Coordination Cage-Based Emulsifiers: Templated Formation of Metal Oxide Microcapsules Monitored by In Situ LC-TEM.

Metallo-supramolecular self-assembly has yielded a plethora of discrete nanosystems, many of which show competence in capturing guests and catalyzing chemical reactions. However, the potential of low-molecular bottom-up self-assemblies in the development of structured inorganic materials has rarely been methodically explored so far. Herein, we present a new type of metallo-supramolecular surfactant with the ability to stabilize non-aqueous emulsions for a significant period. The molecular design of the surfactant is based on a heteroleptic coordination cage (CGA-3; CGA=Cage-based Gemini Amphiphile), assembled from two pairs of organic building blocks, grouped around two Pd(II) cations. Shape-complementarity between the differently functionalized components generates discrete amphiphiles with a tailor-made polarity profile, able to stabilize non-aqueous emulsions, such as hexadecane-in-DMSO. These emulsions were used as a medium for the synthesis of spherical metal oxide microcapsules (titanium oxide, zirconium oxide, and niobium oxide) from soluble, water-sensitive alkoxide precursors by allowing a controlled dosage of water to the liquid-liquid phase boundary. Synthesized materials were analyzed by a combination of electron microscopic techniques. In situ liquid cell transmission electron microscopy (LC-TEM) was utilized for the first time to visualize the dynamics of the emulsion-templated formation of hollow inorganic titanium oxide and zirconium oxide microspheres.

Surfactant-loaded capsules as Marangoni microswimmers at the air-water interface: Symmetry breaking and spontaneous propulsion by surfactant diffusion and advection.

We present a realization of a fast interfacial Marangoni microswimmer by a half-spherical alginate capsule at the air-water interface, which diffusively releases water-soluble spreading molecules (weak surfactants such as polyethylene glycol (PEG)), which act as "fuel" by modulating the air-water interfacial tension. For a number of different fuels, we can observe symmetry breaking and spontaneous propulsion although the alginate particle and emission are isotropic. The propulsion mechanism is similar to soap or camphor boats, which are, however, typically asymmetric in shape or emission to select a swimming direction. We develop a theory of Marangoni boat propulsion starting from low Reynolds numbers by analyzing the coupled problems of surfactant diffusion and advection and fluid flow, which includes surfactant-induced fluid Marangoni flow, and surfactant adsorption at the air-water interface; we also include a possible evaporation of surfactant. The swimming velocity is determined by the balance of drag and Marangoni forces. We show that spontaneous symmetry breaking resulting in propulsion is possible above a critical dimensionless surfactant emission rate (Peclet number). We derive the relation between Peclet number and swimming speed and generalize to higher Reynolds numbers utilizing the concept of the Nusselt number. The theory explains the observed swimming speeds for PEG-alginate capsules, and we unravel the differences to other Marangoni boat systems based on camphor, which are mainly caused by surfactant evaporation from the liquid-air interface. The capsule Marangoni microswimmers also exhibit surfactant-mediated repulsive interactions with walls, which can be qualitatively explained by surfactant accumulation at the wall.

Effects of Chirality on the Aggregation Properties of Amide-Bonded Pyridinium Gemini Surfactants.

In a series of experiments, we synthesized and characterized a new type of cationic gemini surfactant, the chiral and the achiral forms, which were compared regarding their surface-active properties. These surfactants show interesting aggregation processes, which are affected by the interplay of different structural characteristics. By substituting the counterions, we found a way to control the solubility of these compounds in order to investigate the behavior of solutions as well as insoluble monolayers. The comparison of the chiral with the meso compound instead of the racemic mixture is a major advantage for the analysis of the effects of chirality because racemates can be understood as a mixed surfactant system with one additional degree of Gibbs freedom. Furthermore, we investigated the viscoelastic behavior of concentrated aqueous surfactant solutions which formed elongated wormlike micelles. A strong effect of the stereochemistry on the aggregation properties of Langmuir layers as well as elongated micelles was found.

