The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring ...sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of β-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.
Both Aroclor and non-Aroclor sources of airborne polychlorinated biphenyls (PCBs) were found in residential homes. We deployed passive air samplers at 16 residences and found PCB-47, PCB-51, and ...PCB-68 to account for up to 50% of measured indoor ΣPCBs (2700 pg m–3). Although PCB-47 and PCB-51 are neurotoxins present in Aroclor mixtures (<2.5 and <0.3 wt %, respectively), we found them at much higher levels than expected for any Aroclor source. PCB-68 is not present in Aroclor mixtures. Another non-Aroclor congener, PCB-11, a byproduct of pigment manufacturing, was found inside and outside of every household and was frequently the predominate congener. We conducted direct measurements of surface emissions and identified finished cabinetry to be a major source of PCB-47, PCB-51, and PCB-68. We hypothesize that these congeners are inadvertent byproducts of polymer sealant manufacturing and produced from the decomposition of 2,4-dichlorobenzoyl peroxide used as an initiator in free-radical polymerization of polyester resins. The presence of these three compounds in polymer products, such as silicone, has been widely noted, but to our knowledge they have never been shown to be a significant environmental source of PCBs.
Porous and fractured aquifers exist in the area of Hurghada, Eastern Desert of Egypt, whose recharge processes through the common flash floods are not identified. Hydrochemical parameters, stable ...isotopes
18
O,
2
H and tritium in floodwater and groundwater were applied in the area subject to study. Additionally, He isotopes were investigated in the deep wells in the faulted zone at the Abu Shaar Plateau.
3
H activity in all sampled points lies below the detection limit excluding a recent recharge component in groundwater. However, the hydrochemical ratios and the stable isotope signature confirm that the shallow wells and springs (Red Sea Hills group) are being recharged from modern precipitation. The hydrochemical parameters of the deep wells at the Abu Shaar Plateau (coastal plain group) confirm another origin for the ions rather than the modern precipitation. Together with the
18
O and
2
H values, the Br/Cl ratio of this group confirms the absence of seawater intrusion component and the role of the fault as a hydraulic barrier. These
18
O and
2
H values deviate from the GMWL confirming an evaporation effect and colder infiltration conditions and reveal strongly a possible mixing with the Nubian Sandstone in the region. The
3
He/
4
He ratio confirms a mantle contribution of 2% from the total He components.
Cardiac magnetic resonance imaging (cMRI) now rates among the established diagnostic procedures for the clarification of cardiac disease patterns. In modern clinical electrophysiology, apart from ...providing basic cardiac diagnostics of patients prior to interventional procedures, the imaging method enables the three-dimensional reconstruction of cardiac target structures of the planned ablation procedure, which can significantly improve the safety and efficacy of the intervention. Furthermore, cMRI has a high significance with respect to risk stratification during implantable cardioverter defibrillator (ICD) evaluation. In addition to an exact determination of ventricular function, its capability for detailed tissue characterization enables the visualization and quantification of fibrotic lesions and scar tissue as potential arrhythmogenic triggers. This anatomic assignment also enables an increased accuracy of the ablation of substrate-based arrhythmia. In comparison to this the interventional cMRI as a direct interface between cMRI and invasive electrophysiology represents a comparably new field of application. Initial clinical experiences in the field of ablation of typical atrial fibrillation could not only confirm the feasibility of the concept but also enabled recognition of the clear advantages of an imaging-guided electrophysiological procedure.
Reaction of the bridged bisbenzimidazolium salts 2,6-bis(N 1-alkyl-N 3 -methylenebenzimidazolium)pyridine dibromide (1, alkyl = methyl; 2, alkyl = ethyl; 3, alkyl = n-propyl; 4, alkyl = n-butyl) with ...palladium acetate yields the palladium pincer complexes of type Pd(L)BrBr, 5−8 (L = 2,6-bis(N 1-alkyl-N 3-methylenebenzimidazolin-2-ylidene)pyridine). Compounds 1, 2·0.5MeOH, 4·CH2Cl2, and 6·MeOH (L = 2,6-bis(N 1-ethyl-N 3-methylenebenzimidazolin-2-ylidene)pyridine) were characterized by X-ray diffraction. The molecular structure of 6 shows a distorted square-planar coordination geometry for the palladium atom. In situ generated pincer complexes 5−8 have been tested as catalysts in Heck-type coupling reactions of different aryl halides with styrene.
