Exploring Biliverdin's Molecular Interactions with Cu- and Fe-Based MOFs: A Unified In Vitro Study with Photoacoustic Analysis

Metal-organic frameworks (MOFs) have shown promise in enhancing the stability of biomolecules. Herein, biliverdin (BVD), a photoacoustic (PA) and fluorescent agent, was immobilized within the pores of NH2-MIL-101 (Fe) (FeMOFs) and on the surface of CuBTC crystallites (CuMOFs). MOFs were found to enhance the fluorescence emission and quench the PA intensity of biliverdin. Fluorescence and PA studies, in tandem with DFT simulations, demonstrated that the spectral interactions between MOFs and BVD resulted from interactions between biliverdin and the MOF pores and surfaces in addition to alterations in the HOMO-LUMO energy gap. The MOF internal structure of the MOF played a role in BVD loading, with the FeMOFs enabling greater BVD encapsulation, while CuMOF interactions with BVD primarily took place on the MOF surface. The role of these surface vs pore interactions in the release of biliverdin was explored. This study demonstrates that the effects of the MOF internal structure, surface interactions, and energy interactions should be taken into consideration for biomolecule loading in MOFs.

Homogeneous Catalyzed Direct Conversion of Furfural to Gamma-Valerolactone

Herein, we report the direct conversion of biomass-derived furfural to γ-valerolactone (GVL) in a one-pot system, using the combination of Ru-MACHO-BH and a Brønsted acid (H3PO4). A GVL yield of 84 % is achieved under mild reaction conditions using 1 mol% of Ru-MACHO-BH and 3.8 M H3PO4(aq) at 100 °C for 7 hours.

Selective Degradation of Technically Relevant Lignin to Vanillic Acid and Protocatechuic Acid

A new and practical method for the thermal degradation of technically relevant bio-based lignin is presented. By heating a solution of lignin in highly concentrated caustic potash, vanillic acid is almost exclusively obtained in yields up to 10.6 wt %. By altering the reaction parameters, the selectivity of the reaction can be shifted towards the demethylation product, protocatechuic acid, which is obtained in a yield of 6.9 wt %. Furthermore, the procedure was applicable to different types of Kraft and organosolv lignin. To create an economically feasible process, ion exchange resins were used for the work-up of the highly caustic reaction media without neutralizing the complete mixture. By the selective removal of the desired vanillic acid from the caustic potash, this alkaline media could directly be reused for at least 5 further lignin degradations without significant loss of yield.

Catalytic Cleavage of the C-O Bonds in Lignin and Lignin Model Compounds by Metal Triflate Catalysts

The effective cleavage of C-O bonds in linkages of lignin was one of the significant strategies promoting lignin valorization. Herein, the strategy of C-O bonds cleavage of lignin using metal triflate as the catalyst was developed. The carboxylic acid or alcohol could be used as the nucleophile to stabilize the reactive intermediates formed during the depolymerization of lignin, and the corresponding ester/ether compounds could be obtained. This catalytic system was suitable for the C-O bond cleavage in α-O-4 and β-O-4 linkages with excellent efficiency. Additionally, reaction conditions were optimized. The reaction mixture was detected by 1 H NMR, and no other byproducts were found. As for treated lignin samples, the cleavage of C-O bonds in linkages was determined by 2D HSQC NMR, the increased content of the phenol hydroxyl group was proved by FT-IR, and the reduced molecular weight was investigated by GPC. Furthermore, multiple phenolic compounds were detected by GC-MS in the reaction mixtures.

Facile Hydrogenolysis of Sugars to 1,2-Glycols by Ru@PPh3/OPPh3 Confined Large-Pore Mesoporous Silica

Tandem hydrogenation vis-à-vis hydrogenolysis of xylose to 1,2-glycols remains a major challenge. Although one-pot conversion of xylose to 1,2-glycols requires stringent conditions, a sustainable approach would be quite noteworthy. We have developed a microwave route for the one-pot conversion of pentose (C5) and hexose (C6) sugars into glycol and hexitol, without pressurized hydrogen reactors. A pronounced hydrogenolysis of sugars to glycols is observed by Ru single atom (SA) on triphenylphosphine/phosphine oxide-modified silica (Ru@SiP), in contrast to Ru SA on pristine (Ru@SiC) and 3-aminopropyl-modified silica (Ru@SiN). A promising "ligand effect" was observed through phosphine modification of silica that presents a 70% overall yield of all reduced sugars (xylitol + glycols) from a 99% conversion of xylose with Ru@SiP. A theoretical study by DFT depicts an electronic effect on Ru-SA by triphenylphosphine that promotes the catalytic hydrogenolysis of sugars under mild conditions. Hence, this research represents an important step for glycols from biomass-derived sources.

