High-resolution 13C nuclear magnetic resonance studies of small unilamellar vesicles containing glycophorin A

Glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, has been incorporated in small unilamellar vesicles containing phosphatidylcholine and phosphatidylethanolamine in varying proportions. Hydrocarbon chains of these two lipids have been selectively enriched with ¹³C and ¹³C-NMR spin relaxation parameters have been monitored in the presence and absence of protein. Perturbations to ¹³C line-widths and spin-lattice relaxation times are found to be small and consistent with relatively weak interactions. The perturbations, though small, show some specificity. The carbonyl carbons in both phosphatidylcholine and phosphatidylethanolamine are broadened, but in addition the olefinic carbons in phosphatidylethanolamine are broadened.     

13C NMR analysis of aporphine alkaloids

The ¹³C NMR spectra of some tertiary and quaternary aporphine alkaloids are recorded and the signals assigned. The substituent shielding effects together with the effects of N- and O-methylation, and the twisting of the biphenyl system, are analysed and utilized in the spectral interpretation.     

13C NMR structural investigation of scleroglucan

This paper concerns the ¹³C NMR signal assignment in the DMSO of a neutral polysaccharide, scleroglucan. The previously proposed chemical structure is confirmed. The ¹³C NMR spectrum shows that scleroglucan is a regular poly (A, B, C, D) type glucan. The relaxation times of the different series of carbon atoms demonstrate that a single, pendant glucose group is attached to each third monomer along the main chain of what is a β(1 → 3)-glucan. Partial acid hydrolysis gives a spectrum analogous to that of the β(1 → 3)-d-glucan, curdlan, and confirms the structure of the polymer backbone.In aqueous solution, no signal has been obtained due to the existence of a rigid, ordered conformation as demonstrated by optical rotation; in the presence of sodium hydroxide, a conformational transition is produced just as with curdlan. The conclusion is that the behaviour of scleroglucan in solution is similar to that of other β(1 → 3)-d-glucans even though it is more soluble.     

Conversion of 2,5-dimethylfuran to 2-hydroxy-5-hydroperoxy-2,5-dimethyldihydrofuran,a true 1O2-derived reaction in aqueous 1O2 generating systems

It has been studied whether 2,5-dimethylfuran (DMF) is a specific ¹O₂ trapping agent in aqueous system. The exposure of DMF to aqueous ¹O₂ generating system (Rose Bengal photooxygenation system) gave 2-hydroxy-5-hydroperoxy-2,5-dimethyldihydrofuran (a hydrated form of endoperoxide, ¹O₂-derived reaction product) and cis-diacetylethylene (cis-DAE), while the bromine-catalyzed autoxidation of DMF afforded only trans-DAE. In Fenton system (·OH generating system) DMF was converted in the main to cis-DAE, but not to the hydrated form of endoperoxide. The exposure of DMF to acetaldehyde-xanthine oxidase system failed to detect the hydrated form of endoperoxide, but chiefly yielded a non-specific oxidation product, cis-DAE.     

Lipid lateral diffusion in oriented lipid/D2O multilayers by pulsed NMR

The temperature and hydration dependences of lipid lateral diffusion in model membrane/D₂O multilayers of dipalmitoyl (DPL), dilauryl (DLL) and egg yolk (EYPC) lecithins were measured using pulsed gradient proton nuclear magnetic resonance (NMR) spin echo techniques. Oriented samples were used to minimize anisotropic dipolar interactions and permit formation of a spin echo. Significantly lipid lateral diffusion is hydration dependent over the range studied (15–40% D₂O w/w), varying in DPL over this range for example by a factor of 2. For the saturated lipids at the same hydration and temperature, diffusion decreases monotonically as the chain length increases. The results tend to be larger, by factors of 2–5, than the earlier electron spin resonance (ESR) spin label results, the differences being attributable in part to the differences in hydration and to the absence of probe effects in this work. The addition of cholesterol (28.6 mol%) decreases diffusion of the lipids. Comparisons with other methods of lateral diffusion measurements are made.     

