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[reaction: see text] Via an X-ray analysis, the sulfonamide bearing R(1) = i-Pr, R(2) = Me, and R(3) = Me is shown to be a tridentate ligand to a Cr(III) salt. This class of ligands, represented by R(1) = t-Bu, R(2) = 2-naphthyl, and R(3) = Me, is effective to achieve an asymmetric Ni/Cr-mediated coupling reaction and, with the C14-C38 segment of halichondrins, its synthetic potential has been demonstrated. A possible mechanism is suggested for the process. 相似文献
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Andualem Damtew Balamurali Sreedhar Andreas Seidel-Morgenstern 《Journal of chromatography. A》2009,1216(28):5355-5364
The potential of applying nonlinear gradients in preparative chromatography is evaluated theoretically and experimentally. The second eluting component of a ternary model mixture is considered as the target component. Systematic gradient resolution experiments were conducted for this mixture using reversed phase chromatography. In preliminary experimental investigations the effect of the mobile phase composition on the specific distribution equilibria was quantified. Concave and convex solvent strength gradients were analysed and compared with conventional linear gradients. Main result of the study is the fact that significant improvement in productivity can be achieved if the gradient shapes are designed carefully. 相似文献
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Theoretical study of preparative chromatography using closed-loop recycling with an initial gradient
Balamurali Sreedhar Andualem Damtew Andreas Seidel-Morgenstern 《Journal of chromatography. A》2009,1216(25):4976-4988
Complementing classical isocratic elution, several more sophisticated operating modes have been proposed and are applied in preparative chromatography in order to improve performance. One such approach is gradient elution, where the solvent strength is altered by varying the fraction of a modifier added to the mobile phase to enhance selectivity and to achieve faster elution. Another useful technique is closed-loop recycling, allowing better peak resolution and increased yields. This study focuses on a modified new scheme which incorporates the advantages of both gradient elution and closed-loop recycling for the separation of a ternary mixture where the intermediately eluting component is the target. A parametric study was carried out using typical adsorption isotherm parameters to elucidate the effects of varying loading factors and parameters specific to the two basic operational modes on production rates and yields. A comparison was also made between the proposed scheme and conventional techniques. It was found that the studied scheme could exploit increased column loadings and offers significantly higher production rates. 相似文献
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Biotechnology-derived varieties of canola, cotton, corn and soybean are being grown in the USA, Canada and other predominantly
grain exporting countries. Although the amount of farmland devoted to production of biotechnology-derived crops continues
to increase, lingering concerns that unintended consequences may occur provide the EU and most grain-importing countries with
justification to regulate these crops. Legislation in the EU requires traceability of grains/oilseeds, food and feed products,
and labelling, when a threshold level of 0.9% w/w of genetically engineered trait is demonstrated to be present in an analytical
sample. The GE content is routinely determined by quantitative PCR (qPCR) and plant genomic DNA provides the template for
the initial steps in this process. A plethora of DNA extraction methods exist for qPCR applications. Implementing standardized
methods for detection of genetically engineered traits is necessary to facilitate grain marketing. The International Organization
for Standardization draft standard 21571 identifies detergent-based methods and commercially available kits that are widely
used for DNA extraction, but also indicates that adaptations may be necessary depending upon the sample matrix. This review
assesses advantages and disadvantages of various commercially available DNA extraction kits, as well as modifications to published
cetyltrimethylammonium bromide methods. Inhibitors are a major obstacle for efficient amplification in qPCR. The types of
PCR inhibitors and techniques to minimize inhibition are discussed. Finally, accurate quantification of DNA for applications
in qPCR is not trivial. Many confounders contribute to differences in analytical measurements when a particular DNA quantification
method is applied and different methods do not always provide concordant results on the same DNA sample. How these differences
impact measurement uncertainty in qPCR is considered. 相似文献
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[reaction: see text] The stable, crystalline Cr(III)/sulfonamide complex 1a is shown to be an effective catalyst for the Ni/Cr-mediated coupling reaction. A possible mechanism is suggested for the process. 1a is also effective for other Cr-mediated coupling reactions. With this catalyst, a concise and efficient synthesis of the C14-C26 segment of halichondrins has been developed. 相似文献
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Jiecheng Chen Belay Mitiku Damtew Xiangrong Zhu 《Frontiers of Mathematics in China》2017,12(2):281-299
We consider the oscillatory hyper Hilbert transform H γ,α,β f(x) = ∫ 0 ∞ f(x - Γ(t))eit-β t-(1+α)dt; where Γ(t) = (t, γ(t)) in ?2 is a general curve. When γ is convex, we give a simple condition on γ such that H γ,α,β is bounded on L 2 when β > 3α, β > 0: As a corollary, under this condition, we obtain the L p -boundedness of H γ,α,β when 2β/(2β - 3α) < p < 2β/(3α). When Γ is a general nonconvex curve, we give some more complicated conditions on γ such that H γ,α,β is bounded on L 2: As an application, we construct a class of strictly convex curves along which H γ,α,β is bounded on L 2 only if β > 2α > 0. 相似文献
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[reaction: see text] The most recently described member of the cacospongionolide class of marine natural products has been assembled using a diastereochemically divergent total synthesis strategy that independently establishes the complete stereochemistry of cacospongionolide F and provides a new entry toward expansion of this phospholipase A(2) inhibitor chemotype. 相似文献
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The marine natural product dysidiolide has been synthesized in a highly diastereoselective fashion that features the sequential transfer of chirality from a cyclohexenone precursor. 相似文献
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