Publications by authors named "Martin A Schroer"

40 Publications

Structure of the endocytic adaptor complex reveals the basis for efficient membrane anchoring during clathrin-mediated endocytosis.

Nat Commun 2021 05 17;12(1):2889. Epub 2021 May 17.

European Molecular Biology Laboratory, Hamburg Outstation, Hamburg, Germany.

During clathrin-mediated endocytosis, a complex and dynamic network of protein-membrane interactions cooperate to achieve membrane invagination. Throughout this process in yeast, endocytic coat adaptors, Sla2 and Ent1, must remain attached to the plasma membrane to transmit force from the actin cytoskeleton required for successful membrane invagination. Here, we present a cryo-EM structure of a 16-mer complex of the ANTH and ENTH membrane-binding domains from Sla2 and Ent1 bound to PIP that constitutes the anchor to the plasma membrane. Detailed in vitro and in vivo mutagenesis of the complex interfaces delineate the key interactions for complex formation and deficient cell growth phenotypes demonstrate its biological relevance. A hetero-tetrameric unit binds PIP molecules at the ANTH-ENTH interfaces and can form larger assemblies to contribute to membrane remodeling. Finally, a time-resolved small-angle X-ray scattering study of the interaction of these adaptor domains in vitro suggests that ANTH and ENTH domains have evolved to achieve a fast subsecond timescale assembly in the presence of PIP and do not require further proteins to form a stable complex. Together, these findings provide a molecular understanding of an essential piece in the molecular puzzle of clathrin-coated endocytic sites.
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http://dx.doi.org/10.1038/s41467-021-23151-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8129110PMC
May 2021

Cotton Textile/Iron Oxide Nanozyme Composites with Peroxidase-like Activity: Preparation, Characterization, and Application.

ACS Appl Mater Interfaces 2021 May 14;13(20):23627-23637. Epub 2021 May 14.

Department of Nanobiotechnology, Biology Centre, ISB, CAS, Na Sadkach 7, 370 05 Ceske Budejovice, Czech Republic.

At present, both native and immobilized nanoparticles are of great importance in many areas of science and technology. In this paper, we have studied magnetic iron oxide nanoparticles and their aggregates bound on woven cotton textiles employing two simple modification procedures. One modification was based on the treatment of textiles with perchloric-acid-stabilized magnetic fluid diluted with methanol followed by drying. The second procedure was based on the microwave-assisted conversion of ferrous sulfate at high pH followed by drying. The structure and functional properties of these modified textiles were analyzed in detail. Scanning electron microscopy of native and modified textiles clearly showed the presence of iron oxide nanoparticles on the surface of the modified cotton fibers. All of the modified textile materials exhibited light to dark brown color depending on the amount of the bound iron oxide particles. Magnetic measurements showed that the saturation magnetization values reflect the amount of magnetic nanoparticles present in the modified textiles. Small-angle X-ray and neutron scattering measurements were conducted for the detailed structural characterization at the nanoscale of both the native and magnetically modified textiles, and different structural organization of nanoparticles in the two kinds of textile samples were concluded. The textile-bound iron oxide particles exhibited peroxidase-like activity when the ,-diethyl--phenylenediamine sulfate salt was used as a substrate; this nanozyme activity enabled rapid decolorization of crystal violet in the presence of hydrogen peroxide. The deposition of a sufficient amount of iron oxide particles on textiles enabled their simple magnetic separation from large volumes of solutions; if necessary, the magnetic response of the modified textiles can be simply increased by incorporation of a piece of magnetic iron wire. The simplicity of the immobilized nanozyme preparation and the low cost of all the precursors enable its widespread application, such as decolorization and degradation of selected organic dyes and other important pollutants. Other types of textile-bound nanozymes can be prepared and used as low-cost catalysts for a variety of applications.
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http://dx.doi.org/10.1021/acsami.1c02154DOI Listing
May 2021

Anomalous SAXS at P12 beamline EMBL Hamburg: instrumentation and applications.

J Synchrotron Radiat 2021 May 14;28(Pt 3):812-823. Epub 2021 Apr 14.

European Molecular Biology Laboratory (EMBL), Hamburg Outstation c/o DESY, Notkestrasse 85, 22607 Hamburg, Germany.

Small-angle X-ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element-specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X-rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
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http://dx.doi.org/10.1107/S1600577521003404DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8127372PMC
May 2021

Selection, biophysical and structural analysis of synthetic nanobodies that effectively neutralize SARS-CoV-2.

Nat Commun 2020 11 4;11(1):5588. Epub 2020 Nov 4.

Centre for Structural Systems Biology (CSSB), DESY and European Molecular Biology Laboratory Hamburg, Notkestrasse 85, D-22607, Hamburg, Germany.

