Daniel Topgaard

Lund University, Lund, Skåne, Sweden

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Publications (102)351.51 Total impact

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    ABSTRACT: We investigate the mechanism responsible for the formation of mesoporous silica formed with the so-called co-structure directing agent (CSDA) route. The synthesis relies on the interaction between silica source (tetraethylorthosilicate), cationic surfactant (C18H37N+(CH3)2(CH2)3N+(CH3)3Br2) and CSDA (carboxyethylsilanetriol), that results in a material functionalized with carboxylic groups. Depending on the concentration of HCl in the synthesis, the structure is defined by Fm-3m (at high pH) and by Fd-3m (at low pH), with a gradual transition in the intermediate pH range. Here we aim at finding the origin for the structural change triggered by pH and investigate the effects of the hydrolysis of the silica source on the overall kinetics of the synthesis. A fast process results in Fm-3m, regardless of pH, and a slow process results in Fd-3m. The hydrolysis step is the important structural control parameter. We studied the cross-linking of silica and CSDA using 29Si NMR. The cross-linking is similar for the two structures, and possibly Fd-3m structure contains slightly more CSDA. 13C PT ssNMR was used to investigate the surfactant mobility/rigidity during the synthesis. The rigidity of the Fm-3m is established much faster than the Fd-3m.
    No preview · Article · Jan 2016 · The Journal of Physical Chemistry C
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    ABSTRACT: Diffusion MRI is a useful probe of tissue microstructure. The conventional diffusion encoding sequence, the single pulsed field gradient, has recently been challenged as more general gradient waveforms have been introduced. Out of these, we focus on q-space trajectory imaging, which generalizes the scalar b-value to a tensor valued entity. To take full advantage of its capabilities, it is imperative to respect the constraints imposed by the hardware, while at the same time maximizing the diffusion encoding strength. We provide a tool that achieves this by solving a constrained optimization problem that accommodates constraints on maximum gradient amplitude, slew rate, coil heating and positioning of radio frequency pulses. The method’s efficacy and flexibility is demonstrated both experimentally and by comparison with previous work on optimization of isotropic diffusion sequences.
    Full-text · Article · Oct 2015 · Journal of Magnetic Resonance
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    ABSTRACT: The understanding of the state of dissolution of cellulose in a certain solvent is a critical step forward in the development of new efficient solvent systems for cellulose. Nevertheless, obtaining such information is not trivial. Recently, polarization transfer solid-state NMR (PTssNMR) was shown to be a very promising technique regarding an efficient and robust characterization of the solution state of cellulose. In the present study, combining PTssNMR, microscopic techniques and X-ray diffraction, a set of alkaline aqueous systems are investigated. The addition of specific additives, such as urea or thiourea, to aqueous NaOH based systems as well as the use of an amphiphilic organic cation, is found to have pronounced effects on the dissolution efficiency of cellulose. Additionally, the characteristics of the regenerated material are strongly dependent on the dissolution system; typically less crystalline materials, presenting smoother morphologies, are obtained when amphiphilic solvents or additives are used.
    Full-text · Article · Oct 2015 · Cellulose
  • Quoc Dat Pham · Daniel Topgaard · Emma Sparr
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    ABSTRACT: Monoterpenes are abundant in essential oil extracted from plants. These relatively small and hydrophobic molecules have shown many important biological fucntions, including antimicrobial activity and membrane penetration enhancement. The interaction between the monoterpenes and lipid bilayers is considered important to the understanding of the biological functions of monoterpenes. In this study we investigate the effect of cyclic and linear monoterpenes on the structure and dynamics of lipids in model membrane. We study the ternary system 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) - monoterpene - water as a model with a focus on dehydrated conditions. By combining complementary techniques, including differential scanning calorimetry (DSC), solid-state nuclear magnetic resonance (ss NMR) and small and wide angle X-ray scattering (SAXS and WAXS), bilayer structure, phase transitions and lipid molecular dynamics are investigated at different water contents. Monoterpenes cause pronounced melting point depression and phase segregation in lipid bilayers, and the extent of these effects depends on the hydration conditions. The addition of a small amount of thymol to the fluid bilayer (volume fraction of 0.03 in the bilayer) leads to an increased order in the acyl-chain close to the bilayer interface. The findings are discussed in relation to biological systems and lipid formulations.
