One-pot chemo-enzymatic conversion of D-xylose to furfuralcohol by sequential dehydration with oxalic acid plus tin-based solid acid and bioreduction with whole-cells

One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

An efficient and sustainable furfurylamine production from biomass-derived furfural by a robust mutant ω-transaminase biocatalyst

Furfurylamine is a key furan-based compound for manufacturing perfumes, fibers, additives, medicines and agrochemicals. It can be obtained by amination of furfural by ω-transaminase (AtAT) from Aspergillus terreus. In this work, site-directed mutant of amino acid residues [Threonine (T) at AT130 was mutated to Methionine (M) and Glutamic acid (E) at AT133 was mutated to Phenylalanine (F)] was used to change in the flexible region of AtAT. The transamination activity and thermostability were significantly improved. In ChCl:MA (30 wt%), furfural (500 mM) was efficiently transformed into furfurylamine (92% yield) with TMEF after 12 h. 101.3 mM of biomass-derived furfural and 129.7 mM of D-xylose-derived furfural were wholly converted into furfurylamine within 5 h, achieving the productivity of 0.465 g furfurylamine/(g xylan in corncob) and 0.302 g furfurylamine/(g D-xylose). This established chemoenzymatic conversion strategy by bridging chemocatalysis and biocatalysis could be utilized in the valorisation of renewable biomass to valuable furans.

Uranium-Doped Zinc, Copper, and Nickel Oxides for Enhanced Catalytic Conversion of Furfural to Furfuryl Alcohol: A Relativistic DFT Study

Transition metal oxides (TMOs) and actinide ones (AnOs) have been widely applied in catalytic reactions due to their excellent physicochemical properties. However, the reaction pathway and mechanism, especially involving TM–An heterometallic centers, remain underexplored. In this respect, relativistic density functional theory (DFT) was used to examine uranium-doped zinc, copper, and nickel oxides for their catalytic activity toward the conversion of furfural to furfuryl alcohol. A comparison was made with their undoped TMOs. It was found that the three TMOs were capable of catalyzing the reaction, where the free energies of adsorption, hydrogenation, and desorption fell between −33.93 and 45.00 kJ/mol. The uranium doping extremely strengthened the adsorption of CuO-U and NiO-U toward furfural, making hydrogenation or desorption much harder. Intriguingly, ZnO-U showed the best catalytic performance among all six catalyst candidates, as its three reaction energies were very small (−10.54–8.12 kJ/mol). The reaction process and mechanism were further addressed in terms of the geometrical, bonding, charge, and electronic properties.

Efficient Synthesis of Furfuryl Alcohol from Corncob in a Deep Eutectic Solvent System

As a versatile and valuable intermediate, furfuryl alcohol (FOL) has been widely used in manufacturing resins, vitamin C, perfumes, lubricants, plasticizers, fuel additives, biofuels, and other furan-based chemicals. This work developed an efficient hybrid strategy for the valorization of lignocellulosic biomass to FOL. Corncob (75 g/L) was catalyzed with heterogenous catalyst Sn-SSXR (2 wt%) to generate FAL (65.4% yield) in a deep eutectic solvent ChCl:LA–water system (30:70, v/v; 180 °C) after 15 min. Subsequently, the obtained FAL liquor containing FAL and formate could be biologically reduced to FOL by recombinant E. coli CF containing aldehyde reductase and formate dehydrogenase at pH 6.5 and 35 °C, achieving the FOL productivity of 0.66 g FOL/(g xylan in corncob). The formed formate could be used as a cosubstrate for the bioreduction of FAL into FOL. In addition, other biomasses (e.g., sugarcane bagasse and rice straw) could be converted into FOL at a high yield. Overall, this hybrid strategy that combines chemocatalysis and biocatalysis can be utilized to efficiently valorize lignocellulosic materials into valuable biofurans.

