Hydrolysis Of Ethers Research Articles

Enhancing Tandem Partial Hydrogenation–Hydrolysis of Diphenyl Ethers to Cyclohexanols with Surface-Oxidized MXene

Enhancing Tandem Partial Hydrogenation–Hydrolysis of Diphenyl Ethers to Cyclohexanols with Surface-Oxidized MXene

Development of Improved Spectrophotometric Assays for Biocatalytic Silyl Ether Hydrolysis.

Reported herein is the development of assays for the spectrophotometric quantification of biocatalytic silicon-oxygen bond hydrolysis. Central to these assays are a series of chromogenic substrates that release highly absorbing phenoxy anions upon cleavage of the sessile bond. These substrates were tested with silicatein, an enzyme from a marine sponge that is known to catalyse the hydrolysis and condensation of silyl ethers. It was found that, of the substrates tested, tert-butyldimethyl(2-methyl-4-nitrophenoxy)silane provided the best assay performance, as evidenced by the highest ratio of enzyme catalysed reaction rate compared with the background (uncatalysed) reaction. These substrates were also found to be suitable for detailed enzyme kinetics measurements, as demonstrated by their use to determine the Michaelis-Menten kinetic parameters for silicatein.

Mechanically Triggered Polymer Deconstruction through Mechanoacid Generation and Catalytic Enol Ether Hydrolysis.

Polymers that amplify a transient external stimulus into changes in their morphology, physical state, or properties continue to be desirable targets for a range of applications. Here, we report a polymer comprising an acid-sensitive, hydrolytically unstable enol ether backbone onto which is embedded gem-dichlorocyclopropane (gDCC) mechanophores through a single postsynthetic modification. The gDCC mechanophore releases HCl in response to large forces of tension along the polymer backbone, and the acid subsequently catalyzes polymer deconstruction at the enol ether sites. Pulsed sonication of a 61 kDa PDHF with 77% gDCC on the backbone in THF with 100 mM H2O for 10 min triggers the subsequent degradation of the polymer to a final molecular weight of less than 3 kDa after 24 h of standing, whereas controls lacking either the gDCC or the enol ether reach final molecular weights of 38 and 27 kDa, respectively. The process of sonication, along with the presence of water and the existence of gDCC on the backbone, significantly accelerates the rate of polymer chain deconstruction. Both acid generation and the resulting triggered polymer deconstruction are translated to bulk, cross-linked polymer networks. Networks formed via thiol-ene cross-linking and subjected to unconstrained quasi-static uniaxial compression dissolve on time scales that are at least 3 times faster than controls where the mechanophore is not covalently coupled to the network. We anticipate that this concept can be extended to other acid-sensitive polymer networks for the stress-responsive deconstruction of gels and solvent-free elastomers.

Investigations on Stability of Polycarboxylate Superplasticizers in Alkaline Activators for Geopolymer Binders.

Calcined clays are interesting starting materials to be used as SCMs (supplementary cementitious materials) in cements or to be converted to geopolymers by activation with a high alkaline activator. The adjustment of the properties in the fresh state, especially regarding the consistency of these binders, is almost exclusively achieved by the addition of water, since commercially available superplasticizers seem to be ineffective in low-calcium geopolymer systems. The aim of this study was a systematic investigation of various PCE (polycarboxylate ester/ether) superplasticizers (methacrylate ester PCE: MPEG, isoprenol ether PCE: IPEG, methallyl ether PCE: HPEG) with respect to their stability in different alkaline activators (NaOH, KOH, sodium and potassium silicate solutions). The effectiveness of superplasticizers (SPs) in low-calcium geopolymer binders was verified by rheological tests. Size exclusion chromatography was used to investigate if structural degradation of the superplasticizers occurs. The investigated PCE superplasticizers showed a thickening effect in the low-calcium geopolymer system. Depending on the alkalinity of the activator solution, a degradation process was detected for all the PCEs investigated. The side chains of the PCEs are cleaved off the backbone by basic ester and ether hydrolysis. The highest degree of degradation was found in sodium and potassium silicate solutions. In alkaline hydroxide solutions, the degradation process increases with increasing alkalinity.

