Chemically surface modified gel (CSMG): An excellent enzyme-immobilization matrix for industrial processes

Phenylboronic Acid and Amino Bifunctional Modified Adsorbent for Quickly Separating Phenolic Acids from Crude Extract of Clerodendranthus spicatus and Evaluation of Their Antioxidant and Hypoglycemic Activities

A novel phenylboronic acid and amino bifunctional modified silica gel (SiO2-NH2-FPBA) was prepared, which was 30-80 μm, had a pore size of 8.69 nm, a specific surface area of 206.89 m2/g, was stable at low temperature, and contained 0.4793 mmol/g of the phenylboronic acid group and 1.6377 mmol/g of the amino group. It was used to develop a rapid separation method for phenolic acids. The results showed that it could adsorb 93.64 mg/g caffeic acid, 89.35 mg/g protocatechuic acid and 79.66 mg/g gallic acid. The adsorption process was consistent with the pseudo-second-order model (R2 > 0.99), and fitted the Langmuir isotherm model well (R2 > 0.99). CH3COOH could effectively desorb phenolic acids (>90%) and did not destroy their structures. When SiO2-NH2-FPBA was added to crude extract of Clerodendranthus spicatus, 93.24% of the phenolic acids could be captured, and twenty-two kinds of phenolic acids were identified by Q Exactive HF LC-MS. Furthermore, the isolated phenolic acids from Clerodendranthus spicatus possessed great DPPH, ABTS, and hydroxyl radicals scavenging activities and ferric reducing power. They also demonstrated effective inhibition of α-amylase and α-glucosidase activities (IC50 = 110.63 ± 3.67 μg/mL and 64.76 ± 0.30 μg/mL, respectively). The findings indicate that SiO2-NH2-FPBA has significant potential in practical applications of separating active constituents from natural resources.

Preparation of a phenylboronic acid and aldehyde bi-functional group modified silica absorbent and applications in removing Cr(vi) and reducing to Cr(iii)

Cr(vi) is a great threat to the ecological environment and human health, so it is urgent to remove Cr(vi) from the environment. In this study, a novel silica gel adsorbent SiO₂-CHO-APBA containing phenylboronic acids and aldehyde groups was prepared, evaluated and applied for removing Cr(vi) from water and soil samples. The adsorption conditions including pH, adsorbent dosage, initial concentration of Cr(vi), temperature and time were optimized. Its ability in removing Cr(vi) was investigated and compared with three other common adsorbents, SiO₂-NH₂, SiO₂-SH and SiO₂-EDTA. Data showed SiO₂-CHO-APBA had the highest adsorption capacity of 58.14 mg g^-1 at pH 2 and could reach adsorption equilibrium in about 3 h. When 50 mg SiO₂-CHO-APBA was added in 20 mL of 50 mg L^-1 Cr(vi) solution, more than 97% of Cr(vi) was removed. A mechanism study revealed that a cooperative interaction of both the aldehyde and boronic acid groups is attributed to Cr(vi) removal. The reducing function was gradually weakened with the consumption of the aldehyde group, which was oxidized to a carboxyl group by Cr(vi). This SiO₂-CHO-APBA adsorbent was successfully used for the removal of Cr(vi) from soil samples with satisfactory results which indicates a good potential in agriculture and other fields.

Two Fe(III)/Eu(III) Salophen complex-based optical sensors for determination of organophosphorus pesticide monocrotophos

