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1.
Artigo em Inglês | MEDLINE | ID: mdl-31790580

RESUMO

The unidirectional liquid spreading without external energy input has presently aroused widespread concern. Recently, on the peristome of Nepenthes alata, a novel 2D unidirectional liquid spreading has been reported. It has been revealed that its exquisite superhydrophilic multistage microstructure, overlapping microcavities with arc-shaped edges and wedge-shaped corners, is the main reason for this phenomenon. To fabricate a peristome-inspired surface, a replica molding method is highly efficient and provides an ideal structure. However, the curved shape of the finally formed surface cannot be adjusted, and a specific surface shows only one type of liquid spreading state, greatly limiting its potential application. Here, we aimed to develop a novel surface tension-assisted replica molding method to fabricate an artificial peristome film. The artificial peristome film was fabricated by pouring styrenic block copolymers (SBS) dissolved in organic solvents into a negative replica prepared in polydimethylsiloxane (PDMS), based on the natural peristome. With volatilizing the organic solvent, the SBS agglomerates formed an artificial peristome film via surface tension effects. More importantly, the PDMS-negative replica swelled in the organic solvent, and then returned to the original size, which is conducive for replicating microstructures. The liquid spreading speed could be dynamically controlled by stretching the artificial peristome film. We demonstrated that the microcavity wedge angle decreases with an increasing stretching ratio. A smaller wedge angle can result in a much stronger unidirectional liquid spreading ability. This study provides insight into the dynamic control of unidirectional liquid spreading for novel pump-free medical microfluidic devices.

2.
BMC Genomics ; 20(1): 930, 2019 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-31801462

RESUMO

BACKGROUND: Salmonella bongori infect mainly cold-blooded hosts, but infections by S. bongori in warm-blooded hosts have been reported. We hypothesized that S. bongori might have diverged into distinct phylogenetic lineages, with some being able to infect warm-blooded hosts. RESULTS: To inspect the divergence status of S. bongori, we first completely sequenced the parakeet isolate RKS3044 and compared it with other sequenced S. bongori strains. We found that RKS3044 contained a novel T6SS encoded in a pathogenicity island-like structure, in addition to a T6SS encoded in SPI-22, which is common to all S. bongori strains so far reported. This novel T6SS resembled the SPI-19 T6SS of the warm-blooded host infecting Salmonella Subgroup I lineages. Genomic sequence comparisons revealed different genomic sequence amelioration events among the S. bongori strains, including a unique CTAG tetranucleotide degeneration pattern in RKS3044, suggesting non-overlapping gene pools between RKS3044 and other S. bongori lineages/strains leading to their independent accumulation of genomic variations. We further proved the existence of a clear-cut genetic boundary between RKS3044 and the other S. bongori lineages/strains analyzed in this study. CONCLUSIONS: The warm-blooded host-infecting S. bongori strain RKS3044 has diverged with distinct genomic features from other S. bongori strains, including a novel T6SS encoded in a previously not reported pathogenicity island-like structure and a unique genomic sequence degeneration pattern. These findings alert cautions about the emergence of new pathogens originating from non-pathogenic ancestors by acquiring specific pathogenic traits.

