170 research outputs found
Explorations of water oxidation catalysis in explicit solvent
In the search for
sustainable energy solutions, the idea of artificial photosynthesis has been
proposed as an approach with which to use water and sunlight to produce
hydrogen. Key in the development of hydrogen production technologies is the
splitting of water using a water oxidation catalyst. In this thesis, the water
splitting catalytic process was investigated using a number of different
computational techniques. Computationally, the water splitting catalytic
process has traditionally been considered statically as a number of snapshots,
and in vacuum. The traditional approaches also often include a number of
correction factors for the charge carriers in the reaction.
But because catalytic processes are dynamic, a novel approach was also
developed in this thesis. With this approach, one can examine the dynamic
transition from one catalytic intermediate to another, in a fully solvated
environment. In optimising water oxidation catalysts it is important to
consider the interaction with the surrounding environment, and how this can
impact the catalytic reaction. Furthermore, in the new approach all the charge
carriersâprotons and electronsâare included in a dynamic simulation. These
techniques give us a better idea of the things needed in the optimisation of
water oxidation catalysts.This research was financed by Leiden University, and co-financed by the Dutch
Ministry of Economic Affairs as part of the BioSolar Cells research project C1.9.
The use of supercomputer facilities was sponsored by NWO Exact and Natural SciencesSolid state NMR/Biophysical Organic Chemistr
Introducing a closed system approach for the investigation of chemical steps involving proton and electron transfer; as illustrated by a copper-based water oxidation catalyst
Solid state NMR/Biophysical Organic Chemistr
Brain aromatase activity and plasma testosterone levels are elevated in aggressive male mice during early ontogeny
Testosterone (T) and estradiol (E(2)) are involved in intraspecific aggressive behavior. Both steroids exert their effects on behavior via the hypothalamus and the amygdala (Am) of the central nervous system (CNS). In these brain areas T is converted to E(2), by the enzyme aromatase. Both the levels of brain aromatase activity (AA) and the effects of T and E(2) on aggressive behavior in adulthood depend on steroidal organization of the CNS during ontogeny. In this study we measured plasma T and in vitro brain AA of male fetuses and neonates derived from two strains of wild house mice, which had been genetically selected for aggression, based upon attack latency. There were no differences in preoptic area (POA) AA levels between selection lines on either embryonic day (E) 17 or 18, or the day after birth (day 1). In the non-aggressive long attack latency (LAL) males the POA AA increases with age, i.e. was higher on E18 than on E17, which is correlated with brain weight (BrW). This was in contrast to aggressive short attack latency (SAL) fetuses, which only showed a slight, but not significant difference between embryonic days or, a correlation with BrW. Neonatally, the POA AA of LAL males tended to decrease in contrast to SAL males. However, SAL neonates had a higher AA in the amygdala (Am) than LAL neonates, whereas no differences exist in the anterior hypothalamus. Thus, a differential brain AA distribution exists in SAL and LAL pups. At day 1 SAL: males show higher AA in the Am than in the hypothalamus (POA + AH), whereas in the LAL strain the AA did not differ between these brain areas. In the LAL males plasma T levels decreased from E17 to day 1, whereas the SAL neonates (day 1) exhibited higher circulating T concentrations than LAL neonates. These results suggest a T-independent aromatase induction prenatally in both selection lines, whereas neonatally the higher plasma T level in the SAL line coincides with higher AA levels:in the Am. Accordingly, a differential pattern of E(2) formation exists in the brains of the two selection lines during ontogeny. The variation in circulating T and maximal brain E(2) formation around birth might result in a differential organization of adult CNS sensitivity to sex steroids and accordingly differences in aggressive behavior.</p
Energetic Effects of a Closed System Approach Including Explicit Proton and Electron Acceptors as Demonstrated by a Mononuclear Ruthenium Water Oxidation Catalyst
Solid state NMR/Biophysical Organic Chemistr
The role of surgery for stage I non-small cell lung cancer in octogenarians in the era of stereotactic body radiotherapy in the Netherlands
ObjectivesResection is the standard treatment for stage I non-small cell lung cancer (NSCLC) in operable patients. Stereotactic body radiotherapy (SBRT) is recommended for inoperable patients. A shift from surgery to SBRT is expected in elderly patients due to increased frailty and competing risks. We assessed the current influence of age on treatment decision-making and overall survival (OS).Materials and methodsWe performed a retrospective cohort study using data from patients with clinical stage I NSCLC diagnosed in 2012â2016 and treated with lobectomy, segmentectomy, wedge resection, or SBRT, retrieved from the Netherlands Cancer Registry. Patient characteristics and OS were compared between SBRT and (sub)lobar resection for patients aged 18â79 and â„80 years.Results and Conclusion8764 patients treated with lobectomy (nâŻ=âŻ4648), segmentectomy (nâŻ=âŻ122), wedge resection (nâŻ=âŻ272), or SBRT (nâŻ=âŻ3722) were included. In 2012â2016, SBRT was increasingly used for octogenarians and younger patients from 75.3% to 83.7% and from 30.8% to 43.2%, respectively. Five-year OS in the whole population was 70% after surgery versus 39% after SBRT and 50% versus 27% in octogenarians. After correction for age, gender, year of diagnosis, and clinical T-stage, OS was equal after lobectomy and SBRT in the first 2 years after diagnosis. However, after >2 years, OS was better after lobectomy than after SBRT.SBRT is the prevailing treatment in octogenarians with stage I NSCLC. While surgery is associated with better OS than SBRT, factors other than treatment modality (e.g. comorbidity) may have had a significant impact on survival. The wider application of SBRT in octogenarians likely reflects the frailty of this group. Registries and trials are required to identify key determinants of frailty in this specific population to improve patient selection for surgery or SBRT.Stem cells & developmental biolog
