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Biomedical subjects

J Kärger

Publications and source records attributed to J Kärger.

14 recordsLinked to original sources
PubMed2003

The gel-forming behaviour of dextran in the presence of KCl: a quantitative 13C and pulsed field gradient (PFG) NMR study.

Although the gel forming ability of certain polysaccharides in the presence of ions is a well-known phenomenon, detailed physicochemical mechanisms of such processes are still unknown. In this investigation high resolution 13C NMR as well as 1H pulsed field gradient (PFG) NMR were used to investigate the mobility of dextran in the sol and in the gel state. Gel-formation of dextran can be easily induced by the addition of large amounts of potassium chloride. No major differences in the T(1) relaxation times of dextran in the sol and in the gel state could be observed. Accordingly, the analysis of the 13C NMR spectroscopic data did not provide any indication of an observable line-broadening upon gel-formation. However, a KCl concentration dependent decrease of signal intensity in comparison to an internal standard was detected. On the other hand, the PFG NMR studies clearly indicated a gradual diminution of the self-diffusion coefficient of the dextran with increasing molecular weight as well as in the presence of potassium chloride. These measurements revealed in agreement with spectroscopic data that at least one potassium ion per monomer subunit (i.e. one glycopyranose residue) is necessary for gel formation.

Carbon Isotopes↗
PubMed2001

Determination of genuine diffusivities in heterogeneous media using stimulated echo pulsed field gradient NMR.

Pulsed field gradient (PFG) NMR diffusion measurements in heterogeneous media may lead to erroneous results due to the disturbing influence of internal magnetic field gradients. Here, we present a simple theoretical model which allows one to interpret data obtained by stimulated spin echo PFG NMR in the presence of spatially varying internal field gradients. Using the results of this theory, the genuine self-diffusion coefficients in heterogeneous media may be extrapolated from the dependence of the apparent diffusivities on the dephasing time of the simulated echo PFG NMR sequence. Experimental evidence that such extrapolation yields satisfactory results for self-diffusion of hexadecane in natural sediments (sand) and of n-octanol in doped MgO pastes is provided.

Journal Article↗
PubMed2000

Pulsed high-field gradient in vivo NMR spectroscopy to measure diffusional water permeability in Corynebacterium glutamicum.

Pulsed high-field gradient in vivo NMR spectroscopy was used to measure diffusional water permeability in cell suspensions of the Gram-positive bacterium Corynebacterium glutamicum. Two different regions of H2O mobility were detected. One was characterized by the apparent coefficient of self-diffusion, D(1 app) = (4.6-12.7)x10(-8) cm(2) s(-1), depending on the observation time t. The other region was characterized by D(2) = 1.4x10(-5) cm(2) s(-1). The value of D(2) was similar to the diffusion coefficient of H2O in free water and in extracellular biological fluids. Restricted diffusion could be demonstrated for the slower process (D(1)). It was attributed to the cytoplasm of the cells. The membrane permeability, P(d H2O), for C. glutamicum was (4.8+/-0.4)x10(-3) cm s(-1). It compared favorably with values reported for human erythrocytes and was higher by a factor of about 100 compared to the diffusional permeability for ethanol, P(d ethanol), in Zymomonas mobilis. Addition of HgCl2, a water channel inhibitor in eukaryotes, decreased P(d H2O) in C. glutamicum by a factor of approximately 8. To our knowledge, these are the first functional studies of water transport in prokaryotes that yielded quantitative data, viz., transmembrane water permeability expressed through D(H2O) and P(d H2O).

Biological Transport, Active↗
PubMed1999

Self-diffusion of water in cartilage and cartilage components as studied by pulsed field gradient NMR.

