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The natural blood protein fibrinogen is a highly potent precursor for the production of various biomaterials due to its supreme biocompatibility and cell interaction. To gain actual materials from fibrinogen, the protein needs to undergo fibrillogenesis, which is mostly triggered via enzymatic processing to fibrin, electrospinning, or drying processes. All of those techniques, however, strongly limit the available structures or the applicability of the material. To overcome the current issues of fibrin(ogen) as material, we herein present a highly feasible, quick, and inexpensive technique for self-assembly of fibrinogen in solution into defined, nanofibrous three-dimensional (3D) patterns. Upon interaction with specific anions in controlled environments, stable and flexible hydrogel-like structures are formed without any further processing. Moreover, the material can be converted into highly porous and elastic aerogels by lyophilization. Both of these material classes have never been described before from native fibrinogen. The observed phenomenon also represents the first enzyme-free process of fibrillogenesis from fibrinogen with significant yield in solution. The produced hydrogels and aerogels were investigated via electron microscopy, IR spectroscopy, and fluorescence spectroscopy, which also confirms the native state of the protein. Additionally, their mechanical properties were compared with actual fibrin and unstructured fibrinogen. The structural features show a striking analogy to actual fibrin, both as hydro- and aerogel. This renders the new material a highly promising alternative for fibrin in biomaterial applications. A much faster initiation of fiber formation, exclusion of possible thrombin residuals, and low-cost reagents are great advantages.

A disulfide polymer that is triggerable by ultrasound, UV, and redox in aqueous solution and can self-assemble with ionic probe molecules into again multitriggerable assemblies is presented. It is ...

Pseudo isocyanine chloride (PIC) has a strong tendency to self-assemble with a concentration dependent temperature threshold separating a regime with small H-oligomers in equilibrium with monomeric PIC from a regime where large J-aggregates form. In complementing the known set of absorption spectra by the spectrum of a trimer, which represents all H-aggregates with N ≥ 3, a full description of the sample composition of PIC in the regime of oligomers became possible by means of UV-vis spectroscopy and gave access to the equilibrium thermodynamics of oligomerisation. Successful interpretation of the concentration dependent temperature threshold as a ceiling temperature of J-aggregation made also accessible equilibrium thermodynamics of the formation of J-aggregates together with a full analysis of composition also in the regime of J-aggregates. Evolution of an invariant spectrum for the J-aggregates demonstrates full consistency of the composition analysis. Complementary light scattering experiments led to a comprehensive characterisation of all aggregate species above and below the aggregation threshold. Once initiated, J-aggregates always grow to a final length of 650 nm. Time-resolved light scattering confirmed that the self-assembly of J-aggregates follows a monomer addition process in analogy to a chain growth in polymer chemistry. Initiation and growth of individual aggregates turned out to be always much faster than the progress of aggregation.

Pseudo‐isocyanine chloride (PIC) is a cationic dyestuff that exhibits self‐assembly in aqueous solution, promoted either by increasing the PIC concentration or by decreasing the temperature. PIC‐aggregates exhibit a characteristic and sharp absorption band as well as a fluorescence band at a wavelength of 573 nm making PIC an interesting candidate to analyze the self‐assembly process in various environments. The present work developed PIC‐based, synthetic model systems, suitable to investigate how macromolecular crowding influences self‐assembly processes. Four synthetic additives were used as potential crowders: Triethylene glycol (TEG), polyethylene glycol (PEG), Ficoll 400 as a highly branched polysaccharide, and sucrose corresponding to the monomeric unit of Ficoll. Combined UV/Vis spectroscopy and time‐resolved light scattering revealed a strong impact of crowding based on excluded volume effects only for Ficoll 400. Sucrose had hardly any influence on the self‐assembly of PIC and PEG and TEG impeded the PIC self‐assembly. Development of such a PIC based model system led over to in‐cell experiments. HeLa cells were infiltrated with PIC solutions well below the aggregation threshold in the infiltrating solution. In the cellular environment, PIC was exposed to a significant crowding and immediately started to aggregate. As was demonstrated by fluorescence imaging, the extent of aggregation can be modulated by exposing the cells to salt‐induced osmotic stress. The results suggest future use of such a system as a sensor for the analysis of in vitro and in vivo crowding effects on self‐assembly processes., Stand out from the crowd! The cationic dyestuff PIC reversibly self‐assembles in aqueous solution. A comparative investigation of such PIC self‐assembly in the presence of synthetic polymers with PIC self‐assembly in living Hela cells suggests PIC as a promising candidate for a sensor to examine the impact of varying cellular conditions like macromolecular crowding on self‐assembly processes of proteins in cells (see figure).

Block copolymers were prepared with two anionic polyelectrolyte blocks: sodium polyacrylate (PA) and sodium polystyrene sulfonate (PSS), in order to investigate their phase behavior in aqueous solution in the presence of Ca2+ cations. Depending on the concentration of polymer and Ca2+ and on the ratio of the block lengths in the copolymer, spherical micelles were observed. Micelle formation arises from the specific interaction of Ca2+ with the PA block only. An extensive small-angle scattering study was performed in order to unravel the structure and dimensions of the block copolymer micelles. Deuteration of the PA block enabled us to perform contrast variation experiments using small-angle neutron scattering at variable ratios of light and heavy water which were combined with information from small-angle X-ray scattering and dynamic light scattering.

