High-Yield and High-Efficiency Conversion of HMF to Levulinic Acid in a Green and Facile Catalytic Process by a Dual-Function Brønsted-Lewis Acid HScCl4 Catalyst.

Lignocellulosic biorefineries have received considerable attention for the purpose of producing high-value chemicals and materials. Levulinic acid (LA) is an important biomass-derived platform chemical that is produced from sugar-based biomass. Unfortunately, the catalysts reported thus far have shortcomings, such as expensive starting materials, complicated synthesis or purification operations, and a low LA yield under harsh reaction conditions. Herein, we develop a novel dual-functional catalyst, HScCl4, by combining Brønsted acid (HCl) and Lewis acid (ScCl3) sites. The as-prepared HScCl4 catalyst shows high efficiency and high selectivity for converting 5-hydroxymethylfurfural (HMF) to LA in a biphasic system consisting of methyl isobutyl ketone (MIBK) and water. The density functional theory (DFT) results show that the synergistic catalytic effect, originating from the Brønsted and Lewis acidic sites of HScCl4, significantly decreases the energy barriers of reactants and intermediates, thus facilitating the conversion of HMF to LA. Moreover, the efficient separation of LA in the water-MIBK biphasic system by extracting LA to the MIBK phase minimizes the side reactions of LA and thus the formation of humins while significantly improving the LA yield. The conversion of HMF and the selectivity for LA are 100 and 95.6% at 120 °C for 35 min, respectively. The free energy (ΔG) and activation energy (E a) of the reaction are -30 kcal mol-1 and 13.7 kJ mol-1, respectively. The developed process provides a green, sustainable, and efficient pathway to produce LA from biomass-derived HMF under mild conditions.

A fluorescent probe based on cucurbit[7]uril for the selective recognition of phenylalanine.

Herein we describe a simple fluorescence quenching method for the selective recognition and determination of the amino acid phenylalanine (Phe). The use of 1H NMR spectroscopy revealed that the alkaloid palmatine (PAL) can encapsulated partially into the cavity of cucurbit[7]uril (Q[7]) in aqueous solution to form a stable 1:1 host-guest inclusion complex. This host-guest complex exhibits fluorescence of moderate intensity. Interestingly, the addition of the Phe results in a dramatic quenching of the fluorescence intensity associated with the inclusion complex. By contrast, the addition of other natural amino acids resulted in no change in the fluorescence. Based on the linear relationship between the fluorescence intensity and the concentration of Phe, the detection of the concentration of Phe in aqueous solution is facile. Thus, a new fluorescence quenching method for the recognition and determination of the Phe has established herein.

Selective recognition and determination of phenylalanine by a fluorescent probe based on cucurbit[8]uril and palmatine.

This paper demonstrated a simple and validated fluorescence enhancing method to selectively recognize and discriminate the amino acid phenylalanine (Phe). 1H NMR spectroscopy reveal that the palmatine (PAL) can be encapsulated into the cucurbit [8]uril (Q [8]) in aqueous solution to form stable 1:2 host-guest inclusion complex PAL2@Q [8], which exhibits moderate intensity fluorescence property. Interestingly, the addition of the Phe into the inclusion complex PAL2@Q [8] leads to dramatically enhancing of the fluorescence intensity. In contrast, the addition of any other natural amino acids into the inclusion complex PAL2@Q [8] gives no fluorescence variation. Furthermore, it is easy to detect the concentration of Phe in target aqueous solution according to the linear relationship between fluorescence intensity and concentration of the Phe.

One-pot synthesis of highly active and hydrothermally stable Pd@mHSiO2 yolk-shell-structured nanoparticles for high-temperature reactions in hydrothermal environments.

