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A novel reproducible process for the preparation of Febuxostat (FX) using a double dosing titration method is achieved by titrating 80 mL of 3 mM Febuxostat sodium salt solution with 15 mM HCl and 6 mM Febuxostat sodium salt solution at a dosing rate of 0.2 mL/min. A new crystalline form (polymorph AQ) is prepared, which is characterized by being the exceptional form produced directly in an aqueous medium, in contrast to the known and registered forms that were produced only in organic solvent systems. The same crystal form is reproduced when crystallized at different temperatures ranging from 10 to 50 °C. However, the pH value at which the onset of nucleation occurs is affected due to its effect on nucleation kinetics. The key parameters affecting the metastable zone are studied. Decreasing the dosing rate can lead to narrowing of the metastable zone and delay in the onset of nucleation. Increasing the temperature can lead to widening of the metastable zone and delay in the onset of nucleation. Analytical ultracentrifugation (AUC) analysis was conducted on supersaturated solutions to investigate the incidence of prenucleation clusters (PNCs) as solute precursors to phase separation. The AUC analysis indicated that nucleation of Febuxostat relies on PNCs as solute precursors and may include liquid–liquid phase separation as an intermediate step.

Despite the advances achieved in the past decade in the seed-mediated synthesis of colloidal single-crystal gold nanorods (Au NRs), the seed size role in the Au NR formation is not fully understood. Moreover, although the anisotropic growth of single-crystal seeds typically occurs at sizes between 4 and 6 nm, synthesizing high-quality Au NRs with sub-10 nm lengths remains challenging. We investigated herein the effect of seed dimensions on the silver-assisted seed-mediated growth of single-crystal Au NRs with lengths below 10 nm in the presence of hexadecyltrimethylammonium bromide (CTAB). A strong relationship was found between the seed dimensions and the yield of Au NR formation, where 3.1 nm seeds displayed an optimal anisotropic grow behavior. This effect could be related to the different abilities of CTAB micelles to passivate gold seeds with distinct dimensions, as suggested by molecular dynamic experiments. Compared with the 1–2 nm seeds traditionally used in the Au NR synthesis, the enhanced ability of 3.1 nm seeds to evolve anisotropically facilitates the growth of high-quality Au NRs with sub-10 nm lengths in an unprecedented manner. An optimal concentration of silver was also critical for the efficient evolution of 3.1 nm seeds into sub-10 nm Au NRs. Moreover, the synthesized small Au NRs were used as anisotropic seeds to fabricate sub-10 nm diameter Au NRs with tunable aspect ratios and core–shell electrocatalysts. The insight gained on the role of seed size enabled us to develop an advanced reproducible and scalable route for the synthesis of Au NRs with sub-10 nm lengths.

Nanocrystalline calcium carbonate (CaCO3) and amorphous CaCO3(ACC) are materials of increasing technological interest. Nowadays, they are mainly synthetically produced by wet reactions using CaCO3reagents in the presence of stabilizers. However, it has recently been discovered that ACC can be produced by ball milling calcite. Calcite and/or aragonite are the mineral phases of mollusk shells, which are formed from ACC precursors. Here, we investigated the possibility to convert, on a potentially industrial scale, the biogenic CaCO3(bCC) from waste mollusk seashells into nanocrystalline CaCO3and ACC. Waste seashells from the aquaculture species, namely oysters (Crassostrea gigas, low-Mg calcite), scallops (Pecten jacobaeus, medium-Mg calcite), and clams (Chamelea gallina, aragonite) were used. The ball milling process was carried out by using different dispersing solvents and potential ACC stabilizers. Structural, morphological, and spectroscopic characterization techniques were used. The results showed that the mechanochemical process produced a reduction of the crystalline domain sizes and formation of ACC domains, which coexisted in microsized aggregates. Interestingly, bCC behaved differently from the geogenic CaCO3(gCC), and upon long milling times (24 h), the ACC reconverted into crystalline phases. The aging in diverse environments of mechanochemically treated bCC produced a mixture of calcite and aragonite in a species-specific mass ratio, while the ACC from gCC converted only into calcite. In conclusion, this research showed that bCC can produce nanocrystalline CaCO3and ACC composites or mixtures having species-specific features. These materials can enlarge the already wide fields of applications of CaCO3, which span from medical to material science.

