New Trends and Future Opportunities in the Enzymatic Formation of C−C,C−N,and C−O bonds

Organic chemistry provides society with fundamental products we use daily. Concerns about the impact that the chemical industry has over the environment is propelling major changes in the way we manufacture chemicals. Biocatalysis offers an alternative to other synthetic approaches as it employs enzymes, Nature's catalysts, to carry out chemical transformations. Enzymes are biodegradable, come from renewable sources, operate under mild reaction conditions, and display high selectivities in the processes they catalyse. As a highly multidisciplinary field, biocatalysis benefits from advances in different areas, and developments in the fields of molecular biology, bioinformatics, and chemical engineering have accelerated the extension of the range of available transformations (E. L. Bell et al., Nat. Rev. Meth. Prim. 2021 , 1, 1–21). Recently, we surveyed advances in the expansion of the scope of biocatalysis via enzyme discovery and protein engineering (J. R. Marshall et al., Tetrahedron 2021 , 82, 131926). Herein, we focus on novel enzymes currently available to the broad synthetic community for the construction of new C−C, C−N and C−O bonds, with the purpose of providing the non-specialist with new and alternative tools for chiral and sustainable chemical synthesis.     

Fatty acids,the immune response,and autoimmunity: A question of n−6 essentiality and the balance between n−6 and n−3

The essentiality of n−6 polyunsaturated fatty acids (PUFA) is described in relation to a thymus/thymocyte accretion of arachidonic acid (20∶4n−6, AA) in early development, and the high requirement of lymphoid and other cells of the immune system for AA and linoleic acid (18∶2n−6, LA) for membrane phospholipids. Low n−6 PUFA intakes enhance whereas high intakes decrease certain immune functions. Evidence from in vitro and in vivo studies for a role of AA metabolites in immune cell development and functions shows that they can limit or regulate cellular immune reactions and can induce deviation toward a T helper (Th)2-like immune response. In contrast to the effects of the oxidative metabolites of AA, the longer-chain n−6 PUFA produced by γ-linolenic acid (18∶3n−6, GLA) feeding decreases the Th2 cytokine and immunoglobulin (Ig)G1 antibody response. The n−6 PUFA, GLA, dihomo-γ-linolenic acid (20∶3n−6, DHLA) and AA, and certain oxidative metabolites of AA can also induce T-regulatory cell activity, e.g., transforming growth factor (IGF)-β-producing T cells; GLA feeding studies also demonstrate reduced proinflammatory interleukin (IL)-1 and tumor necrosis factor (TNF)-α production. Low intakes of long-chain n−3 fatty acids (fish oils) enhance certain immune functions, whereas high intakes are inhibitory on a wide range of functions, e.g., antigen presentation, adhesion molecule expression, Th1 and th2 responses, proinflammatory cytokine and eicosanoid production, and they induce lymphocyte apoptosis. Vitamin E has a demonstrable critical role in long-chain n−3 PUFA interactions with immune functions, often reversing the effects of fish oil. The effect of dietary fatty acids on animal autoimmune disease models depends on both the autoimmune model and the amount and type of fatty acids fed. Diets low in fat, essential fatty acid deficient (EFAD), or high in long-chain n−3 PUFA from fish oils increase survival and reduce disease severity in spontaneous autoantibody-mediated disease, whereas high-fat LA-rich diets increase disease severity. In experimentally induced T cell-mediated autoimmune disease, EFAD diets or diets supplemented with long-chain n−3 PUFA augment disease, whereas n−6 PUFA prevent or reduce the severity. In contrast, in both T cell- and antibody-mediated autoimmune disease, the desaturated/elongated metabolites of LA are protective. PUFA of both the n−6 and n−3 families are clinically useful in human autoimmune-inflammatory disorders, but the precise mechanisms by which these fatty acids exert their clinical effects are not well understood. Finally, the view that all n−6 PUFA are proinflammatory requires revision, in part, and their essential regulatory and developmental role in the immune system warrants appreciation.     

Synthesis,characterization and catalytic properties of La2−x Sr x NiO4−δ

Various compositionsx in the catalyst system La_2–x Sr _x NiO_4– have been prepared by conventional techniques and characterized by X-ray powder diffraction, electron microscopy and BET surface measurements. The catalytic properties of these catalysts have been tested in the propylene oxidation reaction. The catalytic activity can be correlated with the oxygen content and with the strontium substitution.     

