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1.
Food Chem ; 336: 127618, 2021 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-32771896

RESUMO

Litchi fruit were exposed to 0.7 PPM hydrogen water (HW) before storage at 25 ± 1 â„ƒ. HW treatment delayed the pericarp browning and maintained the total soluble solids (TSS) of litchi fruit. Then, a total of 25 antioxidant system-related characters were determined to evaluate the effects of HW on antioxidant system during pericarp browning. Compared with control pericarp, the pericarp of HW-treated litchi fruit exhibited higher levels of superoxide radical (O2-·) scavenging activity, glutathione (GSH), monodehydroascorbate reductase (MDHAR), polyphenol oxidase (PPO) and total flavonoids during whole storage, higher levels of hydrogen peroxide (H2O2), catalase (CAT), glutathione disulfide (GSSG), ascorbate oxidase (AAO) and total phenols only on day 1, and higher levels of ascorbate peroxidase (APX), total anthocyanin, glutathione reductase (GR) and glutathione peroxidases (GPX) at later stage of storage. Those HW-induced antioxidant system-related characters might directly or indirectly enhanced the antioxidant capacity and delayed the pericarp browning of litchi.


Assuntos
Antioxidantes/química , Armazenamento de Alimentos/métodos , Hidrogênio/química , Litchi/metabolismo , Catalase/metabolismo , Análise Discriminante , Flavonoides/química , Flavonoides/metabolismo , Frutas/química , Frutas/efeitos dos fármacos , Frutas/metabolismo , Glutationa Redutase/metabolismo , Hidrogênio/farmacologia , Peróxido de Hidrogênio/metabolismo , Análise dos Mínimos Quadrados , Litchi/química , Litchi/efeitos dos fármacos
2.
Nat Commun ; 11(1): 4899, 2020 09 29.
Artigo em Inglês | MEDLINE | ID: mdl-32994420

RESUMO

Chemical synthesis of amino acids from renewable sources is an alternative route to the current processes based on fermentation. Here, we report visible-light-driven amination of biomass-derived α-hydroxyl acids and glucose into amino acids using NH3 at 50 °C. Ultrathin CdS nanosheets are identified as an efficient and stable catalyst, exhibiting an order of magnitude higher activity towards alanine production from lactic acid compared to commercial CdS as well as CdS nanoobjects bearing other morphologies. Its unique catalytic property is attributed mainly to the preferential formation of oxygen-centered radicals to promote α-hydroxyl acids conversion to α-keto acids, and partially to the poor H2 evolution which is an undesired side reaction. Encouragingly, a number of amino acids are prepared using the current protocol, and one-pot photocatalytic conversion of glucose to alanine is also achieved. This work offers an effective catalytic system for amino acid synthesis from biomass feedstocks under mild conditions.


Assuntos
Alanina/síntese química , Compostos de Cádmio/química , Sulfetos/química , Alanina/química , Biomassa , Catálise/efeitos da radiação , Hidrogênio/química , Ácido Láctico/química , Luz , Modelos Químicos , Oxigênio/química
3.
Yakugaku Zasshi ; 140(9): 1101-1106, 2020.
Artigo em Japonês | MEDLINE | ID: mdl-32879242

RESUMO

Organoselenium compounds have attracted significant interest because of their use as important reagents in organic syntheses and potential biological activities, necessitating the development of simple and general synthetic methods. This article reviews our studies to develop of copper-catalyzed C-Se bond formation reactions via cross coupling and C-H activation. A number of unsymmetrical and symmetrical diaryl selenides were synthesized via Se-arylation of diaryl diselenides or selenium powder with triarylbismuthanes under aerobic conditions, achieving moderate to excellent yields. When the reaction of triphenylbismuthane with elemental Se was monitored with gas chromatography, diphenyl diselenide and diphenyl selenide formation was confirmed. Subsequently, 1-pot 2-step reactions were performed under mild conditions to obtain 3-selanyl imidazo[1,2-a]pyridines from triarylbismuthanes and diimidazopyridyl diselenides, which were generated from imidazo[1,2-a]pyridines and Se powder, in good to excellent yields. It should be noted that all three aryl groups in the bismuth and both selanyl groups in the diaryl diselenide generated from the selenium source were transferred to the coupling products. Cu-catalyzed tandem cyclization of 2-(2-iodophenyl)imidazo[1,2-a]pyridines with selenium for the synthesis of benzo[b]selenophene-fused imidazo[1,2-a]pyridines is also described herein. The molecular structure of the tetracyclic compound features nearly coplanar rings, and the maximum absorption is red-shifted compared to those of imidazo[1,2-a]pyridine and benzoselenophene.


