Cross-linked Aggregates Research Articles

Embedding inulin fructotransferase from Arthrobacter aurescens into novel curdlan-based mesoporous silica microspheres for efficient production of Difructose Anhydride III

A novel strategy was used to produce inulin fructotransferase from Arthrobacter aurescens (Aa-IFTase) embedded in curdlan-based mesoporous silica microspheres (CMSiM-Aa-IFTase). The CMSiM-Aa-IFTase was constructed by co-entrapping cross-linked Aa-IFTase aggregates and curdlan into biomemitic silica, and the curdlan was subsequently removed by digestion with endo-β-1,3-glucanase. During this process, the curdlan served as an agent to introduce pores in silica microspheres. The resulting CMSiM-Aa-IFTase showed higher stability and activity than free Aa-IFTase and mCLEAs-Aa-IFTase (modified cross-linked enzyme aggregates with Aa-IFTase). Furthermore, the CMSiM-Aa-IFTase displayed good reusability and excellent storage stability. The excellent catalytic performances were due to the combinational structure from the cross-linked enzyme aggregates and hard shell of mesoporous silica microspheres, which might decrease the negative interaction between support and enzyme, and improve the mechanical properties. The CMSiM-Aa-IFTase was applicable for efficient production of Difructose Anhydride III (DFA III), and this approach should be highly valuable for preparing various mesoporous composites for catalysis.

Kinetics of gluten protein-insolubilisation during pasta processing: Decoupling between time- and temperature-dependent effects

Durum wheat gluten proteins are essential for pasta quality. Glutenin polymers undergo solubilization mechanisms during pasta processing. This study aims to investigate gluten proteins insolubilisation kinetics during a resting period applied to extruded. The goal is to investigate the contribution of time related recovery of large glutenin polymers and temperature related formation of glutenin cross-linked aggregates in the pasta quality. Extruded pasta were rested for 120 min at 20, 30 or 40 °C prior drying at high temperature (90 °C). Glutenins insolubilisation induced by resting and drying was assessed from the SE-HPLC elution profiles of the SDS-soluble proteins from fresh, rested and dried pasta. Final pasta were characterized for their organoleptic (color, surface roughness) and physical (diameter, cooking time, viscoelasticity index) properties, before and after cooking. Pasta quality is discussed in relation with the gluten network structure and the impact of resting time. Resting of freshly extruded pasta extrusion leads to spontaneous insolubilisations of glutenins by creation of weak interactions. High temperature drying induces a strong drop of solubility of all gluten protein fractions by creation of covalent bonds, impacting equally rested and not rested pasta. Dry and cooked pasta organoleptic and physical properties are not significantly impacted by a resting time.

Bioinspired Histidine⁻Zn2+ Coordination for Tuning the Mechanical Properties of Self-Healing Coiled Coil Cross-Linked Hydrogels.

Natural biopolymeric materials often possess properties superior to their individual components. In mussel byssus, reversible histidine (His)–metal coordination is a key feature, which mediates higher-order self-assembly as well as self-healing. The byssus structure, thus, serves as an excellent natural blueprint for the development of self-healing biomimetic materials with reversibly tunable mechanical properties. Inspired by byssal threads, we bioengineered His–metal coordination sites into a heterodimeric coiled coil (CC). These CC-forming peptides serve as a noncovalent cross-link for poly(ethylene glycol)-based hydrogels and participate in the formation of higher-order assemblies via intermolecular His–metal coordination as a second cross-linking mode. Raman and circular dichroism spectroscopy revealed the presence of α-helical, Zn2+ cross-linked aggregates. Using rheology, we demonstrate that the hydrogel is self-healing and that the addition of Zn2+ reversibly switches the hydrogel properties from viscoelastic to elastic. Importantly, using different Zn2+:His ratios allows for tuning the hydrogel relaxation time over nearly three orders of magnitude. This tunability is attributed to the progressive transformation of single CC cross-links into Zn2+ cross-linked aggregates; a process that is fully reversible upon addition of the metal chelator ethylenediaminetetraacetic acid. These findings reveal that His–metal coordination can be used as a versatile cross-linking mechanism for tuning the viscoelastic properties of biomimetic hydrogels.