Biorefinery Cascade Processing for Converting Corncob to Xylooligosaccharides and Glucose by Maleic Acid Pretreatment

Corncob as an abundant and low-cost waste resource has received increasing attention to produce value-added chemicals, it is rich in xylan and regarded as the most preferable feedstock for preparing high value added xylooligosaccharides. The use of xylooligosaccharides as core products can cut costs and improve the economic efficiency in biorefinery. In this study, maleic acid, as a non-toxic and edible acidic catalyst, was employed to pretreat corncob and produce xylooligosaccharides. Firstly, the response surface methodology experimental procedure was employed to maximize the yield of the xylooligosaccharides; a yield of 52.9% (w/v) was achieved with 0.5% maleic acid (w/v) at 155 °C for 26 min. In addition, maleic acid pretreatment was also beneficial to enhance the enzymatic hydrolysis efficiency, resulting in an enzymatic glucose yield of 85.4% (w/v) with a total of 10% solids loading. Finally, a total of 160 g of xylooligosaccharides and 275 g glucose could be produced from 1000 g corncob starting from the maleic acid pretreatment. Overall, a cascade processing for converting corncob to xylooligosaccharides and glucose by sequential maleic acid pretreatment and enzymatic hydrolysis was successfully designed for the corncob wastes utilization.

Catalytic valorization of biomass for furfuryl alcohol by novel deep eutectic solvent-silica chemocatalyst and newly constructed reductase biocatalyst

Chemoenzymatic cascade catalysis using deep eutectic solvent-silica heterogeneous catalyst and reductase biocatalyst was constructed for synthesizing furfuryl alcohol from biomass in one-pot manner. A novel heterogeneous catalyst B:LA-SG(SiO₂) was firstly prepared by immobilizing deep eutectic solvent Betaine:Lactic acid on silica with sol-gel method using tetraethyl orthosilicate as silicon source. High furfural yield (45.3%) was achieved from corncob with B:LA-SG(SiO₂) catalyst (2.5 wt%) in water at 170 ˚C for 0.5 h. Possible catalytic mechanism for converting biomass into furfural was proposed. Moreover, one newly constructed recombinant E. coli KF2021 cells containing formate dehydrogenase and reductase was utilized to transform corncob-valorized furfural into furfuralcohol at 97.7% yield at pH 7.5 and 40 ˚C via HCOONa-driven coenzyme regeneration. Such a hybrid process was constructed for tandem chemocatalysis and biocatalysis in a same reactor, potentially reducing the operation cost, which had potential application for valorization of biomass to value-added furans.

Efficient Valorization of Sugarcane Bagasse into Furfurylamine in Benign Deep Eutectic Solvent ChCl:Gly-Water

Recently, highly efficient production of valuable furan-based chemicals from available and renewable lignocellulosic biomass has attracted more and more attention via a chemoenzymatic route in an environmentally friendly reaction system. In this work, the feasibility of chemoenzymatically catalyzing sugarcane bagasse into furfurylamine with heterogeneous catalyst and ω-transaminase biocatalyst was developed in the deep eutectic solvent (DES) ChCl:Gly-water. Sulfonated Al-Laubanite was firstly synthesized to catalyze sugarcane bagasse to furfural. SEM, BET, XRD, and FT-IR were used to characterize Al-Laubanite. Catalyst Al-Laubanite structure was significantly different from carrier laubanite. High furfural yield (60.9%) was achieved by catalyzing sugarcane bagasse in 20 min at 170 ℃ and pH 1.0 by Al-Laubanite (2.4 wt%) in the presence of ChCl:Gly (20 wt%). Potential catalytic mechanism was proposed under the optimized catalytic condition. In addition, one recombinant E. coli CV harboring ω-transaminase could completely transform biomass-derived furfural to furfurylamine at 40 °C and pH 7.5 using L-alanine as amine donor in ChCl:Gly-water (20:80, wt:wt). This established chemoenzymatic cascade reaction strategy was successfully utilized for valorization of biomass into furan-based chemicals in the benign ChCl:Gly-water system.

Chemoenzymatic Conversion of Biomass-Derived D-Xylose to Furfuryl Alcohol with Corn Stalk-Based Solid Acid Catalyst and Reductase Biocatalyst in a Deep Eutectic Solvent–Water System

In this work, the feasibility of chemoenzymatically transforming biomass-derived D-xylose to furfuryl alcohol was demonstrated in a tandem reaction with SO42−/SnO2-CS chemocatalyst and reductase biocatalyst in the deep eutectic solvent (DES)–water media. The high furfural yield (44.6%) was obtained by catalyzing biomass-derived D-xylose (75.0 g/L) in 20 min at 185 °C with SO42−/SnO2-CS (1.2 wt%) in DES ChCl:EG–water (5:95, v/v). Subsequently, recombinant E.coli CF cells harboring reductases transformed D-xylose-derived furfural (200.0 mM) to furfuryl alcohol in the yield of 35.7% (based on D-xylose) at 35 °C and pH 7.5 using HCOONa as cosubstrate in ChCl:EG–water. This chemoenzymatic cascade catalysis strategy could be employed for the sustainable production of value-added furan-based chemical from renewable bioresource.

