From zero to hero? Sulfoxides are generally not considered useful ligand entities in asymmetric metal catalysis. However, a chiral disulfoxide as a chelating ligand in the rhodium‐catalyzed 1,4‐addition of aryl boronic acids to cyclic, α,β‐unsaturated ketones and esters gives impressive catalytic results, thus opening the door to future applications of this new chiral ligand class.
An increasing number of studies use blood obtained noninvasively to monitor organohalogen contaminants; however, blood can
be difficult to analyze because of its aqueous nature and high protein content. We compared five methods for extracting polychlorinated
biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine pesticides, and lipids from serum using National
Institute of Standards and Technology Standard Reference Material 1589a PCBs, Pesticides, PBDEs, and Dioxins/Furans in Human
Serum. Liquid:liquid (LLE), cavity-dispersed microwave-assisted (MAE), focused microwave-assisted (FME), solid-phase (SPE),
and pressurized fluid (PFE) extraction techniques were compared. FME extraction yielded the optimal recovery of internal standards
(IS). All methods resulted in similar contaminant concentrations that also agreed with the certified values for SRM 1589a,
except for only a few compounds measured by methods other than FME. Based on these findings, the FME method was determined
to be the best overall extraction method. One procedural factor was found to affect contaminant concentrations; use of IS
carrier solvents that were immiscible with serum (or when the serum was not directly physically mixed with IS) resulted in
a 30% underestimation of organohalogen concentrations. This study offers valid, novel extraction alternatives beyond traditional
methods (e.g., LLE) for blood contaminant measurements.
Figure 相似文献
The selective enzymatic deacetylation of T-2 toxin to give HT-2 toxin has been investigated in aqueous crude extracts of different
cereals and exploited to develop an analytical method for the determination of the sum of T-2 and HT-2 toxins. The method
has been validated for the analysis of total T-2 and HT-2 toxins in maize, wheat, and oats, showing recoveries from 72 to
97% for maize, from 67 to 84% for wheat, and from 61% to 87% for oats, at spiking levels of 20–400 μg/kg, with relative standard
deviation lower than 10%. Liquid chromatography-tandem mass spectrometry was used for quantitative toxin determination. The
potential biological role of this enzymatic conversion and its perspectives for application in the development of antibody-based
analytical techniques are discussed.
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We describe a system that provides a rapid and simple way of forming suspended lipid bilayers within a microfluidic platform from an aqueous droplet. Bilayer lipid membranes are created in a polymeric device by contacting monolayers formed at a two-phase liquid–liquid interface. Microdroplets, containing membrane proteins, are injected onto an electrode positioned above an aperture machined through a conical cavity that is filled with a lipid–alkane solution. The formation of the BLM depends solely on the device geometry and leads to spontaneous formation of lipid bilayers simply by dispensing droplets of buffer. When an aqueous droplet containing transmembrane proteins or proteoliposomes is injected, straightforward electrophysiology measurements are possible. This method is suitable for incorporation into lab-on-a-chip devices and allows for buffer exchange and electrical measurements.
Figure
Bilayer lipid membranes are formed in a polymeric device by injecting water droplets, containing membrane proteins, directly onto an electrode positioned above an aperture machined into a conical cavity, which is initially filled with a lipid-alkane solution. The water droplet slides down the electrode to the aperture at the bottom of the conical reservoir. The geometry of this system enables the spontaneous formation of a BLM. Ion channel activity is recorded between an electrode in the bottom channel and the electrode in the droplet. The technique is scalable and could be configured as a high throughput multi-site biosensing or drug screening platform. 相似文献
Wetting studies regarding amphiphilic molecules and adsorption properties on highly water repellent solid surfaces play key roles in research and technology, with increasing interest both in fundamental and application fields. Nevertheless the wetting properties of aqueous surfactant solutions, non aqueous liquids or immiscible phases on superhydrophobic (SH) solid surfaces have been so far rarely investigated. In this work the authors give an overview on this topic reviewing the literature available together with preliminary results concerning the influence of the distribution properties of surfactants between two immiscible phases. Transition between wetting states can be also considered a possible development of these studies based on switching mechanisms. 相似文献
SRM 1597 Complex Mixture of Polycyclic Aromatic Hydrocarbons from Coal Tar, originally issued in 1987, was recently reanalyzed
and reissued as SRM 1597a with 34 certified, 46 reference, and 12 information concentrations (as mass fractions) for polycyclic
aromatic hydrocarbons (PAHs) and polycyclic aromatic sulfur heterocycles (PASHs) including methyl-substituted PAHs and PASHs.
The certified and reference concentrations (as mass fractions) were based on results of analyses of the coal tar material
using multiple analytical techniques including gas chromatography/mass spectrometry on four different stationary phases and
reversed-phase liquid chromatography. SRM 1597a is currently the most extensively characterized SRM for PAHs and PASHs. 相似文献
By using the recent method of the visibility graph, three time series of oceanic tide level in central Argentina were investigated. The degree distributions show a rich structure; in particular the maximum is due to the main periodic oscillations at 24 hours and 12 hours and higher harmonics. The degree distributions of the residuals (obtained removing from the original signals the cyclic components) suggest that the local effects, linked with the particular coastal conditions of the sites, are discernible for the degree k < 20, while the global effects, linked with linked with the more general and common atmospheric forcing and ocean current conditions, are visible for k > 100. Although a relationship between the spectral exponent α and the exponent of the degree distribution γ of tidal signals can be recognized, this cannot be simply stated due to the very rich and complex structure of time dynamics of tides. The present study, even if still preliminary, show the importance of the visibility graph method in investigating the complex time dynamics of observational and experimental signals. 相似文献
Although Fourier series or integrals of piecewise smooth functions may be slowly convergent, sometimes it is possible to accelerate their speed of convergence by adding and subtracting suitable combination of known functions. 相似文献