Enabling Nucleophilic Reactivity in High-Spin Fe(II) Imido Complexes: From Elementary Steps to Cooperative Catalysis.

ConspectusTransition metal complexes featuring an M═NR bond have received great attention as critical intermediates in the synthesis of nitrogen-containing compounds. In general, the properties of the imido ligand in these complexes are dependent on the nature of the metal center. Thus, the imido ligand tends to be nucleophilic in early transition metal complexes and electrophilic in late transition metal complexes. Nonetheless, the supporting ligand can have a dramatic effect on its reactivity. For example, there are sporadic examples of nucleophilic late transition metal imido complexes, often based on strongly donating supporting ligands. Building on these earlier works, in this Article, we show that the imido ligand in a low-coordinate high-spin bis(carbene)borate Fe(II) complex is able to access previously unknown reaction pathways, ultimately leading to new catalytic transformations. We first focus on the synthesis, characterization, and stoichiometric reactivity of a highly nucleophilic Fe(II) imido complex. The entry point for this system is the intermediate-spin three-coordinate Fe(III) imido complex, which is generated from the reaction of an Fe(I) synthon with an organic azide. Alkali metal reduction leads to a series of M+ (M = Li, Na, K) coordinated and charge-separated (M = K(18-C-6)) high-spin Fe(II) imido complexes, all of which have been isolated and fully characterized. Combined with the electronic structure calculations, these results reveal that the alkali ions moderately polarize the Fe═N bond according to K+ ≈ Na+ < Li+. As a result, the basicity of the imido ligand increases from the charged separated complex to K+, Na+, and Li+ coordinated complexes, as validated by intermolecular proton transfer equilibria. The impact of the counterion on imido ligand reactivity is demonstrated through protonation, alkylation, and hydrogen atom abstraction reactions. The counterion also directs the outcome of [2 + 2] reactions with benzophenone, where alkali coordination facilitates double bond metathesis. Building from here, we describe how the unusual nucleophilicity of the high-spin Fe(II) imido complex revealed in stoichiometric reactions can be extended to new catalytic transformations. For example, a [2 + 2] cycloaddition reaction serves as the basis for the catalytic guanylation of carbodiimides under mild conditions. More interestingly, this complex also exhibits the first ene-like reactivity of an M═NR bond in reactions with alkynes, nitriles, and alkenes. These transformations form the basis of catalytic alkyne and nitrile α-deuteration and pKa-dictated alkene transposition reactions, respectively. Mechanistic studies reveal the critical role of metal-ligand cooperativity in facilitating these catalytic transformations and suggest the new avenues for transition metal imido complexes in catalysis that extend beyond classical nitrene transfer chemistry.

Trimethylsilyldiazomethane Disassembly at a Three-Fold Symmetric Iron Site.

The reaction of equimolar trimethylsilyldiazomethyllithium (LiTMSD) with high spin (S = 2) PhB(AdIm)3FeCl (PhB(AdIm)3- = tris(3-adamantylimidazol-2-ylidene)phenylborate) affords the corresponding N-nitrilimido complex PhB(AdIm)3Fe-N═N═C(SiMe3). This complex can be converted to the thermodynamically more favorable C-isocyanoamido isomer PhB(AdIm)3Fe-C═N═N(SiMe3) by reaction with an additional equivalent of LiTMSD. While the iron(II) complexes are four-coordinate, the diazomethane is bound side-on in the iron(I) congener PhB(AdIm)3Fe(N,N'-κ2-N2C(H)Si(CH3)3). The latter complex adopts high spin (S = 3/2) ground state and features an unusually weak C-H bond. Photolysis of the iron(II) complexes induces N═N bond cleavage, with the iron(II) cyanide PhB(AdIm)3Fe-C≡N and iron(IV) nitride PhB(AdIm)3Fe≡N complexes being the major products of the reaction. The same products are obtained when the iron(I) complex is photolyzed or treated with a fluoride source. The trimethylsilyldiazomethane-derived ligand disassembly reactions are contrasted with those observed for related tris(carbene)amine complexes.

