Abstract The overlap repulsive potentials of ion pairs (Li +?F?, Na+?F? and K+?F?) are calculated by means of generalized Heitler-London method and the numerical results are fitted in the Born-Mayer form, i.e. Dexp (—αR), Then the parameter D for each pair potential is modified to satisfy the crystal equilibrium condition at the experimentally known lattice constant. The redetermined repulsive potentials are applied to calculate the cohesive energies, bulk moduli, equations of state and NaC1–to-CsC1 structural phase transition pressures of LiF, NaF and KF crystals. The results obtained are compared with some other theoretical values and the available experimental data, and good agreement is reached. 相似文献
Following the biosynthesis of polyketide backbones by polyketide synthases (PKSs), post‐PKS modifications result in a significantly elevated level of structural complexity that renders the chemical synthesis of these natural products challenging. We report herein a total synthesis of the widely used polyketide insecticide spinosyn A by exploiting the prowess of both chemical and enzymatic methods. As more polyketide biosynthetic pathways are characterized, this chemoenzymatic approach is expected to become readily adaptable to streamlining the synthesis of other complex polyketides with more elaborate post‐PKS modifications. 相似文献
Controlling selectivity is of central importance to radical chemistry. However, the highly reactive and unstable radical intermediates make this task especially challenging. Herein, a strategy for taming radical redox reactions has been developed, in which solvent‐bonding can alter the reactivity of the generated radical intermediates and thereby drastically alter the reaction selectivity at room temperature. Various β‐oxy sulfoxides and β‐hydroxy sulfides can be facilely obtained, some of which are difficult to synthesize by existing methods. Notably, neither a metal catalyst nor any further additives are necessary in these processes. 相似文献
A novel ferrocenyl anion receptor N, N, N, N-(dimethyl, ethyl, ferrocenecarboxylic amidodimethylene) ammonium fluoborate 2 with multiple binding sites was synthesized. Its anion recognition behaviors were investigated by CV, 1H NMR and UV-vis spectrum. It was found that the combination of two interactions enforced the anion binding ability and the binding selectivity of 2 to phosphate anion. The effects of scan rate on the CV curves of 2 with phosphate were also investigated. In different scan rate, the CV curves kept stable which indicated the strong binding between 2 and phosphate. According to relationships of peak potential, peak currents and scan rate of 2 binding with phosphate, the kinetic parameters of electrode process such as diffusion coefficient Dapp, surface transfer coefficient alphan alpha, and standard rate constant k0 were calculated. 相似文献
Vanadium-based oxides with high theoretical specific capacities and open crystal structures are promising cathodes for aqueous zinc-ion batteries (AZIBs). In this work, the confined synthesis can insert metal ions into the interlayer spacing of layered vanadium oxide nanobelts without changing the original morphology. Furthermore, we obtain a series of nanomaterials based on metal-confined nanobelts, and describe the effect of interlayer spacing on the electrochemical performance. The electrochemical properties of the obtained Al2.65V6O13 ⋅ 2.07H2O as cathodes for AZIBs are remarkably improved with a high initial capacity of 571.7 mAh ⋅ g−1 at 1.0 A g−1. Even at a high current density of 5.0 A g−1, the initial capacity can still reach 205.7 mAh g−1, with a high capacity retention of 89.2 % after 2000 cycles. This study demonstrates that nanobelts confined with metal ions can significantly improve energy storage applications, revealing new avenues for enhancing the electrochemical performance of AZIBs. 相似文献
Reaction of a galactosylated 2-C-(hydroxymethyl)-tetrofuranose with paramolybdate ion-exchange resin in aqueous solution at 67 degrees C gave an equililibrium mixture containing the reactant aldofuranose (42%) and a 2-ketopentofuranose galactosylated at O1 (58%). Observation of this stereospecific rearrangement supports prior arguments that substituents at C2 of the branched-chain aldofuranose reactant are located in a sterically accessible pocket of the putative dimolybdate-saccharide reactive complex during epimerization. This rearrangement provides a new and convenient route to 2-ketosugars glycosylated at the exocyclic C1 position. 相似文献
Nonlinear heat transfer can be exploited to reveal novel transport phenomena and thus enhance people’s ability to manipulate heat flux at will. However, there has not been a mature discipline called nonlinear thermotics like its counterpart in optics or acoustics to make a systematic summary of relevant researches. In the current review, we focus on recent progress in an important part of nonlinear heat transfer, i.e., tailoring nonlinear thermal devices and metamaterials under the Fourier law, especially with temperature-dependent thermal conductivities. We will present the basic designing techniques including solving the equation directly and the transformation theory. Tuning nonlinearity coming from multi-physical effects, and how to calculate effective properties of nonlinear conductive composites using the effective medium theory are also included. Based on these theories, researchers have successfully designed various functional materials and devices such as the thermal diodes, thermal transistors, thermal memory elements, energy-free thermostats, and intelligent thermal materials, and some of them have also been realized in experiments. Further, these phenomenological works can provide a feasible route for the development of nonlinear thermotics.