Zeolitic imidazolate frameworks (ZIFs) represent an important subclass of porous metal organic frameworks (MOFs). The present work continues a previous study on ZIF-71 nanocrystal formation at room temperature (Cryst. Growth Des. 2016, 16, 2002–2010), which proposed a four-step formation process. It introduces a kinetic nucleation and growth model, which satisfactorily reproduces in situ time-resolved static light scattering data measured at room temperature in the previous work and at variable temperatures in the present work. Successful fitting can only be achieved with a precursor reaction being put before particle nucleation. The kinetic analysis provides rate constants for the precursor reaction, for particle nucleation, and for particle growth via monomer addition, and the equilibrium concentration of nonconsumed matter at the end of reaction. The rate constants of the precursor reaction and the nucleation process increase with temperature, which is counterintuitive if compared to classical nucleati...

Complexes between the anionic polyelectrolyte sodium polyacrylate (PA) and an oppositely charged divalent azobenzene dye are prepared in aqueous solution. Depending on the ratio between dye and polyelectrolyte stable aggregates with a well-defined spherical shape are observed. Upon exposure of these complexes to UV light, the trans → cis transition of the azobenzene is excited resulting in a better solubility of the dye and a dissolution of the complexes. The PA chains reassemble into well-defined aggregates when the dye is allowed to relax back into the trans isomer. Varying the temperature during this reformation step has a direct influence on the final size of the aggregates rendering temperature in an efficient way to easily change the size of the self-assemblies. Application of time-resolved small-angle neutron scattering (SANS) to study the structure formation reveals that the cis → trans isomerization is the rate-limiting step followed by a nucleation and growth process.

The human guanylate-binding protein 1 (hGBP1) belongs to the dynamin superfamily proteins and represents a key player in the innate immune response. Farnesylation at the C-terminus is required for hGBP1's activity against microbial pathogens, as well as for its antiproliferative and antitumor activity. The farnesylated hGBP1 (hGBP1fn) retains many characteristics of the extensively studied nonfarnesylated protein and gains additional abilities like binding to lipid membranes and formation of hGBP1fn polymers. These polymers are believed to serve as a protein depot, making the enzyme immediately available to fight the invasion of intracellular pathogens. Here we study the molecular mechanism of hGBP1 polymer formation as it is a crucial state of this enzyme, allowing for a rapid response demanded by the biological function. We employ Forster resonance energy transfer in order to trace intra and intermolecular distance changes of protein domains. Light scattering techniques yield deep insights into the changes in size and shape. The GTP hydrolysis driven cycling between a closed, farnesyl moiety hidden state and an opened, farnesyl moiety exposed state represents the first phase, preparing the molecule for polymerization. Within the second phase of polymer growth, opened hGBP1 molecules can be incorporated in the growing polymer where the opened structure is stabilized, similar to a surfactant molecule in a micelle, pointing the farnesyl moieties into the hydrophobic center and positioning the head groups at the periphery of the polymer. We contribute the molecular mechanism of polymer formation, paving the ground for a detailed understanding of hGBP1 function.

The interior of a cell is a highly packed environment that can be occupied up to 40% by different macromolecules. Such crowded media influence different biochemical processes like protein folding, enzymatic activity, and gene regulation. In this work, we use simulations to study protein stability under the presence of crowding agents that interact with the protein by excluded volume interactions. In general, the presence of crowding agents in the solution enhances the stability of the protein's native state. However, we find that the effects of excluded volume depend not only on crowding occupancy but also the crowders' geometry and size. Specifically, we find that polymeric crowders have stronger influence than spherical crowders and that this effect increases with polymer length, while it decreases with increasing size of spherical crowders. These opposing size effects are explained by the interplay of decreasing excluded volume and demixing, which together determine the change in the entropy of the crowders upon folding of the protein.

Unlike Na+ cations, which interact with fully neutralized poly(acrylic acid) as purely electrostatic entities, cations like Ag+, Mg2+, and Ca2+ exhibit specific interactions with the COO– residues of anionic polyacrylates. The present work analyzes the interaction of all four cations with a layer of polyacrylate chains grafted onto spherical polystyrene core as an outer shell. First and foremost the analysis answers the question on how these specific interactions influence the nature of the shell and solution behavior of the spherical polyelectrolyte brushes. It could be unambiguously demonstrated that Ag+, Mg2+, and Ca2+ cations induce a drastic shrinking of the polyacrylate shells at cation concentrations lower by 2–3 orders of magnitude compared to the transition of a fully stretched osmotic brush to a shrunken salted brush accomplished with Na+ cations. Ag+ induces a particularly abrupt contraction, which comes close to the annealing of such brushes achieved with a neutralization by protons. Finally, ...

Vimentin intermediate filaments (IFs) are part of a family of proteins that constitute one of the three filament systems in the cytoskeleton, a major contributor to cell mechanics. One property that distinguishes IFs from the other cytoskeletal filament types, actin filaments and microtubules, is their highly hierarchical assembly pathway, where a lateral association step is followed by elongation. Here we present an innovative technique to follow the elongation reaction in solution and in situ by time-resolved static and dynamic light scattering, thereby precisely capturing the relevant time and length scales of seconds to minutes and 60–600 nm, respectively. We apply a quantitative model to our data and succeed in consistently describing the entire set of data, including particle mass, radius of gyration, and hydrodynamic radius during longitudinal association.

