Isomeric Products Research Articles

Anion-π Interaction in a Diketopyrrolopyrrole Derivative.

In this work, an N-substituted diketopyrrolopyrrole (DPP) derivative Ph-DPP was synthesized, showing interaction toward Lewis alkaline anions such as F-. The typical electron-transfer-dominated anion-π interaction product Ph-DPP•- and unexpected isomer product i-Ph-DPP were both observed, and their formation mechanism was studied by density functional theory calculations, suggesting that a deprotonation initiation route is favored, which gives interesting insight for understanding the debatable role of F- in such non-covalent intermolecular interactions.

Mechanistic Analysis of Alkyne Haloboration: A DFT, MP2, and DLPNO-CCSD(T) Study.

Stereocontrol of the alkyne haloboration reaction has received attention in many experimental but few theoretical studies. Here we present a detailed quantum-chemical study of mechanisms leading to Z versus E isomers of haloboration products, considering acetylene and propyne combined with BCl3, BBr3, and BI3. Calculations using B3LYP-D3, MP2, and DLPNO-CCSD(T) methods are used to study polar reactions between the alkyne and BX3 in the absence and presence of an additional halide anion whose content in the reaction mixture can be controlled experimentally. The formation of anti-haloboration products via radical mechanisms is also explored, namely, by adding BX3 to (Z)-halovinyl radical. For the anti-haloboration of propyne, the radical route is prohibited by the regiochemistry of the initiating halopropenyl radical, while the polar route is unlikely due to a competitive allene generation. In contrast, energetically accessible routes exist for both syn- and anti-bromoboration of acetylene; hence, careful control of reaction conditions is necessary to steer the stereochemical outcome. Methodologically, MP2 results correspond better to the DLPNO-CCSD(T) energies than the B3LYP-D3 results in terms of both reaction barrier heights and relative ordering of energetically close stationary points.

Utilization of Loaded Cobalt onto MCM-48 Mesoporous Catalyst as a Heterogeneous Reaction in a Fixed Bed Membrane Reactor to Produce Isomerization Product from n-Heptane

The use of catalytic membranes as microstructured reactors without a separative function has proved effective. High catalytic activity is possible with minimal mass transport resistances if the reactant mixture is pushed to flow through the pores of a membrane that has been impregnated with catalyst. In this study, n-heptane (C7H16) was hydrocracked and hydro-isomerized within a plug-flow zeolitic catalytic membrane-packed bed reactor. The metallic cobalt (Co) precursor at 3 wt.% was loaded onto support mesoporous materials MCM-48 to synthesize heterogeneous catalysis. The prepared MCM-48 was characterized by utilizing characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FTIR), nitrogen adsorption–desorption isotherms, and the Brunauer–Emmett–Teller (BET) surface area. The structural and textural characteristics of MCM-48 after encapsulation with Co were also investigated. The analyses were performed before and after metal loading. According to the results, the 3 wt.% Co/MCM-48 of metallic catalyst in a fixed bed membrane reactor (MR) appears to have an excellent catalytic activity of ~83% during converting C7H16 at 400 °C, whereas a maximum selectivity was approximately ~65% at 325 °C. According to our findings, the synthesized catalyst exhibits an acceptable selectivity to isomers with multiple branches, while making low aromatic components. In addition, a good catalytic stability was noticed for this catalyst over the reaction. Use of 3 wt.% Co/MCM-48 catalyst led to the highest isomerization selectivity as well as n-heptane conversion. Therefore, the heterogeneous catalysis MCM-48 is a promising option/ alternative for traditional hydrocracking and hydro-isomerization processes.

The gradient fabrication and optimization of metal-acid bifunctional catalysts for the hydrogenation of n-C16 to produce bio-jet fuel component

In the two-step hydrogenation of oil to produce bio-jet fuel, the yield of bio-jet fuel is determined by the hydrotreatment of long-chain alkanes over a metal–acid bifunctional catalyst. A strategy that the catalyst with better isomerization is conductive to the hydrotreatment of long-chain alkanes to produce jet fuel component is proposed. Based on the hollow silicon sphere (HSS), catalysts with different acid strength, diffusion performance, and intimacy between Pt and acid bifunctional sites were designed to gradually optimize the isomerization performance. After the gradient optimization of weak acid, strong diffusion performance, and minor-nanoscale intimacy between Pt and acid sites, the gradient catalysts exhibited a constantly improving yield of isomer product and jet fuel component. The yolk-shell WHSS@Pt catalyst with three levels of simultaneous optimization performed the favorable yield of jet fuel component (37 wt.%), which can be attributed to the combination of weak acid, strong diffusion performance, and minor-nanoscale intimacy between bifunctional sites that are beneficial to the isomerization of long-chain alkanes.