We have used four different analytical techniques (electron microscopy (TEM), dynamic light scattering (DLS), analytical ultracentrifugation (AUC), and small angle X-ray scattering (SAXS) to measure the length and width as well as the diffusion coefficients of gold nanorods of different aspect ratio. All four methods could reproduce the trends in aspect ratio, and both length and width could be extracted once the ligand shell was accounted for. The CTAB bilayer coating was determined to have a thickness of 3.34, 3.02, and 3.26 nm by SAXS, DLS, and AUC, respectively. TEM nevertheless yielded the best predictions for the nanorod ensemble surface plasmon resonance by using COMSOL simulations. All four methods yielded better fits when the rods were treated as spherically capped cylinders.

A novel approach for the production of a bioinspired dentine replacement material is introduced. An apatite–gelatin nanocomposite material was cross-linked with various cross-linkers. These nanocomposites have a high resemblance to mammalian dentine regarding its composition and properties. A precipitation reaction was used to produce apatite–gelatin nanocomposites as starting materials. Cross-linking of the gelatin has to be performed to produce dentine-like and thus tough and robust apatite–gelatin nanocomposites. Therefore, the efficacy of various protein cross-linkers was tested, and the resulting materials were characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, and EXAFS as well as CHNS analysis and tested for their mechanical performance using Vickers hardness measurements as well as for their dissolution stability in EDTA. Especially glutaraldehyde, proanthocyanidins, and transglutaminase gave promising results with hardness values of up to 63 HV0.2. To further improve the material properties, we combined the effective cross-linker transglutaminase with casein, which led to an improved interconnection between the single nanocomposite platelets. By doing so, a cross-linked composite was obtained, which shows even higher hardness values than does human dentine, at 76 HV0.2. The combination of apatite–gelatin nanocomposites with an effective cross-linker resulted in a bioinspired material with composition and properties close to those of human dentine.

Cationic complex coacervates are contemplated for various medical applications controlling carrier or release processes. Here, lower Mwpoly(allylamine hydrochloride) (15 kg/mol) and (hydrogen)phosphate as cross-linking units were chosen to facilitate a sufficient coacervation and subsequently a controllable phosphate release, essential for consecutive mineralization reactions. In addition, the rheological characteristics of the obtained coacervates were assessed, exhibiting a pronounced liquid character, which enables beneficial properties toward remineralization applications such as high wettability and moldability. In light of our results, macroscopic hydrogels are considered for the first time as an ion source for the mineralization of crystalline calcium phosphate phases, representing an entirely new class of preceding mineralization species for potential applications in dentistry and osteology.

Hierarchical structures of CoOOH, NiOOH and MnOOH have been successfully prepared in aqueous solution at ambient temperature, and comprehensive characterizations demonstrated their formation mechanism which can provide valuable references for optimizing the synthesis conditions of hierarchical oxyhydroxides.

Magic-size clusters are ultrasmall, transient species that appear early during semiconductor nanocrystal growth and have been assigned to stoichiometrically and geometrically well-defined structures. Yet, a direct analysis has proved difficult due to their limited stability and challenging isolation. Analytical ultracentrifugation is a promising tool to analyze these compounds, because it circumvents the need to purify and, thereby, destabilize the clusters, while yielding information on their sedimentation and diffusion behavior, size, shape, and composition. We employ a multiwavelength detector that allows the detection of whole UV/vis absorption spectra during centrifugation to separate and identify individual magic-size clusters in crude reaction mixtures sampled directly from the colloidal syntheses. Analytical ultracentrifugation thus constitutes an elegant, independent, high-resolution, and statistically significant method to show the stepwise growth of magic-size clusters, confirming recent growth models.

Formation of superstructures from colloidal dispersion involves a continuous increase in particle concentration, resulting in increasingly more complicated interparticle interaction. At high particle concentration, the presence of the super-crowding effect, strong non-ideality in addition to significant light absorption and scattering makes particle analysis very difficult. Here we report quantitative molecular, microscopic and macroscopic experimental results on like-charged colloids with concentration up to 60 vol%, close to the densest possible packing of spheres. It is achieved by conducting sedimentation–diffusion-equilibrium analytical ultracentrifugation (SE-AUC) on a concentrated dispersion of colloidal silica nanoparticles in a refractive-index-matching solvent. Surprisingly, we observed the self-association and even colloidal gel formation of like-charged colloids at very high concentration. Further experiments indicate that the attraction force may be counter-ion mediated. These results represent an important step forward in understanding complicated interparticle interaction in extremely high concentration, which is vital for the controlled fabrication of colloidal superstructures.