3.
BMJ Open ; 9(11): e031918, 2019 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-31712344

RESUMO

OBJECTIVES: To describe the prehospital and in-hospital delays to care and factors associated with the delays among patients with ST-segment elevation myocardial infarction (STEMI) in non-percutaneous coronary intervention (PCI) hospitals in China. DESIGN, SETTING AND PARTICIPANTS: We analysed data from a large registry-based quality of care improvement trial conducted from 2011 to 2014 among 101 non-PCI hospitals in China. A total of 7312 patients with STEMI were included. Prehospital delay was defined as time from symptom onset to hospital arrival >120 min, first ECG delay as time from arrival to first ECG >10 min, thrombolytic therapy delay as time from first ECG to thrombolytic therapy >10 min and in-hospital delay as time from arrival to thrombolytic therapy >30 min. Logistic regressions with generalised estimating equations were preformed to identify the factors associated with each delay. RESULTS: The rates of prehospital delay, first ECG delay, thrombolytic therapy delay and in-hospital delay were 67.1%, 31.4%, 85.8% and 67.8%, respectively. Patients who were female, older than 65 years old, illiterate, farmers, onset during late night and forenoon, had heart rate ≥100 beats/m at admission were more likely and patients who had history of myocardial infarction, hypertension or SBP <90 mm Hg at admission were less likely to have prehospital delay. First ECG delay was more likely to take place in patients arriving on regular hours. Thrombolytic therapy delay rate was lower in patients who had prehospital delay or first ECG delay but higher in those with heart rate ≥100 beats/m at admission. In-hospital delay rate was lower in patients with a history of dyslipidaemia and those who arrived during regular hours. CONCLUSION: Chinese patients with STEMI in low medical resource areas suffered severe prehospital and in-hospital delays to care. Future efforts should be made to improve the prehospital delay among vulnerable populations with low socioeconomic status. TRIAL REGISTRATION NUMBER: NCT01398228; Post-results.

4.
Fish Physiol Biochem ; 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31701282

RESUMO

An 8-week feeding trial was conducted to investigate the effects of enzyme-treated soy protein (ETSP) supplementation in low protein diets on growth performance as well as flesh sensory quality and healthiness in on-growing grass carp. A total of 540 on-growing grass carp (initial average weight 325.72 ± 0.60 g) were fed six diets, which included a normal protein diet (28% crude protein) and five low protein diets (26% crude protein) supplemented with graded levels of ETSP (0.0, 0.8, 1.2, 1.6, and 2.0%). The results showed that reducing dietary protein by 2% decreased percentage weight gain, feed intake, and flesh flavor (aspartic acid, glutamic acid, histidine, and 5'-inosinic acid contents) and healthiness-related indices (linolenic acid (LA) and docosahexaenoic acid (DHA) contents and polyunsaturated fatty acids to saturated fatty acids ratio). Under the condition of reducing dietary protein by 2%, 0.8-1.2% ETSP supplementation restored above parameters to levels equal or superior to those in 28% crude protein diet group. Although reducing dietary protein by 2% did not deteriorate flesh tenderness and juiciness, 0.8-1.2% ETSP supplementation in low protein diets also improved the two indices compared with 28% crude protein diet. Moreover, ETSP-improved flesh quality was partly related to increased muscle antioxidant enzymes activities and their mRNA levels. In addition, ESTP-enhanced antioxidant enzyme mRNA levels were partly associated with the upregulation of NF-E2-related factor 2 (Nrf2) and target of rapamycin (TOR) signaling. Collectively, 0.8-1.2% ETSP supplementation in low protein diets improved growth performance as well as flesh sensory quality and healthiness in on-growing grass carp.

5.
Artigo em Inglês | MEDLINE | ID: mdl-31745766

RESUMO

The anoxic and reductive aquatic environment is formed easily in summer due to the global warming, which may accelerate endogenous release. In this experiment, four different dosages of calcium peroxide (CaO2) were adopted to study the control effects of nutrients release from the sediments in the simulated landscape waters. The results demonstrated that CaO2 addition could effectively improve the physicochemical properties and microbial composition in sediments, and an obvious improvement was achieved with a larger dosage. It was observed that the surface sediments of experiment groups were oxidized to form a capping barrier between the sediment and overlying water, which might cut off the pollutant diffusion in sediment. Meanwhile, CaO2 could decrease the nutrients concentration in water obviously, and the reduced effect was positively correlated with the CaO2 dosage. Compared with the nutrients release fluxes in CK (105.89 mg-TN m-2 day-1, 106.48 mg-NH4+-N m-2 day-1, 4.14 mg-TP m-2 day-1, and 4.30 mg-SRP m-2 day-1), the CaO2 dosages of 0.12 and 0.18 kg m-2 could entirely inhibit the nutrients release from sediment, and partially reduce the original pollutants in the overlying water. However, 0.18 kg m-2 CaO2 would cause a higher increase of pH value and NO2--N concentration, and bring potential risk to the aquatic ecosystem. Therefore, 0.12 kg-CaO2 m-2-sediment was selected as the optimal dosage by considering the control effect, economic cost, and potential risk comprehensively. In general, this study provided a quantitative usage method of CaO2, which is convenient and effective to prevent or control the nutrients release from sediment caused by anoxic and reductive condition in summer.