Monocrotophos (MP), an organophosphorus pesticide, poses a serious threat to human health, so a rapid and simple technique is needed to detect it. In this study, two novel optical sensors for MP detection were created using the Fe(III) Salophen complex and Eu(III) Salophen complex, respectively. One sensor is an Fe(III) Salophen complex (I-N-Sal), which can bind MP selectively and form a supramolecule, resulting in a strong resonance light scattering (RLS) signal at 300 nm. Under the optimum conditions, the detection limit was 30 nM, the linear range was 0.1-1.1 μM, the correlation coefficient R² = 0.9919, and the recovery rate range was 97.0-103.1%. Interaction properties between the sensor I-N-Sal and MP and the RLS mechanism were investigated using density functional theory (DFT). And another sensor is based on the Eu(III) Salophen complex and 5-aminofluorescein derivatives. The Eu(III) Salophen complex was immobilized on the surface of amino-silica gel (Sigel-NH₂) particles as the solid phase receptor (ESS) of MP and 5-aminofluorescein derivatives as the fluorescent (FL)-labeled receptor (N-5-AF) of MP, which can selectively bind the MP and form a sandwich-type supramolecule. Under the optimum conditions, the detection limit was 0.4 μM, the linear range was 1.3-7.0 μM, the correlation coefficient R² = 0.9983, and the recovery rate range was 96.6-101.1%. Interaction properties between the sensor and MP were investigated by UV-vis, FT-IR, and XRD. Both sensors were successfully applied to the determination of MP content in tap water and camellia.

Mesocellular Silica Foams (MCFs) with Tunable Pore Size as a Support for Lysozyme Immobilization: Adsorption Equilibrium and Kinetics, Biocomposite Properties

The effect of the porous structure of mesocellular silica foams (MCFs) on the lysozyme (LYS) adsorption capacity, as well as the rate, was studied to design the effective sorbent for potential applications as the carriers of biomolecules. The structural (N2 adsorption/desorption isotherms), textural (SEM, TEM), acid-base (potentiometric titration), adsorption properties, and thermal characteristics of the obtained lysozyme/silica composites were studied. The protein adsorption equilibrium and kinetics showed significant dependence on silica pore size. For instance, LYS adsorption uptake on MCF-6.4 support (pore diameter 6.4 nm) was about 0.29 g/g. The equilibrium loading amount of LYS on MCF-14.5 material (pore size 14.5 nm) increased to 0.55 g/g. However, when the pore diameter was larger than 14.5 nm, the LYS adsorption value systematically decreased with increasing pore size (e.g., for MCF-30.1 was only 0.27 g/g). The electrostatic attractive interactions between the positively charged lysozyme (at pH = 7.4) and the negatively charged silica played a significant role in the immobilization process. The differences in protein adsorption and surface morphology for the biocomposites of various pore sizes were found. The thermal behavior of the studied bio/systems was conducted by TG/DSC/FTIR/MS coupled method. It was found that the thermal degradation of lysozyme/silica composites was a double-stage process in the temperature range 165-420-830 °C.

Hydrogen Production from Energy Poplar Preceded by MEA Pre-Treatment and Enzymatic Hydrolysis

The need to pre-treat lignocellulosic biomass prior to dark fermentation results primarily from the composition of lignocellulose because lignin hinders the processing of hard wood towards useful products. Hence, in this work a two-step approach for the pre-treatment of energy poplar, including alkaline pre-treatment and enzymatic saccharification followed by fermentation has been studied. Monoethanolamine (MEA) was used as the alkaline catalyst and diatomite immobilized bed enzymes were used during saccharification. The response surface methodology (RSM) method was used to determine the optimal alkaline pre-treatment conditions resulting in the highest values of both total released sugars (TRS) yield and degree of lignin removal. Three variable parameters (temperature, MEA concentration, time) were selected to optimize the alkaline pre-treatment conditions. The research was carried out using the Box-Behnken design. Additionally, the possibility of the re-use of both alkaline as well as enzymatic reagents was investigated. Obtained hydrolysates were subjected to dark fermentation in batch reactors performed by Enterobacter aerogenes ATCC 13048 with a final result of 22.99 mL H₂/g energy poplar (0.6 mol H₂/mol TRS).