Development of magnetic cross-linked peroxidase aggregates on starch as enhancement template and their application for decolorization.

The cross-linked enzyme aggregates (CLEAs) technology has been considered as an efficient and carrier free immobilizing method. The importance of this method comes from its simplicity and low-cost procedure, along with the utilization probability of the crude enzyme extract. The functionalized magnetic cross linked peroxidase aggregate (MNPs-TA-CLEAs-peroxidase) was prepared successfully using different aggregation agents, followed by crosslinking with glutaraldehyde. Herein, peroxidase enzyme was extracted from cabbage leaves. The beneficial of immobilized peroxidase was confirmed by decolorization studies of different types of dyes. Even the small amount of MNPs-TA-starch-CLEAs-peroxidase was able to remove a higher content of methylene blue, Congo red, indigo carmine, and malachite green (93.18, 90.0, 68.0 and 55.0%), respectively, comparing to the free enzyme. The ability of MNPs-CLEAs-peroxidase to decolorize different types of dyes, may give a suggestion of its possible usage in environmental biotechnology, especially in wastewater treatment.

Cross-linked esterase aggregates (CLEAs) using nanoparticles as immobilization matrix

The present study focusses on the enhancement of the catalytic activity and stability of an acetylesterase enzyme isolated from Staphylococcus spp. as Cross-Linked Enzyme Aggregates (CLEAs). The various parameters governing the activity of CLEAs were optimized. The magnetite and graphene oxide nanoparticles were successfully prepared via the chemical co-precipitation and Hummer's method, respectively. These nanoparticles supported the preparation as magnetite nanoparticle-supported cross-Linked Enzyme Aggregates (MGNP-CLEAs) and graphene oxide-supported Cross-Linked Enzyme Aggregates (GO-CLEAs). The activity and stability of these immobilized CLEAs were compared with the free enzyme at various temperature, pH, and organic solvents along with its storage stability and reusability. The immobilized preparations were analyzed by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectroscopy (FT-IR) techniques. Acetylesterase precipitated with 60% saturated ammonium sulfate salt (SAS) solution and cross-linked with 100 mM glutaraldehyde for 4 h at 30 °C was found to be optimal to produce CLEAs with highest activity recovery of 99.8%. The optimal pH at 8.0 and temperature at 30 °C remained the same for both the free and immobilized enzyme, respectively. Storage stability significantly improved for the immobilized enzyme as compared to free enzyme. SEM showed type-I aggregate and FT-IR revealed the successful immobilization of the enzyme. MGNP-CLEAs were found to have better activity and stability in comparison to other immobilized preparations.

A microfluidic sensor for detecting chlorophenols using cross-linked enzyme aggregates (CLEAs).

Chlorophenols have a strong medicinal smell and can be detected by the human nose at parts-per-million levels. Therefore, continuous monitoring of chlorophenols in water supplies is highly important. Herein, we reported a microfluidic sensor which can be used to detect 2,4-dichlorophenol (2,4-DCP) in real time with a limit of detection of around 0.1 ppm. The microfluidic sensor is a membrane-less galvanic cell which consists of two laminar flows running in parallel inside a straight channel. The sensor measures the potential difference between a solution containing 2,4-DCP and a reference solution containing acetate buffer. In a continuous-flow mode, the cell potential is proportional to the concentration of 2,4-DCP. To render specificity for the sensor, we incorporate a pre-treatment section where the incoming solution containing 2,4-DCP is split into two streams. One of the streams is brought into contact with cross-linked laccase aggregates (which catalyzes the hydrolysis of 2,4-DCP) and the second stream is taken as a reference solution. By comparing the potential difference between the two streams, we can determine the concentration of 2,4-DCP with high specificity. The microfluidic sensor platform is potentially useful for real-time detection of micropollutants present in aquatic systems with high sensitivity and specificity.