Dodecyl amine edge functionalized few-layer graphene oxide quantum dots were synthesized in good yields. The covalent functionalization was demonstrated with NMR and AFM-IR. The resulting structure and particle size was measured with AFM and HRTEM. The thermal stability of the compound was investigated and showed a stability of up to 220 °C. The modified graphene oxide quantum dots showed excellent solubility in various organic solvents, including ethers, methanol, toluene, n-hexane, heptane, xylene, dichloromethane and toluene. The stability of a resulting toluene solution was also proven by static light scattering measurements over several days. The excellent solubility gives the possibility of an efficient and fast spray application of the functionalized graphene oxide quantum dots to steel surfaces. Hence, the macroscopic friction behavior was investigated with a Thwing-Albert FP-2250 friction tester. A thin film of the dodecyl amine functionalized graphene oxide quantum dots on steel lowered the friction coefficient from 0.17 to 0.11 and revealed a significant corrosion inhibition effect.

Dilute solutions of sodium poly(styrene sulfonate) (NaPSS) in the presence of Al3+, Ca2+, and Ba2+ were analysed by means of isothermal titration calorimetry (ITC) in order to investigate the heat effect of bond formation between those cations and the anionic SO3− residues of NaPSS. The selection of the cations was guided by the solution behavior of the corresponding PSS salts from a preceding study [M. Hansch et al., J. Chem. Phys. 148(1), 014901 (2018)], where bonds between Ba2+ and anionic PSS showed an increasing solubility with decreasing temperature and Al3+ exhibited the inverse trend. Unlike to Al3+ and Ba2+, Ca2+ is expected to behave as a purely electrostatically interacting bivalent cation and was thus included in the present study. Results from ITC satisfactorily succeeded to explain the temperature-dependent solution behavior of the salts with Al3+ and Ba2+ and confirmed the non-specific behavior of Ca2+. Additional ITC experiments with salts of Ca2+ and Ba2+ and sodium poly(acrylate) complemented the results on PSS by data from a chemically different polyanion. Availability of these joint sets of polyanion-cation combinations not only offers the chance to identify common features and subtle differences in the solution behavior of polyelectrolytes in the presence of multi-valent cations but also points to a new class of responsive materials.Dilute solutions of sodium poly(styrene sulfonate) (NaPSS) in the presence of Al3+, Ca2+, and Ba2+ were analysed by means of isothermal titration calorimetry (ITC) in order to investigate the heat effect of bond formation between those cations and the anionic SO3− residues of NaPSS. The selection of the cations was guided by the solution behavior of the corresponding PSS salts from a preceding study [M. Hansch et al., J. Chem. Phys. 148(1), 014901 (2018)], where bonds between Ba2+ and anionic PSS showed an increasing solubility with decreasing temperature and Al3+ exhibited the inverse trend. Unlike to Al3+ and Ba2+, Ca2+ is expected to behave as a purely electrostatically interacting bivalent cation and was thus included in the present study. Results from ITC satisfactorily succeeded to explain the temperature-dependent solution behavior of the salts with Al3+ and Ba2+ and confirmed the non-specific behavior of Ca2+. Additional ITC experiments with salts of Ca2+ and Ba2+ and sodium poly(acrylate) complem...

The early stages of silica polymerization in aqueous solution proceed according to a mechanism based on three steps: nucleation, particle growth, and agglomeration of the particles. Application of time-resolved static and dynamic light scattering as a powerful in situ technique in combination with spectrophotometric analysis of the monomer consumption based on the molybdenum blue method was carried out to further investigate this 3-step process. Experiments were carried out at four different initial silicic acid contents covering a range between 350 and 750 ppm in the presence of either 10 mM NaCl or 5 mM of a mixture of CaCl2 and MgCl2. The process in all cases was initiated with a drop of pH to 7. Addition of the salts made possible an analysis of the impact of an electrolyte on the process. Independent of the presence or absence of salt, particle growth in step two proceeded as a monomer-addition process without being interfered significantly by Ostwald-ripening. The growing particles were compact with...

In this report, we summarize our theoretical and experimental investigations on the zeolitic imidazolate framework (ZIF) system [Zn(dcim)2] (dcim=4,5-dichloroimidazolate) that have been published recently. These comprise: (1) a theoretical study on hypothetical conformational [Zn(dcm)2]-SOD polymorphs with the same underlying sodalite (SOD) topology but distinct dcim linker orientations, (2) a synthetic work that resulted in the experimental realization of the most stable predicted (trigonal) SOD-type framework conformer and improved synthetic protocols for a previously discovered cubic SOD-type material, (3) a detailed structural analysis of the trigonal and cubic SOD-type materials, (4) a comparative characterization of the SOD-type materials by gas physisorption measurements, (5) a synthetic work that resulted in the discovery of a complete series of intermediate frameworks with the trigonal and cubic SOD-type materials as the end members, and (6) time-resolved in-situ light and stopped-flow synchrotron small-angle and wide-angle X-ray scattering experiments on the rapid crystallization of the RHO-type polymorph (ZIF-71). In addition, we report as yet unpublished work, concerning time-resolved in-situ angular-dispersive synchrotron X-ray diffraction experiments on RHO-/SOD-type phase selection via the coordination modulation approach during competitive formation of the RHO-type and SOD-type materials.

