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- ItemGlycerylphytate as an ionic crosslinker for 3D printing of multi-layered scaffolds with improved shape fidelity and biological features(London : Royal Society of Chemistry, 2020) Mora-Boza, A.; Włodarczyk-Biegun, M.K.; Del Campo, A.; Vázquez-Lasa, B.; Román, J.S.The fabrication of intricate and long-term stable 3D polymeric scaffolds by a 3D printing technique is still a challenge. In the biomedical field, hydrogel materials are very frequently used because of their excellent biocompatibility and biodegradability, however the improvement of their processability and mechanical properties is still required. This paper reports the fabrication of dual crosslinked 3D scaffolds using a low concentrated (<10 wt%) ink of gelatin methacryloyl (GelMA)/chitosan and a novel crosslinking agent, glycerylphytate (G1Phy) to overcome the current limitations in the 3D printing field using hydrogels. The applied methodology consisted of a first ultraviolet light (UV) photopolymerization followed by a post-printing ionic crosslinking treatment with G1Phy. This crosslinker provides a robust framework and avoids the necessity of neutralization with strong bases. The blend ink showed shear-thinning behavior and excellent printability in the form of a straight and homogeneous filament. UV curing was undertaken simultaneously to 3D deposition, which enhanced precision and shape fidelity (resolution ≈150 μm), and prevented the collapse of the subsequent printed layers (up to 28 layers). In the second step, the novel G1Phy ionic crosslinker agent provided swelling and long term stability properties to the 3D scaffolds. The multi-layered printed scaffolds were mechanically stable under physiological conditions for at least one month. Preliminary in vitro assays using L929 fibroblasts showed very promising results in terms of adhesion, spreading, and proliferation in comparison to other phosphate-based traditional crosslinkers (i.e. TPP). We envision that the proposed combination of the blend ink and 3D printing approach can have widespread applications in the regeneration of soft tissues.
- ItemTwo-Phase Fluid Flow Experiments Monitored by NMR(Les Ulis : EDP Sciences, 2020) Hiller, Thomas; Hoder, Gabriel; Amann-Hildenbrand, Alexandra; Klitzsch, Norbert; Schleifer, NorbertWe present a newly developed high-pressure nuclear magnetic resonance (NMR) flow cell, which allows for the simultaneous determination of water saturation, effective gas permeability and NMR relaxation time distribution in two-phase fluid flow experiments. We introduce both the experimental setup and the experimental procedure on a tight Rotliegend sandstone sample. The initially fully water saturated sample is systematically drained by a stepwise increase of gas (Nitrogen) inlet pressure and the drainage process is continuously monitored by low field NMR relaxation measurements. After correction of the data for temperature fluctuations, the monitored changes in water saturation proved very accurate. The experimental procedure provides quantitative information about the total water saturation as well as about its distribution within the pore space at defined differential pressure conditions. Furthermore, the relationship between water saturation and relative (or effective) apparent permeability is directly determined. © The Authors, published by EDP Sciences, 2020.
- ItemTowards a methanol economy based on homogeneous catalysis: methanol to H2 and CO2 to methanol(Cambridge : Soc., 2015) Alberico, E.; Nielsen, M.The possibility to implement both the exhaustive dehydrogenation of aqueous methanol to hydrogen and CO2 and the reverse reaction, the hydrogenation of CO2 to methanol and water, may pave the way to a methanol based economy as part of a promising renewable energy system. Recently, homogeneous catalytic systems have been reported which are able to promote either one or the other of the two reactions under mild conditions. Here, we review and discuss these developments.
- ItemTuning the interplay between nematicity and spin fluctuations in Na1-x Li x FeAs superconductors(London : Nature Publishing Group, 2018) Baek, S.-H.; Bhoi, D.; Nam, W.; Lee, B.; Efremov, D.V.; Büchner, B.; Kim, K.H.Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. Despite intense debate for many years, however, whether nematicity is driven by spin or orbital fluctuations remains unsettled. Here, by use of transport, magnetization, and 75As nuclear magnetic resonance (NMR) measurements, we show a striking transformation of the relationship between nematicity and spin fluctuations (SFs) in Na1-x Li x FeAs; For x ≤ 0.02, the nematic transition promotes SFs. In contrast, for x ≥ 0.03, the system undergoes a non-magnetic phase transition at a temperature T 0 into a distinct nematic state that suppresses SFs. Such a drastic change of the spin fluctuation spectrum associated with nematicity by small doping is highly unusual, and provides insights into the origin and nature of nematicity in FeSCs.
