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991.
ChristophA. Schalley Gabriele Silva CarlFriedrich Nising Petra Linnartz 《Helvetica chimica acta》2002,85(6):1578-1596
A series of new rotaxanes with axles different in length was prepared. Following the synthetic protocol utilizing a known anion template effect (Scheme 1), surprisingly low yields in the order of 2–5% were obtained (Scheme 3), which furthermore significantly depended on the nature of the stopper (Fig. 1). Variations in the synthetic procedures and computational results from Monte Carlo simulations allowed us to analyze the origin of these findings: The rotaxane wheel 3 acts as a noncovalently bound ‘protecting group' for the stopper nucleophile. The protection of the nucleophilic phenolate O‐atom depends much on the steric demands of the stoppers (see 2 vs. 10 ) which induce different conformations of the wheel. Based on this model, an improved synthetic scheme is suggested. 相似文献
992.
Leilei Zhang Maha M. Ismail Gabriele Rocchetti Nesrin M. Fayek Luigi Lucini Fatema R. Saber 《Molecules (Basel, Switzerland)》2022,27(2)
Background: A high mortality rate is associated with about 80% of all infections worldwide, mainly due to antimicrobial resistance. Various antimicrobial and cytotoxic activities have been proposed for Meliaceae species. This study aimed to evaluate the in vitro anti-virulence and cytotoxic effect of the leaf extracts of Aphanamixis polystachya, Toona ciliata and Melia azedarach against five MRSA strains and on three cancer cell lines, followed by biological correlation to their encompassed phytoconstituents. Material and Methods: We explored three plants of this family against a panel of Methicillin-resistant Staphylococcus aureus (MRSA) strains and several cancer cell lines to select the most promising candidates for further in vivo and preclinical studies. The phytochemical composition was evaluated by UHPLC–QTOF–MS untargeted profiling. Cell viability was assessed by SRB assay. Minimum Inhibitory Concentration was carried out by using the agar micro-dilution technique. Inhibition of biofilm formation and preformed biofilm disruption were assessed spectrophotomertically, according to the Sultan and Nabil method (2019). Results: A total of 279 compounds were putatively annotated to include different phytochemical classes, such as flavonoids (108), limonoids/terpenoids (59), phenolic acids (49) and lower-molecular-weight phenolics (39). A. polystachya extract showed the most potent cytotoxic activity against Huh-7, DU-145 and MCF-7 cell lines (IC50 = 3, 3.5 and 13.4 µg mL−1, respectively), followed by M. azedarach, with no effect recorded for T. ciliata extract. Furthermore, both A. polystachya and M. azedarach extracts showed promising anti-virulence and antimicrobial activities, with A. polystachya being particularly active against MRSA. These two latter extracts could inhibit and disrupt the biofilm, formed by MRSA, at sub-lethal concentrations. Interestingly, the extracts inhibited hemolysin-α enzyme, thus protecting rabbit RBCs from lysis. A. polystachya extract reduced the pigmentation and catalase enzyme activity of tested pigmented strains better than M. azedarach at both tested sub-MICs. Consequently, susceptibility of the extract-treated cells to oxidant killing by 200 mM H2O2 increased, leading to faster killing of the cells within 120 min as compared to the extract-non-treated cells, likely due to the lower antioxidant-scavenging activity of cells exhibiting less staphyloxanthin production. Conclusion: These findings suggested that both A. polystachya and M. azedarach natural extracts are rich in bioactive compounds, mainly limonoids, phenolics and oxygenated triterpenoids, which can combat MRSA biofilm infections and could be considered as promising sources of therapeutic cytotoxic, antibiofilm and anti-virulence agents. 相似文献
993.
Three superalgebras osp(1; 2; F) (F = R, C, H) and corresponding three supergroups are considered. The transformation laws of spinors with anticommuting components for 3-dimensional (O(2, 1) ≃ Sp(2; R)), 4-dimensional (O(3, 1) ≃ Sp(2, C)) and 5-dimensional (O(4, 1) ≃ Sp(2; H)) Lorentz group are extended in a supersymmetric way by introducing nonlinear realizations of the supergroups OSp(1, 2; F). The affine Grassmann spinors in all three cases are obtained by suitable “flat” limit of the nonlinear realization. Different gradings and different contractions of osp(1,2; F) (F = R, C, H) superalgebras are considered. 相似文献
994.