Assuntos
Carbono/química , Cobre/química , Hidrogênio/química , Compostos Organosselênicos/síntese química , Catálise , Ciclização , Ligação de Hidrogênio , Fenômenos de Química Orgânica
4.
Proc Natl Acad Sci U S A ; 117(37): 22873-22879, 2020 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-32900930

RESUMO

All life on Earth is built of organic molecules, so the primordial sources of reduced carbon remain a major open question in studies of the origin of life. A variant of the alkaline-hydrothermal-vent theory for life's emergence suggests that organics could have been produced by the reduction of CO2 via H2 oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analog-and proposed evolutionary predecessor-of the Wood-Ljungdahl acetyl-CoA pathway of modern archaea and bacteria. The first energetic bottleneck of the pathway involves the endergonic reduction of CO2 with H2 to formate (HCOO-), which has proven elusive in mild abiotic settings. Here we show the reduction of CO2 with H2 at room temperature under moderate pressures (1.5 bar), driven by microfluidic pH gradients across inorganic Fe(Ni)S precipitates. Isotopic labeling with 13C confirmed formate production. Separately, deuterium (2H) labeling indicated that electron transfer to CO2 does not occur via direct hydrogenation with H2 but instead, freshly deposited Fe(Ni)S precipitates appear to facilitate electron transfer in an electrochemical-cell mechanism with two distinct half-reactions. Decreasing the pH gradient significantly, removing H2, or eliminating the precipitate yielded no detectable product. Our work demonstrates the feasibility of spatially separated yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes. Beyond corroborating the ability of early-Earth alkaline hydrothermal systems to couple carbon reduction to hydrogen oxidation through biologically relevant mechanisms, these results may also be of significance for industrial and environmental applications, where other redox reactions could be facilitated using similarly mild approaches.


Assuntos
Dióxido de Carbono/química , Ciclo do Carbono , Transporte de Elétrons , Hidrogênio/química , Concentração de Íons de Hidrogênio , Fontes Hidrotermais/química , Oxirredução , Força Próton-Motriz
5.
Proc Natl Acad Sci U S A ; 117(34): 20453-20461, 2020 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-32817473

RESUMO

Subseafloor mixing of high-temperature hot-spring fluids with cold seawater creates intermediate-temperature diffuse fluids that are replete with potential chemical energy. This energy can be harnessed by a chemosynthetic biosphere that permeates hydrothermal regions on Earth. Shifts in the abundance of redox-reactive species in diffuse fluids are often interpreted to reflect the direct influence of subseafloor microbial activity on fluid geochemical budgets. Here, we examine hydrothermal fluids venting at 44 to 149 °C at the Piccard hydrothermal field that span the canonical 122 °C limit to life, and thus provide a rare opportunity to study the transition between habitable and uninhabitable environments. In contrast with previous studies, we show that hydrocarbons are contributed by biomass pyrolysis, while abiotic sulfate (SO4 2-) reduction produces large depletions in H2 The latter process consumes energy that could otherwise support key metabolic strategies employed by the subseafloor biosphere. Available Gibbs free energy is reduced by 71 to 86% across the habitable temperature range for both hydrogenotrophic SO4 2- reduction to hydrogen sulfide (H2S) and carbon dioxide (CO2) reduction to methane (CH4). The abiotic H2 sink we identify has implications for the productivity of subseafloor microbial ecosystems and is an important process to consider within models of H2 production and consumption in young oceanic crust.


