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1.
J Am Chem Soc ; 146(4): 2474-2483, 2024 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-38227949

RESUMO

Hopf et al. reported the high-temperature 6π-electrocyclization of cis-hexa-1,3-diene-5-yne to benzene in 1969. Subsequent studies using this cyclization have been limited by its very high reaction barrier. Here, we show that the reaction barrier for two model systems, (E)-1,3,4,6-tetraphenyl-3-hexene-1,5-diyne (1a) and (E)-3,4-bis(4-iodophenyl)-1,6-diphenyl-3-hexene-1,5-diyne (1b), is decreased by nearly half on a Au(111) surface. We have used scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) to monitor the Hopf cyclization of enediynes 1a,b on Au(111). Enediyne 1a undergoes two sequential, quantitative Hopf cyclizations, first to naphthalene derivative 2, and finally to chrysene 3. Density functional theory (DFT) calculations reveal that a gold atom from the Au(111) surface is involved in all steps of this reaction and that it is crucial to lowering the reaction barrier. Our findings have important implications for the synthesis of novel graphene nanoribbons. Ullmann-like coupling of enediyne 1b at 20 °C on Au(111), followed by a series of Hopf cyclizations and aromatization reactions at higher temperatures, produces nanoribbons 12 and 13. These results show for the first time that graphene nanoribbons can be synthesized on a Au(111) surface using the Hopf cyclization mechanism.

2.
Phys Rev Lett ; 132(4): 046201, 2024 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-38335341

RESUMO

Atomically precise graphene nanoflakes called nanographenes have emerged as a promising platform to realize carbon magnetism. Their ground state spin configuration can be anticipated by Ovchinnikov-Lieb rules based on the mismatch of π electrons from two sublattices. While rational geometrical design achieves specific spin configurations, further direct control over the π electrons offers a desirable extension for efficient spin manipulations and potential quantum device operations. To this end, we apply a site-specific dehydrogenation using a scanning tunneling microscope tip to nanographenes deposited on a Au(111) substrate, which shows the capability of precisely tailoring the underlying π-electron system and therefore efficiently manipulating their magnetism. Through first-principles calculations and tight-binding mean-field-Hubbard modeling, we demonstrate that the dehydrogenation-induced Au-C bond formation along with the resulting hybridization between frontier π orbitals and Au substrate states effectively eliminate the unpaired π electron. Our results establish an efficient technique for controlling the magnetism of nanographenes.

3.
Epilepsy Behav ; 154: 109748, 2024 May.
Artigo em Inglês | MEDLINE | ID: mdl-38640553

RESUMO

OBJECTIVE: Comorbid depression and anxiety in patients with epilepsy (PWE) are common and frequently under-treated, thus, causing poor health-related quality of life (HRQoL). However, little is known regarding the interconnections between anxious/depressive symptoms and the dimensions of HRQoL. Therefore, we conducted a network analysis to explore these relationships in detail among Chinese adult PWE. METHODS: A cohort of adult PWE was consecutively recruited from the First Affiliated Hospital of Chongqing Medical University. HRQoL, depression, and anxiety were measured with Quality of Life in Epilepsy Inventory-31, Neurological Disorders Depression Inventory for Epilepsy, and Generalized Anxiety Disorder 7-Item Scale, respectively. A regularized partial correlation network was constructed to investigate the interconnections between symptoms of anxiety/depression and the dimensions of HRQoL. We calculated expected influence (EI) and bridge expected influence (BEI) values to identify the most influential nodes. RESULTS: A total of 396 PWE were enrolled in this study, 78.1% of whom had focal onset epilepsy. The prevalence of anxiety and depression was 30.3% and 28.8%, respectively. The symptoms "frustrated" and "uncontrollable worry" had the highest EI values, whereas "emotional well-being", "seizure worry", "difficulty finding pleasure", and "nervousness or anxiety" had the highest BEI values. CONCLUSION: This study provides new insights into the relationships among anxiety, depression, and HRQoL. Critical central symptoms and bridge symptoms identified in the network might help to quickly identify PWE comorbid anxiety and depression in busy outpatient settings, thereby enabling early intervention and enhancing quality of life.