6.
Fish Shellfish Immunol ; 95: 105-116, 2019 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-31610288

RESUMO

The current study aimed to investigate the effects and mechanisms of dietary soybean ß-conglycinin in immune function and oxidative damage among different intestinal segments of juvenile grass carp (Ctenopharyngodon idella). 240 fish (13.77 ±â€¯0.10 g) were fed control or 8% ß-conglycinin diet for 7 weeks. Dietary ß-conglycinin caused inconsistent suppression effects on the innate immune by decreasing complement component, lysozyme, antimicrobial peptide and acid phosphatase among different intestinal segments. Meanwhile, dietary ß-conglycinin caused inflammation in the mid and distal intestine by raising pro-inflammatory cytokines and declining anti-inflammatory cytokines mRNA levels, while more serious in the distal intestine than in the mid intestine. Furthermore, dietary ß-conglycinin regulating inflammatory cytokines might be associated with transcription factors nuclear factor-κB P65 (NF-κB P65) nucleus translocation and target of rapamycin (TOR) phosphorylation in the distal intestine but only related to TOR phosphorylation in the mid intestine. Interestingly, in the proximal intestine, dietary ß-conglycinin decreased both pro-inflammatory and anti-inflammatory cytokines mRNA level, and did not affect NF-κB P65 nucleus translocation and TOR phosphorylation. For oxidative damage, dietary ß-conglycinin exposure elevated both malondialdehyde (MDA) and protein carbonyl (PC) contents in the distal intestine, which might be attributed to the suppression of the Mn-SOD, catalase (CAT) and glutathione peroxidase (GPx) activities. In the mid intestine, dietary ß-conglycinin only increased PC content in association with the low activities of CAT, GPx and glutathione peroxidase (GR). Unexpectedly, in the proximal intestine, dietary ß-conglycinin did not significantly change MDA and PC contents while decreased antioxidant enzyme activities. Furtherly, dietary ß-conglycinin affect the antioxidant enzyme activity might be regulated by the varying pattern of nuclear factor-erythroid 2-related factor 2 (Nrf2) nucleus translocation among these three intestinal segments. In summary, dietary ß-conglycinin caused intestinal inflammation and oxidative damage in association with NF-κB, TOR and Nrf2 signaling molecules, which were varying among the three intestinal segments of grass carp.

7.
Am J Pathol ; 2019 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-31610177

RESUMO

Triple-negative breast cancer (TNBC) is a heterogeneous disease with an unfavorable prognosis and no specific targeted therapies. The role of non-SMC condensin I complex subunit D2 (NCAPD2), a regulatory subunit of the condensin I complex that mainly participates in chromosome condensation and segregation, has not been reported in cancer. We therefore evaluated the prognostic value and biological function of NCAPD2 in TNBC. The expression of NCAPD2 was studied in 179 TNBC tissues by immunohistochemistry, and associations among NCAPD2 expression, clinicopathologic features, and the prognosis information of patients with TNBC were analyzed. The mRNA expression profiles of 99 TNBC tissues were also studied, and cell biological behaviors were detected when NCAPD2 was altered in three TNBC cell lines. NCAPD2 expression was positively associated with lymph node metastasis (P = 3.84 × 10-06), poor overall survival (P = 0.0033), and worse disease-free survival (P = 0.0013) of patients with TNBC. Moreover, knockdown of NCAPD2 might cause G2/M arrest through the p53 signaling pathway, which led to proliferation inhibition, polyploid cell production, and cell apoptosis and inhibited the invasiveness of TNBC cells. For the first time, we report the close association between NCAPD2 and cancer and demonstrate that NCAPD2 plays an important role in TNBC progression and acts as an independent poor prognostic factor and a potential therapeutic target for TNBC.

