Petrik Galvosas

Publications of Petrik Galvosas

• Paramagnetic relaxation enhancement (PRE) as a tool for probing diffusion in environmentally relevant porous media.

  Authors: Filipe Furtado, Petrik Galvosas, Frank Stallmach, Ulf Roland, Jörg Kärger, Frank-Dieter Kopinke

  Environmental science & technology. 08/2011; 45(20):8866-72.

  The transport diffusivity of the paramagnetic molecule 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was measured by monitoring its influence on the NMR transverse relaxation time (T₂) on surroundingThe transport diffusivity of the paramagnetic molecule 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was measured by monitoring its influence on the NMR transverse relaxation time (T₂) on surrounding water protons - also known as paramagnetic relaxation enhancement (PRE). Due to the nature of the PRE effect, few paramagnetic molecules are able to simultaneously reduce the T₂ of many NMR active nuclei, which represents a significant gain in sensitivity. In an aqueous solution, the minimal detectable TEMPO concentration was around 70 ppm. The value of the diffusivity was estimated by fitting the relaxation data, collected as a function of time, with the appropriate solutions of the second Fick's law in respect to the corresponding sample geometry and dimensions. Considering the experimentally determined TEMPO relaxivity in water ("TEMPO-water relaxivity"; R(TEMPO) = (1.05 ± 0.12) × 10⁻³ ppm⁻¹ s⁻¹), the obtained diffusion coefficients (D) of TEMPO in homogeneous solution and in a water saturated sand column (D(bulk) = (6.7 ± 0.4) × 10⁻¹⁰ m² s⁻¹ and D(sand) = (1.4 ± 0.5) × 10⁻¹⁰ m² s⁻¹, respectively) are in good agreement with the expected values (literature values: D(bulk) = 6.6 × 10⁻¹⁰ m² s⁻¹, 1.3 × 10⁻¹⁰ m² s⁻¹ < D(sand) < 2.3 × 10⁻¹⁰ m² s⁻¹). This new approach enables one to determine the diffusivity of paramagnetic molecules in homogeneous (aqueous solution) and porous media with basic NMR equipment, at low concentrations and in a noninvasive manner.

• Mobile aliphatic domains in humic substances and their impact on contaminant mobility within the matrix.

  Authors: Khanneh Wadinga Fomba, Petrik Galvosas, Ulf Roland, Jörg Kaerger, Frank-Dieter Kopinke

  Environmental science & technology. 06/2011; 45(12):5164-9.

  Using a novel NMR option, magic angle spinning pulsed field gradient (MAS PFG) NMR, the mobility of aliphatic domains in humic substances in the presence of toluene (about 4.5 wt. %) has beenUsing a novel NMR option, magic angle spinning pulsed field gradient (MAS PFG) NMR, the mobility of aliphatic domains in humic substances in the presence of toluene (about 4.5 wt. %) has been monitored. Results show a strong correlation between the diffusivities of the mobile aliphatic chains and those of the adsorbed toluene molecules in the matrix as a function of temperature. Particularly, a strong influence of structural relaxation of the humic matrix on the diffusivity of toluene is observed. Our findings confirm that the aliphatic domains in humic substances play an important role in the mobility of sorbed contaminants within this matrix. These findings further confirm the potential of MAS PFG NMR method in monitoring diffusion processes in particulate humic substances.

• Nanoporous glass as a model system for a consistency check of the different techniques of diffusion measurement.

  Authors: Christian Chmelik, Dirk Enke, Petrik Galvosas, Oliver Gobin, Andreas Jentys, Hervé Jobic, Jörg Kärger, Cordula B Krause, Jens Kullmann, Johannes Lercher, Sergej Naumov, Douglas M Ruthven, Tobias Titze

  Chemphyschem : a European journal of chemical physics and physical chemistry. 03/2011; 12(6):1130-4.

