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981.
982.
983.
The ion-pair acidities of organic acids in THF are fundamental to synthetic organic chemistry. Although the ion-pair acidities of a number of carbon acids have been experimentally measured by Streitwieser and co-workers, it is important to develop a theoretical method that can accurately predict these quantities because not all the organic acids (e.g., very weak acids or complex synthetic intermediates with multiple acidic positions) are amenable to experimental characterization. In the present study is reported the first theoretical protocol for predicting the cesium ion-pair acidities in THF whose reliability has been tested against almost all the available experimental data. It is found that the root-mean-square error of the current theoretical model equals 1.2 pK units. With the newly developed theoretical method in hand, the structures of cesium ion pairs of different types of carbon acids are then studied. The cesium ion-pair acidities in THF and absolute ionic acidities in DMSO are also systematically compared, which confirms Streitwieser's previous finding that the two scales of acidities have only minor difference. Significantly, from detailed energy analysis the mechanism for the "fortunate" match of the two scales of acidities is found. That is, the combined process of the Cs binding ("micro"-solvation) and the solvation of the ion pair resembles the one-step solvation of a carbanion in DMSO. Finally, it is found that the cesium ion-pair acidities of nitrogen acids in THF have only minor difference from the absolute ionic acidities in DMSO. Consequently, one can easily estimate the cesium ion-pair acidities of almost all types of organic nitrogen acids in THF on the basis of Bordwell's data. 相似文献
984.
This paper reports on a novel application of a ligand field model for the detection of the local molecular structure of a coordination complex. By diagonalizing the complete energy matrices of the electron-electron repulsion, the ligand field and the spin-orbit coupling for the d5 configuration ion in a trigonal ligand field, the local distortion structure of the (MnO6)10- coordination complex for Mn2+ ions doped into CaCO3, have been investigated. Both the second-order zero-field splitting parameter b(0)2 and the fourth-order zero-field splitting parameter b(0)4 are taken simultaneously in the structural investigation. From the electron paramagnetic resonance (EPR) calculations, the local structure distortion, DeltaR=-0.169 A to -0.156 A, Deltatheta=0.996 degrees to 1.035 degrees for Mn2+ ions in calcite single crystal, DeltaR=-0.185 A to -0.171 A, Deltatheta=3.139 degrees to 3.184 degrees for Mn2+ ions in travertines, and DeltaR=-0.149 A to -0.102 A, Deltatheta=0.791 degrees to 3.927 degrees for Mn2+ ions in shells are determined, respectively. These results elucidate a microscopic origin of various ligand field parameters which are usually used empirically for the interpretation of EPR and optical absorption experiments. It is found that the theoretical results of the EPR and optical absorption spectra for Mn2+ ions in CaCO3 are in good agreement with the experimental findings. Moreover, to understand the detailed physical and chemical properties of the doped CaCO3, the theoretical values of the fourth-order zero-field splitting parameters b(0)4 for Mn2+ ions in travertines and shells are reported first. 相似文献
985.
986.
Mao AJ Kuang XY Tan XM Wang H Li JF 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(3-4):890-893
The relationship between the impurity structures and the electron paramagnetic resonance (EPR) parameters D, (a-F) have been studied by diagonalizing the complete energy matrices for Mn2+ ion in [Mg(H2O)6]SnCl6 single crystal in a trigonal ligand field within a weak-field-representation. It is shown that the local lattice structure around Mn2+ ion in [Mg(H2O)6]SnCl6 exhibits an elongation distortion which is different at 290 K and 77 K. The local structure parameters R=2.223+/-0.027A, theta=52.966+/-0.004 degrees and R=2.205+/-0.030A, theta=53.155+/-0.047 degrees for Mn2+ ion in [Mg(H2O)6]SnCl6 are determined at different temperatures 290 K and 77 K, respectively, and EPR parameters D and (a-F) can also get a satisfactory explanation simultaneously. 相似文献
987.
