Lipid Monolayer on Cell Surface Protein Templates Functional Extracellular Lipid Assembly

When the ancestors of men moved from aquatic habitats to the drylands, their evolutionary strategy to restrict water loss is to seal the skin surface with lipids. It is unknown how these rigid ceramide-dominated lipids with densely packed chains squeeze through narrow extracellular spaces and how they assemble into their complex multilamellar architecture. Here it is shown that the human corneocyte lipid envelope, a monolayer of ultralong covalently bound lipids on the cell surface protein, templates the functional barrier assembly by partly fluidizing and rearranging the free extracellular lipids in its vicinity during the sculpting of a functional skin lipid barrier. The lipid envelope also maintains the fluidity of the extracellular lipids during mechanical stress. This local lipid fluidization does not compromise the permeability barrier. The results provide new testable hypotheses about epidermal homeostasis and the pathophysiology underlying diseases with impaired lipid binding to corneocytes, such as congenital ichthyosis. In a broader sense, this lipoprotein-mediated fluidization of rigid (sphingo)lipid patches may also be relevant to lipid rafts and cellular signaling events and inspire new functional materials.

NMR-identification of the interaction between BRCA1 and the intrinsically disordered monomer of the Myc-associated factor X

The breast cancer susceptibility 1 (BRCA1) protein plays a pivotal role in modulating the transcriptional activity of the vital intrinsically disordered transcription factor MYC. In this regard, mutations of BRCA1 and interruption of its regulatory activity are related to hereditary breast and ovarian cancer (HBOC). Interestingly, so far, MYC's main dimerization partner MAX (MYC-associated factor X) has not been found to bind BRCA1 despite a high sequence similarity between both oncoproteins. Herein, we show that a potential reason for this discrepancy is the heterogeneous conformational space of MAX, which encloses a well-documented folded coiled-coil homodimer as well as a less common intrinsically disordered monomer state-contrary to MYC, which exists mostly as intrinsically disordered protein in the absence of any binding partner. We show that when the intrinsically disordered state of MAX is artificially overpopulated, the binding of MAX to BRCA1 can readily be observed. We characterize this interaction by nuclear magnetic resonance (NMR) spectroscopy chemical shift and relaxation measurements, complemented with ITC and SAXS data. Our results suggest that BRCA1 directly binds the MAX monomer to form a disordered complex. Though probed herein under biomimetic in-vitro conditions, this finding can potentially stimulate new perspectives on the regulatory network around BRCA1 and its involvement in MYC:MAX regulation.

Strain and Strain Recovery of Human Hair from the Nano- to the Macroscale

In this study, in operandi SAXS experiments were conducted on samples of human hair with a varying degree of strain (2% within the elastic region and 10% beyond). Four different features in the SAXS patterns were evaluated: The intermediate filament distance perpendicular to and the distance from the meridional arc in the load direction, as well as the distances of the lipid bilayer peak in and perpendicular to the load direction. From the literature, one concludes that polar lipids in the cuticle are the origin of the lipid peak in the SAXS pattern, and this study shows that the observed strain in the lipids is much lower than in the intermediate filaments. We support these findings with SEM micrographs, which show that the scales in the cuticle deform much less than the cortex. The observed deformation of the intermediate filaments is very high, about 70% of the macrostrain, and the ratio of the transverse strain to the longitudinal strain at the nanoscale gives a Poisson ratio of νnano = 0.44, which is typical for soft matter. This work also finds that by varying the time period between two strain cycles, the typical strain recovery time is about 1000 min, i.e., one day. After this period, the structure is nearly identical to the initial structure, which suggests an interpretation that this is the typical time for the self-healing of hair after mechanical treatment.

Green hydrothermal synthesis yields perylenebisimide-SiO2 hybrid materials with solution-like fluorescence and photoredox activity

