2,5-Diformylfuran (2,5-DFF) is an important biomass chemical with broad application prospects. A vanadium pentoxide (V2O5)/ceramic powder catalyst (V-CP) was designed and synthesized in this study, and its structure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and specific surface area analysis (BET). The catalytic properties of the V-CP catalyst were evaluated. The results show that 5-hydroxymethylfurfural (5-HMF) can be completely converted to 2,5-DFF at 140 °C under atmospheric pressure in the presence of oxygen as the oxidant in dimethyl sulfoxide (DMSO) for 5 h, and the yield of 2,5-DFF was 85.7%. After recycling the catalyst 5 times, the catalytic effect decreased slightly, and the catalyst showed good recovery performance. Furthermore, a one-pot method for the preparation of 2,5-DFF was proposed by using fructose as the raw material and V2O5/ceramic-dilute sulfuric acid as the catalyst. The fructose was dehydrated to form 5-HMF, and 2,5-DFF was generated by the V-CP catalytic oxidation of 5-HMF. The 2,5-DFF yield was 68.4%. The results of this study provide a valuable reference for the efficient one-pot synthesis of biomass-based furan chemicals.

In this study, we proposed a bioinspired approach for the deposition and zwitteration of hyaluronic acid (HA) with a reduced glutathione (GSH) to form a composite layer that functions as a low fouling coating. A polyanion of the HA–dopamine conjugate (HADA) possessing catechol groups was synthesized by carbodiimide chemistry between HA and dopamine. Then, the dopamine conjugated biofunctional polymers (HADA) were grafted onto Au substrates via the transformation of catechol into a quinone group under mild oxidative conditions followed by a reaction with GSH to avoid undesired adhesion and also to shield the exposed Au substrate. Analysis of XPS spectra and wettability indicated that HADA and GSH were successfully grafted onto Au substrates. Surface plasmon resonance analysis showed that both HADA and further GSH modified surfaces exhibited reduced nonspecific adsorption. The attachment of GSH to HADA modified surfaces (HADA-G) resulted in better antifouling performance, with a low or ultralow protein adsorption of 0–7.51 ng cm−2 when exposed to single protein solutions, and a reduction in nonspecific adsorption from cow's milk to 10% compared to that of bare gold. The enhanced antifouling performance of HADA-G modified surfaces was likely due to the zwitterionic structure in GSH, which can induce stronger surface hydration through electrostatic interactions as well as the hydrogen bonding induced by HADA. Our results provide a facile and universal approach to surface modification and demonstrate the benefits of using a composite layer for the design of low fouling surfaces.

Enzyme-responsive supramolecular hydrogels are a new class of smart materials and have enormous potential to be used in biology and medicine. In this study, α-chymotrypsin was proposed to promote the self-assembly of amino acid derivatives for the preparation of such supramolecular hydrogels. It is found that α-chymotrypsin significantly shortens the gelation time from 8 days (or no gelation occurred within 2 weeks) to 10 min–4 h depending on the structure of amino acid derivatives. The chemical compositions and microstructures of the hydrogels were further investigated by LC-MS, microscopy and spectroscopy techniques. The results show that the transparent hydrogels consist of long nanofibers with approximately 20 nm in diameter. These nanofibers are composed of Fmoc-amino acid and amino acid, which were formed from the hydrolysis of amino acid ester, with a molar ratio of 4.346:1 (Fmoc-F/F) and 0.548:1 (Fmoc-F/Y), respectively. Furthermore, the molecular simulation was performed to investigate the specific recognition of α-chymotrypsin to amino acid derivatives. The results indicate that the enzyme–substrate interactions are responsible for promoting the supramolecular self-assembly of these amino acid derivatives into fibrous hydrogels. In addition to being the first example of enzyme–substrate interaction-promoted supramolecular self-assembly, this novel concept opens up the possibility of making use of various enzymes and their substrates (or analogues) in the discovery of new supramolecular materials with enzyme responsiveness.