    No preview · Article · Sep 2015 · Langmuir
  • Jenny Algotsson · Jan Forsman · Daniel Topgaard · Olle Söderman
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    ABSTRACT: The delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) method can be used to assess the content of glycosaminoglycan in cartilage. In in vitro and model studies, the content of glycosaminoglycan is often expressed in terms of a fixed charge density (FCD). Values of the fixed charge density obtained using the dGEMRIC method differs from values obtained using other methods. The purpose of this work was to further clarify the origin of this discrepancy. dGEMRIC experiments were performed in a μMRI setup on a custom-designed, well-defined model system capturing the relevant ionic features of cartilage. The model system allows for good control over and systematic variation of relevant parameters. The experimental data was compared with results from Monte Carlo simulations on a coarse-grained model. Application of ideal Donnan theory on data obtained from experiments as well as simulations lead to underestimation of the fixed charge density, in agreement with previous studies. To obtain more accurate estimates of the fixed charge density using the dGEMRIC method, interionic interactions need to be taken into account in the Donnan analysis. Furthermore, the results suggest that the combination of μMRI dGEMRIC experiments and Monte Carlo simulations are useful tools for an improved understanding of these effects. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    No preview · Article · Sep 2015 · Magnetic Resonance in Medicine
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    ABSTRACT: Stejskal and Tanner's ingenious pulsed field gradient design from 1965 has made diffusion NMR and MRI the mainstay of most studies seeking to resolve microstructural information in porous systems in general and biological systems in particular. Methods extending beyond Stejskal and Tanner's design, such as double diffusion encoding (DDE) NMR and MRI, may provide novel quantifiable metrics that are less easily inferred from conventional diffusion acquisitions. Despite the growing interest on the topic, the terminology for the pulse sequences, their parameters , and the metrics that can be derived from them remains inconsistent and disparate among groups active in DDE. Here, we present a consensus of those groups on terminology for DDE sequences and associated concepts. Furthermore, the regimes in which DDE metrics appear to provide microstruc-tural information that cannot be achieved using more conventional counterparts (in a model-free fashion) are elucidated. We highlight in particular DDE's potential for determining microscopic diffusion anisotropy and microscopic fractional anisot-ropy, which offer metrics of microscopic features independent of orientation dispersion and thus provide information complementary to the standard, macroscopic, fractional anisotropy conventionally obtained by diffusion MR. Finally, we discuss future vistas and perspectives for DDE. Magn Reson Med 000:000–000, 2015. V C 2015 Wiley Periodicals, Inc.
    Full-text · Article · Sep 2015 · Magnetic Resonance in Medicine
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    ABSTRACT: Whole wheat pasta offers improved nutritional value compared with regular pasta but lacks appeal to many consumers owing to its negative organoleptic properties, such as texture and taste. Various approaches have been studied to improve these properties in whole wheat products. Optimizing bran particle size showed its potential in noodles, but studies of its effects in pasta are scarce. Therefore, we produced spaghetti enriched with bran fractions similar in chemical composition but with varying median particle sizes of 90, 160, 370, and 440 μm. The effect of bran particles and their median size on dried and cooked pasta was studied by light microscopy and three-dimensional magnetic resonance imaging. In general, bran particle size did not influence the macrostructure in cooked spaghetti. However, larger bran particles created a more heterogeneous microstructure in contrast to smaller particles and affected starch granule swelling. Sensory analysis indicated a preference for pasta containing smaller particles. Our results give new insight into the microstructural features responsible for the negative consumer appeal, and they could be used to guide future efforts in designing improved pasta formulations.