Acid-Functionalized Artificial Enzymes with Tunable Selectivity for Vinyl Ether Hydrolysis.

Enzymes often employ catalytic groups with a medium or low intrinsic activity for highly challenging catalytic tasks. In this work, we report nanoparticle catalysts with accurately positioned carboxylic acids through either a covalent or noncovalent imprinting technique. The rationally designed active site allows the catalysis to be highly selective or quite unselective with respect to the substrate. With the proper catalyst, the hydrolysis proceeds smoothly in neutral water or even a slightly basic solution at room temperature.

Vinyl Halide‐Modified Unsaturated Cyclitols are Mechanism‐Based Glycosidase Inhibitors

AbstractSuitably configured allyl ethers of unsaturated cyclitols act as substrates of β‐glycosidases, reacting via allylic cation transition states. Incorporation of halogens at the vinylic position of these carbasugars, along with an activated leaving group, generates potent inactivators of β‐glycosidases. Enzymatic turnover of these halogenated cyclitols (F, Cl, Br) displayed a counter‐intuitive trend wherein the most electronegative substituents yielded the most labile pseudo‐glycosidic linkages. Structures of complexes with the Sulfolobus β‐glucosidase revealed similar enzyme‐ligand interactions to those seen in complexes with a 2‐fluorosugar inhibitor, the lone exception being displacement of tyrosine 322 from the active site by the halogen. Mutation of Y322 to Y322F largely abolished glycosidase activity, consistent with lost interactions at O5, but minimally affected (7‐fold) rates of carbasugar hydrolysis, yielding a more selective enzyme for unsaturated cyclitol ether hydrolysis.

Vinyl Halide-Modified Unsaturated Cyclitols are Mechanism-Based Glycosidase Inhibitors.

Suitably configured allyl ethers of unsaturated cyclitols act as substrates of β-glycosidases, reacting via allylic cation transition states. Incorporation of halogens at the vinylic position of these carbasugars, along with an activated leaving group, generates potent inactivators of β-glycosidases. Enzymatic turnover of these halogenated cyclitols (F, Cl, Br) displayed a counter-intuitive trend wherein the most electronegative substituents yielded the most labile pseudo-glycosidic linkages. Structures of complexes with the Sulfolobus β-glucosidase revealed similar enzyme-ligand interactions to those seen in complexes with a 2-fluorosugar inhibitor, the lone exception being displacement of tyrosine 322 from the active site by the halogen. Mutation of Y322 to Y322F largely abolished glycosidase activity, consistent with lost interactions at O5, but minimally affected (7-fold) rates of carbasugar hydrolysis, yielding a more selective enzyme for unsaturated cyclitol ether hydrolysis.

Proteases: An overview on its recent industrial developments and current scenario in the revolution of biocatalysis

In recent years there is tremendous growth in the utilization of alkaline protease as an industrial catalyst. The extensive usage of chemicals for various applications in industries is usually associated with severe health effects and environmental problems. In this context, the scientific world mainly aims to substitute these toxic compounds with healthy environmental benign products for a good life. So, the chemicals are replaced by various enzymes among which microbial enzymes especially proteases are mostly employed in the modern corporate sectors in the manufacture of detergents, leather, food products and also in waste management techniques. The present review summarizes the various industrial applications of alkaline protease, different factors influencing its production like isolation source, optimum pH, temperature, the effect of inhibitor and metal ions on alkaline protease producing microorganisms. Furthermore the biocatalytic activity of alkaline protease in various organic transformations namely Knoevenagel condensation, Domino reaction, Aldol reaction, transesterification reaction, resolution of amino acids in organic solvents, kinetic resolution of carboxylic acids, strained amides, peptide synthesis by alcalase cross-linked enzyme aggregates (CLEA), enantioselective hydrolysis of prochiral dinitril, enzymatic desymmetrization of Ganciclovir, enantioselective aminoacid ester hydrolysis and fragmentation of p-amido benzyl ethers have been compiled in the current review.

