Hydride complexes of copper, silver, and gold encompass a broad array of structures, and their distinctive reactivity has enabled dramatic recent advances in synthesis and catalysis. This Review ...summarizes the synthesis, characterization, and key stoichiometric reactions of isolable or observable coinage metal hydrides. It discusses catalytic processes in which coinage metal hydrides are known or probable intermediates, and presents mechanistic studies of selected catalytic reactions. The purpose of this Review is to convey how developments in coinage metal hydride chemistry have led to new organic transformations, and how developments in catalysis have in turn inspired the synthesis of reactive new complexes.
Clostridium difficile is the most commonly reported nosocomial pathogen in the United States and is an urgent public health concern worldwide. Over the past decade, incidence, severity and costs ...associated with C. difficile infection (CDI) have increased dramatically. CDI is most commonly initiated by antibiotic-mediated disruption of the gut microbiota; however, non-antibiotic-associated CDI cases are well documented and on the rise. This suggests that unexplored environmental, nutrient and host factors probably influence CDI. Here we show that excess dietary zinc (Zn) substantially alters the gut microbiota and, in turn, reduces the minimum amount of antibiotics needed to confer susceptibility to CDI. In mice colonized with C. difficile, excess dietary Zn severely exacerbated C. difficile-associated disease by increasing toxin activity and altering the host immune response. In addition, we show that the Zn-binding S100 protein calprotectin has antimicrobial effects against C. difficile and is an essential component of the innate immune response to CDI. Taken together, these data suggest that nutrient Zn levels have a key role in determining susceptibility to CDI and severity of disease, and that calprotectin-mediated metal limitation is an important factor in the host immune response to C. difficile.
The expanded-ring N-heterocyclic carbenes 6Dipp and 7Dipp (6Dipp = 1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene and 7Dipp = ...1,3-bis(2,6-diisopropylphenyl)-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene) support isolable neutral copper hydride dimers. (6Dipp)CuH2 reacts with 1-hexene to give (6Dipp)copper(I) hexyl by 1,2-insertion and with benzyl isonitrile to afford an η1-formimidoyl by 1,1-insertion.
The amount of plastic waste resulting from agricultural practices is increasing and this trend is expected to continue. Although plastics are essential for certain farming tasks, their impact on the ...environment is becoming a major issue of concern. Mismanaged larger plastics can disintegrate into microplastics and make their way into soils, surface and groundwater sources. Microplastics are extremely persistent and have the potential to facilitate the transfer of contaminants through the environment, potentially affecting terrestrial and aquatic wildlife. A descriptive survey was conducted on a sample of farmers (n = 430) in Ireland to assess their attitudes on agricultural plastic waste management and their awareness and perceptions of the impacts of microplastics and plastics on the environment. This study found that most farmers (88.2%) are concerned about the amount of plastic waste generated by farming activities. Agricultural plastic disposal methods vary and recycling rates mostly depend on the type of plastic, the cost of recycling and access to facilities. Most farmers view agricultural plastics negatively due to their impact on the environment but also because of the monetary and logistical burdens associated with them. Farmers were relatively aware of microplastics (57.5%), but overall more farmers felt they knew more about plastic pollution than microplastic pollution and these issues in aquatic systems. This was also evident when it came to their perception of the risks plastics pose on the environment with more farmers believing that aquatic environments are at greater risk than the terrestrial environments. Future research efforts must focus on plastic and microplastic pollutions in soils to inform policy-makers and to create greater public awareness. In addition to this, several developments are needed in a collective effort by governments, policy-makers and other stakeholders to reduce plastic and microplastic problems in agriculture.
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•Most farmers are concerned about the amount of plastic waste generated by agriculture.•Agricultural plastic disposal methods vary by the type of plastic, the cost of recycling and access to facilities.•Farmers understand that plastics are necessary for tasks on the farm.•Farmers also associate agricultural plastics with logistical and monetary burdens and their negative impact on the environment.•Most farmers believe that aquatic environments are under more threat by plastic pollution in comparison to the terrestrial environments.
Catalysts consisting of atomically dispersed Pt (Ptiso) species on CeO2 supports have received recent interest due to their potential for efficient metal utilization in catalytic convertors. However, ...discrepancies exist between the behavior (reducibility, interaction strength with adsorbates) of high surface area Ptiso/CeO2 systems and of well-defined surface science and computational model systems, suggesting differences in Pt local coordination in the two classes of materials. Here, we reconcile these differences by demonstrating that high surface area Ptiso/CeO2 synthesized at low Pt loadings (<0.1% weight) exhibit resistance to reduction and sintering up to 500 °C in 0.05 bar H2 and minimal interactions with COproperties previously seen only for model system studies. Alternatively, Pt loadings >0.1 weight % produce a distribution of sub-nanometer Pt structures, which are difficult to distinguish using common characterization techniques, and exhibit strong interactions with CO and weak resistance to sintering, even in 0.05 bar H2 at 50 °Cproperties previously seen for high surface area materials. This work demonstrates that low metal loadings can be used to selectively populate the most thermodynamically stable adsorption sites on high surface area supports with atomically dispersed metals. Further, the site uniformity afforded by this synthetic approach is critical for the development of relationships between atomic scale local coordination and functional properties. Comparisons to recent studies of Ptiso/TiO2 suggest a general compromise between the stability of atomically dispersed metal catalysts and their ability to interact with and activate molecular species.
