共查询到9条相似文献,搜索用时 15 毫秒
1.
Mahmoud A. A. Ibrahim Mohammed N. I. Shehata Al-shimaa S. M. Rady Hassan A. A. Abuelliel Heba S. M. Abd Elhafez Ahmed M. Shawky Hesham Farouk Oraby Tamer H. A. Hasanin Mahmoud E. S. Soliman Nayra A. M. Moussa 《International journal of molecular sciences》2022,23(21)
The effects of Lewis basicity and acidity on σ-hole interactions were investigated using two sets of carbon-containing complexes. In Set I, the effect of Lewis basicity was studied by substituting the X3/X atom(s) of the NC-C6H2-X3 and NCX Lewis bases (LB) with F, Cl, Br, or I. In Set II, the W-C-F3 and F-C-X3 (where X and W = F, Cl, Br, and I) molecules were utilized as Lewis acid (LA) centers. Concerning the Lewis basicity effect, higher negative interaction energies (Eint) were observed for the F-C-F3∙∙∙NC-C6H2-X3 complexes compared with the F-C-F3∙∙∙NCX analogs. Moreover, significant Eint was recorded for Set I complexes, along with decreasing the electron-withdrawing power of the X3/X atom(s). Among Set I complexes, the highest negative Eint was ascribed to the F-C-F3∙∙∙NC-C6H2-I3 complex with a value of −1.23 kcal/mol. For Set II complexes, Eint values of F-C-X3 bearing complexes were noted within the −1.05 to −2.08 kcal/mol scope, while they ranged from −0.82 to −1.20 kcal/mol for the W-C-F3 analogs. However, Vs,max quantities exhibited higher values in the case of W-C-F3 molecules compared with F-C-X3; preferable negative Eint were ascribed to the F-C-X3 bearing complexes. These findings were delineated as a consequence of the promoted contributions of the X3 substituents. Dispersion forces (Edisp) were identified as the dominant forces for these interactions. The obtained results provide a foundation for fields such as crystal engineering and supramolecular chemistry studies that focus on understanding the characteristics of carbon-bearing complexes. 相似文献
2.
Vanadium oxides based materials are well known to play an active role as catalysts in many chemical processes of technological
importance like for example hydrocarbon oxidation reactions or selective catalytic reduction of NO
x
in the presence of ammonia. Usually the (010) surface is pointed out as the most important, however one has to underline
that other low-indices surfaces are by far less studied. In the present study the electronic structure of V2O5(001) and (100) surfaces are determined by ab initio DFT methods using gradient-corrected RPBE exchange-correlation functional.
As models of surface sections different embedded V14O45H20, V14O44H18, and V21O65H25 clusters are considered for the (001) surface and V12O40H20, V14O46H22, V16O52H24 for the (100) surface. Detailed analyses of the electronic structure of each cluster are performed using charge density distributions,
Mayer bond orders, electrostatic potential maps, character of frontier orbitals, and density of states (total as well as partial,
atom projected). Results of the calculations show that overall negative charge of the surface oxygen sites scales with their
coordination independent of the surface orientation. Terminal oxygen O(1) is charged the least negatively while doubly coordinated
atoms –O(2) and Oe(2) have charge twice as large. This indicates that bridging (for (001) and (100) netplanes) and edging (only for (001) netplane)
oxygen sites are more nucleophilic than terminal vanadyl sites, which becomes important in view of the reactivity of the different
sites for surface chemical reactions. Vanadium atoms present at these surfaces are positively charged (electrophilic) and
may play a role of electron acceptors. The unsaturated surfaces show a strong tendency to surface relaxation that manifest
by large relaxation energies. 相似文献
3.
4.
A combined study of molecular dynamics (MD) simulation, experimental, and linear regression analysis method is presented for hindered phenol of 3,9‐bis[1,1‐dimethyl‐2‐{b‐(3‐tertbutyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy}ethyl]‐2,4,8,10‐tetraoxaspiro‐[5,5]‐undecane (AO‐80)/nitrile‐butadiene rubber/linear phenolic resin (AO‐80/NBR/PR) composites with different AO‐80 contents to quantitatively establish the relations between microstructure and damping performance. The number of hydrogen bonds (NHBs), the fractional free volume (FFV), and the binding energy (Ebinding) of AO‐80/NBR/PR composites with different AO‐80 content are calculated by MD simulation from the microscopic scale. Damping parameters, including the loss factor peak (tan δmax) and the loss peak area (TA) (tan δ > 0.3), are obtained by dynamic mechanical analysis from macroscopic scale. The quantitative relationships between microstructure parameters (NHBs, Ebinding, and FFV) and macroscopic damping properties (tan δmax and TA) are obtained by linear regression analysis. This research is expected to provide a theoretical guidance for improving the damping performance of rubber‐based organic hybrid composites. 相似文献
5.
Taking the solvent water into account, the energetics of the reactions of O3 with Br? leading to BrO3 ? have been calculated by Density Functional Theory at the B3LYP/6–311+G(d)/SCRF =COSMO level. Br? reversibly forms an adduct, BrOOO?, (ΔG?=?+6 kJ mol?1) that decays spin allowed into BrO? and O2(1Δg) (ΔG?=?+13 kJ mol?1). BrO? undergoes an oxidation to BrO2 ? and a reduction to Br?. This may be accounted for if two different adducts, OBrOOO? and BrOOOO?, decay into BrO? plus O2 and Br? plus 2 O2. After cyclization, OBrOOO? may also lead to Br? plus 2 O2. 相似文献
6.