Treatment of Pd(PPh3)4 with 2‐bromo‐4‐methylpyridine, C5H3N(CH3)Br, in dichloromethane at ?20 °C causes the oxidative addition reaction to produce the palladium complex [Pd(PPh3)2 {η1‐C5H3N(CH3)}(Br)], 2 , by substituting two triphenylphosphine ligands. In a dichloromethane solution of complex 2 at room temperature for 3 h, it undergoes displacement of the triphenylphosphine ligand to form the dipalladium complex [Pd(PPh3)Br]2{μ,η2‐C5H3N(CH3)}2, 3 , in which the two 4‐methylpyridine ligands coordinated through carbon to one metal center and bridging the other metal through the nitrogen atom. Complexes 2 and 3 are characterized by X‐ray diffraction analyses. 相似文献
988.
By analyzing EPR and optical spectra, the local lattice structures of (NiF6)4− clusters in perovskite fluorides RbMF3 (M = Cd2+, Ca2+, Mg2+) series in tetragonal and trigonal ligand field are studied. A compression distortion relative to the regular octahedron for the RbCdF3:Ni2+ and RbCaF3:Ni2+ systems is determined. Furthermore, on the basis of the complete energy matrices we found that ZFS parameter D dependence on spin–orbit coupling coefficient ζ is not a strictly quadratic relation as shown by the fourth-order perturbation formula. Finally, the curves of g versus k and g versus k for these three systems are plotted which satisfy an approximately linear relation. 相似文献
989.
Berman ES Fortson SL Checchi KD Wu L Felton JS Wu KJ Kulp KS 《Journal of the American Society for Mass Spectrometry》2008,19(8):1230-1236
Characterizing chemical changes within individual cells is important for determining fundamental mechanisms of biological processes that will lead to new biological insights and improved disease understanding. Analyzing biological systems with imaging and profiling mass spectrometry (MS) has gained popularity in recent years as a method for creating chemical maps of biological samples. To obtain mass spectra that provide relevant molecular information about individual cells, samples must be prepared so that salts and other cell culture components are removed from the cell surface and that the cell contents are rendered accessible to the desorption beam. We have designed a cellular preparation protocol for imaging/profiling MS that removes the majority of the interfering species derived from the cellular growth medium, preserves the basic morphology of the cells, and allows chemical profiling of the diffusible elements of the cytosol. Using this method, we are able to reproducibly analyze cells from three diverse cell types: MCF7 human breast cancer cells, Madin-Darby canine kidney (MDCK) cells, and NIH/3T3 mouse fibroblasts. This preparation technique makes possible routine imaging/profiling MS analysis of individual cultured cells, allowing for understanding of molecular processes within individual cells. 相似文献
990.
Jian-Bin Luo Jun-Hua Wei Dr. Zhi-Zhong Zhang Zi-Lin He Prof. Dai-Bin Kuang 《Angewandte Chemie (International ed. in English)》2023,62(7):e202216504
Glass is a group of materials with appealing qualities, including simplicity in fabrication, durability, and high transparency, and they play a crucial role in the optics field. In this paper, a new organic–inorganic metal halide luminescent glass exhibiting >78 % transmittance at 506–800 nm range together with a high photoluminescence quantum yield (PLQY) of 28.5 % is reported through a low-temperature melt-quenching approach of pre-synthesized (HTPP)2MnBr4 (HTPP=hexyltriphenylphosphonium) single crystal. Temperature-dependent X-ray diffraction, polarizing microscopy, and molecular dynamics simulations were combined to investigate the glass-crystal interconversion process, revealing the disordered nature of the glassy state. Benefiting from the transparent nature, (HTPP)2MnBr4 glass yields an outstanding spatial resolution of 10 lp mm−1 for X-ray imaging. The superb optical properties and facility of large-scale fabrication distinguish the organic–inorganic metal halide glass as a highly promising class of materials for optical devices. 相似文献