    No preview · Article · Jun 2015 · Cereal Chemistry
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    ABSTRACT: We introduce a nuclear magnetic resonance method for quantifying the shape of axially symmetric microscopic diffusion tensors in terms of a new diffusion anisotropy metric, D Δ, which has unique values for oblate, spherical, and prolate tensor shapes. The pulse sequence includes a series of equal-amplitude magnetic field gradient pulse pairs, the directions of which are tailored to give an axially symmetric diffusion-encoding tensor b with variable anisotropy b Δ. Averaging of data acquired for a range of orientations of the symmetry axis of the tensor b renders the method insensitive to the orientation distribution function of the microscopic diffusion tensors. Proof-of-principle experiments are performed on water in polydomain lyotropic liquid crystals with geometries that give rise to microscopic diffusion tensors with oblate, spherical, and prolate shapes. The method could be useful for characterizing the geometry of fluid-filled compartments in porous solids, soft matter, and biological tissues.
    Full-text · Article · Mar 2015 · The Journal of Chemical Physics
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    ABSTRACT: Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 μs. The reorientational dynamics of the C–H bonds is conventionally verified by measurements of 13C or 2H nuclear magnetic resonance (NMR) longitudinal relaxation rates R 1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C–H bond effective reorientational correlation time τ e, which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of 13C R 1 and R 1ρ relaxation rates, as well as 1H−13C dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of τ e from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g1 methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the τ e-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental τ e-profiles can be used to study subtle effects on C–H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C–H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes.
    No preview · Article · Jan 2015 · The Journal of Chemical Physics
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    ABSTRACT: Macroscopic properties of pasta, such as the texture, are formed during cooking by a complex interplay of water and heat with the structuring agents starch and gluten. The impact of the starch-to-gluten ratio on microstructure and water distribution in pasta was analyzed by a multi-scale approach combining magnetic resonance imaging (MRI) and light microscopy. The cooking process and thus the water distribution was monitored non-invasively using 1H MRI in real-time with a temporal resolution of 45 s. Our MRI set-up allowed following the water ingress by imaging the reduction of the uncooked core. The water ingress rate was neither dependent on pasta composition nor on the presence of salt in the cooking media (0.7% NaCl). Starch-rich samples showed a more homogeneous water distribution in the gelatinized zone, which was mirrored in a more homogeneous microstructure. In contrast, gluten-rich samples showed both a heterogeneous water distribution and microstructure. Thus, the gluten content affected local water content in the gelatinized zone but not the water ingress.
    No preview · Article · Dec 2014 · Food Research International
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    ABSTRACT: Abstract The anisotropy of water diffusion in brain tissue is affected by both disease and development. This change can be detected using diffusion MRI and is often quantified by the fractional anisotropy (FA) derived from diffusion tensor imaging (DTI). Although FA is sensitive to anisotropic cell structures, such as axons, it is also sensitive to their orientation dispersion. This is a major limitation to the use of FA as a biomarker for “tissue integrity”, especially in regions of complex microarchitecture. In this work, we seek to circumvent this limitation by disentangling the effects of microscopic diffusion anisotropy from the orientation dispersion. The microscopic fractional anisotropy (μFA) and the order parameter (OP) were calculated from the contrast between signal prepared with directional and isotropic diffusion encoding, where the latter was achieved by magic angle spinning of the q-vector (qMAS). These parameters were quantified in healthy volunteers and in two patients; one patient with meningioma and one with glioblastoma. Finally, we used simulations to elucidate the relation between FA and μFA in various micro-architectures. Generally, μFA was high in the white matter and low in the gray matter. In the white matter, the largest differences between μFA and FA were found in crossing white matter and in interfaces between large white matter tracts, where μFA was high while FA was low. Both tumor types exhibited a low FA, in contrast to the μFA which was high in the meningioma and low in the glioblastoma, indicating that the meningioma contained disordered anisotropic structures, while the glioblastoma did not. This interpretation was confirmed by histological examination. We conclude that FA from DTI reflects both the amount of diffusion anisotropy and orientation dispersion. We suggest that the μFA and OP may complement FA by independently quantifying the microscopic anisotropy and the level of orientation coherence.