The coronavirus SARS-CoV-2 is the cause of the ongoing COVID-19 pandemic. Therapeutic neutralizing antibodies constitute a key short-to-medium term approach to tackle COVID-19. However, traditional antibody production is hampered by long development times and costly production. Here, we report the rapid isolation and characterization of nanobodies from a synthetic library, known as sybodies (Sb), that target the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. Several binders with low nanomolar affinities and efficient neutralization activity were identified of which Sb23 displayed high affinity and neutralized pseudovirus with an IC of 0.6 µg/ml. A cryo-EM structure of the spike bound to Sb23 showed that Sb23 binds competitively in the ACE2 binding site. Furthermore, the cryo-EM reconstruction revealed an unusual conformation of the spike where two RBDs are in the 'up' ACE2-binding conformation. The combined approach represents an alternative, fast workflow to select binders with neutralizing activity against newly emerging viruses.
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http://dx.doi.org/10.1038/s41467-020-19204-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7642358PMC
November 2020

Investigation of pH-Responsiveness inside Lipid Nanoparticles for Parenteral mRNA Application Using Small-Angle X-ray Scattering.

Langmuir 2020 11 27;36(44):13331-13341. Epub 2020 Oct 27.

Department of Pharmaceutics and Biopharmaceutics, Institute of Pharmaceutical and Biomedical Sciences, Johannes Gutenberg University Mainz, Staudingerweg 5, D-55099 Mainz, Germany.

Messenger ribonucleic acid (mRNA)-based nanomedicines have shown to be a promising new lead in a broad field of potential applications such as tumor immunotherapy. Of these nanomedicines, lipid-based mRNA nanoparticles comprising ionizable lipids are gaining increasing attention as versatile technologies for fine-tuning toward a given application, with proven potential for successful development up to clinical practice. Still, several hurdles have to be overcome to obtain a drug product that shows adequate mRNA delivery and clinical efficacy. In this study, pH-induced changes in internal molecular organization and overall physicochemical characteristics of lipoplexes comprising ionizable lipids were investigated using small-angle X-ray scattering and supplementary techniques. These changes were determined for different types of ionizable lipids, present at various molar fractions and N/P ratios inside the phospholipid membranes. The investigated systems showed a lamellar organization, allowing an accurate determination of pH-dependent structural changes. The differences in the pH responsiveness of the systems comprising different ionizable lipids and mRNA fractions could be clearly revealed from their structural evolution. Measurements of the degree of ionization and pH-dependent mRNA loading into the systems by fluorescence assays supported the findings from the structural investigation. Our approach allows for direct in situ determination of the structural response of the lipoplex systems to changes of the environmental pH similar to that observed for endosomal uptake. These data therefore provide valuable complementary information for understanding and fine-tuning of tailored mRNA delivery systems toward improved cellular uptake and endosomal processing.
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http://dx.doi.org/10.1021/acs.langmuir.0c02446DOI Listing
November 2020

Slowing down of dynamics and orientational order preceding crystallization in hard-sphere systems.

Sci Adv 2020 Oct 21;6(43). Epub 2020 Oct 21.

Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.

Despite intensive studies in the past decades, the local structure of disordered matter remains widely unknown. We show the results of a coherent x-ray scattering study revealing higher-order correlations in dense colloidal hard-sphere systems in the vicinity of their crystallization and glass transition. With increasing volume fraction, we observe a strong increase in correlations at both medium-range and next-neighbor distances in the supercooled state, both invisible to conventional scattering techniques. Next-neighbor correlations are indicative of ordered precursor clusters preceding crystallization. Furthermore, the increase in such correlations is accompanied by a marked slowing down of the dynamics, proving experimentally a direct relation between orientational order and sample dynamics in a soft matter system. In contrast, correlations continuously increase for nonequilibrated, glassy samples, suggesting that orientational order is reached before the sample slows down to reach (quasi-)equilibrium.
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http://dx.doi.org/10.1126/sciadv.abc5916DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7577711PMC
October 2020

Hybrid Biopolymer and Lipid Nanoparticles with Improved Transfection Efficacy for mRNA.

Cells 2020 09 5;9(9). Epub 2020 Sep 5.

Department of Pharmaceutics and Biopharmaceutics, Johannes Gutenberg University Mainz, D-55131 Mainz, Germany.