Controlling Reaction Routes in Noble‐Metal‐Catalyzed Conversion of Aryl Ethers

AbstractHydrogenolysis and hydrolysis of aryl ethers in the liquid phase are important reactions for accessing functionalized cyclic compounds from renewable feedstocks. On supported noble metals, hydrogenolysis is initiated by a hydrogen addition to the aromatic ring followed by C−O bond cleavage. In water, hydrolysis and hydrogenolysis proceed by partial hydrogenation of the aromatic ring prior to water or hydrogen insertion. The mechanisms are common for the studied metals, but the selectivity to hydrogenolysis increases in the order Pd<Rh<Ir<Ru≈Pt in decalin and water; the inverse was observed for the selectivity to hydrolysis in water. Hydrogenolysis selectivity correlates with the Gibbs free energy of hydrogen adsorption. Hydrogenolysis has the highest standard free energy of activation and a weak dependence on H2 pressure, thus, the selectivity to hydrogenolysis is maximized by increasing temperature and decreasing H2 pressure. Selectivity to C−O bond cleavage reaches >95 % in water and alkaline conditions.

Controlling Reaction Routes in Noble-Metal-Catalyzed Conversion of Aryl Ethers.

Hydrogenolysis and hydrolysis of aryl ethers in the liquid phase are important reactions for accessing functionalized cyclic compounds from renewable feedstocks. On supported noble metals, hydrogenolysis is initiated by a hydrogen addition to the aromatic ring followed by C−O bond cleavage. In water, hydrolysis and hydrogenolysis proceed by partial hydrogenation of the aromatic ring prior to water or hydrogen insertion. The mechanisms are common for the studied metals, but the selectivity to hydrogenolysis increases in the order Pd<Rh<Ir<Ru≈Pt in decalin and water; the inverse was observed for the selectivity to hydrolysis in water. Hydrogenolysis selectivity correlates with the Gibbs free energy of hydrogen adsorption. Hydrogenolysis has the highest standard free energy of activation and a weak dependence on H2 pressure, thus, the selectivity to hydrogenolysis is maximized by increasing temperature and decreasing H2 pressure. Selectivity to C−O bond cleavage reaches >95 % in water and alkaline conditions.

Dimethyl Ether Hydrolysis over WO3/γ-Al2O3 Supported Catalysts

Dimethyl ether (DME) is considered an alternative hydrogen carrier with potential use in fuel cells and automotive and domestic applications. Dimethyl ether hydrolysis to methanol is a thermodynamically limited reaction catalyzed by solid-acid catalysts, mainly Al2O3 and zeolites. Moreover, it is the rate-limiting step of the DME steam reforming reaction, which is employed for the production of hydrogen fuel for fuel cell feeding. In the present study, the performance of WO3/Al2O3 catalysts (0–44% wt. WO3) was tested in DME hydrolysis reaction. The catalysts were characterized by means of N2-physisorption, XRD, Raman spectroscopy, XPS, NH3-TPD and 2,6-di-tert-butylpyridine adsorption experiments. The reaction rate of DME hydrolysis exhibited a volcanic trend as a function of tungsten surface density, while the best-performing catalyst was 37WO3/Al2O3, with a tungsten surface density of 7.4 W/nm2, noting that the theoretical monolayer coverage for the specific system is 4–5 W/nm2. Brønsted acidity was directly associated with the catalytic activity, following the same volcanic trend as a function of tungsten surface density. Blocking of Brønsted acid sites with 2,6-di-tert-butylpyridine led to a dramatic decrease in hydrolysis rates by 40 times, proving that Brønsted acid sites are primarily responsible for the catalytic activity. Thus, the type and strength rather than the concentration of acid sites are the key factors influencing the catalytic activity.