8.
Chin Med J (Engl) ; 132(20): 2501-2502, 2019 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-31613819
9.
Phys Chem Chem Phys ; 21(39): 22048-22056, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31565718

RESUMO

Molecules with planar tetracoordinate carbons (ptCs) are exotic in chemical bonding, and they are normally designed according to the 18-electron rule. Here we report on the viability of ptC clusters with as few as 12 valence electrons, which represent the lower limit in terms of electron counting. Specifically, we have computationally designed a class of ternary 12-electron ptC clusters, CBe3X3+ (X = H, Li, Na, Cu, Ag), based on a rhombic CBe32- unit. Computer structural searches reveal that the ptC species are global minima, whose C center is coordinated in-plane by three Be atoms and a terminal X atom via robust C-Be/C-X bonding, either covalent or ionic. The other two X atoms are on the periphery and each bridge two Be atoms. Bonding analyses show that the ptC core is governed by delocalized 2π/6σ bonding, that is, double π/σ aromaticity, which collectively conforms to the 8-electron counting. Additional 4 electrons contribute to peripheral Be-X-Be and Be-Be σ bonding. The delocalized 2π/6σ frameworks appear to be universal for all ptC clusters, ranging from 18-electron down to 12-electron systems. In other words, the ptC species are dictated entirely by the 8-electron counting. Predicted vertical electron affinities of these ptC clusters range from 3.13 to 5.48 eV, indicative of superalkali or pseudoalkali cations.

11.
Br J Nutr ; : 1-37, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31637992

RESUMO

The experiment was conducted to investigate the effects of dietary threonine (Thr) on growth performance, and muscle growth, protein synthesis and antioxidant related signaling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. The total of 1200 fish (14.19 ± 0.13 g) were randomly distributed into six groups with four replicates each, fed six diets with graded level of Thr (9.5, 11.5, 13.5, 15.4, 17.4, and 19.3 g kg-1 diets) for 56 days. Results showed (P< 0.05) that dietary Thr (1) increased percent weight gain (PWG), specific growth rate (SGR), feed efficiency (FE), and protein efficiency ratio (PER); (2) up-regulated growth hormone (GH), insulin-like growth factor 1 (IGF-1), proliferating cell nuclear antigen (PCNA), myogenic regulation factors (MyoD, Myf5, MyoG, and Mrf4), and MyHC mRNA levels; (3) increased muscle protein content via regulating AKT/TOR signaling pathway; (4) decreased malondialdehyde (MDA) and protein carbonyl (PC) contents, increased CAT, GST, GR, and GSH activities, up-regulated mRNA levels of antioxidant enzymes related to NFE2-related factor 2 (Nrf2) and γ-glutamylcysteine ligase catalytic subunit (GCLC). These results suggest that Thr has potential role to improve muscle growth and protein synthesis, which might be due to the regulation of GH-IGF system, muscle growth related gene, antioxidative capacity, and protein synthesis related signaling pathways. Based on the quadratic regression analysis of SGR, the Thr requirement of hybrid catfish (14.19-25.77 g) was estimated to be 13.77 g kg-1 of the diet (33.40 g kg-1 of dietary protein).

