Acid-base Catalyst Research Articles

A nucleobase-driven P450 peroxidase system enables regio- and stereo-specific formation of C─C and C─N bonds

P450 peroxidase activities are valued for their ability to catalyze complex chemical transformations using economical H2O2; however, they have been largely underexplored compared to their monooxygenase and peroxygenase activities. In this study, we identified an unconventional P450 enzyme, PtmB, which catalyzes the dimerization of purine nucleobases and tryptophan-containing diketopiperazines (TDKPs), yielding C3-nucleobase pyrroloindolines and nucleobase-TDKP dimers. Unlike typical TDKP P450 enzymes reliant on NAD(P)H cofactors and electron transfer systems, PtmB, and its analogs exhibit remarkable peroxidase activity in synthesizing adenine and other modified 6-aminopurine nucleobase-TDKP dimers. Structural analysis of the PtmB-substrate complex, mutation assays, and computational investigations reveal adenine's dual role as both substrate and acid-base catalyst in activating H2O2 to generate Compound I (Cpd I). This initiates a specific radical cascade reaction, facilitating the formation of precise C─C and C─N bonds. Biochemical assays and molecular dynamics simulations demonstrate that adenine's 6-NH2 hydrogen-bonding networks induce necessary conformational changes for H2O2 activation, thereby driving peroxidase activity. This study unveils an unusual catalytic mechanism for the P450 peroxidase system and underscores the pivotal role of nucleobases in enzyme-mediated reactions, which offers different prospects for developing P450 peroxidases and nucleobase-based biocatalysts.

Biodiesel production from sheep fat catalyzed by CaO-SrO(x)/BCs(y) acid-base bifunctional catalyst and process optimization

Biodiesel production from sheep fat catalyzed by CaO-SrO(x)/BCs(y) acid-base bifunctional catalyst and process optimization

Construction of Spatially Separated Acid-Base Sites inside and outside Metal-Organic Framework Nanocrystals for Efficient Cascade Reactions.

The development of acid-base catalysts for one-pot cascade reactions remains challenging because of the inherent incompatibility of inorganic acid and base active sites. Here, we introduced an innovative approach that employs spatial separation to construct separated inorganic acid-base sites, achieving sequence control of acid-base cascade reactions. The as-prepared bifunctional catalyst applied metal-organic framework (MOF) nanocrystals as spatial separators, with the inside microcavities loaded with 1 nm inorganic polyoxometalate acid H3PMo12O40 clusters (NENU-5) and the outside crystal surface covered with basic CuCo layered double hydroxide (CuCo-LDH) nanosheets. By applying the resultant NENU-5@CuCo-LDH catalyst to cascade deacetalization-Knoevenagel condensation, over 99% of the benzaldehyde dimethyl acetal (BDMA) was transformed into the final benzylidene cyanoacetate (BCA) with a 99% yield at 80 °C and solvent-free conditions. Compared to the random NENU-5+CuCo-LDH, the NENU-5@CuCo-LDH with spatially separated acid-base sites indicated a higher reaction rate due to the designed reaction sequence and the shorter mass transfer pathway. Moreover, this hierarchical structure showed inherent shape selectivity and extraordinary stability. This study introduces spatial separation to address the incompatibility issue between inorganic acid and base active sites, offering novel perspectives for acid-base systems.

Heterobimetallic Synergism in Triple-Redox 2D Framework for Largely Boosted Water Oxidation and Flanked Carboxylic-Acid-Triggered Unconventional Tandem Catalysis.