A detailed light scattering investigation is presented on dilute solutions of two long-chain sodium polyacrylates (NaPA) in the presence of monovalent Ag+ ions in 0.01 M NaNO3 aqueous solution at a pH of 9. The relevance for the investigation is based on two features: (i) despite its monovalency, Ag+ is expected to exhibit a much more complex interaction pattern with NaPA than salts based on alkaline cations do; (ii) aqueous solutions of AgNO3 nucleate Ag–nanoparticle formation in the presence of NaPA under UV light, which may be modulated by the solution behavior. Our study revealed the following results. Addition of a low amount of Ag+ ions leads to an aggregation of PA-chains without considerable coil shrinking. At a ratio of silver ions per monomer of 0.001 ≤ [Ag+]/[COO–] ≤ 0.05, combined static and dynamic light scattering (SLS/DLS) suggests formation of homogeneous low density aggregates. Further increase of the Ag+ ion concentration results in a formation of dense unstable aggregates. At ratios of ...

Silica polymerization in a supersaturated aqueous solution of sodium silicate is a fundamental mineralization process with broad relevance for technical applications as well as for biological processes. To contribute to a better understanding of the mechanism underlying the polymerization of sodium silicate under ambient conditions, a combined multiangle static and dynamic light scattering study on the evolution of particle mass and size is applied for the first time in a time-resolving manner. The light scattering experiments are complemented by a time-resolved analysis of the decay of the concentration of monomeric silicate by means of the silicomolybdate method. Particle formation was investigated at a variable concentration of silicate at pH 7 and 8. The joint experiments revealed a loss of monomers, which is parallel to the formation of compact, spherical particles growing by a monomer-addition process. An increase in the silicate content of up to 750 ppm increased the extent of nucleation and at the same time decreased the lag time observed between the start of the reaction and the actual onset of the growth of particles. Once the silica content is considerably larger than 1000 ppm, the formation of particles is succeeded by particle-particle agglomeration leading to larger fractal-like particles. By the time agglomeration becomes noticeable with light scattering, the monomer concentration has already reached its equilibrium value. An increase in the pH to 8 again revealed particle formation via a monomer-addition process. However, the extent of nucleation was increased and particle-particle agglomeration was inhibited even at an initial silica content of 2000 ppm.

A small angle neutron scattering (SANS) study is presented, which investigates the impact of a modulator on nucleation and growth of MOF-5 nanoparticles. Two DMF solutions, one with the secondary building unit Zn4O(C6H5COO)6 (SBU) and one with terephthalic acid (BDC) as a linker, were mixed, and 5 min after generation of the mixture, monodentate 4-n-decylbenzoic acid was added as a modulator agent. Time-resolved SANS during the initial stages of the particle formation process offered insight into morphological transformations during the first hours. Subsequently, it could be demonstrated that a shell is formed by the modulator wrapping around the growing MOF-5 particles while directing the formation of MOF-5 nanoparticles. This has been made possible by an identification of a mixture of deuterated and hydrogenated solvent (DMF), which matches the scattering contrast of MOF-5, thus giving access to the scattering signal of the modulator.

A binary dyestuff aggregate with a distinct stoichiometry is formed in dilute aqueous solution upon addition of Mg2+ ions. The aggregation process was investigated with time-resolved multiangle static light scattering resulting in a sequence of static scattering curves. The scattering curves were analyzed with respect to the aggregation kinetics as well as the structure of the growing aggregates. The aggregation kinetics was based on the time evolution of the weight-averaged molar mass values extracted from the intercepts of the static scattering curves. A kinetic model that considers solely a nucleation step and monomer addition in its most simple form was developed in order to describe the evolution of time-dependent mass data. In addition, a kinetic model introduced by Lomakin et al. (Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 1125) for the description of beta-amyloid aggregation was adapted to the same experimental data. Application of the two kinetic models offered significant information on the role of magnesium ions within the aggregation process and provided a deeper understanding of the aggregation mechanism. Correlation of the size parameters extracted from the initial slopes of the scattering curves with the respective mass data as well as direct fitting of the scattering curves with the wormlike chain model yield a consistent set of model parameters.

The present work investigates PMMA colloids in a polymer matrix of linear chains as a simple and suitable system for complex nanocomposites. The investigation was based on SANS experiments, which were enabled by the use of deuterated colloids immersed in a matrix of linear hydrogenated chains. Cross-linked deuterated PMMA-colloids were synthesized with two different sizes (70 and 140 nm) by means of the surfactant-free emulsion polymerization method and the swelling behavior adjusted by varying the amount of added cross-linker (1.5 and 15.0 mol-%) at each size respectively. Colloid–polymer blends were prepared from colloid–polymer solutions. SANS experiments on these blends consistently revealed that colloids with a low cross-linking density could be homogeneously distributed throughout the matrix of linear chains. Fits with model form factors indicated the structure of fuzzy spheres for these molecularly dispersed microgels, which are slightly swollen with respect to their size and shape in H2O. Contrary...

The present work investigates the formation of well-defined heteroaggregates from a binary mixture of a red and a yellow azo-dyestuff in the presence of Mg(2+) ions. Combined static and dynamic light scattering together with laser induced liquid bead ion desorption mass spectrometry (LILBID-MS) has been applied to characterize the states of the pure red dye and the pure yellow dye as well as of their mixture in aqueous solution without Mg(2+). These experiments indicated that a structural reorganization on a molecular scale takes place as soon as the two dyes are combined. Solutions of the combined red and yellow dye contain micelle-like mixed entities with a size of a few tenths of nanometers. Upon the addition of Mg(2+), these micelles vanish in favor of elongated heteroaggregates, which grow by a stepwise addition of smaller building units. As unraveled by UV/vis spectroscopy, the heteroaggregates that are formed from the red and yellow azo dye in the presence of Mg(2+) obey a stoichiometric ratio of the two components of 1:1. A new multiangle scattering instrument allowed us for the first time to follow this aggregation process at the stoichiometric ratio by time-resolved combined static and dynamic light scattering, thereby providing further aspects of the worm-like nature of the growing heteroaggregates.

