排序方式: 共有91条查询结果,搜索用时 15 毫秒
21.
Volodymyr Buturlim Michał Falkowski Mykhaylo Paukov Oleksandra Koloskova Daria Drozdenko Milan Dopita 《哲学杂志》2019,99(15):1881-1898
Uranium Laves phase UTi2 does not exist in a pure form, but can be stabilised by the presence of hydrogen, which can be absorbed in concentration exceeding 5?H atoms/f.u. Low temperature specific heat, magnetic susceptibility, and resistivity indicate that UTi2H5 is a spin fluctuator close to the verge of magnetic ordering. Its susceptibility follows at high temperatures the Curie–Weiss law with U effective moment µeff[ ?= 3.1?µB/U and paramagnetic Curie temperature Θp = ?200 K. The temperature dependence of specific heat exhibits a pronounced and weakly field dependent upturn in Cp/T versus T below 10 K reflecting the effect of spin fluctuations. It can be described by an additional T½ term. The Sommerfeld coefficient γ = 256?mJ/mol K2 classifies the compound as a mid-weight heavy fermion. Spin fluctuations are affecting also electrical and thermal transport and thermoelectric power, which all resemble UAl2. A lattice anomaly at ≈ 240?K, attributed to the melting of hydrogen sublattice, reflects in most of bulk properties. 相似文献
22.
Autschbach J Jensen L Schatz GC Tse YC Krykunov M 《The journal of physical chemistry. A》2006,110(7):2461-2473
The optical rotations for six organic molecules (verbenone, fenchone, camphor, nopinone, Tr?ger's base, dimethyl-cyclopropane) and the transition metal complex [Co(en)(3)](3+) were calculated as a function of wavelength using time-dependent density functional theory (TDDFT). In the calculations, a realistic behavior of the optical rotation in the vicinity of an electronic transition was obtained by using a phenomenological damping parameter of the order of 0.2 eV (0.007 au). In comparison with experiment, for the molecules studied here the sign and order of magnitude of the optical rotation as well as the excitation energies were reasonably well reproduced in most computations. These findings apply to the investigated wavelength ranges typically between about 200 and 650 nm even when using comparatively small basis sets. Such calculations might therefore routinely be applied to help assigning the absolute configurations of chiral molecules. Supplementary calculations of the circular dichroism (CD) and comparison with experimental CD were used for further assessment of the optical rotation calculations. In particular, a combined study of optical rotation and CD turned out to be useful in cases where the optical rotatory dispersion in a specific energy range exhibits a considerable blue or red shift or where it is difficult to reproduce because of an interplay of several competing Cotton effects. The influence of basis set, density functional, and the damping parameter was also investigated. 相似文献
23.
A comparison of two theoretical methods based on time-dependent density functional theory for the calculation of the linear dispersive and absorptive properties of chiral molecules has been made. For this purpose, a recently proposed computational method for the calculation of circular dichroism (CD) spectra from the imaginary part of the optical rotation parameter has been applied to six rigid organic molecules. The results have been compared to the CD spectra obtained from the rotatory strengths and from the Kramers-Kronig transformation of optical rotatory dispersion (ORD) curves. We have also investigated a criterion based on the Kramers-Kronig integration formula to determine a number of excitations in truncated CD spectra which may yield a reasonable low frequency resonant ORD. It has been tested by calculating the ORD from the sum-over-states formula both in the nonresonant and resonant regions. Finally, we have applied these methods to model the resonant optical activity of proline at low pH. 相似文献
24.
Kovalska VB Volkova KD Losytskyy MY Tolmachev OI Balanda AO Yarmoluk SM 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(2):271-277
The influence of methyl-, 2-hydroxyethyl-, dimethyl-, diethyl- and benzoyl-amino substituents in the 6,6'-positions of benzothiazole heterocycle of trimethine cyanines on their spectral-luminescent properties and behavior in presence of DNA, RNA and BSA was studied. It was shown that incorporation of 6,6'-substituents generally leads to the increase in dyes tendency to aggregation, resulting in the considerable decrease in the emission intensity of the disubstituted dyes as compared to the unsubstituted ones. Emission of the studied 6,6'-disubstited dyes in DNA presence is considerably more intensive than in presence of RNA, that points on the existing of DNA binding preference for the mentioned dyes. Insertion of benzoyl-amino groups into the 6,6'-positions permitted us to design the DNA-sensitive dyes on the basis of symmetric trimethine cyanines with unsubstituted polymethine chain, while typically such dyes slightly respond on the presence of biopolymers. 6,6'-Benzoyl-amino-disubstituted trimethine cyanines are proposed as efficient dyes for DNA detection. 相似文献
25.