    Full-text · Article · Oct 2014 · NeuroImage
  • D. Bernin · V. Koch · M. Nydén · D. Topgaard

    No preview · Article · Sep 2014
  • Daniel Topgaard
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    ABSTRACT: Microscopic diffusion anisotropy in porous materials can be quantified from diffusion NMR data acquired with a combination of directional and isotropic diffusion encoding. A drawback with current pulses sequences for isotropic encoding is that they all rely on spin echo sequences, which are only applicable to pore liquids with long transverse relaxation times and porous materials with negligible internal magnetic field gradients. To mitigate these problems, we introduce a pulse sequence based on consecutive stimulated echo blocks with bipolar gradient pulse pairs giving equal diffusion encoding in three successive directions. By varying the angles between these directions, the pulse sequence can be tuned to give either directional or isotropic diffusion encoding. We demonstrate the new pulse sequence by experiments on detergent/water liquid crystals with lamellar, bicontinuous cubic, and reverse 2D hexagonal structures.
    No preview · Article · Aug 2014 · Microporous and Mesoporous Materials
  • S. Gustavsson · L. Alves · B. Lindman · D. Topgaard
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    ABSTRACT: Polarization transfer solid-state NMR is shown to give molecular-level information about both dissolved and solid cellulose in aqueous dissolution media with sodium hydroxide or tetrabutylammonium hydroxide, thus paving the way for future studies of the molecular details of cellulose dissolution.
    No preview · Article · Jul 2014 · RSC Advances
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    ABSTRACT: A combination of NMR Chemical Shift Imaging and self-diffusion experiments is shown to give a detailed molecular picture of the events that occur when drug-loaded tablets of hydrophobically modified poly(acrylic acid) swell in water in the presence or absence of surfactant. The hydrophobic substituents on the polymer bind and trap the surfactant molecules in mixed micelles, leading to a slow effective transport of the surfactant. The transport occurs via a small fraction of individually dissolved surfactant molecules in the water domain. Due to the efficient binding of surfactant, the penetrating water is found to diffuse past the penetrating surfactant into the polymer matrix, pushing the surfactant front outwards as the matrix swells. The added surfactant has little effect on the transport of griseofulvin, because both undissolved solid drug and surfactant-solubilized drug functions as reservoirs that essentially follow the polymer as it swells. However, the added surfactant nevertheless has a strong indirect effect on the release of griseofulvin, through the effect of the surfactant on the solubility and erosion of the polymer matrix. The surfactant effectively solubilizes the hydrophobically modified polymer, making it fully miscible with water, leading to a more pronounced swelling and a slower erosion of the polymer matrix.
    No preview · Article · Jul 2014 · The Journal of Physical Chemistry B
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    Diana Bernin · Vanessa Koch · Magnus Nydén · Daniel Topgaard
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    ABSTRACT: The ability of lyotropic liquid crystals to form intricate structures on a range of length scales can be utilized for the synthesis of structurally complex inorganic materials, as well as in devices for controlled drug delivery. Here we employ magnetic resonance imaging (MRI) for non-invasive characterization of nano-, micro-, and millimeter scale structures in liquid crystals. The structure is mirrored in the translational and rotational motion of the water, which we assess by measuring spatially resolved self-diffusion tensors and [Formula: see text] spectra. Our approach differs from previous works in that the MRI parameters are mapped with spatial resolution in all three dimensions, thus allowing for detailed studies of liquid crystals with complex millimeter-scale morphologies that are stable on the measurement time-scale of 10 hours. The [Formula: see text] data conveys information on the nanometer-scale structure of the liquid crystalline phase, while the combination of diffusion and [Formula: see text] data permits an estimate of the orientational distribution of micrometer-scale anisotropic domains. We study lamellar phases consisting of the nonionic surfactant C10E3 in [Formula: see text]O, and follow their structural equilibration after a temperature jump and the cessation of shear. Our experimental approach may be useful for detailed characterization of liquid crystalline materials with structures on multiple length scales, as well as for studying the mechanisms of phase transitions.