Nanoparticle assemblies with long-range packing order and preferred crystallographic orientation of building blocks, i.e., mesocrystals, are of high interest not only because of their unique physical properties but also due to their complex structure and morphogenesis. In this study, faceted mesocrystals have been assembled from the dispersion of truncated cubic-shaped iron oxide nanoparticles stabilized by oleic acid (OA) molecules using the nonsolvent “gas phase diffusion technique” into an organic solvent. The effects of synthesis conditions as well as of the nanoparticle size and shape on the structure and morphogenesis of mesocrystals were examined. The interactions of OA-capped iron oxide nanoparticles with solvent molecules were probed by analytical ultracentrifugation and double difference pair distribution function analysis. It was shown that the structure of the organic shell significantly depends on the nature and polarity of solvent molecules. For the nonpolar solvents, the interaction of the aliphatic chains of OA molecules with the solvent molecules is favorable and the chains extend into the solvent. The solvation shell around the nanoparticles is more extended in nonpolar and more compact in polar solvents. There is a clear trend for more spherical particles to be assembled into the fccsuperlattice, whereas less truncated cubes form rhombohedral and tetragonal structures. The observed changes in packing symmetry are reminiscent of structural polymorphism known for “classical” (atomic and molecular) crystals.

One aspect of the research on mesocrystals nowadays focuses on applications, whereby such applications demand mesocrystals with a tunable size. To achieve this task, more effort needs to be undertaken to understand how mesocrystals form, which parameters influence mesocrystal formation, and which kind of structure results from the nanoparticle assembly. Within this communication, we demonstrate for faceted mesocrystals assembled from iron oxide nanocubes stabilized by oleic acid that the proper choice of crystallization conditions in the gas phase diffusion setup is essential to achieve this task. The appropriate choice of substrate, dispersion and destabilizing agents, additive, nanocrystal concentration, crystallization kinetics, and duration allows growing faceted iron oxide mesocrystals with sizes ranging from a few micrometers up to almost a millimeter. By these findings supported by light and scanning electron microscopy, we show that in this system, heterogeneous nucleation is the predominant mechanism for mesocrystal formation on a solid substrate. Additionally, other surfactants than oleic acid can also act as molecular additives to support mesocrystal growth. These findings should be transferable to tune the size and quality of other self-assembled mesocrystals.

The concept of nanoparticles (NPs) as building blocks offers new possibilities to produce complex and tailored structures from the nano- to the mesoscale. In order to control a “polymerization” of particles, knowledge of the mechanism and kinetics of the reaction are necessary. We show that controlled assembly of cetylpyridinium chloride-stabilized gold NPs utilizing induced dipole–dipole interactions can lead to the formation of defined one-dimensional structures in solution. Three different shaped NPs (cubes, octahedra, and truncated cuboctahedra) were investigated individually. The assembly process is analogous to a step growth polymerization and is quantitatively describable with kinetics of a polyesterification. In situ kinetic studies reveal that there is an ideal particle size and shape for the induced dipole-driven assembly. Even small changes in size have remarkable effects on the assembly behavior. We further demonstrate that the transition from oriented assembly to oriented attachment requires a critical particle size (critical interface area) resulting from a size-dependent energy barrier for the crystallographic fusion. A combination of ideal size, shape, and degree of destabilization enables controlled oriented attachment of gold NPs in solution to chainlike structures under ambient conditions.

The crystallization mechanisms of organic molecules in solution are not well-understood. The mechanistic scenarios where crystalline order evolves directly from the molecularly dissolved state (“classical”) and from initially formed amorphous intermediates (“nonclassical”) are suggested and debated. Here, we studied crystallization mechanisms of two widely used analgesics, ibuprofen (IbuH) and etoricoxib (ETO), using direct cryogenic transmission electron microscopy (cryo-TEM) imaging. In the IbuH case, parallel crystallization pathways involved diverse phases of high and low density, in which the instantaneous formation of final crystalline order was observed. ETO crystallization started from well-defined round-shaped amorphous intermediates that gradually evolved into crystals. This mechanistic diversity is rationalized by introducing a continuum crystallization paradigm: order evolution depends on ordering in the initially formed intermediates and efficiency of molecular rearrangements within them, and there is a continuum of states related to the initial order and rearrangement rates. This model provides a unified view of crystallization mechanisms, encompassing classical and nonclassical pictures.

