Selective Cleavage Research Articles

Simultaneous Oxidative Cleavage of Lignin and Reduction of Furfural via Efficient Electrocatalysis by P-Doped CoMoO4.

Electrochemical oxidative lignin cleavage and coupled 2-furaldehyde reduction provide a promising approach for producing high-value added products. However, developing efficient bifunctional electrocatalysts with noble-metal-like activity still remains a challenge. Here, an efficient electrochemical strategy is reported for the selective oxidative cleavage of Cα -Cβ bonds in lignin into aromatic monomers by tailoring the electronic structure through P-doped CoMoO4 spinels (99% conversion, highest monomer selectivity of 56%). Additionally, the conversion and selectivity of 2-furaldehyde reduction to 2-methyl furan reach 87% and 73%, respectively. In situ Fourier transform infrared and density functional theory analysis reveal that an upward shift of the Ed upon P-doping leads to an increase in the antibonding level, which facilitates the Cα -Cβ adsorption of the lignin model compounds, thereby enhancing the bifunctional electrocatalytic activity of the active site. This work explores the potential of a spinel as a bifunctional electrocatalyst for the oxidative cracking of lignin and the reductive conversion of small organic molecules to high-value added chemicals via P-anion modulation.

Use of a Photocleavable Initiator to Characterize Polymer Chains Grafted onto a Metal Plate with the Grafting-from Method.

The thorough characterization of polymer chains grafted through a "grafting-from" process onto substrates based on the determination of number (Mn) and weight (Mw) average molar masses, as well as dispersity (Ɖ), is quite challenging. It requires the cleavage of grafted chains selectively at the polymer-substrate bond without polymer degradation to allow their analysis in solution with steric exclusion chromatography, in particular. The study herein describes a technique for the selective cleavage of PMMA grafted onto titanium substrate (Ti-PMMA) using an anchoring molecule that combines an atom transfer radical polymerization (ATRP) initiator and a UV-cleavable moiety. This technique allows the demonstration of the efficiency of the ATRP of PMMA on titanium substrates and verification that the chains were grown homogeneously.

Unraveling the active states of WO3-based catalysts in the selective conversion of cellulose to glycols

Tungsten-based catalysts, including crystalline WO3 and H2WO4, have been reported to be efficient for the selective cleavage of C−C bonds of sugar intermediates involved in the conversion of cellulose to ethylene glycol and propylene glycol in combination with hydrogenation catalysts under H2 atmosphere. However, there is still not a consensus on the actual states of these catalysts during the reaction. Herein, we demonstrate that both WO3 and H2WO4 tended to undergo reduction to hydrogen tungsten bronze (HxWO3) species in the cellulose reaction, consisting of H0.23WO3 and H0.33WO3, which were then re-oxidized to WO3 upon exposure to ambient air after the reaction. Both WO3 and HxWO3 were insoluble in water and acted as the heterogeneous catalysts in the cellulose reaction, as further validated by the strong dependence of the catalytic activity of WO3 on its crystallite size and surface area. Such identification of the heterogeneous HxWO3 species, albeit exemplified here only from the in situ reduction of WO3 and H2WO4 in the cellulose reaction, unravels the active state of the tungsten-based catalysts under reductive reaction conditions.

Structural confirmation of synthetic cannabinoids in seized electronic cigarette oil: A combined mass spectrometric and computational study.

Synthetic cannabinoids are some of the most used and abused new psychoactive substances, because they can produce a stronger intense pleasure than natural cannabis. Most of the new synthetic cannabinoids are structurally similar to existing synthetic cannabinoids and can be obtained by modifying partial structures of the latter without changing their effects. Therefore, the derivatization rules and common fragmentation patterns of synthetic cannabinoids could be used for rapid screening and structural identification of them. The derivatization rules of synthetic cannabinoids are summarized, and the common fragmentation pattern of synthetic cannabinoids including three typical cleavage pathways was explored and extended in this work based on combined mass spectrometry (MS) and density functional theory studies. Five synthetic cannabinoids in electronic cigarette oil from a drug case were separated and characterized using gas chromatography with MS and liquid chromatography coupled to high-resolution quadrupole Orbitrap MS. The structures of five synthetic cannabinoids in seized electronic cigarette oil were deduced from electron impact ion source (EI) MS and high-resolution electrospray ionization (ESI) MSn data, along with the derivatization rules and common fragmentation pattern of synthetic cannabinoids. The proposed structures of these synthetic cannabinoids were further verified via reference substances. Computational study showed that selective cleavage of these compounds was mainly controlled by spin population in EI-MS, but a tunneling effect arose from proton transfer in ESI-MSn detection, which has been rarely reported in previous works. Our results showed that EI-MS was suitable for identifying synthetic cannabinoids with aromatic ketone structure, which could also be extended to adamantane linked group. Nevertheless, synthetic cannabinoids with carbamoyl linked group were better characterized by high-resolution ESI-MSn compared to EI-MS. This study demonstrated a method with promising potential for rapid and reliable screening of synthetic cannabinoids in mixtures with enhanced detection throughput and operation simplicity.