Urinary Metabolites of Polycyclic Aromatic Hydrocarbons of Rural Population in Northwestern China: Oxidative Stress and Health Risk Assessment.

Polycyclic aromatic hydrocarbon (PAH) exposure is suspected to be linked to oxidative damage. Herein, ten PAH human exposure biomarkers [hydroxylated PAH metabolites (OH-PAHs)] and five oxidative stress biomarkers (OSBs) were detected in urine samples collected from participants living in a rural area (n = 181) in Northwestern China. The median molar concentration of ΣOH-PAHs in urine was 47.0 pmol mL-1. The 2-hydroxynaphthalene (2-OHNap; median: 2.21 ng mL-1) was the dominant OH-PAH. The risk assessment of PAH exposure found that hazard index (HI) values were <1, indicating that the PAH exposure of rural people in Jingyuan would not generate significant cumulative risks. Smokers (median: 0.033) obtained higher HI values than nonsmokers (median: 0.015, p < 0.01), suggesting that smokers face a higher health risk from PAH exposure than nonsmokers. Pearson correlation and multivariate linear regression analysis revealed that ΣOH-PAH concentrations were significant factors in increasing the oxidative damage to deoxyribonucleic acid (DNA) (8-hydroxy-2'-deoxyguanosine, 8-OHdG), ribonucleic acid (RNA) (8-oxo-7,8-dihydroguanine, 8-oxoGua), and protein (o, o'-dityrosine, diY) (p < 0.05). Among all PAH metabolites, only 1-hydroxypyrene (1-OHPyr) could positively affect the expression of all five OSBs (p < 0.05), suggesting that urinary 1-OHPyr might be a reliable biomarker for PAH exposure and a useful indicator for assessing the impacts of PAH exposure on oxidative stress. This study is focused on the relation between PAH exposure and oxidative damage and lays a foundation for the study of the health effect mechanism of PAHs.

Catalytic 1,3-Proton Transfer in Alkenes Enabled by Fe═NR Bond Cooperativity: A Strategy for pKa-Dictated Regioselective Transposition of C═C Double Bonds.

Transition metal catalyzed alkene double bond transposition usually involves metal hydride intermediates. Despite significant advances in the design of catalysts that dictate product selectivity, control over substrate selectivity is less advanced and transition metal catalysts that selectively transpose double bonds in substrates containing multiple 1-alkene functionalities are rare. Herein, we report that the three-coordinate high spin (S = 2) Fe(II) imido complex [Ph2B(tBuIm)2Fe═NDipp][K(18-C-6)THF2] (1-K(18-C-6)) catalyzes 1,3-proton transfer from 1-alkene substrates to afford 2-alkene transposition products. Mechanistic investigations involving kinetics, competition, and isotope labeling studies, supported by experimentally calibrated DFT computations, strongly support an unusual nonhydridic mechanism for alkene transposition that is enabled by the cooperative action of the iron center and basic imido ligand. As dictated by the pKa of the allylic protons, this catalyst enables the regioselective transposition of C═C double bonds in substrates containing multiple 1-alkenes. The high spin (S = 2) state of the complex allows a wide scope of functional groups to be tolerated, including those that are typical catalyst poisons, such as amines, N-heterocycles, and phosphines. These results demonstrate a new strategy for metal-catalyzed alkene transposition with predictable substrate regioselectivity.

Alkali Metal Ions Dictate the Structure and Reactivity of an Iron(II) Imido Complex.