Unstable distal clavicular fractures treated surgically are associated with high failure rates and hardware-related complications. Newer techniques have shown promising early clinical results with ...fewer hardware complications; however, their biomechanical performance has not been assessed. This study biomechanically compared a distal-third locking plate with 3 newer techniques that incorporate coracoid fixation into the construct.
The study randomized 36 adult fresh frozen cadaveric shoulders to 4 groups: (1) distal-third locking plate (P); (2) distal-third locking plate with a coracoid button augmentation (P + CB); (3) coracoclavicular button (CB); and (4) coracoclavicular button with coracoclavicular ligament reconstruction using semitendinosus allograft (CB + CC). After fixation, each specimen was stressed in the coronal plane. Cyclic displacement, load at 10-mm displacement, and ultimate load to failure were measured.
All 3 experimental groups biomechanically outperformed the locking plate. Mean load to failure was significantly higher in the CB (343 ± 76 N) and CB + CC (349 ± 94 N) groups compared with the P group (193 ± 52 N). There was also significantly less cyclic displacement in the CB (4.3 ± 1.9 mm) and CB + CC (4.4 ± 1.9 mm) groups compared with the P group (8.2 ± 2.9 mm). With respect to load at 10 mm of displacement, which essentially measures a clinical failure, the P + CB (235 ± 112 N), CB (253 ± 111 N), and CB+CC (238 ± 76 N) experimental groups significantly outperformed the P group (96 ± 29 N).
CB and CB + CC techniques demonstrated more than 75% greater strength than the traditional locking plate alone. Coupled with greater overall construct strength and lower-profile hardware, these newer techniques may result in improved clinical outcome and fewer hardware-related complications.
N-Heterocyclic carbenes (NHCs) bind strongly to gold and other metals. This work experimentally probes the effect of NHCs on the work function (WF) of gold for the first time, theoretically analyzes ...the origin of this effect, and examines the effectiveness of NHC-modified gold as an electron-injecting electrode. UV photoelectron spectroscopy shows the WF of planar gold is reduced by nearly 2 eV to values of 3.3–3.5 eV. This effect is seen for NHCs with various heterocyclic cores, and with either small or large N,N′-substituents. DFT calculations indicate the WF reduction results from both the interface dipole formed between the NHC and the gold and from the NHC molecular dipole. For N,N′-diisopropyl-NHCs, an important contributor to the former is charge transfer associated with coordination of the carbene carbon atom to gold. In contrast, the carbene carbon of N,N′-2,6-diisopropylphenyl-NHCs is not covalently bound to gold, resulting in a lower interface dipole; however, a larger molecular dipole partially compensates for this. Single-layer C60 diodes with NHC-modified gold as the bottom electrode demonstrate high rectification ratios and show that these electrodes can act as effective electron-injecting contacts, suggesting they may be useful for a variety of materials applications.
The electrophilic fluorination of N-heterocyclic carbene (NHC) copper(I) vinyls results in fluoroalkene formation. Alkynes can be converted to cis-(β-fluorovinyl)boronates by a reaction with an ...(NHC)copper(I) boryl generated in situ, followed by N-fluorobenzenesulfonimide (NFSI). This sequence gives rise to anti-Markovnikov fluorination products from terminal alkynes. Oxidation of a cis-(β-fluorovinyl)trifluoroboronate yields an α-fluoroketone, whereas a palladium-catalyzed Suzuki–Miyaura coupling yields a tetrasubstituted monofluoroalkene.
The selective estrogen-receptor modulator (SERM) tamoxifen became the first U.S. Food and Drug Administration (FDA)-approved agent for reducing breast cancer risk but did not gain wide acceptance for ...prevention, largely because it increased endometrial cancer and thromboembolic events. The FDA approved the SERM raloxifene for breast cancer risk reduction following its demonstrated effectiveness in preventing invasive breast cancer in the Study of Tamoxifen and Raloxifene (STAR). Raloxifene caused less toxicity (versus tamoxifen), including reduced thromboembolic events and endometrial cancer. In this report, we present an updated analysis with an 81-month median follow-up. STAR women were randomly assigned to receive either tamoxifen (20 mg/d) or raloxifene (60 mg/d) for 5 years. The risk ratio (RR; raloxifene:tamoxifen) for invasive breast cancer was 1.24 (95% confidence interval CI, 1.05-1.47) and for noninvasive disease, 1.22 (95% CI, 0.95-1.59). Compared with initial results, the RRs widened for invasive and narrowed for noninvasive breast cancer. Toxicity RRs (raloxifene:tamoxifen) were 0.55 (95% CI, 0.36-0.83; P = 0.003) for endometrial cancer (this difference was not significant in the initial results), 0.19 (95% CI, 0.12-0.29) for uterine hyperplasia, and 0.75 (95% CI, 0.60-0.93) for thromboembolic events. There were no significant mortality differences. Long-term raloxifene retained 76% of the effectiveness of tamoxifen in preventing invasive disease and grew closer over time to tamoxifen in preventing noninvasive disease, with far less toxicity (e.g., highly significantly less endometrial cancer). These results have important public health implications and clarify that both raloxifene and tamoxifen are good preventive choices for postmenopausal women with elevated risk for breast cancer.
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