  The remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of aThe remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of a hierarchy of transport resistances in addition to the diffusional resistance of the pore system and their differing influence due to the differing diffusion path lengths covered by the different measuring techniques. We report diffusion measurements with nanoporous glasses where the existence of such resistances could be avoided. Molecular propagation over diffusion path lengths from hundreds of nanometers up to millimeters was thus found to be controlled by a uniform mechanism, appearing in coinciding results of microscopic and macroscopic diffusion measurement.

• Guest diffusion in interpenetrating networks of micro- and mesopores.

  Authors: Filipe Furtado, Petrik Galvosas, Maraisa Gonçalves, Frank-Dieter Kopinke, Sergej Naumov, Francisco Rodríguez-Reinoso, Ulf Roland, Rustem Valiullin, Jörg Kärger

  Journal of the American Chemical Society. 02/2011; 133(8):2437-43.

  Pulsed field gradient NMR is applied for monitoring the diffusion properties of guest molecules in hierarchical pore systems after pressure variation in the external atmosphere. Following previousPulsed field gradient NMR is applied for monitoring the diffusion properties of guest molecules in hierarchical pore systems after pressure variation in the external atmosphere. Following previous studies with purely mesoporous solids, also in the material containing both micro- and mesopores (activated carbon MA2), the diffusivity of the guest molecules (cyclohexane) is found to be most decisively determined by the sample "history": at a given external pressure, diffusivities are always found to be larger if they are measured after pressure decrease (i.e., on the "desorption" branch) rather than after pressure increase (adsorption branch). Simple model consideration reproduces the order of magnitude of the measured diffusivities as well as the tendencies in their relation to each other and their concentration dependence.

• Tracing pore-space heterogeneities in X-type zeolites by diffusion studies.

  Authors: Ziad Adem, Jürgen Caro, Filipe Furtado, Petrik Galvosas, Cordula B Krause, Jörg Kärger

  Langmuir : the ACS journal of surfaces and colloids. 01/2011; 27(1):416-9.

  Pore-space homogeneity of zeolite NaX was probed by pulsed field gradient (PFG) NMR diffusion studies with n-butane as a guest molecule. At a loading of 0.75 molecules per supercage, a wide spectrumPore-space homogeneity of zeolite NaX was probed by pulsed field gradient (PFG) NMR diffusion studies with n-butane as a guest molecule. At a loading of 0.75 molecules per supercage, a wide spectrum of diffusivities was observed. Guest molecules in the (well-shaped) zeolite crystallites were thus found to experience pore spaces of quite different properties. After loading enhancement to 3 molecules per supercage, however, molecular propagation ideally followed the laws of normal diffusion in homogeneous media. At sufficiently high guest concentrations, sample heterogeneity was thus found to be of no perceptible influence on the guest mobilities anymore.

• Self-assembly and diffusion of block copolymer templates in SBA-15 nanochannels.

  Authors: Konstantin Ulrich, Petrik Galvosas, Jörg Kärger, Farida Grinberg, Jarian Vernimmen, Vera Meynen, Pegie Cool

  The journal of physical chemistry. B. 03/2010; 114(12):4223-9.

  Molecular dynamics of triblock copolymers under confinement by the nanochannels of SBA-15 was investigated using pulsed field gradient (PFG) NMR spectroscopy with high-intensity field gradientMolecular dynamics of triblock copolymers under confinement by the nanochannels of SBA-15 was investigated using pulsed field gradient (PFG) NMR spectroscopy with high-intensity field gradient pulses. The mesoporous material SBA-15 was synthesized using the surfactant Pluronic P123 (EO(20)-PO(70)-EO(20)). The diffusion of P123 in mixtures with water was studied both in bulk and under the condition of confinement by the mesoporous channels of SBA-15. As a result, at room temperature the diffusion of P123 in SBA-15 is more than a factor three smaller than that of the same polymer in the bulk mixture with water. A pronounced atypical temperature dependence of the measured diffusivities was observed both in the confined and in the bulk systems. This atypical temperature dependence was attributed to the transition from the aggregated state to the molecular solution and gave an evidence for a qualitative similarity of the supermolecular organization of the Pluronic/water mixtures under confinements and in the bulk. Confinements were shown to produce significant effects on diffusion properties of Pluronic molecules. The diffusivity of self-associates forming up at room temperature was considerably diminished in comparison to the bulk systems. In contrast, at low temperatures diffusion of the individually dissolved molecules was comparably fast, but subjected to anisotropy induced by channels.