A fish-bone-shaped and thermochemically stable 2D metal-organic framework (MOF) with multimodal active center-decked pore-wall is devised. Redox-active [Co2(COO)4] node and thiazolo[5,4-d]thiazole functionalization benefit this mixed-ligand MOF exhibiting electrochemical water oxidation with 375mV overpotential at 10mA cm-2 current density and 78mV per dec Tafel slope in alkaline medium. Pair of oppositely oriented carboxylic acids aids postmetalation with transition metal ions to engineer heterobimetallic materials. Notably, overpotential of Ni2+ grafted triple-redox composite reduces to 270mV with twofold declined Tafel slope than the parent MOF, ranking among the best-reported values, and outperforming majority of related catalysts. Significantly, turnover frequency and charge transfer resistance display 35.5 and 1.4-fold upsurge, respectively, with much uplifted chronopotentiometric stability and increase active surface area owing to synergistic Co(II)-Ni(II) coupling. The simultaneous presence of ─COOH and nitrogen-rich moieties renders this hydrogen-bonded MOF as acid-base synergistic catalyst for recyclable deacetalization-Knoevenagel reaction with >99% product yield under solvent-free mild condition. Besides control experiments, unique role of ─COOH as hydrogen-bond donor site in substrate activation is validated from comparing the performances of molecular-shearing approach-derived structurally similar unfunctionalized MOF, and the heterobimetallic composite. To the best of tandem Knoevenagel condensation, larger-sized acetal exhibits poor yield of α,β-unsaturated dicyanides, and demonstrates pore-fitting-mediated size-selectivity.

Conversion of Used Cooking Oil into Biodiesel by Utilizing Zirconia Catalyst as Acid Catalyst (SO4/ZrO2) and Base Catalyst (ZrO2/CaO)

Conversion of Used Cooking Oil into Biodiesel by Utilizing Zirconia Catalyst as Acid Catalyst (SO4/ZrO2) and Base Catalyst (ZrO2/CaO)

Sustainable repurpose of waste melamine foam into bifunctional catalysts for efficient CO2 capture and conversion

Global climate change has driven the scientific community to improve the utilization of a critical C1 resource carbon dioxide (CO2) through carbon capture utilization (CCU) technology. The cycloaddition of CO2 with epoxides provides perfect atom economy and economic feasibility to produce versatile cyclic carbonates used in various industries. However, the stable nature of CO2 and epoxides requires highly active catalysts. In this work, the repurpose of nitrogenous waste melamine foams (MFs) as high-performance catalysts for the cycloaddition of CO2 was explored. The pyrolyzed MF was modified with Cu to prepare a series of acid-base bifunctional porous catalysts (MFC-X-Cu). The results demonstrate that the acid-base synergy of the MFC-X-Cu catalysts increases the efficiency of the cycloaddition of various epoxides, yielding target products at 96–99% under mild conditions. Moreover, the characterization results revealed that the superior performance of MFC-X-Cu stems from its hollow structure and acid-base synergy, which are derived from nitrogen species in the repurposed MF and the post-modified copper component. The catalyst maintained consistent catalytic efficiency over five cycles, highlighting its strong recyclability. This work presents an eco-friendly and sustainable approach towards carbon neutrality by utilizing modified waste materials for CO2 conversion into high-value chemicals.

A highly photostable UVA filter derived from avobenzone

Avobenzone was derivatized to avo-glycerol by replacing the p-methoxy group with glycerol at the ortho position. Avo-glycerol exhibited absorption in the UVA range (315–400 nm), similar to avobenzone, indicating good UVA coverage. Unlike avobenzone, a solution of avo-glycerol in an aprotic solvent demonstrates remarkable photostability, with no significant decrease in absorbance at the UVA range after 6 h irradiation. This suggests that the hydroxyl group in avo-glycerol functions as an efficient acid-base catalyst in enolization. Consequently, the rapid enolization of the photochemically generated keto form prevents its accumulation. This inherent photostability of avo-glycerol eliminates the need for photo stabilizers in sunscreen formulations and provides greater flexibility in selecting other sunscreen components.

Endowing Three-Dimensional Porous Wood with Hydrophobicity/Superhydrophobicity Based on Binary Silanization.

