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21.
Akhat V. Il'Yasov Ildus A. Nuretdinov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):479-482
Spectra of a nuclear magnetic resonance of seleno- and telluro-phosphorus compounds on nuclei 77Se, 125Te, 31P are described. The dependences of spectral parameters on a structure of the substitutes at phosphorus atom in these compounds are discussed. 相似文献
22.
Two‐component relativistic density functional theory (DFT) with the second‐order Douglas–Kroll–Hess (DKH2) one‐electron Hamiltonian was applied to the calculation of nuclear magnetic resonance (NMR) shielding constant. Large basis set dependence was observed in the shielding constant of Xe atom. The DKH2‐DFT‐calculated shielding constants of I and Xe in HI, I2, CuI, AgI, and XeF2 agree well with those obtained by the four‐component relativistic theory and experiments. The Au NMR shielding constant in AuF is extremely more positive than in AuCl, AuBr, and AuI, as reported recently. This extremely positive shielding constant arises from the much larger Fermi contact (FC) term of AuF than in others. Interestingly, the absolute values of the paramagnetic and the FC terms are considerably larger in CuF and AuF than in others. The large paramagnetic term of AuF arises from the large d‐components in the Au dπ –F pπ and Au sdσ–F pσ molecular orbitals (MOs). The large FC term in AuF arises from the small energy difference between the Au sdσ + F pσ and Au sdσ–F pσ MOs. The second‐order magnetically relativistic effect, which is the effect of DKH2 magnetic operator, is important even in CuF. This effect considerably improves the overestimation of the spin‐orbit effect calculated by the Breit–Pauli magnetic operator. © 2013 Wiley Periodicals, Inc. 相似文献
23.
Yoichi Ishibai Takashi Nishikawa Shigeyoshi Miyagishi 《Journal of Dispersion Science and Technology》2013,34(8):1093-1098
Nano‐sized TiO2 sol was prepared through a wet synthesis process. The synthesis procedure involved hydrolysis of TiCl4, acid treatment, and a SiO2 surface‐modifying process. Before surface modification, the TiO2 suspension was treated with acid to remove Na ions, soluble TiO2, and other impurities. The acid treatment of a TiO2 suspension at a higher temperature was proved to be useful for effective SiO2 modification. The colloidal sol provided high transparency in visible light as well as excellent UV‐shielding properties. Surface modification of TiO2 particles with SiO2 greatly improved both the dispersing stability in neutral pH and the photostability of TiO2 colloidal sol. 相似文献
24.
Nuclear Magnetic Resonance (NMR) parameters including isotropic and anisotropic chemical shielding parameters (CSI, CSA) and electronic structures were calculated using Density Functional Theory (DFT) for Disiline-doped Aluminum Nitride Nanotubes (Disiline-AlNNTs). The 27Al and 15N nuclear magnetic resonance (NMR) was calculated by means of the GIAO, CSGT, and IGAIM methods. Geometry optimizations were carried out at the B3LYP/6-311+G* level of theory using the Gaussian 98 program suite. The calculated parameters indicate that the Al and N atoms located at the mouths of nanotube have the smallest and largest chemical shielding isotropic (CSI) values among those of other identical ones, respectively. In the Disiline-doped model, the NMR parameters of those nuclei directly bonded to the C and Si atoms show significant changes, while other nuclei changes are inferior. 相似文献
25.
