Giant spin-orbit effects on H-1 and C-13 NMR shifts for uranium(VI) complexes revisited: role of the exchange-correlation response kernel, bonding analyses, and new predictions

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Previous relativistic quantum-chemical predictions of unusually large H-1 and C-13 NMR chemical shifts for ligand atoms directly bonded to a diamagnetic uranium(VI) center (P. Hrobarik, V. Hrobarikova, A. H. Greif and M. Kaupp, Angew. Chem., Int. Ed., 2012, 51, 10884) have been revisited by two- and four-component relativistic density functional methods. In particular, the effect of the exchange-correlation response kernel, which had been missing in the previously used two-component version of the Amsterdam Density Functional program, has been examined. Kernel contributions are large for cases with large spin-orbit (SO) contributions to the NMR shifts and may amount to up to similar to 30% of the total shifts, which means more than a 50 ppm difference for the metal-bonded carbon shifts in some extreme cases. Previous calculations with a PBE-40HF functional had provided overall reasonable predictions, due to cancellation of errors between the missing kernel contributions and the enhanced exact-exchange (EXX) admixture of 40%. In the presence of an exchange-correlation kernel, functionals with lower EXX admixtures give already good agreement with experiments, and the PBE0 functional provides reasonable predictive quality. Most importantly, the revised approach still predicts unprecedented giant H-1 NMR shifts between +30 ppm and more than +200 ppm for uranium(VI) hydride species. We also predict uranium-bonded C-13 NMR shifts for some synthetically known organometallic U(VI) complexes, for which no corresponding signals have been detected to date. In several cases, the experimental lack of these signals may be attributed to unexpected spectral regions in which some of the C-13 NMR shifts can appear, sometimes beyond the usual measurement area. An extremely large uranium-bonded C-13 shift above 550 ppm, near the upper end of the diamagnetic C-13 shift range, is predicted for a known pincer carbene complex. Bonding analyses allow in particular the magnitude of the SO shifts, and of their dependence on the functional, on the ligand position in the complex, and on the overall electronic structure to be better appreciated, and improved confidence ranges for predicted shifts have been obtained

The Birth of a Galaxy: Primordial Metal Enrichment and Stellar Populations

By definition, Population III stars are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas-phase, leading to large characteristic masses. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10^{-6} - 10^{-3.5} Z_\odot. We present an adaptive mesh refinement radiation hydrodynamics simulation that follows the transition from Population III to II star formation. The maximum spatial resolution of 1 comoving parsec allows for individual molecular clouds to be well-resolved and their stellar associations to be studied in detail. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5 percent to nearly the cosmic fraction in halos with merger histories rich in halos above 10^7 solar masses. A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10^{-3} Z_\odot and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Lyman alpha (DLA) systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t-Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.Comment: 11 pages, 7 figures; replaced with accepted version to ApJ; additional movies and images can be found at http://www.astro.princeton.edu/~jwise/research/GalaxyBirth.htm

Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment

We utilize metal-poor stars in the local, ultra-faint dwarf galaxies (UFDs; L_tot < 10^5 L_sun) to empirically constrain the formation process of the first galaxies. Since UFDs have much simpler star formation histories than the halo of the Milky Way, their stellar populations should preserve the fossil record of the first supernova (SN) explosions in their long-lived, low-mass stars. Guided by recent hydrodynamical simulations of first galaxy formation, we develop a set of stellar abundance signatures that characterize the nucleosynthetic history of such an early system if it was observed in the present-day universe. Specifically, we argue that the first galaxies are the product of chemical "one-shot" events, where only one (long-lived) stellar generation forms after the first, Population III, SN explosions. Our abundance criteria thus constrain the strength of negative feedback effects inside the first galaxies. We compare the stellar content of UFDs with these one-shot criteria. Several systems (Ursa Major II, and also Coma Berenices, Bootes I, Leo IV, Segue 1) largely fulfill the requirements, indicating that their high-redshift predecessors did experience strong feedback effects that shut off star formation. We term the study of the entire stellar population of a dwarf galaxy for the purpose of inferring details about the nature and origin of the first galaxies "dwarf galaxy archaeology". This will provide clues to the connection of the first galaxies, the surviving, metal-poor dwarf galaxies, and the building blocks of the Milky Way.Comment: 9 pages (emulateapj), 2 figures, ApJ in pres

Determination of Pericardial Adipose Tissue Increases the Prognostic Accuracy of Coronary Artery Calcification for Future Cardiovascular Events

