排序方式: 共有342条查询结果,搜索用时 15 毫秒
41.
It is well-known that many covalently bonded atoms of group VI have specific positive regions of electrostatic potential (σ-holes) through which they can interact with Lewis bases. This interaction is called ‘chalcogen bond’ by analogy with halogen bond and hydrogen bond. In this study, ab initio calculations are performed to predict and characterise chalcogen···π interactions in XHS···HCCH and XHSe···HCCH complexes, where X = F, Cl, Br, CN, OH, OCH3, NH2, CH3. For the complexes studied here, XHS(Se) and HCCH are treated as a Lewis acid and a Lewis base, respectively. The CCSD(T)/aug-cc-pVTZ interaction energies of this type of σ-hole bonding range from ?1.18 to ?4.83 kcal/mol. The calculated interaction energies tend to increase in magnitude with increasing positive electrostatic potential on the extension of X–S(Se) bond. The stability of chalcogen···π complexes is attributed mainly to electrostatic and correlation effects. The nature of chalcogen···π interactions is unveiled by means of the atoms in molecules, natural bond orbital, and electron localisation function analyses. 相似文献
42.
ABSTRACTAn ab initio study, at the MP2/aug-cc-pVTZ level of theory, is performed to study σ-hole bond in binary XH3C···CNY complexes, where X = CN, F, NO2, CCH and Y = H, OH, NH2, CH3, C2H5, Li. This type of interaction is labelled as ‘carbon bond’, since a covalently bonded carbon atom acts as the Lewis acid in these systems. The geometrical and energetic parameters of the resulting complexes are analysed in details. The interaction energies of these complexes are between ?4.97 kJ/mol in (HCC)H3C···CNH and ?23.07 kJ/mol in (O2N)H3C···CNLi. It is found that the electrostatic interaction plays a key role in the overall stabilisation of these carbon-bonded complexes. To deepen the understanding of the nature of the carbon-bonding, the molecular electrostatic potential, natural bond orbital, quantum theory of atoms in molecules and non-covalent interaction index analyses are also used. Our results indicate that the carbon bond is favoured over the C-H···C hydrogen bond in the all complexes considered and may suggest the possible important roles of the C···C interactions in the crystal growth and design. 相似文献
43.
An elementary proof of a formula for the 2-norm distance from a normal matrix A to the set of matrices with a multiple zero
eigenvalue is given. Earlier, the authors obtained this formula as an implication of a nontrivial result due to A. N. Malyshev.
Bibliography: 4 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 50–56. 相似文献
44.
Let \((R,\mathfrak {m})\) be a Noetherian local ring, I be an ideal of R, and M be a finitely generated R-module such that \({\text {H}}_I^t(M)\) is Artinian and I-cofinite, where \(t={\text {cd}}\,(I,M)\). In this paper, we give some equivalent conditions for the property Also, we show that if \({\text {H}}_I^t(M)\) satisfies the property \((*)\), then \({\text {H}}_I^t(M)\cong {\text {H}}_{\mathfrak {m}}^t(M/N)\) for some submodule N of M with \({\text {dim}}\,(M/N)=t\).
相似文献
$$\begin{aligned} {\text {Ann}}\,_R\left( 0:_{{\text {H}}_I^t (M)} \mathfrak {p}\right) =\mathfrak {p}~\text {for all prime ideals }~ \mathfrak {p}\supseteq {\text {Ann}}\,_R{\text {H}}_I^t(M).(*) \end{aligned}$$
45.
D. Nazari 《Journal of Computational and Applied Mathematics》2010,234(3):883-891
In this paper, the fractional differential transform method is developed to solve fractional integro-differential equations with nonlocal boundary conditions. The method is described and illustrated with numerical examples. The results reveal that the method is accurate and easy to apply. 相似文献
46.
Mehdi D. Esrafili Parisasadat Mousavian Fariba Mohammadian-Sabet 《Molecular physics》2013,111(6):726-733
ABSTRACTThe aim of this study is to investigate the influence of a hydrogen- or lithium-bonding interaction on the cooperativity of chalcogen bonds in linear NCH···(OCX)2–5 and NCLi···(OCX)2-5 clusters (X?=?S, Se). The nature of interactions in the optimised structures is analysed by means of molecular electrostatic potential, quantum theory of atoms in molecules, natural bond orbital and electron density difference methods. According to our results, the formation of a lithium-bonding interaction in NCLi···(OCX)2-5 clusters induces a large increase in the strength of X···O chalcogen bonds, and hence their cooperativity. This can be mainly rationalised in terms of the electrostatic nature of chalcogen bonds as well as the fundamental orbital interaction between the interacting OCX subunits. The results of this study provide a theoretical evidence for the tuning of chalcogen bonds cooperativity by a hydrogen- or lithium-bonding. 相似文献
47.