Wood, as a natural biomass material, has long been a research focus. Superhydrophobic modified wood, in particular, has shown great promise in a myriad of engineering applications such as architecture, landscape, and shipbuilding. However, commercial development has encountered significant resistance due to preparation difficulties and sometimes unsatisfactory performance. In this study, hydrophobic/superhydrophobic wood comodified with methyltrimethoxysilane (MTMS) and 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDTMS) was fabricated by a one-step sol-gel method that uses an in situ growth process. Low-molecular-weight MTMS was allowed to permeate the three-dimensional porous wood interior. Then, acid-base catalysts were used to regulate the hydrolytic condensation process of MTMS and PFDTMS composite silanes to generate micro/nano hierarchical structures with low surface energy on the wood surface. The physicochemical characteristics of modified wood were investigated and the reaction mechanism established. The modified wood displayed excellent internal hydrophobicity/surface superhydrophobicity, water-moisture resistance, and dimensional stability at low fluorine concentrations. The resulting superhydrophobic surface provided stain resistance, self-cleaning ability, and loading capacity in water while exhibiting good mechanochemical stability; wood mechanical strength was also enhanced. This methodology created a superhydrophobic surface and bulk hydrophobization of wood in one step. Beyond wood, this approach is expected to provide a promising approach for functional modification of other porous composite materials.

Preparation and characterization of micro-cellular melamine foam supported SiO2 aerogel for building thermal insulation

This study aims to complement the advantages of SiO2 aerogel and melamine foam (MF) to produce high-performance building insulation materials. The optimal sol–gel scheme was determined by controlling system temperature, water content, amount of ethanol and amount of acid-base catalyst (orthogonal experiment). The density and porosity of MF/SiO2 aerogel were regulated by adjusting aging time, aging temperature and type of aging agent. Furthermore, the effects of different volume fractions hydrophobic modifier on the surface free energy and wettability of MF/SiO2 aerogel were also investigated. The experiment results showed that the prepared MF/SiO2 aerogel satisfies requirements for low density (0.089 g/cm3), low thermal conductivity at room temperature (0.0256 W m−1·K−1), and excellent hydrophobic performance (the contact angle was 140.1°). Meanwhile, it was found that SiO2 aerogel was stably and uniformly distributed in the pores of the MF and effectively enhanced the mechanical property (a maximum compressive strength of 0.2058 MPa), heat-shielding performance, flame retardant property, and sound absorption capacity(αmax = 0.76, αave = 0.31).Therefore, the MF/SiO2 aerogel composites exhibit exceptional application potential in comparison to conventional building insulation materials (such as EPS, Rock wool board, etc.) due to their significantly low thermal conductivity and remarkable flame retardant properties.

Proton Transfer via Arginine with Suppressed pKa Mediates Catalysis by Gentisate and Salicylate Dioxygenase.

Gentisate and salicylate 1,2-dioxygenases (GDO and SDO) facilitate aerobic degradation of aromatic rings by inserting both atoms of dioxygen into their substrates, thereby participating in global carbon cycling. The role of acid-base catalysts in the reaction cycles of these enzymes is debatable. We present evidence of the participation of a proton shuffler during catalysis by GDO and SDO. The pH dependence of Michaelis-Menten parameters demonstrates that a single proton transfer is mandatory for the catalysis. Measurements at variable temperatures and pHs were used to determine the standard enthalpy of ionization (ΔHion°) of 51 kJ/mol for the proton transfer event. Although the observed apparent pKa in the range of 6.0-7.0 for substrates of both enzymes is highly suggestive of a histidine residue, ΔHion° establishes an arginine residue as the likely proton source, providing phylogenetic relevance for this strictly conserved residue in the GDO family. We propose that the atypical 3-histidine ferrous binding scaffold of GDOs contributes to the suppression of arginine pKa and provides support for this argument by employing a 2-histidine-1-carboxylate variant of the enzyme that exhibits elevated pKa. A reaction mechanism considering the role of the proton source in stabilizing key reaction intermediates is proposed.

A confined catalysis strategy: Lewis acid-base (B/Br) and hydrogen bond donor (-OH) multi-functionalized core-shell catalyst for CO2 cycloaddition

