield were different from those attained for the biocatalyst’s operational stability. Possible reasons for the increase in both activity and stability of lipase immobilized on CPS in the presence of PEG 1500 are discussed in light of the influence of surface hydrophilic/hydrophobic balance.