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81.
82.
Ibrahim MA 《Journal of computational chemistry》2011,32(12):2564-2574
A halogen bond is a noncovalent bond between a halogen atom (X) and a Lewis base (Y). This type of bond is attributed to the anisotropic distribution of the charge density on the halogen atom, resulting in the formation of a positive cap (called the σ-hole) centered on the A-X axis. The current research is the first reported molecular mechanical study of halogen bonding, the positive region centered on the halogen atom was represented by an extra-point (EP) of charge. The correlation between the X-EP distance and the X…Y bond length was explored to determine the optimal position of the EP. A test set of 27 halogen-containing molecules complexed to various Lewis bases was studied using molecular mechanical potentials. The molecular mechanical minimized halogen bond lengths and binding energies were in good agreement with the corresponding quantum mechanical values. The EP inclusion on the halogen atom resulted in an improvement in the accuracy of the electrostatic-potential derived charges. The solvation free energies of halobenzene molecules relative to benzene were calculated with and without EP inclusion to assess the accuracy of the developed approach. Molecular mechanical study of halo derivatives of benzotriazole complexed to cyclin-dependent protein kinase 2 (CDK2) was performed, and MM-PB(GB)SA binding energies were calculated as a case study in finding potent halogenated inhibitors that can serve as antitumor drugs. 相似文献
83.
84.
Oriol Pujolàs 《International Journal of Theoretical Physics》2003,42(6):1369-1394
We review the effective potential due to massive bulk scalar fields in higher-dimensional warped brane models found in Flachi et al. (Quantum stabilization of moduli in higher dimensional brane models, arXiv:hep-th/0301, 2003) specializing it to a slice of AdS6 compactified on the circle. This model contains two moduli that parametrize the interbrane distance and the size of S
1, or equivalently the positions of the two branes. Their values determine the Planck/EW hierarchy, in a combination of large volume and redshift effects. It is found that the observed hierarchy is compatible with both moduli stabilized by the Casimir forces without fine-tuning (except for the one needed to match the cosmological constant). This contrasts with the Randall—Sundrum model, where gauge fields in the bulk are needed. 相似文献
85.
V. N. Knyukshto A. M. Shul’ga E. I. Sagun É. I. Zen’kevich 《Journal of Applied Spectroscopy》1998,65(6):943-951
It is established experimentally for the first time that Zn-octaethylporphyrin in a solution of dried methyl cyclohexane is
in unliganded form in the temperature interval of 293-77 K. This form is characterized by the shortest-wave position of absorption
and luminescence spectra, the independence of the degrees of fluorescence and phosphorescence polarizations from the excitation
wavelength, and high phosphorescence time (τT=126 μsec) and quantum yield (φp=0.085) at 77 K. Adding electrodonor components to the methyl cyclohexane or going over to
alcohol-containing polar media leads to the formation of a monoliganded form of ZnOEP, for which we observe a bathochromic
shift of ≈150–350 cm−1 for Q(0,0) absorption and luminescence bands, a splitting of ≈50–100 cm−2 for the Q(0, 0) absorption band, and phosphorescence quenching (τT=60 μsec, φp=0.05-0.03 at 77 K). The effects revealed are explained by a decrease in the symmetry of a ZnOEP molecule in extra
liganding and by an increase in the probability of nonradiative activation for a T1-state due to the extra ligand being involved in the exchange of electron-excitation energy and to the enhancement of a spin-orbital
coupling as a result of the disturbance of the planarity, of a macrocycle.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 900–907, November–December, 1998. 相似文献
86.
水电站尾水平台振动现场测试研究 总被引:1,自引:0,他引:1
水电站尾水平台在正常运行时发现有较大的振动。通过现场实测的方法确定了在各种工况下其上的附加动应力。采用随机振动相关分析的方法确定了引起尾水平台振动的主要原因。实测表明尾水管出口处水流对出水导墙的冲刷是引起尾水平台振动的主要原因。根据现场实测结果,提出提高尾水平台运行安全性的方法。 相似文献
87.