Rational Design of an Amphiphilic Coordination Cage-Based Emulsifier.

Self-assembled, porous coordination cages with a functional interior find application in controlled guest inclusion/release, drug delivery, separation processes, and catalysis. However, only few studies exist that describe their utilization for the development of self-assembled materials based on their 3-dimensional shape and external functionalization. Here, dodecyl chain-containing, acridone-based ligands (LA) and shape-complementary phenanthrene-derived ligands (LB) are shown to self-assemble to heteroleptic coordination cages cis-[Pd2(LA)2(LB)2]4+ acting as a gemini amphiphile (CGA-1; Cage-based Gemini Amphiphile-1). Owing to their anisotropic decoration with short polar and long nonpolar side chains, the cationic cages were found to assemble into vesicles with diameters larger than 100 nm in suitable polar solvents, visualized by cryo-TEM and Liquid-Cell Transmission Electron Microscopy (LC-TEM). LC-TEM reveals that these vesicles aggregate into chains and necklaces via long-range interactions. In addition, the cages show a rarely described ability to stabilize oil-in-oil emulsions.

Strong Deformation of Ferrofluid-Filled Elastic Alginate Capsules in Inhomogenous Magnetic Fields.

We present a new system based on alginate gels for the encapsulation of a ferrofluid drop, which allows us to create millimeter-sized elastic capsules that are highly deformable by inhomogeneous magnetic fields. We use a combination of experimental and theoretical work in order to characterize and quantify the deformation behavior of these ferrofluid-filled capsules. We introduce a novel method for the direct encapsulation of unpolar liquids by sodium alginate. By adding 1-hexanol to the unpolar liquid, we can dissolve sufficient amounts of CaCl2 in the resulting mixture for ionotropic gelation of sodium alginate. The addition of polar alcohol molecules allows us to encapsulate a ferrofluid as a single phase rather than an emulsion without impairing ferrofluid stability. This encapsulation method increases the amount of encapsulated magnetic nanoparticles resulting in high deformations of approximately 30% (in height-to-width ratio) in inhomogeneous magnetic field with magnetic field variations of 50 mT over the size of the capsule. This offers possible applications of capsules as actuators, switches, or valves in confined spaces like microfluidic devices. We determine both elastic moduli of the capsule shell, Young's modulus and Poisson's ratio, by employing two independent mechanical methods, spinning capsule measurements and capsule compression between parallel plates. We then show that the observed magnetic deformation can be fully understood from magnetic forces exerted by the ferrofluid on the capsule shell if the magnetic field distribution and magnetization properties of the ferrofluid are known. We perform a detailed analysis of the magnetic deformation by employing a theoretical model based on nonlinear elasticity theory. Using an iterative solution scheme that couples a finite element/boundary element method for the magnetic field calculation to the solution of the elastic shape equations, we achieve quantitative agreement between theory and experiment for deformed capsule shapes using the Young modulus from mechanical characterization and the surface Poisson ratio as a fit parameter. This detailed analysis confirms the results from mechanical characterization that the surface Poisson ratio of the alginate shell is close to unity, that is, deformations of the alginate shell are almost area conserving.

Adsorption Behavior of Lysozyme at Titanium Oxide-Water Interfaces.

We present an in situ X-ray reflectivity study of the adsorption behavior of the protein lysozyme on titanium oxide layers under variation of different thermodynamic parameters, such as temperature, hydrostatic pressure, and pH value. Moreover, by varying the layer thickness of the titanium oxide layer on a silicon wafer, changes in the adsorption behavior of lysozyme were studied. In total, we determined less adsorption on titanium oxide compared with silicon dioxide, while increasing the titanium oxide layer thickness causes stronger adsorption. Furthermore, the variation of temperature from 20 to 80 °C yields an increase in the amount of adsorbed lysozyme at the interface. Additional measurements with variation of the pH value of the system in a region between pH 2 and 12 show that the surface charge of both protein and titanium oxide has a crucial role in the adsorption process. Further pressure-dependent experiments between 50 and 5000 bar show a reduction of the amount of adsorbed lysozyme with increasing pressure.