Corrosion of HIPed β-Si6−zAlzOzN8−z (z =0, 1, 2, 3) ceramics by NaCl vapor

Tests for the corrosion of β-Si_6−zAl_zO_zN_8−z (z =0, 1, 2, 3) (β-Si₃N₄ and β-SiAlON) ceramics were carried out at 1300 °C for 3–24 h in NaCl vapor of various concentrations (1.67 × 10⁻², 3.33 × 10⁻², 5.0 × 10⁻² g l⁻¹), which was carried by flowing Ar gas. The densified Si₃N₄ and SiAlON ceramics were fabricated by HIPing under N₂ of 150 MPa at 1700 °C. The corroded surface was observed by optical and scanning electron microscopy (OM and SEM). The phases produced during corrosion were identified by X-ray diffraction. The thickness of the corroded scale was determined by cross sectional SEM observation. The Si₃N₄ ceramics were hardly corroded by NaCl vapor, while the z=1 and 2 SiAlONs were slightly corroded with the formation of bubbles on the surface; the z=3 ceramics were severely corroded with the formation of Al₂O₃ needle crystals and fine mullite crystals, depending on the NaCl vapor concentration. Quantitative X-ray microanalysis showed that 2 at.% Na is contained in all the scales of the SiAlONs. The severe corrosion of the z=3 SiAlON was explained on the basis of the kinetic results for the thickness of the scale.     

Ketonization of fatty methyl esters over Sn−Ce−Rh−O catalyst

A mixture of methyl esters of fatty acids obtained by transterification of nonerucic rape oil was ketonized. The starting material, diluted with methanol, was converted at atmospheric pressure over a catalyst that contained Sn, Ce, and Rh oxides in a molar ratio of 90:9:1. At a temperature of 385°C ketones were obtained with a total yield of 63% at the 96% conversion of starting material. The reported experiments prove that catalysts other than iron that are active in ketonization of primary alcohols can be successfully used in ketonization of esters of fatty acids. The kind of diluent used plays a crucial role in the conversion.     

Effect of 18∶1n−9, 20∶5n−3, and 22∶6n−3 on lipid accumulation and secretion by atlantic salmon hepatocytes

We have studied the effects of dietary FA on the accumulation and secretion of [³H]glycerolipids by salmon hepatocytes in culture. Atlantic salmon were fed diets supplemented with either 100% soybean oil (SO) or 100% fish oil (FO), and grew from an initial weight of 113±5 g to a final weight of 338 ±19 g. Hepatocytes were isolated from both dietary groups and incubated with [³H]glycerol in an FA-free medium; a medium supplemented with 0.75 mM of one of three FA—18∶1n−9, 20∶5n−3, or 22∶6n−3—or a medium supplemented with 0.75 mM of the sulfur-substituted FA analog tetradecylthioacetic acid (TTA), which cannot undergo β-oxidation. Incubations were allowed to proceed for 1,2,6, or 24 h. The rate of the secretion of radioactive glycerolipids with no FA added was 36% lower from hepatocytes isolated from fish fed the FO diet than it was from hepatocytes isolated from fish fed the SO diet. Hepatocytes incubated with 18∶1n−9 secreted more [³H]TAG than when incubated with no FA, whereas hepatocytes incubated with 20∶5n−3 or TTA secreted less labeled TAG than when incubated with no FA. This observation was independent of the feeding group. Hepatocytes incubated with 22∶6n−3 secreted the highest amounts of total [³H]glycerolipids compared with the other treatments, owing to increased secretion of phospholipids and mono- and diacylglycerols (MDG). In contrast, the same amounts of [³H]TAG were secreted from these cells as from cells incubated in an FA-free medium. The lipid-lowering effect of FO is thus independent of 22∶6n−3, showing that 20∶5n−3 is the FA that is responsible for the lipid-lowering effect. The ratio of TAG to MDG in lipids secreted from hepatocytes to which 20∶5n−3 or TTA had been added was lower than that in lipids secreted from hepatocytes incubated with 18∶1n−9 or 22∶6n−3, suggesting that the last step in TAG synthesis was inhibited. Morphometric measurements revealed that hepatocytes incubated with 20∶5n−3 accumulated significantly more cellular lipid than cells treated with 18∶1n−9, 22∶6n−3, TTA, or no treatment. The area occupied by mitochondria was also greater in these cells. The present study shows that dietary FO reduces TAG secretion from salmon hepatocytes and that 20∶5n−3 mediates this effect.     