The intrinsic high diffusion rate of colloids at low Péclet number results in an extremely fast crystallization process and instant formation of colloidal crystals, even at an ultracentrifugal field of extremely high intensity. By introducing a small number of clusters in sedimention, it should be possible to slow down the crystallization process, thus making the assembly order tunable in preparative ultracentrifugation experiments. Here, we used sodium dodecyl sulfate-stabilized polystyrene nanoparticles (with a size dispersity of 1.07) dispersed in a solution of high ionic strength. Sedimentation and assembly of these nanoparticles were done using preparative ultracentrifugation at various angular velocities. The sedimentation process was also analyzed in situ by analytical ultracentrifugation in real time. By creating as low as 3% of clusters into these nearly uniformly sized polystyrene nanoparticle dispersions during the sedimentation process, the superstructure order becomes easily tunable between glassy and crystalline. Theoretical calculations complemented the experiments to explain the mechanism of cluster formation in sedimentation. This work provides a novel methodology to produce superstructures with a tunable packing order for colloids at low Péclet number.

Biomineralization occurs in aqueous environments. Despite the ubiquity and relevance of CaCO3biomineralization, the role of water in the biomineralization process has remained elusive. Here, we demonstrate that water reorganization accompanies CaCO3biomineralization for sea urchin spine generation in a model system. Using surface-specific vibrational spectroscopy, we probe the water at the interface of the spine-associated protein during CaCO3mineralization. Our results show that, while the protein structure remains unchanged, the structure of interfacial water is perturbed differently in the presence of both Ca2+and CO32–compared to the addition of only Ca2+. This difference is attributed to the condensation of prenucleation mineral species. Our findings are consistent with a nonclassical mineralization pathway for sea urchin spine generation and highlight the importance of protein hydration in biomineralization.

We describe a route to synthesize a mechanically stable, non-flammable poly(acrylic acid)–calcium salt (the so-called mineral plastic) foam whose structure can be tailored. Main steps of the foam synthesis are: (1) foaming of the PAA-containing solution, (2) gelation of the continuous foam phase, and (3) drying of the hydrogel foam. The main challenge was to formulate an aqueous solution with a large amount of poly(acrylic acid), PAA, and calcium to yield a mechanically stable foam. The resulting PAA-based solid foams with pore sizes of around 220 μm can easily be dissolved, i.e.recycled, in an acidic solution.

Controlling the assembly and disassembly of nanoscale protein cages for the capture and internalization of protein or non-proteinaceous components is fundamentally important to a diverse range of bionanotechnological applications. Here, we study the reversible, pressure-induced dissociation of a natural protein nanocage, E. colibacterioferritin (Bfr), using synchrotron radiation small-angle X-ray scattering (SAXS) and circular dichroism (CD). We demonstrate that hydrostatic pressures of 450 MPa are sufficient to completely dissociate the Bfr 24-mer into protein dimers, and the reversibility and kinetics of the reassembly process can be controlled by selecting appropriate buffer conditions. We also demonstrate that the heme B prosthetic group present at the subunit dimer interface influences the stability and pressure lability of the cage, despite its location being discrete from the interdimer interface that is key to cage assembly. This indicates a major cage-stabilizing role for heme within this family of ferritins.

The determination of solubility limits of compounds in water is unprecise and relies on certain prerequisites such as UV–vis absorption activity. In this study, we designed an experimental approach based on potentiometric titrations to determine solubility limits of various organic compounds by exploiting their pH-active carboxylic acid groups. By applying the law of mass action, utilizing a double-dosing method ensuring a constant compound concentration, it is possible to determine the intrinsic solubility limits, which are independent of the pH value. The derived equations enable the precise and fast determination of intrinsic solubility limits of organic compounds in aqueous solutions within 2–4 h. Moreover, it is shown how the pKavalue can be determined based on titrations carried out at two different compound concentrations.