Hybrid nanoparticles from lipidic and polymeric components were assembled to serve as vehicles for the transfection of messenger RNA (mRNA) using different portions of the cationic lipid DOTAP (1,2-Dioleoyl-3-trimethylammonium-propane) and the cationic biopolymer protamine as model systems. Two different sequential assembly approaches in comparison with a direct single-step protocol were applied, and molecular organization in correlation with biological activity of the resulting nanoparticle systems was investigated. Differences in the structure of the nanoparticles were revealed by thorough physicochemical characterization including small angle neutron scattering (SANS), small angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). All hybrid systems, combining lipid and polymer, displayed significantly increased transfection in comparison to lipid/mRNA and polymer/mRNA particles alone. For the hybrid nanoparticles, characteristic differences regarding the internal organization, release characteristics, and activity were determined depending on the assembly route. The systems with the highest transfection efficacy were characterized by a heterogenous internal organization, accompanied by facilitated release. Such a system could be best obtained by the single step protocol, starting with a lipid and polymer mixture for nanoparticle formation.
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http://dx.doi.org/10.3390/cells9092034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7563888PMC
September 2020

Hydration in aqueous osmolyte solutions: the case of TMAO and urea.

Phys Chem Chem Phys 2020 May 14;22(20):11614-11624. Epub 2020 May 14.

European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble, France.

The hydration and hydrogen-bond topology of small water solvated molecules such as the naturally occurring organic osmolytes trimethylamine N-oxide (TMAO) and urea are under intense investigation. We aim at furthering the understanding of this complex hydration by combining experimental oxygen K-edge excitation spectra with results from spectra calculated via the Bethe-Salpeter equation based on structures obtained from ab initio molecular dynamics simulations. Comparison of experimental and calculated spectra allows us to extract detailed information about the immediate surrounding of the solute molecules in the solvated state. We quantify and localize the influence of the solute on the hydrogen bond network of the water solvent and find spectroscopic fingerprints of a clear directional asymmetry around TMAO with strong and local kosmotropic influence around TMAO's NO head group and slight chaotropic influence around the hydrophobic methyl groups. The influence of urea on the local water network is qualitatively similar to that of TMAO but weaker in magnitude. The strongest influence of both molecules on the shape of the oxygen K-edge spectra is found in the first hydration shells.
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http://dx.doi.org/10.1039/c9cp06785jDOI Listing
May 2020

Structural Kinetics of MsbA Investigated by Stopped-Flow Time-Resolved Small-Angle X-Ray Scattering.

Structure 2020 03 30;28(3):348-354.e3. Epub 2019 Dec 30.

The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany; Department of Chemistry, Institute for Biochemistry and Molecular Biology, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany. Electronic address:

Recent structures of full-length ATP-binding cassette (ABC) transporter MsbA in different states indicate large conformational changes during the reaction cycle that involve transient dimerization of its nucleotide-binding domains (NBDs). However, a detailed molecular understanding of the structural changes and associated kinetics of MsbA upon ATP binding and hydrolysis is still missing. Here, we employed time-resolved small-angle X-ray scattering, initiated by stopped-flow mixing, to investigate the kinetics and accompanying structural changes of NBD dimerization (upon ATP binding) and subsequent dissociation (upon ATP hydrolysis) in the context of isolated NBDs as well as full-length MsbA in lipid nanodiscs. Our data allowed us to structurally characterize the major states involved in the process and determine time constants for NBD dimerization and dissociation. In the full-length protein, these structural transitions occur on much faster time scales, indicating close-proximity effects and structural coupling of the transmembrane domains with the NBDs.
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http://dx.doi.org/10.1016/j.str.2019.12.001DOI Listing
March 2020

Effect of the concentration of protein and nanoparticles on the structure of biohybrid nanocomposites.

Biopolymers 2020 Feb 3;111(2):e23342. Epub 2019 Dec 3.

Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia.

We present colloidal nanocomposites formed by incorporating magnetite Fe O nanoparticles (MNPs) with lysozyme amyloid fibrils (LAFs). Preparation of two types of solutions, with and without addition of salt, was carried out to elucidate the structure of MNPs-incorporated fibrillary nanocomposites and to study the effect of the presence of salt on the stability of the nanocomposites. The structural morphology of the LAFs and their interaction with MNPs were analyzed by atomic force microscopy and small-angle x-ray scattering measurements. The results indicate that conformational properties of the fibrils are dependent on the concentration of protein, and the precise ratio of the concentration of the protein and MNPs is crucially important for the stability of the fibrillary nanocomposites. Our results confirm that despite the change in fibrillary morphology induced by the varying concentration of the protein, the adsorption of MNPs on the surface of LAF is morphologically independent. Moreover, most importantly, the samples containing salt have excellent stability for up to 1 year of shelf-life.
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http://dx.doi.org/10.1002/bip.23342DOI Listing
February 2020

Kinetics of pressure-induced nanocrystal superlattice formation.

Phys Chem Chem Phys 2019 Oct 18;21(38):21349-21354. Epub 2019 Sep 18.

The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany and Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.