Fully Bio-based Poly(ketal-ester)s by Ring-opening Polymerization of a Bicylcic Lactone from Glycerol and Levulinic Acid.

A fully renewable bio-based bicyclic lactone containing a five-membered cyclic ketal moiety, 7-methyl-3,8,10-trioxabicyclo[5.2.1]decan-4-one (TOD), was synthesized through a two-step acid-catalyzed process from glycerol and levulinic acid. The ring-opening polymerization (ROP) of TOD at 30°C with benzyl alcohol (BnOH) as the initiator and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst can afford high molar mass PTOD with a cis-2.4-disubstitued 2-methyl 1,3-dioxolane moiety in its repeating unit. PTOD is an amorphous polymer with a glass transition temperature (Tg ) of 13°C. It can be hydrolyzed into structurally defined small molecules under acidic or basic conditions by the selective cleavage of either the cyclic ketal or the ester linkage respectively. The TBD-catalyzed copolymerization of L-lactide (L-LA) and TOD at -20°C was investigated. It was confirmed that L-LA polymerized quickly with racemization to form PLA, followed by a slow incorporation of TOD into the formed PLA chains via transesterification. By varying the feed ratios of L-LA to TOD, a series of random copolymers (PLA-co-PTOD) with different TOD incorporation ratios and tunable Tg s were obtained. Under acidic conditions, PLA-co-PTOD degrades much faster than PLA via the selective cleavage of the cyclic ketal linkages. This work provides insights for the development of more sustainable and acid-accelerated degradable alternatives to aliphatic polyesters.

Selective hydrogenolysis of lignin in the presence of Ni3Fe1 alloy supported on zirconium phosphate

Lignin is a promising renewable starting material for various value-added petrochemicals and high-quality fuels. However, current techniques for utilization of this natural aromatic biopolymer are challenging by the poor selectivity of desired products and the serious char formation. In this study, we provide a novel and efficient approach for selective hydrogenolysis of lignin using the cost-effective catalyst of Ni3Fe1 nanoparticles supported on zirconium phosphates. 77.0 % of lignin is converted, yielding 19.6 % monophenols, whereas, the formation of biochar is insignificant (1.7 %) at the conditions of 260 °C for 5 h in a 2.0 MPa hydrogen. Importantly, 42.1 % of these obtained monophenols are identified to be a versatile bulk chemical of para ethyl phenol (yield of 8.2 %), because of the selective cleavage of the p-coumaryl units of the lignin. The results of catalyst characterization further reveal that the formation of Ni3Fe1 nanoparticle facilitates the breakage of the specific structure of lignin and suppresses the phenolic oligomer's recondensation, which consequently enhance the lignin hydrogenolysis and char inhibition. These insights unveil that the production of bulk chemicals from sustainable resources is realizable through the rational design of catalytic processes, which substantially increase the economic feasibility of biomass biorefinery.

Ultrasmall amorphous zirconia nanoparticles catalyse polyolefin hydrogenolysis

Carbon–carbon bond cleavage reactions, adapted to deconstruct aliphatic hydrocarbon polymers and recover the intrinsic energy and carbon value in plastic waste, have typically been catalysed by metal nanoparticles or air-sensitive organometallics. Metal oxides that serve as supports for these catalysts are typically considered to be inert. Here we show that Earth-abundant, non-reducible zirconia catalyses the hydrogenolysis of polyolefins with activity rivalling that of precious metal nanoparticles. To harness this unusual reactivity, our catalytic architecture localizes ultrasmall amorphous zirconia nanoparticles between two fused platelets of mesoporous silica. Macromolecules translocate from bulk through radial mesopores to the highly active zirconia particles, where the chains undergo selective hydrogenolytic cleavage into a narrow, C18-centred distribution. Calculations indicated that C–H bond heterolysis across a Zr–O bond of a Zr(O)2 adatom model for unsaturated surface sites gives a zirconium hydrocarbyl, which cleaves a C–C bond via β-alkyl elimination.