Chemical synthesis,compositional, morphological,structural, optical and magnetic properties of Zn1−xDyxS nanoparticles

Zn_1−xDy_xS (x=0, 0.02 and 0.04) nanoparticles (NPs) were synthesized by chemical refluxing technique at 100 °C. The prepared samples were analyzed by studying their compositional, morphological, structural, optical and magnetic properties. EDS analysis confirmed the presence of zinc, dysprosium and sulfur in the samples in near stoichiometric ratio. The X-ray diffraction patterns do not show any Dy related peaks for the as-synthesized ZnS nanoparticles. The average diameter of the particles confirmed by TEM studies, was in the range 2–4 nm. Raman studies revealed that all the samples are single phase and exhibit cubic structure. From DRS studies, the band-gap was found to be in the range of 3.85–3.70 eV. All the doped ZnS nanoparticles exhibit ferromagnetic behavior with the Curie temperature higher than room temperature and the magnetic properties of doped ZnS nanoparticles depend on the concentration of Dy ions.     

N,N−二甲基−二硫代甲酰胺丙磺酸钠对THPED体系化学镀铜的影响

研究了N,N?二甲基?二硫代甲酰胺丙磺酸钠(DPS)作为添加剂对以四羟丙基乙二胺(THPED)为单一配位剂的化学镀铜体系的沉积速率、镀层形貌和晶体结构的影响。结果发现,当DPS的质量浓度从0 mg/L增大到1.0 mg/L时,沉积速率从2.91μm/h提高到6.73μm/h,所得镀层结晶均匀、细致。线性扫描伏安测量结果表明,DPS是通过促进甲醛的阳极氧化来加速化学镀过程。本体系的Cu镀层主要呈面心立方多晶取向,DPS的添加会令晶面取向从(220)转变为(111)。     

Recent Advances in Electrochemical,Ni-Catalyzed C−C Bond Formation

Nickel-catalyzed cross-electrophile coupling (XEC) is an efficient method to form carbon-carbon bonds and has become an important tool for building complex molecules. While XEC has most often used stoichiometric metal reductants, these transformations can also be driven electrochemically. Electrochemical XEC (eXEC) is attractive because it can increase the greenness of XEC and this potential has resulted in numerous advances in recent years. The focus of this review is on electrochemical, Ni-catalyzed carbon-carbon bond forming reactions reported since 2010 and is categorized by the type of anodic half reaction: sacrificial anode, sacrificial reductant, and convergent paired electrolysis. The key developments are highlighted and the need for more scalable options is discussed.     

热处理对锌−镍−磷−纳米二氧化硅复合电镀层性能的影响

先采用由110 g/L ZnCl_2、100 g/L NiCl_2·6H_2O、80 g/L CH_3COONH_4、40 g/L CH_3COONa、5～10g/L NaH_2PO_2·H_2O、180 g/L KCl、0.04～0.08 g/L十二烷基硫酸钠和4～6 g/L纳米SiO_2 (平均粒径7～40 nm)组成的镀液,在pH为4～5、温度为45℃和电流密度为1.5 A/dm2的条件下电镀20 min得到厚度为30～40μm的Zn-Ni-P-纳米SiO_2复合镀层。然后在氮气保护和不同温度(200、300、400和500℃)下热处理2 h。研究了热处理温度对复合镀层微观结构、显微硬度和耐蚀性的影响。结果表明,经300℃热处理的Zn-Ni-纳米SiO_2复合镀层的综合性能较好,显微硬度为198 HV,耐蚀性最好。     

High dietary 18∶3n−3 increases the 18∶3n−3 but not the 22∶6n−3 content in the whole body, brain, skin, epididymal fat pads, and muscles of suckling rat pups