The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds; however, insight from structure/function relationships is limited. Here, alkali metal reduction of the Fe(III) imido complex [Ph2B(tBuIm)2Fe═NDipp] (1) provides the series of structurally characterized Fe(II) imido complexes [Ph2B(tBuIm)2Fe═NDippLi(THF)2] (2), [Ph2B(tBuIm)2Fe═NDippNa(THF)3] (3), and [Ph2B(tBuIm)2Fe═NDippK]2 (4), in which the alkali metal cations coordinate the imido ligand. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe═N bond distance from that in the charge separated complex [Ph2B(tBuIm)2Fe═NDipp][K(18-C-6)THF2] (5), with the longest bond observed for the smallest alkali metal ion. In contrast to 5, the imido ligands in 2-4 can be protonated and alkylated to afford Fe(II) amido complexes. Combined experimental and computational studies reveal that the alkali metal polarizes the Fe═N bond, and the basicity of imido ligand increases according to 5 < 4 ≈ 3 < 2. The basicity of the imido ligands influences the relative rates of reaction with 1,4-cyclohexadiene, specifically by gating access to complex 5, which is the species that is active for HAT. All complexes 2-4 react with benzophenone form metastable Fe(II) intermediates that subsequently eliminate the metathesis product Ph2C═NDipp, with relative rates dependent on the alkali metal ion. By contrast, the same reaction with 5 does not lead to the formation of Ph2C═NDipp. These results demonstrate that the coordination of alkali metal ions dictate both the structure and reactivity of the imido ligand and moreover can direct the reactivity of reaction intermediates.

Ene Reactivity of an Fe═NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes.

Herein, we report the reactions of an Fe(II) imido complex [Ph2B(tBuIm)2Fe═NDipp]- (1) with internal alkynes and isobutyronitrile, affording the Fe amido allenyl complexes [Ph2B(tBuIm)2Fe(NHDipp)((R1)C═C═C(R2)(H))]- (R1 = Et or nPr; R2 = Me or Et, 2-5) and the Fe amido keteniminate complex [Ph2B(tBuIm)2Fe(NHDipp)(N═C═CMe2)K(THF)]n (8-K), respectively. These transformations represent the previously unknown ene-like reactivity of a metal-ligand multiple bond. Stoichiometric reactions of 2 and 8-K with DippNH2 lead to the regeneration of 3-hexyne and isobutyronitrile, respectively, with concomitant formation of the bis(anilido) complex [Ph2B(tBuIm)2Fe(NHDipp)2]- (9). These results provide the platform for 1 as an efficient catalyst for the selective α-deuteration of nitriles and alkynes by RND2. These results demonstrate a new reaction mode for metal imido complexes and suggest new avenues for using the imido ligand in catalysis.

Catalytic Carbodiimide Guanylation by a Nucleophilic, High Spin Iron(II) Imido Complex.

Reduction of the three-coordinate iron(III) imido [Ph2B(tBuIm)2Fe═NDipp] (1) affords [Ph2B(tBuIm)2Fe═NDipp][K(18-C-6)THF2] (2), a rare example of a high-spin (S = 2) iron(II) imido complex. Unusually for a late metal imido complex, the imido ligand in 2 has nucleophilic character, as demonstrated by the reaction with DippNH2, which establishes an equilibrium with the bis(anilido) complex [Ph2B(tBuIm)2Fe(NHDipp)2][K(18-C-6)THF2] (3). In an unusual transformation, formal insertion of iPrN═C═NiPr into the Fe═N(imido) bond yields the guanidinate [Ph2B(tBuIm)2Fe(iPrN)2CNDipp][K(18-C-6)THF2] (4). Reaction of 4 with excess DippNH2 provides 3, along with the guanidine (iPrNH)2C═NDipp. As suggested by these stoichiometric reactions, 2 is an efficient catalyst for the guanylation of carbodiimides, converting a wide range of aniline substrates under mild conditions.

Isomaltulose Exhibits Prebiotic Activity, and Modulates Gut Microbiota, the Production of Short Chain Fatty Acids, and Secondary Bile Acids in Rats.