Fluorine Scan of Inhibitors of the Cysteine Protease Human Cathepsin L: Dipolar and Quadrupolar Effects in the π‐Stacking of Fluorinated Phenyl Rings on Peptide Amide Bonds
下载免费PDF全文
![点击此处可从《ChemMedChem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Maude Giroud Dr. Michael Harder Dr. Bernd Kuhn Dr. Wolfgang Haap Dr. Nils Trapp Dr. W. Bernd Schweizer Prof. Dr. Tanja Schirmeister Prof. Dr. François Diederich 《ChemMedChem》2016,11(10):1042-1047
The π‐stacking of fluorinated benzene rings on protein backbone amide groups was investigated, using a dual approach comprising enzyme–ligand binding studies complemented by high‐level quantum chemical calculations. In the experimental study, the phenyl substituent of triazine nitrile inhibitors of human cathepsin L (hCatL), which stacks onto the peptide amide bond Gly67?Gly68 at the entrance of the S3 pocket, was systematically fluorinated, and differences in inhibitory potency were measured in a fluorimetric assay. Binding affinity is influenced by lipophilicity (clog P), the dipole and quadrupole moments of the fluorinated rings, but also by additional interactions of the introduced fluorine atoms with the local environment of the pocket. Generally, the higher the degree of fluorination, the better the binding affinities. Gas phase calculations strongly support the contributions of the molecular quadrupole moments of the fluorinated phenyl rings to the π‐stacking interaction with the peptide bond. These findings provide useful guidelines for enhancing π‐stacking on protein amide fragments. 相似文献
7.
Xuetong Zhao Hui Zhang Qianqian Zhang Zhishuai Qu Alan Warren Di Wu Xiangrui Chen 《International journal of molecular sciences》2022,23(3)
Three Dysteria species, D. crassipes Claparède & Lachmann, 1859; D. brasiliensis Faria et al., 1922; and D. paracrassipes n. sp., were collected from subtropical coastal waters of the East China Sea, near Ningbo, China. The three species were studied based on their living morphology, infraciliature, and molecular data. The new species D. paracrassipes n. sp. is very similar to D. crassipes in most morphological features except the preoral kinety, which is double-rowed in the new species (vs. single-rowed in D. crassipes). The difference in the small ribosomal subunit sequences (SSU rDNA) between these two species is 56 bases, supporting the establishment of the new species. The Ningbo population of D. crassipes is highly similar in morphology to other known populations. Nevertheless, the SSU rDNA sequences of these populations are very different, indicating high genetic diversity and potentially cryptic species. Dysteria brasiliensis is cosmopolitan with many described populations worldwide and four deposited SSU rDNA sequences. The present work supplies morphological and molecular information from five subtropical populations of D. brasiliensis that bear identical molecular sequences but show significant morphological differences. The findings of this study provide an opportunity to improve understanding of the morphological and genetic diversity of ciliates. 相似文献
8.
The induction period of dehydrogenation and aromatization of methane over Mo/HZSM-5 was studied by combining a pulse reaction
method with TPSR, UV laser Raman, and 13C CPMAS NMR techniques. BET and XRD results showed that Mo species were well dispersed on/in the zeolite. TPSR in CH4 stream revealed that Mo species were reduced in at least two different stages before the formation of benzene. TPR results
were in agreement with TPSR results. The two stages might be attributed to the reduction of two kinds of Mo6+ species to low valence Mo species. One was polymolybdate MoO3, and the other was crystalline MoO3. UV Raman spectra showed the existence of octahedrally coordinated polymolybdate species. XRD, however, did not detect any
crystalline MoO3, possibly because they were too small to be detected with this technique. Pulse reaction results indicated that pre-reduction
of the catalyst and formation of carbonaceous deposit could shorten the induction period. It is concluded that the formation
of active sites during the induction period via partial reduction of Mo6+ species and formation of carbonaceous deposit on partially reduced Mo species is of significance for methane aromatization
over Mo/HZSM-5.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Musubu Takahashi Tomoya Fujie Tsuyoshi Nakano Takato Hara Yasuhiro Shinkai Ryoko Takasawa Yasushi Hara Yoshito Kumagai Chika Yamamoto Toshiyuki Kaji 《International journal of molecular sciences》2021,22(21)
Transforming growth factor-β1 (TGF-β1) occurs at high levels at damage sites of vascular endothelial cell layers and regulates the functions of vascular endothelial cells. Reactive sulfur species (RSS), such as cysteine persulfide, glutathione persulfide, and hydrogen persulfide, are cytoprotective factors against electrophiles such as reactive oxygen species and heavy metals. Previously, we reported that sodium trisulfide, a sulfane sulfur donor, promotes vascular endothelial cell proliferation. The objective of the present study was to clarify the regulation and significance of RSS synthesis in vascular endothelial cells after exposure to TGF-β1. Bovine aortic endothelial cells in a culture system were treated with TGF-β1 to assess the expression of intracellular RSS, the effect of RSS on cell proliferation in the presence of TGF-β1, induction of RSS-producing enzymes by TGF-β1, and intracellular signal pathways that mediate this induction. The results suggest that TGF-β1 increased intracellular RSS levels to modulate its inhibitory effect on proliferation. The increased production of RSS, probably high-molecular-mass RSS, was due to the induction of cystathionine γ-lyase and cystathionine β-synthase, which are RSS-producing enzymes, and the induction was mediated by the ALK5-Smad2/3/4 and ALK5-Smad2/3-ATF4 pathways in vascular endothelial cells. TGF-β1 regulates vascular endothelial cell functions such as proliferation and fibrinolytic activity; intracellular high-molecular-mass RSS, which are increased by TGF-β1, may modulate the regulation activity in vascular endothelial cells. 相似文献