Exploring the synthesis of a new group of chiral ammonium salts with specific configurations at the stereogenic nitrogen centers.

A group of new chiral dications with a fixed, specific configuration at the stereogenic nitrogen center was created. Stereoselective synthesis and recrystallization give the diastereomerically and enantiomerically pure dications, including a chiral amphiphile with surface-active properties.

About the role of surfactants on the magnetic control over liquid interfaces.

The behavior of magnetically responsive aqueous Fe(III) surfactant solutions at liquid interfaces is analyzed. Such surfactants attracted much attention, because of the ability to manipulate interfaces by magnetic fields without any use of magnetic nanoparticles. A detailed analysis of the surface properties proves that the mixing of paramagnetic electrolyte solution with anionic, cationic and nonionic surfactants yields the similar magnetic response and no effect of the surfactant charge can be observed. We conclude that the observed magnetic shiftability of interfaces is caused by a combination of the paramagnetic behavior of the bulk liquid and a reduction of the surface tension. Thus, this work gives an alternative interpretation of the properties of "magnetic surfactants" compared to the ones claimed in the literature.

Is the antioxidative effectiveness of a bilberry extract influenced by encapsulation?

BACKGROUND: Bilberries (Vaccinium myrtillus L.) have been suggested to have preventive properties against diseases associated with oxidative stress such as colon cancer or inflammatory bowel diseases. Therefore the gastrointestinal tract is regarded as a potential target for prevention. In this study the antioxidative properties of a commercially available anthocyanin-rich bilberry extract (BE) were investigated in comparison with four different BE-loaded microcapsule systems. As markers to describe the antioxidant status in this cellular system, intracellular reactive oxygen species (ROS) levels, oxidative DNA damage and total glutathione (tGSH) levels were monitored. RESULTS: Incubations with the BE-loaded capsule systems showed an increase in cellular glutathione levels and reduction of ROS levels at high BE concentrations (100-500 µg mL(-1) ) and a positive effect on the formation of DNA strand breaks (5-10 µg mL(-1) BE). The biological properties of BE-loaded pectin amide core-shell capsules, whey protein matrix capsules and coated apple pectin matrix capsules were comparable to those of the non-encapsulated BE. CONCLUSION: Overall, the BE and the encapsulated BE types tested have antioxidative activity under the studied assay conditions in terms of the prevention of oxidative DNA damage, the reduction of intracellular ROS and the enhancement of cellular tGSH.

Elastometry of deflated capsules: elastic moduli from shape and wrinkle analysis.

Elastic capsules, prepared from droplets or bubbles attached to a capillary (as in a pendant drop tensiometer), can be deflated by suction through the capillary. We study this deflation and show that a combined analysis of the shape and wrinkling characteristics enables us to determine the elastic properties in situ. Shape contours are analyzed and fitted using shape equations derived from nonlinear membrane-shell theory to give the elastic modulus, Poisson ratio and stress distribution of the membrane. We include wrinkles, which generically form upon deflation, within the shape analysis. Measuring the wavelength of wrinkles and using the calculated stress distribution gives the bending stiffness of the membrane. We compare this method with previous approaches using the Laplace-Young equation and illustrate the method on two very different capsule materials: polymerized octadecyltrichlorosilane (OTS) capsules and hydrophobin (HFBII) coated bubbles. Our results are in agreement with the available rheological data. For hydrophobin coated bubbles, the method reveals an interesting nonlinear behavior consistent with the hydrophobin molecules having a rigid core surrounded by a softer shell.

Discovery of the primary aphid (Hemiptera: Aphidomorpha) and scale insect (Hemiptera: Coccomorpha) type specimens from the collection of Theodor Hartig (18051880).

Theodor Hartigs aphid and scale insect type specimens have been presumed lost or destroyed for the last 140 years. Here we document their discovery at the Bavarian State Collection of Zoology (Zoologische Staatssammlung Mnchen, ZSM), in Munich, Germany. These specimens include primary types for 24 aphid, three adelgid, and two armored scale insect species named by Hartig between 1834 and 1851, as well as other specimens of unknown importance.