Colloidosomes are promising carriers for immobilizing enzyme for catalytic purposes in aqueous/organic media. However, they often suffer from one or more problems regarding catalytic performance, stability, and recyclability. Here, we report a novel approach for the synthesis of cross-linkable colloidosomes by the selective polymerization of dopamine at oil/water interfaces in a Pickering emulsion. An efficient enzyme immobilization method was further developed by covalently bonding enzymes to the polydopamine (PDA) layer along with the formation of such colloidosomes with lipase as a model enzyme. In this enzyme system, the PDA layer served as a cross-linking layer and enzyme support for simultaneously enhancing the colloidosomes’ stability and improving surface availability of the enzymes for catalytic reaction. It was found that the specific activity of lipases immobilized on the colloidosome shells was 8 and 1.4 times higher than that of free lipase and encapsulated lipase positioned in the aqueous cores of colloidosomes, respectively. Moreover, the immobilized lipases demonstrated excellent operational stability and recyclability, retaining 86.6% of enzyme activity after 15 cycles. It is therefore reasonable to expect that this novel approach for enzyme immobilization has great potential to serve as an important technique for the construction of biocatalytic systems.Keywords: colloidosomes; enzyme immobilization; Pickering emulsion; poly(dopamine); silica nanoparticles;

Encapsulation of enzymes during the creation of an emulsion is a simple and efficient route for enhancing enzyme catalysis in organic media. Herein, we report a capsule with a shell comprising a monolayer of silica Janus particles (JPs) (referred to as a monolayer capsule) and a Pickering emulsion for the encapsulation of enzyme molecules for catalysis purposes in organic media using amphiphilic silica JPs as building blocks. We demonstrate that the JP capsules had a monolayer shell consisting of closely packed silica JPs (270 nm). The capsules were on average 5–50 μm in diameter. The stability of the JP capsules (Pickering emulsion) was investigated with the use of homogeneous silica nanoparticles as a control. The results show that the emulsion stabilized via amphiphilic silica JPs presented no obvious changes in physical appearance after 15 days, indicating the high stability of the emulsions and JP capsules. Furthermore, the lipase from Candida sp. was chosen as a model enzyme for encapsulation within the JP capsules during their formation. The catalytic performance of lipase was evaluated according to the esterification of 1-hexanol with hexanoic acid. It was found that the specific activity of the encapsulated enzymes (28.7 U mL–1) was more than 5.6 times higher than that of free enzymes in a biphasic system (5.1 U mL–1). The enzyme activity was further increased by varying the volume ratio of water to oil and the JPs loadings. The enzyme-loaded capsule also exhibited high stability during the reaction process and good recyclability. In particular, the jellification of agarose in the JP capsules further enhanced their operating stability. We believe that the monolayer structure of the JP capsules, together with their high stability, rendered the capsules to be ideal enzyme carriers and microreactors for enzyme catalysis in organic media because they created a large interfacial area and had low mass transfer resistance through the monolayer shell.Keywords: capsule; enzyme immobilization; Janus particle; Pickering emulsion; self-assembly

The aim of this study was to explore the influence of amphiphilic and zwitterionic structures on the resistance of protein adsorption to peptide self-assembled monolayers (SAMs) and gain insight into the associated antifouling mechanism. Two kinds of cysteine-terminated heptapeptides were studied. One peptide had alternating hydrophobic and hydrophilic residues with an amphiphilic sequence of CYSYSYS. The other peptide (CRERERE) was zwitterionic. Both peptides were covalently attached onto gold substrates via gold–thiol bond formation. Surface plasmon resonance analysis results showed that both peptide SAMs had ultralow or low protein adsorption amounts of 1.97–11.78 ng/cm2 in the presence of single proteins. The zwitterionic peptide showed relatively higher antifouling ability with single proteins and natural complex protein media. We performed molecular dynamics simulations to understand their respective antifouling behaviors. The results indicated that strong surface hydration of peptide SAMs contributes to fouling resistance by impeding interactions with proteins. Compared to the CYSYSYS peptide, more water molecules were predicted to form hydrogen-bonding interactions with the zwitterionic CRERERE peptide, which is in agreement with the antifouling test results. These findings reveal a clear relation between peptide structures and resistance to protein adsorption, facilitating the development of novel peptide-containing antifouling materials.Keywords: antifouling; biosensor; nonspecific adsorption; peptides; SPR;