The facile synthesis of yolk-shell-structured nanoparticles (YSNPs) with mobile active metal cores and mesoporous inorganic-organic hybrid silica shells (mHSiO2) is important for their applications. In this work, Pd@mHSiO2 YSNPs have been synthesized in aqueous solution at 95 °C by a one-pot method without the need for extensive purification and separation steps. The method is simple and facile, and ingeniously combines the controlled synthesis of Pd nanocubes, coating of mesoporous silica, and transition from core-shell-structured nanoparticles (CSNPs) to YSNPs. 29Si NMR spectroscopy, FTIR spectroscopy, and detailed control experiments have demonstrated that the incorporation of 1,2-bis(trimethoxysilyl)ethane (BTME) modifies the degree of condensation between the outer hybrid silica layer and the inner pure silica section, and that high temperature water is really responsible for dissolving the inner pure silica layer leading to a transition from the CSNPs to the YSNPs. The obtained Pd@mHSiO2 YSNPs have a controllable diameter, tunable shell thickness, a high specific surface area, and uniform mesoporosity. Thermal stability tests have indicated that the Pd@mHSiO2 YSNPs are remarkably stable at high temperatures up to 650 °C. Importantly, the Pd@mHSiO2 YSNPs exhibit a much higher catalytic activity and hydrothermal stability than Pd@mSiO2 CSNPs or Pd/mHSiO2 NSs in the conversion of levulinic acid (LA) into γ-valerolactone (GVL), because the hollow voids provide low mass-transfer resistance and improve the accessibility of the catalytic sites, and the incorporation of organic groups enhances the hydrothermal stability of the outer shell.

Rapid colorimetric determination of dopamine based on the inhibition of the peroxidase mimicking activity of platinum loaded CoSn(OH)6 nanocubes.

Platinum nanoparticles were loaded on CoSn(OH)6 nanocubes via a co-precipitation method. The material (NCs) is shown to be a viable peroxidase mimic that catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by hydrogen peroxide (H2O2) to generate oxidized TMB (oxTMB) with absorption at 652 nm. The formation of the blue color can be observed in <30 s. Thus, a visual and colorimetric assay was worked out for H2O2. It has a detection limit as low as 4.4 µM and works in the 5 to 200 µM concentration range. The method was also used to detect dopamine (DA) which is found to inhibit the enzyme mimicking activity of the NCs. Hence, less blue color is formed in its presence. The respective DA assay has a linear response in the 5.0 to 60 µM concentration range and a 0.76 µM detection limit. Graphical abstractSchematic diagram of a visual colorimetric method for determination of H2O2 and dopamine (DA) with the aid of color change of 3,3',5,5'-tetramethylbenzidine (oxTMB), based on the peroxidase-like activity of Pt/CoSn(OH)6 nanocubes.

Peroxidase mimetic activity of porphyrin modified ZnFe2O4/reduced graphene oxide and its application for colorimetric detection of H2O2 and glutathione.

Artificial nanoenzymes which can overcome some drawbacks of natural enzymes is a challenging topic in the biosensor field. Herein, we demonstrated 5, 10, 15, 20-tetrakis (4-carboxylpheyl)-porphyrin modified magnetic ZnFe2O4 nanoparticles loaded on the surface of reduced graphene oxide (Por-ZnFe2O4/rGO), which exhibited intrinsic peroxidase-like activity and rapidly oxidized the peroxidase substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue product (OxTMB) distinguished by naked eyes. Interestingly, by comparative study of different nanomaterials ZnFe2O4 nanoparticles, ZnFe2O4/rGO and Por-ZnFe2O4, Por-ZnFe2O4/rGO was proved to possess the highest peroxidase-like activity. Electron spin resonance (ESR) verified the catalytic activity of Por-ZnFe2O4/rGO for H2O2 was due to hydroxyl radical from decomposition of H2O2. Temperature and pH strongly affected the peroxidase-like activity of Por-ZnFe2O4/rGO nanocomposites. Under optimal conditions (pH = 4, 40 °C), the constructed sensor based on the catalytic activity of the Por-ZnFe2O4/rGO could be conveniently used for colorimetric detection of H2O2 in the range of 0.7-30 µM with the detection limit of 0.54 µM. Moreover, the colorimetric sensor based on Por-ZnFe2O4/rGO exhibited a good linear response to glutathione (GHS) in the range of 2-40 µM with a low detection limit of 0.76 µM. The detection of GHS can be easily realized through the obvious color change by naked eyes without any complicated instrumentation.

Supramolecular Fluorescence Probe Based on Twisted Cucurbit[14]uril for Sensing Fungicide Flusilazole.