In vitro experiments have indicated prebiotic activity of isomaltulose, which stimulates the growth of probiotics and the production of short chain fatty acids (SCFAs). However, the absence of in vivo trials undermines these results. This study aims to investigate the effect of isomaltulose on composition and functionality of gut microbiota in rats. Twelve Sprague-Dawley rats were divided into two groups: the IsoMTL group was given free access to water containing 10% isomaltulose (w/w), and the control group was treated with normal water for five weeks. Moreover, 16S rRNA sequencing showed that ingestion of isomaltulose increased the abundances of beneficial microbiota, such as Faecalibacterium and Phascolarctobacterium, and decreased levels of pathogens, including Shuttleworthia. Bacterial functional prediction showed that isomaltulose affected gut microbial functionalities, including secondary bile acid biosynthesis. Targeted metabolomics demonstrated that isomaltulose supplementation enhanced cholic acid concentration, and reduced levels of lithocholic acid, deoxycholic acid, dehydrocholic acid, and hyodeoxycholic acid. Moreover, the concentrations of propionate and butyrate were elevated in the rats administered with isomaltulose. This work suggests that isomaltulose modulates gut microbiota and the production of SCFAs and secondary bile acids in rats, which provides a scientific basis on the use of isomaltulose as a prebiotic.

Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance.

A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η1-allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.

Iron(II) Complexes of an Anionic Bis(ylide)diphenylborate Ligand.

Double deprotonation of the salt [Ph2B(PMe3)2][OTf] (1) provides access to a bis(ylide)diphenylborate ligand that is readily transferred in situ to iron(II). Depending on the reaction stoichiometry, both the "ate" complex [Ph2B(Me2PCH2)2Fe(µ-Cl)2Li(THF)2] (2) and the homoleptic complex [Ph2B(Me2PCH2)2]2Fe(3) can be prepared from FeCl2(THF)1.5. Further reaction of 3 with FeCl2(THF)1.5 produces the chloride-bridged dimer [Ph2B(Me2PCH2)2Fe(µ-Cl)2Fe(CH2PMe2)2BPh2](4). Attempts to reduce or alkylate 4 provide 3 as the only isolable product, likely a consequence of the low steric hindrance of the bis(ylide)diphenylborate ligand. On the other hand, reaction of 4 with the strong field ligand CNtBu provides the six-coordinate, diamagnetic complex [Ph2B(Me2PCH2)2Fe(CNtBu)4][Cl](5). Electronic structure calculations for the bis(ylide)diphenylborate ligand and homoleptic complex 3 suggest that the C(ylide) atoms are strong σ-donors with little π-bonding character. These initial results suggest the potential for this bis(ylide)diphenylborate ligand in coordination chemistry.

Relationship among porcine lncRNA TCONS_00010987, miR-323, and leptin receptor based on dual luciferase reporter gene assays and expression patterns.

OBJECTIVE: Considering the physiological and clinical importance of leptin receptor (LEPR) in regulating obesity and the fact that porcine LEPR expression is not known to be controlled by lncRNAs and miRNAs, we aim to characterize this gene as a potential target of SSC-miR-323 and the lncRNA TCONS_00010987. METHODS: Bioinformatics analyses revealed that lncRNA TCONS_00010987 and LEPR have SSC-miR-323-binding sites and that LEPR might be a target of lncRNA TCONS_00010987 based on cis prediction. Wild-type and mutant TCONS_00010987-target sequence fragments and wild-type and mutant LEPR 3'-UTR fragments were generated and cloned into pmiR-RB-REPORTTM-Control vectors to construct respective recombinant plasmids. HEK293T cells were co-transfected with the SSC-miR-323 mimics or a negative control with constructs harboring the corresponding binding sites and relative luciferase activities were determined. Tissue expression patterns of lncRNA TCONS_00010987, SSC-miR-323, and LEPR in Anqing six-end-white (AQ, the obese breed) and Large White (LW, the lean breed) pigs were detected by real-time quantitative polymerase chain reaction; backfat expression of LEPR protein was detected by western blotting. RESULTS: Target gene fragments were successfully cloned, and the four recombinant vectors were constructed. Compared to the negative control, SSC-miR-323 mimics significantly inhibited luciferase activity from the wild-type TCONS_00010987-target sequence and wild-type LEPR-3'-UTR (p<0.01 for both) but not from the mutant TCONS_00010987-target sequence and mutant LEPR-3'-UTR (p>0.05 for both). Backfat expression levels of TCONS_ 00010987 and LEPR in AQ pigs were significantly higher than those in LW pigs (p<0.01), whereas levels of SSC-miR-323 in AQ pigs were significantly lower than those in LW pigs (p<0.05). LEPR protein levels in the backfat tissues of AQ pigs were markedly higher than those in LW pigs (p<0.01). CONCLUSION: LEPR is a potential target of SSC-miR-323, and TCONS_00010987 might act as a sponge for SSC-miR-323 to regulate LEPR expression.