Enrico Milani Gabriele Milani Antonio Tralli 《International Journal of Solids and Structures》2008,45(20):5258-5288
The study of masonry vaults should take into account the essentials of the material “masonry” – i.e. heterogeneity, almost no resistance to tension combined with a good compressive strength and a high friction coefficient, as well as the overall importance of the geometry for achieving the equilibrium.In this paper, a new six-noded triangular curved element, specifically developed for the kinematic limit analysis of masonry shells, is presented. Plastic dissipation is allowed only at the interfaces (generalized cylindrical hinges) between adjoining elements for combined membrane actions, bending moment, torsion and out-of-plane shear, as it is required for the analysis of thick (Reissner–Mindlin) shells. An upper bound of the collapse load is so obtained, since, looking at the dual formulation, the admissibility of the stress state is imposed only at the element boundaries. Masonry strength domain at each interface between contiguous triangular elements is evaluated resorting to a suitable upper bound FE homogenization procedure. The model is assessed through several numerical simulations on a number of masonry shells experimentally tested until collapse. In particular, the dependence of the collapse multiplier on the mesh and on the material parameters (sensitivity analysis) is thoroughly discussed. 相似文献
995.
Mineral filler magnesium oxide (MgO) has been modified by a grafting process initiated by electron beam treatment. The methacrylic acid (MAA), methyl methacrylate (MM) and maleic anhydride (MA) were used as modifying monomers. The products of performed modification has been investigated by FTIR, DSC and TG methods. Modified fillers have been used in compositions with polyethylene (LDPE). Structure of the samples has been investigated by the SEM method. Mechanical properties of selected samples have been studied and discussed. The optimal results depends on dose level which is specific for certain monomers, ratio and type of monomers used and for grafting process. This paper presents data released to influence the type of monomer on properties of grafted filler. The obtained samples of filling polyethylene were characterized generally by better dispersibility and some mechanical properties. 相似文献
996.
Abeer H. Elmaidomy Eman Maher Zahran Raya Soltane Ahlam Alasiri Hani Saber Che Julius Ngwa Gabriele Pradel Faisal Alsenani Ahmed M. Sayed Usama Ramadan Abdelmohsen 《Molecules (Basel, Switzerland)》2022,27(17)
Malaria is one of the most important infectious diseases worldwide. The causative of the most severe forms of malaria, Plasmodium falciparum, has developed resistances against all the available antimalarial drugs. In the present study, the phytochemical investigation of the green seaweed Halimeda macroloba has afforded two new compounds 1–2, along with 4 known ones 3–6. The structures of the compounds had been confirmed using 1& 2D-NMR and HRESIMS analyses. Extensive machine-learning-supported virtual-screening suggested cytochrome-C enzyme as a potential target for compound 2. Docking, absolute-binding-free-energy (ΔGbinding) and molecular-dynamics-simulation (MDS) of compound 2 revealed the strong binding interaction of this compound with cytochrome-C. In vitro testing for crude extract and isolated compounds revealed the potential in vitro inhibitory activity of both extract and compound 2 against P. falciparum. The crude extract was able to inhibit the parasite growth with an IC50 value of 1.8 ± 0.35 µg/mL. Compound 2 also showed good inhibitory activity with an IC50 value of 3.2 ± 0.23 µg/mL. Meanwhile, compound 6 showed moderate inhibitory activity with an IC50 value of 19.3 ± 0.51 µg/mL. Accordingly, the scaffold of compound 2 can be considered as a good lead compound for the future development of new antimalarial agents. 相似文献
997.
Antonio Cala Peralta Gabriele Soriano Jesús G. Zorrilla Marco Masi Alessio Cimmino Mnica Fernndez-Aparicio 《Molecules (Basel, Switzerland)》2022,27(21)
The study of allelopathic activity of plants and the isolation and characterization of the responsible allelochemicals can lead to the development of environment friendly alternative approaches to weed control. Conyza species are invasive weeds that use allelopathic activity as part of a successful strategy to outcompete neighboring plants. Broomrape weeds are parasitic plants that use host-induced germination and the formation of a haustorium as strategies to infect host plants. The control of broomrape infection in most affected crops is limited or non-existing. In the current study, we investigated the allelopathic activity of Conyza bonariensis organic extracts in suicidal germination and radicle growth of four broomrape species (Orobanche crenata, Orobanche cumana, Orobanche minor and Phelipanche ramosa). A bioactivity-driven fractionation of Conyza bonariensis extracts led to the identification of two germination-inducing molecules and two growth-inhibitory compounds. The germination-inducing metabolites had species-specific activity being hispidulin active on seeds of O. cumana and methyl 4-hydroxybenzoate active in P. ramosa. The growth-inhibitory metabolites (4Z)-lachnophyllum lactone and (4Z,8Z)-matricaria lactone strongly inhibited the radicle growth of all parasitic weed species studied. Some structure–activity relationships were found as result of the study herein presented. 相似文献
998.