Inhibition of the Decomposition Pathways of Ruthenium Olefin Metathesis Catalysts: Development of Highly Efficient Catalysts for Ethenolysis

Ruthenium-based Hoveyda-type olefin metathesis catalysts bearing novel rigid spirocyclic alkyl amino carbenes (CAACs) have been developed. They are characterized by exceptional stability toward decomposition through β-elimination and bimolecular pathways, thus enabling unprecedented efficiency in the cross-metathesis of seed oil-derived fatty acid esters with ethylene (ethenolysis). Catalyst loading as low as 100 ppb was applied to the ethenolysis of the model substrate methyl oleate, leading to a remarkable turnover number (TON) of 2.6 million, significantly higher than previously reported (TON 340 000 at 1 ppm and 744 000 at 0.5 ppm catalyst loading). Ethenolysis of methyl esters derived from high oleic sunflower oil and rapeseed oil, readily available on an industrial scale, inexpensive, and renewable feedstocks, was for the first time effectively carried out with 0.5 ppm catalyst loading with TON as high as 964 000.

Recent Progress and Opportunity of Metal Single-Atom Catalysts for Biomass Conversion Reactions

The conversion of lignocellulosic biomass into platform chemicals and fuels by metal single atoms is a new domain in solid catalysis research. Unlike the conventional catalysis route, single-atom catalysts (SACs) proliferate maximum utilization efficiency, high catalytic activity, and good selectivity to the desired product with an ultralow loading of the active sites. More strikingly, SACs show a unique cost-effective pathway for the conversion of complex sugar molecules to value-added chemicals in high yield and selectivity, which may be hindered by conventional metal nanoparticles. Primarily, SACs having adjustable active sites could be easily modified using sophisticated synthetic techniques based on their intended reactions. This review covers current research on the use of SACs with a strong emphasis on the fundamentals of catalyst design, and their distinctive activities in each type of reaction (hydrogenation, hydrogenolysis, hydrodeoxygenation, oxidation, and dehydrogenation). Furthermore, the fundamental insights into the superior actions of SACs within the opportunity and prospects for the industrial-scale synthesis of value-added products from the lignocelluloses are covered.

Synthesis and catalytic activity of well-defined Co(I) complexes based on NHC-phosphane pincer ligands

A new methodology for the preparation of Co(I)-NHC (NHC = N-heterocyclic carbene) complexes, namely, [Co(PCNHCP)(CO)2][Co(CO)4] (1) and [Co(PCNHCP)(CO)2]BF4 (2), has been developed (PCNHCP = 1,3-bis(2-(diphenylphosphanyl)ethyl)-imidazol-2-ylidene). Both complexes can be straightforwardly prepared by direct reaction of their parent imidazolium salts with the Co(0) complex Co2(CO)8. Complex 1 efficiently catalyses the reductive amination of furfural and levulinic acid employing silanes as reducing agents under mild conditions. Furfural has been converted into a variety of secondary and tertiary amines employing dimethyl carbonate as the solvent, while levulinic acid has been converted into pyrrolidines under solventless conditions. Dehydrocoupling of the silane to give polysilanes has been observed to occur as a side reaction of the hydrosilylation process.

A flexible physical protection process for lignin extraction

Research on lignin valorization has gained ground, driven by its potential to replace fossil-based phenolics in bio-based applications. Technical lignins are structurally complex and still poorly characterized, prompting the need for novel extraction processes for lignin of high analytical quality. In this context, a two-step cyclic extraction process for lignin was contrasted with a one-step cyclic extraction. The latter was shown to preserve the native structure of the spruce lignin product better and improved the yields of both the extracted lignin and residual fiber fraction. The application of the one-step cyclic extraction process to birchwood resulted in a similar protection of the lignin structure. Overall, a flexible physical protection (FPP) process for extraction of lignin with an abundance of native bonds is presented. The lignin product has a high abundance of ether bonds and hydroxyl functionalities, which are of interest in biochemical, polymer, and material applications.