In organic-inorganic hybrid materials' (HMs) synthesis, it is intrinsically challenging to, at the same time, achieve (i) the concomitant synthesis of the components, (ii) nanoscopic interpenetration of the components, and (iii) covalent linking of the components. We here report the one-pot hydrothermal synthesis (HTS) of inorganic-organic HMs consisting of perylene bisimide (PBI) dyes and silica, using nothing but water as the medium and directly from the corresponding bisanhydrides, n-alkyl amines, and alkoxysilane precursors. First, in the absence of a functionalized alkoxysilane for linking, a mixture of the products, PBI and SiO₂, is obtained. This evinces that the two products can be synthesized in parallel in the same vessel. Except for minor micromorphological changes, the concomitant synthesis does not affect each component's physicochemical properties. The PBI/SiO₂ mixtures do not show synergistic properties. Second, through adding the linker aminopropyltriethoxysilane (APTS), covalently-linked class II hybrids are obtained. These PBI@SiO₂ class II hybrids show synergistic materials properties: increased thermal stability is obtained in combination with nanoscopic homogeneity. The PBI moieties are dissolved in the solid SiO₂ matrix, while being covalently linked to the matrix. This leads to solution-like fluorescence with vibronic fine-structure of the dyes. Moreover, through tuning the SiO₂ amount, the band gaps of the class II hybrid materials can be systematically shifted. We exploit these optoelectronic properties by using the PBI@SiO₂ hybrids as heterogeneous and reusable photoredox catalysts for the reduction of aryl halides. Finally, we present a detailed small-angle X-ray scattering and powder X-ray diffraction study of PBI@SiO₂ synthesized at various reaction times, revealing the existence of an ordered PBI-oligomeric silesquioxane-type intermediate, which subsequently further condenses to the final nanoscopically homogeneous PBI@SiO₂ material. These ordered intermediates point at HTS' propensity to favor crystallinity (to date known for organic and inorganic compounds, respectively) to also apply to hybrid structures, and shed additional light on the long-standing question of structure formation in the early stages of sol-gel processes: they corroborate Brown's hypothesis (1965) that trifunctional hydroxysilanes form surprisingly well controlled oligomers in the early stages of polycondensation.

Grasping the Lithium hype: Insights into modern dental Lithium Silicate glass-ceramics

OBJECTIVES

Lithium-based glass-ceramics are currently dominating the landscape of dental restorative ceramic materials, with new products taking the market by storm in the last years. Though, the difference among all these new and old products is not readily accessible for the practitioner, who faces the dilemma of reaching a blind choice or trusting manufacturers' marketing brochures. To add confusion, new compositions tend to wear material terminologies inherited from vanguard dental lithium disilicates, disregarding accuracy. Here we aim to characterize such materials for their microstructure, crystalline fraction, glass chemistry and mechanical properties.

METHODS

Eleven commercial dental lithium-based glass ceramics were evaluated: IPS e.max® CAD, IPS e.max® Press, Celtra® Duo, Suprinity® PC, Initial™ LiSi Press, Initial™ LiSi Block, Amber® Mill, Amber® Press, N!CE®, Obsidian® and CEREC Tessera™. The chemical composition of their base glasses was measured by X-Ray Fluorescence Spectroscopy (XRF) and Inductive Coupled Plasma Optical Emission Spectroscopy (ICP-OES), as well as the composition of their residual glass by subtracting the oxides bound in the crystallized fraction, characterized by X-Ray Diffraction (XRD) and Rietveld refinement, and quantified accurately using the G-factor method (QXRD). The crystallization behavior is revealed by differential scanning calorimetry (DSC) curves. Elastic constants are provided from Resonant Ultrasound Spectroscopy (RUS) and the fracture toughness measured by the Ball-on-Three-Balls method (B3B- K Ic). The microstructure is revealed by field-emission scanning electron microscopy (FE-SEM).

RESULTS

The base glasses showed a wide range of SiO₂ /Li₂O ratios, from 1.5 to 3.0, with the degree of depolymerization dropping from ½ to 2/3 of the initial connectivity. Materials contained Li₂SiO₃+Li₃PO₄, Li₂SiO₃+Li₃PO₄+Li₂Si₂O₅, Li₂Si₂O₅+Li₃PO₄+ Cristobalite and/or Quartz and Li₂Si₂O₅+Li₃ PO₄+LiAlSi₂O₆, in crystallinity degrees from 45 to 80 vol%. Crystalline phases could be traced to their crystallization peaks on the DSC curves. Pressable materials and IPS e.max® CAD were the only material showing micrometric phases, with N!CE® and Initial™ LiSi Block showing solely nanometric crystals, with the rest presenting a mixture of submicrometric and nanometric particles. Fracture toughness from 1.45 to 2.30 MPa√m were measured, with the linear correlation to crystalline fraction breaking down for submicrometric and nanometric crystal phases.

SIGNIFICANCE

Dental lithium-based silicate glass-ceramics cannot be all put in the same bag, as differences exist in chemical composition, microstructure, crystallinity and mechanical properties. Pressable materials still perform better mechanically than CAM/CAM blocks, which loose resistance to fracture when crystal phases enter the submicrometric and nanometric range.