Matthew R. Mehlenbacher Rahma Elsiesy Rabina Lakha Rhiza Lyne E. Villones Marina Orman Christina L. Vizcarra Gabriele Meloni Dean E. Wilcox Rachel N. Austin 《Chemical science》2022,13(18):5289
Metallothioneins (MTs) are a ubiquitous class of small metal-binding proteins involved in metal homeostasis and detoxification. While known for their high affinity for d10 metal ions, there is a surprising dearth of thermodynamic data on metals binding to MTs. In this study, Zn2+ and Cu+ binding to mammalian metallothionein-3 (MT-3) were quantified at pH 7.4 by isothermal titration calorimetry (ITC). Zn2+ binding was measured by chelation titrations of Zn7MT-3, while Cu+ binding was measured by Zn2+ displacement from Zn7MT-3 with competition from glutathione (GSH). Titrations in multiple buffers enabled a detailed analysis that yielded condition-independent values for the association constant (K) and the change in enthalpy (ΔH) and entropy (ΔS) for these metal ions binding to MT-3. Zn2+ was also chelated from the individual α and β domains of MT-3 to quantify the thermodynamics of inter-domain interactions in metal binding. Comparative titrations of Zn7MT-2 with Cu+ revealed that both MT isoforms have similar Cu+ affinities and binding thermodynamics, indicating that ΔH and ΔS are determined primarily by the conserved Cys residues. Inductively coupled plasma mass spectrometry (ICP-MS) analysis and low temperature luminescence measurements of Cu-replete samples showed that both proteins form two Cu4+–thiolate clusters when Cu+ displaces Zn2+ under physiological conditions. Comparison of the Zn2+ and Cu+ binding thermodynamics reveal that enthalpically-favoured Cu+, which forms Cu4+–thiolate clusters, displaces the entropically-favoured Zn2+. These results provide a detailed thermodynamic analysis of d10 metal binding to these thiolate-rich proteins and quantitative support for, as well as molecular insight into, the role that MT-3 plays in the neuronal chemistry of copper.Metallothioneins (MTs) are a ubiquitous class of small metal-binding proteins involved in metal homeostasis and detoxification. 相似文献
999.
Dr. Daniela Intrieri Dr. Daniela Maria Carminati Dr. Paolo Zardi Dr. Caterina Damiano Dr. Gabriele Manca Prof. Emma Gallo Dr. Carlo Mealli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16591-16605
A symbiotic experimental/computational study analyzed the Ru(TPP)(NAr)2-catalyzed one-pot formation of indoles from alkynes and aryl azides. Thirty different C3-substituted indoles were synthesized and the best performance, in term of yields and regioselectivities, was observed when reacting ArC≡CH alkynes with 3,5-(EWG)2C6H3N3 azides, whereas the reaction was less efficient when using electron-rich aryl azides. A DFT analysis describes the reaction mechanism in terms of the energy costs and orbital/electronic evolutions; the limited reactivity of electron-rich azides was also justified. In summary, PhC≡CH alkyne interacts with one NAr imido ligand of Ru(TPP)(NAr)2 to give a residually dangling C(Ph) group, which, by coupling with a C(H) unit of the N-aryl substituent, forms a 5+6 bicyclic molecule. In the process, two subsequent spin changes allow inverting the conformation of the sp2 C(Ph) atom and its consequent electrophilic-like attack to the aromatic ring. The bicycle isomerizes to indole via a two-step outer sphere H-migration. Eventually, a ′Ru(TPP)(NAr)′ mono-imido active catalyst is reformed after each azide/alkyne reaction. 相似文献
1000.
Dr. Yuichi Onda Dr. Gabriele Bassi Abdullah Elsayed Franziska Ulrich Sebastian Oehler Louise Plais Dr. Jörg Scheuermann Prof. Dr. Dario Neri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(24):7160-7167
The synthesis and characterization of a novel DNA-encoded library of macrocyclic peptide derivatives are described; the macrocycles are based on three sets of proteinogenic and non-proteinogenic amino acid building blocks and featuring the use of copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction for ring closure. The library (termed YO-DEL) which contains 1 254 838 compounds, was encoded with DNA in single-stranded format and was screened against target proteins of interest using affinity capture procedures and photocrosslinking. YO-DEL selections yielded specific binders against serum albumins, carbonic anhydrases and NKp46, a marker of activated Natural Killer cells. 相似文献