Assuntos
Fontes Hidrotermais/química , Temperatura Alta , Hidrogênio/química , Fontes Hidrotermais/microbiologia , Oxirredução , Água do Mar/química
6.
Nat Commun ; 11(1): 3880, 2020 08 05.
Artigo em Inglês | MEDLINE | ID: mdl-32759942

RESUMO

Geological sources of H2 and abiotic CH4 have had a critical role in the evolution of our planet and the development of life and sustainability of the deep subsurface biosphere. Yet the origins of these sources are largely unconstrained. Hydration of mantle rocks, or serpentinization, is widely recognized to produce H2 and favour the abiotic genesis of CH4 in shallow settings. However, deeper sources of H2 and abiotic CH4 are missing from current models, which mainly invoke more oxidized fluids at convergent margins. Here we combine data from exhumed subduction zone high-pressure rocks and thermodynamic modelling to show that deep serpentinization (40-80 km) generates significant amounts of H2 and abiotic CH4, as well as H2S and NH3. Our results suggest that subduction, worldwide, hosts large sources of deep H2 and abiotic CH4, potentially providing energy to the overlying subsurface biosphere in the forearc regions of convergent margins.


Assuntos
Ecossistema , Hidrogênio/química , Metano/química , Minerais/química , Compostos Orgânicos/química , Termodinâmica , Amônia/química , Fenômenos Químicos , Fenômenos Geológicos , Sulfeto de Hidrogênio/química , Fenômenos Mecânicos , Fenômenos de Química Orgânica , Alcaloides de Triptamina e Secologanina/química , Erupções Vulcânicas
7.
Nature ; 584(7819): 75-81, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32760044

RESUMO

Chemical reactions that reliably join two molecular fragments together (cross-couplings) are essential to the discovery and manufacture of pharmaceuticals and agrochemicals1,2. The introduction of amines onto functionalized aromatics at specific and pre-determined positions (ortho versus meta versus para) is currently achievable only in transition-metal-catalysed processes and requires halogen- or boron-containing substrates3-6. The introduction of these groups around the aromatic unit is dictated by the intrinsic reactivity profile of the method (electrophilic halogenation or C-H borylation) so selective targeting of all positions is often not possible. Here we report a non-canonical cross-coupling approach for the construction of anilines, exploiting saturated cyclohexanones as aryl electrophile surrogates. Condensation between amines and carbonyls, a process that frequently occurs in nature and is often used by (bio-)organic chemists7, enables a predetermined and site-selective carbon-nitrogen (C-N) bond formation, while a photoredox- and cobalt-based catalytic system progressively desaturates the cyclohexene ring en route to the aniline. Given that functionalized cyclohexanones are readily accessible with complete regiocontrol using the well established carbonyl reactivity, this approach bypasses some of the frequent selectivity issues of aromatic chemistry. We demonstrate the utility of this C-N coupling protocol by preparing commercial medicines and by the late-stage amination-aromatization of natural products, steroids and terpene feedstocks.


Assuntos
Compostos de Anilina/síntese química , Hidrogênio/química , Processos Fotoquímicos , Aminação , Aminas/química , Compostos de Anilina/química , Produtos Biológicos/síntese química , Produtos Biológicos/química , Catálise/efeitos da radiação , Cicloexanonas/química , Oxirredução/efeitos da radiação , Processos Fotoquímicos/efeitos da radiação , Esteroides/síntese química , Esteroides/química , Terpenos/síntese química , Terpenos/química
8.
Chemosphere ; 261: 127719, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32758927

RESUMO

Conversion of aniline wastes to value-added products is always a promising method to treat aniline wastewater. In this study, a selective oxidation of aniline contaminants by Bi2·15WO6 was carried out under visible light and alkaline conditions. Kinetic results show that the oxidation rates of aniline increase with increasing pH values under visible light. UV-vis absorption spectra and GC-MS analysis confirm that azobenzene is the primary oxidation product with aminophenol and N,N'-diphenylhydrazine as the secondary products. The analyses from Mott-Schottky, electrochemical impedance spectroscopy (EIS), transient photocurrent and photoluminescence (PL) further indicate that OH- promotes the separation and transfer of photogenerated electron-hole pairs on the surface of Bi2·15WO6, thus facilitating oxidation of aniline. Quenching experiments and electron spin resonance (ESR) analysis confirm that h+ is the predominant specie in the Bi2·15WO6 system and aniline radical cation (PhNH2•+) is an important intermediate. The Hammett and ΔBDEN-H plots further reveal that e- abstraction from aniline with the formation of PhNH2•+, followed by H+ abstraction from PhNH2•+ with the formation of anilino radicals (PhNH•), is the prerequisite for the formation of N,N'-diphenylhydrazine, which is then oxidized to azobenzene via the hydrogen-abstraction pathway. This work provides a cost-effective method to selectively oxidize aniline to azobenzene.