Relationship between porcine miR-20a and its putative target low-density lipoprotein receptor based on dual luciferase reporter gene assays.

OBJECTIVE: Mutations in low-density lipoprotein receptor (LDLR), which encodes a critical protein for cholesterol homeostasis and lipid metabolism in mammals, are involved in cardiometabolic diseases, such as familial hypercholesterolemia in pigs. Whereas microRNAs (miRNAs) can control LDLR regulation, their involvement in circulating cholesterol and lipid levels with respect to cardiometabolic diseases in pigs is unclear. We aimed to identify and analyze LDLR as a potential target gene of SSC-miR-20a. METHODS: Bioinformatic analysis predicted that porcine LDLR is a target of SSC-miR-20a. Wild-type and mutant LDLR 3'-untranslated region (UTR) fragments were generated by polymerase chain reaction (PCR) and cloned into the pGL3-Control vector to construct pGL3 Control LDLR wild-3'-UTR and pGL3 Control LDLR mutant-3'-UTR recombinant plasmids, respectively. An miR-20a expression plasmid was constructed by inserting the porcine pre-miR-20a-coding sequence between the HindIII and BamHI sites in pMR-mCherry, and constructs were confirmed by sequencing. HEK293T cells were co-transfected with the miR-20a expression or pMR-mCherry control plasmids and constructs harboring the corresponding 3'-UTR, and relative luciferase activity was determined. The relative expression levels of miR-20a and LDLR mRNA and their correlation in terms of expression levels in porcine liver tissue were analyzed using reverse-transcription quantitative PCR. RESULTS: Gel electrophoresis and sequencing showed that target gene fragments were successfully cloned, and the three recombinant vectors were successfully constructed. Compared to pMR-mCherry, the miR-20a expression vector significantly inhibited wild-type LDLR-3'-UTR-driven (p<0.01), but not mutant LDLR-3'-UTR-driven (p>0.05), luciferase reporter activity. Further, miR-20a and LDLR were expressed at relatively high levels in porcine liver tissues. Pearson correlation analysis revealed that porcine liver miR-20a and LDLR levels were significantly negatively correlated (r = -0.656, p<0.05). CONCLUSION: LDLR is a potential target of miR-20a, which might directly bind the LDLR 3'-UTR to post-transcriptionally inhibit expression. These results have implications in understanding the pathogenesis and progression of porcine cardiovascular diseases.

Bis(dinitrogen)cobalt(-1) Complexes with NHC Ligation: Synthesis, Characterization, and Their Dinitrogen Functionalization Reactions Affording Side-on Bound Diazene Complexes.

