Search results for " nuclear magnetic resonance spectroscopy"
showing 10 items of 173 documents
Protein structure prediction assisted with sparse NMR data in CASP13
2019
CASP13 has investigated the impact of sparse NMR data on the accuracy of protein structure prediction. NOESY and 15 N-1 H residual dipolar coupling data, typical of that obtained for 15 N,13 C-enriched, perdeuterated proteins up to about 40 kDa, were simulated for 11 CASP13 targets ranging in size from 80 to 326 residues. For several targets, two prediction groups generated models that are more accurate than those produced using baseline methods. Real NMR data collected for a de novo designed protein were also provided to predictors, including one data set in which only backbone resonance assignments were available. Some NMR-assisted prediction groups also did very well with these data. CAS…
Spectroscopic studies of the interaction of 3-(2-thienyl)-[1,2,3]triazolo[1,5-a]pyridine with 2,6-dimethyl-β-cyclodextrin and ctDNA
2016
The inclusion complexation behavior of 3-(2-thienyl)-[1,2,3]triazolo[1,5-a] pyridine (TTP) with native β-cyclodextrin and derivatized cyclodextrins was investigated. Stability constants for complexes with 1 : 1 molar ratios were calculated from phase solubility diagrams. The solubilizing efficiency of the TTP inclusion complex is enhanced in the order of DMβCD > HPβCD > βCD. The TTP-DMβCD inclusion complex was further characterized in solution by means of absorption, fluorescence, 2D NMR and molecular modeling methods. The thermodynamic studies indicate that the inclusion of TTP into the cyclodextrin cavity is mainly an enthalpy-driven process. The 2D NMR studies revealed that the thienyl m…
Ambident PCN Heterocycles: N- and P-Phosphanylation of Lithium 1,3-Benzazaphospholides
2009
Synthetic and structural aspects of the phosphanylation of 1,3-benzazaphospholides 1(Li), ambident benzofused azaphosphacyclopentadienides, are presented. The unusual properties of phospholyl-1,3,2-diazaphospholes inspired us to study the coupling of 1(Li) with chlorodiazaphospholene 2, which led to the N-substituted product 3. Reaction of 1(Li) with chlorodiphenyl- and chlorodicyclohexylphosphane likewise gave N-phosphanylbenzazaphospholes 4 and 5, whereas with the more bulky di-tert-butyl- and di-1-adamantylchlorophosphanes, the diphosphanes 6 and 7 are obtained; in the case of 7 they are isolated as a dimeric LiCl(THF) adduct. Structural information was provided by single-crystal X-ray d…
A novel caryophyllene type sesquiterpene lactone from Asparagus falcatus (Linn.); Structure elucidation and anti-angiogenic activity on HUVECs
2011
Abstract In this study the novel caryophyllene type sesquiterpene lactone (aspfalcolide) has been isolated from the leaves of Asparagus falcatus (Linn.) and characterized by IR, 1D NMR, 2D NMR, EI–MS, HR–ESI–MS and X-ray single crystal diffraction analysis. The aspfalcolide crystallizes in the orthorhombic space group P212121 with a = 6.37360(10), b = 7.6890(2), c = 27.3281(6) A, α = β = γ = 90° and Z = 4. One intermolecular O–H⋯O hydrogen bond enforces these natural molecules to form infinite chains through the crystal. Aspfalcolide was screened for its anti-angiogenic activity in human umbilical vein endothelial cells (HUVECs) and the result showed the remarkable inhibitory effect of aspf…
Induction of ambuic acid derivatives by the endophytic fungus Pestalotiopsis lespedezae through an OSMAC approach
2021
Abstract Ten new ambuic acid derivatives, pestallic acids H–Q including one new iodinated natural product along with two known compounds, ambuic acid and ambuic acid 18-acetate, were obtained through fermentation of the endophytic fungus Pestalotiopsis lespedezae on solid rice medium with 3.5% NaI. Pestallic acids H–Q were undetectable in cultures of the fungus grown on solid rice medium lacking NaI or in those where NaI had been replaced by NaCl or NaBr. The structures of the new metabolites were established on basis of 1D/2D NMR and HRESIMS data. Their absolute configurations were determined by Mosher’s method and TDDFT-ECD calculations. The compounds failed to show antibacterial activity…