PCB Emissions from Paint Colorants Jahnke, Jacob C; Hornbuckle, Keri C
Environmental science & technology,
05/2019, Letnik:
53, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Polychlorinated biphenyls (PCBs) are known human carcinogens that are byproducts of pigment manufacturing and found in colorants used to tint consumer paints sold in the United States and elsewhere. ...PCBs have the potential to be emitted from paint containing these pigments. To quantify the gas-phase emissions of ∑PCBs, we used polyurethane foam (PUF) to capture emissions from freshly applied colorants. Some PCB emissions were detected on the PUF after 1 day. After 6 weeks, all PCBs found in the colorant were also found on the PUF. Even the fully chlorinated PCB209 was emitted from green colorant. Mono- and dichlorinated PCBs were released from the colorant at a faster rate than the higher chlorinated congeners. By the end of the experiment, all the lower chlorinated congeners were absent from the colorant while more than 75% of the higher chlorinated congeners remained in the sample. The rate of PCB emissions from paint colorants is a function of the surface/air equilibrium coefficient, and the presence of water accelerates the emissions. Although concentrations of PCBs in colorants are less than 285 ng g–1, PCB emissions from colorants in paint can cause environmentally relevant concentrations of ≥500 pg m–3 within hours of painting a room.
Many polychlorinated biphenyl (PCB) congeners are found in both legacy Aroclor mixtures and modern materials, and both contribute to PCBs levels in ambient air. The various sources of PCBs make it ...difficult to quantify the relative importance of emissions from remaining legacy materials and emissions of PCBs released from production and use of modern products. To address this challenge, we utilized active and passive sampling, analytical methods optimized for PCBs, and Positive Matrix Factorization (PMF) and cos theta to examine the chemical signature of PCBs in Chicago air. Here we report our findings for over 640 samples collected over 7 years and analyzed for all 209 congeners. We conclude that Aroclor sources (1254, 1016/1242, and 1260) are consistent and dominant contributors to Chicago air. However, non-Aroclors sources accounted for 13%–16% of the total PCBs measured. Our analysis indicates non-Aroclor sources explain 99% of PCB11, 90% of PCB 68, and 58–69% of congeners with 8 to 10 chlorines in Chicago air. All of these are known to be emitted from paints or silicone polymers. Additionally, we identified over 20 congeners that have non-Aroclor contributions of more than 50% including PCB 3 (4-monochlorobiphenyl, 83% non-Aroclor) as well as 7 congeners of unknown sources: PCBs 43, 46, 55, 89, 96, 137, and 139 + 140. Non-Aroclor emission sources contribute to the entire range of congeners from mono- to deca-chlorobiphenyls. We found evidence of highly localized non-Aroclor sources including a signature similar to that of green paint. We also found source signals similar to the PCB congeners volatilizing from and absorbing to neighboring Lake Michigan. The measured profiles vary from season to season: lower chlorinated congeners dominate in winter months while higher chlorinated congeners contribute more in summer.
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•Non-Aroclor emission sources contribute to all homolog groups.•Chicago air has a signal of PCB congeners volatilizing from and absorbing to neighboring Lake Michigan•Non-Aroclor sources account for 13%–16% of the total PCBs measured.
Dobutamine stress MR (DSMR) is highly accurate for the detection of inducible wall motion abnormalities (IWMAs). Adenosine has a more favorable safety profile and is well established for the ...assessment of myocardial perfusion. We evaluated the diagnostic value of IWMAs during dobutamine and adenosine stress MR and adenosine MR perfusion compared with invasive coronary angiography.
Seventy-nine consecutive patients (suspected or known coronary disease, no history of prior myocardial infarction) scheduled for cardiac catheterization underwent cardiac MR (1.5 T). After 4 minutes of adenosine infusion (140 microg x kg(-1) x min(-1) for 6 minutes), wall motion was assessed (steady-state free precession), and subsequently perfusion scans (3-slice turbo field echo-echo planar imaging; 0.05 mmol/kg Gd-BOPTA) were performed. After a 15-minute break, rest perfusion was imaged, followed by standard DSMR/atropine stress MR. Wall motion was classified as pathological if > or =1 segment showed IWMAs. The transmural extent of inducible perfusion deficits (<25%, 25% to 50%, 51% to 75%, and >75%) was used to grade segmental perfusion. Quantitative coronary angiography was performed with significant stenosis defined as >50% diameter stenosis. Fifty-three patients (67%) had coronary artery stenoses >50%; sensitivity and specificity for detection by dobutamine and adenosine stress and adenosine perfusion were 89% and 80%, 40% and 96%, and 91% and 62%, respectively. Adenosine IWMAs were seen only in segments with >75% transmural perfusion deficit.