Mitochondrial Lipofuscin and Thermomitochondrial Lipofuscin in Homogenates of Rat Organs

Abstract—The amounts of lipofuscin (age pigment) were compared in four organs of rats: the liver, the kidney, the heart muscle, and the brain, as well as in a suspension of ghosts of hepatic mitochondria. It was shown that liver lipofuscin, which absorbs UV light at 360 nm and fluoresces at 460 nm, is predominantly formed due to mitochondrial processes. The lowest lipofuscin content was observed in the heart muscle; in the other organs studied, the levels of lipofuscin calculated per mg of protein were approximately the same. The spectral data and the lifetime of the excited state suggest that a considerable contribution to the fluorescence of lipofuscin in various organs belongs to mitochondrial lipofuscin. Along with lipofuscin, a fluorescent pigment, all organs were shown to contain non-fluorescent protein aggregates: their level was the highest in the heart muscle and the lowest in the liver. Among them, a significant portion were covalently cross-linked aggregates that were not destroyed by detergent treatment. Moderate heating of the organ homogenates caused the formation of thermolipofuscin. The level of thermolipofuscin production was the highest in the brain and the lowest in the heart. Apparently, a significant portion of the thermolipofuscin that formed in organ homogenates was thermomitochondrial lipofuscin from the membranes of damaged mitochondria. The formation of thermolipofuscin strongly involved aromatic residues: tyrosine and tryptophan.

Influence of protein concentration and coagulation temperature on rennet-induced gelation characteristics and curd microstructure

This study characterized the coagulation properties and defined the cutting window (CW; time between storage modulus values of 35 and 70 Pa) using rheometry for milk standardized to 4, 5, or 6% protein and set at 28, 32, or 36°C. Milks were standardized to a protein-to-fat ratio of approximately 1 by blending ultrafiltration retentate, skim milk, and whole milk. The internal curd microstructure for selected curd samples was analyzed with transmission electron microscopy and scanning electron microscopy. Lowering the coagulation temperature caused longer rennet coagulation time and time to reach storage modulus of 35 Pa, translating into a wider CW. It also led to a lower maximum curd-firming rate (MCFR) with lower firmness at 40 min at a given protein level. Increasing protein levels resulted in the opposite effect, although without an effect on rennet coagulation time at a given temperature. On coagulation at 28°C, milk with 5% protein resulted in a similar MCFR (∼4 Pa/min) and CW (∼8.25 min) compared with milk with 4% protein at 32°C, which reflects more standard conditions, whereas increasing milk to 6% protein resulted in more than doubling of the curd-firming rate (MCFR = 9.20 Pa/min) and a shorter CW (4.60 min). Gels set at 28°C had lower levels of rearrangement of protein network after 40 min compared with those set at 36°C. Protein levels, on the other hand, had no influence on the levels of protein network rearrangement, as indicated by loss tangent values. The internal structure of curd particles, as investigated by both scanning electron microscopy and transmission electron microscopy, appeared to have less cross-linking and smaller casein aggregates when coagulated at 28°C compared with 36°C, whereas varying protein levels did not show a marked effect on aggregate formation. Overall, this study showed a marked interactive effect between coagulation temperature and protein standardization of milk on coagulation properties, which subsequently requires adjustment of the CW during cheesemaking. Lowering of the coagulation temperature greatly altered the curd microstructure, with a tendency for less syneresis during cutting. Further research is required to quantify the changes in syneresis and in fat and protein losses to whey due to changes in the microstructure of curd particles arising from the different coagulation conditions applied to the protein-fortified milk.