Lipoxygenase Inhibitory Activity of Some Extracts Prepared from Flaxseed (Linum usitatissimumv L.)

Background: Lignans are biologically important phenolic compounds that exist in different levels of various plants; yet, flaxseed is one of the richest sources of such compounds. Lipoxygenase enzymes are associated with many inflammatory-related diseases such as arthritis, allergic asthma, psoriasis, cardiovascular disease, kidney disease, skin diseases, and neuropsychiatric disorders, as in Alzheimer's disease. Not only are these enzymes involved in many types of cancers, but they are also very crucial to find new LOX inhibitors to treat human diseases such as cancer or cardiovascular disease. Screening for lipoxygenase inhibitory activities of flaxseeds lignans extracts in various methods is reported in this work. Methods: Extracts of samples of flaxseeds (Linum usitatissmum) were prepared using the following methods: a- extraction with continuous stirring with 80% ethanol, b- extraction with a mixture of equal volumes of diethyl ether and ethyl acetate after direct acid hydrolysis, c- Extraction with 50% ethanol followed by alkaline hydrolysis. Total flavonoids, total phenolic of these extracts were compared. The scavenging potential of free radicals was determined using the DPPH method. The inhibitory potential against the lipoxygenase enzyme was determined by using the soybean lipoxygenase enzyme. Results: The highest phenolic content was in the extract prepared with ethanol 80% with continuous stirring, with phenolic content of (126.848 mg GAE /g). While the highest flavonoid was content in the extract prepared with a mixture of equal volumes of diethyl ether and ethyl acetate after direct acid hydrolysis, with flavonoid content reached (7.8 mg QE / g). Moreover, the scavenging potential of free radicals expressed in terms of IC50 (μg/ml) showed extraction with a mixture of equal volumes of diethyl ether and ethyl acetate after direct acid hydrolysis exhibited higher antioxidant capacity (IC50=22.257±0.095 μg/ml) followed by 80% ethanol extract. The median inhibitory concentration (IC50) was calculated according to the LOX enzyme inhibitory method. The IC50 value of a mixture of equal volumes of diethyl ether and ethyl acetate after direct acid hydrolysis extract of flaxseeds is 73.689±0.585 μg/ml. Conclusion: The mixture of equal volumes of diethyl ether and ethyl acetate extract after direct acid hydrolysis gives stronger scavenging potential of free radicals and lipoxygenase inhibitory effects than the other extracts in this study. Therefore, according to the results we got in our study, flaxseed extracts can be a potential source of novel therapeutics to treat many diseases related to the LOX enzyme.

Uranyl-Photocatalyzed Hydrolysis of Diaryl Ethers at Ambient Environment for the Directional Degradation of 4-O-5 Lignin.

Uranyl-photocatalyzed hydrolysis of diaryl ethers has been established to achieve two types of phenols at room temperature under normal pressure. The single electron transfer process was disclosed by a radical quenching experiment and Stern–Volmer analysis between diphenyl ether and uranyl cation catalyst, followed by oxygen atom transfer process between radical cation of diphenyl ether and uranyl peroxide species. The 18O-labeling experiment precisely demonstrates that the oxygen source is water. Further application in template substrates of 4-O-5 linkages from lignin and 30-fold efficiency of flow operation display the potential application for phenol recovery via an ecofriendly and low-energy consumption protocol.

Study on pharmacological properties and cell absorption metabolism of novel daidzein napsylates.