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) was used to investigate the self-diffusion behavior of water molecules in cartilage, polymeric cartilage components, and different model polymers. The short-time self-diffusion coefficients (diffusion time delta approximately/= 13 msec) are found to decrease steadily with decreasing water content. This holds equally well for cartilage and cartilage components. The short-time diffusion coefficients are subjected to a rather nonspecific obstruction effect and mainly depend on the water content of the sample. The long-time diffusion coefficients in cartilage (delta approximately/= 500 msec), however, reflect structural properties of this tissue. Measurements with varying observation times as well as experiments involving enzymatic treatment of articular cartilage suggest that the collagenous network in cartilage is likely to be responsible for the observed restricted diffusion.

Animals↗
PubMed1999

Investigating one-dimensional diffusion by quasielastic neutron scattering: a theoretical approach.

Scattering functions and full widths at half maximum for quasielastic neutron scattering (QENS) are calculated for diffusion in systems of one-dimensional channels. The self-correlation function for diffusion in isotropically oriented channels is given and it is found that this function diverges at the origin. The calculations are carried out for both normal and single-file diffusion and the influence of the ballistic phase is investigated. It is found that the ballistic phase influences the scattering functions very strongly for large diffusion coefficients. QENS data from the literature are analyzed with respect to this influence. The influence of three different resolution functions (triangular, Gaussian, and Lorentzian) is considered.

Journal Article↗
PubMed1999

Network of characterizing functions for stationary populations.

A variety of open systems in nature and society exist under dynamic equilibrium, maintained by statistical counterbalance between the entering and leaving of individuals and the stationarity of the exchange processes. A network of functions characterizing the dynamics of such a stationary population is established and discussed, which allows the mutual transference of system properties without the need of any explicit information about the microdynamic processes. In order to illustrate the potential benefit of these interdependence relations, examples taken from diverse branches of research (adsorption and reaction kinetics, demographic analysis, and coronary blood flow diagnosis) are given.

Journal Article↗
PubMed1996

Pulsed field gradient NMR and nuclear magnetic relaxation studies of water mobility in hydrated collagen II.

Transverse nuclear magnetic relaxation and self-diffusion of water were measured in hydrated collagen II. Self-diffusion measurements were conducted by pulsed field gradient NMR (PFG NMR) and weighting of the different species in the signal by variable T2 relaxation in the experiment. Two fractions of water protons were detected, one with a short T2 value but high diffusivity and one with a long T2 value and low, completely restricted diffusion. The distance of the diffusion barriers was determined to be 2.3 microns. Possible reasons for the restriction in the movement of the water molecules in comparison with structural models of collagen II are discussed.

Collagen↗
PubMed1996

PFG NMR tracer exchange measurements of xenon in zeolites.

Understanding mass transport phenomena in zeolites at a molecular level is of prime importance to the study of zeolite catalysis. Among the techniques applicable, PFG NMR has been shown to provide vital information about diffusion of hydrocarbons in zeolites. Here this technique is used to study xenon as a probe molecule, because of its chemical inertness and the large differences in chemical shift of the xenon atoms in the sorbed and gas phase.

Diffusion↗
PubMed1994

PFG NMR self-diffusion measurements in microporous adsorbents.

A survey is given on the possibilities of pulsed field gradient (PFG) NMR to study molecular diffusion in beds of microporous adsorbent particles (zeolite crystallites). Depending on the given adsorbate-adsorbent system, the PFG NMR data on intracrystalline diffusion are both in agreement and disagreement with the results of uptake measurements. Two novel routes to unveil the origin of such discrepancies are described.

Adsorption↗
PubMedDate not supplied

NMR studies of water diffusion and relaxation in hydrating slag-based construction materials.

The NMR relaxation properties of hydrating blast-furnace slag cements have recently been shown to be dominated by the effect of water self-diffusion in internal magnetic field gradients in the pastes. While this was suggested on the basis of NMR relaxometry and magnetic susceptibility data, we report here the results from first direct studies of the water self-diffusion in the hydrating paste using a specialized PFG sequence and very intensive magnetic field gradient pulses.

Construction Materials↗