Evidence for Ruthenium(II) Peralkene Complexes as Catalytic Species during the Isomerization of Terminal Alkenes in Solution.

The isomerization (chain-walking) reaction of terminal to internal alkenes is catalyzed by part-per-million amounts of practically any Ru source when the reaction is carried out with a neat terminal alkene. Here, we provide evidence that the soluble starting Ru sources evolve to catalytically active peralkene Ru(II) species under reaction conditions. These species may also explain the isomerization products found during other Ru-catalyzed alkene processes, i.e., alkene metathesis reactions. A Finke-Watzky mechanism for catalyst formation is consistent with the evidence obtained.

BIOETHANOL CONVERSION INTO HIGH-OCTANE COMPONENTS OF MOTOR FUEL IN THE PRESENCE OF COBALT-CONTAINING HZSM-5 TYPE ZEOLITES

The influence of the concentration of cobalt introduced into HZSM-5 on its acidic and catalytic properties in the transformation of ethanol into high-octane components of motor fuels has been studied in the plug-flow unit within the temperature range of 300-450 °С. The unmodified НZSM-5 zeolite is shown to be highly selective to aromatization products (27.5-47.6 %) and С1-С3 alkanes (25.8-37.1 %). A significant increase in selectivity to isomerisation products (from 17.2-19.8 to 34.0-42.7 %) is established for cobalt-modified (1.0-3.0 wt. %) zeolite catalysts within the temperature range 300-350 °C. The highest increase in the selectivity of modified catalysts to aromatisation products (32.7-40.7 %) is observed within the temperature interval of 400-450 °С. The effect of modification on the acid properties of HZSM-5 zeolite has been studied using the temperature-programmed desorption of ammonia. It is shown that the changes of the catalytic properties of HZSM-5 zeolite are connected with a considerable decrease in the concentration of strong Brønsted acid centres (from 538 to 317 μmol/g), with the formation of new stronger Lewis acid centres (37-80 μmol/g) including cobalt ions and acid-base Coδ+-Oδ- type pairs capable of strong polarization and activation of C-H bonds in the intermediates. Selectivity to the products of isomerisation and aromatization on the modified catalysts is regulated by cobalt concentration and process temperature. The highest selectivity to isomerisation products (42.7 %) is achieved over the 2 % Co/HZSM-5 catalyst at a temperature of 300 °C. The catalysate obtained over the 2 % Co/HZSM-5 catalyst at 300 °С corresponds to Euro-5 standard in the content of isoparaffin (56.4 %) and aromatic (29.8 %) hydrocarbons, benzene (0.6 %) and olefins (1.1 %).

The Effect of Iron Oxide Nanoparticles on the Menaquinone-7 Isomer Composition and Synthesis of the Biologically Significant All-Trans Isomer.

Menaquinone-7 (MK-7) is the most therapeutically valuable K vitamin owing to its excellent bioavailability. MK-7 occurs as geometric isomers, and only all-trans MK-7 is bioactive. The fermentation-based synthesis of MK-7 entails various challenges, primarily the low fermentation yield and numerous downstream processing steps. This raises the cost of production and translates to an expensive final product that is not widely accessible. Iron oxide nanoparticles (IONPs) can potentially overcome these obstacles due to their ability to enhance fermentation productivity and enable process intensification. Nevertheless, utilisation of IONPs in this regard is only beneficial if the biologically active isomer is achieved in the greatest proportion, the investigation of which constituted the objective of this study. IONPs (Fe3O4) with an average size of 11 nm were synthesised and characterised using different analytical techniques, and their effect on isomer production and bacterial growth was assessed. The optimum IONP concentration (300 μg/mL) improved the process output and resulted in a 1.6-fold increase in the all-trans isomer yield compared to the control. This investigation was the first to evaluate the role of IONPs in the synthesis of MK-7 isomers, and its outcomes will assist the development of an efficient fermentation system that favours the production of bioactive MK-7.

Aryl-to-Vinyl 1,4-Nickel Migration/Reductive Cross-Coupling Reaction for the Stereoselective Synthesis of Multisubstituted Olefins.