Assuntos
Compostos de Anilina/química , Bismuto/química , Hidrogênio/química , Luz , Compostos de Tungstênio/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Catálise , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , Fotoquímica , Águas Residuárias/química
9.
J Breath Res ; 14(4): 041002, 2020 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-32663815

RESUMO

Fructose intake is associated with increased consumption of processed foods, specifically in the context of nutritional supplements. To assess gastrointestinal symptoms and hydrogen production after the ingestion of a fructose solution in runners, healthy and sick persons. Hydrogen test (H2 test) was performed after the intake a solution with 50 g fructose along with the application of a questionnaire to evaluate the gastrointestinal symptoms during the H2 test in three groups: Athletes group (AG); control group (CG) with healthy subjects; and non-alcoholic fatty liver disease group (NAFLDG). Statistical analysis was performed with analysis of variance at a p < 0.05 significance level. The AG was the largest H2 producer followed by the CG with significant difference between the AG and NAFLDG (p ≤ 0.05). Most participants remained asymptomatic, but the strongest correlation was the symptom of bloating GC (R = 0.625), eructation in NAFLD (R = 0.481) and diarrhea in CG (R = 0.345) and AG (R = 0.338) The result of the present study suggests the production of hydrogen by the colon following the administration of fructose is higher in athletes compared with healthy individuals and persons with NAFLD, showing that fructose intake may be an interesting point of dietary management, especially in elite professionals.


Assuntos
Frutose/química , Hidrogênio/química , Intestinos/fisiopatologia , Hepatopatia Gordurosa não Alcoólica/fisiopatologia , Corrida/fisiologia , Adulto , Feminino , Humanos , Masculino
10.
Nat Commun ; 11(1): 3783, 2020 07 29.
Artigo em Inglês | MEDLINE | ID: mdl-32728021

RESUMO

Current thermochemical methods to generate H2 include gasification and steam reforming of coal and natural gas, in which anthropogenic CO2 emission is inevitable. If biomass is used as a source of H2, the process can be considered carbon-neutral. Seaweeds are among the less studied types of biomass with great potential because they do not require freshwater. Unfortunately, reaction pathways to thermochemically convert salty and wet biomass into H2 are limited. In this study, a catalytic alkaline thermal treatment of brown seaweed is investigated to produce high purity H2 with substantially suppressed CO2 formation making the overall biomass conversion not only carbon-neutral but also potentially carbon-negative. High-purity 69.69 mmol-H2/(dry-ash-free)g-brown seaweed is produced with a conversion as high as 71%. The hydroxide is involved in both H2 production and in situ CO2 capture, while the Ni/ZrO2 catalyst enhanced the secondary H2 formation via steam methane reforming and water-gas shift reactions.


Assuntos
Carbono/isolamento & purificação , Hidrogênio/isolamento & purificação , Energia Renovável , Alga Marinha/química , Álcalis/química , Biomassa , Carbono/química , Catálise , Temperatura Alta , Hidrogênio/química , Vapor
11.
Food Chem ; 333: 127430, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-32679413

RESUMO

Phytosterols (PS) are a group of sterols distributed in foods and plants, where it is prone to oxidation. In this work, we studied the reaction mechanism of phytosterols, using density functional theory (DFT) calculation and experimental methods to study the photooxidation of phytosterols. Under LED light illumination, experimental photooxidation of these phytosterols gives rise to the prior three kind oxides of phytosterol: 6α-OH, 7α-OH, and 7ß-OH. The mechanistic investigations by DFT suggest that singlet oxygen (1O2)-mediated photooxidation (Type II mechanism) generated radical adds to the C5 and C6 on the B Ring of steroid nucleus and reaction in C7 initiated from C5 products through rearrangement pathway. Furthermore, the stereoselectivity at C5, C6 and C7 provides a mechanistic guide for phytosterols photooxidation. These efforts are expected to serve as an essential exploratory study for the oxidation mechanism of phytosterols in the complex food matrix and antioxidation technology for phytosterols.