- ItemEvaluation of single-sided nuclear magnetic resonance technology for usage in geosciences(Bristol : IOP Publ. Ltd., 2022) Costabel, Stephan; Hiller, Thomas; Dlugosch, Raphael; Kruschwitz, Sabine; Müller-Petke, MikeBecause of its mobility and ability to investigate exposed surfaces, single-sided (SiS) nuclear magnetic resonance (NMR) technology enables new application fields in geosciences. To test and assess its corresponding potential, we compare longitudinal (T 1) and transverse (T 2) data measured by SiS NMR with those of conventional geoscientific laboratory NMR. We use reference sandstone samples covering a broad range of pore sizes. Our study demonstrates that the lower signal-to-noise ratio of SiS NMR data generally tends to slightly overestimated widths of relaxation time distributions and consequently pore size distributions. While SiS and conventional NMR produce very similar T 1 relaxation data, unbiased SiS NMR results for T 2 measurements can only be expected for fine material, i.e. clayey or silty sediments and soils with main relaxation times below 0.05s . This limit is given by the diffusion relaxation rate due to the gradient in the primary magnetic field associated with the SiS NMR. Above that limit, i.e. for coarse material, the relaxation data is strongly attenuated. If considering the diffusion relaxation time of 0.2 s in the numerical data inversion process, the information content >0.2s is blurred over a range larger than that of conventional NMR. However, our results show that principle range and magnitudes of the relaxation time distributions are reconstructed to some extent. Regarding these findings, SiS NMR can be helpful to solve geoscientific issues, e.g. to assess the hydro-mechanical properties of the walls of underground facilities or to provide local soil moisture data sets for calibrating indirect remote techniques on the regional scale. The greatest opportunity provided by the SiS NMR technology is the acquisition of profile relaxation data for rocks with significant bedding structures at the μm scale. With this unique feature, SiS NMR can support the understanding and modeling of hydraulic and diffusional anisotropy behavior of sedimentary rocks.
- ItemHydraulic characterisation of iron-oxide-coated sand and gravel based on nuclear magnetic resonance relaxation mode analyses(Munich : EGU, 2018) Costabel, Stephan; Weidner, Christoph; Müller-Petke, Mike; Houben, GeorgThe capability of nuclear magnetic resonance (NMR) relaxometry to characterise hydraulic properties of iron-oxide-coated sand and gravel was evaluated in a laboratory study. Past studies have shown that the presence of paramagnetic iron oxides and large pores in coarse sand and gravel disturbs the otherwise linear relationship between relaxation time and pore size. Consequently, the commonly applied empirical approaches fail when deriving hydraulic quantities from NMR parameters. Recent research demonstrates that higher relaxation modes must be taken into account to relate the size of a large pore to its NMR relaxation behaviour in the presence of significant paramagnetic impurities at its pore wall. We performed NMR relaxation experiments with water-saturated natural and reworked sands and gravels, coated with natural and synthetic ferric oxides (goethite, ferrihydrite), and show that the impact of the higher relaxation modes increases significantly with increasing iron content. Since the investigated materials exhibit narrow pore size distributions, and can thus be described by a virtual bundle of capillaries with identical apparent pore radius, recently presented inversion approaches allow for estimation of a unique solution yielding the apparent capillary radius from the NMR data. We found the NMR-based apparent radii to correspond well to the effective hydraulic radii estimated from the grain size distributions of the samples for the entire range of observed iron contents. Consequently, they can be used to estimate the hydraulic conductivity using the well-known Kozeny–Carman equation without any calibration that is otherwise necessary when predicting hydraulic conductivities from NMR data. Our future research will focus on the development of relaxation time models that consider pore size distributions. Furthermore, we plan to establish a measurement system based on borehole NMR for localising iron clogging and controlling its remediation in the gravel pack of groundwater wells.