Sealing liquid-filled pectinate capsules with a shellac coating.

Liquid-filled pectinate capsules have a large potential for the controlled and site-specific delivery of liquid drugs. Earlier studies have shown that pure pectinate capsules can store drugs only for a few minutes. Here, we show that the retention time can be extended to several hours by coating the capsules with the natural resin shellac. A bilberry extract containing anthocyanins with promising therapeutic properties was used as model drug to characterize the permeability of the capsules by in vitro drug release measurements. Characterizing the structure of the double-layered capsule membranes by NMR microscopy, we optimized the capsule production by adjusting the pH-value in the coating process and the gelation time of the pectinate hydrogel layer. A comparison of the layer thicknesses with drug release measurements reveals that capsules with the thinnest shellac layers provide the best entrapment. Additional squeezing experiments show that the shellac layer makes the capsules also mechanically more stable.

Mechanical properties of liquid-filled shellac composite capsules.

This paper describes the mechanical properties of thin-walled, liquid-filled composite capsules consisting of calcium pectinate and shellac. In a series of experiments we measured the deformation of these particles in a spinning drop apparatus. For different pH-values we studied the elastic properties of these particles and compared the obtained results with the mechanical response measured by squeezing capsule experiments. In analogy to these experiments, we also investigated liquid-filled unloaded calcium pectinate capsules without the addition of shellac. The deformation properties of these experiments and the surface Young moduli were in good agreement. Furthermore we investigated the liquid-filled calcium pectinate and the composite capsules by NMR microscopy. These experiments allowed investigations of the membrane thickness and the kinetics of membrane growing. Additional characterizations by stress controlled small amplitude surface shear experiments of similar composed gel layers provided coherent results for the surface Young modulus.

Dissolution of iron oxide nanoparticles inside polymer nanocapsules.

The structure of poly(organosiloxane) nanocapsules partially filled with iron oxide cores of different sizes was revealed by small angle X-ray scattering and X-ray diffraction. The nanocapsules are synthesized by the formation of a poly(organosiloxane) shell around iron oxide nanoparticles and the simultaneous partial dissolution of these cores. Due to the high scattering contrast of the iron oxide cores compared to the polymer shell, the particle size distribution of the cores inside the capsules can be measured by small angle X-ray scattering. Additional information can be revealed by X-ray diffraction, which gives insights into the formation of the polymer network and the structure of the iron oxide cores. The study shows how the crystallinity and size of the nanoparticles as well as the shape and width of the size distribution can be altered by the synthesis parameters.

A new family of nonionic dendritic amphiphiles displaying unexpected packing parameters in micellar assemblies.

In this paper we report on the synthesis of a new family of nonionic dendritic amphiphiles that self-assemble into defined supramolecular aggregates. Our approach is based on a modular architecture consisting of different generations of hydrophilic polyglycerol dendrons [G1-G3] connected to hydrophobic C(11) or C(16) alkyl chains via mono- or biaromatic spacers, respectively. All amphiphiles complex hydrophobic compounds as demonstrated by solubilization of Nile Red or pyrene. The structure of the supramolecular assemblies as well as the aggregation numbers are strongly influenced by the type of the dendritic headgroup. While the [G1] amphiphiles form different structures such as ringlike and fiberlike micelles, the [G2] and [G3] derivatives aggregate toward spherical micelles of low polydispersity clearly proven by transmission electron microscopy (TEM) measurements. In the case of the biaromatic [G2] derivative, the structural persistence of the micelles allowed a three-dimensional structure determination from the TEM data and confirmed the aggregation number obtained by static light scattering (SLS) measurements. On the basis of these data, molecular packing geometries indicate a drastic mass deficit of alkyl chains in the hydrophobic core volume of spherical micelles. It is noteworthy that these highly defined micelles contain as little as 15 molecules and possess up to 74% empty space. This behavior is unexpected as it is very different from classical detergent micelles such as sodium dodecyl sulfate (SDS), where the hydrophobic core volume is completely filled by alkyl chains.