Valorisation of corncob into furfuryl alcohol and furoic acid via chemoenzymatic cascade catalysis

Heterogeneous tin-based sulfonated graphite (Sn-GP) catalyst was prepared with graphite as carrier. The physicochemical properties of Sn-GP were captured by FT-IR, XRD, SEM and BET. Organic acids with different pKa values were used to assist Sn-GP for transforming corncob (CC), and a linear equation (Furfural yield  = - 7.563 ×  pKa  + 64.383) (R2  =  0.9348) was fitted in acidic condition. Using sugarcane bagasse, reed leaf, chestnut shell, sunflower stalk and CC as feedstocks, co-catalysis of CC (75.0 g/L) with maleic acid (pKa  =  1.92) (0.5 wt%) and Sn-GP (3.6 wt%) yielded the highest furfural yield (47.3%) for 0.5 h at 170 °C. An effective furfural synthesis was conducted via co-catalysis with Sn-GP and maleic acid. Subsequently, E. coli CG-19 and TS completely catalyzed the conversion of corncob-derived FAL to furfurylalcohol and furoic acid, respectively. Valorisation of available renewable biomass to furans was successfully developed in tandem chemoenzymatic reaction.

Enhanced enzymatic saccharification of sorghum straw by effective delignification via combined pretreatment with alkali extraction and deep eutectic solvent soaking

Hydrogen bond donor (HBD) in ChCl-based deep eutectic solvent (DESs) had significant influence on the Sorghum straw (SS) pretreatment. Lactic acid (LAC) was chosen as the appropriate HBD for preparing ChCl-based DES to pretreat Sorghum straw (SS). Furthermore, sequential pretreatment with dilute sodium hydroxide (0.75 wt%) for 1 h at 121 °C and ChCl:LAC soaking at 140 °C for 40 min was applied to pretreat SS for removing lignin (78.4%) and xylan (67.6%). Hydrolysis for 72 h, the reducing sugar yield reached 94.9%. Moreover, relationships of delignification and xylan removal with saccharification were explored after pretreatment. Finally, the fermentability of SS-hydrolysates was verified by bioethanol fermentation by S. cerevissiae with the yield of 0.45 g ethanol/g glucose. No significant inhibition was observed on ethanol fermentation. Obviously, establishment of high-efficient combination pretreatment with alkali extraction and ChCl:LAC soaking was successfully demonstrated for enhancing enzymatic saccharification of SS.

Improved one-pot synthesis of furfural from corn stalk with heterogeneous catalysis using corn stalk as biobased carrier in deep eutectic solvent-water system

Using acid-treated corn stalk (CS) as biobased carrier, heterogeous SO₄^2-/SnO₂-CS catalyst was firstly prepared to catalyze CS into fufural in deep eutectic solvent-water system. The physical properties of SO₄^2-/SnO₂-CS were captured by FT-IR, NH₃-TPD, XRD, XPS, and BET. SO₄^2-/SnO₂-CS (1.2 wt%) could be used to catalyze CS (75.0 g/L) with MgCl₂ (15.0 g/L) to produce furfural (102.3 mM) in the yield of 68.2% for 0.5 h at 170 °C in ChCl:EG-water (20:80, v:v). Moreover, enhanced synthesis of furfural was explored based on the structure changes of CS, furfural yields and formation of byproducts. Finally, the potential catalytic mechanism for catalyzing CS into furfural and byproducts was proposed using SO₄^2-/SnO₂-CS as catalyst in ChCl:EG-water containing MgCl₂. In summary, this established ChCl:EG-water system and optimized catalytic condition facillitated to synthesize furfural from biomass with biobased solid acid catalyst.