Bivalent lead ions as representative main group heavy metal cations form specific interactions with the negatively charged COO– residues of sodium polyacrylate chains in dilute aqueous solution. The interactions eventually lead to aggregation and precipitation of sodium polyacrylate chains partially neutralized with Pb2+ cations. The present work outlines a small-angle X-ray (SAXS) and light scattering study of the polyacrylate chains undergoing changes in coil conformation and successive aggregation while approaching and crossing the Pb2+-induced precipitation threshold. The study reveals a coil shrinking while approaching the precipitation threshold. Anomalous SAXS (ASAXS) complemented this information with a first insight into the spatial distribution of the Pb2+ cations captured by the polyacrylate chains together with a semiquantitative estimation of the amount of Pb2+ cations located within the collapsed domains of the shrinking chains. Conformational aspects of the shrinking coils could be establis...

Anomalous small angle scattering measurements have been applied to diluted solutions ofanionic polyacrylates decorated by specifically-interacting Pb$^{2+}$ cations, revealing partial collapseof the polyacrylate into pearl-like subdomains with a size on the order of a few nanometers. Fromthe pure-resonant scattering contribution of the Pb$^{2+}$ cations, and from subsequent analysis ofthe resonant-invariant, the amount of Pb$^{2+}$ cations condensed onto the polyanions with respect tothe total amount of Pb$^{2+}$ cations in the solvent was estimated. In order to scrutinize systematiclimitations in the determination of the chemical concentrations of resonant scattering counterionsin the collapsed phase, Monte Carlo simulations have been performed. The simulations are basedon structural confinements at variable size in the range of few nanometers, which represent thecollapsed subdomains in the polyanions. These confinements were gradually filled to a high degreeof the volume fraction with resonant scattering counterions giving access to a resonant-invariant ata variable degree of filling. The simulations revealed in the limit of small structures a significantunderestimation of the true degree of filling of the collapsed subdomains when determining chemicalconcentrations of Pb$^{2+}$ cations from the resonant invariant.

The condensation of counterions is an important aspect of charged macromolecules. Therefore an experimental characterization of the condensation of counterions is desirable. In this contribution two experimental techniques for the characterization of counterion condensation are introduced and compared: Anomalous Small Angle X-Ray Scattering (ASAXS) is able to probe the spatial distribution of counterions and electrophoresis nuclear magnetic resonance (NMR) measures counterion condensation via the effective charge obtained from the dynamic behaviour of molecules and complexes in an electric field.

A detailed in situ scattering study has been carried out on the formation of amorphous calcium carbonate (ACC) particles modulated by the presence of small amounts of sodium polyacrylate chains. The work is aiming at an insight into the modulation of ACC formation by means of two polyacrylate samples differing in their molecular weight by a factor of 50. The ACC formation process was initiated by an in situ generation of CO(3)(2-) ions via hydrolysis of 10 mM dimethylcarbonate in the presence of 10 mM CaCl(2). Analysis of the formation process by means of time-resolved small-angle X-ray and light scattering in the absence of any additives provided evidence for a monomer addition mechanism for the growth of ACC particles. ACC formation under these conditions sets in after a lag-period of some 350 s. In the presence of sodium polyacrylate chains, calcium polyacrylate aggregates are formed during the lag-period, succeeded by a modulated ACC growth in a second step. The presence of anionic polyacrylate chains changed the shape of the growing particles toward loose and less homogeneous entities. In the case of low amounts (1.5-7.5 mg/L) of the long chain additive with 97 kDa, the size of the aggregates is comparable to the size of the successively formed hybrid particles. No variation of the lag-period has been observed in this case. Use of the short chain additive with 2 kDa enabled increase of the additive concentration up to 100 mg/L and resulted in a significant increase of the lag-period. This fact, together with the finding that the resulting hybrid particles remained stable in the latter case, identified short chain sodium polyacrylates as more efficient modulators than long chain polyacrylates.

The kinetics and mechanism of crystallization of the dense zinc imidazolate framework with zni topology, from comparatively dilute methanol solutions containing Zn(NO3)·6H2O and imidazole with variation of the zinc-to-imidazole ratio, were followed in situ by time-resolved static and dynamic light scattering. The light scattering data revealed that metastable primary particles of about 100 nm in diameter form rapidly upon mixing the component solutions. After a lag time that is dependent on the imidazole concentration, the primary particles aggregate into secondary particles by a monomer addition mechanism with the primary particles as the monomers. Complementary scanning electron microscopy revealed that further evolution of the secondary particles is a complex process involving polycrystalline intermediates, the non-spherical morphologies of which depend on the initial zinc-to-imidazole ratio. Time and location of the first appearance of crystalline order could so far not be established. The pure-phase ZIF-zni crystals obtained after 240 min are twins. The aspect ratio of the tetragonal crystals can be controlled via the zinc-to-imidazole ratio. © 2011 The Owner Societies.

Polymers showing an upper critical solution temperature (UCST) in water are rare. Recently, the nonionic homopolymer poly(N-acryloyl glycinamide) (poly(NAGA)) has been shown to exhibit a sharp uppe...