Colloidal nanocrystals (NC) are known to self-organize into superlattices that promise many applications ranging from medicine to optoelectronics. Recently, the formation of high-quality PEGylated gold NC was reported at high hydrostatic pressure and high salt concentrations. Here, we study the formation kinetics of these superlattices after pressure jumps beyond their crystallisation pressure by means of small-angle X-ray scattering with few ms experimental resolution. The timescale of NC formation was found to be reduced the larger the width of the pressure jump. This is connected to an increase of crystal quality, i.e., the faster the NC superlattice forms, the better the crystal quality. In contrast to the formation kinetics, the melting of the NC superlattice is approximately one order of magnitude slower and shows linear kinetics.
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http://dx.doi.org/10.1039/c9cp04658eDOI Listing
October 2019

Dynamics of soft nanoparticle suspensions at hard X-ray FEL sources below the radiation-damage threshold.

IUCrJ 2018 Nov 19;5(Pt 6):801-807. Epub 2018 Oct 19.

Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany.

The application of X-ray photon correlation spectroscopy (XPCS) at free-electron laser (FEL) facilities enables, for the first time, the study of dynamics on a (sub-)nanometre scale in an unreached time range between femtoseconds and seconds. For soft-matter materials, radiation damage is a major limitation when going beyond single-shot applications. Here, an XPCS study is presented at a hard X-ray FEL on radiation-sensitive polymeric poly(-isopropylacrylamide) (PNIPAM) nanoparticles. The dynamics of aqueous suspensions of densely packed silica-PNIPAM core-shell particles and a PNIPAM nanogel below the radiation-damage threshold are determined. The XPCS data indicate non-diffusive behaviour, suggesting ballistic and stress-dominated heterogeneous particle motions. These results demonstrate the feasibility of XPCS experiments on radiation-sensitive soft-matter materials at FEL sources and pave the way for future applications at MHz repetition rates as well as ultrafast modes using split-pulse devices.
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http://dx.doi.org/10.1107/S2052252518013696DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6211528PMC
November 2018

Hydration in aqueous solutions of ectoine and hydroxyectoine.

Phys Chem Chem Phys 2018 Nov;20(44):27917-27923

European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble, France.

We explore the influence of the two osmolytes ectoine and hydroxyectoine on the structure of pure water and aqueous NaCl solutions using non-resonant X-ray Raman scattering spectroscopy at the oxygen K-edge. Both ectoine and hydroxyectoine are naturally occurring organic osmolytes synthesized by halophilic organisms that live in high-salt and other extreme environments. We find that X-ray spectroscopic data at the oxygen K-edge are consistent with a scenario where both osmolytes affect the hydrogen bonding network of water on a local scale to in effect increase tetrahedral order. This supports the proposed stabilizing mechanism of the osmolytes for proteins: preferential exclusion of the osmolytes from the proteins' surface and preferential hydration of the macromolecules instead of complex alterations to the structure of water on a bulk scale. The effect of NaCl on water, a disruption of hydrogen bonds and tetrahedral order, acts in opposition to the localized water-binding effects of ectoine and hydroxyectoine. For ternary mixtures of osmolyte in the presence of NaCl, the effects seen in the spectra are found to be additive such that the mixed solutes generate a level of oppositional frustration in the water network.
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http://dx.doi.org/10.1039/c8cp05308aDOI Listing
November 2018

Water-Mediated Protein-Protein Interactions at High Pressures are Controlled by a Deep-Sea Osmolyte.

Phys Rev Lett 2018 Jul;121(3):038101

Faculty of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Strasse 4a, 44227 Dortmund, Germany.

The influence of natural cosolvent mixtures on the pressure-dependent structure and protein-protein interaction potential of dense protein solutions is studied and analyzed using small-angle X-ray scattering in combination with a liquid-state theoretical approach. The deep-sea osmolyte trimethylamine-N-oxide is shown to play a crucial and singular role in its ability to not only guarantee sustainability of the native protein's folded state under harsh environmental conditions, but it also controls water-mediated intermolecular interactions at high pressure, thereby preventing contact formation and hence aggregation of proteins.
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http://dx.doi.org/10.1103/PhysRevLett.121.038101DOI Listing
July 2018

Pressure-Stimulated Supercrystal Formation in Nanoparticle Suspensions.

J Phys Chem Lett 2018 Aug 6;9(16):4720-4724. Epub 2018 Aug 6.

The Hamburg Centre for Ultrafast Imaging (CUI) , 22761 Hamburg , Germany.

