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排序方式: 共有430条查询结果,搜索用时 15 毫秒
21.
Dr. Sophie Carron Dr. Maarten Bloemen Prof. Luce Vander Elst Prof. Sophie Laurent Prof. Thierry Verbiest Prof. Tatjana N. Parac‐Vogt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4521-4527
A new prototype consisting of ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles decorated with europium(III) ions encapsulated in a DO3A organic scaffold was designed as a platform for further development of bimodal contrast agents for MRI and optical imaging. The USPIO nanoparticles act as negative MRI contrast agents, whereas the europium(III) ion is a luminophore that is suitable for use in optical imaging detection. The functionalized USPIO nanoparticles were characterized by TEM, DLS, XRD, FTIR, and TXRF analysis, and a full investigation of the relaxometric and optical properties was conducted. The typical luminescence emission of europium(III) was observed and the main red emission wavelength was found at 614 nm. The relaxometric study of these ultrasmall nanoparticles showed r2 values of 114.8 mm ?1Fes?1 at 60 MHz, which is nearly double the r2 relaxivity of Sinerem®. 相似文献
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Sabbe MK Saeys M Reyniers MF Marin GB Van Speybroeck V Waroquier M 《The journal of physical chemistry. A》2005,109(33):7466-7480
A complete and consistent set of 95 Benson group additive values (GAV) for the standard enthalpy of formation of hydrocarbons and hydrocarbon radicals at 298 K and 1 bar is derived from an extensive and accurate database of 233 ab initio standard enthalpies of formation, calculated at the CBS-QB3 level of theory. The accuracy of the database was further improved by adding newly determined bond additive corrections (BAC) to the CBS-QB3 enthalpies. The mean absolute deviation (MAD) for a training set of 51 hydrocarbons is better than 2 kJ mol(-1). GAVs for 16 hydrocarbon groups, i.e., C(C(d))(3)(C), C-(C(d))(4), C-(C(t))(C(d))(C)(2), C-(C(t))(C(d))(2)(C), C-(C(t))(C(d))(3), C-(C(t))(2)(C)(2), C-(C(t))(2)(C(d))(C), C-(C(t))(2)(C(d))(2), C-(C(t))(3)(C), C-(C(t))(3)(C(d)), C-(C(t))(4), C-(C(b))(C(d))(C)(H), C-(C(b))(C(t))(H)(2), C-(C(b))(C(t))(C)(H), C-(C(b))(C(t))(C)(2), C(d)-(C(b))(C(t)), for 25 hydrocarbon radical groups, and several ring strain corrections (RSC) are determined for the first time. The new parameters significantly extend the applicability of Benson's group additivity method. The extensive database allowed an evaluation of previously proposed methods to account for non-next-nearest neighbor interactions (NNI). Here, a novel consistent scheme is proposed to account for NNIs in radicals. In addition, hydrogen bond increments (HBI) are determined for the calculation of radical standard enthalpies of formation. In particular for resonance stabilized radicals, the HBI method provides an improvement over Benson's group additivity method. 相似文献
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Maarten C. Krol Cornelis J. M. Huige Cornelis Altona 《Journal of computational chemistry》1990,11(7):765-790
The anomeric effect of the functional groups X = C?N, C?CH, COOH, COO?, O? CH3, NH2, and NH+3 has been studied with ab initio techniques. Geometry effects upon rotation around the central C? O bond in X? CH2? O? CH3 have been compared in the various compounds. The energy differences between the conformers with a gauche and trans (X? C? O? C) arrangement were calculated at the 6-31G* level in the fully optimized 4-21G geometries. Energy differences calculated at the 4-21G level appeared not to be reliable, especially for the groups X that contain non-sp3 hybridized atoms. The 6-31G* energy differences indicate a normal anomeric effect for X = COO?, O? CH3, and NH2(g+) (ca. 13 kJ/mol) and a small anomeric effect for X = COOH, C?N, and C?CH (ca. 6 kJ/mol). For X = NH2(t) and NH+3 a reverse anomeric effect occurs. These observations are in line with experimental results and evidence is given for a competition among various stereoelectronic interactions that occur at the same anomeric center. Geometry variations can be understood in terms of simple rules associated with anomeric orbital interactions. Trends followed when the group X is varied cannot be related in a straightforward way to the energy differences between the trans and the gauche forms in these compounds. Only the variation in the gauche torsion angle X? C? O? C follows roughly the same trend. 相似文献
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van Bommel MR Berghe IV Wallert AM Boitelle R Wouters J 《Journal of chromatography. A》2007,1157(1-2):260-272
Chromatographic and spectroscopic techniques are evaluated for the analysis of early synthetic dyes. The research focuses on the analysis of dyestuffs that were developed and used in the period 1850-1900, which has not been well investigated so far. The aim of this study was to develop and evaluate techniques that can be applied in the field of culture and art. A selection of 65 synthetic dyestuffs was chosen to investigate the usefulness of the analytical techniques applied. As a case study three embroideries, designed by the well-known 19th century French painter Emile Bernard, were investigated to obtain more information about the use and behaviour of synthetic dyes. 相似文献
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Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements
Dr. Justus S. Diercks Dr. Juan Herranz Dr. Kathrin Ebner Dr. Nataša Diklić Dr. Maximilian Georgi Piyush Chauhan Dr. Adam H. Clark Dr. Maarten Nachtegaal Prof. Dr. Alexander Eychmüller Prof. Dr. Thomas J. Schmidt 《Angewandte Chemie (International ed. in English)》2023,62(16):e202216633
In recent years, operando/in situ X-ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA-spectra with a satisfactory signal-to-noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion- and mass-transport limitations. To shed light on the impact of this variable on the spectro-electrochemical results, in this study we investigate Pd-hydride formation in carbon-supported Pd-nanoparticles (Pd/C) and an unsupported Pd-aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL-thickness largely determines the hydride formation trends inferred from spectro-electrochemical experiments, therewith calling for the minimization of the CL-thickness in such experiments and the use of complementary thin-film control measurements. 相似文献
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We present first experimental evidence for quantum reflection, originating exclusively from an attractive potential between an atom and a solid surface, at energies far from the threshold E(i)-->0. The system of light and stable 3He atoms scattering from an alpha-quartz crystal allows confirmation of recent theory on quantum reflection up to its asymptotic behavior, determined by the nonretarded van der Waals potential -C(3)/r(3). From the data, the gas-solid interaction potential is deduced quantitatively, covering the energy region, in which retardation plays a role. 相似文献
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