Assuntos
Ansiedade , Depressão , Epilepsia , Qualidade de Vida , Humanos , Qualidade de Vida/psicologia , Feminino , Masculino , Adulto , Epilepsia/psicologia , Epilepsia/epidemiologia , Epilepsia/complicações , Depressão/epidemiologia , Depressão/psicologia , Ansiedade/psicologia , Ansiedade/epidemiologia , Pessoa de Meia-Idade , Adulto Jovem , Escalas de Graduação Psiquiátrica , Estudos de Coortes , Adolescente , Idoso , Comorbidade
4.
Phys Chem Chem Phys ; 25(38): 26145-26151, 2023 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-37740334

RESUMO

Titanium disulfide (TiS2) has drawn considerable attention in materials, physics, and chemistry thanks to its potential applications in batteries, supercapatteries and thermoelectric devices. However, the simplified and controlled synthesis of high-quality TiS2 remains a great challenge. In this study, a straightforward widely accessible approach to the one-step chemical vapor transport (CVT) process is presented. Meanwhile, combining high-pressure (HP) Raman spectroscopy measurements and first-principles calculations, the pressure-induced phase transition of TiS2 from P3̄m1 phase (phase I) to C2/m phase (phase II) at 16.0 GPa and then to P6̄2m phase (phase III) at 32.4 GPa was disclosed. The discovery of HP being within the Weyl semi-metallic phase represents a significant advancement towards understanding the electronic topological states, discovering new physical phenomena, developing new electronic devices, and gaining insight into the properties of elementary particles.

5.
Phys Rev Lett ; 128(20): 206802, 2022 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-35657877

RESUMO

High-quality stanene films have been actively pursued for realizing not only quantum spin Hall edge states without backscattering, but also intrinsic superconductivity, two central ingredients that may further endow the systems to host topological superconductivity. Yet to date, convincing evidence of topological edge states in stanene remains to be seen, let alone the coexistence of these two ingredients, owing to the bottleneck of growing high-quality stanene films. Here we fabricate one- to five-layer stanene films on the Bi(111) substrate and observe the robust edge states using scanning tunneling microscopy/spectroscopy. We also measure distinct superconducting gaps on different-layered stanene films. Our first-principles calculations further show that hydrogen passivation plays a decisive role as a surfactant in improving the quality of the stanene films, while the Bi substrate endows the films with nontrivial topology. The coexistence of nontrivial topology and intrinsic superconductivity renders the system a promising candidate to become the simplest topological superconductor based on a single-element system.

6.
Phys Rev Lett ; 125(4): 046801, 2020 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-32794806

RESUMO

A quantum spin hall insulator is manifested by its conducting edge channels that originate from the nontrivial topology of the insulating bulk states. Monolayer 1T^{'}-WTe_{2} exhibits this quantized edge conductance in transport measurements, but because of its semimetallic nature, the coherence length is restricted to around 100 nm. To overcome this restriction, we propose a strain engineering technique to tune the electronic structure, where either a compressive strain along the a axis or a tensile strain along the b axis can drive 1T^{'}-WTe_{2} into an full gap insulating phase. A combined study of molecular beam epitaxy and in situ scanning tunneling microscopy or spectroscopy then confirmed such a phase transition. Meanwhile, the topological edge states were found to be very robust in the presence of strain.

7.
Nanotechnology ; 31(30): 305708, 2020 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-32259801

RESUMO

Low dimensional superconductors have many unusual properties. When 0-dimensional superconductors reach the nanometer scale, the superconducting energy gap can be enhanced due to the shell effect. At the same time, the single electron Coulomb blockade effect can also be observed on metal nanoparticles if they are weakly coupled to the environment. So, if a superconducting nanoparticle is isolated well from the environment, the superconducting gap and the Coulomb gap would couple together, making the tunneling spectrum more complicated and interesting. Here Sn nanoparticles were deposited on the surface of STO (111). The charging energy of a nanoparticle mainly depends on its size and is comparable to the superconducting gap when the isolated particle is large enough. The superconducting energy gap can be deduced from the coupling tunneling spectrum and the shell effect is observed. The method to deduce the superconducting gap here is simpler than when fit using the Dynes density of states. Owing to the increased superconducting gap and critical field, the studied nanoparticles may find applications in studies of the properties of Majorana fermions.

8.
Proteins ; 85(11): 1967-1974, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28643349

RESUMO

RlmN is a radical S-adenosylmethionine (SAM) enzyme that catalyzes the C2 methylation of adenosine 2503 (A2503) in 23S rRNA and adenosine 37 (A37) in several Escherichia coli transfer RNAs (tRNA). The catalytic reaction of RlmN is distinctly different from that of typical SAM-dependent methyltransferases that employs an SN 2 mechanism, but follows a ping-pong mechanism which involves the intermediate methylation of a conserved cysteine residue. Recently, the x-ray structure of a key intermediate in the RlmN reaction has been reported, allowing us to perform combined quantum mechanics and molecular mechanics (QM/MM) calculations to delineate the reaction details of RlmN at atomic level. Starting from the Cross-Linked RlmN C118A-tRNA complex, the possible mechanisms for both the formation and the resolution of the cross-linked species (IM2) have been illuminated. On the basis of our calculations, IM2 is formed by the attack of the C355-based methylene radical on the sp2 -hybridized C2 of the adenosine ring, corresponding to energy barrier of 14.4 kcal/mol, and the resolution of IM2 is confirmed to follow a radical fragmentation mechanism. The cleavage of C'-S' bond of mC355-A37 cross-link is in concert with the deprotonation of C2 by C118 residue, which is the rate-limiting step with an energy barrier of 17.4 kcal/mol. Moreover, the cleavage of C'-S' bond of IM2 can occur independently, that is, it does not require the loss of an electron of IM2 and the formation of disulfide bond between C355 and C118 as precondition. These findings would deepen the understanding of the catalysis of RlmN.