In recent years, a significant number of metal-based catalysts were synthesized for the CO2 cycloaddition reaction. However, the leaking of active metal elements resulted in various environmental issues. To prevent the loss of active components and enhance the catalyst lifespan, a confined catalysis strategy involving a multi-functionalized core-shell catalyst with Lewis acid-base (B/Br) and hydrogen bond donor (-OH) was designed. It was noteworthy that B-mSiO2@MCM-IMOH featured multifunctional catalytic active sites, including Lewis acid-base (B/Br) and hydrogen bond donor (-OH), and the cooperative effect of B, Br and -OH significantly improved the catalytic activity. Therefore, B-mSiO2@MCM-IMOH demonstrated outstanding catalytic performance for the CO2 cycloaddition reaction. In addition, the core-shell molecular sieve, serving as a confined catalytic carrier, effectively enhanced the stability and recyclability of the catalyst. Utilizing DFT calculations, a cooperative catalytic mechanism was proposed involving Lewis acid-base (B/Br) and hydrogen bond donor (-OH). The synergistic interaction between B/Br and -OH markedly reduced the energy barrier for the ring-opening of propylene oxide from 58.6 kcal·mol−1 to 21.5 kcal·mol−1, thus facilitating the PO-CO2 cycloaddition reaction.

Acid-base synergistic effect towards catalytic transfer hydrogenation reactions

Catalytic transfer hydrogenation (CTH) of aldehydes/ketones by using alcohols as hydrogen donors is an attractive and environmentally friendly hydrogenation technology, which has evoked widespread attention in synthesis of fine chemicals from biomass resources. In this work, a Co-Al mixed metal oxide catalyst (Co1Al2-MMO-200) was obtained through structural topological transformation process of layered double hydroxides, which was used in the CTH reaction of furfural with isopropanol. Notably, the reaction rate achieves 0.023 mol g−1 h−1, which is preponderate to acid-base catalysts earlier reported. The joint research based on CO2-TPD, NH3-TPD and poisoning experiment substantiates that the synergy effect of acid-base sites plays an essential role in this catalytic system. Isotopic labelling MS, in-situ FT-IR and DFT studies further verify that the CTH reaction of furfural occurs via the Meerwein-Ponndorf-Verley (MPV) route, in which the basic site promotes the deprotonation of isopropanol whilst the acid site facilitates the formation of a six-membered ring transition state. This work demonstrates an acid-base synergetic catalysis for the CTH reaction by revealing the structure-property correlation and exploring reaction route, which is instructive for designing high-performance heterogenous catalysts.

CO2 derived ABA triblock all-polycarbonate thermoplastic elastomer with ultra-high elastic recovery

Although triblock polycarbonate thermoplastic elastomers (TPEs) have recently attracted great interests due to their biodegradability, insufficient attentions have been paid to improving the elastomeric properties. Through a tandem reaction strategy involving CO2 / allyl glycidyl ether (AGE) / cyclohexene oxide (CHO), poly(cyclohexene carbonate)-b-poly(allyl glycidyl ether carbonate)-b-poly(cyclohexene carbonate) (PCAC) is successfully synthesized using a metal-free Lewis acid-base pair catalyst. The synthesized PCACs are pure well-defined ABA triblock all-polycarbonate, which is supported by 1H NMR, gel permeation chromatography (GPC), and diffusion-ordered spectroscopy (DOSY). A simple modification by grafting alkylthiol chains to PCAC results in excellent TPEs named PCAC-g-S-CaH2a+1 (PCASaC). The synthesized TPEs are characterized by atomic force microscopy (AFM), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and mechanical test. They demonstrate a semi-network and semi-domain phase separation structure, wide service temperature range, good strength, high elongation, and extremely high elastic recovery properties. This low-cost, biodegradable, high-performance TPE shows great potential for applications in biomedical, wearable products, sports equipment, and other fields.

Advances in Synthesis of Indazole Variants: A Comprehensive Review of Transition Metal, Acid/Base and Green Chemistry-based Catalytic Approaches

Background:: Indazole is a heterocyclic motif widely used in medicinal chemistry due to its positive photophysical properties. The development of new methods for synthesizing the indazole scaffold is of great importance in drug discovery. Methods:: This study presents a detailed review of current advances in indazole synthesis, focusing on catalyst-based and green chemistry approaches. The analysis is classified based on acid-base and transition-metal catalysts and green chemistry methods. Catalyst-based advances have given a new impetus to the synthesis of this effective pharmacophore. Results:: The extensive literature on indazole synthesis demonstrates the notable progress achieved through catalyst-based approaches. These methods have enabled researchers to create a wide range of indazole derivatives and analogs, facilitating their application in pharmaceutical products and organic molecules. The use of acid-base and transition-metal catalysts has been particularly effective in enhancing the efficiency and selectivity of indazole synthesis. Conclusion:: Indazoles and their variants are widely used in pharmaceutical products and organic molecules. The recent literature indicates that catalyst-based approaches have resulted in significant advancements in indazole synthesis. This review may be useful for researchers in medicinal chemistry, content chemistry, and agrochemistry.