12.
J Investig Med ; 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31619486

RESUMO

The nasopharyngeal tract traps mainly coarse particles in inhaled air. Soluble carcinogenic compounds, endotoxins, and trace metals contained in these particles are potential causes of inflammation and oxidative stress which could enhance carcinogenesis. The aim of this study was to determine the association between coarse particulate matter (PM10-2.5) and nasopharyngeal cancer (NPC). A total of 521,098 men (355 cases and 520,743 non-cases), aged ≥40 years were included in this study. Data were retrieved from the Taiwan Cancer Registry, the Adult Preventive Medical Services Database, and the Air Quality Monitoring Database. PM10-2.5 was significantly associated with a higher risk of NPC after adjusting for SO2, NOx, O3, age, body mass index, smoking, alcohol drinking, betel nut chewing, exercise, hypertension, diabetes, and hyperlipidemia. With PM10-2.5<20.44 µg/m3 as the reference, the ORs and 95% CIs were 1.47; 1.03-2.11, 1.34; 0.94-1.91, and 1.68; 1.16-2.44 for 20.44≤PM10-2.5<24.08, 24.08≤PM10-2.5<29.27, and PM10-2.5≥29.27 µg/m3, respectively. PM10-2.5 remained significantly associated with a higher risk of NPC after further adjustments were made for the aforementioned covariates and PM2.5 The ORs; 95% CIs were 1.42; 0.96 to 2.12, 1.41; 0.94 to 2.10, and 1.71; 1.10 to 2.66 for 20.44≤PM10-2.5<24.08, 24.08≤PM10-2.5<29.27, and PM10-2.5≥29.27 µg/m3, respectively. In conclusion, PM10-2.5 was significantly associated with a higher risk of NPC in Taiwanese men.

13.
Nat Commun ; 10(1): 4122, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31511503

RESUMO

Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces remains a great challenge. Here, competing reactions of a prochiral alkyne on Ag(111): two-dimensional (2D) homochiral Glaser coupling and heterochiral cross-coupling with a Bergman cyclization step have been examined. We demonstrate control strategies in steering the reactions between the homochiral and heterochiral pathways by tuning the precursor substituents and the kinetic parameters, as confirmed by high-resolution scanning probe microscopy (SPM). Control experiments and density functional theory (DFT) calculations reveal that the template effect of organometallic chains obtained under specific kinetic conditions enhances Glaser coupling between homochiral molecules. In contrast, for the reaction of free monomers, the kinetically favorable reaction pathway is the cross-coupling between two heterochiral molecules (one of them involving cyclization). This work demonstrates the application of kinetic control to steer chiral organic coupling pathways at surfaces.

14.
Carbohydr Polym ; 225: 115257, 2019 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-31521312

RESUMO

Extracellular matrix degradability meditates cell behaviors and gains increasing importance in the development of implantation materials for tissue engineering. Here, we developed a fully biodegradable hydrogel combining the unique features of synthetic polyphosphate polymer and natural polysaccharide polymer. Polyphosphate copolymer poly(butynyl phospholane)-random-poly(ethylethylene phosphate) (PBYP-r-PEEP) bearing pendent alkynes was synthesized through a facile one-pot reaction. Subsequently, thiol-yne "click" reaction was employed to fabricate the fully degradable and photocrosslinked hydrogel by mixing PBYP-r-PEEP with thiolated biodegradable hyaluronic acid (HA-SH). The generated HA/PPE hydrogels show viscoelastic properties and enzymatic biodegradability, supporting the growth of human mesenchymal stem cells (hMSCs). HA/PPE hydrogel is permissive to the covalent conjugation of cell-adhesive peptide RGD, which can enhance the cell-cell interactions. This HA/PPE hydrogel system provides a fully biodegradable platform that can support hMSCs growth and facilitate the formation of cell clustering, expanding the range of fully degradable materials for tissue engineering and regenerative medicine.