Assuntos
Processos Fotoquímicos , Fitosteróis/química , Alcenos/química , Teoria da Densidade Funcional , Hidrogênio/química , Luz , Oxidantes Fotoquímicos/química , Oxirredução , Óxidos/química , Esteroides/química
12.
Arch Biochem Biophys ; 690: 108474, 2020 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-32687799

RESUMO

Kynurenine 3-monoxygenase (KMO) catalyzes the conversion of l-kynurenine (L-Kyn) to 3-hydroxykynurenine (3-OHKyn) in the pathway for tryptophan catabolism. We have investigated the effects of pH and deuterium substitution on the oxidative half-reaction of KMO from P. fluorescens (PfKMO). The three phases observed during the oxidative half reaction are formation of the hydroperoxyflavin, hydroxylation and product release. The measured rate constants for these phases proved largely unchanging with pH, suggesting that the KMO active site is insulated from exchange with solvent during catalysis. A solvent inventory study indicated that a solvent isotope effect of 2-3 is observed for the hydroxylation phase and that two or more protons are in flight during this step. An inverse isotope effect of 0.84 ± 0.01 on the rate constant for the hydroxylation step with ring perdeutero-L-Kyn as a substrate indicates a shift from sp2 to sp3 hybridization in the transition state leading to the formation of a non-aromatic intermediate. The pH dependence of transient state data collected for the substrate analog meta-nitrobenzoylalanine indicate that groups proximal to the hydroperoxyflavin are titrated in the range pH 5-8.5 and can be described by a pKa of 8.8. That higher pH values do not slow the rate of hydroxylation precludes that the pKa measured pertains to the proton of the hydroperoxflavin. Together, these observations indicate that the C4a-hydroperoxyflavin has a pKa ≫ 8.5, that a non-aromatic species is the immediate product of hydroxylation and that at least two solvent derived protons are in-flight during oxygen insertion to the substrate aromatic ring. A unifying mechanistic proposal for these observations is proposed.


Assuntos
Hidrogênio/química , Quinurenina 3-Mono-Oxigenase/química , Quinurenina 3-Mono-Oxigenase/metabolismo , Cinurenina/química , Pseudomonas fluorescens/química , Catálise , Domínio Catalítico , Deutério/química , Dinitrocresóis/metabolismo , Flavinas/química , Concentração de Íons de Hidrogênio , Hidroxilação , Cinética , Oxigenases de Função Mista/metabolismo , Oxirredução , Estresse Oxidativo , Oxigênio/química , Prótons , Solventes/química
13.
Nature ; 583(7817): 548-553, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32480398

RESUMO

Tertiary stereogenic centres containing one fluorine atom are valuable for medicinal chemistry because they mimic common tertiary stereogenic centres containing one hydrogen atom, but they possess distinct charge distribution, lipophilicity, conformation and metabolic stability1-3. Although tertiary stereogenic centres containing one hydrogen atom are often set by enantioselective desymmetrization reactions at one of the two carbon-hydrogen (C-H) bonds of a methylene group, tertiary stereocentres containing fluorine have not yet been constructed by the analogous desymmetrization reaction at one of the two carbon-fluorine (C-F) bonds of a difluoromethylene group3. Fluorine atoms are similar in size to hydrogen atoms but have distinct electronic properties, causing C-F bonds to be exceptionally strong and geminal C-F bonds to strengthen one another4. Thus, exhaustive defluorination typically dominates over the selective replacement of a single C-F bond, hindering the development of the enantioselective substitution of one fluorine atom to form a stereogenic centre5,6. Here we report the catalytic, enantioselective activation of a single C-F bond in an allylic difluoromethylene group to provide a broad range of products containing a monofluorinated tertiary stereogenic centre. By combining a tailored chiral iridium phosphoramidite catalyst, which controls regioselectivity, chemoselectivity and enantioselectivity, with a fluorophilic activator, which assists the oxidative addition of the C-F bond, these reactions occur in high yield and selectivity. The design principles proposed in this work extend to palladium-catalysed benzylic substitution, demonstrating the generality of the approach.