Novel daidzein napsylates (DD4 and DD5) were synthesized by microwave irradiation, according to structural modification of daidzein (DAI) using the principle of pharmacokinetic transformation. The pharmacological properties of DD4 and DD5 were evaluated via high performance liquid chromatography (HPLC) and calculated based on the drug design software ChemAxon 16.1.18. The cell uptake changes of DD4 and DD5 were investigated to analyse the structure–property relationship. The metabolisms of DD4 and DD5 were analysed by HPLC-mass spectrometry in human aortic vascular smooth muscle cells (HAVSMCs) and their possible metabolic pathways were inferred in vivo. The results showed that the solubility of DD4 and DD5 was increased by 2.79 × 105 and 2.16 × 105 times compared to that of DAI, separately, in ethyl acetate. The maximum absorption rates of DD4 and DD5 were enhanced by 4.3–4.5 times relative to DAI. Preliminary studies on metabolites of DD4 and DD5 in HAVSMCs showed that DD4 and DD5 were hydrolysed into DAI under the action of intracellular hydrolase in two ways, ester hydrolysis or ether hydrolysis. Then, DAI was combined with glucuronic acid to form daidzein monoglucuronate under the action of uridine diphosphate (UDP)-glucuronidase. Meanwhile, it was also found that metabolite M5 of DD5 could undergo glucuronidation under the action of UDP-glucuronosyltransferase and competitive sulphation under the action of sulphotransferase to produce its sulfate conjugate M7. Analysis of structure–property relationships indicated that the absorption and utilization of drugs is closely relative to the physical properties and could be improved by adjusting the liposolubility. The pharmaceutical properties were optimized comprehensively after DAI was modified by naphthalene sulphonate esterification. This indicates that this kind of derivatives may have relatively good absorption and transport characteristics and biological activities in vivo. The research on biological activities of the new derivatives (DD4 and DD5) is ongoing in our laboratory.

Kinetics and Mechanism of the Hydrolysis of Benzyl Ether Bonds in Aqueous–Organic Media

Kinetic parameters (rate constant, energy of activation, and entropy of activation) of the acid-catalyzed hydrolysis of the benzyl ethers (3,4-dimethoxyphenyl)-(2-methoxyphenoxy)methane and (4-hydroxy-3-methoxyphenyl)methoxymethane are determined for a wide range of compositions for mixtures of water and organic solvents (dioxane, DMSO, and acetic acid). It is shown that the acid-catalyzed hydrolysis of these benzyl ethers in mixtures of water and aprotic solvents occurs as a reaction of bimolecular nucleophilic substitution. In aqueous acetic acid solutions, the mechanism of hydrolysis can be bimolecular or unimolecular, depending on the structure of the ether and the content of the organic solvent. The effect the solvents have on the rate and mechanism of the studied reaction is discussed in terms of solvation concepts.

Synthesis of -Hydroxy -Proline: Potential for Organocataly-sis Reactions

A chiral organic molecule, L-proline catalyzed an enantioselective transformation reaction has becoming interesting synthetic protocol especially in the area of organocatalysis. Herein, a synthetic approach towards -hydroxy--proline starting from bicyclic lactone lactam is hereby described. The syntheses utilized dicarboxylation reaction of bicyclic lacton lactam, followed by ether hydrolysis of the bicyclic ether and oxidation reaction of the primary alcohol. The synthetic strategy disclosed here allows further the enantioselective synthesis of a variety of unnatural amino acids based on -proline structure.

Ether Hydrolysis, Ether Thiolysis, and the Catalytic Power of Etherases in the Disassembly of Lignin.

The recycling of much of the carbon in Nature depends on the breakdown of polymers in woody matter, notably cellulose (a polyacetal) and lignin (a polyether). Here, we show that equilibrium favors ether hydrolysis in water, although the rates of spontaneous hydrolysis of ethers are too slow to measure in neutral solution except at temperatures approaching the critical point of water. Circumventing that kinetic obstacle, glutathione-dependent etherases from white-rot fungi are known to employ the thiolate group of glutathione to attack guaiacyl ethers. Experiments at elevated temperatures indicate that thioglycolate attacks diethyl ether in water, in the absence of enzymes, with a rate constant of 6 × 10-11 M-1 s-1 at 25 °C and that ether thiolysis is strongly favored thermodynamically, with a Keq value of 2.5 × 106 (ΔG = -8.7 kcal/mol). Compared with the rate of non-enzymatic thiolysis, the lignin-degrading etherases LigE and LigF produce 1015-fold rate enhancements, among the largest that have been observed for an enzyme acting on two substrates.