Ali Darehkordi Maryam Hosseini Fariba Rahmani 《Journal of heterocyclic chemistry》2019,56(4):1306-1311
Syntheses of fused heterobicyclic systems containing 1,2,4‐triazolopyridinone moieties were accomplished by heterocyclization of 1,6‐diamino‐2‐oxo‐4‐phenyl‐1,2‐dihydropyridine‐3,5‐dicarbonitriles and ninhydrin in ethanol and in the presence of boric acid as a catalyst in 30 min at room temperature. All compounds have been screened for their photophysical properties. Results showed that all compounds exhibit near infrared emissions at 876 nm. 相似文献
48.
Hojjatollah Nazari Shohreh Azadi Shadie Hatamie Mahsa Soufi Zomorrod Khadijeh Ashtari Masoud Soleimani Simzar Hosseinzadeh 《先进技术聚合物》2019,30(8):2086-2099
The graphene‐based nanocomposites are considered as great candidates for enhancing electrical and mechanical properties of nonconductive scaffolds in cardiac tissue engineering. In this study, reduced graphene oxide‐silver (rGO‐Ag) nanocomposites (1 and 2 wt%) were synthesized and incorporated into polyurethane (PU) nanofibers via electrospinning technique. Next, the human cardiac progenitor cells (hCPCs) were seed on these scaffolds for in vitro studies. The rGO‐Ag nanocomposites were studied by X‐ray diffraction (XRD), Raman spectroscopy, and transmission electron microscope (TEM). After incorporation of rGO‐Ag into PU nanofibers, the related characterizations were carried out including scanning electron microscope (SEM), TEM, water contact angle, and mechanical properties. Furthermore, PU and PU/nanocomposites scaffolds were used for in vitro studies, wherein hCPCs showed good cytocompatibility via 3‐(4, 5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay and considerable attachment on the scaffold using SEM studies. Real‐time polymerase chain reaction (PCR) and immunostaining studies confirmed the upregulation of cardiac specific genes including GATA‐4, T‐box 18 (TBX 18), cardiac troponin T (cTnT), and alpha‐myosin heavy chain (α‐MHC) in the PU/rGO‐Ag scaffolds in comparison with neat PU ones. Therefore, these nanofibrous rGO‐Ag–reinforced PU scaffolds can be considered as suitable candidates in cardiac tissue engineering. 相似文献
49.
Aqsa Habib Mansoureh Nazari V. Muhammad Adnan Iqbal Haq Nawaz Bhatti M.B. Khadeer Ahmed A.M.S. Abdul Majid 《Journal of Saudi Chemical Society》2019,23(7):795-808
The promising biomedical applications of silver complexes stimulated the researchers to test these compounds against cancer. The present research work was designed to achieve this goal. In this work, a series of 5-methyl benzimidazole based N-Heterocyclic carbene ligands and respective silver(I) complexes were synthesized and tested on cancer cell lines to assess their anticancer activity. Unsymmetrically substituted benzimidazole was found unique in its reactivity and generation of a single product during NHC ligand formation was only possible after two successive alkylations with same alkyl halide. The corresponding Ag(I)-NHC adducts were obtained by in situ deprotonation of the NHC ligands. Synthesized compounds were characterized by various physcio-chemical and spectroscopic methods. Single crystal X-ray diffraction study of complex 7 revealed its mononuclear structure. Preliminary in vitro anticancer study of azolium salts and respective Ag(I)-NHC complexes against human breast cancer (MDA-MB-231), colon cancer (HCT-116) and normal endothelial cells (EA.hy926) cells revealed that all the compounds are more cytotoxic to cancer cells than normal cells and the complexes are relatively more potent compared to the corresponding NHC ligands. It was found that increased chain length and presence of methyl substituent on benzimidazole ring enhance the biopotency of Ag(I)-NHC complexes. The synthesized compounds were further studied for pro-apoptotic mechanism of action via Rhodamine 123 test. The tested compounds were found to induce apoptosis via extrinsic mitochondrial pathway. 相似文献
50.
Ramezanizadeh Mahdi Ahmadi Mohammad Ali Ahmadi Mohammad Hossein Alhuyi Nazari Mohammad 《Journal of Thermal Analysis and Calorimetry》2019,137(1):307-316
Journal of Thermal Analysis and Calorimetry - Due to the enhanced thermophysical specifications of nanofluids, such as thermal conductivity, these types of fluids are appropriate candidates for... 相似文献