Regioselective protein oxidative cleavage enabled by enzyme-like recognition of an inorganic metal oxo cluster ligand

Oxidative modifications of proteins are key to many applications in biotechnology. Metal-catalyzed oxidation reactions efficiently oxidize proteins but with low selectivity, and are highly dependent on the protein surface residues to direct the reaction. Herein, we demonstrate that discrete inorganic ligands such as polyoxometalates enable an efficient and selective protein oxidative cleavage. In the presence of ascorbate (1 mM), the Cu-substituted polyoxometalate K8[Cu2+(H2O)(α2-P2W17O61)], (CuIIWD, 0.05 mM) selectively cleave hen egg white lysozyme under physiological conditions (pH =7.5, 37 °C) producing only four bands in the gel electropherogram (12.7, 11, 10, and 5 kDa). Liquid chromatography/mass spectrometry analysis reveals a regioselective cleavage in the vicinity of crystallographic CuIIWD/lysozyme interaction sites. Mechanistically, polyoxometalate is critical to position the Cu at the protein surface and limit the generation of oxidative species to the proximity of binding sites. Ultimately, this study outlines the potential of discrete, designable metal oxo clusters as catalysts for the selective modification of proteins through radical mechanisms under non-denaturing conditions.

Hybridization of CuO with BiVO4 as an Efficient and Stable Photocatalyst for Selective Cleavage of Lignin C–C Bonds

Hybridization of CuO with BiVO₄ as an Efficient and Stable Photocatalyst for Selective Cleavage of Lignin C–C Bonds

Enhancement of hydrodeoxygenation catalytic performance through the addition of copper to molybdenum oxide-based catalysts

The role of copper promoter and carbon support on the activity, selectivity, and stability of molybdenum oxide was determined for bulk and carbon-supported molybdenum oxide catalysts in phenol hydrodeoxygenation (HDO). The catalytic performance was correlated to the physicochemical properties determined using ICP-AES, XRD, XPS, Raman, TPR, H2O-TPD, and oxygen chemisorption. The results showed that at the studied reaction conditions (atmospheric pressure, 330 ºC, gas phase), the employment of activated carbon as support and the addition of copper improved phenol conversion from 1 (with MoO3) to 28% (with CuMo/C), maintaining high selectivity to benzene (around 100%) while characterization studies evidence the formation of mainly CuMoO4 species in bulk samples and metallic copper, Cu2O, and MoO2 on carbon-supported ones. The incorporation of copper in the molybdenum oxide catalysis promoted the reduction of molybdenum, the creation of oxygen vacancies, and the H• formation, all factors favoring the selective CO bond cleavage. Stability tests of the most active catalysts, Mo/C_H2 and CuMo_H2, showed that deactivation happened, but the direct deoxygenation route remained preferential throughout the reaction time with high selectivity to benzene (up to 98%). Deactivation was related to the lower concentration of available active sites (oxygen vacancies).

Biocatalysis of Steroids by Mycobacterium sp. in Aqueous and Organic Media.

Mycobacterium sp. can convert steroids such as β-sitosterol, campesterol, and cholesterol, by selective side-chain cleavage and oxidation of the C3 hydroxyl group to a ketone, into key intermediates that can be easily functionalized to yield commercially interesting pharmaceutical products. In aqueous systems, the biocatalysis is limited by the low solubility of the steroids in water. Several strategies have been introduced to tackle this limitation, e.g., formation of cyclodextrin-steroid complexes and generation of aqueous microdispersions with steroid particle size in the range of hundreds of nanometers. Still, the introduction of an organic phase acting as a substrate and/or product reservoir is a well-established and relatively easy to implement strategy to overcome the sparing water solubility of steroid molecules. However, the organic phase has to be carefully chosen to prevent tampering with the activity/viability of microbial cells.In this chapter, we describe the methodology for the biocatalysis of β-sitosterol to 4-androstene-3,17-dione (AD) and 1,4-androstadiene-3,17-dione (ADD), both in aqueous and organic:aqueous systems. In the latter case, both traditional organic solvents and green solvents are proposed.