We report on a simple and straightforward method that enables the rapid room-temperature production of nanocrystals (finely tuned in size between ∼10 and 65 nm) and microcrystals (∼1 μm) of the prototypical microporous zeolitic imidazolate framework (ZIF) material ZIF-8. Control of crystal size is achieved in a novel approach by employing an excess of the bridging bidentate ligand and various simple auxiliary monodentate ligands with different chemical functionalities (carboxylate, N-heterocycle, alkylamine). The function of the monodentate ligands can be understood as a modulation of complex formation and deprotonation equilibria during crystal nucleation and growth. Using time-resolved static light scattering, the functioning of modulating ligands is monitored for the first time by in situ experiments, which offered significant insight into the crystal growth processes. Formation of nanocrystals is characterized by continuous, comparatively slow nucleation and fast crystal growth occurring on a time sca...

Sodium polyacrylate (NaPA) in dilute aqueous solution at an ionic strength of [NaNO3] = 0.01M establishes a rich phase behavior in the presence of low amounts of silver cations, which were introduced at a few millimoles or less by replacing the corresponding amount of Na+ cations. Beyond an extremely low level of Ag+ cations, anionic PA chains aggregate. By increasing the concentration of Ag+, the aggregates become denser and keep on growing without limit. Once a certain range of [Ag+] is reached, the instantaneously formed dense aggregates remain stable. Irradiation of the PA aggregate solutions with UV-light induces formation of silver nanoparticles (Ag-Nps). Based on a combination of UV-vis spectroscopy, light scattering, transmission electron microscopy, and small angle neutron scattering, the mechanism of this NaPA assisted formation of Ag-Nps is studied. One focus of the study is lying on the effect of the two different solution states of dense aggregates, corresponding to the unstable growing AgPA aggregates and to the stable AgPA aggregates and another focus is aiming at the characterisation of the morphology of the generated hybrid particles composed of Ag-Nps and hosting PA chains.

A new binary colloidal system is designed with each colloidal component being able to exclusively interact with the colloids of the second component, respectively. The colloids are based on cross-linked polystyrene and polymerized by means of surfactant-free emulsion polymerization with either 4-hydroxyl styrene or 4-vinyl pyridine as comonomers. The comonomers are selected to decorate the colloids with complementary H-bond donors or acceptors. Characterization of the colloids by light scattering in CHCl(3) results in particle radii covering a regime of 130 nmR270 nm and indicates a narrow particle size distribution for all prepared samples. The colloids are slightly swollen compared to their state in H(2)O. The corresponding size ratio expressed as the radius of the small colloids divided by the radius of the large colloids in CHCl(3) extends over a regime of 0.52R(S)/R(L)0.85. IR analysis indicates strong hydrogen bonds between a colloidal component and the complementary molecular functions, that is, phenol or pyridine. If both colloidal components are directly combined as suspension in CHCl(3) a fast heteroaggregation is observed. This aggregation slows down and becomes accessible to an analysis by means of time-resolved static light scattering if the suspensions get sufficiently dilute. Fast aggregation can be totally inhibited if capping agents like phenol to cap the 4-vinyl pyridine functions are added as highly concentrated solutions. Dried samples of those binary suspensions equilibrated with an appropriate amount of phenol show the first indication for an ordered binary assembly.

In this article, we investigate tapping mode atomic force microscopy images of intermediate states along the coil to globule transition of sodium polyacrylate coils containing Ca2+ as specifically binding ions. The structural correlations within single adsorbed molecules are established using power spectral density (PSD) curves. The PSD curves of several single molecules are averaged to give the so called 2D form factor so as to obtain information of higher statistical merit. A proper interpretation of the 2D form factor and comparison with form factor analysis of the very same sample solution available through small angle neutron scattering provides an alternative quantification of changes in conformation which a single polyacrylate molecule undergoes as it moves from 3D solution to 2D surface and is inevitably distorted in shape because of sample history. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1553–1561, 2010

Long chain sodium polyacrylate polymers in dilute aqueous solution respond extremely sensitive to the addition of small, stoichiometric amounts of Ca2+ ions. Essential features of this response are a considerable shrinking of the coil dimensions and an additional sensitivity of the coil dimensions toward a change in temperature. To reveal details of this shrinking process, the conformational changes in response to the addition of alkaline earth cations at two different temperatures are investigated by means of light and neutron scattering and by AFM on the same samples, respectively. Partially collapsed coils at 15 °C were further shrunken and modified in shape by increasing the temperature to 30 °C. The scattering curves from the intermediates at 30 °C could successfully be interpreted with a pearl necklace model, which includes a low amount of pearls per polymer separated by 80 nm from each other. AFM investigations of adsorbed chains confirm the drastic conformational changes inferred to the system wit...

