Search results for " Nuclear magnetic resonance"
showing 10 items of 248 documents
A biocompatible ZnNa2-based metal–organic framework with high ibuprofen, nitric oxide and metal uptake capacity
2020
Metal organic frameworks (MOFs) have received significant attention in recent years in the areas of biomedical and environmental applications. Among them, mixed metal MOFs, although promising, are relatively few in number in comparison with their homometallic analogues. The employment of benzophenone-4,4′-dicarboxylic acid (bphdcH2) in mixed metal MOF chemistry provided access to a 3D MOF, [Na2Zn(bphdc)2(DMF)2]n (NUIG1). NUIG1 displays a new topology and is a rare example of a mixed metal MOF based on 1D rod secondary building units. UV-vis, HPLC, TGA, XRPD, solid state NMR and computational studies indicated that NUIG1 exhibits an exceptionally high Ibuprofen (Ibu) and nitric oxide adsorpt…
Unusual oleanane-type saponins from Arenaria montana
2010
Three oleanane-type saponins, 3-O-β-d-glucopyranosylechinocystic acid 28-O-β-d-xylopyranosyl-(1→4)-[α-l-rhamnopyranosyl-(1→2)]-α-l-rhamnopyranosyl ester (1), 3-O-β-d-glucopyranosylechinocystic acid 28-O-α-l-arabinopyranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-[α-l-rhamnopyranosyl-(1→2)]-α-l-rhamnopyranosyl ester (2), 3-O-β-d-glucopyranosylcaulophyllogenin 28-O-β-d-apiofuranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-[β-d-apiofuranosyl-(1→3)]-α-l-rhamnopyranosyl-(1→2)-α-l-rhamnopyranosyl ester (3) were isolated from the whole plant of Arenaria montana. Their unusual structures for the Caryophyllaceae family were established mainly by 2D NMR techniques and mass spectrometry.
New organotin(IV) complexes with L-Arginine,Nα-t-Boc-L-Arginine and L-Alanyl-L-Arginine.Synthesis, structural investigations and cytotoxic activity
2010
Abstract Novel diorganotin(IV) derivatives of l -Arginine (HArg), N α -( tert -Butoxycarbonyl)- l -Arginine (Boc–Arg–OH) and l -Ala- l -Arg (H 2 Ala–Arg), H 2 NC( NH)NH(CH 2 ) 3 CH(NHR′)CO 2 H, where R′ = H in HArg, R′ = C(O)OC(CH 3 ) 3 in Boc–Arg–OH, R′ = H 2 NCH(CH 3 )CO in H 2 Ala–Arg and triorganotin(IV) derivatives of Boc–Arg–OH have been synthesized and structurally characterized. The complexes were investigated by FT-IR and 119 Sn Mossbauer in the solid state and by 1 H, 13 C, 119 Sn and 1 H– 1 H COSY NMR spectroscopy, in solution. The spectroscopic characterization leading to the proposed molecular structures was accomplished on the basis of these experiments. l -Arginine appears to…
Measurement of untruncated nuclear spin interactions via zero- to ultralow-field nuclear magnetic resonance
2015
Zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the coupling averages to zero under isotropic molecular tumbling. Under partial alignment, this information is retained in the form of so-called residual dipolar couplings. We report zero- to ultra-low-field NMR measurements of residual dipolar couplings in acetonitrile…
Cytotoxic labdane diterpenes and bisflavonoid atropisomers from leaves of Araucaria bidwillii
2017
Abstract Chemical investigation of a methanolic extract of leaves from Araucaria bidwillii (Araucariaceae) from Egypt afforded four new labdane diterpenoidal metabolites (1–4) together with one known diterpene, 7-oxocallitrisic acid (5), two triterpenoidal metabolites, 2-O-acetyl-11-keto-boswellic acid (6) and β-sitosterol-3-O-glucopyranoside (7), phloretic acid (8), and two methylated bisflavonoids, agathisflavone-4′,7,7″-trimethyl ether (9) and cupressuflavone-4′,7,7″-trimethyl ether (10). The new metabolites 1–4 were unambiguously identified by applying extensive 1D and 2D NMR spectroscopic studies as well as HRESIMS. The relative and absolute configurations of 1–4 were determined using …