Nanoparticles can self-organize into "supercrystals" with many potential applications. Different paths can lead to nanoparticle self-organization into such periodic arrangements. An essential step is the transition from an amorphous state to the crystalline one. We investigate how pressure can induce a phase transition of a nanoparticle model system in water from the disordered liquid state to highly ordered supercrystals. We observe reversible pressure-induced supercrystal formation in concentrated solutions of gold nanoparticles by means of small-angle X-ray scattering. The supercrystal formation occurs only at high salt concentrations in the aqueous solution. The pressure dependence of the structural parameters of the resulting crystal lattices is determined. The observed transition can be reasoned with the combined effect of salt and pressure on the solubility of the organic PEG shell that passivates the nanoparticles.
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http://dx.doi.org/10.1021/acs.jpclett.8b02145DOI Listing
August 2018

Smaller capillaries improve the small-angle X-ray scattering signal and sample consumption for biomacromolecular solutions.

J Synchrotron Radiat 2018 Jul 26;25(Pt 4):1113-1122. Epub 2018 Jun 26.

European Molecular Biology Laboratory (EMBL), Hamburg Outstation c/o DESY, Notkestrasse 85, 22607 Hamburg, Germany.

Radiation damage by intense X-ray beams at modern synchrotron facilities is one of the major complications for biological small-angle X-ray scattering (SAXS) investigations of macromolecules in solution. To limit the damage, samples are typically measured under a laminar flow through a cell (typically a capillary) such that fresh solution is continuously exposed to the beam during measurement. The diameter of the capillary that optimizes the scattering-to-absorption ratio at a given X-ray wavelength can be calculated a priori based on fundamental physical properties. However, these well established scattering and absorption principles do not take into account the radiation susceptibility of the sample or the often very limited amounts of precious biological material available for an experiment. Here it is shown that, for biological solution SAXS, capillaries with smaller diameters than those calculated from simple scattering/absorption criteria allow for a better utilization of the available volumes of radiation-sensitive samples. This is demonstrated by comparing two capillary diameters d (d = 1.7 mm, close to optimal for 10 keV; and d = 0.9 mm, which is nominally sub-optimal) applied to study different protein solutions at various flow rates. The use of the smaller capillaries ultimately allows one to collect higher-quality SAXS data from the limited amounts of purified biological macromolecules.
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http://dx.doi.org/10.1107/S1600577518007907DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6038601PMC
July 2018

Heterogeneous local order in self-assembled nanoparticle films revealed by X-ray cross-correlations.

IUCrJ 2018 May 28;5(Pt 3):354-360. Epub 2018 Apr 28.

Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany.

We report on the self-assembly of gold nanoparticles coated with a soft poly(ethylene glycol) shell studied by X-ray cross-correlation analysis. Depending on the initial concentration of gold nanoparticles used, structurally heterogeneous films were formed. The films feature hot spots of dominating four- and sixfold local order with patch sizes of a few micrometres, containing 10-10 particles. The amplitude of the order parameters suggested that a minimum sample amount was necessary to form well ordered local structures. Furthermore, the increasing variation in order parameters with sample thickness demonstrated a high degree of structural heterogeneity. This wealth of information cannot be obtained by the conventional microscopy techniques that are commonly used to study nanocrystal superstructures, as illustrated by complementary scanning electron microscopy measurements.
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http://dx.doi.org/10.1107/S2052252518005407DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5929381PMC
May 2018

Recent developments in small-angle X-ray scattering and hybrid method approaches for biomacromolecular solutions.

Emerg Top Life Sci 2018 Apr;2(1):69-79

European Molecular Biology Laboratory (EMBL), Hamburg Outstation c/o DESY, Notkestrasse 85, Hamburg 22607, Germany.

Small-angle X-ray scattering (SAXS) has become a streamline method to characterize biological macromolecules, from small peptides to supramolecular complexes, in near-native solutions. Modern SAXS requires limited amounts of purified material, without the need for labelling, crystallization, or freezing. Dedicated beamlines at modern synchrotron sources yield high-quality data within or below several milliseconds of exposure time and are highly automated, allowing for rapid structural screening under different solutions and ambient conditions but also for time-resolved studies of biological processes. The advanced data analysis methods allow one to meaningfully interpret the scattering data from monodisperse systems, from transient complexes as well as flexible and heterogeneous systems in terms of structural models. Especially powerful are hybrid approaches utilizing SAXS with high-resolution structural techniques, but also with biochemical, biophysical, and computational methods. Here, we review the recent developments in the experimental SAXS practice and in analysis methods with a specific focus on the joint use of SAXS with complementary methods.
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http://dx.doi.org/10.1042/ETLS20170138DOI Listing
April 2018

A Multiperspective Approach to Solvent Regulation of Enzymatic Activity: HMG-CoA Reductase.

Chembiochem 2018 01 21;19(2):153-158. Epub 2017 Dec 21.

Fakultät für Chemie und Biochemie, Organische Chemie I, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780, Bochum, Germany.