Assuntos
Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Metiltransferases/química , Metiltransferases/metabolismo , Simulação de Dinâmica Molecular , Domínio Catalítico , Ligação Proteica , S-Adenosilmetionina
9.
Proteins ; 85(8): 1518-1528, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28486790

RESUMO

Porphyromonas gingivalis peptidylarginine deiminase (PPAD) catalyzes the citrullination of peptidylarginine, which plays a critical role in the rheumatoid arthritis (RA) and gene regulation. For a better understanding of citrullination mechanism of PPAD, it is required to establish the protonation states of active site cysteine, which is still a controversial issue for the members of guanidino-group-modifying enzyme superfamily. In this work, we first explored the transformation between the two states: State N (both C351 and H236 are neutral) and State I (both residues exist as a thiolate-imidazolium ion pair), and then investigated the citrullination reaction of peptidylarginine, using a combined QM/MM approach. State N is calculated to be more stable than State I by 8.46 kcal/mol, and State N can transform to State I via two steps of substrate-assisted proton transfer. Citrullination of the peptidylarginine contains deamination and hydrolysis. Starting from State N, the deamination reaction corresponds to an energy barrier of 18.82 kcal/mol. The deprotonated C351 initiates the nucleophilic attack to the substrate, which is the key step for deamination reaction. The hydrolysis reaction contains two chemical steps. Both the deprotonated D238 and H236 can act as the bases to activate the hydrolytic water, which correspond to similar energy barriers (∼17 kcal/mol). On the basis of our calculations, C351, D238, and H236 constitute a catalytic triad, and their protonation states are critical for both the deamination and hydrolysis processes. In view of the sequence similarity, these findings may be shared with human PAD1-PAD4 and other guanidino-group-modifying enzymes. Proteins 2017; 85:1518-1528. © 2017 Wiley Periodicals, Inc.


Assuntos
Arginina/química , Proteínas de Bactérias/química , Citrulina/química , Cisteína/química , Hidrolases/química , Porphyromonas gingivalis/química , Prótons , Motivos de Aminoácidos , Arginina/análogos & derivados , Ácido Aspártico/química , Proteínas de Bactérias/metabolismo , Sítios de Ligação , Domínio Catalítico , Cristalografia por Raios X , Histidina/química , Hidrolases/metabolismo , Hidrólise , Simulação de Dinâmica Molecular , Porphyromonas gingivalis/enzimologia , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Desiminases de Arginina em Proteínas , Teoria Quântica , Especificidade por Substrato , Termodinâmica
10.
Phytochemistry ; 225: 114173, 2024 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-38851474

RESUMO

Saponins are bioactive components of many medicinal plants, possessing complicated chemical structures and extensive pharmacological activities, but the production of high-value saponins remains challenging. In this study, a 6'-O-glucosyltransferase PpUGT7 (PpUGT91AH7) was functionally characterized from Paris polyphylla Smith var. yunnanensis (Franch.) Hand. -Mazz., which can transfer a glucosyl group to the C-6' position of diosgenin-3-O-rhamnosyl-(1 â†’ 2)-glucoside (1), pennogenin-3-O-rhamnosyl-(1 â†’ 2)-glucoside (2), and diosgenin-3-O-glucoside (5). The KM and Kcat values of PpUGT7 towards the substrate 2 were 8.4 µM and 2 × 10-3 s-1, respectively. Through molecular docking and site-directed mutagenesis, eight residues were identified to interact with the sugar acceptor 2 and be crucial for enzyme activity. Moreover, four rare ophiopogonins and ginsenosides were obtained by combinatorial biosynthesis, including an undescribed compound ruscogenin-3-O-glucosyl-(1 â†’ 6)-glucoside (10). Firstly, two monoglycosides 9 and 11 were generated using a known sterol 3-O-ß-glucosyltransferase PpUGT80A40 with ruscogenin (7) and 20(S)-protopanaxadiol (8) as substrates, which were further glycosylated to the corresponding diglycosides 10 and 12 under the catalysis of PpUGT7. In addition, compounds 7-11 were found to show inhibitory effects on the secretion of TNF-α and IL-6 in macrophages RAW264.7. The findings provide valuable insights into the enzymatic glycosylation processes in the biosynthesis of bioactive saponins in P. polyphylla var. yunnanensis, and also serve as a reference for utilizing UDP-glycosyltransferases to construct high-value or rare saponins for development of new therapeutic agents.