The aryl-to-vinyl nickel 1,4-migration (1,4-Ni migration) reaction has been reported for the first time. The generated alkenyl Ni species undergo a reductive coupling reaction with unactivated brominated alkanes affording a series of trisubstituted olefins. This tandem reaction exhibits mild conditions, a broad substrate scope, high regioselectivity, and excellent Z/E stereoselectivity. A series of controlled experiments have shown that the critical 1,4-Ni migration process is reversible. In addition, the alkenyl nickel intermediates obtained after migration are highly Z/E stereoselective and do not undergo Z/E isomerization. The obtained trace isomerization products are caused by the instability of the product.

Aryl‐to‐Vinyl 1,4‐Nickel Migration/Reductive Cross‐Coupling Reaction for the Stereoselective Synthesis of Multisubstituted Olefins

AbstractThe aryl‐to‐vinyl nickel 1,4‐migration (1,4‐Ni migration) reaction has been reported for the first time. The generated alkenyl Ni species undergo a reductive coupling reaction with unactivated brominated alkanes affording a series of trisubstituted olefins. This tandem reaction exhibits mild conditions, a broad substrate scope, high regioselectivity, and excellent Z/E stereoselectivity. A series of controlled experiments have shown that the critical 1,4‐Ni migration process is reversible. In addition, the alkenyl nickel intermediates obtained after migration are highly Z/E stereoselective and do not undergo Z/E isomerization. The obtained trace isomerization products are caused by the instability of the product.

Compilation of isomeric ratios of light particle induced nuclear reactions

Experimental isomeric ratios of light (A ≤ 4) particle-induced nuclear reactions were compiled for the product nuclides having metastable states with half-lives longer than 0.1 s. The experimental isomeric ratio data were taken from the EXFOR library and reviewed. When an experiment reports isomer production cross sections instead of isomeric ratios, the cross sections taken from the EXFOR library were converted to the isomeric ratios by us. During compilation, questionable data (e.g., preliminary data compiled in EXFOR in parallel with their final data, sum of isomer production cross sections larger than the total production cross sections) were excluded. As an application of the new compilation, goodness-of-fit was studied for the isomeric ratios predicted by the reaction model code TALYS-1.96. A text file and plots of the compiled isomer production cross sections and isomeric ratios are provided as supplemental materials.

178m2Hf isomer production cross-sections for Ta target irradiated by α-particles in the energy range from 36 to 92 MeV

178m2Hf isomer production cross-sections were measured when natural tantalum targets were irradiated by alpha particles in the energy range of 36–92 MeV. The simulations of these cross-sections in the TALYS-1.4 code showed that the main contribution to the 178m2Hf isomer production is given by (α, αp2n), (α, 3p4n) and (α, 3Hep3n) nuclear reactions. In the range of α-particle energies of 58–92 MeV, the theoretical results coincided well with the experimental ones, and based on this, the cross-sections of the 178gHf ground state production were estimated. allowing to calculate the isomer ratios as well. The obtained values are in good agreement with the trend of changes for the isomer ratios obtained in the nuclear reactions with lower-energy alpha particles and other targets.

Deciphering the photolysis products and biological concerns of triclosan under UVC and UVA

Triclosan (TCS) is omnipresent in the environment and has drawn increasing attention due to its potential adverse effects on human health. Direct photolysis of TCS readily occurs, especially in the surface layers of waters that receive abundant ultraviolet radiation during the daytime. However, biological concerns and the identification of toxic products during TCS photolysis have been explored limitedly. Therefore, in the present work, the structural characterization of the photolysis products by UVC and UVA were performed based on the mass spectra and fragmental ions. The results displayed that TCS was more readily eliminated by UVC than UVA, and the product species were completely different when TCS was degraded by UVC and UVA, respectively. Two products, m/z 235 and m/z 252, were produced via reductive dechlorination and nucleophilic substitution with UVC, while three dioxin-like isomer products were generated by dechlorination, cyclization and hydroxylation. Furthermore, the results of biological concerns suggested that the elimination of TCS did not represent the disappearance of biological risks. Specifically, more hazardous and photolysis products were formed during TCS photolysis with ultraviolets. For instance, the dioxin-like isomer products were highly microtoxic and genotoxic, and mildly antiestrogenic. The positive findings highlighted the biological concerns of TCS photolysis by ultraviolet radiation in the aquatic environment.