Sticking polydisperse hydrophobic magnetite nanoparticles to lipid membranes.

The formation of a layer of hydrophobic magnetite (Fe(3)O(4)) nanoparticles stabilized by lauric acid is analyzed by in situ X-ray reflectivity measurements. The data analysis shows that the nanoparticles partially disperse their hydrophobic coating. Consequently, a Langmuir layer was formed by lauric acid molecules that can be compressed into an untilted condensed phase. A majority of the nanoparticles are attached to the Langmuir film integrating lauric acid residue on their surface into the Langmuir film. Hence, the particles at the liquid-gas interface can be identified as so-called Janus beads, which are amphiphilic solids having two sides with different functionality.

Deformation of liquid-filled calcium alginate capsules in a spinning drop apparatus.

This paper describes the mechanical properties of thin-walled, liquid-filled calcium alginate capsules by measuring the deformation of these particles in a spinning drop apparatus. By variation of the guluronic acid content of the alginate, the polymerization time and the calcium and alginate concentration we systematically studied the elastic properties of these capsules. In a series of experiments we observed for the first time new types of irreversibly deformed capsules, which can be described by plastic deformation. For comparison purposes, we also investigated liquid-filled calcium alginate particles in squeezing capsule experiments. The qualitative and quantitative results of both experiments in terms of the deformation properties and the surface Young moduli were in good agreement. Furthermore we also investigated liquid-filled calcium alginate particles by NMR microscopy to characterize the capsules in view of their membrane thickness. These results, in combination with the spinning capsule experiments allowed us to measure the kinetics of surface gelation and the mechanism of membrane growing.

Cytotoxicity of insulin within its self-assembly and amyloidogenic pathways.

Solvational perturbations were employed to selectively tune the aggregational preferences of insulin at 60 degrees C in vitro in purely aqueous acidic solution and in the presence of the model co-solvent ethanol (EtOH) (at 40%(w/w)). Dynamic light scattering (DLS), thioflavin T (ThT)-fluorescence, Fourier transform infrared (FTIR) and atomic force microscopy (AFM) techniques were employed to characterize these pathways biophysically with respect to the pre-aggregational assembly of the protein, the aggregation kinetics, and finally the aggregate secondary structure and morphology. Using cell viability assays, the results were subsequently correlated with the cytotoxicity of the insulin species that form in the two distinct aggregation pathways. In the cosolvent-free solution, predominantly dimeric insulin self-assembles via the well-known amyloidogenic pathway, yielding exclusively fibrillar aggregates, whereas in the solution containing EtOH, the aggregation of predominantly monomeric insulin proceeds via a pathway that leads to exclusively non-fibrillar, amorphous aggregates. Initially present native insulin assemblies as well as partially unfolded monomeric species and low molecular mass oligomeric aggregates could be ruled out as direct and major cytotoxic species. Apart from the slower overall aggregation kinetics under amorphous aggregate promoting conditions, which is due to the chaotropic nature of high EtOH concentrations, however, both pathways were unexpectedly found to evoke insulin aggregates that were cytotoxic to cultured rat insulinoma cells. The observed kinetics of the decrease of cell viabilities correlated well with the results of the DLS, ThT, FTIR and AFM studies, revealing that the formation of cytotoxic species correlated well with the formation of large-sized, beta-sheet-rich assemblies (>500 nm) of both fibrillar and amorphous nature. These results suggest that large-sized, beta-sheet-rich insulin assemblies of both fibrillar and amorphous nature are toxic to pancreatic beta-cells. In the light of the ongoing discussion about putative cytotoxic effects of prefibrillar and fibrillar amyloid aggregates, our results support the hypothesis that, in the case of insulin, factors other than the specific secondary or quarternary structural features of the various different aggregates may define their cytotoxic properties. Two such factors might be the aggregate size and the aggregate propensity to expose hydrophobic surfaces to a polar environment.