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase was investigated in different organic cosolvents by means of kinetic and calorimetric measurements, molecular dynamics simulations, and small-angle X-ray scattering. The combined experimental and theoretical techniques were essential to complement each other's limitations in the investigation of the complex interaction pattern between the enzyme, different solvent types, and concentrations. In this way, the underlying mechanisms for the loss of enzyme activity in different water-miscible solvents could be elucidated. These include direct inhibitory effects onto the active center and structural distortions.
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http://dx.doi.org/10.1002/cbic.201700596DOI Listing
January 2018

Structuralization of magnetic nanoparticles in 5CB liquid crystals.

Soft Matter 2017 Nov;13(43):7890-7896

Institute of Experimental Physics, Slovak Academy of Sciences, Watsonová 47, 04001, Košice, Slovakia.

This work is devoted to the study of highly stable composite systems of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) doped with CoFeO magnetic nanoparticles. Ferronematic samples were prepared with two different weight concentrations: sample A 0.085 wt% and sample B 0.062 wt%. The interaction of CoFeO nanoparticles with the liquid crystal was investigated by small-angle X-ray-scattering and magnetization measurements. The obtained results reveal aggregates formed by magnetic nanoparticles that are oriented in the nematic phase. Moreover, the prepared samples show unexpected behaviour of a sudden change in magnetization, which is unusual for such ferronematics.
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http://dx.doi.org/10.1039/c7sm01234aDOI Listing
November 2017

Tuning the Size of Thermoresponsive Poly(N-Isopropyl Acrylamide) Grafted Silica Microgels.

Gels 2017 Sep 17;3(3). Epub 2017 Sep 17.

Institute of Physical Chemistry, University of Hamburg, 20146 Hamburg, Germany.

Core-shell microgels were synthesized via a free radical emulsion polymerization of thermoresponsive poly-(-isopropyl acrylamide), pNipam, on the surface of silica nanoparticles. Pure pNipam microgels have a lower critical solution temperature (LCST) of about 32 °C. The LCST varies slightly with the crosslinker density used to stabilize the gel network. Including a silica core enhances the mechanical robustness. Here we show that by varying the concentration gradient of the crosslinker, the thermoresponsive behaviour of the core-shell microgels can be tuned. Three different temperature scenarios have been detected. First, the usual behaviour with a decrease in microgel size with increasing temperature exhibiting an LCST; second, an increase in microgel size with increasing temperature that resembles an upper critical solution temperature (UCST), and; third, a decrease with a subsequent increase of size reminiscent of the presence of both an LCST, and a UCST. However, since the chemical structure has not been changed, the LCST should only change slightly. Therefore we demonstrate how to tune the particle size independently of the LCST.
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http://dx.doi.org/10.3390/gels3030034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6318582PMC
September 2017

Microsecond Structural Rheology.

J Phys Chem Lett 2017 Aug 20;8(15):3581-3585. Epub 2017 Jul 20.

Deutsches Elektronen-Synchrotron DESY , Notkestraße 85, 22607 Hamburg, Germany.

The relationship between the local structure of complex liquids and their response to shear is generally not well understood. This concerns, in particular, the formation of particle strings in the flow direction or hydroclusters, both important for the understanding of shear thinning and thickening phenomena. Here, we present results of a microfocus X-ray scattering experiment on spherical silica colloids in a liquid jet at high shear rates. Along and across the jet, we observe direction-dependent modifications of the structure factor of the suspension, suggesting the formation of differently ordered clusters in compression lines and as particle strings. With increasing distance from the orifice, the structure relaxes to the unsheared case with a typical relaxation 10 times larger as the time scale of Brownian motion. These results provide the first experimental flow characterization of a complex fluid at high shear rates detecting cluster formation and relaxation with micrometer and microsecond resolution.
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http://dx.doi.org/10.1021/acs.jpclett.7b01355DOI Listing
August 2017

Stabilizing effect of TMAO on globular PNIPAM states: preferential attraction induces preferential hydration.

Phys Chem Chem Phys 2016 Nov;18(46):31459-31470

Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany. and The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany.

We study the effect of the organic co-solute trimethylamine N-oxide (TMAO) on the volume phase transition of microgel particles made from poly(N-isopropylacrylamide) (PNIPAM) using dynamic light scattering (DLS) and all-atom molecular dynamics (MD) simulations. The DLS measurements reveal a continuous TMAO-induced shrinking process from a coil to a globular state of PNIPAM microgel particles. Analyzing the DLS data by the phenomenological Flory-Rehner theory verifies the stabilization of the globular state of the particles in the presence of TMAO. Complementary atomistic MD simulations highlight a pronounced accumulation of TMAO molecules around PNIPAM chains. We observe a significant preferential attraction between TMAO and the globular state of PNIPAM, which is additionally stabilized by a larger number of hydrating water molecules compared to pure aqueous solutions. Further DLS measurements were also conducted on PNIPAM suspensions with the co-solute urea added. The observed differences compared with the results obtained for TMAO support the proposed mechanism.
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http://dx.doi.org/10.1039/c6cp05991kDOI Listing
November 2016

Ligand Layer Engineering To Control Stability and Interfacial Properties of Nanoparticles.