Carbon Nano-onions: Potassium Intercalation and Reductive Covalent Functionalization

Herein we report the synthesis of covalently functionalized carbon nano-onions (CNOs) via a reductive approach using unprecedented alkali-metal CNO intercalation compounds. For the first time, an in situ Raman study of the controlled intercalation process with potassium has been carried out revealing a Fano resonance in highly doped CNOs. The intercalation was further confirmed by electron energy loss spectroscopy and X-ray diffraction. Moreover, the experimental results have been rationalized with DFT calculations. Covalently functionalized CNO derivatives were synthesized by using phenyl iodide and n-hexyl iodide as electrophiles in model nucleophilic substitution reactions. The functionalized CNOs were exhaustively characterized by statistical Raman spectroscopy, thermogravimetric analysis coupled with gas chromatography and mass spectrometry, dynamic light scattering, UV-vis, and ATR-FTIR spectroscopies. This work provides important insights into the understanding of the basic principles of reductive CNOs functionalization and will pave the way for the use of CNOs in a wide range of potential applications, such as energy storage, photovoltaics, or molecular electronics.

Toughening by revitrification of Li2SiO3 crystals in Obsidian® dental glass-ceramic

As a predominantly lithium-metasilicate-containing glass-ceramic, Obsidian® (Glidewell Laboratories, USA) has a peculiar composition and microstructure among other dental lithium silicates, warranting an evaluation of the crystallization process to establish relationships between microstructural evolution and mechanical properties. Blocks of the pre-crystallized material were processed into slices measuring 12 × 12 × 1.5 mm³ and subjected to the mandatory crystallization firing by interruption the heating ramp at temperatures between 700 °C and 820 °C (dwell time between 0 min and 10 min). The crystallization peaks of the base and the pre-crystallized glass were obtained by differential scanning calorimetry (DSC). The coefficient of thermal expansion and the glass transition temperature were derived from differential thermal analysis (DTA). X-ray diffraction (XRD) was performed to quantify and characterize the crystal phase fraction, whose microstructural changes were visualised using FE-SEM. The ball-on-three-balls surface crack in flexure method was used to track the evolution of fracture toughness. The microstructural evolution during crystallization firing was characterized by two regimes of growth: (i) the progressive revitrification (dissolution) of the 5 μm-sized Li₂SiO₃ polycrystals manifested at the boundaries of nanometric single coherent scattering domains (CSDs); (ii) the non-isothermal period is marked by an Ostwald ripening process characterized by the growth of the single crystalline structures into 0.5 μm polycrystals. The decrease in the crystal fraction of Li₂SiO₃ crystals from 41 vol.% to 37 vol.% is accompanied by the formation of a small amount of Li₃PO₄ (6 vol.%), maintaining the total crystal phase fraction mostly constant. The K_Ic accompanied the reverse trend of crystallinity, departing from 1.63 ± 0.02 MPa√m at the pre-crystallized stage to 1.84 ± 0.06 MPa√m after 10 min at 820 °C in a linear trend. Toughening appeared counter-intuitive in view of the decreasing crystal fraction and size, to rather relate to the relaxation of the residual stresses in the interstitial glass due to the spheroidization of the initially anisotropic, elongated Li₂SiO₃ crystals into round, nearly equiaxed particles, as let suggest from the disappearance of the extensive microcracking.

Ageing bone fractures: The case of a ductile to brittle transition that shifts with age

Human bone becomes increasingly brittle with ageing. Bones also fracture differently under slow and fast loadings, being ductile and brittle, respectively. The effects of a combination of these two factors have never been examined before. Here we show that cortical bone is most fracture-resistant at the physiologically prevalent intermediate strain rates of 10^-3 s^-1 to 10^-2 s^-1 such as they occur in walking or running, slightly weaker at slower quasistatic and much weaker at fast impact loading rates. In young cortical bone (15 years of age) the ductile-to-brittle transition (DBT) occurs at strain rates of 10^-2 s^-1, in old cortical bone (85 yrs) at speeds lower by a factor of 10 to 40. Other research has shown that the energy required to break bone (per unit of fracture surface) drops as much as 60% between these two ages. Therefore, DBT seems to compound the well-known phenomenon of 'brittle old bones'. Old bones can only cope with slow movement, young ones with both slow and fast movement. These observed material characteristics of (i) a shift of the DBT and (ii) a reduced energy absorption capacity appear to contribute at least as much to the loss of bone quality as the various quantity based (lowered bone density and mineral content) explanations of the past. They also provide a new powerful paradigm, which allows us to demonstrate mechanically, and uniquely, how human bone becomes increasingly brittle with age.