β-Sitosterol Bioconversion in Small-Scale Devices: From Microtiter Plates to Microfluidic Reactors.

Small-scale devices are routinely used as low-cost miniaturized bioreactors due to the large number of experiments that can be conducted simultaneously under similar conditions and replicate all functions of bench-scale reactors at dramatically smaller volumes. Microtiter plates, due to the standard footprint, can be integrated with liquid handling systems and associated equipment, expanding considerably their application and use. However, care has to be taken to operate the microtiter plates in optimized mixing and oxygen transfer conditions, preventing medium evaporation in prolonged experiment runs. Recently, to increase data quality, microbioreactors have emerged as an alternative to shaken systems. These systems offer higher degree of control over key process variables and when combined with sensing technology increase dramatically the reliability of translational process data. In this chapter, we describe the production of 4-androstene-3,17-dione (androstenedione (AD)), a key pharmaceutical steroid intermediate, by Mycobacterium sp. NRRL B-3805 via the selective cleavage of the side-chain of β-sitosterol using 24-well microtiter plates and microfluidic microbioreactors.

A copper(ii) peptide helicate selectively cleaves DNA replication foci in mammalian cells

We report a CuII peptide helicate that selectively binds DNA 3WJs in cells, damaging DNA replication foci by ROS production, thus demonstrating for the first time the selective cleavage of this noncanonical DNA structure with a chemical nuclease.

A recoverable polyoxometalate-ionic liquid catalyst for selective cleavage of lignin β-O-4 models under mild conditions

A recoverable polyoxometalate-ionic liquid (POM-IL) catalyst has been successfully constructed to selectively and effectively convert various β-O-4 lignin models into aromatic acids and phenols under mild homogeneous conditions.

Selective cleavage of Cα–Cβbonds in lignin models using a bifunctional pyridinium photocatalystviaa PCET process

A pyridinium-based photocatalyst possessing both redox-active and hydrogen acceptor sites has been developed for the conversion of lignin models to afford benzaldehyde and phenyl formate as the main products through selective cleavage of C–C bonds.

Wavelength-Dependent, Orthogonal Photoregulation of DNA Liberation for Logic Operations

In this study, we synthesized two phosphoramidites based on 2,7-bis-{4-nitro-8-[3-(2-propyl)-styryl]}-9,9-bis-[1-(3,6-dioxaheptyl)]-fluorene (BNSF) and 4,4'-bis-{8-[4-nitro-3-(2-propyl)-styryl]}-3,3'-di-methoxybiphenyl (BNSMB) structures as visible light-cleavable linkers for oligonucleotide conjugation. In addition to the commercial ultraviolet (UV) photocleavable (PC) linker, the BNSMB linker was further applied as a building component to construct photoregulated DNA devices as duplex structures, which are functionalized with fluorophores and quenchers. Selective cleavage of PC and BNSMB is achieved in response to ultraviolet (UV) and visible light irradiations as two inputs, respectively. This leads to controllable dissociation of pieces of DNA fragments, which is followed by changes of fluorescence emission as signal outputs of the system. By tuning the number and position of the photocleavable molecules, fluorophores, and quenchers, various DNA devices were developed, which mimic the functions of Boolean logic gates and achieve logic operations in AND, OR, NOR, and NAND gates in response to two different wavelengths of light inputs. By sequence design, the photolysis products can be precisely programmed in DNA devices and triggered to release in a selective and/or sequential manner. Thus, this photoregulated DNA device shows potential as a wavelength-dependent drug delivery system for selective control over the release of multiple individual therapeutic oligonucleotide-based drugs. We believe that our work not only enriches the library of photocleavable phosphoramidites available for bioconjugation but also paves the way for developing spatiotemporal-controlled, orthogonal-regulated DNA-based logic devices for a range of applications in materials science, polymers, chemistry, and biology.

Upgrading Polyurethanes into Functional Ureas through the Asymmetric Chemical Deconstruction of Carbamates.