MALDI-MS screening of microbial colonies with isomer resolution to select fatty acid desaturase variants

Creating controlled lipid unsaturation locations in oleochemicals can be a key to many bioengineered products. However, evaluating the effects of modifications to the acyl-ACP desaturase on lipid unsaturation is not currently amenable to high-throughput assays, limiting the scale of redesign efforts to <200 variants. Here, we report a rapid MS assay for profiling the positions of double bonds on membrane lipids produced by Escherichia coli colonies after treatment with ozone gas. By MS measurement of the ozonolysis products of Δ6 and Δ8 isomers of membrane lipids from colonies expressing recombinant Thunbergia alata desaturase, we screened a randomly mutagenized library of the desaturase gene at 5 s per sample. Two variants with altered regiospecificity were isolated, indicated by an increase in 16:1 Δ8 proportion. We also demonstrated the ability of these desaturase variants to influence the membrane composition and fatty acid distribution of E. coli strains deficient in the native acyl-ACP desaturase gene, fabA. Finally, we used the fabA deficient chassis to concomitantly express a non-native acyl-ACP desaturase and a medium-chain thioesterase from Umbellularia californica, demonstrating production of only saturated free fatty acids.

Photonuclear production of nuclear isomers using bremsstrahlung induced by laser-wakefield electrons

Photonuclear production of nuclear isomers using bremsstrahlung induced by laser-wakefield electrons

Radiolysis of diamide phenanthroline extractant: exploring the mechanism of HNO3 enhancing the extraction and An/Ln separation performance after irradiation

The stability of organic extractant molecules against radiolysis is critical in the field of actinides and lanthanides (An/Ln) separations. In order to evaluate the radiolytic effects on the extraction performance, the solutions of N,N’-diethyl-N,N’-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) in n-octanol were subjected to γ-irradiation in the presence and absence of 3 mol/L HNO3 aqueous phase. Et-Tol-DAPhen diluted in n-octanol was almost completely decomposed after irradiation and exhibits decreased extraction ability at an absorbed dose of about 384 kGy, along with the appearance of various degradation products. Et-Tol-DAPhen, which was diluted in n-octanol, was completely decomposed upon irradiation in the presence of 3 mol/L HNO3 aqueous phase. However, it exhibited higher DU and SFU/Eu values than before irradiation, as well as degradation products that were also generated. The structures of some isomers of radiolytic products were investigated by density functional theory (DFT) calculations, the radiolysis pathways and products of Et-Tol-DAPhen extractants were obtained, and the radiolysis pathways and products of Et-Tol-DAPhen extractants was proposed. The radiolytic products mainly originated from amide bond and NC bond cleavage of side group substituents, and some resulted from interaction with n-octanol radicals generated during radiolysis. The presence of HNO3 can inhibit the radiolysis of Et-Tol-DAPhen to a certain extent and cause enhanced extraction ability. Moreover, the DFT calculations reveal that the radiolytic products produced in presence of 3 mol/L HNO3 aqueous phase also have efficient extraction performance towards UO22+. The understanding of the radiolysis pathways and products of extractants, based on radiation chemical effects is expected to be helpful for developing new strategies for extractants with long-term performance.

Development of Highly Efficient Hydroisodeparaffinization Catalysts Based on Micro-Mesoporous SAPO-31: New Approaches in the Synthesis of SAPO-31 and the Preparation of Bifunctional Catalysts

A method is proposed for the synthesis of micro-mesoporous SAPO-31 with a high external surface area and large mesopore volume using tetraethoxysilane as a source of silicon. The synthesis of SAPO-31 is based on the principles underlying the Stöber process approach, which allows control of the pore diameter and volume and, hence, the external surface area of the product material. The use of the proposed methods for depositing the hydro-dehydrogenating component on the synthesized micro-mesoporous SAPO-31 made it possible to obtain highly efficient bifunctional hydroisodeparaffinization catalysts with the platinum or palladium content not higher than 0.2 wt.%. As a result, the process temperature can be decreased by 50–60 °C in comparison with the known analogs. Therewith, for example, in the test reaction of n-decane hydroisodeparaffinization at a temperature of 300 °C and feed rate of 1.5 h−1, the conversion above 90%, and the 97–98% yield of liquid products, the 95% selectivity to isomeric products were achieved.