Exchange coupling in a frustrated trimetric molecular magnet reversed by a 1D nano-confinement

Single-molecule magnets exhibit magnetic ordering due to exchange coupling between localized spin components that makes them primary candidates as nanometric spintronic elements. Here we manipulate exchange interactions within a single-molecule magnet by nanometric structural confinement, exemplified with single-wall carbon nanotubes that encapsulate trimetric nickel(ii) acetylacetonate hosting three frustrated spins. It is revealed from bulk and Ni 3d orbital magnetic susceptibility measurements that the carbon tubular confinement allows a unique one-dimensional arrangement of the trimer in which the nearest-neighbour exchange is reversed from ferromagnetic to antiferromagnetic, resulting in quenched frustration as well as the Pauli paramagnetism is enhanced. The exchange reversal and enhanced spin delocalisation demonstrate the means of mechanically and electrically manipulating molecular magnetism at the nanoscale for nano-mechatronics and spintronics.

Lattice Opening upon Bulk Reductive Covalent Functionalization of Black Phosphorus

The chemical bulk reductive covalent functionalization of thin-layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral routes.

Ovalbumin Epitope SIINFEKL Self-Assembles into a Supramolecular Hydrogel

Here we show that the well-known ovalbumin epitope SIINFEKL that is routinely used to stimulate ovalbumin-specific T cells and to test new vaccine adjuvants can form a stable hydrogel. We investigate properties of this hydrogel by a range of spectroscopic and imaging techniques demonstrating that the hydrogel is stabilized by self-assembly of the peptide into nanofibres via stacking of β-sheets. As peptide hydrogels are known to stimulate an immune response as adjuvants, the immunoactive properties of the SIINFEKL peptide may also originate from its propensity to self-assemble into a hydrogel. This finding requires a re-evaluation of this epitope in adjuvant testing.

Surface-Active Ionic Liquids in Catalytic Water Splitting

We report the application of surface-active ionic liquids as ligands and optional reaction media in iridium-catalyzed water oxidations. Three novel catalysts with N,N-dialkylimidazolidin-2-ylidene ligands based on amphiphilic imidazolium ionic liquids were synthesized and characterized. Excellent turn-over frequencies of up to 0.92s−1 were obtained in catalytic water splitting, and activity was maintained for five consecutive catalytic cycles, with an overall turn-over number of 8967. The addition of external surface-active ionic liquid showed unexpected behaviour, because strongly enhanced initial reaction rates were observed.

Cycle Stability and Hydration Behavior of Magnesium Oxide and Its Dependence on the Precursor-Related Particle Morphology

Thermochemical energy storage is considered as an auspicious method for the recycling of medium-temperature waste heat. The reaction couple Mg(OH)₂⁻MgO is intensely investigated for this purpose, suffering so far from limited cycle stability. To overcome this issue, Mg(OH)₂, MgCO₃, and MgC₂O₄·2H₂O were compared as precursor materials for MgO production. Depending on the precursor, the particle morphology of the resulting MgO changes, resulting in different hydration behavior and cycle stability. Agglomeration of the material during cyclization was identified as main reason for the decreased reactivity. Immersion of the spent material in liquid H₂O decomposes the agglomerates restoring the initial reactivity of the material, thus serving as a regeneration step.

Exploring the Formation of Black Phosphorus Intercalation Compounds with Alkali Metals

Black phosphorus intercalation compounds (BPICs) with alkali metals (namely: K and Na) have been synthesized in bulk by solid‐state as well as vapor‐phase reactions. By means of a combination of in situ X‐ray diffraction, Raman spectroscopy, and DFT calculations the structural behavior of the BPICs at different intercalation stages has been demonstrated for the first time. Our results provide a glimpse into the very first steps of a new family of intercalation compounds, with a distinct behavior as compared to its graphite analogues (GICs), showing a remarkable structural complexity and a dynamic behavior.

Unifying Principles of the Reductive Covalent Graphene Functionalization

Covalently functionalized graphene derivatives were synthesized via benchmark reductive routes using graphite intercalation compounds (GICs), in particular KC₈. We have compared the graphene arylation and alkylation of the GIC using 4-tert-butylphenyldiazonium and bis(4-(tert-butyl)phenyl)iodonium salts, as well as phenyl iodide, n-hexyl iodide, and n-dodecyl iodide, as electrophiles in model reactions. We have put a particular focus on the evaluation of the degree of addition and the bulk functionalization homogeneity (H_bulk). For this purpose, we have employed statistical Raman spectroscopy (SRS), and a forefront characterization tool using thermogravimetric analysis coupled with FT-IR, gas chromatography, and mass spectrometry (TGA/FT-IR/GC/MS). The present study unambiguously shows that the graphene functionalization using alkyl iodides leads to the best results, in terms of both the degree of addition and the H_bulk. Moreover, we have identified the reversible character of the covalent addition chemistry, even at temperatures below 200 °C. The thermally induced addend cleavage proceeds homolytically, which allows for the detection of dimeric cleavage products by TGA/FT-IR/GC/MS. This dimerization points to a certain degree of regioselectivity, leading to a low sheet homogeneity (H_sheet). Finally, we developed this concept by performing the reductive alkylation reaction in monolayer CVD graphene films. This work provides important insights into the understanding of basic principles of reductive graphene functionalization and will serve as a guide in the design of new graphene functionalization concepts.