The objective of this study was to test the hypothesis that increasing maternal dietary 18∶3n−3 by decreasing the 18∶2n−6/18∶3n−3 ratio will increase the 18∶3n−3 and 22∶6n−3 content of the whole body, liver, skin (epidermis, dermis, and subcutaneous tissue), epididymal fat pads, and muscles (arms and legs) of 2-wk-old rat pups. Sprague-Dawley dams at parturition were fed semipurified diets containing either a low (18∶2n−6 to 18∶3n−3 ratio of 24.7∶1) or a high (18∶2n−6 to 18∶3n−3 ratio of 1.0∶1) 18∶3n−3 fatty acid content. During the first 2 wk of life, rat pups received only their dams' milk. Fatty acid composition of the pups' stomach contents (dams' milk), whole body, brain, liver, skin, epididymal fat pads, and muscles was determined. The stomach fatty acid composition of 18∶3n−3 reflected the dams' diet. The content of 18∶3n−3 in whole body, brain, liver, skin, epididymal fat pads, and muscles was significantly (P<0.05) greater in rat pups fed the high compared with the low 18∶3n−3 fatty acid diet. The 22∶6n−3 content of the whole body, brain, skin, epididymal fat pads, and muscles was not quantitatively different in rat pups fed either the low or high 18∶3n−3 fatty acid diet. The 20∶5n−3 and 22∶5n−3 content of the whole body, skin, and epididymal fat pads was significantly increased in rat pups fed the high compared with the low 18∶3n−3 fatty acid diet. High content of 18∶3n−3 was found in the skin of rat pups fed either a low or high 18∶3n−3 fatty acid diet. These findings demonstrate that high maternal dietary 18∶3n−3 significantly increases the 18∶3n−3 but not the 22∶6n−3 content of the whole body, brain, skin, epididymal fat pads, and muscles with approximately 39 and 41% of the whole body 18∶3n−3 content being deposited in the skin of suckling rat pups fed either the low or high 18∶3n−3 diet, respectively.     

Synthesis,Characterization, and Spectroscopic Analysis of NdxY1−xTiNbO6 Microwave Ceramics

Solid solutions of Nd_xY_1−xTiNbO₆ ceramics were prepared through the solid-state ceramic route. The materials were calcined at 1250°C and sintered in the range 1400–1550°C. The structure of the system was analyzed using the X-ray diffraction and vibrational spectroscopic analysis. The morphology and the sintering behavior of the samples were analyzed using scanning electron microscopy. The dielectric constant (ɛ_r), temperature coefficient of resonant frequency (τ_f), and the unloaded quality factor (Q_u) were measured in the microwave frequency region using the cavity resonator method. The ɛ_r and τ_f increased with an increase in the concentration of Nd in the solid solutions. Nearly zero temperature coefficient of resonant frequency was obtained for the Nd_0.6Y_0.4TiNbO₆ ceramic. Samples are of high quality factor and are useful for microwave applications.     

N,N-二甲基甲酰胺体系电沉积铋−碲热电薄膜

在N,N-二甲基甲酰胺(DMF)有机溶剂中先通过阴极极化曲线和循环伏安曲线测试研究了Bi(III)、Te(IV)离子及二者混合时在金电极上电沉积的电化学行为.再在不同电位下电沉积制备了Bi-Te热电薄膜,研究了沉积电位对Bi-Te薄膜性能的影响.结果表明,Bi(III)、Te(IV)及Bi-Te在金电极上的电沉积均属于...     

Novel epoxy/expandable graphite halogen-free flame retardant composites−preparation, characterization, and properties

In this work, expandable graphite (EG) was grafted using a coupling agent, 3-isocyanatopropyltriethoxysilane (IPTS). EG has a -O-C₂H₅ (-OEt) functional group which reacts with a polymer matrix through the sol-gel reaction. EG was functionalized by the coupling agent to form a covalent bonding between organic and inorganic phases, increasing the compatibility between the fillers and polymer, and thereby enhancing the thermal stability of the composites. FT-IR and X-ray photoelectron spectroscopy (XPS) were adopted to characterize the grafting reaction between IPTS and EG. Thermogravimetric analysis (TGA), the derivative of thermogravimetric weight (DTG) and the difference between the thermogravimetric weights (TG△) were employed to calculate the thermal stability of the composites. The limiting oxygen index (LOI) was utilized to classify the composites by flame retardancy. A scanning electron microscope (SEM) was applied to observe their morphology, and the behavior of expansion was discussed after the materials were burnt. TGA/MS was used to analyze the gas products during thermal degradation. The results demonstrate that functionalized EG can improve the thermal stability of composites and increase the flame retardancy.     