Bile acid–cysteamine conjugates: Structural properties, gelation, and toxicity evaluation
2011
Abstract Design, synthesis, and characterization of six novel bile acid–cysteamine conjugates together with investigation of their structural studies, gelation properties, and preliminary toxicity evaluation, are reported. Solid state properties of selected compounds were studied by means of X-ray diffraction and 13C CPMAS NMR spectroscopy. N-(2-thioethyl)-3α,7α,12α-trihydroxy-5β-cholan-24-amide was shown to exhibit (pseudo)polymorphism, and a single crystal structure of its non-stoichiometric hydrate is reported herein. Cholyl and dehydrocholyl derivatives bearing three functionalities in their steroidal backbone were shown to undergo self-assembly leading to gelation in certain organic so…
Facile synthesis of 5β-cholane-sym-triazine conjugates starting from metformin and bile acid methyl esters: Liquid and solid state NMR characterizati…
2009
Abstract Four bile acid-triazine conjugates: N2′,N2′-dimethyl-6′-(3α-hydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (lithocholyl triazine, 4a), N2′,N2′-dimethyl-6′-(3α,7α-dihydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (chenodeoxycholyl triazine, 4b), N2′,N2′-dimethyl-6′6′-(3α,12α-dihydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (deoxycholyl triazine) (4c), and N2′,N2′-dimethyl-6′-(3α,7α,12α-trihydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (cholyl triazine) (4d) have been prepared and characterized by liquid and solid state NMR. An improved synthetic method produced better yields and an easier purification procedure for 4d than reported in the liter…
Study of the Curing Process of DGEBA Epoxy Resin Through Structural Investigation
2015
In this work, a multi-scale approach with different analytical methods is applied to study the curing process and the structural properties of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin. This monomer, thermally cured using 4,4′-diaminodiphenilsulfone (DDS) as hardener, is analyzed after 10, 45, 90, and 120 min of reaction time at 180 °C to obtain information on samples with different cross-linking densities. Samples are also characterized after extraction in acetone in order to obtain structural information on the insoluble parts. For this purpose, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), solid-state nuclear magnetic resonance (ss-NMR),…
Sulfated Lupane Triterpene Derivatives and a Flavone C-Glycoside from Gypsophila repens
2007
A new sulfated lupane triterpene, Gypsophilin (1), and its glucosyl ester, Gypsophilinoside (2) were isolated from the roots of Gypsophila repens whereas a new flavone C-glycoside (3) was obtained from the aerial parts. Their structures were established as (3beta)-3-O-(sulfo)lup-20(29)-en-23,28-dioic acid (1), (3beta)-3-O-(sulfo)lup-20(29)-en-23,28-dioic acid -28-O-beta-D-glucopyranosyl ester (2) and luteolin-7-O-alpha-L-arabinopyranosyl-6-C-beta-glucopyranoside (3) by spectroscopic methods such as 1D and 2D NMR, HR-ESI-MS and FAB-MS.
Effect of electron-withdrawing substituents on the electrophilicity of carbonyl carbons
2005
Indexación: Scopus The substituent effects on the carbonyl carbon atom for a series of twelve substituted phenyl acetates have been rationalized using a global electrophilicity index. This index is linearly correlated with the experimental reaction rate coefficients. We found that, in contrast to the proposed interpretation based on experimental 13C NMR chemical shifts and ground state destabilization calculations, the electrophilicity of carbonyl compounds increases due to the effect promoted by electron-withdrawing groups in these systems. https://www.sciencedirect.com/science/article/pii/S0040402004018046?via%3Dihub