Solvent-driven electron trapping and mass transport in reduced graphites to access perfect graphene

Herein, we report on a significant discovery, namely, the quantitative discharging of reduced graphite forms, such as graphite intercalation compounds, graphenide dispersions and graphenides deposited on surfaces with the simple solvent benzonitrile. Because of its comparatively low reduction potential, benzonitrile is reduced during this process to the radical anion, which exhibits a red colour and serves as a reporter molecule for the quantitative determination of negative charges on the carbon sheets. Moreover, this discovery reveals a very fundamental physical–chemical phenomenon, namely a quantitative solvent reduction induced and electrostatically driven mass transport of K⁺ ions from the graphite intercalation compounds into the liquid. The simple treatment of dispersed graphenides suspended on silica substrates with benzonitrile leads to the clean conversion to graphene. This unprecedented procedure represents a rather mild, scalable and inexpensive method for graphene production surpassing previous wet-chemical approaches.

Graphite intercalation compounds are promising precursors for the reductive exfoliation of graphene. Here, the authors unveil the discharging mechanism of reduced graphitic compounds in a solid/liquid phase reaction, and further demonstrate its practical use for graphene production.

Confined linear carbon chains as a route to bulk carbyne

Strong chemical activity and extreme instability in ambient conditions characterize carbyne, an infinite sp(1) hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for production, and even more so for application. We report a method for the bulk production of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk production of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne's bulk production.

Surface-active ionic liquids in micellar catalysis: impact of anion selection on reaction rates in nucleophilic substitutions

A series of surface-active ionic liquids based on the 1-dodecyl-3-methylimidazolium cation and different anions was synthesized and applied for micellar catalysis of nucleophilic substitutions.

A series of surface-active ionic liquids based on the 1-dodecyl-3-methylimidazolium cation and different anions such as halides and alkylsulfates was synthesized. The aggregation behavior of these ionic liquids in water was characterized by surface tension, conductivity measurements and UV-Vis spectroscopy in order to determine the critical micelle concentration (CMC) and to provide aggregation parameters. The determination of surface activity and aggregation properties of amphiphilic ionic liquids was accompanied by SAXS studies on selected surface-active ionic liquids. The application of these surface-active ionic liquids with different anions was tested in nucleophilic substitution reactions for the degradation of organophosphorus compounds. Kinetic studies via UV-Vis spectrophotometry showed a strong acceleration of the reaction in the micellar system compared to pure water. In addition, an influence of the anion was observed, resulting in a correlation between the anion binding to the micelle and the reaction rate constants, indicating that the careful choice of the surface-active ionic liquid can considerably affect the outcome of reactions.

Hierarchically Mesostructured Polyisobutylene-Based Ionic Liquids

The formation and design of a hierarchically nanostructured poly(isobutylene)-based ionic liquid (PIB-ILs) is reported, displaying assembly into classical multiplets and an additional ordering of the aromatic counteranions. Three PIB-ILs (Mn = 3600 and 8600 g mol(-1) ), bearing imidazolium (1a), N-methylpyrrolidinium (1b), and triethylammonium cations (1c) together with the aromatic 2-(methylthio)benzoate anion are prepared via a combination of living carbocationic polymerization, "click" reactions and subsequent anion metathesis. The morphology of the novel PIB-ILs as well as its temperature-dependent behavior has been studied via small angle X-ray scattering, displaying two different transition temperatures: one originating from ordering of micelles within a cylinder, and the second from cylinder-cylinder arrangement. Furthermore, the incorporation of an aromatic, rigid, and bulky 2-(methylthio)benzoate anion into the PIB-ILs effects the formation of an internal assembly consisting of stacked cylindrical structures, composed from the mesoscale ordering of ionic "multiplets" characteristic for classical ionomers and from the typical distance of the cylinders themselves.