13C NMR spectroscopy of Pyrrolizidine alkaloids

The ¹³C NMR spectra of nine pyrrolizidine alkaloids of the macrocyclic diester type, seven of the corresponding N-oxides and of the parent base retronecine have been recorded and the signals assigned. The 13C NMR signals were found to be sensitive to structural variation in both the diester moiety and the heterocyclic ring system, providing useful information for structural elucidation, particularly when the ¹H NMR spectra may be difficult to interpret.     

13C and31P NMR spectroscopic studies on glucose metabolism inTribolium confusum

Nuclear magnetic resonance (NMR) technology was applied to study the glucose metabolism inTribolium confusum (Coleoptera).¹³C signals of D-(1-¹³C)glucose eaten by beetles were clearly detected in such metabolites of the glucose metabolism as glycogen, trehalose, triacylglycerol, alanine and proline by¹³C-NMR. After glucose feeding the³¹P-NMR spectra ofT. confusum showed the signal intensity increases in arginine-phosphate, sugar-phosphate and uridine diphosphoglucose. The results demonstrated the potential of NMR analysis for the study of glucose metabolism inT. confusum.     

13C NMR spectra of olean-18-ene derivatives

The ¹³C NMR signals of sixteen derivatives of olean-18-ene-triterpenes have been assigned.     

13C NMR spectral analysis of some isoquinoline alkaloids

The ¹³C NMR spectra of some isoquinoline and tetrahydroisoquinoline alkaloids and their corresponding N-methosalts and of the bisbenzylisoquinoline alkaloid isochondodendrine were recorded and the signals assigned. The substituent shielding effects and the ¹³C¹H long range couplings were analysed and utilized in the spectral interpretation.     

13C NMR spectral analysis of grindelane diterpenoid acids

The ¹³C NMR spectra of methyl grindelate and some of its derivatives were recorded and the signals assigned. Based on these assignments and on a comparison with previously reported data, information regarding the structures and stereochemistry of the products under study was obtained.     

13C NMR analysis of alkaloids from peschiera fuchsiaefolia

Fractionation of an ethereal extract of Peschiera fuchsiaefolia resulted in the isolation of decarbomethoxyvoacamine, demethylvoacamine, voacamidine, perivine, 16-epiaffinine and voacanginehydroxyindolenine, together with the previously reported alkaloids voacamine, voacangine, voachalotine and affinisine. Analysis of the ¹³C NMR spectra of the bisindole alkaloids and of 16-epiaffinine is reported.     

Observation of carbon labelling in cell metabolites using proton spin echo NMR

A heteronuclear spin echo experiment is described which allows detection of both ¹²C and ¹³C labelled species in a ¹H spectrum. Fractional labelling of ¹³C labelled metabolites can thus be observed. The method is illustrated with a study of the exchange of ¹³C label between the methyl groups of alanine and pyruvate catalysed by the enzyme alanine aminotransferase (E.C. 2.6.1.2) both in the human erythrocyte and $\text{in}\text{,}\text{vitro}$.     

A 13C NMR study of the biosynthesis of the anthraquinone dothistromin by Dothistroma pini

A ¹³C-NMR study of the biosynthesis of dothistromin by Dothistroma pini was undertaken. The biosynthetic labelling pattern in this bistetrahydr     

13C NMR spectral analysis of lignans from Araucaria angustifolia

Pinoresinol dimethyl ether, secoisolariciresinol, lariciresinol, isolariciresinol and isolariciresinol-4′-methyl ether were isolated from the knots of dead trees of Araucaria angustifolia. The ¹³C NMR spectra of these compounds, their methyl and acetyl derivatives, and the corresponding one of matairesinol, have been recorded and the signals assigned. On the basis of these assignments, the structure of the new monomethyl ether of isolariciresinol has been established.     

13C NMR analysis of podophyllotoxin and some of its derivatives

The ¹³C NMR spectra of podophyllotoxin and some of its derivatives were recorded and the signals assigned. Based on these assignments and on comparison with previously reported ¹H NMR data, information regarding the stereochemistry and conformations of the products under study was obtained.     

Biosynthesis of Pr toxin from [1,2-13C]acetate: occurrence of induced 13C13C coupling

The biosynthesis of PR toxin was studied by incorporation of [1,2-¹³C]acetate. The biosynthesis of the eremophilane skeleton of PR toxin follows th