Assuntos
Carbono/química , Flúor/química , Alcenos/química , Catálise , Cátions , Halogenação , Hidrogênio/química , Irídio/química , Compostos Organofosforados/química , Oxirredução , Paládio/química
14.
Nature ; 584(7819): 69-74, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32512577

RESUMO

Enzymes are increasingly explored for use in asymmetric synthesis1-3, but their applications are generally limited by the reactions available to naturally occurring enzymes. Recently, interest in photocatalysis4 has spurred the discovery of novel reactivity from known enzymes5. However, so far photoinduced enzymatic catalysis6 has not been used for the cross-coupling of two molecules. For example, the intermolecular coupling of alkenes with α-halo carbonyl compounds through a visible-light-induced radical hydroalkylation, which could provide access to important γ-chiral carbonyl compounds, has not yet been achieved by enzymes. The major challenges are the inherent poor photoreactivity of enzymes and the difficulty in achieving stereochemical control of the remote prochiral radical intermediate7. Here we report a visible-light-induced intermolecular radical hydroalkylation of terminal alkenes that does not occur naturally, catalysed by an 'ene' reductase using readily available α-halo carbonyl compounds as reactants. This method provides an efficient approach to the synthesis of various carbonyl compounds bearing a γ-stereocentre with excellent yields and enantioselectivities (up to 99 per cent yield with 99 per cent enantiomeric excess), which otherwise are difficult to access using chemocatalysis. Mechanistic studies suggest that the formation of the complex of the substrates (α-halo carbonyl compounds) and the 'ene' reductase triggers the enantioselective photoinduced radical reaction. Our work further expands the reactivity repertoire of biocatalytic, synthetically useful asymmetric transformations by the merger of photocatalysis and enzyme catalysis.


Assuntos
Alcenos/química , Alcenos/metabolismo , Hidrogênio/química , Hidrogênio/metabolismo , Luz , Oxirredutases/metabolismo , Processos Fotoquímicos/efeitos da radiação , Álcoois/química , Álcoois/metabolismo , Alquilação/efeitos da radiação , Biocatálise/efeitos da radiação , Biomassa , Carboxiliases/metabolismo , Flavinas/metabolismo , Modelos Químicos , Modelos Moleculares , Estereoisomerismo
15.
Proc Natl Acad Sci U S A ; 117(26): 14756-14763, 2020 06 30.
Artigo em Inglês | MEDLINE | ID: mdl-32546521

RESUMO

Since the initial discovery of low-temperature alkaline hydrothermal vents off the Mid-Atlantic Ridge axis nearly 20 y ago, the observation that serpentinizing systems produce abundant H2 has strongly influenced models of atmospheric evolution and geological scenarios for the origin of life. Nevertheless, the principal mechanisms that generate H2 in these systems, and how secular changes in seawater composition may have modified serpentinization-driven H2 fluxes, remain poorly constrained. Here, we demonstrate that the dominant mechanism for H2 production during low-temperature serpentinization is directly related to a Si deficiency in the serpentine structure, which itself is caused by low SiO2(aq) concentrations in serpentinizing fluids derived from modern seawater. Geochemical calculations explicitly incorporating this mechanism illustrate that H2 production is directly proportional to both the SiO2(aq) concentration and temperature of serpentinization. These results imply that, before the emergence of silica-secreting organisms, elevated SiO2(aq) concentrations in Precambrian seawater would have generated serpentinites that produced up to two orders of magnitude less H2 than their modern counterparts, consistent with Fe-oxidation states measured on ancient igneous rocks. A mechanistic link between the marine Si cycle and off-axis H2 production requires a reevaluation of the processes that supplied H2 to prebiotic and early microbial systems, as well as those that balanced ocean-atmosphere redox through time.


Assuntos
Evolução Biológica , Hidrogênio/química , Água do Mar/química , Atmosfera , Ciências da Terra , Planeta Terra , Fontes Hidrotermais , Ferro/química , Oxirredução , Dióxido de Silício/química
16.
Top Curr Chem (Cham) ; 378(4): 42, 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32524210

RESUMO

8-Aminoquinoline is a common nitrogen-containing heterocyclic framework in many natural products, functional materials and useful drugs. It has been developed as a powerful bidentate directing group or ligand auxiliary in the field of C-H bond activation/functionalization in recent years. In this context, the synthesis of substituted 8-aminoquinoline is of great importance. In this review we focus on the functionalization of positions C2-C7 on the 8-aminoquinoline ring, which involves the formation of C-C and C-Z (Z = heteroatom) bonds by transition metal catalysts, photocatalysts or metal-free conditions. Mechanistically, a single electron transfer (SET) pathway is suggested in most cases.


Assuntos
Aminoquinolinas/química , Carbono/química , Elementos de Transição/química , Hidrogênio/química
17.
Chemosphere ; 251: 126364, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32443231

RESUMO

This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C-H bonds served as the anchor points for attracting NO3- anions close to the electrode surface, and thus accelerating the formation of NO3-(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C-H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate.