Objectives: Pericardial adipose tissue (PAT) is associated with coronary artery plaque accumulation and the incidence of coronary heart disease. We evaluated the possible incremental prognostic value of PAT for future cardiovascular events. Methods: 145 patients (94 males, age 60 10 years) with stable coronary artery disease underwent coronary artery calcification (CAC) scanning in a multislice CT scanner, and the volume of pericardial fat was measured. Mean observation time was 5.4 years. Results: 34 patients experienced a severe cardiac event. They had a significantly higher CAC score (1,708 +/- 2,269 vs. 538 +/- 1,150, p 400, 3.5 (1.9-5.4; p = 0.007) for scores > 800 and 5.9 (3.7-7.8; p = 0.005) for scores > 1,600. When additionally a PAT volume > 200 cm(3) was determined, there was a significant increase in the event rate and relative risk. We calculated a relative risk of 2.9 (1.9-4.2; p = 0.01) for scores > 400, 4.0 (2.1-5.0; p = 0.006) for scores > 800 and 7.1 (4.1-10.2; p = 0.005) for scores > 1,600. Conclusions:The additional determination of PAT increases the predictive power of CAC for future cardiovascular events. PAT might therefore be used as a further parameter for risk stratification. Copyright (C) 2012 S. Karger AG, Base

SPECT myocardial perfusion imaging as an adjunct to coronary calcium score for the detection of hemodynamically significant coronary artery stenosis

Background: Coronary artery calcifications (CAC) are markers of coronary atherosclerosis, but do not correlate well with stenosis severity. This study intended to evaluate clinical situations where a combined approach of coronary calcium scoring (CS) and nuclear stress test (SPECT-MPI) is useful for the detection of relevant CAD. Methods: Patients with clinical indication for invasive coronary angiography (ICA) were included into our study during 08/2005- 09/2008. At first all patients underwent CS procedure as part of the study protocol performed by either using a multidetector computed tomography (CT) scanner or a dual-source CT imager. CAC were automatically defined by dedicated software and the Agatston score was semi-automatically calculated. A stress-rest SPECT-MPI study was performed afterwards and scintigraphic images were evaluated quantitatively. Then all patients underwent ICA. Thereby significant CAD was defined as luminal stenosis >= 75% in quantitative coronary analysis (QCA) in >= 1 epicardial vessel. To compare data lacking Gaussian distribution an unpaired Wilcoxon-Test (Mann-Whitney) was used. Otherwise a Students t-test for unpaired samples was applied. Calculations were considered to be significant at a p-value of 0 significant CAD was confirmed by ICA, and excluded in 152/284 (53.5%) patients. Sensitivity for CAD detection by CS alone was calculated as 99.2%, specificity was 30.3%, and negative predictive value was 98.5%. An additional SPECT in patients with CS&gt;0 increased specificity to 80.9% while reducing sensitivity to 87.9%. Diagnostic accuracy was 84.2%. Conclusions: In patients without CS=0 significant CAD can be excluded with a high negative predictive value by CS alone. An additional SPECT-MPI in those patients with CS>0 leads to a high diagnostic accuracy for the detection of CAD while reducing the number of patients needing invasive diagnostic procedure

Favourable neurological outcome following paediatric out-of-hospital cardiac arrest: a retrospective observational study

BACKGROUND Out-of-hospital cardiac arrest (OHCA) in children is rare and can potentially result in severe neurological impairment. Our study aimed to identify characteristics of and factors associated with favourable neurological outcome following the resuscitation of children by the Swiss helicopter emergency medical service. MATERIALS AND METHODS This retrospective observational study screened the Swiss Air-Ambulance electronic database from 01-01-2011 to 31-12-2021. We included all primary missions for patients ≤ 16 years with OHCA. The primary outcome was favourable neurological outcome after 30 days (cerebral performance categories (CPC) 1 and 2). Multivariable linear regression identified potential factors associated with favourable outcome (odd ratio - OR). RESULTS Having screened 110,331 missions, we identified 296 children with OHCA, which we included in the analysis. Patients were 5.0 [1.0; 12.0] years old and 61.5% (n = 182) male. More than two-thirds had a non-traumatic OHCA (67.2%, n = 199), while 32.8% (n = 97) had a traumatic OHCA. Thirty days after the event, 24.0% (n = 71) of patients were alive, 18.9% (n = 56) with a favourable neurological outcome (CPC 1 n = 46, CPC 2 n = 10). Bystander cardiopulmonary resuscitation (OR 10.34; 95%CI 2.29-51.42; p = 0.002) and non-traumatic aetiology (OR 11.07 2.38-51.42; p = 0.002) were the factors most strongly associated with favourable outcome. Factors associated with an unfavourable neurological outcome were initial asystole (OR 0.12; 95%CI 0.04-0.39; p < 0.001), administration of adrenaline (OR 0.14; 95%CI 0.05-0.39; p < 0.001) and ongoing chest compression at HEMS arrival (OR 0.17; 95%CI 0.04-0.65; p = 0.010). CONCLUSION In this study, 18.9% of paediatric OHCA patients survived with a favourable neurologic outcome 30 days after treatment by the Swiss helicopter emergency medical service. Immediate bystander cardiopulmonary resuscitation and non-traumatic OHCA aetiology were the factors most strongly associated with a favourable neurological outcome. These results underline the importance of effective bystander and first-responder rescue as the foundation for subsequent professional treatment of children in cardiac arrest