Biocatalysts based on nanozeolite-enzyme complexes: Effects of alkoxysilane surface functionalization and biofuel production using microalgae lipids feedstock

Nanozeolites with different crystallographic structures (Nano/TS1, Nano/GIS, Nano/LTA, Nano/BEA, Nano/X, and Nano-X/Ni), functionalized with (3-aminopropyl)trimethoxysilane (APTMS) and crosslinked with glutaraldehyde (GA), were studied as solid supports for Thermomyces lanuginosus lipase (TLL) immobilization. Physicochemical characterizations of the surface-functionalized nanozeolites and nanozeolite-enzyme complexes were performed using XRD, SEM, AFM, ATR-FTIR, and zeta potential measurements. The experimental enzymatic activity results indicated that the nanozeolitic supports functionalized with APTMS and GA immobilized larger amounts of enzymes and provided higher enzymatic activities, compared to unfunctionalized supports. Correlations were observed among the nanozeolite surface charges, the enzyme immobilization efficiencies, and the biocatalyst activities. The catalytic performance and reusability of these enzyme-nanozeolite complexes were evaluated in the ethanolysis transesterification of microalgae oil to fatty acid ethyl esters (FAEEs). TLL immobilized on the nanozeolite supports functionalized with APTMS and GA provided the most efficient biocatalysis, with FAEEs yields above 93% and stability during five reaction cycles. Lower FAEEs yields and poorer catalytic stability were found for nanozeolite-enzyme complexes prepared only by physical adsorption. The findings indicated the viability of designing highly efficient biocatalysts for biofuel production by means of chemical modulation of nanozeolite surfaces. The high biocatalyst catalytic efficiency observed in ethanolysis reactions using a lipid feedstock that does not compete with food production is an advantage that should encourage the industrial application of these biocatalysts.

High sucrolytic activity by invertase immobilized onto magnetic diatomaceous earth nanoparticles

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Innovative biocatalyst with good properties to produce invert sugar.

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mDE-APTES-invertase showed 92.5% of residual specific activity.

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High sucrolytic activity (3358 U mg⁻¹ protein) by mDE-APTES-invertase was obtained.

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Remarkable results of thermal and storage stability, and reuse for mDE-APTES-invertase were found.

Invertase immobilized on magnetic diatomaceous earth nanoparticles (mDE-APTES-invertase) with high sucrolytic activity was obtained by an easy and low-cost method. An experimental design was carried out to investigate the best immobilization conditions and it allowed obtaining an immobilized derivative with a residual specific activity equal to 92.5%. Then, a second experimental design selected the mDE-APTES-invertase with higher specific activity in relation to other derivatives reported in the literature (2.42-fold). Thermal and storage stability for immobilized invertase were found to be 35 °C for 60 min (85% retained activity) and 120 days storage period (80% retained activity), respectively. Besides, a residual activity higher than 60% and 50% were observed for mDE-APTES-invertase after reuse in short and long term, respectively. Given the simple and efficient method to obtain an immobilized derivative with high activity, the mDE nanoparticles appear to be a promising matrix for invertase immobilization as well as for other biomolecules.

Enzymes immobilized in mesoporous silica: a physical-chemical perspective

Mesoporous materials as support for immobilized enzymes have been explored extensively during the last two decades, primarily not only for biocatalysis applications, but also for biosensing, biofuels and enzyme-controlled drug delivery. The activity of the immobilized enzymes inside the pores is often different compared to that of the free enzymes, and an important challenge is to understand how the immobilization affects the enzymes in order to design immobilization conditions that lead to optimal enzyme activity. This review summarizes methods that can be used to understand how material properties can be linked to changes in enzyme activity. Real-time monitoring of the immobilization process and techniques that demonstrate that the enzymes are located inside the pores is discussed by contrasting them to the common practice of indirectly measuring the depletion of the protein concentration or enzyme activity in the surrounding bulk phase. We propose that pore filling (pore volume fraction occupied by proteins) is the best standard for comparing the amount of immobilized enzymes at the molecular level, and present equations to calculate pore filling from the more commonly reported immobilized mass. Methods to detect changes in enzyme structure upon immobilization and to study the microenvironment inside the pores are discussed in detail. Combining the knowledge generated from these methodologies should aid in rationally designing biocatalyst based on enzymes immobilized in mesoporous materials.

