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1.
ACS Nano ; 15(10): 16896-16903, 2021 10 26.
Artigo em Inglês | MEDLINE | ID: mdl-34652898

RESUMO

Facing the scientific question of the origin of chirality in life, water is considered to play a crucial role in driving many biologically relevant processes in vivo. Water has been demonstrated in vitro to be related to chiral generation, amplification, and inversion, while the underlying mechanism is still not fully understood. Real-space evidence at the single-molecule level is thus urgently required to understand the role of water molecules in biomolecular chirality related issues. Herein, we choose one of the RNA bases, the biomolecule uracil (U), which self-assembles into racemic hydrogen-bonded structures. Upon water exposure, surprisingly, racemic structures could be transformed to homochiral water-involved structures, resulting in an unexpected chiral separation on the surface. The origin of chiral separation is due to preferential binding between water and the specific site of U molecules, which leads to the formation of the energetically most favorable homochiral (U-H2O-U)2 cluster as seed for subsequent chiral amplification. Such a water-driven self-assembly process may also be extended to other biologically relevant systems such as amino acids and sugars, which would provide general insights into the role that water molecules may play in the origin of homochirality in vivo.


Assuntos
Aminoácidos , Água , Nanotecnologia , RNA , Estereoisomerismo
2.
Drug Test Anal ; 2021 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-34405558

RESUMO

In recent years, overseas anti-obesity drugs including amfepramone have flowed into China through the internet or personal import by travelers. Amfepramone is controlled in China and is not available as a pharmaceutical product. It is obtainable either through the internet or imported by individuals across the border. The abuse of amfepramone is causing serious health problems. A method for the detection and quantification of amfepramone and its metabolite cathinone in human hair was developed and fully validated using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Approximately 10 mg of hair was weighed and pulverized with extraction solvent (a mixture of methanol: acetonitrile: 2 mM ammonium formate [pH 5.3] [25:29:46, v/v/v]). The limit of detection (LOD) and the limit of quantitation (LOQ) were 5 and 10 pg/mg, respectively. The method was linear over a concentration range from 10 to 10,000 pg/mg. The accuracy varied from -9.3% to 2.3%, with acceptable intra- and inter-day precision. The validated method was successfully applied to 17 authentic cases. The amfepramone concentrations ranged from 11.7 to 209 pg/mg, with a median of 30.2 pg/mg, and the hair cathinone concentrations ranged from 11.9 to 507 pg/mg, with a median of 54.0 pg/mg. This is the first report of amfepramone concentrations in human hair from amfepramone users. Cathinone can be incorporated into hair after amfepramone use.

3.
J Am Chem Soc ; 143(33): 12955-12960, 2021 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-34397213

RESUMO

Ladder phenylenes (LPs) composed of alternating fused benzene and cyclobutadiene rings have been synthesized in solution with a maximum length no longer than five units. Longer polymeric LPs have not been obtained so far because of their poor stability and insolubility. Here, we report the synthesis of linear LP chains on the Au(111) surface via dehalogenative [2+2] cycloaddition, in which the steric hindrance of the methyl groups in the 1,2,4,5-tetrabromo-3,6-dimethylbenzene precursor improves the chemoselectivity as well as the orientation orderliness. By combining scanning tunneling microscopy and noncontact atomic force microscopy, we determined the atomic structure and the electronic properties of the LP chains on the metallic substrate and NaCl/Au(111). The tunneling spectroscopy measurements revealed the charged state of chains on the NaCl layer, and this finding is supported by density functional theory calculations, which predict an indirect bandgap and antiferromagnetism in the polymeric LP chains.