Reaction of bone nanostructure to a biodegrading Magnesium WZ21 implant - A scanning small-angle X-ray scattering time study

Understanding the implant-bone interaction is of prime interest for the development of novel biodegrading implants. Magnesium is a very promising material in the class of biodegrading metallic implants, owing to its mechanical properties and excellent immunologic response during healing. However, the influence of degrading Mg implants on the bone nanostructure is still an open question of crucial importance for the design of novel Mg implant alloys. This study investigates the changes in the nanostructure of bone following the application of a degrading WZ21 Mg implant (2wt% Y, 1wt% Zn, 0.25wt% Ca and 0.15wt% Mn) in a murine model system over the course of 15months by small angle X-ray scattering. Our investigations showed a direct response of the bone nanostructure after as little as 1month with a realignment of nano-sized bone mineral platelets along the bone-implant interface. The growth of new bone tissue after implant resorption is characterized by zones of lower mineral platelet thickness and slightly decreased order in the stacking of the platelets. The preferential orientation of the mineral platelets strongly deviates from the normal orientation along the shaft and still roughly follows the implant direction after 15months. We explain our findings by considering geometrical, mechanical and chemical factors during the process of implant resorption.

STATEMENT OF SIGNIFICANCE

The advancement of surgical techniques and the increased life expectancy have caused a growing demand for improved bone implants. Ideally, they should be bio-resorbable, support bone as long as necessary and then be replaced by healthy bone tissue. Magnesium is a promising candidate for this purpose. Various studies have demonstrated its excellent mechanical performance, degradation behaviour and immunologic properties. The structural response of bone, however, is not well known. On the nanometer scale, the arrangement of collagen fibers and calcium mineral platelets is an important indicator of structural integrity. The present study provides insight into nanostructural changes in rat bone at different times after implant placement and different implant degradation states. The results are useful for further improved magnesium alloys.

Nickel clusters embedded in carbon nanotubes as high performance magnets

Ensembles of fcc nickel nanowires have been synthesized with defined mean sizes in the interior of single-wall carbon nanotubes. The method allows the intrinsic nature of single-domain magnets to emerge with large coercivity as their size becomes as small as the exchange length of nickel. By means of X-ray magnetic circular dichroism we probe electronic interactions at nickel-carbon interfaces where nickel exhibit no hysteresis and size-dependent spin magnetic moment. A manifestation of the interacting two subsystems on a bulk scale is traced in the nanotube’s magnetoresistance as explained within the framework of weak localization.

Different synthesis protocols for Co3O4 -CeO2 catalysts--part 1: influence on the morphology on the nanoscale

Co₃O₄-modified CeO₂ (Co/Ce 1:4) was prepared by a combination of sol–gel processing and solvothermal treatment. The distribution of Co was controlled by means of the synthesis protocol to yield three different morphologies, namely, Co₃O₄ nanoparticles located on the surface of CeO₂ particles, coexistent Co₃O₄ and CeO₂ nanoparticles, or Co oxide structures homogeneously distributed within CeO₂. The effect of the different morphologies on the properties of Co₃O₄–CeO₂ was investigated with regard to the crystallite phase(s), particle size, surface area, and catalytic activity for CO oxidation. The material with Co₃O₄ nanoparticles finely dispersed on the surface of CeO₂ particles had the highest catalytic activity.

Timescales of self-healing in human bone tissue and polymeric ionic liquids

Strain (stress-free) relaxation in mechanically prestrained bone has a time constant of 75 s. It occurs by a reorganization of the proteoglycan-glycoprotein matrix between collagen fibers, which requires ionic interactions. Dissolving and relinking the ionic bonds is thus an important tool of nature to enable plastic deformation and to develop self-healing tissues. A way to transfer this approach to technical materials is the attachment of ionic end groups to polymeric chains. In these classes of materials, the so-called polymeric ionic liquids, structural recovery of thermally disorganized material is observed. A time constant between minutes and a week could be achieved, also by ionic rearrangement. The same mechanism, rearrangement of ionic bonds, can lead to vastly different relaxation times when the ionic interaction is varied by exchange of the cationic end groups or the anions.

Covalent embedding of Ni2+/Fe3+ cyanometallate structures in silica by sol-gel processing

Compound [Ni(AEAPTS)2]3[Fe(CN)6]2 (AEAPTS = N-(2-aminoethyl)-3-aminopropyltrimethoxysilane), in which Ni(2+) and Fe(3+) ions are ferromagnetically coupled through cyano bridges, was prepared. Sol-gel processing of the AEAPTS derivative resulted in incorporation of the cyanometallate in silica. The obtained material is magnetically ordered below 22 K with an effective magnetic moment μeff of 4.46 μB at room temperature, a maximum of 8.60 μB at approximately 15 K and a narrow hysteresis at 2 K, with a saturation remanence of about 300 emu mol(-1) and a coercitivity of 0.03 T.