- ItemInterplay of charge density waves, disorder, and superconductivity in 2H-TaSe2 elucidated by NMR([London] : IOP, 2022) Baek, Seung-Ho; Sur, Yeahan; Kim, Kee Hoon; Vojta, Matthias; Büchner, BerndSingle crystals of pristine and 6% Pd-intercalated 2H‐TaSe2 have been studied by means of 77Se nuclear magnetic resonance. The temperature dependence of the 77Se spectrum, with an unexpected line narrowing upon Pd intercalation, unravels the presence of correlated local lattice distortions far above the transition temperature of the charge density wave (CDW) order, thereby supporting a strong-coupling CDW mechanism in 2H‐TaSe2. While, the Knight shift data suggest that the incommensurate CDW transition involves a partial Fermi surface gap opening. As for spin dynamics, the 77Se spin-lattice relaxation rate T1-1 as a function of temperature shows that a pseudogap behavior dominates the low-energy spin excitations even within the CDW phase, and gets stronger along with superconductivity in the Pd-6% sample. We discuss that CDW fluctuations may be responsible for the pseudogap as well as superconductivity, although the two phenomena are unlikely to be directly linked each other.
- ItemEnhanced pore space analysis by use of μ-CT, MIP, NMR, and SIP(Göttingen : Copernicus Publ., 2018) Zhang, Zeyu; Kruschwitz, Sabine; Weller, Andreas; Halisch, MatthiasWe investigate the pore space of rock samples with respect to different petrophysical parameters using various methods, which provide data on pore size distributions, including micro computed tomography (μ-CT), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and spectral-induced polarization (SIP). The resulting cumulative distributions of pore volume as a function of pore size are compared. Considering that the methods differ with regard to their limits of resolution, a multiple-length-scale characterization of the pore space is proposed, that is based on a combination of the results from all of these methods. The approach is demonstrated using samples of Bentheimer and Röttbacher sandstone. Additionally, we compare the potential of SIP to provide a pore size distribution with other commonly used methods (MIP, NMR). The limits of resolution of SIP depend on the usable frequency range (between 0.002 and 100 Hz). The methods with similar resolution show a similar behavior of the cumulative pore volume distribution in the overlapping pore size range. We assume that μ-CT and NMR provide the pore body size while MIP and SIP characterize the pore throat size. Our study shows that a good agreement between the pore radius distributions can only be achieved if the curves are adjusted considering the resolution and pore volume in the relevant range of pore radii. The MIP curve with the widest range in resolution should be used as reference.
- ItemStudying hydrogen bonding and dynamics of the acetylate groups of the Special Pair of Rhodobacter sphaeroides WT([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Gräsing, Daniel; Dziubińska-Kühn, Katarzyna M.; Zahn, Stefan; Alia, A.; Matysik, JörgAlthough the cofactors in the bacterial reaction centre of Rhodobacter sphaeroides wild type (WT) are arranged almost symmetrically in two branches, the light-induced electron transfer occurs selectively in one branch. As origin of this functional symmetry break, a hydrogen bond between the acetyl group of PL in the primary donor and His-L168 has been discussed. In this study, we investigate the existence and rigidity of this hydrogen bond with solid-state photo-CIDNP MAS NMR methods offering information on the local electronic structure due to highly sensitive and selective NMR experiments. On the time scale of the experiment, the hydrogen bond between PL and His-L168 appears to be stable and not to be affected by illumination confirming a structural asymmetry within the Special Pair.
- ItemVariation of the Chemical Composition of Waste Cooking Oils upon Bentonite Filtration(Basel : MDPI, 2019) Mannu, Alberto; Vlahopoulou, Gina; Urgeghe, Paolo; Ferro, Monica; Del Caro, Alessandra; Taras, Alessandro; Garroni, Sebastiano; Rourke, Jonathan P.; Cabizza, Roberto; Petretto, Giacomo L.The chemical composition and the color of samples of waste cooking oils (WCOs) were determined prior to and after filtration on two different pads of bentonite differing in particle size. The volatile fraction was monitored by headspace solid-phase microextraction (HS-SPME) coupled with gas-chromatography, while the variation of the composition of the main components was analyzed by 1H NMR. Both techniques allowed the detection of some decomposition products, such as polymers, terpenes, and derivatives of the Maillard process. The analysis of the chemical composition prior to and after bentonite treatment revealed a tendency for the clays to retain specific chemical groups (such as carboxylic acids or double bonds), independent of their particle size. A pair comparison test was conducted in order to detect the sensory differences of the intensity of aroma between the WCO treated with the two different bentonites. In addition, characterization of the bentonite by means of powder X-ray diffraction (XRD) and thermogravimetric measurements (TG) was performed. © 2019 by the authors.