Cp2Mo(OH)(OH2)]+‐Catalyzed Hydrolysis of Mono‐ and Difunctional Ethers: Theoretical Understanding of Their Divergent Reactivity

The reaction mechanism of [Cp2Mo(OH)(OH2)]+‐catalyzed hydrolysis of ethyl vinyl, divinyl, and diethyl ethers was theoretically investigated. The reaction pathway evolving through the coordination of the ether oxygen to Mo is notably disfavored, as experimentally suggested. This is the only operative coordination mode for diethyl ether and explains why this monofunctional ether is not hydrolyzed by molybdocenes. However, difunctional ethers containing a functionality susceptible to activation like the vinyl group present an alternative reaction pathway proceeding through the coordination of the vinyl terminal carbon to Mo with accessible rate‐determining Gibbs energy barriers of 29.3 kcal/mol (divinyl ether) and 22.2 kcal/mol (ethyl vinyl ether). In these cases, the catalyst withdraws electron density from the unsaturated bonds and prepares the group for an easy OH‐nucleophilic attack. This explains the molybdocene‐catalyzed hydrolysis of ethyl vinyl ether experimentally observed and, more interestingly, reveals what the crucial role of the functional groups linked to the ether oxygen really is in the viability of these reactive processes.

Synthesis and characterization of Cu-X/γ-Al2O3 catalyst by intermittent microwave irradiation for hydrogen generation from dimethyl ether steam reforming

A series of Cu-X/?-Al2O3 (X = Fe, Co, Ni) catalysts were synthesized by a rapid intermittent microwave irradiation method for hydrogen generation from dimethyl ether steam reforming. Different parameters, such as the promoters of X (X = Fe, Co, Ni), microwave irradiation procedure and the ratio of metal to ?-Al2O3, were investigated. The results show that 2Cu-Fe/72?-Al2O3 has the best performance, for which the agglomeration is prevented, CuO is well dispersed and the catalytic activity is improved. Promoter iron oxide in 2Cu-Fe/9?-Al2O3 facilitates the watergas shift reaction, which lead to an increase in the conversion of CO to CO2 and hydrogen yield. Particularly, the 2Cu-Fe/72?-Al2O3 catalyst, with the best molar ratio of metal to ?-Al2O3, shows a dimethyl ether conversion of &gt;99% and a hydrogen yield of &gt;98% and produces the lowest CO content of 1.4%, indicating that the synergism between dimethyl ether hydrolysis and methanol reforming requires an appropriate balance between the metallic Cu-Fe and the acid ?-Al2O3. The intermittent microwave irradiation technique provides a simple but effective method of the Cu-Fe/?-Al2O3 synthesis with a good catalyst performance for the dimethyl ether steam reforming.

Stereoselective one-pot synthesis of polypropionates

Polypropionates—motifs with alternating methyl and hydroxy groups—are important segments of many natural products possessing high bioactivity and therapeutic value. Synthetic access to these structures remains an area of intensive interest, focusing on the establishment of the contiguous stereocentres and a desire for operational simplicity. Here we report an efficient strategy for the stereoselective assembly of polypropionates with three or four stereocentres through a three-step relay process that include Diels–Alder reaction, silylenol ether hydrolysis and Baeyer–Villiger oxidation. The stereochemistry and functionality of the resulting polypropionates depend on the substitution pattern of the diene and dienophile substrates of the Diels–Alder cycloaddition. More importantly, the relay sequence is effectively performed in one pot, and the product could potentially undergo the same sequence for further elaboration. Finally, the C1–C9 segment of the macrolide etnangien is constructed with four of the six stereogenic centres established using the relay sequence.