A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
The conditions for obtaining a high efficiency of energy exchange upon two-wave interactions in dynamic holograms are found by analysis and numerical simulation of a system of nonlinear equations. Use of an asymmetric scheme of beam interaction in a medium with two nonlinearities, one of which determines the amplitude and relaxation time of a grating and the other of which provides phase modulation of the interacting beams, is proposed. It is shown that such a scheme in combination with the specific properties of a medium makes it possible to radically reduce the requirements for the nonlinearity of a medium and the intensity of a light flux in limiting systems, as well as to significantly decrease the time of the transition process. As a result, it becomes possible to attain an efficiency of energy transfer higher than 90% and to increase the corresponding attenuation of a high-power beam by almost two orders of magnitude, which is of interest for optical limiting of intense light fluxes. 相似文献
As part of a multi-centre European project, FOOD-PCR, the feasibility of a novel approach for production of dried bacterial DNA that could be used as certified reference materials (CRM) was assessed. Selected strains of Salmonella typhimurium, Listeria monocytogenes, Escherichia coli O157, Campylobacter jejuni and Yersinia enterocolitica were used to produce genomic DNA (gDNA). These preparations gave support to method development for qualitative polymerase chain reaction (PCR) detection methods for food-borne pathogens. Purified gDNA was transformed into stable and dry gDNA by using polypropylene vials as carrier and applying a vacuum-drying technique. The gDNA preparations were shown to be sufficiently stable under ambient transport conditions without cooling and proved to have long-term stability at 5°C of at least 22 months. The dried DNA was easily reconstituted by addition of distilled water then gentle shaking. These studies have shown that production of stable and dry bacterial gDNA material is feasible and could help satisfy the increasing need for certified reference DNA positive control samples in the field of PCR testing for detection and verification of food-borne microbial pathogens.
The potential approaches for third-party assessment of reference material producers are revisited and the activities of the
Reference Materials (RM) Unit of the Institute for Reference Materials and Measurements (IRMM) to obtain accreditation to
ISO Guide 34 and ISO 17025 are described. Accreditation was related to the Unit as all matrix RM activities of the institute
are concentrated there. A management system was established that allows sufficient flexibility to be applicable to a wide
range of RMs while being precise enough to ensure compliance with ISO Guides 30, 31 and especially 34 and 35. Accreditation
was achieved in 2004 with independent scopes for testing and RM production and was confirmed and extended in 2005. The key
aspects of the RM Unit's management system for RM production are presented.
Presented at BERM-10, April 2006, Charleston, SC, USA 相似文献
Abstract— Biophysical and photobiological properties of a group of bacteriochlorins were compared with efficacy of these products for photodynamic therapy of murine tumors. Predictive factors for selective photosensitization in vivo include affinity binding to lipoproteins greater than albumin, extinction coefficient at the wavelength of irradiation and tumor/skin distribution. Efficacy was correlated with circulating plasma levels of the different sensitizers but not with the photodynamic therapy response in cell culture. 相似文献
A capillary electrophoretic (CE) method was developed for the separation of diastereoisomers of a new human immunodeficiency virus (HIV) protease inhibitor TMC114. In total 16 isomers of this drug have been synthesized (eight pairs of enantiomers). We succeeded in the separation of the eight diastereoisomers, but no enantiomers could be separated. Because of the high similarity and water-insolubility of these isomers, the separation is a real challenge. Different CE modes were tried out: capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), micellar electrokinetic capillary chromatography (MEKC), and microemulsion electrokinetic capillary chromatography (MEEKC). Only MEEKC offered resolution of these compounds. 相似文献
The use of temperature as a variable in liquid chromatography enables the facile alteration of eluotropic strength without the need to change solvent composition. The ability to change eluotropic strength via temperature alone means that thermal gradients can be used to mimic the effects of solvent gradients but without many of the unwanted effects of changes in solvent composition. Here we illustrate the use of thermal gradients as a means of controlling chromatographic separations using either constant flow or, with the flow rate increased to maintain isobaric conditions, constant pressure, performed using columns packed with 1.7 μm particles. A model is described that can be used to used to predict flow, pressure and temperature under gradient conditions. Practical experimental factors such as the need for post column cooling and the use of frit restrictors in order to obtain optimum results are described. 相似文献
Two libraries of alpha-substituted alkynes has been prepared on solid phase using a sequential Sonogashira/Nicholas reaction approach. The scope of nucleophiles in the Nicholas reaction on solid phase has been investigated, including carbon, oxygen, nitrogen, sulfur, fluoride, and hydride nucleophiles. The conditions for the reaction sequence have been optimized in terms of Lewis acid, catalyst for the Sonogashira step, temperature, reaction time, and decomplexation method, enabling the five-step sequence to be performed in 1 day. 相似文献
Fluorescence emission spectra indicate that oligomers containing both hematoporphyrin and its dehydration products (vinyl porphyrins) comprise the tumor-localizing fraction of HPD. In the relatively polar solvent methanol, the vinyl porphyrins exhibit reduced fluorescence yields while the hematoporphyrin residues are relatively resistant to fluorescence quenching by Fe+3. In the less polar solvent tetrahydrofuran, fluorescence from oligomeric vinyl porphyrins was enhanced, and Fe+3-induced quenching of oligomeric hematoporphyrin promoted. These, together with other studies in biological systems, suggest a substantial degree of interaction among the porphyrin units contained in these oligomers, as a function of the polarity of the environment. 相似文献