Ormosil gels doped with engineered catechol 1,2 dioxygenases for chlorocatechol bioremediation

Enzymes entrapped in wet, nanoporous silica gel have great potential as bioreactors for bioremediation because of their improved thermal, chemical, and mechanical stability with respect to enzymes in solution. The B isozyme of catechol 1,2 dioxygenase from Acinetobacter radioresistens and its mutants of Leu69 and Ala72, designed for an increased reactivity toward the environmental pollutant chlorocatechols, were encapsulated using alkoxysilanes and alkyl alkoxysilanes as precursors in varying proportions. Encapsulation of the mutants in a hydrophobic tetramethoxysilane/dimethoxydimethylsilane-based matrix yielded a remarkable 10- to 12-fold enhancement in reactivity toward chlorocatechols. These gels also showed a fivefold increase in relative reactivity toward chlorocatechols with respect to the natural substrate catechol, thus compensating for their relatively low activity for these substrates in solution. The encapsulated enzyme, unlike the enzyme in solution, proved resilient in assays carried out in urban wastewater and bacteria-contaminated solutions mimicking environmentally relevant conditions. Overall, the combination of a structure-based rational design of enzyme mutants, and the selection of a suitable encapsulation material, proved to be a powerful approach for the production and optimization of a potential bioremediation device, with increased activity and resistance toward bacterial degradation.

Enzyme immobilization: an update

Compared to free enzymes in solution, immobilized enzymes are more robust and more resistant to environmental changes. More importantly, the heterogeneity of the immo-bilized enzyme systems allows an easy recovery of both enzymes and products, multiple re-use of enzymes, continuous operation of enzymatic processes, rapid termination of reactions, and greater variety of bioreactor designs. This paper is a review of the recent literatures on enzyme immobilization by various techniques, the need for immobilization and different applications in industry, covering the last two decades. The most recent papers, patents, and reviews on immobilization strategies and application are reviewed.

New biofuel integrating glycerol into its composition through the use of covalent immobilized pig pancreatic lipase

By using 1,3-specific Pig Pancreatic lipase (EC 3.1.1.3 or PPL), covalently immobilized on AlPO(4)/Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%). Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1%) compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses) without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the different results in the Arrhenius parameters (Ln A and Ea). However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture.

Double-receptor sandwich supramolecule sensing method for the determination of ATP based on uranyl-salophen complex and aptamer

In this study, we report a double-receptor sandwich supramolecule sensing method for the determination of adenosine triphosphate (ATP). One receptor is a uranyl-salophen complex which can bind the triphosphate group in ATP selectively, and another is an anti-adenosine aptamer which is a single-stranded oligonucleotide and can recognize the adenosine group in ATP specifically. The uranyl-salophen complex was immobilized on the surface of amino-silica gel particles and used as the solid phase receptor of ATP. The anti-adenosine aptamer was labeled with a fluorescent group and used as the labeled receptor of ATP. In the procedure of ATP detection, ATP was first combined with the solid phase receptor and then conjugated with the labeled receptor to form a sandwich-type supramolecule. The conditions of fabricating solid phase receptor and the influence of manifold variables on the determination were studied. The experimental results demonstrate that the method has a number of advantages such as high selectivity, high sensitivity, good stability and low cost. Under optimal conditions, the linear range for detection of ATP is 0.2-5.0 nmol/mL with a detection limit of 0.037 nmol/mL. The proposed method was successfully applied for the determination of ATP in real samples with the recoveries of 96.8-103.3%.

Response surface analysis of nano-ureases from Canavalia ensiformis and Cajanus cajan

Ureases isolated from leguminous sources, Canavalia ensiformis and Cajanus cajan were immobilized onto gold nanoparticles (nano-ureases). Optimization of the urease immobilization was carried using response surface methodology based on Central Composite Design. Immobilization efficiency of nano-urease from C. ensiformis and C. cajan were found to be 215.10% and 255.92%, respectively. The methodology adopted has deviation of 2.56% and 3.01% with respect to experimental values in case of C. ensiformis and C. cajan, respectively. Nano-urease from C. cajan has broad physico-chemical parameters with pH optimum from 7.1 to 7.3 and temperature optimum from 50 to 70°C. Nano-urease from C. ensiformis has sharp pH and temperature optima at 7.3 and 70°C, respectively. Fourier transform infra-red spectroscopy has revealed involvement of groups viz. amino, glycosyl moiety, etc. in urease immobilization onto gold nano-particles. Transmission and scanning electron micrographs revealed that arrangement of urease onto gold nano-particles from C. ensiformis was uniform while it was localized in case of C. cajan. Nano-urease from C. ensiformis has higher specificity and catalysis toward urea as compared to nano-urease from C. cajan. Nano-ureases from both sources are equally stable for 6 months under dried conditions and can be used for 10 washes.