Characterization of cross-linked amyloglucosidase aggregates from Aspergillus fumigatus KIBGE-IB33 for continuous production of glucose

Current research deals with immobilization of amyloglucosidase through carrier-free approach using cross-linking strategy. Cross-linked amyloglucosidase aggregates (CLAAs) with aggregation yield of 94% were prepared in 04 h by incorporating 40% ammonium sulfate and 1.5% glutaraldehyde in enzyme solution. CLAAs were characterized by optimizing various conditions including reaction time, pH, temperature and substrate concentration. It was noticed that after cross-linking no change in optimum reaction time and substrate concentration was observed however, a 5-degree shift in optimum temperature from 60 °C to 65 °C was obtained as compared to soluble amyloglucosidase. Activation energy (Ea) of amyloglucosidase as calculated from Arrhenius plot was 5.5 kcal mol−1 and 5.2 kcal mol−1 for soluble and cross-linked aggregates, respectively. Stability studies revealed that CLAAs can be used at higher temperatures for longer time period than soluble amyloglucosidase. Furthermore, data of recycling studies showed that CLAAs can be efficiently reused for 20 cycles with the retention of 63% of its initial activity. Due to the continuous reusability of CLAAs, the product formation is also increased 8 times from 5.71 mg ml−1 (soluble enzyme) to 46.548 mg ml−1 (CLAAs). Findings of this research show that carrier-free strategy is more effective for continuous hydrolysis of starch and production of glucose.

Preparation of Magnetic Cross-Linked Amyloglucosidase Aggregates: Solving Some Activity Problems

The preparation of Cross-Linked Enzyme Aggregates (CLEAs) is a simple and cost-effective technique capable of generating insoluble biocatalysts with high volumetric activity and improved stability. The standard CLEA preparation consists of the aggregation of the enzyme and its further crosslinking, usually with glutaraldehyde. However, some enzymes have too low a content of surface lysine groups to permit effective crosslinking with glutaraldehyde, requiring co-aggregation with feeders rich in amino groups to aid the formation of CLEAs. The co-aggregation with magnetic particles makes their handling easier. In this work, CLEAs of a commercial amyloglucosidase (AMG) produced by Aspergillus niger were prepared by co-aggregation in the presence of polyethyleneimine (PEI) or starch with aminated magnetic nanoparticles (MNPs) or bovine serum albumin (BSA). First, CLEAs were prepared only with MNPs at different glutaraldehyde concentrations, yielding a recovered activity of around 20%. The addition of starch during the precipitation and crosslinking steps nearly doubled the recovered activity. Similar recovered activity (around 40%) was achieved when changing starch by PEI. Moreover, under the same conditions, AMG co-aggregated with BSA was also synthesized, yielding CLEAs with very similar recovered activity. Both CLEAs (co-aggregated with MNPs or BSA) were four times more stable than the soluble enzyme. These CLEAs were evaluated in the hydrolysis of starch at typical industrial conditions, achieving more than 95% starch-to-glucose conversion, measured as Dextrose Equivalent (DE). Moreover, both CLEAS could be reused for five cycles, maintaining a DE of around 90%. Although both CLEAs had good properties, magnetic CLEAs could be more attractive for industrial purposes because of their easy separation by an external magnetic field, avoiding the formation of clusters during the filtration or centrifugation recovery methods usually used.

Catalytic phenol removal using entrapped cross-linked laccase aggregates

Laccase was immobilized using a combinatorial strategy of cross-linking and entrapping in mesoporous silica to prepare entrapped enzyme species including simply adsorbed, entrapped cross-linked enzyme (E-CLE) and entrapped cross-linked enzyme aggregate (E-CLEA) to explore their potential in phenol removal. Parameters including pH, temperature, time and cross-linker concentration were optimized to achieve an immobilized product with highest laccase specific activity. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the immobilization products. The storage and operational stability analysis were also carried out. Accordingly, E-CLEAs showed improved thermal and pH stabilities and activity retention in hydrophobic and hydrophilic solvents. Moreover, based on the resulted half-lives (t1/2) for free and insoluble laccases, the improved storage stability is reported for E-CLEAs at 1.71 and 20.88 days for them, respectively. In addition, the immobilized biocatalyst exhibited good operational stability and reusability through maintaining up to 79% of its initial activity after 20 cycles of successive operations. In conclusion, E-CLEAs have catalytic potential in efficient phenol removal and advantages of the insolubilized form of laccase as E-CLEAs make it an appealing system in applications such as possible treatment of phenol-contaminated wastewater.