Synthesis of Polysubstituted Pyridines via Nitrogen-doped Graphene Catalyzed One-Pot Multicomponent Reaction under Solvent-Free Conditions

Abstract: Polysubstituted pyridine derivatives were produced with high to excellent yields in the presence of nitrogen-doped graphene (NDG) as a dual acid-based catalyst. NDG efficiently catalyzes the multicomponent reaction between arylaldehydes, diethyl-acetylene dicarboxylates, malononitrile, and ammonium acetate under solvent-free conditions at 80°C to afford the polysubstituted pyridines in short reaction times. The structures of the synthesized pyridines were established by Ft-IR, 1H, and 13C NMR spectroscopic analysis. The advantages of this method include the in-situ oxidation of prepared 1,4-dihydropyridines, one-pot procedure, solventless system, operational simplicity, and no column chromatography. Additionally, neither toxic solvents nor catalysts are needed, and the procedure can be very reliable among the reported methodologies. The yields and reaction times in the presence of four times recycled catalyst are in comparable to the fresh catalyst.

Recent advances in co-immobilization of organic acids and bases for cooperative and tandem catalysis

Acid–base bifunctional catalysts have been extensively used for a series of CC bond formation reactions. Among these catalysts, organic acid–base catalysts have attracted wide attention due to their structural variety, conformational dynamics, and enantioselectivity. To prevent mutual deactivation, a simple, effective, and versatile strategy is the attachment of both acid and base onto the surfaces of supports. In particular, the co-immobilization of organic acids and bases not only enhances synergistic effects in cooperative catalysis but also improves yields to desired products by controlling the diffusion of intermediates in tandem catalysis, leading to significant improvements in energy and atom efficiency. In this review, we highlight recent works addressing the broad topic of the co-immobilization of organic acids and bases for cooperative and tandem catalysis. We mainly focus on the synthetic strategies for silica-supported organic acid–base catalysts and polymer-supported organic acid–base catalysts. Furthermore, we summarize and discuss the structure–activity relationships of these catalysts. Last, the remaining issues and prospects will be discussed to advance the rational design and engineering of co-immobilized acid–base bifunctional catalysts.

Precisely constructing Ce-loaded sulfur resistant catalyst for efficient methane dry reforming

Previous studies have shown that pure cerium dioxide as Lewis acid-base catalyst can effectively resist sulfur poisoning. At a certain H2S concentration, it can effectively promote methane dry reforming reaction, while the selection of a suitable support is of great significance to reduce the dosage of cerium, thus reducing the production cost and improving the reaction efficiency simultaneously. The hydroxyapatite (HAP) chosen as the support in this work has the advantages of low cost, easy preparation and high stability. Meanwhile, it is verified that ion exchange occurred on the surface of HAP contributes to higher amount of Ce3+and oxygen vacancies, when compared with other carriers, as proved by XPS, Raman, EPR, and in situ NH3-DRIFTS, thus forming higher amount of Lewis acid-base active sites and improving the reforming activity. Besides, H2S acceleration mechanism over oxygen vacancy induced catalyst is also proposed in this work.