Zinc Catalyzed Hydroboration of Esters and Nitriles with Pinacolborane

We developed a bench-stable iminopyridine-ligated zinc complex for the effective catalytic hydroboration of esters and nitriles under solvent-free conditions. Various esters and nitriles bearing different functionalities were selectively reduced to form corresponding alcohols and amines in good yields. Detailed Hammett plots are provided to explain the electronic effects on the phenyl ring.

Ru-Catalyzed Direct Asymmetric Reductive Amination of Bio-Based Levulinic Acid and Ester for the Synthesis of Chiral Pyrrolidinone

Direct asymmetric reductive amination of bio-based levulinic acid (LA) to the enantioenriched 5-methylpyrrolidinone is achieved by using a readily available chiral Ru/bisphosphine catalyst with excellent enantioselectivity (up to 96 % ee) and high isolated yield (up to 89 %). Methyl levulinate (ML), a byproduct from the industrial production of 2,5-furandicarboxylic acid (FDCA), can be used instead of LA with similar reactivity and selectivity. Mass spectrometry and isotope labelling studies indicate that the chiral lactam is formed via imine-enamine tautomerization/cyclization followed by asymmetric hydrogenation of the cyclic enamide.

Selective Biocatalytic Defunctionalization of Raw Materials

Biobased raw materials, such as carbohydrates, amino acids, nucleotides, or lipids contain valuable functional groups with oxygen and nitrogen atoms. An abundance of many functional groups of the same type, such as primary or secondary hydroxy groups in carbohydrates, however, limits the synthetic usefulness if similar reactivities cannot be differentiated. Therefore, selective defunctionalization of highly functionalized biobased starting materials to differentially functionalized compounds can provide a sustainable access to chiral synthons, even in case of products with fewer functional groups. Selective defunctionalization reactions, without affecting other functional groups of the same type, are of fundamental interest for biocatalytic reactions. Controlled biocatalytic defunctionalizations of biobased raw materials are attractive for obtaining valuable platform chemicals and building blocks. The biocatalytic removal of functional groups, an important feature of natural metabolic pathways, can also be utilized in a systemic strategy for sustainable metabolite synthesis.

An efficient catalytic method for the borohydride reaction of esters using diethylzinc as precatalyst

A cheap and easily available ZnEt2 is an effective precatalyst, which can be used for the hydroboration reaction of various organic carbonates and esters with HBpin.

Advances in Diels-Alder/aromatization of biomass furan derivatives towards renewable aromatic hydrocarbons

The effective upgrading of renewable resources into high value-added chemicals is of great significance to achieve the sustainable economic development, as well as the implementation of carbon neutral technologies practically....

Catalytic Transformation of Biomass-Derived Furfurals to Cyclopentanones and Their Derivatives: A Review

Furfural (FF) and 5-(hydroxymethyl)furfural (HMF) are well-recognized biomass-derived chemical building blocks with established applications and markets for several of their derivatives. Attaining a wide spectrum of petrochemicals is the primary target of a biorefinery that employs FF and HMF as the chemical feedstock. In this regard, cyclopentanone (CPN) is a crucial petrochemical intermediate used for synthesizing a diverse range of compounds with immense commercial prospects. The hydrogenative ring rearrangement of FF to CPN in an aqueous medium under catalytic hydrogenation conditions was first reported in 2012, whereas the first report on the catalytic conversion of HMF to 3-(hydroxymethyl)cyclopentanone (HCPN) was published in 2014. Over the past decade, several investigations have been undertaken in converting FF and HMF to CPN and HCPN, respectively. The research studies aimed to improve the scalability, selectivity, environmental footprint, and cost competitiveness of the process. A blend of theoretical and experimental studies has helped to develop efficient, inexpensive, and recyclable heterogeneous catalysts that work under mild reaction conditions while providing excellent yields of CPN and HCPN. The time is ripe to consolidate the data in this area of research and analyze them rigorously in a review article. This work will assist both beginners and experts of this field in acknowledging the accomplishments to date, recognize the challenges, and strategize the way forward.

Homogeneous Catalyzed Valorization of Furanics: A Sustainable Bridge to Fuels and Chemicals

The development of efficient biomass valorization is imperative for the future sustainable production of chemicals and fuels. Particularly, the last decade has witnessed the development of a plethora of effective and selective transformations of bio-based furanics using homogeneous organometallic catalysis under mild conditions. In this review, we describe some of the advances regarding the conversion of target furanics into value chemicals, monomers for high-performance polymers and materials, and pharmaceutical key intermediates using homogeneous catalysis. Finally, the incorporation of furanic skeletons into complex chemical architectures by multifunctionalization routes is also described.