Lipofuscin and Mitolipofuscin in the Organs of Young and Adult Rats

The levels of lipofuscin (aging pigment) were compared in four organs (liver, kidney, heart, brain) of young and adult rats, as well as in the suspension of hepatic mitochondria. Mitochondrial lipofuscin—mitolipofuscin fluorescing in the blue region—was seen to make the major contribution to hepatic lipofuscin. It is clear that mitolipofuscin also makes a significant contribution in other organs. The age-related accumulation of lipofuscin was shown to occur in all rat organs, but in the brain least of all. In addition to fluorescent lipofuscin, non-fluorescent protein aggregates were found in all organs, mostly in the heart. A considerable portion is covalently cross-linked aggregates not destroyed by detergents. Their number also increases with age.

Remarkable stability of Candida antarctica lipase B immobilized via cross-linking aggregates (CLEA) in deep eutectic solvents

The combination of Deep-eutectic-solvents (DES) with water as “co-solvent” enables a low-viscous reaction medium that keeps its “non-conventional” nature and thus enables synthetic lyophilization reactions (e.g. esterification) catalyzed by hydrolases. Substrates with different polarity may be employed. This paper shows how the enzyme immobilization with cross-linking aggregates (CLEA) leads to highly stable and active immobilized catalysts in different DES. As a remarkable case, when choline chloride-glycerol DES is used, CLEA derivatives of Candida antarctica lipase B (CLEA-CALB) are stable for at least 14 days without any loss of activity. The immobilized biocatalysts are applied in non-viscous DES-water blends (8% v/v) to catalyze the esterification of benzoic acid and glycerol to furnish glyceryl monobenzoate (α-MBG) in productivities of ∼35 g α-MBG L−1d−1. Compared to other commercial immobilized CALB, the CLEA-CALB derivatives rendered more product (higher conversions by 30%). Moreover, CLEA derivatives were successfully reused for six times without any loss of activity. Given the ease of immobilization (CLEA), their excellent performance in DES and the low viscosity of the DES-water blends, the reported approach may be useful for many synthetic procedures and even for continuous processes with largely optimized outcomes.

Effect of peroxyl radicals on the structure and gel properties of isolated rabbit meat myofibrillar proteins

SummaryWe investigated the effect of peroxyl radicals (ROO·), which are products of lipid peroxidation, on the structure and gel properties of myofibrillar proteins (MPs) isolated from rabbit meat. 2,2′‐Azobis(2‐amidinopropane) dihydrochloride (AAPH) was heated to stably derive ROO·. As the AAPH concentration increased, the protein carbonyl compounds significantly accumulated (P < 0.05), and the total sulfhydryl content was significantly lost (P < 0.05). Circular dichroism spectra, UV absorption spectra, intrinsic fluorescence spectra and surface hydrophobicity revealed that ROO· caused protein unfolding and conformational changes in MPs. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) analysis indicated that moderate (0–3 mm) and relatively high (5 and 10 mm) AAPH concentrations could lead to protein crosslinking and protein aggregation, respectively. These changes in protein structure could influence the gelling properties of MPs. Low‐level protein oxidation could increase gel strength and water holding capacity, whereas high‐level protein oxidation could reduce gel properties.

Molecular Biology of Exfoliation Syndrome.