The host-guest complex of the common dye, thioflavin T (ThT), and twisted cucurbit[14]uril (tQ[14]) was selected as a fluorescent probe to determine non-fluorescent triazole fungicides, including flusilazole, azaconazole, triadimefon, tebuconazole, tricyclazole, flutriafol, penconazole, and triadimenol isomer A, in an aqueous solution. The experimental results reveal that the ThT@tQ[14] probe selectively responded to flusilazole with significant fluorescence quenching and a detection limit of 1.27 × 10-8 mol/L. In addition, the response mechanism involves not only a cooperation interaction-ThT occupies a side-cavity of the tQ[14] host and the triazole fungicide occupies another side-cavity of the tQ[14] host-but also a competition interaction in which both ThT and the triazole fungicide occupy the side-cavities of the tQ[14] host.

A Study of the Interaction Between Cucurbit[8]uril and Alkyl-Substituted 4-Pyrrolidinopyridinium Salts.

The interaction between cucuribit[8]uril (Q[8]) and a series of 4-pyrrolidinopyridinium salts bearing aliphatic substituents at the pyridinium nitrogen, namely 4-(C4 H8 N)C5 H5 NRBr, where R=Et (g1), n-butyl (g2), n-pentyl (g3), n-hexyl (g4), n-octyl (g5), n-dodecyl (g6), has been studied in aqueous solution by 1 H NMR spectroscopy, electronic absorption spectroscopy, isothermal titration calorimetry and mass spectrometry. Single crystal X-ray diffraction revealed the structure of the host-guest complexes for g1, g2, g3, and g5. In each case, the Q[8] contains two guest molecules in a centrosymmetric dimer. The orientation of the guest molecule changes as the alkyl chain increases in length. Interestingly, in the solid state, the inclusion complexes identified are different from those observed in solution, and furthermore, in the case of g3, Q[8] exhibits two different interactions with the guest. In solution, the length of the alkyl chain plays a significant role in determining the type of host-guest interaction present.

Isobutane/2-butene alkylation catalyzed by Brønsted-Lewis acidic ionic liquids.

The alkylation reaction of isobutane with 2-butene to yield C8-alkylates was performed using Brønsted-Lewis acidic ionic liquids (ILs) comprising various metal chlorides (ZnCl2, FeCl2, FeCl3, CuCl2, CuCl, and AlCl3) on the anion. IL 1-(3-sulfonic acid)-propyl-3-methylimidazolium chlorozincinate [HO3S-(CH2)3-mim]Cl-ZnCl2 (x=0.67) exhibited outstanding catalytic performance, which is attributed to the appropriate acidity, the synergistic effect originating from its double acidic sites and the promoting effect of water on the formation and transfer of protons. The Lewis acidic strength of IL played an important role in improving IL catalytic performance. A 100% conversion of 2-butene with 85.8% selectivity for C8-alkylate was obtained under mild reaction conditions. The IL reusability was good because its alkyl sulfonic acid group being tethered covalently, its anion [Zn2Cl5]- inertia to the active hydrogen, and its insolubility in the product. IL [HO3S-(CH2)3-mim]Cl-ZnCl2 had potential applicability in the benzene alkylation reaction with olefins and halohydrocarbons.

Preparation and characterization of petroleum-based mesophase pitch by thermal condensation with in-process hydrogenation.

A petroleum aromatic-rich component was used to prepare mesophase pitch by thermal condensation. In-process hydrogenation method was employed to achieve the hydrogenation reaction of intermediates generated during the thermal reaction using tetrahydronaphthalene (THN) as a hydrogen donor. Impacts of in-process hydrogenation on the properties of intermediates and mesophase pitches were investigated. It was found that the in-process hydrogenation was conducive to the generation of hydrogenated intermediates with concentrated extracted component distribution, uniform molecular structure and abundant naphthenic structures. The characterizations of mesophase pitches showed that the in-process hydrogenation contributed to the preparation of mesophase pitch with concentrated extracted component distribution, low softening point, large domain structure and ordered crystal structure. This was due to the increasing contents of naphthenic structures in intermediates. Moreover, the increase of methylene bridges in the product was the critical reason for improving the product's properties.

Higher catalytic activity of porphyrin functionalized Co3O 4 nanostructures for visual and colorimetric detection of H2 O2 and glucose.