Late-transition-metal-based catalysts are widely used in N2 fixation reactions, but the reactivity of late-transition-metal N2 complexes, besides iron N2 complexes, has remained poorly understood as their N2 complexes were thought to be labile and hard to functionalize. By employing a monodentate N-heterocyclic carbene (NHC), 1,3-dicyclohexylimidazol-2-ylidene (ICy) as ligand, the cobalt(0)- and cobalt(-1)-N2 complexes, [(ICy)3Co(N2)] (1) and [(ICy)2Co(N2)2M]n (M = K, 2a; Rb, 2b; Cs, 2c), respectively, were synthesized from the stepwise reduction of (ICy)3CoCl by the corresponding alkaline metals under a N2 atmosphere. Complexes 2a-c in their solid states adopt polymeric structures. The N-N distances (1.145(6)-1.162(5) Å) and small N-N infrared stretchings (ca. 1800 and 1900 cm-1) suggest the strong N2 activation of the end-on N2 ligands in 2a-c. One electron oxidation of 1 by [Cp2Fe][BF4] gave the cobalt(I) complex devoid of N2 ligand [(ICy)3Co][BF4] (3). The bis(dinitrogen)cobalt(-1) complexes 2a-c undergo protonation reaction with triflic acid to give N2H4 in 24-30% yields (relative to cobalt). Complexes 2a-c could also react with silyl halides to afford diazene complexes [(ICy)2Co(η2-R3SiNNSiR3)] (R = Me, 6a; Et, 6b) that are the first diazene complexes of late transition metals prepared from N2 functionalization. Characterization data, in combination with calculation results, suggest the electronic structures of the diazene complexes as low-spin cobalt(II) complexes containing dianionic ligand [η2-R3SiNNSiR3]2-. Complexes 1, 2a-c, 6a, 6b, and (ICy)2CoCl2 proved to be effective catalysts for the reductive silylation of N2 to afford N(SiMe3)3. These NHC-cobalt catalysts display comparable turnover numbers (ca. 120) that exceed the reported 3d metal catalysts. The fine performance of the NHC-cobalt complexes in the stoichiometric and catalytic N2-functionalization reactions points out the utility of low-valent low-coordinate group 9 metal species for N2 fixation.

Low-Coordinate NHC-Cobalt(0)-Olefin Complexes: Synthesis, Structure, and Their Reactions with Hydrosilanes.

The one-pot reaction of CoCl2 with 1 or 2 equiv of N-heterocyclic carbene (NHC) ligands, vinyltrimethylsilane (vtms), and 2 equiv of reducing reagents (KC8 or Na(Hg)) proved an effective protocol for the synthesis of three-coordinate NHC-cobalt(0)-olefin complexes, and by which the new low-coordinate cobalt(0) complexes [(NHC)Co(vtms)2] (NHC = 1,3-di(2',6'-diethylphenyl)-4,5-(CH2)4-imidazol-2-ylidene (cyIDep), 6; 1,3-diadamantylimidazol-2-ylidene (IAd), 7) and [(NHC)2Co(vtms)] (NHC = 1-(2',4',6'-trimethylphenyl)-3-cyclohexylimidazol-2-ylidene (IMesCy), 8; 1,3-dicyclohexylimidazol-2-ylidene (ICy), 9) were prepared in moderate yields and further characterized by spectroscopic methods. The NHC-cobalt(0)-vtms complexes can serve as low-coordinate NHC-cobalt(0) precursors to react with hydrosilanes. From the reactions of Ph2SiH2 with the corresponding NHC-cobalt(0)-vtms complexes, the cobalt silyl complexes [(cyIDep)(H)Co(µ-η2:η2-H2SiPh2)(µ-η2-HSiPh2)2Co(H)(cyIDep)] (10), [(NHC)Co(µ-η2-SiHPh2)2Co(NHC)] (NHC = IPr, 13; IAd, 14), and [(IMesCy)2Co(H)(SiHPh2)] (15) were synthesized. Further reactivity studies established the thermal decomposition of 10 to give [(cyIDep)Co(µ-η2-HSiPh2)2Co(cyIDep)] (11), H2, and Ph2SiH2, the reaction of 11 with ButNC (4.5 equiv) to afford [(cyIDep)(ButNC)Co(µ-η2-HSiPh2)2Co(CNBut)3] (12) and cyIDep, as well as the conversion of 15 to a silyl-functionalized NHC-cobalt(II) complex 16 upon eliminating H2. These cobalt silyl complexes have been characterized by single-crystal X-ray diffraction studies, NMR, absorption, and infrared spectroscopies, as well as elemental analyses. The diversified reaction outcomes demonstrate the rich reaction chemistry of low-coordinate NHC-cobalt(0) complexes.