• New Option for Characterizing the Mobility of Organic Compounds in Humic Acids.

  Authors: Khanneh Wadinga Fomba, Petrik Galvosas, Ulf Roland, Jörg Kärger, Frank-Dieter Kopinke

  Environmental science & technology. 11/2009; 43(21):8264-8269.

  A new NMR option for monitoring the mobility of organic contaminants in SOM in the solid state has been successfully applied for the first time. This recently available noninvasive technique, magicA new NMR option for monitoring the mobility of organic contaminants in SOM in the solid state has been successfully applied for the first time. This recently available noninvasive technique, magic angle spinning pulsed-field gradient (MAS PFG) NMR, combines both NMR spectroscopy and diffusometry to selectively monitor the diffusion of compounds sorbed in porous media or polymer matrices. Using this technique, the diffusion of toluene in humic acid particles has been studied. Measurements were performed under varying temperatures from 25 to 80 degrees C. The obtained diffusion coefficients were found to be in good agreement with those obtained from computer simulations reported elsewhere. Our results show a strong influence of the interaction of toluene with humic acid on its diffusion in the matrix even at elevated temperatures of up to 80 degrees C. The Arrhenius plot of the diffusivities shows a decrease in the activation energy of diffusion above 50 degrees C by a factor of 3. This change of activation energy is attributed to a structural change in the humic acid matrix that influences the mobility of toluene.

• Intracrystalline Transport Resistances in Nanoporous Zeolite X.

  Authors: Armin Feldhoff, Jürgen Caro, Hervé Jobic, Jacques Ollivier, Cordula B Krause, Petrik Galvosas, Jörg Kärger

  Chemphyschem : a European journal of chemical physics and physical chemistry. 09/2009;

  By applying pulsed-field gradient nuclear magnetic resonance (PFG NMR) in comparison to quasi-elastic neutron scattering (QENS), we sense by measurement of the diffusion of n-octane on differentBy applying pulsed-field gradient nuclear magnetic resonance (PFG NMR) in comparison to quasi-elastic neutron scattering (QENS), we sense by measurement of the diffusion of n-octane on different length scales, transport resistances in faujasite type X (which is isostructural with type Y and differs by the lower Si/Al ratio only) with mutual distances of less than 300 nm. Direct observation of the real structure of zeolite X by transmission electron microscopy identifies them as stacking faults of mirror-twin type on (111)-type planes of the cubic framework. Thus, direct experimental proof is given that, in general, nanoporous host systems such as zeolite crystals cannot be considered as a mere arrangement of cavities. It is rather the presence of structural defects that dominates their properties as soon as transport phenomena with practical relevance, including chemical conversion by heterogeneous catalysis and chemical separation by molecular sieving and selective adsorption, become relevant.

• Effects of self-assembly on diffusion mechanisms of triblock copolymers in aqueous solution.

  Authors: Konstantin Ulrich, Petrik Galvosas, Jörg Kärger, Farida Grinberg

  Physical review letters. 02/2009; 102(3):037801.

  Molecular dynamics of self-assembling triblock copolymers in a mixture with water was explored using nuclear magnetic resonance (NMR) diffusometry with high-intensity field gradient pulses. WithMolecular dynamics of self-assembling triblock copolymers in a mixture with water was explored using nuclear magnetic resonance (NMR) diffusometry with high-intensity field gradient pulses. With varying concentration, the diffusivities are found to cover 4 orders of magnitude. The dramatic changes in both the rates and patterns of polymer propagation can be attributed to their ordering in supermolecular formations and prove to be a sensitive means for probing structural and dynamic features of self-aggregation which only now, owing to recent progress in NMR diffusometry, have become accessible to direct observation.

• Scaling Law of Poly(ethylene oxide) Chain Permeation through a Nanoporous Wall.