4.
Forensic Sci Int ; 323: 110790, 2021 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-33894686

RESUMO

Ayahuasca is a psychoactive beverage widely used in religious ceremonies in Amazonia. Dimethyltryptamine is the main active compound of ayahuasca. Dimethyltryptamine has many hazardous effects, including hallucinations. In the present study, a fast and reliable UPLC-MS/MS method was developed and validated for the quantitation of dimethyltryptamine in hair samples. Twenty-milligram hair samples were pulverized with methanol below 4 °C. After ultrasonication, centrifugation and filtration, 200 µL of supernatant was placed into an autosampler vial for LC-MS/MS analysis. The lower limit of quantitation (LLOQ) was 3 pg/mg. The resulting calibration curve for dimethyltryptamine fit the expression y = 281.50213x + 0.00231 (R2 = 0.992). Acceptable intraday and interday precision (RSD < 15%) and accuracy (92-113%) were achieved. The dilution integrity was deemed acceptable based on accuracy (96%) and precision (1.8%). The validated method was successfully applied to 28 forensic cases. The concentrations of dimethyltryptamine ranged from 3 to 1109 pg/mg.

5.
Drug Test Anal ; 13(6): 1127-1135, 2021 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-33554459

RESUMO

In recent years, diphenidol [1,1-diphenyl-4-piperidino-1-butanol] has been one of the drugs that appears in suicide cases, but there are few research data on its metabolic pathways and main metabolites. Metabolite identification plays a key role in drug safety assessment and clinical application. In this study, in vivo and in vitro samples were analyzed with ultra-high-performance liquid chromatography-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry. Structural elucidation of the metabolites was performed by comparing their molecular weights and product ions with those of the parent drug. As a result, 10 Phase I metabolites and 5 glucuronated Phase II metabolites were found in a blood sample and a urine sample from authentic cases. Three other Phase I metabolites were identified in the rat liver microsomes incubation solution. The results showed that the main metabolic pathways of diphenidol in the human body include hydroxylation, oxidation, dehydration, N-dealkylation, methylation, and conjugation with glucuronic acid. This study preliminarily clarified the metabolic pathways and main metabolites of diphenidol. For the development of new methods for the identification of diphenidol consumption, we recommend using M2-2 as a marker of diphenidol entering the body. The results of this study provide a theoretical basis for the pharmacokinetics and forensic scientific research of diphenidol.

6.
J Mol Biol ; 433(5): 166795, 2021 03 05.
Artigo em Inglês | MEDLINE | ID: mdl-33422522

RESUMO

The SCFSKP2 ubiquitin ligase relieves G1 checkpoint control of CDK-cyclin complexes by promoting p27KIP1 degradation. We describe reconstitution of stable complexes containing SKP1-SKP2 and CDK1-cyclin B or CDK2-cyclin A/E, mediated by the CDK regulatory subunit CKS1. We further show that a direct interaction between a SKP2 N-terminal motif and cyclin A can stabilize SKP1-SKP2-CDK2-cyclin A complexes in the absence of CKS1. We identify the SKP2 binding site on cyclin A and demonstrate the site is not present in cyclin B or cyclin E. This site is distinct from but overlapping with features that mediate binding of p27KIP1 and other G1 cyclin regulators to cyclin A. We propose that the capacity of SKP2 to engage with CDK2-cyclin A by more than one structural mechanism provides a way to fine tune the degradation of p27KIP1 and distinguishes cyclin A from other G1 cyclins to ensure orderly cell cycle progression.


Assuntos
Ciclina A/química , Quinase 2 Dependente de Ciclina/química , Inibidor de Quinase Dependente de Ciclina p27/química , Pontos de Checagem da Fase G1 do Ciclo Celular , Proteínas Quinases Associadas a Fase S/química , Sítios de Ligação , Quinases relacionadas a CDC2 e CDC28/química , Quinases relacionadas a CDC2 e CDC28/genética , Quinases relacionadas a CDC2 e CDC28/metabolismo , Ciclina A/genética , Ciclina A/metabolismo , Ciclina E/química , Ciclina E/genética , Ciclina E/metabolismo , Quinase 2 Dependente de Ciclina/genética , Quinase 2 Dependente de Ciclina/metabolismo , Inibidor de Quinase Dependente de Ciclina p27/genética , Inibidor de Quinase Dependente de Ciclina p27/metabolismo , Regulação da Expressão Gênica , Células HEK293 , Humanos , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Proteólise , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Proteínas Quinases Associadas a Fase S/genética , Proteínas Quinases Associadas a Fase S/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Transdução de Sinais
7.
Neuropsychobiology ; 80(4): 279-287, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33238265