    Full-text · Article · Jun 2014 · PLoS ONE
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    Full-text · Conference Paper · May 2014
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    ABSTRACT: In this work we present the first in vivo experiments employing magic angle spinning of the q-vector (qMAS) to map the microscopic anisotropy of the brain. This technique allows for the parameterization of anisotropy that is unaffected by the orientation dispersion. This means that the anisotropy is probed on a sub-voxel scale, and can potentially be useful in complex white matter geometries and gray matter, where conventional metrics such as FA are confounded by the tissue micro architecture.
    Full-text · Conference Paper · May 2014
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    ABSTRACT: The outermost layer of the skin, the stratum corneum (SC), is a lipid-protein membrane that experiences considerable osmotic stress from a dry and cold climate. The natural moisturizing factor (NMF) comprises small and polar substances, which like osmolytes can protect living systems from osmotic stress. NMF is commonly claimed to increase the water content in the SC and thereby protect the skin from dryness. In this work we challenge this proposed mechanism, and explore the influence of NMF on the lipid and protein components in the SC. We employ natural-abundance (13)C solid-state NMR methods to investigate how the SC molecular components are influenced by urea, glycerol, pyrrolidone carboxylic acid (PCA), and urocanic acid (UCA), all of which are naturally present in the SC as NMF compounds. Experiments are performed with intact SC, isolated corneocytes and model lipids. The combination of NMR experiments provides molecularly resolved qualitative information on the dynamics of different SC lipid and protein components. We obtain completely novel molecular information on the interaction of these NMF compounds with the SC lipids and proteins. We show that urea and glycerol, which are also common ingredients in skin care products, increase the molecular mobility of both SC lipids and proteins at moderate relative humidity where the SC components are considerably more rigid in the absence of these compounds. This effect cannot be attributed to increased SC water content. PCA has no detectable effect on SC molecular mobility under the conditions investigated. It is finally shown that the more apolar compound, UCA, specifically influences the mobility of the SC lipid regions. The present results show that the NMF components act to retain the fluidity of the SC molecular components under dehydrating conditions in such a way that the SC properties remain largely unchanged as compared to more hydrated SC. These findings provide a new molecular insight into how small polar molecules in NMF and skin care products act to protect the human skin from drying.
    Full-text · Article · May 2014 · Soft Matter
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    ABSTRACT: Diffusion tensor imaging (DTI) is the method of choice for non-invasive investigations of the structure of human brain white matter (WM). The results are conventionally reported as maps of the fractional anisotropy (FA), which is a parameter related to microstructural features such as axon density, diameter, and myelination. The interpretation of FA in terms of microstructure becomes ambiguous when there is a distribution of axon orientations within the image voxel. In this paper, we propose a procedure for resolving this ambiguity by determining a new parameter, the microscopic fractional anisotropy (μFA), which corresponds to the FA without the confounding influence of orientation dispersion. In addition, we suggest a method for measuring the orientational order parameter (OP) for the anisotropic objects. The experimental protocol is capitalizing on a recently developed diffusion nuclear magnetic resonance (NMR) pulse sequence based on magic-angle spinning of the q-vector. Proof-of-principle experiments are carried out on microimaging and clinical MRI equipment using lyotropic liquid crystals and plant tissues as model materials with high μFA and low FA on account of orientation dispersion. We expect the presented method to be especially fruitful in combination with DTI and high angular resolution acquisition protocols for neuroimaging studies of gray and white matter.
    Full-text · Article · Feb 2014 · Frontiers of Physics

Publication Stats

1k Citations
351.51 Total Impact Points

Institutions

  • 2001-2015
    • Lund University
      • Department of Physical Chemistry
      Lund, Skåne, Sweden
  • 2010
    • University of Coimbra
      Coímbra, Coimbra, Portugal
    • University of Oslo
      • Department of Chemistry
      Kristiania (historical), Oslo County, Norway
  • 2004-2009
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, California, United States