Biomedical subjects

Nikolaus M Loening

Publications and source records attributed to Nikolaus M Loening.

7 recordsLinked to original sources

PubMed2006

Qualitative and quantitative measurements of hydrogen bond mediated scalar couplings in acyclic 1,3-diols.

[Structure: see text] OH...OH hydrogen bond mediated scalar couplings have been observed in acyclic syn- and anti-1,3-diols using a 2D 1H COSYLR NMR experiment and quantified with an uncertainty of +/-0.02 Hz with a selective-excitation spin-echo NMR experiment. A theoretical investigation confirmed the importance of the hydrogen bond in mediating the spin-spin coupling in these systems.

Hydrocarbons, Acyclic↗

PubMed2005

Quantification of phosphocholine and glycerophosphocholine with 31P edited 1H NMR spectroscopy.

Choline and the related compounds phosphocholine (PC) and glycerophosphocholine (GPC) are considered to be important metabolites in oncology. Past studies have demonstrated correlations linking the relative ratios and concentrations of these metabolites with the development and progression of cancer. Currently, in vivo and tissue ex vivo magnetic resonance spectroscopy methods have mostly centered on measuring the total concentration of these metabolites and have difficulty in differentiating between them. Here, a new scheme that uses (31)P edited (1)H spectroscopy to quantify the concentrations of choline, PC and GPC in biological samples is reported and its applicability is demonstrated using samples of human brain tumor extracts. This method is particularly well-suited for analytical situations where the PC and GPC resonances are not sufficiently resolved and/or are obscured by other metabolites. Consequently, this scheme has the potential to be used for the analysis of choline compounds in ex vivo tissue samples.

Biomarkers, Tumor↗

PubMed2004

Solid-phase synthesis and 1H and 13C high-resolution magic angle spinning NMR of 13C-labeled resin-bound saccharides.

We show how high-resolution magic angle-spinning NMR spectroscopy can be used to characterize 13C-labeled saccharides that have been prepared using solid-phase synthesis techniques while they are still bound to a solid-support resin. With the use of 13C-labeled glucose as the starting material, we have successfully synthesized mono-, di- and trisaccharides with uniform 13C labeling of the saccharide rings. Using these materials, we have been able to assign the 13C and 1H spectra and to characterize various impurities on the resin beads.

Algorithms↗

PubMed2003

Processing DOSY spectra using the regularized resolvent transform.

A new method for processing diffusion ordered spectroscopy (DOSY) data is presented. This method, the regularized resolvent transform (iRRT-the i denoting the adaptation of the method to evaluate the inverse Laplace transform), is better than conventional processing techniques for generating 2D DOSY spectra using data that has poor chemical shift resolution. From the same data, it is possible to use the iRRT to generate 1D subspectra corresponding to different components of the sample mixture; these subspectra compare favorably to 1D spectra of the pure substances. Both the 2D spectra and the 1D subspectra offer a vast improvement over results generated using a conventional processing technique (non-linear least-squares fitting). Consequently, we present the iRRT as a stable and reliable tool for solving the inverse Laplace transform problem present in experiments such as DOSY.

Acyclic Monoterpenes↗

PubMed2003

Single-scan longitudinal relaxation measurements in high-resolution NMR spectroscopy.

Several single-scan experiments for the measurement of the longitudinal relaxation time (T1) are proposed. These experiments result in fast and accurate determinations of the relaxation rate, are relatively robust to pulse imperfections, and preserve information about the chemical shift. The method used in these experiments is to first encode the T1 values as a spatial variation of the magnetization and then to read out this variation either by applying a weak gradient during acquisition or by sequentially observing different slices of the sample. As a result, it is possible to reduce the time necessary to determine the T1 values by one or two orders of magnitude. This time saving comes at the expense of the signal-to-noise level of the resulting spectrum and some chemical shift resolution.

Adenosine Monophosphate↗

PubMed2002

Solution-state dynamic nuclear polarization at high magnetic field.

The goal of dynamic nuclear polarization (DNP) is to enhance NMR signals by transferring electron spin polarization to the nuclei. Although mechanisms such as the solid effect and thermal mixing can be used for DNP in the solid state, currently, the only practical mechanism in solutions is the Overhauser effect (OE), which usually arises due to dipolar relaxation between electrons and the nuclei. At magnetic fields greater than approximately 1 T, dipolar relaxation does not result in a useful enhancement and therefore the conventional wisdom is that DNP should not work in solutions at high magnetic fields. However, scalar relaxation due to time-dependent scalar couplings has a different magnetic field dependence and can lead to substantial OE enhancements. At room temperature and at a magnetic field of 5 T (211 MHz for protons, 140 GHz for electrons), we have observed that scalar relaxation between electrons and nuclei results in NMR signal enhancements of 180, 42, -36, and 8, for 31P, 13C, 15N, and 19F, respectively.

Magnetic Resonance Spectroscopy↗

PubMed2002

Temperature accuracy and temperature gradients in solution-state NMR spectrometers.

In solution-state NMR spectrometers, there is a systematic deviation between the temperature of the sample and the temperature reported by the spectrometer. In addition, temperature gradients are often present in the sample. The size of both the temperature deviations and the temperature gradients depends on several factors, including the temperature, the flow rate of the heating/cooling gas, and the amount of radiofrequency heating.

Journal Article↗