299 research outputs found
The Catalytic Enantioselective, Protecting Group-Free Total Synthesis of (+)-Dichroanone
Herein we report the first enantioselective total synthesis of (+)-dichroanone, confirming the absolute configuration of the natural product. This protecting group-free route features the first application of our enantioselective Tsuji allylation in the context of a natural product total synthesis. Additionally, this 11-step preparation of the molecule from commercial material features a novel Kumada-aromatization strategy and a rapid sequence for the conversion of a phenol to a hydroxy-p-benzoquinone
A Facile and Modular Synthesis of Phosphinooxazoline Ligands
The copper(I) iodide catalyzed phosphine/aryl halide coupling procedure of Buchwald et al. provides modular, robust, and scaleable access to phosphinooxazoline (PHOX) ligands. The advantages of this method are highlighted by the convenient synthesis of PHOX ligands with varied steric and electronic properties, which would be challenging to synthesize by other protocols
The Catalytic Enantioselective, Protecting Group-Free Total Synthesis of (+)-Dichroanone
Herein we report the first enantioselective total synthesis of (+)-dichroanone, confirming the absolute configuration of the natural product. This protecting group-free route features the first application of our enantioselective Tsuji allylation in the context of a natural product total synthesis. Additionally, this 11-step preparation of the molecule from commercial material features a novel Kumada-aromatization strategy and a rapid sequence for the conversion of a phenol to a hydroxy-p-benzoquinone
Depth-resolved measurements of the Meissner screening profile in surface-treated Nb
We report depth-resolved measurements of the Meissner screening profile in
several surface-treated Nb samples using low-energy muon spin rotation
(LE-SR). In these experiments, implanted positive muons, whose stopping
depths below Nb's surface were adjusted between ~10 nm to ~150 nm, reveal the
field distribution inside the superconducting element via their spin-precession
(communicated through their radioactive decay products). We compare how the
field screening is modified by different surface treatments commonly employed
to prepare superconducting radio frequency (SRF) cavities used in accelerator
beamlines. In contrast to an earlier report [A. Romanenko et al., Appl. Phys.
Lett. 104 072601 (2014)], we find no evidence for any "anomalous" modifications
to the Meissner profiles, with all data being well-described by a London model.
Differences in screening properties between surface treatments can be explained
by changes to the carrier mean-free-paths resulting from dopant profiles near
the material's surface.Comment: 15 pages, 5 figures, 2 table
The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications
The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 °C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones
Magnesium(II)-ATP Complexes in 1-Ethyl-3-Methylimidazolium Acetate Solutions Characterized by 31Mg β-Radiation-Detected NMR Spectroscopy
The complexation of MgII with adenosine 5â˛-triphosphate (ATP) is omnipresent in biochemical energy conversion, but is difficult to interrogate directly. Here we use the spin-urn:x-wiley:14337851:media:anie202207137:anie202207137-math-0001 β-emitter 31Mg to study MgII-ATP complexation in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) solutions using β-radiation-detected nuclear magnetic resonance (β-NMR). We demonstrate that (nuclear) spin-polarized 31Mg, following ion-implantation from an accelerator beamline into EMIM-Ac, binds to ATP within its radioactive lifetime before depolarizing. The evolution of the spectra with solute concentration indicates that the implanted 31Mg initially bind to the solvent acetate anions, whereafter they undergo dynamic exchange and form either a mono- (31Mg-ATP) or di-nuclear (31MgMg-ATP) complex. The chemical shift of 31Mg-ATP is observed up-field of 31MgMg-ATP, in accord with quantum chemical calculations. These observations constitute a crucial advance towards using β-NMR to probe chemistry and biochemistry in solution
A Facile and Modular Synthesis of Phosphinooxazoline Ligands
The copper(I) iodide catalyzed phosphine/aryl halide coupling procedure of Buchwald et al. provides modular, robust, and scaleable access to phosphinooxazoline (PHOX) ligands. The advantages of this method are highlighted by the convenient synthesis of PHOX ligands with varied steric and electronic properties, which would be challenging to synthesize by other protocols
Direct measurement of the Meissner screening profile in superconductor-superconductor bilayers using low-energy muon spin rotation
Superconducting radio frequency (SRF) cavities, which are critical components
in many particle accelerators, need to be operated in the Meissner state to
avoid strong dissipation from magnetic vortices. For a defect-free
superconductor, the maximum attainable magnetic field for operation is set by
the superheating field, , which directly depends on the
surface current. In heterostructures composed of different superconductors, the
current in each layer depends not only on the properties of the individual
material, but also on the electromagnetic response of the adjacent layers