Jorge A. Vila Yelena A. Arnautova Osvaldo A. Martin Harold A. Scheraga 《Journal of computational chemistry》2014,35(4):309-312
The goal of this study is twofold. First, to investigate the relative influence of the main structural factors affecting the computation of the 13C′ shielding, namely, the conformation of the residue itself and the next nearest‐neighbor effects. Second, to determine whether calculation of the 13C′ shielding at the density functional level of theory (DFT), with an accuracy similar to that of the 13Cα shielding, is feasible with the existing computational resources. The DFT calculations, carried out for a large number of possible conformations of the tripeptide Ac‐G XY ‐NMe, with different combinations of X and Y residues, enable us to conclude that the accurate computation of the 13C′ shielding for a given residue X depends on the: (i) (?,ψ) backbone torsional angles of X ; (ii) side‐chain conformation of X ; (iii) (?,ψ) torsional angles of Y ; and (iv) identity of residue Y . Consequently, DFT‐based quantum mechanical calculations of the 13C′ shielding, with all these factors taken into account, are two orders of magnitude more CPU demanding than the computation, with similar accuracy, of the 13Cα shielding. Despite not considering the effect of the possible hydrogen bond interaction of the carbonyl oxygen, this work contributes to our general understanding of the main structural factors affecting the accurate computation of the 13C′ shielding in proteins and may spur significant progress in effort to develop new validation methods for protein structures. © 2013 Wiley Periodicals, Inc. 相似文献
26.
27.
Polyimide nanocomposites having low-k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior. 相似文献
28.
Jingyun Luo Dexian Yin Kejing Yu Dr. Hongfu Zhou Dr. Bianying Wen Dr. Xiangdong Wang 《Chemphyschem》2022,23(4):e202100778
In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending poly (butylene succinate) (PBS) with carbon nanotubes (CNTs) followed by foaming with supercritical CO2. The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Increasing the CNT content from 0 to 4 wt % leads to an increase of approximately 3 orders of magnitude in storage modulus and nearly 9 orders of magnitude in enhancement of electrical properties. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm3/g. This study provides a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties. 相似文献
29.
Dr. Muntadar A. H. Al-Yassiri 《ChemistryOpen》2021,10(10):976-985
Off-nucleus isotropic magnetic shielding (σiso(r)) and multi-points nucleus independent chemical shift (NICS(0-2 Å)) index were utilized to find the impacts of the isomerization of gas-phase furfuraldehyde (FD) on bonding and aromaticity of FD. Multidimensional (1D to 3D) grids of ghost atoms (bqs) were used as local magnetic probes to evaluate σiso(r) through gauge-including atomic orbitals (GIAO) at density functional theory (DFT) and B3LYP functional/6-311+G(d,p) basis set level of theory. 1D σiso(r) responses along each bond of FD were examined. Also, a σiso(r) 2D-scan was performed to obtain σiso(r) behavior at vertical heights of 0–1 Å above the FD plane in its cis, transition state (TS) and trans forms. New techniques for evaluating 2D σiso(r) cross-sections are also included. Our findings showed that bonds in cyclic and acyclic parts of FD are dissimilar. Unlike the C−O bond of furanyl, the C=O bond of the formyl group is magnetically different. C−C and C−H bonds in furanyl are found similar to those in aromatic rings. A unique σiso(r) trend was observed for the C2−C6 bond during FD isomerization. Based on NICS(0-2 Å) values, the degree of aromaticity follows the order of cis FD<trans FD<furan<TS FD. 相似文献
30.
Overexposure to ultraviolet (UV) with high energy can not only hurt human skin but also accelerate the degradation of organic matter. Hence, the preparation of polymer‐based UV‐shielding nanocomposites has attracted substantial attention due to the low cost, easy processing and wide applications. Notably, the highly efficient UV‐shielding polymer nanocomposites are still hindered by the agglomeration of inorganic anti‐UV nanoparticles (Nps) in polymer matrix and the narrow absorption range of UV‐shielding agents. To overcome the aforementioned bottlenecks, surface engineering of anti‐UV Nps including organic modification and inorganic hybridization has been extensively employed to enhance the UV‐shielding efficiency of composites. Herein, to deliver the readers a comprehensive understanding of the surface engineering of anti‐UV Nps, we systematically summarize the recent advances in surface organic modification and inorganic hybridization related to anti‐UV Nps. The UV‐shielding mechanism and the factors affecting UV‐shielding efficiency of polymer nanocomposites are also discussed. Finally, perspectives on remaining challenges and future development of highly efficient UV‐shielding composites are outlined. 相似文献