Electrochemical and Spectroscopic Study of Mononuclear Ruthenium Water Oxidation Catalysts: A Combined Experimental and Theoretical Investigation
Solid state NMR/Biophysical Organic Chemistr
Near-Unity Electrochemical CO2to CO Conversion over Sn-Doped Copper Oxide Nanoparticles
Bimetallic electrocatalysts have emerged as a viable strategy to tune the electrocatalytic CO2 reduction reaction (eCO2RR) for the selective production of valuable base chemicals and fuels. However, obtaining high product selectivity and catalyst stability remain challenging, which hinders the practical application of eCO2RR. In this work, it was found that a small doping concentration of tin (Sn) in copper oxide (CuO) has profound influence on the catalytic performance, boosting the Faradaic efficiency (FE) up to 98% for carbon monoxide (CO) at -0.75 V versus RHE, with prolonged stable performance (FE > 90%) for up to 15 h. Through a combination of ex situ and in situ characterization techniques, the in situ activation and reaction mechanism of the electrocatalyst at work was elucidated. In situ Raman spectroscopy measurements revealed that the binding energy of the crucial adsorbed *CO intermediate was lowered through Sn doping, thereby favoring gaseous CO desorption. This observation was confirmed by density functional theory, which further indicated that hydrogen adsorption and subsequent hydrogen evolution were hampered on the Sn-doped electrocatalysts, resulting in boosted CO formation. It was found that the pristine electrocatalysts consisted of CuO nanoparticles decorated with SnO2 domains, as characterized by ex situ high-resolution scanning transmission electron microscopy and X-ray photoelectron spectroscopy measurements. These pristine nanoparticles were subsequently in situ converted into a catalytically active bimetallic Sn-doped Cu phase. Our work sheds light on the intimate relationship between the bimetallic structure and catalytic behavior, resulting in stable and selective oxide-derived Sn-doped Cu electrocatalysts
A search for radio emission from double-neutron star merger GW190425 using Apertif
ContextDetection of the electromagnetic emission from coalescing binary neutron stars (BNS) is important for understanding the merger and afterglow. Aims. We present a search for a radio counterpart to the gravitational-wave (GW) source GW190425, a BNS merger, using Apertif on the Westerbork Synthesis Radio Telescope (WSRT). MethodsWe observed a field of high probability in the associated localisation region for three epochs at ÎT\ue2âŹ., =\ue2âŹ., 68, 90, 109 d post merger. We identified all sources that exhibit flux variations consistent with the expected afterglow emission of GW190425. We also looked for possible transients. These are sources that are only present in one epoch. In addition, we quantified our ability to search for radio afterglows in the fourth and future observing runs of the GW detector network using Monte Carlo simulations. ResultsWe found 25 afterglow candidates based on their variability. None of these could be associated with a possible host galaxy at the luminosity distance of GW190425. We also found 55 transient afterglow candidates that were only detected in one epoch. All of these candidates turned out to be image artefacts. In the fourth observing run, we predict that up to three afterglows will be detectable by Apertif. ConclusionsWhile we did not find a source related to the afterglow emission of GW190425, the search validates our methods for future searches of radio afterglows
Translational characterization of the temporal dynamics of metabolic dysfunctions in liver, adipose tissue and the gut during diet-induced NASH development in Ldlr-/-.Leiden mice
BackgroundNAFLD progression, from steatosis to inflammation and fibrosis, results from an interplay of intra- and extrahepatic mechanisms. Disease drivers likely include signals from white adipose tissue (WAT) and gut. However, the temporal dynamics of disease development remain poorly understood.MethodsHigh-fat-diet (HFD)-fed Ldlrâ/â.Leiden mice were compared to chow-fed controls. At t = 0, 8, 16, 28 and 38w mice were euthanized, and liver, WAT depots and gut were analyzed biochemically, histologically and by lipidomics and transcriptomics together with circulating factors to investigate the sequence of pathogenic events and organ cross-talk during NAFLD development.ResultsHFD-induced obesity was associated with an increase in visceral fat, plasma lipids and hyperinsulinemia at t = 8w, along with increased liver steatosis and circulating liver damage biomarkers. In parallel, upstream regulator analysis predicted that lipid catabolism regulators were deactivated and lipid synthesis regulators were activated. Subsequently, hepatocyte hypertrophy, oxidative stress and hepatic inflammation developed. Hepatic collagen accumulated from t = 16 w and became pronounced at t = 28â38 w. Epididymal WAT was maximally hypertrophic from t = 8 w, which coincided with inflammation development. Mesenteric and subcutaneous WAT hypertrophy developed slower and did not appear to reach a maximum, with minimal inflammation. In gut, HFD significantly increased permeability, induced a shift in microbiota composition from t = 8 w and changed circulating gut-derived metabolites.ConclusionHFD-fed Ldlrâ/â.Leiden mice develop obesity, dyslipidemia and insulin resistance, essentially as observed in obese NAFLD patients, underlining their translational value. We demonstrate that marked epididymal-WAT inflammation, and gut permeability and dysbiosis precede the development of NAFLD stressing the importance of a multiple-organ approach in the prevention and treatment of NAFLD.Proteomic
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