  Authors: Rudra Choudhury, Petrik Galvosas, Monika Schönhoff

  The journal of physical chemistry. B. 11/2008;

  This paper presents a study of the permeation of poly(ethylene oxide) (PEO) chains through the nanoporous wall of hollow polymeric capsules prepared by self-assembly of polyelectrolytes. We employThis paper presents a study of the permeation of poly(ethylene oxide) (PEO) chains through the nanoporous wall of hollow polymeric capsules prepared by self-assembly of polyelectrolytes. We employ the method of pulsed field gradient (PFG) NMR diffusion to distinguish chains in different sites, i.e., in the capsule interior and free chains in the dispersion, by their respective diffusion coefficient. From a variation of the observation time, the time scale of the molecular exchange between both sites and thus the permeation rate constant is extracted from a two-site exchange model. Permeation rate constants show two different regimes with a different dependence on chain length. This suggests a transition between two different mechanisms of permeation as the molecular weight is increased. In either regime, the permeation time can be described by a scaling law tau approximately N (b) , with b = (4)/ 3 for short chains and b = (1)/ 3 for long chains. We discuss these exponents, which clearly differ from the theoretical predictions for chain translocation.

• Application of pulsed field gradient NMR with high gradient strength for studies of self-diffusion in lipid membranes on the nanoscale.

  Authors: Konstantin Ulrich, Monica Sanders, Farida Grinberg, Petrik Galvosas, Sergey Vasenkov

  Langmuir : the ACS journal of surfaces and colloids. 08/2008; 24(14):7365-70.

  This work demonstrates the feasibility of noninvasive studies of lipid self-diffusion in model lipid membranes on the nanoscale using proton pulsed field gradient (PFG) NMR spectroscopy with high (upThis work demonstrates the feasibility of noninvasive studies of lipid self-diffusion in model lipid membranes on the nanoscale using proton pulsed field gradient (PFG) NMR spectroscopy with high (up to 35 T/m) gradient amplitudes. Application of high gradients affords for the use of sufficiently small diffusion times under the conditions when the width of the gradient pulses is much smaller than the diffusion time. As a result, PFG NMR studies of partially restricted or anomalous diffusion in lipid bilayers become possible over length scales as small as 100 nm. This length scale is important because it is comparable to the size of membrane domains, or lipid rafts, which are believed to exist in biomembranes. In this work, high-gradient PFG NMR has been applied to study lipid self-diffusion in three-component planar-supported multibilayers (1,2-dioleoyl- sn-glycerol-3-phosphocholine/sphingomyelin/cholesterol). The degree of lipid orientation in the bilayers was determined with (31)P NMR. A special insert was designed to mechanically align the multibilayer stack at the magic angle with respect to the direction of the constant magnetic field to address the detrimental effects of proton dipole-dipole interactions on the NMR signal. This insert is an alternative to the conventional method of magic angle orientation of lipid membranes, the goniometer probe, which is not compatible with commercial high-gradient coils because of the lack of space in the magnet bore. Macroscopic orientation of the multibilayer stacks using the insert was confirmed with (1)H NMR spectroscopic studies and the comparison of results obtained from identical experiments using a goniometer probe for orientation. Diffusion studies were carried out at three different constant magnetic field strengths ( B 0) over a range of temperatures and diffusion times. The measured diffusivities were found to be in agreement with the data obtained previously by techniques that are limited to much larger length scales of diffusion observation than high-gradient PFG NMR.

• Robust spatially resolved pressure measurements using MRI with novel buoyant advection-free preparations of stable microbubbles in polysaccharide gels.

  Authors: Robert H Morris, Martin Bencsik, Nikolaus Nestle, Petrik Galvosas, David Fairhurst, Anil Vangala, Yvonne Perrie, Glen McHale

  Journal of magnetic resonance (San Diego, Calif. : 1997). 05/2008;

  MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubblesMRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25min. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-distearoyl-sn-glycero-3-phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar.

• Dynamical aspects of the adsorption hysteresis phenomenon.