15.
Child Abuse Negl ; 98: 104183, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31521907

RESUMO

BACKGROUND: College students with suicidal ideation (SI) are at high risk of suicide. Adverse childhood experiences (ACEs) are important risk factors for suicidal behavior. Most research in this area has been restricted to 10 conventional ACEs and suggests negative long-term developmental effects from other common childhood adversities such as peer victimization, peer isolation/rejection, exposure to community violence, and low socioeconomic status. OBJECTIVE: To test the unique and cumulative associations of 14 different ACEs with SI among young adults. PARTICIPANTS AND SETTING: Participants were 989 college students from two universities in China's provincial-leveled Hui Autonomous Region. METHODS: Associations between ACEs and SI were analyzed by logistic regression. A Chi-square trend test was used to examine the association between cumulative ACEs and SI. RESULTS: The rates of suicidal ideation, plans, and attempts among the cohort were 11.9%, 3.7%, and 1.6%, respectively; 43.9% had experienced at least one ACE. The strongest predictor of SI in adulthood was peer isolation/rejection, followed by emotional neglect, then low socioeconomic status. There was a cumulative effect of ACEs and SI, whereby the greater the number of ACEs, the greater the likelihood of SI. CONCLUSION: Peer isolation/rejection, emotional neglect, and low socioeconomic status were associated with increased risk of SI in adulthood. Two (peer isolation/rejection and low socioeconomic status) of the three factors that emerged from the analysis are not typically included in ACEs research. There was a cumulative effect of 14 kinds of ACEs on SI among young adults. Early recognition of risk factors is therefore important.

16.
Cancer Res ; 79(23): 5930-5943, 2019 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-31484669

RESUMO

The genetic events occurring in recurrent nasopharyngeal carcinoma (rNPC) are poorly understood. Here, we performed whole-genome and whole-exome sequencing in 55 patients with rNPC and 44 primarily diagnosed NPC (pNPC), with 7 patients having paired rNPC and pNPC samples. Previously published pNPC exome data were integrated for analysis. rNPC and pNPC tissues had similar mutational burdens, however, the number of clonal mutations was increased in rNPC samples. TP53 and three NF-κB pathway components (TRAF3, CYLD, and NFKBIA) were significantly mutated in both pNPC and rNPC. Notably, mutations in TRAF3, CYLD, and NFKBIA were all clonal in rNPC, however, 55.6% to 57.9% of them were clonal in pNPC. In general, the number of clonal mutations in NF-κB pathway-associated genes was significantly higher in rNPC than in pNPC. The NF-κB mutational clonality was selected and/or enriched during NPC recurrence. The amount of NF-κB translocated to the nucleus in samples with clonal NF-κB mutants was significantly higher than that in samples with subclonal NF-κB mutants. Moreover, the nuclear abundance of NF-κB protein was significantly greater in pNPC samples with locoregional relapse than in those without relapse. Furthermore, high nuclear NF-κB levels were an independent negative prognostic marker for locoregional relapse-free survival in pNPC. Finally, inhibition of NF-κB enhanced both radiosensitivity and chemosensitivity in vitro and in vivo. In conclusion, NF-κB pathway activation by clonal mutations plays an important role in promoting the recurrence of NPC. Moreover, nuclear accumulation of NF-κB is a prominent biomarker for predicting locoregional relapse-free survival. SIGNIFICANCE: This study uncovers genetic events that promote the progression and recurrence of nasopharyngeal carcinoma and has potential prognostic and therapeutic implications.See related commentary by Sehgal and Barbie, p. 5915.

17.
Genomics Proteomics Bioinformatics ; 17(3): 287-296, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-31479759

RESUMO

T cells and T cell receptors (TCRs) play pivotal roles in adaptive immune responses against tumors. The development of next-generation sequencing technologies has enabled the analysis of the TCRß repertoire usage. Given the scarce investigations on the TCR repertoire in lung cancer tissues, in this study, we analyzed TCRß repertoires in lung cancer tissues and the matched distant non-tumor lung tissues (normal lung tissues) from 15 lung cancer patients. Based on our results, the general distribution of T cell clones was similar between cancer tissues and normal lung tissues; however, the proportion of highly expanded clones was significantly higher in normal lung tissues than in cancer tissues (0.021% ±â€¯0.002% vs. 0.016% ±â€¯0.001%, P = 0.0054, Wilcoxon signed rank test). In addition, a significantly higher TCR diversity was observed in cancer tissues than in normal lung tissues (431.37 ±â€¯305.96 vs. 166.20 ±â€¯101.58, P = 0.0075, Mann-Whitney U test). Moreover, younger patients had a significantly higher TCR diversity than older patients (640.7 ±â€¯295.3 vs. 291.8 ±â€¯233.6, P = 0.036, Mann-Whitney U test), and the higher TCR diversity in tumors was significantly associated with worse cancer outcomes. Thus, we provided a comprehensive comparison of the TCR repertoires between cancer tissues and matched normal lung tissues and demonstrated the presence of distinct T cell immune microenvironments in lung cancer patients.