Predicting the Conformation of Organic Catalysts Grafted on Silica Surfaces with Different Numbers of Tethering Chains: The Silicopodality Concept

Hybrid catalysts are attracting much attention, since they combine the versatility and efficiency of homogeneous organic catalysis with the robustness and thermal stability of solid materials, for example, mesoporous silica; in addition, they can be used in cascade reactions, for exploring both organic and inorganic catalysis at the same time. Despite the importance of the organic/inorganic interface in these materials, the effect of the grafting architecture on the final conformation of the organic layer (and hence its reactivity) is still largely unexplored. Here, we investigate a series of organosiloxanes comprising a pyridine ring (the catalyst model) and different numbers of alkylsiloxane chains used to anchor it to the MCM-41 surface. The hybrid interfaces are characterized with X-ray powder diffraction, thermogravimetric analyses, Fourier-transform infrared spectroscopy, nuclear magnetic resonance techniques and are modeled theoretically through molecular dynamics (MD) simulations, to determine the relationship between the number of chains and the average position of the pyridine group; MD simulations also provide some insights about temperature and solvent effects.

Recent Progresses of Superhydrophobic Coatings in Different Application Fields: An Overview

With the development of material engineering and coating industries, superhydrophobic coatings with exceptional water repellence have increasingly come into researchers’ horizons. The superhydrophobic coatings with corrosion resistance, self-cleaning, anti-fogging, drag-reduction, anti-icing properties, etc., meet the featured requirements from different application fields. In addition, endowing superhydrophobic coatings with essential performance conformities, such as transparency, UV resistance, anti-reflection, water-penetration resistance, thermal insulation, flame retardancy, etc. plays a remarkable role in broadening their application scope. Various superhydrophobic coatings were fabricated by diverse technologies resulting from the fundamental demands of different fields. Most past reviews, however, provided only limited information, and lacked detailed classification and presentation on the application of superhydrophobic coatings in different sectors. In the current review, we will highlight the recent progresses on superhydrophobic coatings in automobile, marine, aircraft, solar energy and architecture-buildings fields, and discuss the requirement of prominent functionalities and performance conformities in these vital fields. Poor durability of superhydrophobic coating remains a practical challenge that needs to be addressed through real-world application. This review serves as a good reference source and provides insight into the design and optimization of superhydrophobic coatings for different applications.

Chemoenzymatic conversion of Sorghum durra stalk into furoic acid by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis

In this study, chemoenzymatic conversion of Sorghum durra stalk (SDS) into furoic acid was developed by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis method. Dry dewaxed SDS (75 g/L) was catalyzed into furfural at 57.8% yield with heterogeneous Sn-argil (2.0 wt% dosage) in n-ethyl butyrate-H₂O (1:1, v:v) biphasic system using a microwave (600 W) for 10 min at 180 °C. In this biphasic media (pH 6.5), SDS-derived furfural (125.0 mM) was biologically oxidized to furoic acid by immobilized Brevibacterium lutescens cells harboring furfural-oxidizing activity at 30 °C, and furfural was wholly transformed to furoic acid within 24 h. Finally, the recovery and reuse of the Sn-argil catalyst and immobilized biocatalysts were conducted for synthesizing furoic acid from SDS in the biphasic system. This chemoenzymatic route can be attractive for furoic acid production.

Polymorph-Dependent Luminescence Response to Acid Vapors and Its Application in Safety Protection of File Information

A Schiff base, (E)-1-(phenylimino)methyl-2-hydroxylnaphthalene (PIHN), was found to form both nonluminescent and luminescent polymorphs. A unique luminescence "turn on" behavior was observed when the nonluminescent polymorph was fumed with the vapor of aliphatic acids with two or three carbons in the main chain, while the luminescent polymorphs almost did not change the emission color under the same condition. As we know, this is the first report on polymorph-dependent acid response which discloses the influence of crystalline phase on acid-responsive behavior. The formation of hydrogen bonds between PIHN and aliphatic acid is proposed to be the reason for the responsive behavior of the nonemissive polymorph, and such a mechanism is different from the common protonation mechanism. A novel safety protection method of file information has been developed based on the polymorph-dependent luminescence response of PIHN. In addition, we disclose that a crystalline form could show multiple responsive behaviors toward different acids, which benefits the further design of novel acid sensors, such as the sensors that can qualitatively analyze the species of the acid source in an acidic environment.