RESUMO

INTRODUCTION: The interleukin-6/janus kinase 2/signal transducer and activator of transcription 3 (IL-6/JAK2/STAT3) pathway plays an important role in immune function, but little research has focused on this pathway in depression. We sought to examine the relationship between the IL-6/JAK2/STAT3 pathway and depressive-like behavior. METHODS: Using a chronic mild stress (CMS) paradigm, a total of 36 adult male Sprague-Dawley rats were divided into four matched groups: (1) control + vehicle, (2) CMS + vehicle, (3) control + paroxetine, and (4) CMS + paroxetine. We investigated the effects of CMS on depressive-like behavior by using the forced swimming test (FST). Subsequently, the mRNA levels of members of the IL-6/JAK2/STAT3 pathway were assessed by qRT-PCR. RESULTS: We found that rats exposed to CMS displayed a significant increase in immobility time and a decrease in climbing time in the FST. Moreover, mRNA levels of IL-6, JAK2, and STAT3 in the hypothalamus were increased following CMS. We also found that mRNA levels of IL-6, JAK2, and STAT3 were normalized by paroxetine administration, which coincided with normalization of the depressive-like behavior. CONCLUSIONS: The IL-6/JAK2/STAT3 pathway may be activated in depression, and targeting this pathway may provide a novel effective therapeutic approach for the treatment of depression.

8.
Front Chem ; 8: 610312, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33330406

RESUMO

Methyl 2 -[ [ 1- (5- fluoropentyl) indole - 3- carbonyl] amino] -3, 3- dimethyl - butanoate (5F-MDMB-PICA) is a new synthetic cannabinoid characterized by valinate or tert-leucinate moieties. In recent years, 5F-MDMB-PICA has been abused in the form of "spice-like" herbal incenses or electronic cigarette oil. A UHPLC-MS/MS method was developed to detect 5F-MDMB-PICA and its metabolites in human hair. Approximately 20 mg of hair was weighed and pulverized with methanol below 4°C. After ultrasonication, centrifugation and filtration, 200 µL of supernatant was placed into an autosampler vial and analyzed on a Waters Acquity UPLC HSS T3 column (100 mm × 2.1 mm, 1.8 µm particle size) using an acetonitrile-20 mmol/L ammonium acetate (0.1% formic acid, 5% acetonitrile) gradient with a run time of 8 min. The limit of detection (LOD) ranged from 0.5 to 5 pg/mg, and the lower limit of quantitation (LLOQ) ranged from 1 to 5 pg/mg. The method was shown to be linear over a concentration range of 1-200 pg/mg. The linear correlation (R 2) of the calibration curves for all analytes was >0.999. The accuracy varied from 95.4 to 107.4%, while the intra- and inter-day precision RSD values were 0.7-10.6% and 1.7-12.2%, respectively. Recoveries were within the range of 61.1-93.3%, and matrix effects were in the range of 19.1-102.6%. The validated method was successfully applied to the identification and quantification of 5F-MDMB-PICA and its metabolites in hair from authentic forensic cases.

9.
ACS Nano ; 14(8): 10680-10687, 2020 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-32687310

RESUMO

A single-molecule-level understanding of the activity of solvating water molecules in hydrogen-bonded assemblies would provide insights into the properties of the first hydration shells. Herein, we investigate the solvation of one of the DNA bases, cytosine, whose glassy-state network formed on Au(111) contains diverse types of hydrogen-bonded dimer configurations with hierarchical strengths. Upon water exposure, a global structural transformation from interwoven chain segments to extended chains was identified by scanning tunneling microscopy and atomic force microscopy. Density functional theory calculation and coarse-grained molecular dynamics simulation indicate that water molecules selectively break the weak-hydrogen-bonded dimers at T-junctions, while the stable ones within chains remain intact. The resulting hydrated chain segments further self-assemble into molecular chains by forming strong hydrogen bonds and spontaneously releasing water molecules. Such an intriguing transformation cannot be realized by thermal annealing, indicating the dynamic nature of water molecules in the regulation of hydrogen bonds in a catalytic manner.