The bis(guanidine)-stabilised zinc complexes [N1,N2-bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]dichloridozinc(II), [Zn(DMEG2e)Cl2] (C1), diacetato[N1,N2-bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II),[Zn(DMEG2e)(CH3COO)2] (C2), and bis[N1,N2-bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II) bis(trifluoromethanesulfonate), [Zn(DMEG2e)2](CF3SO3)2 (C3), have been synthesised and completely characterised by means of X-ray structure analysis, NMR spectroscopy and mass spectrometry. These [bis(guanidine)]zinc complexes were investigated regarding their activity in the bulk polymerisation of D,L-lactide. It could be shown that these compounds are able to act as initiators for lactide polymerisation, and polylactides with molecular weights (Mw) of around 18000–59000 g/mol could be obtained. Variation of the reaction temperature revealed that the molecular weights decrease with increasing temperature. Additionally, the correlation of the intrinsic viscosity with the molecular weight demonstrates that the obtained polymers are linear and structurally homogeneous.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Formation of beta-amyloid plaques is a crucial feature of Alzheimer's disease. In the present work time resolved static light scattering was applied to investigate the size and shape of growing beta-amyloid aggregates preceding plaque formation. The beta-amyloid protein with 40 amino acid residues was used. Salt free buffer solutions and solutions with 0.15M NaCl at 37 degrees C served as the aggregation medium. The focus lay on the first 2h following initiation of the aggregation process which corresponds to the protofibril phase. Addition of the NaCl accelerated the aggregation process considerably. Scattering data from aggregation in saline solutions indicated formation of long fibers which suggest interpretation of data with the worm-like chain model. Two important results were revealed: (i) At the end of the time resolved recordings, the worm-like chain model provided a fully adequate picture for the growing aggregates. Chain stiffness is characterised in terms of the persistence length, which is close to 50 nm. The linear mass density of the growing fibers approached a value of two monomers per nm corresponding to single stranded fibers, which is in accordance with presently existing models for the aggregation of beta-amyloid. The fibers finally reached contour lengths of several thousand nanometers. (ii) The plateau values for the persistence length and linear mass density observed in the final regime are gradually approached from higher values. This observation is inconsistent with simple worm-like chains. Rather does it indicate existence of another species during the initial phase of the aggregation, in addition to monomers and fibers. Aside from further insight into fundamental aspects of beta-amyloid aggregation, time resolved static light scattering provides an appropriate tool for assay tests with drugs designed to interfere with the aggregation process.

The formation of temperature-, concentration-, and pH-responsive hydrogels composed of the symmetric long-chain bolaamphiphile dotriacontane-1,1'-diyl bis[[2-(dimethylammonio)ethyl]phosphate] (Me(2)PE-C32-Me(2)PE) was investigated by rheological, scattering, and spectroscopic techniques. At pH 5, this bolaamphiphile is known to form a dense network of helically structured nanofibers (Köhler et al. Soft Matter 2006, 2, 77-86). Rheological measurements and dynamic light scattering were used to describe the macroscopic behavior of the hydrogels. Small-angle neutron scattering (SANS) and time-resolved static light scattering were applied to get information about the morphology of the self-assembled aggregates. Finally, solid-state 31P NMR spectroscopy was used to gain insight into the mobility of the bolaamphiphile molecules within the fiber aggregates. In comparison with the previously examined trimethylammonio analogue PC-C32-PC, which forms temperature-dependent hydrogels, Me(2)PE-C32-Me(2)PE exhibits additional concentration- and pH-dependent gelling properties. The significantly higher stability of the Me(2)PE-C32-Me(2)PE hydrogel is supported by the SANS data, which indicate the presence of fiber aggregates up to 50 degrees C.

We report five consecutive cases of Anaplasma (A.) phagocytophilum infection (the causative agent of human granulocytic anaplasmosis (HGA)) from western Austria. All infections were acquired between June and August in 2003 and 2004 in the Inn valley (Tyrol, Austria). Four patients required hospitalisation, one patient was treated as an outpatient. During the acute stage of illness, laboratory findings included thrombocytopenia (5/5), elevated C-reactive protein (5/5), elevated neopterin (5/5), elevated lactate dehydrogenase (4/5), and elevation of liver enzymes (4/5). Leukopenia (3/5) and elevated procalcitonin (2/5) were less frequently observed. All patients were treated with tetracyclines, which led to prompt improvement of the clinical conditions. Anti-platelet antibodies were observed in one of four patients, but remained unchanged after complete covalescence.

A new combination of polymer chains and small colloids is presented in order to investigate the behavior of colloid−polymer mixtures in solution (CP) in the protein limit. To this end, hydroxy-functionalized silica particles (OHSil) were prepared according to a procedure [J. Am. Chem. Soc. 2003, 125, 3712], which led to colloid radii as small as 1.2 nm. Compared to this small size, the coil dimensions of the polystyrene (PS) chains used as the polymer component were larger by more than an order of magnitude. Investigation of the CP focused on the dimension of the PS chains in the presence of a varying amount of OHSil colloids. Chain size and shape were characterized by means of light scattering, viscosity experiments, and small-angle neutron scattering (SANS). Two solvents have been used. A mixture of dimethylformamide (DMF) with toluene was isorefractive to the OHSil particles, giving access to single chain behavior of PS. Pure DMF, on the other hand, allowed an efficient contrast matching of OHSil suita...

A synthetic route towards surface modified, monodisperse, spherical particles is presented. The precursor particles exhibit epoxy-functionalities which can be opened afterwards with an appropriate nucleophile. Via this route, dye labeled particles are obtained. Copyright © 2004 John Wiley & Sons, Ltd.

The present work investigates the structure of large polystyrene (PS) chains in two different solvents in the presence of octa-n-propylsilsesquioxane (SILS) molecules. Both solvents are good solvents for the PS chains. Viscosity measurements combined with static and dynamic light scattering revealed a significant shrinking of the PS chain dimensions, with increasing the SILS concentration. At the same time, chain-chain interactions decreased. Highly significant light scattering experiments became possible due to the fact that one of the solvents provided a refractivity which matched the scattering contrast of SILS, thus giving way to an unperturbed picture of the polymer chains. Together with the evaluation of the phase behavior of the PS-SILS mixture in toluene and in a 0-solvent, these results suggest that the PS-SILS mixture represents an interesting model system for colloid-polymer mixtures in the protein limit. Supplementing SANS experiments on SILS in solutions of perdeuterated toluene with perdeuterated PS chains clearly indicated a zone depleted of SILS. In line with this, the crystallization tendency of SILS was increased with increasing PS concentration due to a condensation of SILS in polymer-free domains.