Characterizing the S-layer structure and anti-S-layer antibody recognition on intact Tannerella forsythia cells by scanning probe microscopy and small angle X-ray scattering

Tannerella forsythia is among the most potent triggers of periodontal diseases, and approaches to understand underlying mechanisms are currently intensively pursued. A ~22-nm-thick, 2D crystalline surface (S-) layer that completely covers Tannerella forsythia cells is crucially involved in the bacterium-host cross-talk. The S-layer is composed of two intercalating glycoproteins (TfsA-GP, TfsB-GP) that are aligned into a periodic lattice. To characterize this unique S-layer structure at the nanometer scale directly on intact T. forsythia cells, three complementary methods, i.e., small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and single-molecular force spectroscopy (SMFS), were applied. SAXS served as a difference method using signals from wild-type and S-layer-deficient cells for data evaluation, revealing two possible models for the assembly of the glycoproteins. Direct high-resolution imaging of the outer surface of T. forsythia wild-type cells by AFM revealed a p4 structure with a lattice constant of ~9.0 nm. In contrast, on mutant cells, no periodic lattice could be visualized. Additionally, SMFS was used to probe specific interaction forces between an anti-TfsA antibody coupled to the AFM tip and the S-layer as present on T. forsythia wild-type and mutant cells, displaying TfsA-GP alone. Unbinding forces between the antibody and wild-type cells were greater than with mutant cells. This indicated that the TfsA-GP is not so strongly attached to the mutant cell surface when the co-assembling TfsB-GP is missing. Altogether, the data gained from SAXS, AFM, and SMFS confirm the current model of the S-layer architecture with two intercalating S-layer glycoproteins and TfsA-GP being mainly outwardly oriented.

Various three-dimensional structures connected by Al-O/OH/acetate-Al bonds

In the present work, significantly various structures connected by Al-O/OH/acetate-Al bonds were synthesized in a versatile sol-gel route. The various bond systems result in several three-dimensional (e.g., fibrous, highly porous, and compact) macrostructures. The shared acetate and OH ions provide the fibrous character; the shared OH ions and oxygen-bridges between octahedral Al(III) ions assist in the formation of a porous network; and the oxygen-bridges between differently (octa-, tetra-, and pentahedrally) coordinated Al(III) ions characterize the compact structures. The newly developed synthesis route is a fast and low-energy consumption sol-gel technique. This method applies only two starting materials and does not adopt any basic agent or catalyst. The synthesis is fast because it does not require any time-consuming peptization; a 3-D network forms directly from the initial solution. The low energy consumption arises from the low temperature of reactions (80 °C) and heat treatment (400-600 °C).

Synthesis and properties of highly dispersed ionic silica-poly(ethylene oxide) nanohybrids

We report an ionic hybrid based on silica nanoparticles as the anion and amine-terminated poly(ethylene oxide) (PEO) as a cation. The charge on the nanoparticle anion is carried by the surface hydroxyls. SAXS and TEM reveal an exceptional degree of dispersion of the silica in the polymer and high degree of order in both thin film and bulk forms. In addition to better dispersion, the ionic hybrid shows improved flow characteristics compared to silica/PEO mixtures in which the ionic interactions are absent.

Engineering molecular chains in carbon nanotubes

A range of mono- and bis-functionalised fullerenes have been synthesised and inserted into single-walled carbon nanotubes. The effect of the size and shape of the functional groups of the fullerenes on the resultant 1D arrays formed within the nanotubes was investigated by high resolution transmission electron microscopy and X-ray diffraction. The addition of non-planar, sterically bulky chains to the fullerene cage results in highly ordered 1D structures in which the fullerenes are evenly spaced along the internal nanotube cavity. Theoretical calculations reveal that the functional groups interact with neighbouring fullerene cages to space the fullerenes evenly within the confines of the nanotube. The addition of two functional groups to opposite sides of the fullerene cages results in a further increase in the separation of the fullerene cages within the nanotubes at the cost of lower nanotube filling rates.

Novel sol-gel precursors for thin mesoporous eu(3+)-doped silica coatings as efficient luminescent materials

Europium(III) ions containing mesoporous silica coatings have been prepared via a solvent evaporation-induced self-assembly (EISA) approach of different single-source precursors (SSPs) in the presence of Pluronic P123 as a structure-directing agent, using the spin-coating process. A deliberate tailoring of the chemical composition of the porous coatings with various Si:Eu ratios was achieved by processing mixtures of tetraethylorthosilicate (TEOS) and Eu(3+)-coordinated SSPs. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses demonstrate that the thin metal oxide-doped silica coatings consist of a porous network with a short-range order of the pore structure, even at high europium(III) loadings. Furthermore, luminescence properties were investigated at different temperatures and different degrees of Eu(3+) contents. The photoluminescence spectra clearly show characteristic emission peaks corresponding to the (5)D0 → (7)FJ (J = 0-5) transitions resulting in a red luminescence visible by the eyes, although the films have a very low thickness (150-200 nm).

