38 research outputs found
Reinventing the De Mayo reaction: synthesis of 1,5-diketones or 1,5-ketoesters via visible light [2+2] cycloaddition of beta-diketones or beta-ketoesters with styrenes
[EN] A visible light mediated De Mayo reaction between 1,3-diketones and styrenes following a [2+2] cycloaddition pathway via a photosensitization mechanism gives access to 1,5-diketones. The reaction has been applied to substituted styrenes and aryl- and alkyl-substituted ketones. Moreover, the method converts -ketoesters, -amido esters, and -cyano ketones. Seven membered rings, a frequent structural motif of natural products, are also accessible using this methodology.This work was supported by the Deutsche Forschungsgemein-schaft DFG (GRK 1626, Chemical Photocatalysis). L. M. thanks the Alexander von Humboldt foundation for a postdoctoral fellowship. R. M.-H. thanks the DAAD for a short-term research grant. We thank Ms Regina Hoheisel (University of Regensburg) for her assistance in cyclic voltammetry measurements.MartĂnez-Haya, R.; Marzo, L.; König, B. (2018). Reinventing the De Mayo reaction: synthesis of 1,5-diketones or 1,5-ketoesters via visible light [2+2] cycloaddition of beta-diketones or beta-ketoesters with styrenes. Chemical Communications. 54(82):11602-11605. https://doi.org/10.1039/c8cc07044jS11602116055482Mayo, P. D., & Takeshita, H. (1963). PHOTOCHEMICAL SYNTHESES: 6. THE FORMATION OF HEPTANDIONES FROM ACETYLACETONE AND ALKENES. Canadian Journal of Chemistry, 41(2), 440-449. doi:10.1139/v63-061Begley, M. J., Mellor, M., & Pattenden, G. (1983). New synthetic approaches to fused-ring carbocycles based on intramolecular photocycloadditions of 1,3-dione enol esters. Journal of the Chemical Society, Perkin Transactions 1, 1905. doi:10.1039/p19830001905Oppolzer, W. (1982). The intramolecular [2 + 2] photoaddition/cyclobutane-fragmentation sequence in organic synthesis. Accounts of Chemical Research, 15(5), 135-141. doi:10.1021/ar00077a002Crimmins, M. T. (1988). 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Simulation study of discotic molecules in the vicinity of the isotropicâliquid crystal transition
Freezing of hard spheres confined in narrow cylindrical pores
Monte Carlo simulations for the equation of state and phase behavior of hard spheres confined inside
very narrow hard tubes are presented. For pores whose radii are greater than 1.1 hard sphere
diameters, a sudden change in the density and the microscopic structure of the fluid is neatly
observed, indicating the onset of freezing. In the high-density structure the particles rearrange in
such a way that groups of three particles fit in sections across the por
Computer simulation study of the nematicâvapour interface in the GayâBerne model
We present computer simulations of the vapourânematic interface of the GayâBerne model. We considered situations which correspond to either prolate or oblate molecules. We determine the anchoring of the nematic phase and correlate it with the intermolecular potential parameters. On the other hand, we evaluate the surface tension associated to this interface. We find a corresponding states law for the surface tension dependence on the temperature, valid for both prolate and oblate molecules.FundaciĂłn Portuguesa para la Ciencia y la TecnologĂa EXCL / FIS-NAN / 0083/2012Ministerio de EconomĂa y Competitividad FIS2012-32455Junta de AndalucĂa P09-FQM-493
18-crown-6-sodium cholate complex: thermochemistry, structure and stability
18-crown-6, one of the most relevant crown ethers, and sodium cholate, steroidal surfactant classified as natural bile salt, are components of novel, synthesized coordination complex ; 18-crown-6-sodium cholate (18C6âąNaCh). Like crown ethers, bile salts act as building blocks in supramolecular chemistry in order to design new functionalized materials with a desired structure and properties. In order to obtain thermal behavior of this 1:1 coordination complex, thermogravimetry and differential thermal analysis were used, as well as microscopic observations and differential scanning calorimetry. Temperature dependent infrared spectroscopy (IR) gave a detailed view into phase transitions. The structures during thermal treatment were observed with powder X-ray diffraction, and molecular models of the phases are made. Hard, glassy, colorless compound 18C6âąNaCh goes through crystalline â crystalline polymorphic phase transitions at higher temperatures. The room temperature phase is indexed to a triclinic lattice, while in the high temperature phases molecules take randomly one of the two different configurations in the unit cell, resulting in the 2-fold symmetry. The formation of cholesteric liquid crystalline phase occurs simultaneously with partial decomposition, followed by the isotropisation with simultaneous and complete decomposition at much higher temperature, as obtained by IR. The results provide valuable information about the relationship between molecular structure, thermal properties, and stability of the complex, indicating the importance of an appropriate choice of cation, amphiphilic, and crown ether unit in order to synthesize compounds with desired behavior
Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study
Summary
Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally.
Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies
have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of
the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income
countries globally, and identified factors associated with mortality.
Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to
hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis,
exomphalos, anorectal malformation, and Hirschsprungâs disease. Recruitment was of consecutive patients for a
minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical
status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary
intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause,
in-hospital mortality for all conditions combined and each condition individually, stratified by country income status.
We did a complete case analysis.
Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital
diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal
malformation, and 517 with Hirschsprungâs disease) from 264 hospitals (89 in high-income countries, 166 in middleincome
countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male.
Median gestational age at birth was 38 weeks (IQR 36â39) and median bodyweight at presentation was 2·8 kg (2·3â3·3).
Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income
countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups).
Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome
countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries;
pâ€0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients
combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88â4·11],
p<0·0001; middle-income vs high-income countries, 2·11 [1·59â2·79], p<0·0001), sepsis at presentation (1·20
[1·04â1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention
(ASA 4â5 vs ASA 1â2, 1·82 [1·40â2·35], p<0·0001; ASA 3 vs ASA 1â2, 1·58, [1·30â1·92], p<0·0001]), surgical safety
checklist not used (1·39 [1·02â1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed
(ventilation 1·96, [1·41â2·71], p=0·0001; parenteral nutrition 1·35, [1·05â1·74], p=0·018). Administration of
parenteral nutrition (0·61, [0·47â0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65
[0·50â0·86], p=0·0024) or percutaneous central line (0·69 [0·48â1·00], p=0·049) were associated with lower mortality.
Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome,
middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will
be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger
than 5 years by 2030
Stability of Nematic and Smectic Phases in Rod-Like Mesogens with OrientationâDependent Attractive Interactions
Vibrational study of isolated 18-crown-6 ether complexes with alkaline-earth metal cations
Laser infrared multiple photon dissociation (IRMPD) spectroscopy has been employed to probe the C-O and C-C stretching vibrational modes of 18-crown-6 ether (18c6) complexes with alkaline-earth metals (Mg2+, Ca2+, Sr2+ and Ba2+) stored in the cell of a Fourier Transform Ion Cyclotron Resonance mass spectrometer. Computations at the B3LYP/6-311++G(2d,2p) and B3LYP/aug-cc-pVDZ levels of theory agree well with the most salient features of the experimental spectra and allow to characterize the lower energy conformers for each type of complex. A pronounced shift of the C-O stretching band, but not of the C-C band, is found in comparison to the similar IRMPD spectra reported previously for the 18c6 complexes with alkali metals. This is attributed to the tighter coordination and stronger binding of the divalent alkaline-earth cations to the oxygen sites, and to the degree of folding of the crown ether backbone. Nevertheless, the conformational landscape and symmetry constraints of the complexes follow a pattern similar to that found for the alkali metal cations. The most stable conformers evolve from compact D2 geometries for the smaller cations, Mg2+ and Ca2+, to more open C2 configurations for Sr2+ and to a planar D3d structure for Ba2+