Kinetics and bioreactor studies of immobilized invertase on polyurethane rigid adhesive foam

A new support, polyurethane rigid adhesive foam (PRAF), which can be used to cover internal surface of metallic tubes, was used to immobilize invertase for application in an enzymatic bioreactor. The kinetic parameters were: Km--46.5±1.9 mM (PRAF-invertase) and 61.2±0.1 mM (free enzyme) and Vmax 42.0±4.3 U/mg protein/min (PRAF-invertase) and 445.3±24.0 U/mg protein/min (free invertase). The PRAF-invertase derivative maintained 50.1% of initial activity (69.17 U/g support) for 8 months (4°C) and was not observed microbial contamination. The bioreactor showed the best production of inverted sugar syrup using up-flow rate (0.48 L/h) with average conversion of 10.64±1.5% h(-1) at feeding rate (D) of 104 h(-1). The operational inactivation rate constant (kopi) and half-life were 1.92×10(-4) min(-1) and 60 h (continue use). The PRAF spray support looks promising as a new alternative to produce immobilized derivatives on reactor surfaces.

Enzyme stabilization and immobilization by sol-gel entrapment

While biocatalysts show tremendous potential for the industrial production of fine chemicals, their integration into large-scale processes has been slow. One of the main reasons for slow acceptance in industry is the inherent instability of the enzymes. Recent developments in bioengineering have shed some light on methods of improving enzyme stability. One method that has been used for many decades, successfully to varying degrees, has been the immobilization of enzymes. To this regards, silica gels have attracted much attention because of the ease of surface functionalization, high surface areas, mechanical and thermal stability, and resistance to both chemical and biological attack. We have previously shown the immobilization of invertase on silica gels with high immobilized activity and significantly improved stability. Here, we provide greater details on the methods for effecting the immobilization.

Degradation of polycyclic aromatic hydrocarbons by free and nanoclay-immobilized manganese peroxidase from Anthracophyllum discolor

Manganese peroxidase (MnP) produced by Anthracophyllum discolor, a Chilean white rot fungus, was immobilized on nanoclay obtained from volcanic soil and its ability to degrade polycyclic aromatic hydrocarbons (PAHs) compared with the free enzyme was evaluated. At the same time, nanoclay characterization was performed. Nanoclay characterization by transmission electronic microscopy showed a particle average size smaller than 100 nm. The isoelectric points (IEP) of nanoclay and MnP from A. discolor were 7.0 and 3.7, respectively, as determined by micro electrophoresis migration and preparative isoelectric focusing. Results indicated that 75% of the enzyme was immobilized on the nanoclay through physical adsorption. As compared to the free enzyme, immobilized MnP from A. discolor achieved an improved stability to temperature and pH. The activation energy (Ea) value for immobilized MnP (51.9 kJ mol(-1)) was higher than that of the free MnP (34.4 kJ mol(-1)). The immobilized enzyme was able to degrade pyrene (>86%), anthracene (>65%), alone or in mixture, and to a less extent fluoranthene (<15.2%) and phenanthrene (<8.6%). Compared to free MnP from A. discolor, the enzyme immobilized on nanoclay enhanced the enzymatic transformation of anthracene in soil. Overall results indicate that nanoclay, a carrier of natural origin, is a suitable support material for MnP immobilization. In addition, immobilized MnP shows an increased stability to high temperature, pH and time storage, as well as an enhanced PAHs degradation efficiency in soil. All these characteristics may suggest the possible use of nanoclay-immobilized MnP from A. discolor as a valuable option for in situ bioremediation purposes.