Structural flexibility of RNA as molecular basis for Hfq chaperone function

In enteric bacteria, many small regulatory RNAs (sRNAs) associate with the RNA chaperone host factor Q (Hfq) and often require the protein for regulation of target mRNAs. Previous studies suggested that the hexameric Escherichia coli Hfq (Hfq(Ec)) binds sRNAs on the proximal site, whereas the distal site has been implicated in Hfq-mRNA interactions. Employing a combination of small angle X-ray scattering, nuclear magnetic resonance and biochemical approaches, we report the structural analysis of a 1:1 complex of Hfq(Ec) with a 34-nt-long subsequence of a natural substrate sRNA, DsrA (DsrA(34)). This sRNA is involved in post-transcriptional regulation of the E. coli rpoS mRNA encoding the stationary phase sigma factor RpoS. The molecular envelopes of Hfq(Ec) in complex with DsrA(34) revealed an overall asymmetric shape of the complex in solution with the protein maintaining its doughnut-like structure, whereas the extended DsrA(34) is flexible and displays an ensemble of different spatial arrangements. These results are discussed in terms of a model, wherein the structural flexibility of RNA ligands bound to Hfq stochastically facilitates base pairing and provides the foundation for the RNA chaperone function inherent to Hfq.

Microcracks and osteoclast resorption activity in vitro

During bone remodeling osteoclasts resorb bone, thus removing material, e.g., damaged by microcracks, which arises as a result of physiological loading and could reduce bone strength. Such a process needs targeted bone resorption exactly at damaged sites. Osteocytic signaling plays a key role in this process, but it is not excluded that osteoclasts per se may possess toposensitivity to recognize and resorb damaged bone since it has been shown that resorption spaces are associated with microcracks. To address this question, we used an in vitro setup of a pure osteoclast culture and mineralized substrates with artificially introduced microcracks and microscratches. Histomorphometric analyses and statistical evaluation clearly showed that these defects had no effect on osteoclast resorption behavior. Osteoclasts did not resorb along microcracks, even when resorption started right beside these damages. Furthermore, quantification of resorption on three different mineralized substrates, cortical bone, bleached bone (bone after partial removal of the organic matrix), and dentin, revealed lowest resorption on bone, significantly higher resorption on bleached bone, and highest resorption on dentin. The difference between native and bleached bone may be interpreted as an inhibitory impact of the organic matrix. However, the collagen-based matrix could not be the responsible part as resorption was highest on dentin, which contains collagen. It seems that osteocytic proteins, stored in bone but not present in dentin, affect osteoclastic action. This demonstrates that osteoclasts per se do not possess a toposensitivity to remove microcracks but may be influenced by components of the organic bone matrix.

Nanoparticle assemblies as probes for self-assembled monolayer characterization: correlation between surface functionalization and agglomeration behavior

The ordering of dodecyl chains has been investigated in mixed monolayers of phosphonic acid capping agents on the surface of hydrothermally prepared zirconia nanocrystals. Methyl-, phenyl-, pyryl-, and tert-butylphosphonic acids have been used to investigate series with different mixing ratios with dodecylphosphonic acid as the cocapping agent for the mixed monolayer formation. Fourier transform infrared (FTIR) studies revealed that an increasing amount (different for each type) of coadsorbed capping agent reduces the ordering of the dodecyl chains significantly. Small-angle X-ray scattering (SAXS) verified that with increasing amount of cocapping agent the agglomeration of the particles decreases. The strong correlation of the agglomeration behavior with the ordering of the surface-bound alkyl chains leads to the conclusion that interparticle bilayers, formed via long alkyl chain packing, are responsible and can be controlled on a molecular level by coadsorbing various molecules. On the basis of this correlation, nanoparticles can be used as probes for self-assembled monolayer investigation by an indirect structural method (SAXS) and correlated with the routine spectroscopical method for the chemical analysis of surface groups (FTIR).

Effect of interparticle interactions on size determination of zirconia and silica based systems – A comparison of SAXS, DLS, BET, XRD and TEM

The aim of this work is a systematic comparison of size characterisation methods for two completely different model systems of oxide nanoparticles, i.e. amorphous spherical silica and anisotropic facet-shaped crystalline zirconia. Size and/or size distribution were determined in a wide range from 5 to 70 nm using small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), nitrogen sorption (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM). A nearly perfect coincidence was observed only for SAXS and TEM for both types of particles. For zirconia nanoparticles considerable differences between different measurement methods were observed.