Nucleation phenomena play an important role in our world, and understanding them is of major interest. However, we lack analytical methods with the sufficient temporal and spatial resolution to analyze nucleation processes. In this work we used CTAB-stabilized gold nanocubes as a model system for nucleation, meaning the nanoparticles act like ions or atoms and built up larger superstructures comparable to normal nucleation phenomena. Thereby we analyzed the heterogeneous nucleation of the gold nanocubes on hydrophobized and negatively charged mica surfaces with a combination of UV–vis–NIR spectroscopy and light microscopy. With the plasmon resonance of the gold nanocubes we gained valuable information about the early nucleation of the particles and their concentration in solution via UV–vis–NIR spectroscopy. The combination with a light microscope enabled the simultaneous detection of nucleated species on the surfaces and opened the possibility to analyze the kinetics of the heterogeneous nucleation process. With this, we were able to determine the nucleation rates. While the hydrophobized surfaces did not influence the nucleation of the gold nanocubes, the negatively charged surfaces greatly promoted the nucleation. Thereby, we could demonstrate that the combination of simple and commonly available light microscopy and optical spectroscopies in general is a suitable and easy strategy to analyze heterogeneous nucleation processes directly in solution on a relevant statistical basis.

Supramolecular adhesives have attracted a great deal of attention in recent years, resulting in their development for different applications. However, creating supramolecular adhesives with reversible and reusable properties is still a challenge. Here, a synthesis route to obtain supramolecular adhesives is presented in which no polymeric compounds are involved in the preparation. The adhesive is formed by intermolecular coulomb forces between amorphous magnesium carbonate nanoparticles and the low-molecular-weight drug ibuprofen, which results in an amorphous composite material that is transparent, shapeable, stretchable, and self-healing, making it reusable. It is demonstrated that this hybrid material provides a simple means of gluing a wide variety of materials, including metals, glass, paper, and plastics, and that is reversible and possesses reusability. The material disrupts the traditional concept of polymer-based adhesives and may be used as a sustainable mineral plastic in applications such as 3D printing.

Magnesium-stabilized amorphous calcium carbonate (Mg-ACC), amorphous magnesium calcium silicate hydrate (MCSH), and hydroxyapatite (HAp) are prepared by a precipitation method. By cold-pressing these particles, it is possible to produce porous bulk discs with a narrow pore size distribution. These porous inorganic discs (Mg-ACC, MCSH, and HAp) are investigated as stationary phases to study the chromatographic behavior and adsorption ability of rhodamine B, methylene blue, and ribonuclease. The adsorption affinities of different biomolecules can be easily observed and evaluated through this method. Furthermore, by infiltrating fabricated opaque porous discs with benzyl ether, which has a similar refractive index as the used inorganic particles (Mg-ACC, MCSH, and HAp), their optical properties significantly change and the discs become translucent. Moreover, by infiltrating the MCSH discs with a light-curing polymer, translucent composites with good surface hardness are fabricated. By doping particles with ions such as Ni2+, Co2+, Fe3+, and Eu3+, the color and UV–visible spectrum of the bulk discs can be adjusted. Typically, by using iron-doped MCSH particles as the inorganic matrix, nanocomposites, which show a steep UV-absorption edge at 400 nm, are fabricated. Our work provides a simple and economical method to evaluate the affinity of biomolecules to inorganic materials and a novel way to fabricate translucent hard composite materials. The fabricated nanocomposite discs show a great UV shielding effect and superior surface hardness compared to polymethyl methacrylate and commercial sunglasses, suggesting their potential as new sunglass materials.

Natural and synthetic composite materials as yet elude a complete understanding of their formation from organic and inorganic constituents. Addressing the interactions between organic additives and metastable inorganic precursors during mineral nucleation and growth is a critical challenge. In this study, we elucidate additive-controlled mineralization by a novel approach for the in situ continuous monitoring of a widely applied diffusion-based methodology, assisted by the quantitative assessment of mineral nucleation. The formation of amorphous superstructures is attributed to a complex interplay between additives and mineral species viz. ions, ion-clusters, and amorphous precursors as well as a unique phase behavior of the additive molecules relative to the maturing mineral phase. A pH-dependent conditioning of nucleation and demixing of transient liquid-like additive-ion complexes are shown to play critical roles in tuning mineral architecture. Thus, the modulation of mineral precursors and mineralization conditions by additive species determine material composition and morphology.