Regio- and stereoselective hydrosilylation of alkynes catalyzed by three-coordinate cobalt(I) alkyl and silyl complexes.

A three-coordinate cobalt(I) complex exhibits high catalytic efficiency and selectivity as well as good functional group compatibility in alkyne hydrosilylation. [Co(IAd)(PPh3)(CH2TMS)] (1) (IAd = 1,3-diadamantylimidazol-2-ylidene) facilitates regio- and stereoselective hydrosilylation of terminal, symmetrical internal, and trimethylsilyl-substituted unsymmetrical internal alkynes to produce single hydrosilylation products in the forms of ß-(E)-silylalkenes, (E)-silylalkenes, and (Z)-α,α-disilylalkenes, respectively, in high yields. The comparable catalytic efficiency and selectivity of the Co(I) silyl complex [Co(IAd)(PPh3)(SiHPh2)] that was prepared from the reaction of 1 with H2SiPh2, and the isolation of an alkyne Co(I) complex [Co(IAd)(η(2)-PhC≡CPh)(CH2TMS)] from the reaction of 1 with the acetylene, point out a modified Chalk-Harrod catalytic cycle for these hydrosilylation reactions. The high selectivity is thought to be governed by steric factors.

Effects of Psychological Stress on Multiple Sclerosis via HPA Axis-mediated Modulation of Natural Killer T Cell Activity.

The involvement of psychological stress and Natural Killer T (NKT) cells in the pathophysiology of multiple sclerosis has been identified in the progression of this disease. Psychological stress can impact disease occurrence, relapse, and severity through its effects on the Hypothalamic- Pituitary-Adrenal (HPA) axis and immune responses. NKT cells are believed to play a pivotal role in the pathogenesis of multiple sclerosis, with recent evidence suggesting their distinct functional alterations following activation of the HPA axis under conditions of psychological stress. This review summarizes the associations between psychological stress, NKT cells, and multiple sclerosis while discussing the potential mechanism for how NKT cells mediate the effects of psychological stress on this disease.

Microbiota dynamics and volatile metabolite generation during sausage fermentation.

Microorganism metabolic activity is critical for the formation of unique flavors in fermented meat products. To clarify the relationship between the formation of the special flavor of fermented meat and microorganisms, high-throughput sequencing and gas chromatography-ion mobility spectrometry were used to analyze microorganisms and volatile compounds in naturally fermented sausage. The findings revealed 91 volatile compounds and 4 key microorganisms, including Lactobacillus, Weissella, Leuconostoc, and Staphylococcus. The key microorganisms were positively correlated with the formation of 21 volatile compounds. The validation results showed that the contents of volatile compounds such as heptanal, octanal, 2-pentanone, and 1-octen-3-ol increased significantly after inoculation with Lb. sakei M2 and S. xylosus Y4. These two bacteria are the key microorganisms that produce the special flavor of fermented sausage. The present study can provide a theoretical basis for the directional development of fermented meat products, the preparation of special flavor enhancers, and expedited fermentation processes.

Transcriptomic Profiling of Meat Quality Traits of Skeletal Muscles of the Chinese Indigenous Huai Pig and Duroc Pig.

The Huai pig is a well-known indigenous pig breed in China. The main advantages of Huai pigs over Western commercial pig breeds include a high intramuscular fat (IMF) content and good meat quality. There are significant differences in the meat quality traits of the same muscle part or different muscle parts of the same variety. To investigate the potential genetic mechanism underlying the meat quality differences in different pig breeds or muscle groups, longissimus dorsi (LD), psoas major (PM), and biceps femoris (BF) muscle tissues were collected from two pig breeds (Huai and Duroc). There were significant differences in meat quality traits and amino acid content. We assessed the muscle transcriptomic profiles using high-throughput RNA sequencing. The IMF content in the LD, PM, and BF muscles of Huai pigs was significantly higher than that in Duroc pigs (p < 0.05). Similarly, the content of flavor amino acids in the three muscle groups was significantly higher in Huai pigs than that in Duroc pigs (p < 0.05). We identified 175, 110, and 86 differentially expressed genes (DEGs) between the LD, PM, and BF muscles of the Huai and Duroc pigs, respectively. The DEGs of the different pig breeds and muscle regions were significantly enriched in the biological processes and signaling pathways related to muscle fiber type, IMF deposition, lipid metabolism, PPAR signaling, cAMP signaling, amino acid metabolism, and ECM-receptor interaction. Our findings might help improve pork yield by using the obtained DEGs for marker-assisted selection and providing a theoretical reference for evaluating and improving pork quality.