Hydrophobic N-diazeniumdiolates and the aqueous interface of sodium dodecyl sulfate (SDS) micelles.

Zwitterionic diazeniumdiolates of the form RN[N(O)NO(-)](CH(2))(2)NH(2) (+)R, where R=CH(3) (1), (CH(2))(3)CH(3) (2), (CH(2))(5)CH(3) (3), and (CH(2))(7)CH(3) (4) were synthesized by reaction of the corresponding diamines with nitric oxide. Spectrophotometrically determined pK(a)(O) values, attributed to protonation at the terminal oxygen of the diazeniumdiolate group, show shifts to higher values in dependence of the chain lengths of R. The pH dependence of the decomposition of NO donors 1-3 was studied in buffered solution between pH 5 and 8 at 22 degrees C, from which pK(a)(N) values for protonation at the amino nitrogen, leading to release of NO, were estimated. It is shown that the decomposition of these diazeniumdiolates is markedly catalyzed by anionic SDS micelles. First-order rate constants for the decay of 1-4 were determined in phosphate buffer pH 7.4 at 22 degrees C as a function of SDS concentration. Micellar binding constants, K(SM), for the association of diazeniumdiolates 1-3 with the SDS micelles were also determined, again showing a significant increase with increasing length of the alkyl side chains. The decomposition of 1-3 in micellar solution is quantitatively described by using the pseudo-phase ion-exchange (PIE) model, in which the degree of micellar catalysis is taken into account through the ratio of the second-order rate constants (k(2m)/k(2w)) for decay in the micelles and in the bulk aqueous phase. The decay kinetics of 1-3 were further studied in the presence of cosolvents and nonionic surfactants, but no effect on the rate of NO release was observed. The kinetic data are discussed in terms of association to the micelle-aqueous phase interface of the negatively charged micelles. The apparent interfacial pH value of SDS micelles was evaluated from comparison of the pH dependence of the first-order decay rate constants of 2 and 3 in neat buffer and the rate data obtained for the surfactant-mediated decay. For a bulk phase of pH 7.4, an interfacial pH of 5.7-5.8 was determined, consistent with the distribution of H(+) in the vicinity of the negatively charged micelles. The data demonstrate the utility of 2 and 3 as probes for the determination of the apparent pH value in the Stern region of anionic micelles.

Production, deformation and mechanical investigation of magnetic alginate capsules.

In this article we investigated the deformation of alginate capsules in magnetic fields. The sensitivity to magnetic forces was realised by encapsulating an oil in water emulsion, where the oil droplets contained dispersed magnetic nanoparticles. We solved calcium ions in the aqueous emulsion phase, which act as crosslinking compounds for forming thin layers of alginate membranes. This encapsulating technique allows the production of flexible capsules with an emulsion as the capsule core. It is important to mention that the magnetic nanoparticles were stable and dispersed throughout the complete process, which is an important difference to most magnetic alginate-based materials. In a series of experiments, we used spinning drop techniques, capsule squeezing experiments and interfacial shear rheology in order to determine the surface Young moduli, the surface Poisson ratios and the surface shear moduli of the magnetically sensitive alginate capsules. In additional experiments, we analysed the capsule deformation in magnetic fields. In spinning drop and capsule squeezing experiments, water droplets were pressed out of the capsules at elevated values of the mechanical load. This phenomenon might be used for the mechanically triggered release of water-soluble ingredients. After drying the emulsion-filled capsules, we produced capsules, which only contained a homogeneous oil phase with stable suspended magnetic nanoparticles (organic ferrofluid). In the dried state, the thin alginate membranes of these particles were rather rigid. These dehydrated capsules could be stored at ambient conditions for several months without changing their properties. After exposure to water, the alginate membranes rehydrated and became flexible and deformable again. During this swelling process, water diffused back in the capsule. This long-term stability and rehydration offers a great spectrum of different applications as sensors, soft actuators, artificial muscles or drug delivery systems.