  Authors: Rustem Valiullin, Sergej Naumov, Petrik Galvosas, Jörg Kärger, Peter A Monson

  Magnetic resonance imaging. 06/2007; 25(4):481-4.

  Equilibrium and nonequilibrium transport properties of adsorbates in mesoporous Vycor porous glass have been experimentally studied using nuclear magnetic resonance techniques. With the knownEquilibrium and nonequilibrium transport properties of adsorbates in mesoporous Vycor porous glass have been experimentally studied using nuclear magnetic resonance techniques. With the known geometrical characteristics of porous glass and with measured self-diffusivities, transient sorption curves have been quantitatively compared to those predicted within a Fick's law model. This model correctly describes data outside a hysteresis region. In contrast, in the hysteresis region, a two-step mechanism of density relaxation is required to explain the behavior. These two mechanisms are identified as diffusion at early stages and activated density redistribution at later stages of adsorption. The latter mechanism, being intrinsically slow in nature, is anticipated to prevent the system from reaching equilibrium.

• On the use of 2D correlation and exchange NMR spectroscopy in organic porous materials.

  Authors: Petrik Galvosas, Ying Qiao, Monika Schönhoff, Paul T Callaghan

  Magnetic resonance imaging. 06/2007; 25(4):497-500.

  Two-dimensional (2D) nuclear magnetic resonance (NMR) methods for the investigation of correlation and exchange have been introduced in recent years and have been applied to a range of differentTwo-dimensional (2D) nuclear magnetic resonance (NMR) methods for the investigation of correlation and exchange have been introduced in recent years and have been applied to a range of different systems. Here, we report on the use of 2D NMR diffusion-diffusion correlation spectroscopy for the investigation of diffusion anisotropy in cellular plant tissues and of diffusion-diffusion exchange spectroscopy for the study of the diffusive exchange of dextran in a dispersion of polyelectrolyte multilayer hollow capsules. Furthermore, diffusion-relaxation correlation spectroscopy was applied to both systems.

• Recent Fourier and Laplace perspectives for multidimensional NMR in porous media.

  Authors: Paul T Callaghan, Christoph H Arns, Petrik Galvosas, Mark W Hunter, Ying Qiao, Kate E Washburn

  Magnetic resonance imaging. 06/2007; 25(4):441-4.

  Multidimensional NMR techniques used in the measurement of molecular displacements, whether by diffusion or advection, and in the measurement of nuclear spin relaxation times are categorised.Multidimensional NMR techniques used in the measurement of molecular displacements, whether by diffusion or advection, and in the measurement of nuclear spin relaxation times are categorised. Fourier-Fourier, Fourier-Laplace and Laplace-Laplace methods are identified, and recent developments discussed in terms of the separation, correlation and exchange perspective of multidimensional NMR spectroscopy.

• Exploration of molecular dynamics during transient sorption of fluids in mesoporous materials.

  Authors: Rustem Valiullin, Sergej Naumov, Petrik Galvosas, Jörg Kärger, Hyung-June Woo, Fabien Porcheron, Peter A Monson

  Nature. 11/2006; 443(7114):965-8.

  In recent years, considerable progress has been made in the development of novel porous materials with controlled architectures and pore sizes in the mesoporous range. An important feature of theseIn recent years, considerable progress has been made in the development of novel porous materials with controlled architectures and pore sizes in the mesoporous range. An important feature of these materials is the phenomenon of adsorption hysteresis: for certain ranges of applied pressure, the amount of a molecular species adsorbed by the mesoporous host is higher on desorption than on adsorption, indicating a failure of the system to equilibrate. Although this phenomenon has been known for over a century, the underlying internal dynamics responsible for the hysteresis remain poorly understood. Here we present a combined experimental and theoretical study in which microscopic and macroscopic aspects of the relaxation dynamics associated with hysteresis are quantified by direct measurement and computer simulations of molecular models. Using nuclear magnetic resonance techniques and Vycor porous glass as a model mesoporous system, we have explored the relationship between molecular self-diffusion and global uptake dynamics. For states outside the hysteresis region, the relaxation process is found to be essentially diffusive in character; within the hysteresis region, the dynamics slow down dramatically and, at long times, are dominated by activated rearrangement of the adsorbate density within the host material.