Assuntos
Citosina , Água , Catálise , Hidrogênio , Ligação de Hidrogênio
10.
ACS Omega ; 5(16): 9550-9557, 2020 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-32363307

RESUMO

Direct growth of single-crystal compound semiconductors on nonepitaxial substrates is a promising route for device processing simplification in electronic and optoelectronic applications. However, the nonepitaxial growth technique for 2D single crystals is still a fundamental challenge. Here, we demonstrate that the macroscopic 2D interface of liquid metals and nonepitaxial solid substrates could be universally designed for the chemical vapor deposition growth of crystalline compound semiconductors. By adopting a sandwiched solid metal/liquid metal/solid substrate environment, millimeter-scale 2D GaS, 2D GaSe, and 1D GaTe single crystals of high quality were synthesized at the interface of liquid gallium and nonepitaxial substrates. Evidence shows that the particle-catalyst-free vapor-liquid-solid growth is driven by screw dislocations. Furthermore, we successfully extend the growth strategy to various metal chalcogenides (Sn, In, Cu, and Ag) and pnictides (Sb). Our work opens up a new route for the direct growth of single-crystalline compound semiconductors on nonepitaxial substrates.

11.
ACS Nano ; 14(5): 6331-6338, 2020 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-32396329

RESUMO

The involvement of metal atoms in molecular assemblies has enriched the structural and functional diversity of two-dimensional supramolecular networks, where metal atoms are incorporated into the architecture via coordination or ionic bonding. Here we present a temperature-variable study of the self-assembly of the 1,3,5-tribromobenzene (TriBB) molecule on Cu(111) that reveals the involvement of nonbonded adatoms in the molecular matrix. By means of scanning tunneling microscopy and noncontact atomic force microscopy, we demonstrate the molecular-level details of a phase transition of TriBB assembly from the close-packed to porous honeycomb structures at 78 K. This is an unexpected transformation because the close-packed phase is thermodynamically favored in view of its higher molecular density and more intermolecular bonds as compared to the honeycomb lattice. A comprehensive density functional theory calculation suggests that Cu adatoms should be involved in the formation of the honeycomb network, where the Cu adatoms help stabilize the molecular assembly via enhanced van der Waals interactions between TriBB molecules and the underlying substrate. Both calculation and experimental results suggest no chemical bonding or direct charge transfer between the adatoms and the molecules, thus the electronic characteristics of the Cu adatoms trapped in the molecular confinement are close to the intrinsic ones on a clean metal surface and different from those in the traditional coordination-bonded framework. The nonbonded metal adatoms embedded self-assemblies may complement the metal-organic coordination system and can be used to tailor the chemical reactivity and electronic properties of supramolecular structures.

12.
J Am Chem Soc ; 142(18): 8085-8089, 2020 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-32321241

RESUMO

The structural transformation from symmetric cumulene to broken-symmetry polyyne within a one-dimensional (1-D) atomic carbon chain is a signature of Peierls distortion. Direct observation of such a structural transformation with single-bond resolution is, however, still challenging. Herein, we design a molecule with a cumulene moiety (Br2C═C═C═CBr2) and employ STM tip manipulation to achieve the molecular skeleton rearrangement from a cumulene to a diyne moiety (Br-C≡C-C≡C-Br). Furthermore, by an on-surface reaction strategy, thermally induced entire debromination (:C═C═C═C:) leads to the formation of a 1-D organometallic polyyne (-C≡C-C≡C-Au-) with a semiconducting characteristic, which implies that a Peierls-like transition may occur in a rationally designed molecular system with limited length.