Supramolecular self-assembly offers an efficient pathway for creating macroscopically chiral structures in biology and materials science. Here, a new peptide consisting of an N-(9-fluorenylmethoxycarbonyl) headgroup connected to an aromatic phenylalanine-tryptophan dipeptide and terminated with zwitterionic lysine (Fmoc-FWK) and its cationic form (Fmoc-FWK-NH2) were designed for self-assembly into chiral structures. It was found that the Fmoc-FWK peptide self-assembled into left-handed helical nanoribbons at pH 11.2–11.8, whereas it formed nanofibers at pH 5 and 12 and large flat ribbons composed of many nanofibers in the pH range of 6–11. However, only nanofibers were observed in the cases of Fmoc-FWK-NH2 at different values. A series of structural characterizations based on CD, FTIR, UV–vis and fluorescence spectroscopy reveal that the electrostatic and aromatic interactions and the associated hydrogen bonding direct the self-assembly into various structures. The enhanced π–π stacking and hydrogen bonding were found in the helical nanoribbons. This difference in intermolecular interactions should be derived from the ionization of carboxyl and amino groups from lysine residues at different pH values. Furthermore, we performed molecular dynamics simulations to gain insight into the assembly mechanisms. The results imply that a relatively rigid molecular conformation and the strong intramolecular aromatic interaction between Trp and Fmoc groups favor chiral self-assembly. This study is the first attempt to design a Fmoc-tripeptide for the fabrication of helical structures with macroscopic chirality, which provides a successful example and allows us to create new peptide-based chiral assembly systems.

Antifouling surfaces capable of reducing nonspecific protein adsorption from natural complex media are highly desirable in surface plasmon resonance (SPR) biosensors. A new protein-resistant surface made through the chemical grafting of easily available hyaluronic acid (HA) onto gold (Au) substrate demonstrates excellent antifouling performance against protein adsorption. AFM images showed the uniform HA layer with a thickness of ∼10.5 nm on the Au surface. The water contact angles of Au surfaces decreased from 103° to 12° with the covalent attachment of a carboxylated HA matrix, indicating its high hydrophilicity mainly resulted from carboxyl and amide groups in the HA chains. Using SPR spectroscopy to investigate nonspecific adsorption from single protein solutions (bovine serum albumin (BSA), lysozyme) and complex media (soybean milk, cow milk, orange juice) to an HA matrix, it was found that ultralow or low protein adsorptions of 0.6–16.1 ng/cm2 (e.g., soybean milk: 0.6 ng/cm2) were achieved on HA-Au surfaces. Moreover, anti-BSA was chosen as a model recognition molecule to characterize the immobilization capacity and the antifouling performance of anti-BSA/HA surfaces. The results showed that anti-BSA/HA sensor surfaces have a high anti-BSA loading of 780 ng/cm2, together with achieving the ultralow (<3 ng/cm2 for lysozyme and soybean milk) or low (<17 ng/cm2 for cow milk and 10% blood serum) protein adsorptions. Additionally, the sensor chips also exhibited a high sensitivity to BSA over a wide range of concentrations from 15 to 700 nM. Our results demonstrate a promising antifouling surface using extremely hydrophilic HA as matrix to resist nonspecific adsorption from complex media in SPR biosensors.Keywords: antifouling; biosensor; hyaluronic acid; nonspecific adsorption; SPR

High solids enzymatic hydrolysis is a promising process to increase the concentrations of fermentable sugars for ethanol production. Here, we reported an integrated strategy incorporating decrystallization and fed-batch operation to enhance the enzymatic hydrolysis of lignocellulose at high solid loadings. The effect of concentration of phosphoric acid on the decrystallization and enzymatic hydrolysis of cellulose was investigated. The results showed that 86 wt% phosphoric acid could completely break the crystalline structure, achieving a high cellulose conversion and hydrolysis rate (89% within 4 h) in batch operation (5% solid loading). In the fed-batch operation, we designed two different enzyme feeding strategies, in which the enzymes were added either at start-up or along with the fresh substrate. The results indicated that fed-batch hydrolysis can be carried out at a final high solids loading of 30%, resulting in a glucose concentration as high as 143.5 g L−1 within 27 hours. Meanwhile, a stable and high cellulose conversion was achieved in fed-batch operation with the enzymes divided over the substrate feed, which should be dependent on the decrystallization of the substrate. Our findings provide a practical way to enhance enzymatic hydrolysis at high solid loadings and also propose a feasible enzyme feeding strategy in fed-batch operation.

