Grethe Vestergaard Jensen
Aarhus University
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Publication
Featured researches published by Grethe Vestergaard Jensen.
Nano Letters | 2011
Jing Wang; Uffe Birk Jensen; Grethe Vestergaard Jensen; Stepan Shipovskov; Vijay S. Balakrishnan; Daniel E. Otzen; Jan Skov Pedersen; Flemming Besenbacher; Duncan S. Sutherland
Weak protein-nanoparticle (NP) interactions are studied in a low binding regime as a model for the soft protein corona around nanoparticles in complex biological fluids. Noncovalent, reversible interactions between Subtilisin Carlsberg (SC) and silica NPs shows significant alteration in conformation and enzymatic activity in a NP-size dependent manner. Very weak interactions between SC and silica NPs were revealed by centrifugation-based separations and further supported by small-angle X-ray scattering, while bovine serum albumin was used as a strongly interacting reference. Secondary and tertiary structure changes of SC were studied via circular dichroism and correlated to enzymatic activity where the enzyme kinetics showed a critical role for nanoparticle size.
Journal of the American Chemical Society | 2013
Grethe Vestergaard Jensen; Reidar Lund; Jérémie Gummel; Michael Monkenbusch; Theyencheri Narayanan; Jan Skov Pedersen
Self-assembly of amphiphilic molecules into micelles occurs on very short times scales of typically some milliseconds, and the structural evolution is therefore very challenging to observe experimentally. While rate constants of surfactant micelle kinetics have been accessed by spectroscopic techniques for decades, so far no experiments providing detailed information on the structural evolution of surfactant micelles during their formation process have been reported. In this work we show that by applying synchrotron small-angle X-ray scattering (SAXS) in combination with the stopped-flow mixing technique, the entire micelle formation process from single surfactants to equilibrium micelles can be followed in situ. Using a sugar-based surfactant system of dodecyl maltoside (DDM) in dimethylformamide (DMF), micelle formation can be induced simply by adding water, and this can be followed in situ by SAXS. Mixing of water and DMF is an exothermic process where the micelle formation process occurs under nonisothermal conditions with a temperature gradient relaxing from about 40 to 20 °C. A kinetic nucleation and growth mechanism model describing micelle formation by insertion/expulsion of single molecules under nonisothermal conditions was developed and shown to describe the data very well.
Journal of Biological Chemistry | 2013
Axel Abelein; Jørn Døvling Kaspersen; Søren Bang Nielsen; Grethe Vestergaard Jensen; Gunna Christiansen; Jan Skov Pedersen; Jens Danielsson; Daniel E. Otzen; Astrid Gräslund
Background: β-Structured oligomers of the amyloid β peptide are considered neurotoxic and on-pathway to amyloid fibril formation. Results: Surfactant-induced co-aggregated oligomers show dynamic rapid exchange with free peptide during a slow fibril formation process. Conclusion: β-Structure inducing small molecules kinetically promote peptide assembly into co-aggregates. Significance: Knowledge about molecular mechanisms of peptide aggregation modulators is potentially helpful for therapeutic purposes. Intermediate amyloidogenic states along the amyloid β peptide (Aβ) aggregation pathway have been shown to be linked to neurotoxicity. To shed more light on the different structures that may arise during Aβ aggregation, we here investigate surfactant-induced Aβ aggregation. This process leads to co-aggregates featuring a β-structure motif that is characteristic for mature amyloid-like structures. Surfactants induce secondary structure in Aβ in a concentration-dependent manner, from predominantly random coil at low surfactant concentration, via β-structure to the fully formed α-helical state at high surfactant concentration. The β-rich state is the most aggregation-prone as monitored by thioflavin T fluorescence. Small angle x-ray scattering reveals initial globular structures of surfactant-Aβ co-aggregated oligomers and formation of elongated fibrils during a slow aggregation process. Alongside this slow (minutes to hours time scale) fibrillation process, much faster dynamic exchange (kex ∼1100 s−1) takes place between free and co-aggregate-bound peptide. The two hydrophobic segments of the peptide are directly involved in the chemical exchange and interact with the hydrophobic part of the co-aggregates. Our findings suggest a model for surfactant-induced aggregation where free peptide and surfactant initially co-aggregate to dynamic globular oligomers and eventually form elongated fibrils. When interacting with β-structure promoting substances, such as surfactants, Aβ is kinetically driven toward an aggregation-prone state.
Membranes | 2015
Joachim Erich Otto Habel; Michael Hansen; Søren Kynde; Nanna Larsen; Søren Roi Midtgaard; Grethe Vestergaard Jensen; Julie Bomholt; Anayo Ogbonna; Kristoffer Almdal; Alexander Schulz; Claus Hélix-Nielsen
In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes.
Lab on a Chip | 2016
Aghiad Ghazal; Josiane P. Lafleur; Kell Mortensen; Jörg Peter Kutter; Lise Arleth; Grethe Vestergaard Jensen
The increasingly narrow and brilliant beams at X-ray facilities reduce the requirements for both sample volume and data acquisition time. This creates new possibilities for the types and number of sample conditions that can be examined but simultaneously increases the demands in terms of sample preparation. Microfluidic-based sample preparation techniques have emerged as elegant alternatives that can be integrated directly into the experimental X-ray setup remedying several shortcomings of more traditional methods. We review the use of microfluidic devices in conjunction with X-ray measurements at synchrotron facilities in the context of 1) mapping large parameter spaces, 2) performing time resolved studies of mixing-induced kinetics, and 3) manipulating/processing samples in ways which are more demanding or not accessible on the macroscale. The review covers the past 15 years and focuses on applications where synchrotron data collection is performed in situ, i.e. directly on the microfluidic platform or on a sample jet from the microfluidic device. Considerations such as the choice of materials and microfluidic designs are addressed. The combination of microfluidic devices and measurements at large scale X-ray facilities is still emerging and far from mature, but it definitely offers an exciting array of new possibilities.