13.
Drug Des Devel Ther ; 14: 715-730, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32158191

RESUMO

Introduction: Enrofloxacin is used in the treatment of a wide variety of bacterial infections in mammals. However, its poor solubility limits the clinical use. Methods: In order to improve the solubility of enrofloxacin, the enrofloxacin mesylate (EM) were obtained by a chemical synthesis method. The characterization of EM was carried out using ultraviolet scan (UV), synchronous thermal analysis (SDT), fourier transform infrared spectrometer (FTIR) and mass spectrometry (MS), nuclear magnetic resonance (NMR) and X-ray powder diffraction analysis (XRPD). Acute toxicity of EM in Kunming mice was studied. Besides, pharmacokinetic studies were performed in New Zealand rabbits at a single oral dose of 10 mg/kg, and the antibacterial activity of EM was also evaluated. Results: EM was successfully synthesized and purified. The stoichiometric ratio of mesylate to enrofloxacin was 1:1 and the aqueous solubility of EM was 483.01±4.06 mg/mL, the solubility of EM was about 2000 times higher than enrofloxacin. The oral lethal dose (LD50) of EM was 1168.364 mg/kg, and the pharmacokinetics indicated that the oral relative bioavailability of EM was about 1.79 times and 1.48 times higher than that of enrofloxacin and enrofloxacin hydrochloride, respectively. In addition, the in vitro antibacterial activity of EM was not significantly changed compared with enrofloxacin and enrofloxacin hydrochloride. Conclusion: EM has higher solubility, low toxicity for oral use, and increases the oral bioavailability in rabbit. This study may be of benefit for the development of new enrofloxacin drugs.


Assuntos
Antibacterianos/farmacocinética , Enrofloxacina/farmacocinética , Staphylococcus aureus/efeitos dos fármacos , Animais , Antibacterianos/síntese química , Antibacterianos/química , Relação Dose-Resposta a Droga , Enrofloxacina/síntese química , Enrofloxacina/química , Camundongos , Camundongos Endogâmicos , Testes de Sensibilidade Microbiana , Estrutura Molecular , Coelhos , Solubilidade
14.
Fish Shellfish Immunol ; 97: 523-530, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31881328

RESUMO

Interferon (IFN) is a vital antiviral factor in host in the early stages after the viral invasion. Meanwhile, viruses have to survive by taking advantage of the cellular machinery and complete their replication. As a result, viruses evolved several immune escape mechanisms to inhibit host IFN expression. However, the mechanisms used to escape the host's IFN system are still unclear for infectious hematopoietic necrosis virus (IHNV). In this study, we report that the N protein of IHNV inhibits IFN1 production in rainbow trout by degrading the MITA. Firstly, the upregulation of IFN1 promoter activity stimulated by poly I:C was suppressed by IHNV infection. Consistent with this result, the overexpression of the N protein of IHNV blocked the IFN1 transcription that was activated by poly I:C and MITA. Secondly, MITA was remarkably decreased by the overexpression of N protein at the protein level. Further analysis demonstrated that the N protein targeted MITA and promoted the ubiquitination of MITA. Taken together, these data suggested that the production of rainbow trout IFN1 could be suppressed by the N protein of IHNV via degrading MITA.


Assuntos
Proteínas de Peixes/genética , Vírus da Necrose Hematopoética Infecciosa/imunologia , Interferons/imunologia , Proteínas de Membrana/genética , Proteínas do Nucleocapsídeo/imunologia , Oncorhynchus mykiss/imunologia , Animais , Antivirais/farmacologia , Células HEK293 , Interações entre Hospedeiro e Microrganismos/imunologia , Humanos , Vírus da Necrose Hematopoética Infecciosa/genética , Proteínas do Nucleocapsídeo/genética , Oncorhynchus mykiss/virologia , Poli I-C/farmacologia , Infecções por Rhabdoviridae , Ubiquitinação
15.
J Agric Food Chem ; 67(44): 12264-12272, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31613615

