Inductively coupled plasma mass spectrometry (ICP-MS) techniques are widely used for determination of long-lived radionuclides and their isotopic ratios in the nuclear fields. Uranium (U) and Plutonium (Pu) isotopes have been determined by many researchers with ICP-MS due to its relatively high sensitivity and short measurement time. In this work, an inter-laboratory comparison exercise among the Nordic countries was performed, focusing on the measurement of U and Pu isotopes in certified reference materials by ICP-MS. The performance and characters of different ICP-MS instruments are evaluated and discussed in this paper. 相似文献
Dehydroalanine (Dha) residues are attractive noncanonical amino acids that occur naturally in ribosomally synthesised and post-translationally modified peptides (RiPPs). Dha residues are attractive targets for selective late-stage modification of these complex biomolecules. In this work, we show the selective photocatalytic modification of dehydroalanine residues in the antimicrobial peptide nisin and in the proteins small ubiquitin-like modifier (SUMO) and superfolder green fluorescent protein (sfGFP). For this purpose, a new water-soluble iridium(III) photoredox catalyst was used. The design and synthesis of this new photocatalyst, [Ir(dF(CF3)ppy)2(dNMe3bpy)]Cl3, is presented. In contrast to commonly used iridium photocatalysts, this complex is highly water soluble and allows peptides and proteins to be modified in water and aqueous solvents under physiologically relevant conditions, with short reaction times and with low reagent and catalyst loadings. This work suggests that photoredox catalysis using this newly designed catalyst is a promising strategy to modify dehydroalanine-containing natural products and thus could have great potential for novel bioconjugation strategies. 相似文献
We present the equations and methodology for the theoretical prediction of the conductance, permeability and selectivity of a K+ channel on the basis of atomic scale models for it. The methodology involves the use of Langevin dynamics and activated trajectories in order to obtain translocation free energies, rate constants and transmission coefficients for an ion going through the channel. The models are for the Inward Rectifier K+ channel (IRK1) which is a member of a family of ion-selective K+ channels. The IRK1 channel is biologically important because of its role in cardiac pacemaker function. The models we use for the IRK1 channel are developed from a model of the Shaker voltage-gated K+ channel. We find that the theoretically predicted conductance is too low by three orders of magnitude. We attribute this underestimate to a specific structural defect in the model used. Perhaps our most significant result is that the computed conductance is tremendously sensitive to the structural details of the so-called ‘P-loop’ that lines the outer half of the permeation pathway of the channel. This sensitivity may be useful in future studies on ion channel proteins for which the structure is not known from X-ray crystallography. In addition, this sensitivity may help determine whether X-ray structures of these proteins correspond to open or closed conformations. 相似文献
Abstract The effects of temperature are discussed when the ZnS:Cu,Al,Au (P22G) phosphor powder is bombarded by a 2 keV electron beam with a current density of 88 mA/cm2 at an oxygen pressure of 2 × 10?6 Torr at temperatures between 25 and 300°C. The rate of surface reaction decreases at higher temperatures due to the reduction in the mean stay time of the O2 on the surface which is vital for the reactions according to an electron stimulated surface chemical reaction model. A direct correlation between the temperature and the initial cathodoluminescence (CL) brightness which depicts thermal quenching of the CL was observed. 相似文献
Abstract The synthesis of a variety of substituted bisphenol A polysulfones, including nitro, amino, aminomethyl, ethyl, and methyl derivatives, is described. Nuclear magnetic resonance (NMR) (both proton and carbon, and several 2-D experiments) data confirm conclusions on the substitution site based on arguments on inductive effects in the phenyl rings. The proton ortho to the oxygen in the bisphenol A (BPA) residue is replaced in electrophilic substitution reactions. The degree of substitution was also calculated from the NMR results. The ethyl and methyl derivatives were expected, from the starting reactants, to each have a BPA ring substituted. The NMR data showed that, on the average, this is true. The nitro derivative also has substitution in every BPA ring, while the amino and aminomethyl derivatives have only intermittent BPA rings substituted. Measured degrees of substitution (DS) varied from 0.11 to 2.25. 相似文献
This article presents a series of ring‐extended gramicidin S derivatives, 9 – 14 , that have four ornithine residues as polar protonated side chains and one modified turn region containing a mono‐functionalized cis‐δ‐oxetane, δ‐furanoid, or δ‐pyranoid sugar amino acid residue. Of the GS analogs evaluated, we identified compound 7 , which contains the mono‐benzyloxy cis‐δ‐pyranoid sugar amino acid, as having a better biological profile than the clinically applied topical antibiotic gramicidin S. 相似文献
In order to deliver reliable results for a multitude of different scenarios, e.g. emergency preparedness, environmental monitoring, nuclear decommissioning and waste management, there is a constant process of method development in the field of radioanalytical chemistry. This work presents the results of a method comparison exercise aimed at quantifying 90Sr and 239,240Pu in environmental soil samples, with the intention of evaluating the performance and applicability of different methods. From the methods examined in this work, recommendations are given in order to find a radioanalytical measurement procedure, for 90Sr and 239,240Pu analysis, which is fit-for-purpose for a particular scenario.