The importance of systematic and efficient recycling of all forms of plastic is no longer a matter for debate. Constituting the sixth most produced polymer family worldwide, polyurethanes, which are used in a broad variety of applications (buildings, electronics, adhesives, sealants, etc.), are particularly important to recycle. In this study, polyurethanes are selectively recycled to obtain high value-added molecules. It is demonstrated that depolymerization reactions performed with secondary amines selectively cleave the C-O bond of the urethane group, while primary amines unselectively break C-O and C-N bonds. The selective cleavage of C-O bonds, catalyzed by an acid:base mixture, led to the initial polyol and a functional diurea in several hours to a few minutes for both model polyurethanes and commercial polyurethane foams. Different secondary amines were employed as nucleophiles to synthesize a small library of diureas obtained in good to excellent yields. This study not only targets the recovery of the initial polyol but also aims to form new diureas which are useful building blocks for the polymerization of innovative materials.

Transient Kinetics of Short-Chain Perfluoroalkyl Sulfonate with Radiolytic Reducing Species

The role of the short-lived hydrated electron (eaq–) has recently begun to be appreciated in per- and polyfluoroalkyl substances (PFAS) remediations; nevertheless, few studies to date focused on short-chain PFAS, and their effective defluorination has been limited by an insufficient mechanistic understanding, which starts with the elusive initial step of eaq– reduction. Herein, this study uses pulse radiolysis to clarify the rate constant of the eaq– reaction with a highly recalcitrant short-chain PFAS, perfluorobutanesulfonate (PFBS, C4F9SO3–), and verify chain length dependence. The measured values contradict earlier results from laser photolysis but reconcile with the apparent degradation profiles and theoretical predictions. Besides, we first disclose radiolytic carbon dioxide radicals (CO2–•) to defluorinate PFBS with an initial reaction constant of 4.8 × 107 M–1 s–1, and it achieves selective cleavage on the more obstinate C–F bond than eaq– even under a neutral condition. Quantitative 60Co γ-ray irradiation experiments further show that initial reduction occurs through a defluorination pathway rather than a desulfurization pathway, and the redox potential of PFBS exceeds −2.0 eV. This radiolytic study addressed the long-standing mechanistic contradictions regarding short-chain PFAS degradation and suggested ionizing radiation as a versatile and direct treatment technique.

Zeolitic Imidazolate Framework Decorated Molybdenum Carbide Catalysts for Hydrodeoxygenation of Guaiacol to Phenol

Bimetallic zeolitic imidazolate framework (BMZIF)-decorated Mo carbide catalysts were designed for the catalytic hydrodeoxygenation of guaiacol to produce phenol with high selectivity. A uniform layer of BMZIF was systematically coated onto the surface of the MoO3 nanorods. During carbonization at 700 °C for 4 h, BMZIF generated active species (ZnO, CoO) on highly dispersed N-doped carbons, creating a porous shell structure. Simultaneously, the MoO3 nanorod was transformed into the Mo2C phase. The resulting core@shell type Mo2C@BMZIF-700 °C (4 h) catalyst promoted a 97% guaiacol conversion and 70% phenol selectivity under 4 MPa of H2 at 330 °C for 4 h, which was not achieved by other supported catalysts. The catalyst also showed excellent selective cleavage of the methoxy group of lignin derivatives (syringol and vanillin), which makes it suitable for selective demethoxylation in future biomass catalysis. Moreover, it exhibits excellent recyclability and stability without changing the structure or active species.

Highly dispersed CdS on C3N4 for selective cleavage of Cβ-O-4 bonds in lignin model compound under blue light

Photocatalytic cleavage of lignin Cβ-O-4 bonds is a very effective method to promote the high-value utilization of lignin because lignin can provide a large number of aromatics. However, the higher carrier recombination rate severely inhibits the efficiency of photocatalytic cleavage of Cβ-O-4 bonds in lignin model compound. Here, heterojunction photocatalysts CdS-C3N4 were successfully synthesized through the photodeposition of different masses of CdS on the surface of C3N4. The obtained photocatalyst CdS-C3N4 can effectively break the lignin Cβ-O-4 bonds in 2-Phenoxy-1-phenylethanol (lignin model compound) and the products formed are mainly phenol (Phol) and acetophenone (Ap). More importantly, the yields of Phol and Ap were up to 86.5% and 74.3%, after only irradiation for 1.5 h, respectively, under optimum conditions. A mechanistic study showed that photocatalytic reaction follows a photogenerated electron-hole coupled mechanism. The high photocatalytic performance of CdS-C3N4 is mainly ascribed to the fast photogenerated electron-hole separation capability and good dispersion of CdS on C3N4. This work offers an idea for selective cleavage of lignin Cβ-O-4 bonds by constructing a heterojunction photocatalyst.