Colloid–polymer (CP) mixtures extend between two limiting cases, the colloid limit with the polymer coil size small compared to the colloid radius R col and the protein limit with the colloidal particles much smaller in size than the radius of gyration of the polymer chains R g . In the present work, model systems are developed for the protein limit. The colloid–solvent pairs are optimized in terms of their isorefractivity in order to facilitate the characterization of large polystyrene chains in suspensions of small colloids. The degree of isorefractivity of colloidal particles was successfully evaluated in terms of a reduced scattering intensity. Two polystyrene samples with radii of gyration of R g = 96 nm and R g = 78 nm , respectively, are used. The radii of the colloidal particles are close to R col = 12 nm , leading to size ratios of R g / R col = 8 and R g / R col = 6.5 . Four colloid solvent systems were found to be suitable for polymer characterization by light scattering, one based on silica particles and three systems with acrylate particles. The present investigation is focused on the three acrylate systems: poly(methyl methacrylate) in ethyl benzoate (ETB) at 7 °C, poly(ethyl methacrylate) in toluene at 7 °C and poly(ethyl methacrylate) in ETB at 40 °C. Characterization of PS chains is for the first time performed in colloid concentrations up to 2.5% by weight. In all cases, the size and shape of the polymer chains remain unchanged. A slight mismatch of the colloid scattering or a limited colloid solubility prevented investigation of PS chains at higher colloid concentration.

The distribution of Sr counterions around negatively charged sodium polyacrylate chains (NaPA) in aqueous solution was studied by anomalous small-angle X-ray scattering. Different ratios of the concentrations of SrCl2/[NaPA] reveal dramatic changes in the scattering curves. At the lower ratio the scattering curves indicate a coil-like behavior, while at the higher ratio the scattering curves are contracted to smaller q-values, caused by the collapse of the NaPA coil. The form factor of the scattering contribution of the counterions was separated and analyzed. For the scattering curves of the collapsed chains, this analysis agrees with the model of a pearl necklace, consisting of collapsed sphere-like subdomains which are connected by stretched chain segments. An averaged radius of the pearls of 19 nm and a distance between neighbouring pearls close to 60 nm could be established for the collapsed state of the NaPA chains.

The particle scattering behaviour of a pearl necklace chain is derived. The chain is composed of sphere-like pearls, separated by rod-like segments of fixed length, which have no angular restrictions. By calculating several series of model scattering curves, the important structural features are retrieved. The model is believed to be useful in interpreting intermediate structures of collapsing macromolecules or polyelectrolytes. A first application to a shrinking polyelectrolyte coil generated by molecular dynamic simulations (Limbach and Holm, J.Phys.Chem. 2003) is presented and used to discuss the potentials and limits of the model.

A synthetic route is presented for the preparation of electrically charged colloidal particles with either sign from the same precursor. In the first step, methyl methacrylate was copolymerized with ω-bromoalkyl acrylate and a cross-linker, leading to monodisperse, bromo-functionalized colloids. Substitution of the bromo-functions by either trimethylamine of Na 2 SO 3 transformed the neutral precursors into positively or negatively charged particles, respectively. The charge density could be varied in two ways: (i) by varying the fraction of bromo-functionalized monomers; (ii) by increasing the degree of substitution of the bromo-functions. Derivation of the charged particles from the same precursor colloid made it easier to explain various interesting physical properties of the charged colloidal particles. Higher charge densities were achieved for the cationic colloids. If a threshold value for the charge density of 55 μC .cm -2 was surpassed, the particles showed a significant swelling in aqueous solution.

Calcium ions were used to induce a shrinking process with sodium polyacrylate coils in aqueous 0.01 M NaCl. By means of light scattering, four solutions with promising intermediates were selected for a detailed investigation by small-angle neutron scattering. All intermediates were half as large in size as the corresponding unperturbed dimensions but still had radii of gyration that were 45% larger than the hydrodynamic radius. The resulting SANS curves showed power laws typical for objects with a sharp boundary. They were compared with various model curves. From these models, a mixture of spheres and dumbbells resulted in theoretical curves that agreed best with experiments. The sphere size of single spheres and spheres in dumbbells was roughly 10 nm. Two spheres on a dumbbell had an averaged distance larger by almost an order of magnitude. The results are considered to be compatible with pearl necklace-like transition states of shrinking polyelectrolyte chains.

Combined static and dynamic light scattering was used to characterise a variety of sodium poly(acrylate) samples in dilute aqueous solutions with added NaCl. An increase of the NaCl content resulted in a decrease of the solvent quality. On the basis of these findings, two solvent conditions were selected for a detailed investigation of the coil size as a function of the molar mass Mw: aqueous 0.1 M NaCl represents a thermodynamically good solvent and aqueous 1.5 M NaCl is close to a Θ-solvent. If the NaCl content was kept within this range of 0.1 M≤[NaCl]≤1.5 M, a single Kuhn segment length of l k =4.2 nm and an excluded volume parameter of ω0=−0.04 for the corresponding neutral monomer [Muthukumar et al. Macromolecules 30; 1997: 8375] were able to adequately describe coil expansion as a function of the molar mass and the content of added salt. Towards lower salt contents, Muthukumar's approach which is based on the excluded volume parameter ω0, the Kuhn segment length lk and an effective charge density f became increasingly inadequate.