Ozonolysis of α-angelica lactone: a renewable route to malonates

Industrially relevant intermediates such as malonic acid, malonates and 3-oxopropionates can be easily accessed by ozonolysis of α-angelica lactone, derived from the platform chemical levulinic acid. The roles of the solvent and of the quenching conditions are of key importance for the outcome of the reaction.

Reactive Chromatography Applied to Ethyl Levulinate Synthesis: A Proof of Concept

Levulinic acid (LA) has been highlighted as one of the most promising platform chemicals, providing a wide range of possible derivatizations to value-added chemicals as the ethyl levulinate obtained through an acid catalyzed esterification reaction with ethanol that has found application in the bio-fuel market. Being a reversible reaction, the main drawback is the production of water that does not allow full conversion of levulinic acid. The aim of this work was to prove that the chromatographic reactor technology, in which the solid material of the packed bed acts both as stationary phase and catalyst, is surely a valid option to overcome such an issue by overcoming the thermodynamic equilibrium. The experiments were conducted in a fixed-bed chromatographic reactor, packed with Dowex 50WX-8 as ion exchange resin. Different operational conditions were varied (e.g., temperature and flow rate), pulsing levulinic acid to the ethanol stream, to investigate the main effects on the final conversion and separation efficiency of the system. The effects were described qualitatively, demonstrating that working at sufficiently low flow rates, LA was completely converted, while at moderate flow rates, only a partial conversion was achieved. The system worked properly even at room temperature (303 K), where LA was completely converted, an encouraging result as esterification reactions are normally performed at higher temperatures.

Recyclable Ir Nanoparticles for the Catalytic Hydrogenation of Biomass-Derived Carbonyl Compounds

The valorisation of biomass-derived platform chemicals via catalytic hydrogenation is an eco-friendly tool which allows us to recover bio-based building blocks and produce fine chemicals with high industrial appeal. In the present study, a novel surfactant-type triazolyl-thioether ligand was prepared, showing excellent catalytic activity in the presence of bis(1,5-cyclooctadiene)diiridium(I) dichloride [Ir(COD)Cl]2 for the hydrogenation of furfural, cinnamaldehyde, levulinic acid, 5-hydroxymethylfurfural, vanillin, and citral. Easy recovery by liquid/liquid extraction allowed us to recover the catalyst, which could then be efficiently recycled up to 11 times for the hydrogenation of furfural. In-depth analysis revealed the formation of spherical structures with metal nanoparticles as big as 2–6 nm surrounded by the anionic ligand, preventing iridium nanoparticle degradation.

Selective and Scalable Synthesis of Sugar Alcohols by Homogeneous Asymmetric Hydrogenation of Unprotected Ketoses

Sugar alcohols are of great importance for the food industry and are promising building blocks for bio-based polymers. Industrially, they are produced by heterogeneous hydrogenation of sugars with H₂ , usually with none to low stereoselectivities. Now, we present a homogeneous system based on commercially available components, which not only increases the overall yield, but also allows a wide range of unprotected ketoses to be diastereoselectively hydrogenated. Furthermore, the system is reliable on a multi-gram scale allowing sugar alcohols to be isolated in large quantities at high atom economy.

Palladium supported on magnesium hydroxyl fluoride: an effective acid catalyst for the hydrogenation of imines and N-heterocycles

Heterogeneous palladium catalysts were prepared for the effective hydrogenation of imines and N-heterocycles at low loadings without any acid additive.

The solvent determines the product in the hydrogenation of aromatic ketones using unligated RhCl3 as catalyst precursor

RhCl3-catalysed hydrogenation/hydrodeoxygenation of aromatic ketones produced alkylcyclohexanes in TFE and cyclohexyl alkyl alcohols in water at moderate temperatures. Rh-nanoparticles were found to be the true catalysts.