Langmuir 2016 08 26;32(31):7897-907. Epub 2016 Jul 26.

Institute for Physical Chemistry, University of Hamburg , Grindelallee 117, 20146 Hamburg, Germany.

The use of mixed ligand layers including poly(ethylene glycol)-based ligands for the functionalization of nanoparticles is a very popular strategy in the context of nanomedicine. However, it is challenging to control the composition of the ligand layer and maintain high colloidal and chemical stability of the conjugates. A high level of control and stability are crucial for reproducibility, upscaling, and safe application. In this study, gold nanoparticles with well-defined mixed ligand layers of α-methoxypoly(ethylene glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) and 11-mercaptoundecanoic acid (MUA) were synthesized and characterized by ATR-FTIR spectroscopy and gel electrophoresis. The colloidal and chemical stability of the conjugates was tested by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and UV/vis spectroscopy based experiments, and their interactions with cells were analyzed by elemental analysis. We demonstrate that the alkylene spacer in PEGMUA is the key feature for the controlled synthesis of mixed layer conjugates with very high colloidal and chemical stability and that a controlled synthesis is not possible using regular PEG ligands without the alkylene spacer. With the results of our stability tests, the molecular structure of the ligands can be clearly linked to the colloidal and chemical stabilization. We expect that the underlying design principle can be generalized to improve the level of control in nanoparticle surface chemistry.
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http://dx.doi.org/10.1021/acs.langmuir.6b01704DOI Listing
August 2016

Influence of TMAO and urea on the structure of water studied by inelastic X-ray scattering.

Phys Chem Chem Phys 2016 Jun 7;18(24):16518-26. Epub 2016 Jun 7.

European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble, France.

We present a study on the influence of the naturally occurring organic osmolytes tri-methylamine N-oxide (TMAO) and urea on the bulk structure of water using X-ray Raman scattering spectroscopy. Addition of TMAO is known to stabilize proteins in otherwise destabilizing aqueous urea solutions. The experimental X-ray Raman scattering spectra change systematically with increasing solute concentration revealing different effects on the structure of water due to the presence of the two osmolytes. Although these effects are distinct for both molecular species, they have mutually compensating influences on the spectra of the ternary water-TMAO-urea mixtures. This compensation effect seen in the spectra vanishes only at the highest studied ternary concentration of 4 M : 4 M (TMAO : urea). Our experiment shows that the hydrogen-bonding structure of water remains rather intact in the presence of the aforementioned osmolytes if both of them are present.
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http://dx.doi.org/10.1039/c6cp01922fDOI Listing
June 2016

Concentration dependent effects of urea binding to poly(N-isopropylacrylamide) brushes: a combined experimental and numerical study.

Phys Chem Chem Phys 2016 Feb;18(7):5324-35

Institut für Computerphysik, Universität Stuttgart, D-70569 Stuttgart, Germany.

The binding effects of osmolytes on the conformational behavior of grafted polymers are studied in this work. In particular, we focus on the interactions between urea and poly(N-isopropylacrylamide) (PNIPAM) brushes by monitoring the ellipsometric brush thickness for varying urea concentrations over a broad temperature range. The interpretation of the obtained data is supported by atomistic molecular dynamics simulations, which provide detailed insights into the experimentally observed concentration-dependent effects on PNIPAM-urea interaction. In particular, in the low concentration regime (cu ≤ 0.5 mol L(-1)) a preferential exclusion of urea from PNIPAM chains is observed, while in the high concentration regime (2 ≤ cu ≤ 7 mol L(-1)) a preferential binding of the osmolyte to the polymer surface is found. In both regimes, the volume phase transition temperature (Ttr) decreases with increasing urea concentration. This phenomenon derives from two different effects depending on urea concentration: (i) for cu ≤ 0.5 mol L(-1), the decrease of Ttr is explained by a decrease of the chemical potential of bulk water in the surrounding aqueous phase; (ii) for cu ≥ 2 mol L(-1), the lower Ttr is explained by the favorable replacement of water molecules by urea, which can be regarded as a cross-linker between adjacent PNIPAM chains. Significant effects of the concentration-dependent urea binding on the brush conformation are noticed: at cu = 0.5 mol L(-1), although urea is loosely embedded between the hydrated polymer chains, it enhances the brush swelling by excluded volume effects. Beyond 0.5 mol L(-1), the stronger interaction between PNIPAM and urea reduces the chain hydration, which in combination with cross-linking of monomer units induces the shrinkage of the polymer brush.
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http://dx.doi.org/10.1039/c5cp07544kDOI Listing
February 2016

Sequential Single Shot X-ray Photon Correlation Spectroscopy at the SACLA Free Electron Laser.