Junpei Harada 《Fortschritte der Physik》2016,64(6-7):510-515
Gauge coupling unification is studied within the framework where there are extra Higgs doublets and E6 exotic fields. Supersymmetric models and nonsupersymmetric models are investigated, and a catalog of models with gauge coupling unification is presented. 相似文献
88.
Katia Arena Francesco Cacciola Francesca Rigano Paola Dugo Luigi Mondello 《Journal of separation science》2020,43(9-10):1781-1789
Olea europaea, meaning “European olive,” is a small tree belonging to the family Oleaceae, occurring in the Mediterranean Basin. Olive oil is an essential component of a balanced diet because of its nutritional value. Among micronutrients, phenolic compounds did show important beneficial effects for human health. The majority of the research studies on the phenol content are carried out by liquid chromatography combined to photodiode array and/or mass spectrometry detection; however, because of matrix complexity, one‐dimensional liquid chromatography cannot be sometimes sufficient to obtain rewarding separations, requiring more advanced analytical techniques. In this work, comprehensive two‐dimensional liquid chromatography, incorporating RP‐Amide and C18 stationary phases, in the first and second dimension, respectively, both under reversed phase conditions, was investigated for the determination of the phenolic fraction in extra virgin olive oil samples. As far as detection is concerned, triple quadrupole mass spectrometry was employed under multi reaction monitoring mode offering superior selectivity and sensitivity. The reduction of matrix effects, when using comprehensive two‐dimensional liquid chromatography with respect to conventional one‐dimensional liquid chromatography, was assessed by comparing the slopes of calibration curves built from standard solutions and spiked olive oil samples. 相似文献
89.
J. R. Mureika 《International Journal of Theoretical Physics》2007,46(1):130-142
An interdisciplinary physical theory of emergent consciousness has previously been proposed, stemming from quantum computation-like
behavior between 109 or more entangled molecular qubit states (microtubulin). This model relies on the Penrose-Diósi gravity-driven wavefunction
collapse framework, and thus is subject to any secondary classical and quantum gravity effects. Specifically, if large extra
spatial dimensions exist in the Universe, then the resulting corrections to Newtonian gravity cause this model to suffer serious
difficulties. It is shown that if the extra dimensions are larger than 100 fm in size, then this model of consciousness is
unphysical. If the dimensions are on the order of 10 fm in size, then a significantly smaller number of microtubulin than
originally predicted are required to satisfy experimental constraints. Some speculation on evolution of consciousness is also
offered, based on the possibility that the size of these extra dimensions may have been changing over the history of the Universe.
PACS numbers: 87.16.Ka, 03.67.Lx, 04.50.+h. 相似文献
90.
通过测定不同温度范围的热力学平衡常数、焓变、熵变、自由能变和补偿温度,研究了枯草杆菌α-淀粉酶在几种色谱介质上的热力学和超热力学。结果表明,在RP-C18反相介质、Zn2+螯合的Sepharose fast-flow亲和介质和WCX-1阳离子交换介质上,当温度分别在13-30和30-50℃范围时,它们的lnKSL分别随绝对温度的倒数线性变化;而在PEG-400和修饰的PEG-400疏水色谱介质上,当温度分别在13-40和13-30℃范围时,它们的lnKSL分别随绝对温度的倒数线性减小,但当温度分别高于40℃和30℃时,它们则随绝对温度的倒数剧烈减小。通过研究不同温度范围的焓变、熵变、自由能变和α-淀粉酶构象变化之间的关系,发现在RP-C18反相和Zn2+螯合的Sepharose fast-flow亲和介质上在30- 50 ℃温度范围内,在WCX-1阳离子交换介质上在13-30 ℃温度范围内,α-淀粉酶的吸附过程由焓变和熵变共同所支配,而在Zn2+螯合的Sepharose fast-flow亲和介质上在13- 30 ℃温度范围内,在WCX-1阳离子交换介质上在30-50 ℃温度范围和在PEG-400 和修饰的PEG-400疏水色谱介质上在13-65 ℃温度范围时,α-淀粉酶的吸附过程仅仅由熵变所控制。最后,通过α-淀粉酶在这些色谱体系中的补偿温度进一步发现,它们的焓变仅仅只能通过它们构象变化所引起的熵变所补偿。 相似文献