5,10,15,20-Tetrakis(4-carboxyl pheyl)-porphyrin (H2TCPP) functionalized chain-like Co3O4 nanoparticles (NPs) were prepared by a facile two-step method. The H2TCPP-Co3O4 nanocomposites were demonstrated to display enhanced peroxidase-like activity than that of pure Co3O4 nanoparticles without modification with H2TCPP molecules, catalyzing oxidation of peroxidase substrate 3,3',5,5'-tetramethyl-benzidine (TMB) in the presence of H2O2 to produce a blue color reaction. Furthermore, H2TCPP-Co3O4 nanocomposites showed typical Michaelis-Menten kinetics and higher affinity to H2O2 and TMB than that of pure Co3O4 NPs alone. Based on H2TCPP-Co3O4 nanocomposites, a simple, sensitive and selective colorimetric method with TMB as the substrate for the detection of H2O2 and glucose was successfully established. This colorimetric method can be used for the colorimetric detection of H2O2 with a low detection limit of 4×10(-7)mol·L(-1) and a dynamic range of 1×10(-6)mol·L(-1) to 75×10(-6)mol·L(-1). This method was designed to detect glucose when combined with glucose oxidase at a low detection limit of 8.6×10(-7)mol·L(-1) and a dynamic range of 1×10(-6)mol·L(-1) to 10×10(-6)mol·L(-1). Results of a fluorescent probe suggested that the peroxidase-mimic activity of the H2TCPP-Co3O4 nanocomposites effectively catalyzed the decomposition of H2O2 into [OH] radicals.

Glucose-sensitive colorimetric sensor based on peroxidase mimics activity of porphyrin-Fe3O4 nanocomposites.

5,10,15,20-Tetrakis(4-carboxyphenyl)-porphyrin-functionalized Fe3O4 nanocomposites (H2TCPP-Fe3O4) were successfully prepared by a simple two-step method. These nanocomposites exhibited ultra-high peroxidase-like activity compared with pure Fe3O4 nanoparticles. Colorless peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) was changed by H2O2 to its blue oxidized state. Kinetic studies indicated that the H2TCPP-Fe3O4 nanocomposites exhibited enhanced affinity toward H2O2 with a higher catalytic activity than Fe3O4 nanoparticles alone. Results of a fluorescent probe suggested that the catalase-mimic activity of the H2TCPP-Fe3O4 nanocomposites effectively catalyzed the decomposition of H2O2 into hydroxyl radicals. A simple, sensitive, and selective visual and colorimetric method with TMB as the substrate was designed to detect glucose when combined with glucose oxidase. This colorimetric method can be used for colorimetric detection of H2O2 with a minimum detection limit of 1.07×10(-6) M and a dynamic range of 5×10(-6) mol·L(-1) to 8×10(-5) mol·L(-1). This method can also be used to detect glucose at a minimum detection limit of 2.21×10(-6) M and a dynamic range of 25×10(-6) mol·L(-1) to 5×10(-6) mol·L(-1). Furthermore, the robustness of the nanocomposites makes them suitable for a wide range of applications in biomedicine and environmental chemistry fields.

[Kinetics model for batch culture of white rot fungus].

In order to understand ligninolytic enzymes production process during culture of white rot fungus, accordingly to direct the design of fermentation process, a kinetics model was built for the batch culture of Phanerochaete chrysosporium. The parameters in the model were calibrated based on the experimental data from free and immobilized culture separately. The difference between each variable's values calculated based on kinetics model and experimental data is within 15%. Comparing parameters for the free and the immobilized culture, it is found that maximum biomass concentrations are both 1.78 g/L; growth rate ratio of immobilized culture (0.6683 d(-1)) is larger than that of free culture (0.5144 d(-1)); very little glucose is consumed for biomass growth in free culture while in immobilized culture much glucose is used and ammonium nitrogen is consumed at a greater rate. Ligninolytic enzymes production process is non-growth related; fungal pellets can produce MnP (231 U/L) in free culture with a production rate of 115.8 U x (g x d)(-1) before peak and 26.1 U x (g x d)(-1) after peak, thus fed-batch is a possible mode to improve MnP production and fermentation efficiency. MnP (410 U/L) and LiP (721 U/L) can be produced in immobilized culture, but MnP and LiP production rate decrease from 80.1 U x (g x d)(-1) and 248.9 U x (g x d)(-1) to 6.04 U x (g x d)(-1) and 0 U x (g x d)(-1), respectively, indicating a proper feed moment is before the enzymes peak during fed-batch culture.