Exfoliation syndrome (XFS) is a common age-related matrix process resulting from excessive production and disordered assembly of elastic microfibrillar components into highly cross-linked fibrillary aggregates throughout the anterior eye segment and various organ systems. The underlying molecular pathophysiology involves a complex interplay of profibrotic protagonists including growth factors, proteolytic enzymes and inhibitors, proinflammatory cytokines, chaperones, and dysregulated stress response pathways including insufficient autophagy. Interaction between individual genetic predisposition and stress factors is a plausible theory explaining the development of XFS in the aging individual. Genome-wide association studies have identified robust genetic associations with LOXL1, CACNA1A, and 5 additional genes including POMP and TMEM136, which provide new biological insights into the pathology of XFS and highlight a role for abnormal matrix cross-linking processes, Ca channel deficiency, blood-aqueous barrier dysfunction, and abnormal ubiquitin-proteasome signaling in XFS pathophysiology. However, the exact pathophysiological mechanisms, the functional role of genetic risk variants, and gene-environment interactions still remain to be characterized.

Aggregation of α- and β- caseins induced by peroxyl radicals involves secondary reactions of carbonyl compounds as well as di-tyrosine and di-tryptophan formation

The present work examined the role of Tyr and Trp in oxidative modifications of caseins, the most abundant milk proteins, induced by peroxyl radicals (ROO•). We hypothesized that the selectivity of ROO• and the high flexibility of caseins (implying a high exposure of Tyr and Trp residues) would favor radical-radical reactions, and di-tyrosine (di-Tyr) and di-tryptophan (di-Trp) formation. Solutions of α- and β-caseins were exposed to ROO• from thermolysis and photolysis of AAPH (2,2′-azobis(2-methylpropionamidine)dihydrochloride). Oxidative modifications were examined using electrophoresis, western blotting, fluorescence, and chromatographic methodologies with diode array, fluorescence and mass detection. Exposure of caseins to AAPH at 37 °C gave fragmentation, cross-linking and protein aggregation. Amino acid analysis showed consumption of Trp, Tyr, Met, His and Lys residues. Quantification of Trp and Tyr products, showed low levels of di-Tyr and di-Trp, together with an accumulation of carbonyls indicating that casein aggregation is, at least partly, associated with secondary reactions between carbonyls and Lys and His residues. AAPH photolysis, which generates a high flux of free radicals increased the extent of formation of di-Tyr in both model peptides and α- and β- caseins; di-Trp was only detected in peptides and α-casein. Thus, in spite of the high flexibility of caseins, which would be expected to favor radical-radical reactions, the low flux of ROO• generated during AAPH thermolysis disfavours the formation of dimeric radical-radical cross-links such as di-Tyr and di-Trp, instead favoring other O2-dependent crosslinking pathways such as those involving secondary reactions of initial carbonyl products.

Cross-linked cytochrome P450 BM3 aggregates promoted by Ru(II)-diimine complexes bearing aldehyde groups

Cross-linked enzyme aggregate (CLEA) methodology has been applied to immobilize cytochrome P450 BM3 variants (F87A and 21B3) with peroxygenase activity. Several Ru(II)-diimine complexes were found to be suitable cross-linking agents, surpassing the traditional glutaraldehyde and dextran aldehyde. They offer modular numbers of aldehyde functionalities and a more rigid framework than their organic counterparts. The F87A CLEAs display significant activity loss compared to the protein in solution. Meanwhile, for the 21B3 CLEAs, high activity recovery (up to 95%) is obtained. In order to minimize enzyme leaching from the CLEA, sodium cyanoborohydride was used to reduce the CLEAs imine bonds. The reduced CLEAs were active for several rounds of reactions leading to an overall increase in protein activity of 170% compared to the free protein in solution.