The authors report two methods to determine electromagnetic and chemical enhancement factors in surface-enhanced Raman scattering (SERS), which are based on saturation property and decay dynamics of photoluminescence and concurrent measurements of photoluminescence and resonance Raman scattering intensities. Considerations for experimental implementation are discussed. This study is expected to facilitate the understanding of SERS mechanisms and the advancement of the usage of SERS in chemical and biological sensor applications. 相似文献
26.
Dr. Marta Viciano-Chumillas Dr. Geneviève Blondin Dr. Martin Clémancey Dr. Jurek Krzystek Dr. Mykhaylo Ozerov Prof. Dr. Donatella Armentano Dr. Alexander Schnegg Dr. Thomas Lohmiller Prof. Dr. Joshua Telser Prof. Francesc Lloret Dr. Joan Cano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14242-14251
A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single-ion magnet behaviour, is reported. This behaviour originates from the close proximity (≈550 cm−1) of the intermediate-spin S=3/2 excited states to the high-spin S=5/2 ground state. More quantitatively, although the ground state is mostly S=5/2, a spin-admixture model evidences a sizable contribution (≈15 %) of S=3/2 to the ground state, which as a consequence experiences large and positive axial anisotropy (D=+19.2 cm−1). Frequency-domain EPR spectroscopy allowed the mS= |±1/2⟩→|±3/2⟩ transitions to be directly accessed, and thus the very large zero-field splitting in this 3d5 system to be unambiguously measured. Other experimental results including magnetisation, Mössbauer, and field-domain EPR studies are consistent with this model, which is also supported by theoretical calculations. 相似文献
27.
Tomoyuki Ichiba Ioannis Karatzas Mykhaylo Shkolnikov 《Probability Theory and Related Fields》2013,156(1-2):229-248
We study finite and countably infinite systems of stochastic differential equations, in which the drift and diffusion coefficients of each component (particle) are determined by its rank in the vector of all components of the solution. We show that strong existence and uniqueness hold until the first time three particles collide. Motivated by this result, we improve significantly the existing conditions for the absence of such triple collisions in the case of finite-dimensional systems, and provide the first condition of this type for systems with a countable infinity of particles. 相似文献
28.
Xu C Losytskyy MY Kovalska VB Kryvorotenko DV Yarmoluk SM McClelland S Bianco PR 《Journal of fluorescence》2007,17(6):671-685
The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties.
They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA
with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under
extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations,
seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence
emission, resistance to displacement by Mg2+, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed
highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers,
and were resistant to displacement by Mg2+. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase
assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form
the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1. 相似文献
29.
[reaction: see text] Ohmefentanyl binds to the rat mu-opiod receptor via two dipeptide sequences (Trp-His and Asp-Tyr) that are separated by 170 residues. A turn-inducing tripeptide, Pro-Aib-Aib, holds the dipeptides in a conformation that binds the narcotic (K(b) = 7.1 x 10(4) M(-)(1)) in THF. Binding is specific for ohmefentanyl over morphine and is accompanied by a conformational change in the heptapeptide host. Control experiments with a Gly-Gly-Gly tripeptide linking the dipeptides show no evidence of binding. 相似文献
30.
Seth M Krykunov M Ziegler T Autschbach J Banerjee A 《The Journal of chemical physics》2008,128(14):144105
Magnetically perturbed time-dependent density functional theory is applied to the calculation of the magnetic circular dichroism (MCD) B terms of closed shell molecules. Two approaches to evaluating B term parameters are described: a sum-over-states-type approach and an approach based on the direct solution of the matrix equations. The advantages and disadvantages and technical challenges of each approach are described. The interpretation of the parameters in terms of ground and excited state perturbations are discussed. Several applications of the methodology are described. Calculations of the MCD of ethene are used to compare the sum-over-states and direct solution approaches and to illustrate the potential for analysis. The other applications involving azabenzes, sulfur-nitrogen heterocycles and quinone molecules are compared with experiment and other theoretical calculations. For the most part, all important features of the observed spectra are reproduced. 相似文献