Search results for "two-dimensional"
showing 10 items of 350 documents
A New Aromatic Compound from the Stem Bark of Terminalia catappa
2015
A new aromatic compound 3,4,5-trimethoxyphenyl-1- O-(4-sulfo)-β-D-glucopyranoside (1), in addition to two triterpenoid saponins (chebuloside II, arjunoglucoside II), two triterpenes (arjunolic acid and 3-betulinic acid) and sitosterol-3- O-β-D-glucopyranoside have been isolated from the barks of Terminalia catappa. Their structures have been established on the basis of spectroscopic techniques (1D/2D NMR) and MS. Their cytotoxicity and anti-inflammatory activity, together with the antioxidant capacity of compound 1 were also evaluated.
Cytotoxic Bufadienolides from the Leaves of Melianthus major
2020
Melianthus major is a medicinal plant endemic to South Africa. Its leaf extract led to the isolation of five new bufadienolides, 2β-acetoxy-3,5-di-O-acetylhellebrigenin (1), 2β-acetoxy-3-O-acetylhellebrigenin (2), 2β-acetoxy-14-deoxy-15β,16β-epoxymelianthugenin (4), 2β-acetoxy-14-deoxy-15β,16β-epoxymelianthusigenin (5), and 2β-hydroxymelianthusigenin (6), and four known analogues. The structures of the compounds were elucidated using NMR and HRESIMS data analyses. The relative configurations were defined by single-crystal X-ray crystallography and NOESY correlations. The isolated compounds exhibited strong cytotoxicity against MCF-7 breast cancer cells and sensitive CCRF-CEM and multidrug-r…
Metabolites from Combretum dolichopetalum and its associated endophytic fungus Nigrospora oryzae--Evidence for a metabolic partnership.
2015
Abstract A new altersolanol derivative, 4-dehydroxyaltersolanol A ( 9 ), along with two known sesquiterpenoids, ( S )-7′-hydroxyabscisic acid ( 7 ) and ( S )-abscisic acid ( 8 ) were obtained from the endophytic fungus, Nigrospora oryzae , isolated from leaves of Combretum dolichopetalum . The host plant yielded six known compounds including ellagic acid ( 1 ), 3, 3′, 4-tri-O-methylellagic acid ( 2 ), arjunolic acid ( 3 ), 4′-dihydrophaseic acid ( 4 ), echinulin ( 5 ) and arestrictin B ( 6 ). Close structural similarities with regard to compounds 4 , 7 and 8 were observed between the metabolites from the host plant and those of the endophytic fungus. Furthermore compounds 5 and 6 are relate…
Steroidal Saponins from the Fruits of Cestrum ruizteranianum
2011
Seven spirostane and furostane-type glycosides were isolated from the aqueous methanolic extract of the fruits of Cestrum ruizteranianum and characterized mainly by 2D NMR spectroscopy and mass spectrometry. These known saponins belong to the Δ5-spirostene and Δ5-furostene series and are reported in this species for the first time.
Phytochemistry of Weigela x “kosteriana variegata” (Caprifoliaceae)
2018
One new triterpene glycoside 3- O-β-D-xylopyranosyl-(1→4)-[β-D-glucopyranosyl-(1→3)]-β-D-xylopyranosyl-(1→4)-β-D-xylopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyloleanolic acid, was isolated from Weigela x “kosteriana variegata” (Caprifoliaceae), with three known ones. Their structures were characterized by a combination of mass spectrometry and 1D and 2D NMR spectrocopic techniques including 1H- and 13C NMR, COSY, TOCSY, NOESY, HSQC, and HMBC experiments. The toxicological properties of some glycosides were determined with a zebrafish-based assay. The results show that the most active compounds were toxic to the larvae in the range of 1 μM.
Steroidal saponins from Chlorophytum deistelianum
2016
Abstract Phytochemical investigation of the aerial parts of Chlorophytum deistelianum led to the isolation of four previously undescribed steroidal saponins called chlorodeistelianosides A–D with five known ones. Their structures were established mainly by extensive 1D and 2D NMR spectroscopic techniques and mass spectrometry as (25R)-3β-[(β- d -glucopyranosyl-(1 → 3)-[α- l -rhamnopyranosyl-(1 → 4)]-β- d -xylopyranosyl-(1 → 3)-[β- d -glucopyranosyl-(1 → 2)]-β- d -glucopyranosyl-(1 → 4)-β- d -galactopyranosyl)oxy]-5α-spirostan-12-one, (24S,25S)-24-[(β- d -glucopyranosyl)oxy]-3β-[(β- d -glucopyranosyl-(1 → 2)-[β- d -xylopyranosyl-(1 → 3)]-β- d -glucopyranosyl-(1 → 4)-β- d -galactopyranosyl)ox…
Antiproliferative oleanane saponins from Polyscias guilfoylei
2008
Three new oleanane saponins (1–3), together with four known ones (4–7), were isolated from the aerial parts of Polyscias guilfoylei. Their structures were elucidated by 1D and 2D NMR experiments, including 1D TOCSY, DQF-COSY, ROESY, HSQC, and HMBC spectroscopy, as well as ESIMS analysis. The antiproliferative activity of all compounds was evaluated using three murine and human cancer cell lines; J774.A1, HEK-293, and WEHI-164. All the compounds were inactive except for 3β- O-[β-D-glucopyranosyl-(1→2)-α-L-arabinopyranosyl]-echinocystic acid 28-[ O-β-D-glucopyranosyl-(1→6) O-β-D-glucopyranosyl] ester (3), which was active against all the cell lines.
Magnetic and electronic phase transitions probed by nanomechanical resonators
2020
The reduced dimensionality of two-dimensional (2D) materials results in characteristic types of magnetically and electronically ordered phases. However, only few methods are available to study this order, in particular in ultrathin insulating antiferromagnets that couple weakly to magnetic and electronic probes. Here, we demonstrate that phase transitions in thin membranes of 2D antiferromagnetic FePS3, MnPS3 and NiPS3 can be probed mechanically via the temperature-dependent resonance frequency and quality factor. The observed relation between mechanical motion and antiferromagnetic order is shown to be mediated by the specific heat and reveals a strong dependence of the Néel temperature of…
Complement and Atherogenesis
1999
Abstract —Complement activation occurs in temporal correlation with the subendothelial deposition of LDL during early atherogenesis, and complement also plays a pathogenetic role in promoting lesion progression. Two lesion components have been identified that may be responsible for complement activation. First, enzymatic degradation of LDL generates a derivative that can spontaneously activate complement, and enzymatically degraded LDL (E-LDL) has been detected in the lesions. Second, C-reactive protein (CRP) colocalizes with complement C5b-9, as evidenced by immunohistological studies of early atherosclerotic lesions, so the possibility exists that this acute phase protein also fulfills a…
Interlayer exciton dynamics in van der Waals heterostructures
2019
Atomically thin transition metal dichalcogenides can be stacked to van der Waals heterostructures enabling the design of new materials with tailored properties. The strong Coulomb interaction gives rise to interlayer excitons, where electrons and holes are spatially separated in different layers. In this work, we reveal the time- and momentum-dependent elementary processes behind the formation, thermalization and photoemission of interlayer excitons for the exemplary MoSe2–WSe2 heterostructure. We identify tunneling of holes from MoSe2 to WSe2 on a ps timescale as the crucial process for interlayer exciton formation. We also predict a drastic reduction of the formation time as a function of…