Assuntos
Ginsenosídeos , Glicosiltransferases , Saponinas , Glicosiltransferases/metabolismo , Glicosiltransferases/química , Saponinas/química , Saponinas/biossíntese , Saponinas/metabolismo , Ginsenosídeos/química , Ginsenosídeos/biossíntese , Ginsenosídeos/metabolismo , Animais , Camundongos , Estrutura Molecular , Células RAW 264.7 , Melanthiaceae/química , Melanthiaceae/enzimologia , Melanthiaceae/metabolismo , Simulação de Acoplamento Molecular , Liliaceae/química
11.
Biomed Pharmacother ; 175: 116784, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38781865

RESUMO

1,8-Cineole is a bicyclic monoterpene widely distributed in the essential oils of various medicinal plants, and it exhibits significant anti-inflammatory and antioxidant activities. We aimed to investigate the therapeutic effect of 1,8-cineole on anti-Alzheimer's disease by using transgenic Caenorhabditis elegans models. Our studies demonstrated that 1,8-cineole significantly relieved Aß1-42-induced paralysis and exhibited remarkable antioxidant and anti-Aß1-42 aggregation activities in transgenic nematodes CL4176, CL2006 and CL2355. We developed a 1,8-cineole/cyclodextrin inclusion complex, displaying enhanced anti-paralysis, anti-Aß aggregation and antioxidant activities compared to 1,8-cineole. In addition, we found 1,8-cineole treatment activated the SKN-1/Nrf-2 pathway and induced autophagy in nematodes. Our results demonstrated the antioxidant and anti-Alzheimer's disease activities of 1,8-cineole, which provide a potential therapeutic approach for Alzheimer's disease.


Assuntos
Doença de Alzheimer , Peptídeos beta-Amiloides , Animais Geneticamente Modificados , Antioxidantes , Caenorhabditis elegans , Eucaliptol , Eucaliptol/farmacologia , Doença de Alzheimer/tratamento farmacológico , Doença de Alzheimer/metabolismo , Animais , Caenorhabditis elegans/efeitos dos fármacos , Antioxidantes/farmacologia , Peptídeos beta-Amiloides/metabolismo , Ciclodextrinas/farmacologia , Ciclodextrinas/química , Fragmentos de Peptídeos/farmacologia , Autofagia/efeitos dos fármacos , Modelos Animais de Doenças
12.
Q J Exp Psychol (Hove) ; 75(8): 1552-1560, 2022 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34609227

RESUMO

It is generally assumed that, to save storage space, features are stored as integrated objects in visual working memory (VWM). Although such an object-based account does not always hold because features can be processed in parallel, a previous study has shown that different features can be automatically bound with their locations (task-irrelevant feature) into an integrated unit, resulting in improved memory performance. The present study was designed to further explore this phenomenon by investigating whether other features, which are not spatial in origin, can act as the binding cue to form such automatic binding. To test this, we used three different features as binding cues (i.e., colour, spatial frequency, and shape) over multiple separate experiments. The results consistently showed that when two features shared the same binding cue, memory performance was better relative to when each of those features had their own binding cue. We conclude that any task-irrelevant feature can act as a binding cue to automatically bind with task-relevant features even across different objects, resulting in memory enhancement.


Assuntos
Sinais (Psicologia) , Memória de Curto Prazo , Cognição , Humanos , Percepção Visual
13.
Front Public Health ; 10: 1051810, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36424973

RESUMO

We use the county-by-county rollout of the program and employ the difference-in-difference (DID) methodology to identify the effects of the implementation of the nutrition improvement program for rural compulsory education students on adolescent health. The results show that the nutrition improvement program reduces the frequency and probability of illness and improves the students' health status. The heterogeneity analysis indicates that the children in western regions and children left behind have a greater marginal improvement. It finds that the nutrition improvement program for rural compulsory education students improves adolescent health through diversifying nutrition intake to alleviate malnutrition and developmental delay in impoverished areas. The program can promote adolescent health in impoverished areas, which has a role in improving regional health disparities and alleviating the intergenerational entrenchment of poverty.


Assuntos
Desnutrição , Estado Nutricional , Criança , Adolescente , Humanos , Estudantes , População Rural , Ingestão de Alimentos
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