Surface Exchange of Oxygen in La1−x Sr x FeO3−δ (x = 0, 0.1)

The electronic charge carrier concentration in La_1?x Sr _x FeO_3?δ was shown to depend on the partial pressure of O₂ (pO ₂). Chemical diffusion coefficient and surface exchange coefficient, k _chem, were determined by conductivity relaxation in O₂/N₂ and CO/CO₂ mixtures. k _chem was proportional to pO ₂ ^1.06 in O₂/N₂, while in CO/CO₂ k _chem was controlled by a reaction mechanism involving both CO and CO₂.     

Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl,SO2, and NO2

Journal of Porous Materials - Two different Mg–Al layered double hydroxides (LDHs), OH?Mg–Al LDH and CO3?Mg–Al LDH, are prepared and utilized for the efficient removal...     

ZrxCo0.8−xNi0.2−xFe2O4-graphene nanocomposite for enhanced structural,dielectric and visible light photocatalytic applications

Zirconium doped nickel cobalt ferrite (Zr_xCo_0.8−xNi_0.2−xFe₂O₄) nanoparticles and Zr_xCo_0.8−xNi_0.2−xFe₂O₄-graphene nanocomposites were synthesized by a cheap and facile co-precipitation method. Annealing was done at 750 °C for 6.5 h. Spinel cubic structure of prepared nanoparticles was confirmed by X-ray powder diffraction (XRD) technique. Crystalline size of nanoparticles was observed in the range of 18–27 nm. Graphene was synthesized by Hummer's method. Formation of rGO was confirmed by UV-visible spectroscopy (UV-vis) and XRD. Zr_xCo_0.8−xNi_0.2−xFe₂O₄-graphene nanocomposites were prepared by ultra-sonication route. Grain size of nanoparticles and dispersion of nanoparticles between rGO layers was determined by Scanning electron microscopy (SEM). In application studies of nanoparticles and their nanocomposites, photocatalytic efficiency of nanoparticles under visible light irradiation was observed by degradation of methylene blue. Charge transfer resistance was measured by electrochemical impedance spectroscopy (EIS) and the variation in dc electrical resistivity was analyzed by room temperature current voltage characteristics (I-V). Dielectric constant was also evaluated in frequency range from 1 MHz to 3 GHz. All these investigations confirmed the possible utilization of these materials for a variety of applications such as visible light photocatalysis, high frequency devices fabrication etc.     

Iron-Catalyzed C−C Bond Formation via Chelation-Assisted C−H Activation

This review provides a brief overview of iron-catalyzed C−C bond forming reactions via heteroatom-assisted C−H bond activation, which have been extensively developed in the last decade. Three major types of reactions are discussed, namely, (1) C−H activation/C−C coupling using organometallic reagents under oxidative conditions, (2) C−H activation/C−C coupling using organic electrophiles under redox-neutral conditions, and (3) C−H activation/C−C coupling using unsaturated hydrocarbons under redox-neutral or oxidative conditions.     

Structural,morphological and electrical properties of Ce1−xRuxO2−δ (x=0.005–0.02) solid solutions

Nanoparticles of ceria–ruthenium oxide solid solutions with composition Ce_1−xRu_xO_2−δ (x=0.005–0.02) were successfully produced by self–propagating room temperature synthesis using reaction between metal nitrates and sodium hydroxide. These compositions were characterized by X–ray powder diffraction (XRD), Raman spectroscopy, specific surface area, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X–ray spectroscopy (EDX). The experimental measurements were complemented by calculations based on the ion–packing model. XRD analysis revealed the presence of single–phase solid solutions with CeO₂ fluorite structure (regardless of dopants concentration) and Raman spectroscopy confirmed the presence of the RuO₂ phase. Electrochemical impedance spectroscopy (EIS) measurements of sintered samples at different temperatures showed that the small ionic radius dopant reduces oxygen vacancies mobility that is responsible for the conductivity of these ceramics.