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The wave functions for calculating gas phase 19F chemical shifts were optimally selected using the factorial design as a multivariate technique. The effects of electron correlation, triple-ξ valance shell, diffuse function, and polarization function on calculated 19F chemical shifts were discussed. It is shown that of the four factors, electron correlation and the polarization functions affect the results significantly. B3LYP/6-31 + G(df,p) wave functions have been proposed as the best and the most efficient level of theory for calculating 19F chemical shifts. An additional series of fluoro compounds were used as a test set and their predicted 19F chemical shifts values confirmed the validity of the approaches. 相似文献
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A novel calix[4]arene derivative with two ferrocenyl Schiff-base groups at the upper rim 3 has been synthesized from 5,17-diformyl-25,27-dipropoxy-26,28-dihydroxy calix[4]arene and 4-ferrocenylaniline via condensation reaction. Reduction of 3 with sodium borohydride led to calix[4]arene derivative 4 with two amino ferrocenyl groups at the upper rim. The ferrocenyl Schiff-base calix[4]arene and its corresponding reduced amine have been purified and characterized by elemental analysis,1H NMR, FTIR, Mass and UV-vis spectral data. Electrochemical properties of compounds 3 and 4 have been investigated. Cyclic voltammograms of 3 and 4 show reversible redox couples of ferrocene/ferrocinium at E1/2=0.401 V and 0.346 V, respectively. Electrochemical studies show these redox active compounds electrochemically recognize trivalent lanthanides La3+ and Ce3+ and divalent Pb2+ and Cu2+cations. With ferrocenyl Schiff-base calix[4]arene 3 an anodic shift as large as 130 mV is observed on addition of one equivalent of Ce3+ ion. Also extraction properties of compound 4 towards some metal cations have been described. It has been observed that compound 4 has a good selectivity for metal cations Fe3+, Cu2+, Pb2+ and Cd2+ against Ni2+ and Co2+. 相似文献
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A simple graphical approach to predict local residue conformation using NMR chemical shifts and density functional theory
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Hoora Shaghaghi Hossein Pasha Ebrahimi Fariba Fathi Niloufar Bahrami Panah Mehdi Jalali‐Heravi Mohsen Tafazzoli 《Journal of computational chemistry》2016,37(14):1296-1305
The dependency of amino acid chemical shifts on φ and ψ torsion angle is, independently, studied using a five‐residue fragment of ubiquitin and ONIOM(DFT:HF) approach. The variation of absolute deviation of 13Cα chemical shifts relative to φ dihedral angle is specifically dependent on secondary structure of protein not on amino acid type and fragment sequence. This dependency is observed neither on any of 13Cβ, and 1Hα chemical shifts nor on the variation of absolute deviation of 13Cα chemical shifts relative to ψ dihedral angle. The 13Cα absolute deviation chemical shifts (ADCC) plots are found as a suitable and simple tool to predict secondary structure of protein with no requirement of highly accurate calculations, priori knowledge of protein structure and structural refinement. Comparison of Full‐DFT and ONIOM(DFT:HF) approaches illustrates that the trend of 13Cα ADCC plots are independent of computational method but not of basis set valence shell type. © 2016 Wiley Periodicals, Inc. 相似文献
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Calix[4]arene derivatives containing ferrocene units at the upper rim have been synthesized and their anion‐binding and sensing investigated towards anions such as chloride, bromide and hydrogen sulfate by cyclic voltammetry. Electrochemical studies show that these redox‐active ligands electrochemically recognize chloride and bromide anions. These compounds have excellent selectivity for chloride and bromide ions, in the comparison with hydrogen sulfate anion. With ferrocenyl Schiff base calix[4]arene 1 an anodic shift as large as 302 mV is observed on addition of four equivalents of Cl− anion. Also electrochemical and UV–vis spectroscopic titrations ferrocenyl calix[4]arene derivatives 1 with chloride and bromide ions and 2 (only with Cl−) indicate a 1:1 binding‐stiochiometry. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Jouyban A Shaghaghi M Zoghi E Karami N Clark BJ Acree WE 《Journal of fluorescence》2011,21(6):2111-2116
Fluorescence intensities of propranolol and atenolol in binary solvent mixtures at various temperatures are measured and mathematical
models are proposed to represent the fluorescence intensity data. The results showed that the proposed models are able to
correlate/predict the data with reasonable error. The fluorescence intensity of pyridoxal HCl in binary solvents at 25 °C
is also determined and represented by the proposed model as an additional test probe. 相似文献
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Saeed K. Amini Hoora Shaghaghi Alex D. Bain Ammar Chabok Mohsen Tafazzoli 《Solid state nuclear magnetic resonance》2010,37(1-2):13-20
The experimental 13C NMR chemical shift components of uracil in the solid state are reported for the first time (to our knowledge), as well as newer data for the 15N nuclei. These experimental values are supported by extensive calculated data of the 13C, 15N and 17O chemical shielding and 17O and 14N electric field gradient (EFG) tensors. In the crystal, uracil forms a number of strong and weak hydrogen bonds, and the effect of these on the 13C and 15N chemical shift tensors is studied. This powerful combination of the structural methods and theoretical calculations gives a very detailed view of the strong and weak hydrogen bond formation by this molecule. Good calculated results for the optimized cluster in most cases (except for the EFG values of the 14N3 and 17O4 nuclei) certify the accuracy of our optimized coordinates for the hydrogen nuclei. Our reported RMSD values for the calculated chemical shielding and EFG tensors are smaller than those reported previously. In the optimized cluster the 6-311+G** basis set is the optimal one in the chemical shielding and EFG calculations, except for the EFG calculations of the oxygen nuclei, in which the 6-31+G** basis set is the optimal one. The optimal method for the chemical shielding and EFG calculations of the oxygen and nitrogen nuclei is the PW91PW91 method, while for the chemical shielding calculations of the 13C nuclei the B3LYP method gives the best results. 相似文献
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Rahmatollah Ghajar Ali Shaghaghi Moghaddam Marco Alfano 《International Journal of Solids and Structures》2011,48(1):208-216
A simplified strategy based on the interaction energy integral is implemented in the finite element framework to evaluate mixed mode Stress Intensity Factors (SIFs) in 3D non-planar cracks. The proposed approach does not require any a priori information about crack front and crack surface curvatures, therefore different arbitrary non-planar cracks can be easily investigated. In particular, both conical and lens-shaped cracks in homogeneous materials are considered as case studies in order to demonstrate the accuracy of the present approach. Finally, the computational strategy is extended to Functionally Graded Materials (FGMs) and the effect of graded material properties (Young’s modulus and Poisson’s ratio) on the SIFs is studied in detail. 相似文献
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