Jürgen Lauterwein

An Evaluation of Various Pulse Sequences for the Suppression of Acoustic Ringing in Oxygen-17 NMR

Abstract Several pulse sequences were examined for their ability to reduce the effects of acoustic ringing in 17O NMR. Both the three-pulse sequence and the extended spin-echo sequence gave satisfactory results when the phases of the pulses were appropriately cycled; however, large offset effects due to finite pulse power were introduced. The efficiency of the extended spin-echo sequence for solvent peak suppression is evaluated. The difficulties in recording extremely broad oxygen resonances ( Δv 1 2 > 8 kHz ) and the limits of their detectability are discussed.

Natural-abundance 17O NMR of monosaccharides☆

Abstract Natural-abundance “high-resolution” 17O NMR spectra of d -glucose, d -mannose, d -galactose, and some methoxy derivatives of d -glucose were recorded in aqueous solution. The sensitivity and spectral resolution was improved by optimizing the accumulation and manipulation of data. The water solvent peak was suppressed through use of 17O-depleted water or displaced by addition of paramagnetic shift reagents. With Dy3+ the 17O NMR spectrum of d -glucose remained unaltered; however, the water peak was shifted outside the carbohydrate spectral region. The 17O NMR resonances were assigned from earlier data for some specifically 17O-enriched monosaccharide derivatives. The anomeric hydroxyl resonances could also be located because of their exchange with the 17O-depleted water. Although the chemical shifts of the monosacharides generally parallel the sequence of chemical shifts for simple primary and secondary alcohols and substituted ethers, several exceptions were found and discussed in terms of steric and electrostatic repulsive forces between oxygens.

Pelargonidin 3-malonylsophoroside from the red Iceland poppy, Papaver nudicaule

Abstract Pelargonidin 3-malonylsophoroside was characterized as a flower pigment in a red form of the Iceland poppy, Papaver nudicaule.

The INEPT experiment for nonselective polarization transfer in 170 NMR

Abstract 17 O INEPT spectra are presented for the first time. They were performed with the shortest pulse sequence without proton decoupling. The optimum interpulse delay, as well as the size of the maximum enhancement, was shown to be in agreement with theory. The application of the 17 O INEPT experiment was limited by the strong proton transverse relaxation due to scalar coupling with the quadrupolar oxygen nucleus. The pulse repetition rates could be increased by the addition of Cr(acac) 3 . 17 O INEPT was most useful in the discrimination between OH and O-alkyl resonances and in the suppression of solvent peaks. Also, 17 O, 1 H couplings could be determined by INEPT which were not resolved in conventional spectra.

Assignment of the quaternary olefinic carbon atoms of β-carotene by 2D 1H, 13C-chemical shift correlation via long-range couplings

The quaternary carbon atoms of β-carotene can be conveniently assigned by heteronuclear correlation via the two-and three-bond couplings with the methyl protons.

Does a 2 ← 5β-turn structure exist in enkephalins?: Study of a fully protected Leu-enkephalin in organic solution by 17O-NMR

The 17O chemical shifts of the Gly-2 and Gly-3 oxygens of a fully protected Leu-enkephalin were measured to be identical in acetone solution. This allows the conclusion that neither of these peptide oxygens is hydrogen bonded and that no specific 2----5 beta-turn structure exists to an appreciable extent.The 17O chemical shifts of the Gly‐2 and Gly‐3 oxygens of a fully protected Leu‐enkephalin were measured to be identical in acetone solution. This allows the conclusion that neither of these peptide oxygens is hydrogen bonded and that no specific 2 ← 5 β‐turn structure exists to an appreciable extent.

A 1H and 13C n.m.r. study of all-trans retinal in dodecyldimethylamine oxide micelles

Abstract Complexes of all-trans retinal with dodecyldimethylamine oxide micelles at neutral pH have been characterized by proton and carbon-13 n.m.r. and u.v. spectroscopy. The chemical shift data show that the aldehyde group of all-trans retinal is directed towards the interfacial Stern layer with the polyene chain and the β-ionone ring solubilized by the hydrocarbon chains of the detergent. No self-association of all-trans retinal has been observed in these micelles.

A study of the cis/trans isomerism of N-acetyl-L-proline in aqueous solution by 17O N.M.R. spectroscopy

The cis and trans isomers of both the enriched carboxy and amide groups of N-acetyl-L-proline can be observed by 17O n.m.r. spectroscopy and are shown in each case to give parallel pH titration curves.