Assuntos
Boro/química , Técnicas Eletroquímicas , Diamante/química , Doping nos Esportes , Eletrodos , Eletrólise/métodos , Hidrogênio/química , Nitratos , Óxidos de Nitrogênio , Oxirredução , Oxigênio , Água
18.
Phys Rev Lett ; 124(17): 174501, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32412279

RESUMO

Very lean hydrogen flames were thought to quench in narrow confined geometries. We show for the first time how flames with very low fuel concentration undergo an unprecedented propagation in narrow gaps: H_{2}-air flames can survive very adverse conditions by breaking the reaction front into isolated flame cells that travel steadily in straight lines or split to perform a fractal-like propagation that resembles the pathway of starving fungi or bacteria. The combined effect of hydrogen mass diffusivity and intense heat losses act as the two main mechanisms that explain the experimental observations.


Assuntos
Hidrogênio/química , Modelos Teóricos , Bactérias/crescimento & desenvolvimento , Bactérias/metabolismo , Fogo , Fungos/crescimento & desenvolvimento , Fungos/metabolismo , Modelos Biológicos , Modelos Químicos
19.
J Vis Exp ; (159)2020 05 09.
Artigo em Inglês | MEDLINE | ID: mdl-32449743

RESUMO

This protocol presents a detailed procedure for the operation of continuous, micron-sized cryogenic cylindrical and planar liquid jets. When operated as described here, the jet exhibits high laminarity and stability for centimeters. Successful operation of a cryogenic liquid jet in the Rayleigh regime requires a basic understanding of fluid dynamics and thermodynamics at cryogenic temperatures. Theoretical calculations and typical empirical values are provided as a guide to design a comparable system. This report identifies the importance of both cleanliness during cryogenic source assembly and stability of the cryogenic source temperature once liquefied. The system can be used for high repetition rate laser-driven proton acceleration, with an envisioned application in proton therapy. Other applications include laboratory astrophysics, materials science, and next-generation particle accelerators.


Assuntos
Hidrogênio/química , Tecnologia/instrumentação , Temperatura Baixa , Termodinâmica
20.
Chem Biol Interact ; 326: 109137, 2020 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-32442417

RESUMO

In the present study eighteen inhibitors of the hydrolytic enzymes of the endocannabinoid system were investigated for antioxidant activity using lipid peroxidation (LP) method. Among the assayed compounds ten belong to carbamates with phenyl [1,1'-biphenyl]-3-ylcarbamate (6), reported for the first time, and eight are retro-amide derivatives of palmitamine. Interestingly, results indicated that most of the tested compounds have good antioxidant properties. In particular, 1,3-di([1,1'-biphenyl]-3-yl)urea (3) shows IC50 = 26 ± 6 µM comparable to ones obtained for standard antioxidants trolox and quercetin (IC50 = 22 ± 6 µM and 23 ± 6 µM, respectively). Compound 3 was investigated further by means of DFT calculations, to clarify a possible mechanism of the antioxidant action. In order to estimate the capability of 3 to act as radical scavenger the structure was optimized at B3LYP/6-311++G** level and the respective bond dissociation enthalpies were calculated. The calculations in non-polar medium predicted as favorable mechanism a donation of a hydrogen atom to the free radical and formation of N-centered radical, while in polar solvents the mechanism of free radical scavenging by SPLET dominates over HAT H-abstraction. The possible radical scavenging mechanisms of another compound with potent antioxidant properties (IC50 = 53 ± 12 µM), the retro-amide derivative of palmitamine (compound 18), was estimated computationally based on the reaction enthalpies of a model compound (structural analogue to 18). The computations indicated that the most favorable mechanisms are hydrogen atom transfer from the hydroxyl group in meta-position of the benzamide fragment in nonpolar medium, and proton transfer from the hydroxyl group in ortho-position of the benzamide fragment in polar medium.


Assuntos
Compostos de Bifenilo/química , Peroxidação de Lipídeos/efeitos dos fármacos , Ureia/química , Anilidas/química , Antioxidantes/química , Benzamidas/química , Ácidos Graxos/química , Depuradores de Radicais Livres/química , Radicais Livres/química , Hidrogênio/química , Ácidos Palmíticos/química , Solventes/química
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