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.

ObjectiveTo determine the clinical manifestations, risk factors, and maternal and perinatal outcomes in pregnant and recently pregnant women with suspected or confirmed coronavirus disease 2019 (covid-19). DesignLiving systematic review and meta-analysis. Data sOurcesMedline, Embase, Cochrane database, WHO COVID-19 database, China National Knowledge Infrastructure (CNKI), and Wanfang databases from 1 December 2019 to 26 June 2020, along with preprint servers, social media, and reference lists. stuDy selectiOnCohort studies reporting the rates, clinical manifestations (symptoms, laboratory and radiological findings), risk factors, and maternal and perinatal outcomes in pregnant and recently pregnant women with suspected or confirmed covid-19. Data extractiOnAt least two researchers independently extracted the data and assessed study quality. Random effects meta-analysis was performed, with estimates pooled as odds ratios and proportions with 95% confidence intervals. All analyses will be updated regularly. results 77 studies were included. Overall, 10% (95% confidence interval 7% to14%; 28 studies, 11 432 women) of pregnant and recently pregnant women attending or admitted to hospital for any reason were diagnosed as having suspected or confirmed covid-19. The most common clinical manifestations of covid-19 in pregnancy were fever (40%) and cough (39%). Compared with non-pregnant women of reproductive age, pregnant and recently pregnant women with covid-19 were less likely to report symptoms of fever (odds ratio 0.43, 95% confidence interval 0.22 to 0.85; I 2 =74%; 5 studies; 80 521 women) and myalgia (0.48, 0.45 to 0.51; I 2 =0%; 3 studies; 80 409 women) and were more likely to need admission to an intensive care unit (1.62, 1.33 to 1.96; I 2 =0%) and invasive ventilation (1.88, 1.36 to 2.60; I 2 =0%; 4 studies, 91 606 women). 73 pregnant women (0.1%, 26 studies, 11 580 women) with confirmed covid-19 died from any cause. Increased maternal age (1.78, 1.25 to 2.55; I 2 =9%; 4 studies; 1058 women), high body mass index (2.38, 1.67 to 3.39; I 2 =0%; 3 studies; 877 women), chronic hypertension (2.0, 1.14 to 3.48; I 2 =0%; 2 studies; 858 women), and pre-existing diabetes (2.51, 1.31 to 4.80; I 2 =12%; 2 studies; 858 women) were associated with severe covid-19 in pregnancy. Pre-existing maternal comorbidity was a risk factor for admission to an intensive care unit (4.21, 1.06 to 16.72; I 2 =0%; 2 studies; 320 women) and invasive ventilation (4.48, 1.40 to 14.37; I 2 =0%; 2 studies; 313 women). Spontaneous preterm birth rate was 6% (95% confidence interval 3% to 9%; I 2 =55%; 10 studies; 870 women) in women with covid-19. The odds of any preterm birth (3.01, 95% confidence interval 1.16 to 7.85; I 2 =1%; 2 studies; 339 women) was high in pregnant women with covid-19 compared with those without the disease. A quarter of all neonates born to mothers with covid-19 were admitted to the neonatal unit (25%) and were at increased risk of admission (odds ratio 3.13, 95% confidence interval 2.05 to 4.78, I 2 =not estimable; 1 st...

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