RESUMO

While silica particles are used extensively in food products, different grades and temperature variants of silica particles have not been compared for their physiochemical and biological properties. Different grades of silica (food-grade nanoparticles (FG-NPs), nonfood-grade nanoparticles (NFG-NPs), and food-grade micron particles (FG-MPs)) and the temperature variants generated by exposing FG-NPs to wet heating, dry heating, and refrigeration were compared for their physicochemical properties and interaction with trypsin. FG-NPs were similar to NFG-NPs and FG-MPs in their elemental composition and amorphous nature but had relatively less branched and ring siloxane groups than the latter ones. There were subtle but noticeable changes in the agglomeration behavior and relative abundance of different silica groups in FG-NPs exposed to food-handling temperatures. Secondary structure and function of trypsin were negatively impacted by FG-NPs and their temperature variants. Silica particles showed a "mixed-type inhibition" of trypsin resulting in partial digestion of bovine serum albumin. In conclusion, our studies showed differences in the surface chemistry of different grades of silica particles and temperature variants of FG-NPs and their negative impact on the structure and function of trypsin.


Assuntos
Aditivos Alimentares/química , Nanopartículas/química , Dióxido de Silício/química , Tripsina/química , Animais , Biocatálise , Bovinos , Hidrodinâmica , Tamanho da Partícula , Soroalbumina Bovina/química , Propriedades de Superfície , Temperatura
16.
Vet Microbiol ; 228: 234-245, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30593373

RESUMO

In the present study, the mechanisms underlying Muscovy duck reovirus (MDRV) p10.8 protein-induced ER stress and apoptosis in DF-1 cells and Muscovy duckling hepatic tissues were explored. On the fifth day post-infection, an increase in the mRNA levels of binding immunoglobulin protein (Bip) and X-box binding protein (XBP1), activation of XBP1/s, and an increase in percentage of apoptotic cells were observed in Muscovy duckling livers. The use of ER stress inducer Tunicamycin and ER stress inhibitor Tauroursodeoxycholic acid demonstrated that MDRV induces apoptosis via ER stress, leading to apoptosis. The use of Tunicamycin increased viral protein synthesis while Tauroursodeoxycholic acid reduced viral protein synthesis, suggesting that MDRV induces ER stress benefiting virus replication. The MDRV p10.8 is the major protein to induce ER stress and apoptosis. We found that p10.8 promotes the conversion of XBP1/u to XBP1/s and expands ER diameter, and increases the percentages of apoptotic cells in DF-1 and duckling liver tissues. To investigate the mechanism underlying the MDRV p10.8-induced ER stress and apoptosis, Western blot, siRNA, and co-immunoprecipitation (Co-IP) assays were performed. We found that the MDRV p10.8 protein up-regulates Bip, p-IRE1, XBP1s, and cleaved-caspase 3. Co-IP results reveal that the MDRV p10.8 protein disassociates the Bip/IRE1 complex. Inhibition of IRE1 by 4-methyl umbelliferone 8-carbaldehyde (4u8c) dramatically reversed the MDRV p10.8-modulated increase in levels of XBP1s and cleaved-caspase 3. Knockdown of XBP1 by siRNA reversed the increased level of p10.8-modulated cleaved-caspase 3. The present study provides mechanistic insights into the MDRV p10.8 protein induces ER stress, resulting in apoptosis via the Bip/IRE1/XBP1 pathway in DF-1 cells and duckling livers.


Assuntos
Apoptose , Doenças das Aves/virologia , Patos/virologia , Estresse do Retículo Endoplasmático , Orthoreovirus Aviário/fisiologia , Infecções por Reoviridae/veterinária , Animais , Linhagem Celular , Fibroblastos , Linfocinas/genética , Linfocinas/metabolismo , Infecções por Reoviridae/virologia , Replicação Viral , Proteína 1 de Ligação a X-Box/genética , Proteína 1 de Ligação a X-Box/metabolismo
17.
ACS Nano ; 12(12): 12612-12618, 2018 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-30513200