ACS Nano | 2016
Sofie Haldrup; Jacopo Catalano; Mogens Hinge; Grethe Vestergaard Jensen; Jan Skov Pedersen; Anders Bentien
The electrokinetic energy conversion (EKEC) of hydraulic work directly into electrical energy has been investigated in charged polymeric membranes with different pore charge densities and characteristic diameters of the nanoporous network. The membranes were synthesized from blends of nitrocellulose and sulfonated polystyrene (SPS) and were comprehensively characterized with respect to structure, composition, and transport properties. It is shown that the SPS can be used as a sacrificial pore generation medium to tune the pore size and membrane porosity, which in turn highly affects the transport properties of the membranes. Furthermore, it is shown that very high EKEC efficiencies (>35%) are encountered in a rather narrow window of the properties of the nanoporous membrane network, that is, with pore diameters of ca. 10 nm and pore charge densities of 4.6 × 10(2) to 1.5 × 10(3) mol SO3(-) m(-3) for dilute solutions (0.03 M LiCl). The high absolute value of the efficiency combined with the determination of the optimal membrane morphology makes membrane-based EKEC devices a step closer to practical applications and high-performance membrane design less empirical.
Journal of Applied Crystallography | 2011
Grethe Vestergaard Jensen; Qing Shi; María J. Hernansanz; Cristiano L. P. Oliveira; G. Roshan Deen; Kristoffer Almdal; Jan Skov Pedersen
The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP–PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8–49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core–shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.
Nano Letters | 2015
Sofie Haldrup; Jacopo Catalano; Michael Ryan Hansen; Manfred Wagner; Grethe Vestergaard Jensen; Jan Skov Pedersen; Anders Bentien
The synthesis, characterization, and electrokinetic energy conversion performance have been investigated experimentally in a charged polymeric membrane based on a blend of nitrocellulose and sulfonated polystyrene. The membrane is characterized by a moderate ion exchange capacity and a relatively porous structure with average pore diameter of 11 nm. With electrokinetic energy conversion, pressure can be converted directly into electric energy and vice versa. From the electrokinetic transport properties, a remarkably large intrinsic maximum efficiency of 46% is found. It is anticipated that the results are an experimental verification of theoretical models that predict high electrokinetic energy conversion efficiency in pores with high permselectivity and hydrodynamic slip flow. Furthermore, the result is a promising step for obtaining efficient low-cost electrokinetic generators and pumps for small or microscale applications.
Journal of Colloid and Interface Science | 2013
Jonas Nordström; Andreas Sundblom; Grethe Vestergaard Jensen; Jan Skov Pedersen; Anders Palmqvist; Aleksandar Matic
Alkaline sodium silicate solutions with SiO2:Na2O molar ratios in the range 4-10 are known to be colloidally unstable manifested in phase separation or gelation. The mechanistic understanding of this instability is generally poor. To improve this situation the microscopic structure of a series of solutions with ratios in the range 3.3-8.9 has been characterised using small-angle X-ray scattering, Dynamic light scattering, Fourier transformed infrared spectroscopy, and (29)Si Nuclear magnetic resonance spectroscopy to cover the relevant length scales related to silica clusters, aggregates, and particles present. In the starting solution, with ratio 3.3, there are silica present in three fractions. The main part is present as small silica clusters with a radius of 0.7 nm. There are also a significant portion of monomers/small oligomeric silica species as well as a minute amount of larger colloidal silica particles. At a higher SiO2:Na2O ratio, above approximately 4, smaller spherical colloidal particles are formed due to condensation reactions. However, as a result of a too high ionic strength the suspension is not stable and the particles aggregate to fractal structures with a size that depends on ratio and ageing time. At the highest SiO2:Na2O ratio, fractals are not formed because of the lower ionic strength and the smaller colloidal particles are stable in the solution. By carefully adding small amounts of NaCl to the high ratio solution it is possible to induce gelation of the solution confirming the hypothesis that the instability region is due to too high electrolyte concentration for the silica species present under those conditions.
Physics and Chemistry of Liquids | 2014
Soheil Sharifi; Grethe Vestergaard Jensen; Jan Skov Pedersen; Othmar Marti; Masoud Amirkhani
We study oil-in-water microemulsions, in particular dispersions of n-decane droplets coated with a monolayer of the surfactant C12E5 in a continuous phase of water. Upon addition of the tri-block poly(propylene-glycol)(PPG)-block-Poly(ethylene-glycol)(PEG)-block-PPG, the depletion interaction between the oil droplets of microemulsion is induced. At constant droplet size, we vary the polymer concentration and there is clear evidence for an increasing depletion interaction of the droplets from structural investigations with small-angle x-ray scattering and photon correlation spectroscopy (PCS). Our results show that the PEG does increase the depletion interaction more than the tri-block PPG-PEG-PPG.