Search results for "Nuclear magnetic resonance"

Optically Detected Magnetic Resonance of Chlorophyll Triplet States in Water-Soluble Chlorophyll Proteins from Lepidium virginicum: Evidence for Exci…

2018

Optically detected magnetic resonance of triplet states populated by photoexcitation in water-soluble chlorophyll proteins (WSCPs) from Lepidium virginicum has been performed using both absorption and fluorescence detection. Well resolved triplet-singlet (T-S) spectra have been obtained and interpreted in terms of electronic interactions among the four chlorophylls (Chls), forming two dimers in the WSCP tetramer. Localization of the triplet state on a single Chl leads to a redistribution of the oscillator strength in the remaining three Chls of the complex. By comparing the spectra with those obtained on a substoichiometric WSCP complex containing only 2 Chls per protein tetramer, we proved…

Coupling of Cholesterol and Cone-shaped Lipids in Bilayers Augments Membrane Permeabilization by the Cholesterol-specific Toxins Streptolysin O and V…

2001

Abstract Vibrio cholerae cytolysin (VCC) forms oligomeric pores in lipid bilayers containing cholesterol. Membrane permeabilization is inefficient if the sterol is embedded within bilayers prepared from phosphatidylcholine only but is greatly enhanced if the target membrane also contains ceramide. Although the enhancement of VCC action is stereospecific with respect to cholesterol, we show here that no such specificity applies to the two stereocenters in ceramide; all four stereoisomers of ceramide enhanced VCC activity in cholesterol-containing bilayers. A wide variety of ceramide analogs were as effective asd-erythro-ceramide, as was diacylglycerol, suggesting that the effect of ceramide …

Electron paramagnetic resonance (EPR) spin trapping of biological nitric oxide

2007

Nitric oxide (NO) is a free radical species with multiple physiological functions. Because of low concentrations and short half-life of NO, its direct measurement in living tissues remains a difficult task. Electron paramagnetic resonance (EPR) spin trapping is probably one of the best suitable platforms for development of new methods for quantification of biological NO. The most reliable EPR-based approaches developed so far are based on the reaction of NO with various iron complexes, both intrinsic and exogenously applied. This review is focused on the current state and perspectives of EPR spin trapping for experimental and clinical NO biology.

Taxane analysis by high performance liquid chromatography-Nuclear magnetic resonance spectroscopy ofTaxus species

1998

High performance liquid chromatography–nuclear magnetic resonance spectroscopic analyses of taxane diterpenoids from three Taxus species were carried out employing a stopped-flow technique. Several taxanes have been identified from 500 mg leaf samples without prior isolation. © 1998 John Wiley & Sons, Ltd.

Lignans from Torreya jackii identified by stopped-flow high-performance liquid chromatography–nuclear magnetic resonance spectroscopy

1999

Abstract Coupled reversed-phase HPLC–NMR spectroscopy has been applied to the rapid detection and identification of plant metabolites of Torreya jackii , a species of Taxaceae. Analysis consisted of gradient HPLC elution and directly coupled 1 H NMR (500 MHz) spectroscopic detection in a stopped-flow mode. Seven lignans were detected and their structures were elucidated, based on their HPLC– 1 H NMR spectra and MS data. The structures were confirmed by isolation of the single components followed by conventional NMR measurements.

Secondary metabolites from the aerial parts of Cytisus villosus Pourr

2017

Phytochemical investigation of the aerial parts of Cytisus villosus Pourr. resulted in the isolation and characterization of a new isoflavan, (3S, 4S)-2′,4′-dihydroxy-3′-methoxy-6,7-methylenedioxyisoflavan- 4-ol (1), and a new monoterpene, (4R,6S)-4-hydroxy-2,2,6-trimethyl-9-oxabicyclo [4.2.1] non-1(8)-en-7-one (2), together with four known flavonoids: geinstein (3), chrysin (4), chrysin -7-O-β-D-glucopyranoside (5) and 2″-O-α-L-rhamnosylorientin (6). The structures of the new compounds were elucidated on the basis of extensive spectroscopic analysis, including 1D, 2D NMR ((1)H, (13)C, COSY, TOCSY, HMBC and HSQC) and HRESIMS. The absolute configurations of 1 and 2 were established by the co…

Alkaloids from the Sponge-Associated FungusAspergillussp.

2012

Seven new alkaloids including tryptoquivaline K (1) and fumiquinazolines K–P (2–7), bearing a rare 1-aminocyclopropane-1-carboxylic acid residue, together with six known compounds (8–13), were isolated from the fungus Aspergillus sp. obtained from the Mediterranean sponge Tethya aurantium. The structures of the new compounds were determined by extensive analysis by 1D and 2D NMR spectroscopy and mass spectrometry. The absolute configurations of tryptoquivaline K (1) and fumiquinazolines K and L (2, 3) were determined by TDDFT ECD calculations of their solution conformers, and the configurational assignment of the related fumiquinazolines M–P (4–7) was achieved by comparison of their ECD spe…

Optical rotatory dispersion and circular dichroism of poly-L-lactide. A reply to a letter by M. Goodman and M. D'alagni (1)

1967

VCD studies on cyclic peptides assembled from L-α-amino acids and a trans-2-aminocyclopentane- or trans-2-aminocyclohexane carboxylic acid.

2010

The increasing interest in peptidomimetics of biological relevance prompted us to synthesize a series of cyclic peptides comprising trans-2-aminocyclohexane carboxylic acid (Achc) or trans-2-aminocyclopentane carboxylic acid (Acpc). NMR experiments in combination with MD calculations were performed to investigate the three-dimensional structure of the cyclic peptides. These data were compared to the conformational information obtained by electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy. Experimental VCD spectra were compared to theoretical VCD spectra computed quantum chemically at B3LYP/6-31G(d) density functional theory (DFT) level. The good agreem…

Lactones from the Sponge-Derived Fungus Talaromyces rugulosus.

2017

The marine-derived fungus Talaromyces rugulosus isolated from the Mediterranean sponge Axinella cannabina and cultured on solid rice medium yielded seventeen lactone derivatives including five butenolides (1–5), seven (3S)-resorcylide derivatives (6–12), two butenolide-resorcylide dimers (13 and 14), and three dihydroisocoumarins (15–17). Among them, fourteen compounds (1–3, 6–16) are new natural products. The structures of the isolated compounds were elucidated by 1D and 2D NMR (Nuclear Magnetic Resonance) spectroscopy as well as by ESI-HRMS (ElectroSpray Ionization-High Resolution Mass Spectrometry). TDDFT-ECD (Time-Dependent Density Functional Theory-Electronic Circular Dichroism) calcul…