We report a green synthesis of novel gold nanoparticle–nanocluster composite nanostructures directly using trypsin as linking and reducing agents. Size exclusion chromatography (SEC) and transmission electron microscopy (TEM) reveals that the as-prepared gold nanocomposite (gold nanoparticles-trypsins-nanoclusters, GNPs-Trys-GNCs) is composed of GNPs (gold nanoparticles) with an average diameter of 5.5 nm and the GNCs (gold nanoclusters, about 1 nm)-embedded trypsins (Trys-GNCs), which are attached to the surface of the GNPs. The specific amino acids in the trypsin molecule, like cysteine, methionine, and tyrosine, combined with the unique spatial structures, enable trypsins to bind and reduce the AuCl4– ions, simultaneously forming GNPs and GNCs in one-pot synthesis. Similar to pure GNPs, the GNPs-Trys-GNCs nanocomposite also exhibits an intense surface plasmon resonance (SPR) absorbance at 520 nm. However, it shows an obvious different optical property in the interaction with Pb2+ ions. In the presence of Pb2+ ions, an increased intensity and a slight red-shift of the SPR peak for the GNPs-Trys-GNCs nanocomposite in the UV–vis spectra were observed, while a decreased intensity and large red-shift for pure GNPs were observed in previous studies. Moreover, we found that the SPR intensity linearly increased with Pb2+ concentration from 1.6 to 32.3 μM (R2 = 0.9731). In addition, high-level Pb2+ ions would induce the aggregation of GNPs-Trys-GNCs nanocomposite accompanied by the formation of precipitate. The unique structure and optical property of the GNPs-Trys-GNCs nanocomposite enable it to be used in heavy metal ions sensing and elimination.Keywords: Biomineralization; Gold nanoclusters; Gold nanoparticles; Nanocomposite; Nanostructure; Protein template;

Enzyme-responsive supramolecular hydrogels are a new class of smart materials and have enormous potential to be used in biology and medicine. In this study, α-chymotrypsin was proposed to promote the self-assembly of amino acid derivatives for the preparation of such supramolecular hydrogels. It is found that α-chymotrypsin significantly shortens the gelation time from 8 days (or no gelation occurred within 2 weeks) to 10 min–4 h depending on the structure of amino acid derivatives. The chemical compositions and microstructures of the hydrogels were further investigated by LC-MS, microscopy and spectroscopy techniques. The results show that the transparent hydrogels consist of long nanofibers with approximately 20 nm in diameter. These nanofibers are composed of Fmoc-amino acid and amino acid, which were formed from the hydrolysis of amino acid ester, with a molar ratio of 4.346:1 (Fmoc-F/F) and 0.548:1 (Fmoc-F/Y), respectively. Furthermore, the molecular simulation was performed to investigate the specific recognition of α-chymotrypsin to amino acid derivatives. The results indicate that the enzyme–substrate interactions are responsible for promoting the supramolecular self-assembly of these amino acid derivatives into fibrous hydrogels. In addition to being the first example of enzyme–substrate interaction-promoted supramolecular self-assembly, this novel concept opens up the possibility of making use of various enzymes and their substrates (or analogues) in the discovery of new supramolecular materials with enzyme responsiveness.

In this study, we proposed a bioinspired approach for the deposition and zwitteration of hyaluronic acid (HA) with a reduced glutathione (GSH) to form a composite layer that functions as a low fouling coating. A polyanion of the HA–dopamine conjugate (HADA) possessing catechol groups was synthesized by carbodiimide chemistry between HA and dopamine. Then, the dopamine conjugated biofunctional polymers (HADA) were grafted onto Au substrates via the transformation of catechol into a quinone group under mild oxidative conditions followed by a reaction with GSH to avoid undesired adhesion and also to shield the exposed Au substrate. Analysis of XPS spectra and wettability indicated that HADA and GSH were successfully grafted onto Au substrates. Surface plasmon resonance analysis showed that both HADA and further GSH modified surfaces exhibited reduced nonspecific adsorption. The attachment of GSH to HADA modified surfaces (HADA-G) resulted in better antifouling performance, with a low or ultralow protein adsorption of 0–7.51 ng cm−2 when exposed to single protein solutions, and a reduction in nonspecific adsorption from cow's milk to 10% compared to that of bare gold. The enhanced antifouling performance of HADA-G modified surfaces was likely due to the zwitterionic structure in GSH, which can induce stronger surface hydration through electrostatic interactions as well as the hydrogen bonding induced by HADA. Our results provide a facile and universal approach to surface modification and demonstrate the benefits of using a composite layer for the design of low fouling surfaces.