Nonclassical crystallization (NCC) summarizes a number of crystallization pathways, which differ from the classical layer-by-layer growth of crystals involving atomic/molecular building units. Common to NCC is that the building units are larger and include nanoparticles, clusters, or liquid droplets, providing multiple handles for their control at each elementary step. Therefore, many different pathways toward the final single crystals are possible and can be influenced by appropriate experimental parameters or additives at each step of crystal growth. NCC allows for a plethora of crystallization strategies toward complex crystalline (hybrid) materials. In this perspective, we summarize the current state of the art with a focus on the new horizons of NCC with respect to mechanistic understanding, high-performance materials, and new applications. This gives a glimpse on what will be possible in the future using these crystallization approaches: Examples are new electrodes and storage materials, (photo)catalysts, building materials, porous or crystalline materials with complex shape, structural hierarchy, and anisotropic single crystals.

Monetite (CaHPO4, DCPA) and hydroxyapatite (Ca10(PO4)6(OH)2, HAp) are promising biomaterials with wide application in the biomedical field. In this study, we propose a novel method to prepare fiber-like DCPA without organic additives for the first time and show that nanostructured HAp can be synthesized without changing the macroscopic morphology of DCPA. Our results show that the temperature, pH, calcium to phosphate ratio (Ca/P), and concentration of NH4+are essential factors in the formation of fiber-like DCPA. The synthesized materials were characterized by powder X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy, and the DCPA → HAp phase transformation process was examined. The growth of HAp on the DCPA crystal can be regulated by the composition of the hydrolyzing solution, forming HAp with its c-axis perpendicular [HAp (001)//DCPA (100)] or parallel [HAp (001)//DCPA (010)] to the elongation direction of the DCPA crystal. At a high concentration of Ca2+in NH4OH solution, octacalcium phosphate was observed as an intermediate phase with its c-axis parallel to elongation of the initial DCPA crystal. The HAp crystals formed after complete transformation of the precursor phases have a preferred crystallographic orientation with c-axis coaxial to the elongation direction of DCPA. In the concentrated NH4OH solution, the direct transformation of DCPA to HAp was observed. At initial stages of the hydrolysis, the c-axis of newly formed HAp is perpendicular to the elongation direction of DCPA. This study provides a new insight into regulation of the crystal growth of DCPA without organic additives and a facile route to form HAp with hierarchical structures.

Nature has taken millennia to come up with unique solutions for providing materials with properties tailored toward versatile demands, making use of the very limited resources available in natural environments. Today, these biomaterials can be used as inspiration by combining and ‘remixing’ the concepts that nature displays to create new bioinspired materials. Here, the authors present materials combining the structural and functional elements of multiple biominerals: the inorganic–organic lamellar structure responsible for the high fracture toughness of nacre; highly mineralized composites, which give different mollusk teeth their very high hardness and strength; and the particle orientation and magnetic anisotropy of magnetosomes, giving magnetotactic bacteria a sensitive means to navigate along geomagnetic field lines. The authors show how the mechanical properties of a composite material can be improved with the addition of each of these elements. Small-angle neutron scattering studies and molecular simulation give additional insights into the mineralization from the very first attached ions to the finished composite.

Cellular machineries guide the bottom-up pathways toward crystal superstructures based on the transport of inorganic precursors and their precise integration with organic frameworks. The biosynthesis of mesocrystalline spines entails concerted interactions between biomolecules and inorganic precursors; however, the bioinorganic interactions and interfaces that regulate material form and growth as well as the selective emergence of structural complexity in the form of nanostructured crystals are not clear. By investigating mineral nucleation under the regulation of recombinant proteins, we show that SpSM50, a matrix protein of the sea urchin spine, stabilizes mineral precursors via vesicle-confinement, a function conferred by a low-complexity, disordered region. Site-specific proteolysis of this domain by a collagenase initiates phase transformation of the confined mineral phase. The residual C-type lectin domain molds the fluidic mineral precursor into hierarchical mesocrystals identical to structural crystal modules constituting the biogenic mineral. Thus, the regulatory functions of proteolytic enzymes can guide biomacromolecular domain constitutions and interfaces, in turn determining inorganic phase transformations toward hybrid materials as well as integrating organic and inorganic components across hierarchical length scales. Bearing striking resemblance to biogenic mineralization, these hybrid materials recruit bioinorganic interactions which elegantly intertwine nucleation and crystallization phenomena with biomolecular structural dynamics, hence elucidating a long-sought key of how nature can orchestrate complex biomineralization processes.