Sci Rep 2015 Nov 27;5:17193. Epub 2015 Nov 27.

Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.

Hard X-ray free electron lasers allow for the first time to access dynamics of condensed matter samples ranging from femtoseconds to several hundred seconds. In particular, the exceptional large transverse coherence of the X-ray pulses and the high time-averaged flux promises to reach time and length scales that have not been accessible up to now with storage ring based sources. However, due to the fluctuations originating from the stochastic nature of the self-amplified spontaneous emission (SASE) process the application of well established techniques such as X-ray photon correlation spectroscopy (XPCS) is challenging. Here we demonstrate a single-shot based sequential XPCS study on a colloidal suspension with a relaxation time comparable to the SACLA free-electron laser pulse repetition rate. High quality correlation functions could be extracted without any indications for sample damage. This opens the way for systematic sequential XPCS experiments at FEL sources.
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http://dx.doi.org/10.1038/srep17193DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4661692PMC
November 2015

Nano-beam X-ray microscopy of dried colloidal films.

Soft Matter 2015 Jul;11(27):5465-72

Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.

We report on a nano-beam small angle X-ray scattering study on densely-packed, dried binary films made out of spherical silica particles with radii of 11.2 and 19.3 nm. For these three-dimensional thin films prepared by drop casting, only a finite number of colloidal particles contributes to the scattering signal due to the small beam size of 400 × 400 nm(2). By scanning the samples, the structure and composition of the silica particle films are determined spatially resolved revealing spatial heterogeneities in the films. Three different types of domains were identified: regions containing mainly large particles, regions containing mainly small particles, and regions where both particle species are mixed. Using the new angular X-ray cross-correlations analysis (XCCA) approach, spatial maps of the local type and degree of orientational order within the silica particle films are obtained. Whereas the mixed regions have dominant two-fold order, weaker four-fold and marginal six-fold order, regions made out of large particles are characterized by an overall reduced orientational order. Regions of small particles are highly ordered showing actually crystalline order. Distinct differences in the local particle order are observed by analyzing sections through the intensity and XCCA maps. The different degree of order can be understood by the different particle size polydispersities. Moreover, we show that preferential orientations of the particle domains can be studied by cross-correlation analysis yielding information on particle film formation. We find patches of preferential order with an average size of 8-10 μm. Thus, by this combined X-ray cross-correlation microscopy (XCCM) approach the structure and orientational order of films made out of nanometer sized colloids can be determined. This method will allow to reveal the local structure and order of self-assembled structures with different degree of order in general.
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http://dx.doi.org/10.1039/c5sm00609kDOI Listing
July 2015

Single shot coherence properties of the free-electron laser SACLA in the hard X-ray regime.

Sci Rep 2014 Jun 10;4:5234. Epub 2014 Jun 10.

1] Deutsches Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany [2] The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany.

We measured the coherence properties of the free-electron laser SACLA on a single shot basis at an X-ray energy of 8 keV. By analysing small-angle X-ray scattering speckle patterns from colloidal dispersions we found a degree of transverse coherence of βt = 0.79 ± 0.09. Taking detector properties into account, we developed a simulation model in oder to determine the degree of coherence from intensity histograms. Finally we calculated a coherence time of τc = 0.1 fs and a pulse duration of 5.2 fs which corresponds with previous predictions.
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http://dx.doi.org/10.1038/srep05234DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4050387PMC
June 2014

Formation of iron containing aggregates at the liquid-air interface.

Colloids Surf B Biointerfaces 2013 Sep 29;109:74-81. Epub 2013 Mar 29.

Helmholtz-Zentrum Geesthacht, Geestacht, Germany.

The early stages of the formation of inorganic aggregates, composed of iron compounds at the solution-air interface, were investigated in situ. The properties of the solution-air interface were changed by using different Langmuir layers. In order to get insight into the evolution of the sample system in situ, the processes were studied by X-ray scattering and spectroscopy techniques. The formation of aggregates was detected under cationic as well as under anionic Langmuir layers. The observed compounds lack long range order which indicates the formation of amorphous structures. This is supported by extended X-ray absorption fine structure measurements showing only minor order in the formed aggregates.
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http://dx.doi.org/10.1016/j.colsurfb.2013.03.006DOI Listing
September 2013