RESUMO

Rationally designed halogenated hydrocarbons are widely used building blocks to fabricate covalent-bonded carbon nanostructures on surfaces through a reaction pathway involving generation and dissociation of organometallic intermediates and irreversible covalent bond formation. Here, we provide a comprehensive picture of the on-surface-assisted homocoupling reaction of 1,3-bis(2-bromoethynyl)benzene on Au(111), aiming for the synthesis of graphdiyne nanostructures. Submolecular resolution scanning tunneling microscopy and noncontact atomic force microscopy observations identify the organometallic intermediates and their self-assemblies formed in the dehalogenation process. The demetallization of the organometallic intermediates at increased temperatures produces butadiyne moieties that spontaneously formed two different covalent structures ( i.e., graphdiyne zigzag chains and macrocycles), whose ratio was found to depend on the initial coverage of organometallic intermediates. At the optimal condition, the stepwise demetallization and cyclization led to a high-yield production of graphdiyne macrocycles up to 95%. Statistical analysis and theoretical calculations suggested that the favored formation of macrocycles resulted from the complex interplay between thermodynamic and kinetic processes involving the organometallic bonded intermediates and the covalently bonded butadiyne moieties.

18.
Nat Commun ; 9(1): 3113, 2018 08 06.
Artigo em Inglês | MEDLINE | ID: mdl-30082699

RESUMO

The synthetic challenges of radialenes have precluded their practical applications. Here, we report a one-step synthetic protocol of [4]radialene on a copper surface. High-resolution scanning tunneling microscopy measurements reveal that such catalytic reaction proceeds readily with high selectivity at the temperature below 120 K. First-principles calculations show that the reaction pathway is characterized by firstly the cooperative inter-molecular hydrogen tautomerization and then the C-C bond formation. The feasibility of such cyclotetramerization reaction can be interpreted by the surface effect of Cu(100), which firstly plays an important role in directing the molecular assembly and then serves as an active catalyst in the hydrogen tautomerization and C-C coupling processes. This work presents not only a novel strategy to the scant number of synthetic methods to produce [4]radialenes via a novel [1 + 1 + 1 + 1] reaction pathway, but also a successful example of C-C bond coupling reactions guided by the surface-induced C-H/π assembly.

19.
ACS Nano ; 12(8): 7959-7966, 2018 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-30016072

RESUMO

Conductive polymers are of great importance in a variety of chemistry-related disciplines and applications. The recently developed bottom-up on-surface synthesis strategy provides us with opportunities for the fabrication of various nanostructures in a flexible and facile manner, which could be investigated by high-resolution microscopic techniques in real space. Herein, we designed and synthesized molecular precursors functionalized with benzal  gem-dibromomethyl groups. A combination of scanning tunneling microscopy, noncontact atomic force microscopy, high-resolution synchrotron radiation photoemission spectroscopy, and density functional theory calculations demonstrated that it is feasible to achieve the direct formation of C-C double-bonded structural motifs via on-surface dehalogenative homocoupling reactions on the Au(111) surface. Correspondingly, we convert the sp3-hybridized state to an sp2-hybridized state of carbon atoms, i. e., from an alkyl group to an alkenyl one. Moreover, by such a bottom-up strategy, we have successfully fabricated poly(phenylenevinylene) chains on the surface, which is anticipated to inspire further studies toward understanding the nature of conductive polymers at the atomic scale.

20.
Nat Commun ; 9(1): 2322, 2018 06 13.
Artigo em Inglês | MEDLINE | ID: mdl-29899408

RESUMO

The carbon-carbon triple bond (-C≡C-) is an elementary constituent for the construction of conjugated molecular wires and carbon allotropes such as carbyne and graphyne. Here we describe a general approach to in situ synthesize -C≡C- bond on Cu(111) surface via homo-coupling of the trichloromethyl groups, enabling the fabrication of individual and arrays of poly(p-phenylene ethynylene) molecular wires. Scanning tunneling spectroscopy reveals a delocalized electronic state extending along these molecular wires, whose structure is unraveled by atomically resolved images of scanning tunneling microscopy and noncontact atomic force microscopy. Combined with density functional theory calculations, we identify the intermediates formed in the sequential dechlorination process, including surface-bound benzyl, carbene, and carbyne radicals. Our method overcomes the limitation of previous on-surface syntheses of -C≡C- incorporated systems, which require the precursors containing alkyne group; it therefore allows for a more flexible design and fabrication of molecular architectures with tailored properties.

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