Biomedical subjects

Harald Jancke

Publications and source records attributed to Harald Jancke.

4 recordsLinked to original sources

PubMed2006

Purity assessment problem in quantitative NMR--impurity resonance overlaps with monitor signal multiplets from stereoisomers.

This paper describes the situation that can emerge when the signals to be evaluated in quantitative NMR measurements-so-called "monitor signals"--consist of several resonance lines from the stereoisomers of the analyte in addition to an impurity signal underneath. The monitor signal problem is demonstrated in the purity assessment of two samples of 2-(isopropylamino)-4-(ethylamino)-6-chloro-1,3,5-triazine (atrazine), a common herbizide which served as analyte in a CCQM intercomparison. It is shown that, in DMSO-d6 solution, a mixture of stereoisomers leads to several individual overlapping singlets, which are further split by spin-spin coupling. A measurement protocol was developed for finding and identifying an impurity that has a signal that is positioned precisely beneath the methyl signal chosen as the monitor signal in one of the samples. Quantitative NMR purity assessment is still possible in this special case, but with higher uncertainty.

Journal Article↗

PubMed2005

Uric acid monohydrate--a new urinary calculus phase.

In our laboratory more than 100,000 urinary calculi have been analysed since 1972. Amongst this huge sample, 15 specimens originating from a total of eight patients were observed showing similar characteristics but escaping unambiguous identification with any of the substances that have been described so far in urinary concrements. Therefore, the unknown substance was submitted to a more extended analytical regimen. Structural analysis by x-ray crystallography turned out to be most successful, identifying the unknown material as uric acid monohydrate. Uric acid monohydrate crystallizes in the monocline space group P2(1)/c. Within the crystal, uric acid and water molecules form continuous layers by hydrogen bonds. This is in contrast to uric acid in its water free and its dihydrate forms, which both crystallize by forming 3-dimensional networks To the best of our knowledge , the existence of a monohydrate form of uric acid has not been reported so far. Accordingly, this is the first report on uric acid monohydrate as a urinary stone component. The frequency of only 0.015% in our survey indicates that uric acid monohydrate is rarely the main component in concrements, in contrast to uric acid and uric acid dihydrate with frequencies of 10% and 6%, respectively. The infrared spectrum of uric acid monohydrate is very similar to that of the other crystal forms of uric acid. Because of this similarity and its low frequency, uric acid monohydrate may have been overlooked as a component of urinary concrements. X-ray diffraction allows for better differentiation in routine stone analysis. All samples of uric acid monohydrate were found by solid state NMR spectroscopy to be highly contaminated by amorphous material. This material consisted of long aliphatic chains reminiscent of lipids and fatty acids, respectively. Concrements consisting of other forms of uric acid or urate lacked this amorphous component. Therefore, a role of this aliphatic material has to be taken into consideration when discussing the conditions that may favour the rare formation of concrements from uric acid monohydrate. As for as the metabolic situation of the affected patients is concerned, no common peculiarities became evident by a retrospective survey.

Aged↗

PubMed2003

Characterization of silsesquioxanes by size-exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Liquid chromatography in combination with spectroscopic methods like matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) or nuclear magnetic resonance (NMR) spectroscopy is a powerful method to characterize silsesquioxanes and silsesquioxane mixtures. As new examples, the formation of silsesquioxyl-substituted silsesquioxanes [(n-octyl)(7)(SiO(1.5))(8)](2)O and [(n-octyl)(7)(SiO(1.5))(8)O](2)[(n-octyl)(6)(SiO(1.5))(8)] as well as the cage rearrangement of octa-[(n-heptyl)silsesquioxane] to larger structures [(n-heptyl)SiO(1.5))](n) up to n=28 are shown.

Journal Article↗

PubMed2002

Non-selective signal loss in the 13C CPMAS NMR spectra of soil organic matter. Investigations of particle size fractions.

In 13C cross-polarisation magic angle spinning (CPMAS) spectra of soil samples, the paramagnetic soil constituents partially discriminate against the signal intensity of the 13C atoms. The aim of the present study was to check to what extent this signal depression depends on the paramagnetic ion content and if it is selective for a certain kind of carbon species. The spectra of a variety of particle size fractions of five quite different soils were recorded. A procedure was developed to compare quantitatively the relative carbon content of the different spectra. It was found that iron ions differ in their efficiency to discriminate against the carbon signals. Nevertheless a strong linear correlation between the detectability of carbon and cube root(wt.%Fe) was observed for both the total signal and the signal of the different carbon species as well. This underlines that iron ions mainly influence the depression of the 13C signal in soil spectra. Furthermore we found, that for C: Fe ratios of 1.5 to 20 non-selective signal losses dominate. Despite a high percentage of non-detectable carbon (up to 90%), the 13C CPMAS spectra of our soil samples correctly reflect the relative composition of soil organic matter.

Carbon Isotopes↗