Construction of heterotrophic-sulfur autotrophic integrated fluidized bed reactor for simultaneous and efficient removal of compound pollution of perchlorate and nitrate in water.

A heterotrophic sulfur autotrophic integrated fluidized bed reactor was established for simultaneous and efficient removal of ClO4- and NO3- from water. The optimum operating conditions forecasted through the response surface method (RSM) were the hydraulic retention time (HRT) of 0.50 h, the influent acetate (CH3COO-) concentration of 55 mg/L and the reflux ratio of 14, contributing to ClO4- and NO3- removal of 98.99% and 99.96%, respectively, without secondary pollution caused by residual carbon (NPOC <3.89 mg/L). Meanwhile, the effluent pH fluctuated in a range of 6.70-8.02 and sulfur-containing by-products (i.e., SO42- and S2-) could be controlled by adjusting operation conditions throughout the experimental stage. The increase of the influent CH3COO- concentration reduced the load borne by autotrophic reduction process and further reduced SO42- production. Shortening HRT, increasing the influent CH3COO- concentration and decreasing the reflux ratio could all reduce alkalinity consumption. Shortening HRT and decreasing the reflux ratio could shorten contact time between sulfur and water and thus inhibit S0 disproportionation. High-throughput sequencing result showed that Proteobacteria and Chlorobi were the dominant bacteria. Sulfurovum, Sulfuricurvum and Ignavibacterium were the major heterotrophic denitrifying bacteria (DB)/perchlorate reducing bacteria (PRB), Ferritrophicum and Geothrix were DB, and Chlorobaculum was S0 disproportionation bacteria.

Analysis of the volatile compounds in Fuliji roast chicken during processing and storage based on GC-IMS.

To investigate the flavor changes of Fuliji roast chicken during processing and storage, the volatile organic compounds (VOCs) during processing (fresh, fried, stewed and sterilized) and storage (1 month, 2 months and 4 months) were determined by gas chromatography ion mobility spectrometry (GC-IMS). A total of 47 kinds of VOCs were identified across seven sampling stages, including aldehydes, hydrocarbons, alcohols, ketones, esters, ethers and heterocyclic compounds. More diverse range of aldehydes, alcohols, ketones and esters have been detected compared to acids, ethers and heterocyclic substances. Fingerprints directly reflect the pattern of VOCs at different stages of growth and decay, revealing that frying and stewing are key processes in flavor formation, and that sterilization and storage processes lead to flavor loss in Fuliji roast chicken. Hexanal, nonanal, octanal, 2-heptanone, 3-octanol, 1-octene-3-alcohol, 1-pentanol and ethyl acetate were mainly generated during the frying process. Benzaldehyde, nonanal, octanal, methyl-5-hepten-2-one, 2-methyl-3-heptanone, 1,8-Cineole, linalool, butyl acetate, ethyl propionate, ethyl acetate, coumarin, 2-furfuryl methyl disulfide and 2-pentyl furan were mainly generated during the stewing process. After sterilization, the content of octanal-D, 2-heptanone-D, 2-Methyl-3-heptanone, pentan-1-ol-D decreased, resulting in the reduction of aroma, lemon flavor and oil flavor of Fuliji roast chicken. Seven flavor markers, including hexanal-D, nonanal-M, octanal-M, heptanal-D, acetone, 3-octanol and ethyl acetate-D, were identified in the evolution of the aroma profile of Fuliji roast chicken.