18.
J Am Chem Soc ; 141(42): 16961-16970, 2019 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-31557018

RESUMO

The generation of metal carbenes from readily available alkynes represents a significant advance in metal carbene chemistry. However, most of these transformations are based on the use of noble-metal catalysts and successful examples of such an asymmetric version are still very scarce. Here a copper-catalyzed enantioselective cascade cyclization of N-propargyl ynamides is reported, enabling the practical and atom-economical construction of diverse chiral polycyclic pyrroles in generally good to excellent yields with wide substrate scope and excellent enantioselectivities (up to 97:3 e.r.). Importantly, this protocol represents the first copper-catalyzed asymmetric diyne cyclization. Moreover, mechanistic studies revealed that the generation of donor/donor copper carbenes is presumably involved in this 1,5-diyne cyclization, which is distinctively different from the related gold catalysis, and thus it constitutes a novel way for the generation of donor/donor metal carbenes.

19.
ACS Nano ; 13(9): 10603-10611, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31498588

RESUMO

Assembly and tessellation of organic species at surfaces are important for the design of advanced materials, particularly for the development of spontaneous self-assemblies of supramolecular systems of increasing complexity. However, there are few examples where the ability to steer the system between supramolecular tessellations has been achieved. Here, we demonstrate a series of steps to reduce and then restore molecular symmetry; those variations impact vertex symmetry and thus generate a series of tessellations that reflect the molecular symmetry. We deposit 4,4'-dihydroxybiphenyl on the Ag(111) surface, then anneal at specific temperatures to achieve stepwise dehydrogenation of the terminal hydroxyls. The symmetry of tessellation vertices in the self-assembled structure also changes, as characterized by scanning tunneling microscopy and synchrotron radiation photoemission spectroscopy. This control over vertex geometry and spontaneous tessellation structure extends our understanding of supramolecular design control and advances architectural complexity for the development of functional surfaces.

20.
Phys Chem Chem Phys ; 21(33): 18338-18345, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31397454

RESUMO

Boron-based clusters possess unusual structural and bonding properties owing to boron's electron-deficiency. We report on the theoretical prediction of two binary B-Na clusters, Na6B7- and Na8B7+, which assume unique sandwich geometries, featuring a perfectly planar B7 wheel and two triangular Na3 or quasi-tetrahedral Na4 ligands. Despite distinct electronegativities of B/Na, the B-Na clusters do not form typical salts. Both sandwich species are dynamically fluxional at 300 K and beyond. Two dynamic modes are observed: an in-plane rotation of the B7 wheel versus twisting of the two Na3/Na4 ligands. Their energy barriers are negligibly small. Natural bond orbital calculations show that the clusters are charge-transfer complexes [Na3]+[B7]3-[Na3]+ and [Na4]2+[B7]3-[Na4]2+, respectively. Chemical bonding analyses indicate that the B7 wheel in the clusters has 6π/6σ double aromaticity and the Na3/Na4 ligands are 2σ aromatic, collectively leading to four-fold π/σ aromaticity. The quasi-tetrahedral Na4 ligand is the simplest example of spherical aromaticity and can also be considered a superatom. Interlayer bonding in the sandwiches is greater than 20 eV, due to electrostatics, which should not be confused with weakly bound species. Four-fold π/σ aromaticity and robust interlayer ionic bonding offer uniform and dilute electron clouds over the sandwiches, facilitating their dual-mode dynamic fluxionality. The Na8B7+ cluster is also a superalkali cation.

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