Sulfonic acid functionalized SBA−15 catalyst and mercaptopropionic acid promotor for the selective synthesis of p,p′−bisphenol A: Replacement to mineral acid−based process

The significance of selective catalysis in producing plastic monomers is crucial to meet sustainability and economic requirements. It is essential to develop a selective solid acid catalyst to replace irrecoverable corrosive mineral acids and thermolabile sulfonated resins for the production of p,p′−bisphenol A (BPA) isomer, a key intermediate in polycarbonate production. However, limited success has been achieved due to low activity and selectivity towards the desired p,p′−BPA isomer. Herein, a mild and selective route is presented for producing p,p′−BPA using SBA-15 functionalized sulfonic acid catalysts. Sulfonic acid-based catalysts with and without alkyl chain linkers, supported on SBA−15, were synthesized to evaluate the effect of acidity, and textual properties on the catalytic efficiency, and product selectivity. Among all the synthesized catalysts, SBA−15−Pr−SO3H exhibited the highest product selectivity. The addition of mercaptopropionic acid (as a promoter) enhanced the catalytic efficiency and afforded ∼99% acetone conversion, with 97.3% p,p′−BPA selectivity. A detailed mechanism with and without the promoter is proposed. The study also highlights the potential of mesoporous SBA−15−supported sulfonic acid catalysts as a selective and efficient catalyst for synthesizing bisphenol derivatives from the lignocellulose biomass−derived platform molecules, addressing challenges posed by fossil resources.

One-pot catalytic conversion of sugars to methyl lactate over acid-base bifunctional Sn/MgO catalysts

Alkyl lactates represent such green added-value chemicals that commonly used as biodegradable green solvents, detergents, pharmaceutical intermediates et al. Catalytic conversion of carbohydrates to methyl lactate (MLA) is a representative way for high-value utilization of biomass and the key lies in the development of highly efficient catalysts. In methanol, strong acid or alkaline catalysts are usually used under high temperature and high pressure, suffering from problems such as low selectivity, high cost or contamination of environment. This study aims to develop an acid-base bifunctional heterogeneous catalyst for the one-pot conversion of sugars to MLA under mild conditions. Sn/Mg composite oxides was synthesized by a coprecipitation method and further modified by poly (vinyl imidazole) ([PVIM]) to tune the hydrophilicity. Effect of polymer and Sn amount, calcination temperature, reaction temperature, catalyst dosage, and substrate concentration were investigated. The acid-base properties were characterized by NH3-TPD, pyridine-FTIR and CO2-TPD analysis. It was found that the presence of medium acid sites and medium base sites played an important role to the cascade reactions of carbohydrates to MLA. An optimum MLA yield of 55.4% was achieved over 10[PVIM]-5Sn/MgO (0.05 g) with complete conversion of glucose (28 mM) at 140 ℃, 2 MPa N2 for 10 h. The reaction conditions are mild and no strong acid or strong base catalyst is required. Furthermore, a possible reaction mechanism was proposed that the introduction of [PVIM] effectively regulated the local microenvironment of active sites and the acid base synergism greatly promoted the retro-aldol condensation, dehydration and hydrogen transfer reactions during the conversion of glucose to MLA.

Nanostructured Solid/Liquid Acid Catalysts for Glycerol Esterification: The Key to Convert Liability into Assets.

Owing to the growing concerns about the dwindling fossil fuel reserves, increasing energy demand, and climate emergency, it is imperative to develop and deploy sustainable energy technologies to ensure future energy supply and to transition to the net-zero world. In this context, there is great potential in the biorefinery concept for supplying drop in biofuels in the form of biodiesel. Biodiesel as a fuel can certainly bridge the gap where electrification or the use of hydrogen is not feasible, for instance, in heavy vehicles and in the farm and marine transportation sectors. However, the biodiesel industry also generates a large amount of crude glycerol as the by-product. Due to the presence of several impurities, crude glycerol may not be a suitable feedstock for all high-value products derived from glycerol, but it fits well with glycerol esterification for producing glycerol acetins, which have numerous applications. This review critically looks at the processes using nanostructured solid/liquid acid catalysts for glycerol esterification, including the economic viability of the scale-up. The homogeneous catalysts reviewed herein include mineral acids and Brønsted acidic ionic liquids, such as SO3H-functionalized and heteropoly acid based ionic liquids. The heterogeneous catalysts reviewed herein include solid acid catalysts such as metal oxides, ion-exchange resins, zeolites, and supported heteropoly acid-based catalysts. Furthermore, the techno-economic analysis studies have shown the process to be highly profitable, confirming the viability of glycerol esterification as a potential tool for economic value addition to the biorefinery industry.