Asymmetrical flow field-flow fractionation (AF4) is a chromatographic separation technique that can be used for a broad range of particles or macromolecules. As an orthogonal method to size exclusion chromatography (SEC) with a much broader separation size range (1–800 nm) AF4 is gaining importance. However, the data evaluation capacities are far behind in comparison to other techniques like analytical ultracentrifugation (AUC). A program for evaluation of data from AF4 with a coupled multiangle laser light scattering (MALLS) detector was developed that allows the determination of the distributions of diffusion coefficients (D), hydrodynamic radii (Rh), molecular weights (Mw), and relative concentrations (RC) of the obtained species. In addition, two algorithms to remove broadening effects via deconvolution were implemented and tested for their validity. The first is an extension of the known diffusion broadening correction applying the entire diffusion coefficient distribution instead of a single diffusion coefficient. The second applies the Richardson–Lucy algorithm for the deconvolution of overlapping signals from stars in astronomy. This program allows a reproducible strong enhancement of the fractogram resolution allowing for entire baseline separations of proteins. The comparison of the values for Mwdetermined by a partial Zimm plot from each data point of the original fractogram and the deconvolved results shows that especially the Richardson–Lucy algorithm maintains a high degree of data robustness.

Titanium Implants In article 2203411by Helmut Cölfen, Zuolin Wang, and co‐workers, a facile method to fabricate Gel‐ACP (gelatin‐amorphous calcium phosphate) coatings on titanium is demonstrated, providing a promising strategy to mimic the initial bone biological apatite and thus obtaining a rapid bone formation at the interface of bone and implant.

The band sedimentation experiment in analytical ultracentrifugation (AUC) allows for the performance of a chemical reaction inside the AUC and also offers separation of individual pure components in a sedimentation velocity experiment. Although this experiment offers exciting possibilities for application, it is barely used. This is related to the bad definition of the initial conditions. Both the duration and the time of the solution overlay during rotor acceleration are not known. In this study, we investigate these conditions under the variation of the overlay volume using recording of interference patterns in a continuous mode during the acceleration of the rotor. It was found that the overlay occurs at rotor speeds between 770 and 2000 rpm, which is very low compared to typical experimental rotor speeds from 3 000 to 60 000 rpm and therefore elucidates that the generated reaction products, respectively, overlaid species are subject to the centrifugal force almost from the beginning. Also, the duration of the overlay is less than 1.2 s, which is very fast compared to hours of centrifugation time for an experiment and we demonstrated that the overlay compartment is completely emptied during overlay allowing for the precise calculation of the meniscus using the known sample sector geometry. Our results show that the initial conditions of the experiment are defined and should make an adapted analysis possible if the interdiffusion of the two solvents is taken into account, which lead to a dynamic density gradient.

In biomineralization and bioinspired mineralization, substrates and additives function synergistically in providing structural control of the mineralized layers including their orientation, polymorph, morphology, hierarchical architecture, etc. Herein, a novel type of granular aragonitic CaCO3–poly(acrylic acid) substrate guides the mineralization of prismatic CaCO3thin films of distinct morphology and polymorph in the presence of different additives including organic compounds and polymers. For instance, weakly charged amino acids lead to columnar aragonite overlayers, while their charged counterparts and organic acids/bases inhibit the overgrowth. Employment of several specific soluble polymer additives in overgrowth instead results in calcitic overlayers with distinct hierarchical architecture, good hardness/Young’s modulus, and under-water superoleophobicity. Interestingly, self-organized patterns in the CaCO3–poly(l-glutamic acid) overlayer are obtained under proper mineralization conditions. We demonstrate that the granular seed comprised of mineralized and polymeric constituents is a versatile platform for obtaining prismatic CaCO3thin films, where structural control can be realized by the employment of different types of additives in overgrowth. We expect the methodology to be applied to a broad spectrum of bioinspired, prismatic-type crystalline products, aiming for the development of high-performance hybrids.