Maltose Production Using Starch from Cassava Bagasse Catalyzed by Cross-Linked β-Amylase Aggregates

Barley β-amylase was immobilized using different techniques. The highest global yield was obtained using the cross-linked enzyme aggregates (CLEA) technique, employing bovine serum albumin (BSA) or soy protein isolate (SPI) as feeder proteins to reduce diffusion problems. The CLEAs produced using BSA or SPI showed 82.7 ± 5.8 and 53.3 ± 2.4% global yield, respectively, and a stabilization effect was observed upon immobilization at neutral pH value, e.g., after 12 h at 55 °C, the free β-amylase is fully inactivated, while CLEAs retained 25 and 15% of activity (using BSA and SPI, respectively). CLEA using SPI was selected because of its easier recovery, being chosen to convert the residual starch contained in cassava bagasse into maltose. This biocatalyst permitted to reach almost 70% of maltose conversion in 4 h using 30.0 g/L bagasse starch solution (Dextrose Equivalent of 15.88) and 1.2 U of biocatalyst per gram of starch at pH 7.0 and 40 °C. After 4 reuses (batches of 12 h) the CLEA using SPI maintained 25.50 ± 0.01% of conversion due to the difficulty of recovering.

Radical cross-linked whey protein aggregates as building blocks of non-heated cold-set gels

In the present study whey protein aggregates were prepared by a simple method, without the need of heating, through the crosslinking of whey protein in the presence of redox initiators (Ascorbic acid + H2O2) as building blocks of non-heated cold-set gels. As an initial screening, the effects of different pH values (9.0–7.0) and redox initiators content were evaluated for gelation ability of the free radical cross-linked soluble aggregates (FRC-SAs). Then, structural alterations whey proteins in the FRC-SAs were investigated by different techniques including SDS-polyacrylamide gel electrophoresis, free sulfhydryl determination, fluorescence spectroscopy, surface hydrophobicity measurement, dynamic light scattering (DLS), circular dichroism (CD), and atomic force microscopy (AFM). Results indicated that disulfide bonds are responsible for the formation of the intermediate aggregates produced by the redox initiators, where alkaline pH led to the more extensive formation of these disulfide based mediated-aggregates. CD and fluorescence spectroscopy data suggested not only conformational alterations in the secondary structure of whey proteins are involved in the aggregation process but also changes in tertiary structure have a significant role. DLS and AFM results revealed that most of the small aggregates sticked together fo form more weighty particles, confirming free radical-triggered aggregation of proteins. Furthermore, it was observed that cross-linking at higher pH increased significantly the strength of resulting gels (P < 0.05). It is shown that electrostatic and hydrophobic interactions played a critical role in gel network formation from non-heated whey protein during acidifying step by glucono-d-lactone (GDL).

Assembly and photochemical properties of mesoporous networks of spinel ferrite nanoparticles for environmental photocatalytic remediation

Spinel ferrite materials have an electronic band structure that is well suited for visible light-induced catalysis, however, their photocatalytic activity remains low due to the daunting charge-carrier separation process. In this article, we report that high-surface-area mesoscopic architectures composed of tightly connected ultrasmall spinel ferrite nanocrystals can efficiently suppress electron-hole recombination, manifesting an exceptional activity and magnetic recyclability in photocatalytic reduction of aqueous Cr(VI). Revealed by electron microscopy, N2 physisorption, and X-ray scattering studies, the resulting materials, which were obtained through a block copolymer-assisted cross-linking aggregation of colloidal nanoparticles, show a 3D interconnected nanoporous structure with a large internal surface area (up to 159 m2 g−1) and exhibit small grain composition (ca. 6–8 nm in size). Through a systematic synthesis of various structural analogues to the spinel ferrite family and optical absorption and electrochemical impedance spectroscopy analyses, we demonstrate that the electronic band structure fits the electronic requirements for both Cr(VI) reduction and water oxidation under UV–vis light irradiation. Among spinel ferrites, ZnFe2O4 presents the highest activity, readily operating without additional sacrificial reagents in photocatalytic detoxification of aqueous Cr(VI), which together with transient gas analysis and fluorescence spectroscopy results suggest a competitive formation of oxygen and hydroxyl radicals at the catalyst surface. These findings provide an essential tool for the delineation of the electronic structure-catalytic property relationship in spinel ferrite nanostructures offering intriguing possibilities for designing new photocatalytic systems for efficient environmental pollution purification and energy conversion.