Uniform Ni species encapsulated in nanocrystalline ZSM–5 with enhanced catalytic performance for upgrading of fatty acids

Acid hydrolysis of silicon source with ethylenediamine complexed Ni as metal precursors was used to synthesis a hierarchical ZSM–5 zeolite supporting Ni catalyst by one-pot method. After sequenced hydrothermal synthesis, calcination and reduction, highly dispersed Ni nanoparticles (NPs) encapsulated in hierarchical ZSM–5 catalyst (Ni@HZ) was obtained. The prepared catalyst was used for upgrading of fatty acids under H2 atmosphere. The Ni@HZ catalyst composed of nanocrystalline aggregates (∼100 nm), induced the generation of abundant intercrystallite mesopores, which promoted the diffusion of the reactants. Moreover, the uniformly distributed Ni NPs internal of nanocrystalline show high thermal stability, thus facilitating the adsorption and spillover of active hydrogen. High conversion rate of palmitic acid and stearic acid with deep deoxygenation were achieved by the synergism of acid and Ni species. Moreover, hierarchical pores in Ni@HZ catalyst improved the selectivity of isomeric products, which benefited the cold flow properties of the upgraded oil.

Bifunctional cobalt catalyst for the synthesis of waxy diesel fuel by the Fischer–Tropsch method – from development to introduction. Part 2. Optimization of the catalyst component composition

The effect exerted by the content of metallic (Co-Al2O3/SiO2 catalyst) and acidic (ZSM-5 zeolite in the H-form) components on the properties of bifunctional catalyst for the integrated synthesis of waxy diesel fuel by the Fischer–Tropsch method was studied. Catalysts represented by a composite mixture with a boehmite binder were characterized by XRD, BET and TPR methods. The testing was performed in a flow reactor with a fixed catalyst bed at a pressure of 2.0 MPa, temperature 240 °С and gas hourly space velocity 1000 h–1. Activity and selectivity of the catalysts as well as the fractional and hydrocarbon composition of the products were investigated in dependence on the ratio of components. It was found that productivity of the synthesis for С5+ hydrocarbons and selectivity for the С11–С18 diesel fraction products with a high content of isomeric products correlated with the ratio of metallic and acidic components in the catalysts. The composition of the catalyst recommended for the diesel fuel production has the 1.17 ratio of metallic and acidic components.

An efficient catalytic and solvent‐free method for the synthesis of mono‐organofunctionalized polymethylhydrosiloxane derivatives

AbstractSynthetic reactions with distinctive physicochemical properties and the study of functional groups during synthesis provide an effective way to design polymers on an individual basis. The functionalization of polymethylhydrosiloxane (PMHS) has been performed via hydrosilylation of PMHS with selected alkenes with different active functional groups. In the reaction of PMHS with selected CC bond‐containing olefins in solvent‐free systems, the most efficient catalyst system can be selected to obtain the PMHS reagents to introduce the desired functional groups while generating only regional isomeric products. On‐line real‐time monitoring techniques, in situ Fourier‐transform infrared (FT‐IR), were utilized to determine the chemical reaction rates and reaction conversions for each chemical reaction, and to assess the merits of the reaction systems. In addition, the structures of the functionalized polymers were characterized using FT‐IR spectroscopy, nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC). The kinetic parameters of typical chemical reaction processes were calculated using Kissinger's equation and Ozawa's equation. The comparisons between solvent and solvent‐free systems were carried out under the same conditions, and the statistics revealed that the solvent‐free system was more efficient than its solvent‐based counterpart. This research on the introduction of monofunctional groups into PMHS side chains might pave the way for a variety of diverse functional groups, thus allowing for the further application of PMHS and its derivatives.

The effect of lactose and its isomerization product lactulose on functional and structural properties of glycated casein

Lactulose is an isomer of lactose, formed under thermal processing of milk. Alkaline conditions favor the isomerization of lactose. As reducing sugar, lactose and lactulose could participate in the Maillard reaction and cause protein glycation in milk products. In this study, the influence of lactose and lactulose on the functional and structural properties of glycated casein was investigated. The results demonstrated that compared with lactose, lactulose led to severer changes in molecular weight, more disordered spatial structure and decrease of tryptophan fluorescence intensity of casein. Besides, the glycation degree and advanced glycation end products (AGEs) results suggested that lactulose exhibited stronger glycation ability than lactose due to the higher proportion of open chain in solution. Furthermore, higher glycation degree induced by lactulose resulted in lower solubility, surface hydrophobicity, digestibility and emulsifying capacity of casein-glycoconjugates compared with lactose. The results of this study are essential for tracking the effects of harmful Maillard reaction products on the quality of milk and dairy products.