• Fast magnetic resonance imaging and velocimetry for liquids under high flow rates.

  Authors: Petrik Galvosas, Paul T Callaghan

  Journal of magnetic resonance (San Diego, Calif. : 1997). 08/2006; 181(1):119-25.

  We here demonstrate the use of NMR velocity imaging techniques to measure flow in a free falling jet of water at speeds up to and on the order of 1m/s. In particular, we show how to adapt the RAREWe here demonstrate the use of NMR velocity imaging techniques to measure flow in a free falling jet of water at speeds up to and on the order of 1m/s. In particular, we show how to adapt the RARE imaging method, based on a CPMG multiple rf pulse train, so that the real and imaginary parts of the signal may be suitably acquired, enabling pulsed gradient spin echo encoding for flow. We term this method "soft-pulse-quadrature-cycled PGSE-RARE" or SPQC-PGSE-RARE. We further demonstrate the use of a one-dimensional (slice selective) imaging method which takes advantage of the cylindrical symmetry of the flow, and considerably shortens the image acquisition time.

• Direct investigation of the fate of NAPL contaminations in a hydrating cement matrix by means of magnetic resonance techniques.

  Authors: Nikolaus Nestle, Petrik Galvosas, Christian Zimmermann, Frank Stallmach, Jörg Kärger

  Environmental science & technology. 03/2004; 38(3):880-5.

  The behavior of nonwatery solvent phases in hydrating cement pastes is of great interest in the context of solidification of wastes containing such phases. In a recent study, the influence of variousThe behavior of nonwatery solvent phases in hydrating cement pastes is of great interest in the context of solidification of wastes containing such phases. In a recent study, the influence of various solvents on the hydration kinetics of cement was studied. In this paper, we present results on the changes in the behavior of the solvent phases themselves during setting of the cement pastes. The methods used in the studies were NMR relaxometry and pulsed field gradient (PFG) NMR diffusometry. To study selectively the behavior of the non-aqueous-phase liquid (NAPL) phases, heavy water was used in the preparation of the cement pastes. The experimental results are in good agreement with the observations from earlier studies concerning the behavior of toluene in hydrating cement. For aliphatic solvents (cyclooctane, n-hexanol), indications for surprisingly large networks of connected droplets in the cement matrices are found.

• Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios.

  Authors: Petrik Galvosas, Frank Stallmach, Jörg Kärger

  Journal of magnetic resonance (San Diego, Calif. : 1997). 03/2004; 166(2):164-73.

  By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (F(p/r) and G(p/r)), magic pulsedBy evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (F(p/r) and G(p/r)), magic pulsed field gradient (MPFG) ratios for the prepare (G(p)/F(p)) and the read (G(r)/F(r)) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the tau-intervals between the pi and pi/2 rf pulses, these two MPFG ratios coincide to eta=G(p/r)/F(p/r)=1-8/[1+(1/3)(delta/tau)(2)]. Since the width of the pulsed field gradients (delta) is bounded by 0< or =delta< or =tau, eta can only be in the range of 5< or =-eta< or =7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.

• PFG NMR and internal magnetic field gradients in plant-based materials.

  Authors: Nikolaus Nestle, Asal Qadan, Petrik Galvosas, Wolfgang Süss, Jörg Kärger

  Magnetic resonance imaging. 10/2002; 20(7):567-73.

  In this contribution, it is demonstrated that inner magnetic field gradients can seriously affect the results of stimulated echo PFG NMR experiments on plant-based materials even if there is noIn this contribution, it is demonstrated that inner magnetic field gradients can seriously affect the results of stimulated echo PFG NMR experiments on plant-based materials even if there is no notable content of paramagnetic substances. Such effects could be observed both in experiments on water in pharmaceutical grade cellulose powder materials and on eggplant fruit tissue. In both cases, it was observed that the effects of internal magnetic field gradients led to different relative values of the diffusion coefficient compared to values obtained with a gradient-compensating pulse sequence.