through boundary conditions at the interfaces. Three prototypical bilayers
[(50 nm)/Nb, (80 nm)/Nb, and
(160 nm)/Nb] are investigated here by depth-resolved
measurements of their Meissner screening profiles using low-energy muon spin
rotation (LE-SR). From fits to a model based on London theory (with
appropriate boundary and continuity conditions), a magnetic penetration depth
for the thin layers of 182.5(31) nm is found, in good agreement with literature values for the bulk
alloy. In contrast, a simple London model without appropriate boundary
conditions overestimates by more than a factor
of two, suggesting that it is inappropriate for quantifying
here. Using the measured
, the maximum vortex-free field,
, of the superconductor-superconductor (SS) bilayer structure
was estimated to be 610(40) mT. The strong suppression of the surface current
in the layer suggests an optimal thickness of 261(14) nm.Comment: 13 pages and 8 figure
An exploration of parentsâ preferences for foot care in juvenile idiopathic arthritis: a possible role for the discrete choice experiment
Background:
An increased awareness of patientsâ and parentsâ care preferences regarding foot care is desirable from a clinical perspective as such information may be utilised to optimise care delivery. The aim of this study was to examine parentsâ preferences for, and valuations of foot care and foot-related outcomes in juvenile idiopathic arthritis (JIA).<p></p>
Methods:
A discrete choice experiment (DCE) incorporating willingness-to-pay (WTP) questions was conducted by surveying 42 parents of children with JIA who were enrolled in a randomised-controlled trial of multidisciplinary foot care at a single UK paediatric rheumatology outpatients department. Attributes explored were: levels of pain; mobility; ability to perform activities of daily living (ADL); waiting time; referral route; and footwear. The DCE was administered at trial baseline. DCE data were analysed using a multinomial-logit-regression model to estimate preferences and relative importance of attributes of foot care. A stated-preference WTP question was presented to estimate parentsâ monetary valuation of health and service improvements.<p></p>
Results:
Every attribute in the DCE was statistically significant (pâ<â0.01) except that of cost (pâ=â0.118), suggesting that all attributes, except cost, have an impact on parentsâ preferences for foot care for their child. The magnitudes of the coefficients indicate that the strength of preference for each attribute was (in descending order): improved ability to perform ADL, reductions in foot pain, improved mobility, improved ability to wear desired footwear, multidisciplinary foot care route, and reduced waiting time. Parentsâ estimated mean annual WTP for a multidisciplinary foot care service was ÂŁ1,119.05.<p></p>
Conclusions:
In terms of foot care service provision for children with JIA, parents appear to prefer improvements in health outcomes over non-health outcomes and service process attributes. Cost was relatively less important than other attributes suggesting that it does not appear to impact on parentsâ preferences.<p></p>
Exploring the feasibility of Conjoint Analysis as a tool for prioritizing innovations for implementation
Background: In an era of scarce and competing priorities for implementation, choosing what to implement is a key decision point for many behavioural change projects. The values and attitudes of the professionals and managers involved inevitably impact the priority attached to decision options. Reliably capturing such values is challenging. Methods: This paper presents an approach for capturing and incorporating professional values into the prioritization of healthcare innovations being considered for adoption. Conjoint Analysis (CA) was used in a single UK Primary Care Trust to measure the priorities of healthcare professionals working with women with postnatal depression. Rating-based CA data was gathered using a questionnaire and then mapped onto 12 interventions being considered as a means of improving the management of postnatal depression. Results: The âimpact on patient careâ and the âquality of supporting evidenceâ associated with the potential innovations were the most influential in shaping priorities. Professionals were least influenced by whether an innovation was an existing national or local priority, or whether current practice in the Trust was meeting minimum standards. Ranking the 12 innovations by the preferences of potential adopters revealed âguided self helpâ was the top priority for implementation and âscreening questions for post natal depressionâ the least. When other factors were considered (such as the presence of routine data or planned implementation activity elsewhere in the Trust), the project team chose to combine the eight related treatments and implement these as a single innovation referred to as âpsychological therapiesâ. Conclusions: Using Conjoint Analysis to prioritise potential innovation implementation options is a feasible means of capturing the utility of stakeholders and thus increasing the chances of an innovation being adopted. There are some practical barriers to overcome such as increasing response rates to conjoint surveys before routine and unevaluated use of this technique should be considered
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