A Sustainable Palladium-Intercalated Montmorillonite Clay Catalytic System for Imine Hydrogenation under Mild Conditions

A series of palladium nanoparticles (Pd NPs) intercalated montmorillonite clay catalysts is reported for hydrogenation of 3-diphenyl prop-2-en-1-imine under mild reaction conditions. Pd/clay catalyst was prepared by a simple wet-impregnation method, and the physicochemical properties were characterized extensively by various techniques including N₂ adsorption, XRD, TEM, XPS and TPR etc., which showed the intercalation of active Pd NPs between the clay layers. The effect of reaction conditions such as catalyst loading, reaction time, temperature and H₂ pressure is explored, and thereby a plausible mechanism is proposed. The optimum amount of 6 wt % Pd/clay catalyst showed significant catalytic activity to yield 3-phenyl propyl aniline with 100 % conversion and selectivity under 5 bar pressure and a shorter reaction period of 3.5 h at 100 °C. The developed catalytic system unveiled excellent reusability over five cycles and hence paved the way for industrial applications.

Synthesis of Tetrahydroquinolines via Borrowing Hydrogen Methodology Using a Manganese PN3 Pincer Catalyst

A straightforward and selective synthesis of 1,2,3,4-tetrahydroquinolines starting from 2-aminobenzyl alcohols and simple secondary alcohols is reported. This one-pot cascade reaction is based on the borrowing hydrogen methodology promoted by a manganese(I) PN³ pincer complex. The reaction selectively leads to 1,2,3,4-tetrahydroquinolines thanks to a targeted choice of base. This strategy provides an atom-efficient pathway with water as the only byproduct. In addition, no further reducing agents are required.

i-Propylammonium Lead Chloride Based Perovskite Photocatalysts for Depolymerization of Lignin Under UV Light

Lignin depolymerization for the purpose of synthesizing aromatic molecules is a growing focus of research to find alternative energy sources. In current studies, the photocatalytic depolymerization of lignin has been investigated by two new iso-propylamine-based lead chloride perovskite nanomaterials (SK9 and SK10), synthesized by the facile hydrothermal method. Characterization was done by Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), UV-Visible (UV-Vis), Photoluminescence (PL), and Fourier-Transform Infrared (FTIR) Spectroscopy and was used for the photocatalytic depolymerization of lignin under UV light. Lignin depolymerization was monitored by taking absorption spectra and catalytic paths studied by applying kinetic models. The %depolymerization was calculated for factors such as catalyst dose variation, initial concentration of lignin, and varying temperatures. Pseudo-second order was the best suited kinetic model, exhibiting a mechanism for lignin depolymerization that was chemically rate controlled. The activation energy (E_a) for the depolymerization reaction was found to be 15 kJ/mol, which is remarkably less than conventional depolymerization of the lignin, i.e., 59.75 kJ/mol, exhibiting significant catalytic efficiencies of synthesized perovskites. Products of lignin depolymerization obtained after photocatalytic activity at room temperature (20 °C) and at 90 °C were characterized by GC-MS analysis, indicating an increase in catalytic lignin depolymerization structural subunits into small monomeric functionalities at higher temperatures. Specifically, 2-methoxy-4-methylphenol (39%), benzene (17%), phenol (10%) and catechol (7%) were detected by GC-MS analysis of lignin depolymerization products.

Heterogeneous Catalyst Design Principles for the Conversion of Lignin into High-Value Commodity Fuels and Chemicals

Lignin valorization has risen as a promising pathway to supplant the use of petrochemicals for chemical commodities and fuels. However, the challenges of separating and breaking down lignin from lignocellulosic biomass are the primary barriers to success. Integrated biorefinery systems that incorporate both homo- and heterogeneous catalysis for the upgrading of lignin intermediates have emerged as a viable solution. Homogeneous catalysis can perform selected chemistries, such as the hydrolysis and dehydration of ester or ether bonds, that are more suitable for the pretreatment and fractionation of biomass. Heterogeneous catalysis, however, offers a tunable platform for the conversion of extracted lignin into chemicals, fuels, and materials. Tremendous effort has been invested in elucidating the necessary factors for the valorization of lignin by using heterogeneous catalysts, with efforts to explore more robust methods to drive down costs. Current progress in lignin conversion has fostered numerous advances, but understanding the key catalyst design principles is important for advancing the field. This Minireview aims to provide a summary on the fundamental design principles for the selective conversion of lignin by using heterogeneous catalysts, including the pairing of catalyst metals, supports, and solvents. The review puts a particular focus on the use of bimetallic catalysts on porous supports as a strategy for the selective conversion of lignin. Finally, future research on the valorization of lignin is proposed on the basis of recent progress.