DSMR is superior to adenosine stress for the induction of IWMAs in patients with significant coronary artery disease. Visual assessment of adenosine stress perfusion is sensitive with a low specificity, whereas adenosine stress MR wall motion is highly specific because it identifies only patients with high-grade perfusion deficits. Thus, DSMR is the method of choice for current state-of-the-art treatment regimens to detect ischemia in patients with suspected or known coronary artery disease but no history of prior myocardial infarction.
Patients with cardiac implantable electronic devices (CIED) necessitate comprehensive cardiovascular magnetic resonance (CMR) examinations. The aim of this study was to provide data on CMR image ...quality and feasibility of functional assessment of the right heart in patients with CIED depending on the device type and imaging sequence used.
120 CIED carriers (Insertable cardiac monitoring system, n = 13; implantable loop-recorder, n = 22; pacemaker, n = 30; implantable cardioverter-defibrillator (ICD), n = 43; and cardiac resynchronization therapy defibrillator (CRT-D), n = 12) underwent clinically indicated CMR imaging using a 1.5 T. CMR protocols consisted of cine imaging and myocardial tissue characterization including T1-and T2-weighted blackblood imaging and late gadolinium enhancement (LGE) imaging. Image quality was evaluated with regard to device-related imaging artifacts per right-ventricular (RV) segment.
RV segmental evaluability was influenced by the device type and CMR imaging sequence: Cine steady-state-free-precision (SSFP) imaging was found to be non-diagnostic in patients with ICD/CRT-D and implantable loop recorders; a significant improvement of image quality was achieved when using cine turbo-field-echo (TFE) sequences with a further improvement on post-contrast TFE imaging. LGE scans were artifact-free in at least 91% of RV segments with best results in patients with a pacemaker or an insertable cardiac monitoring system.
In patients with CIED, artifact-free CMR imaging of the right ventricle was performed in the majority of patients and resulted in highly reproducible evaluability of RV functional parameters. This finding is of particular importance for the diagnosis and follow-up of right-ventricular diseases.
•Artifact-free right heart CMR imaging in CIED patients succeeded in the majority.•CMR image quality resulted in highly reproducible evaluability of RV parameters.•Excellent CMR image quality was achieved even with non-MR-conditional devices.
Follow-up after acute myocarditis is important to detect persisting myocardial dysfunction. However, recovery of atrial function has not been evaluated after acute myocarditis so far. Thirty-five ...patients with strictly defined acute myocarditis underwent cardiovascular magnetic resonance (CMR, 1.5 T) in the acute stage at baseline (BL) and at 3 months follow-up (FU). The study population included 13 patients with biopsy-proven “cardiomyopathy-like” myocarditis (CLM) and 22 patients with “infarct-like” (ILM) clinical presentation. CMR feature tracking (FT) was performed on conventional cine SSFP sequences. Median LA-GLS increased from 33.2 (14.5; 39.2) at BL to 37.0% (25.2; 44.1, P = 0.0018) at FU in the entire study population. Median LA-GLS also increased from 36.7 (26.5; 42.3) at BL to 41.3% (34.5; 44.8, P = 0.0262) at FU in the ILM subgroup and from 11.3 (6.4; 21.1) at BL to 21.4% (14.2; 30.7, P = 0.0186) at FU in the CLM subgroup. Median RA-GLS significantly increased from BL with 30.8 (22.5; 37.0) to FU with 33.7% (26.8; 45.4, P = 0.0027) in the entire study population. Median RA-GLS also significantly increased from 32.7 (25.8; 41.0) at BL to 35.8% (27.7; 48.0, P = 0.0495) at FU in the ILM subgroup and from 22.8 (13.1; 33.9) at BL to 31.0% (26.0; 40.8, P = 0.0266) at FU in the CLM subgroup. Our findings demonstrate recovery of LA and RA function by CMR-FT strain analyses in patients after acute myocarditis independent from clinical presentation. Monitoring of atrial strain could be an important tool for an individual assessment of healing after acute myocarditis.
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