Diterpenoids from Tetraclinis articulata that Inhibit Various Human Leukocyte Functions
2003
Ten new compounds, eight of them pimarane derivatives (1-8), together with a menthane dimer (9) and a totarane diterpenoid (10), were isolated from the leaves and wood of Tetraclinis articulata. The structures of 1-10 were established by using spectroscopic techniques, including 2D NMR spectra. Pimaranes 1-5 were found to possess an unusual cis interannular union of the B and C rings, which, from a biogenetic perspective, could be derived from the hydration of a carbocation at C-8. Compounds 4-6 and a mixture of 7 and 11 modulated different human leukocyte functions at a concentration of 10 microM, mainly the degranulation process measured as myeloperoxidase release and, to a lesser extent,…
2H NMR Time Domain Analysis of Ultraslow Reorientations in Supercooled Liquids
1998
A method for evaluating 2H NMR stimulated echo experiments in the time domain is presented. It exhibits a high sensitivity to molecular reorientation mechanisms for small angles. Reorientations with jump angles below 25degrees can be resolved with a precision of approximately 1degrees so that, e.g., rotational diffusion and finite jump angle mechanisms become distinguishable. The method, applicable to isotropic reorientation models, is thought to extend the domain of 2D exchange spectroscopy where the best resolution is obtained in the large angle range of anisotropic reorientational mechanisms. Application to reorientation in the supercooled melt of ortho-terphenyl is presented. These data…
Laser spectroscopy and the properties of light nuclei near the neutron drip line
1993
The interesting nuclear structure phenomena observed in some light nuclei at the neutron drip line suggest the measurement of basic ground state properties such as spins, magnetic moments and electric quadrupole moments. Here it will be discussed what experiments are presently feasable using laser spectroscopy. For the outstanding example of a “halo” nucleus,11Li, the development of a technique combining β-asymmetry detected optical pumping in a fast beam with NMR spectroscopy has yielded pertinent results, the most recent of which is an experimental value of the nuclear quadrupole moment.
Two-dimensional single- and multiple-quantum correlation spectroscopy in zero-field nuclear magnetic resonance.
2020
We present single- and multiple-quantum correlation $J$-spectroscopy detected in zero ($<\!\!1$~$\mu$G) magnetic field using a \Rb vapor-cell magnetometer. At zero field the spectrum of ethanol appears as a mixture of \carbon isotopomers, and correlation spectroscopy is useful in separating the two composite spectra. We also identify and observe the zero-field equivalent of a double-quantum transition in ${}^{13}$C$_2$-acetic acid, and show that such transitions are of use in spectral assignment. Two-dimensional spectroscopy further improves the high resolution attained in zero-field NMR since selection rules on the coherence-transfer pathways allow for the separation of otherwise overlappi…
Di-n-butyltin oxide as a chemical carbon dioxide capturer
2010
Abstract Several synthetic routes to the decakis(di-n-butyltin(IV)) oxocluster, (n-Bu2SnO)6[(n-Bu2SnOCH3)2(CO3)]2 (1), a diorganotin compound previously shown to belong to the class of organotins able to store carbon dioxide, as well as its reactivity toward dimethyl carbonate (DMC), are described. The synthetic route from n-Bu2SnO and DMC was applied for the preparation of the ethoxy analogue of 1, oxocluster 2, using diethyl carbonate. The structural relationship connecting cluster 1, with its precursor PRE-1 isolated from recycling experiments and n-Bu2SnO is discussed. For this purpose, the reactivity of PRE-1 with trifluoromethanesulfonic acid was investigated in order to trace structu…