We present a simple experimental procedure to obtain CdSe quantum dots from aqueous solution with a controllable size. Double-hydrophilic block copolymers consisting of a poly(ethylene glycol) block and a block of either poly(ethylene imine) or polylysine are used as stabilizers. UV/VIS absorption spectroscopy, analytical ultracentrifugation and transmission electron microscopy are used to examine the resulting quantum dots. The particle size can be simply controlled by adjusting the polymer concentration during synthesis for both block copolymers.

Underwater adhesion is crucial to many marine life forms living a sedentary lifestyle. Amongst them, mussel adhesion has been mostly studied, which inspires numerous investigations of 3,4-dihydroxyphenylalanine (DOPA)-based organic adhesives. In contrast, reef-building oysters represent another important “inorganic” strategy of marine molluscs for adhesion by generating biomineralized organic–inorganic adhesives, which is still rarely studied and no synthetic analogues have ever been reported so far. Here, a novel type of oyster-inspired organic–inorganic adhesive based on a biomineralized polyelectrolyte hydrogel is reported, which consists of polyacrylic acid physically cross-linked by very small amorphous calcium carbonate nanoparticles (<3 nm). The mineral-enhanced polyelectrolyte hydrogel adhesive is shown to be injectable, reusable, and optically clear upon curing in air. Moreover, comparable adhesion performance to DOPA-based adhesives is found for the hydrogel adhesive in both dry and wet conditions, which can even be further enhanced by introducing a small amount of second large cross-linker such as negatively charged nanoparticles. The present mineral hydrogel represents a new type of bio-inspired organic–inorganic adhesive that may find a variety of potential applications in adhesive chemistry.

Nature builds numerous structurally complex composites with fascinating mechanical robustness and functionalities by harnessing biopolymers and amorphous calcium carbonate (ACC). The key to successfully mimicking these natural designs is efficiently stabilizing ACC, but developing highly efficient, biodegradable, biocompatible, and sustainable stabilizing agents remains a grand challenge since anhydrous ACC is inherently unstable toward crystallization in the wet state. Inspired by the stabilized ACC in crustacean cuticles, we report the efficient stabilization ability of the most abundant biopolymer–cellulose nanofibrils (CNFs) for ACC. Through the cooperative stabilizing effect of surface carboxyl groups and a rigid segregated network, the CNFs exhibit long-term stability (more than one month) and achieved a stabilization efficiency of 3.6 and 4.4 times that of carboxymethyl cellulose (CMC) and alginate, respectively, even higher than poly(acrylic acid). The resulting CNF/ACC dispersions can be constructed into transparent composite films with the high strength of 286 MPa and toughness up to 28.5 MJ/m3, which surpass those of the so far reported synthetic biopolymer-calcium carbonate/phosphate composites. The dynamic interfacial interaction between nanocomponents also provides the composite films with good self-healing properties. Owing to their good wet stability, the composite films present high humidity sensitivity for monitoring respiration and finger contact.

Fiona C. Meldrum and Helmut Cölfen chalk up some of the myriad forms and uses of calcium carbonate to burnish a ‘dull’ reputation.

Heterogeneous nucleation processes are involved in many important phenomena in nature, including devastating human diseases caused by amyloid structures or the harmful frost formed on fruits. However, understanding them is challenging due to the difficulties of characterizing the initial stages of the process occurring at the interface between the nucleation medium and the substrate surfaces. This work implements a model system based on gold nanoparticles to investigate the effect of particle surface chemistry and substrate properties on heterogeneous nucleation processes. Using widely available techniques such as UV–vis–NIR spectroscopy and light microscopy, gold nanoparticle-based superstructure formation was studied in the presence of substrates with different hydrophilicity and electrostatic charges. The results were evaluated on grounds of classical nucleation theory (CNT) to reveal kinetic and thermodynamic contributions of the heterogeneous nucleation process. In contrast to nucleation from ions, the kinetic contributions toward nucleation turned out to be larger than the thermodynamic contributions for the nanoparticle building blocks. Electrostatic interactions between substrates and nanoparticles with opposite charges were crucial to enhancing the nucleation rates and decreasing the nucleation barrier of superstructure formation. Thereby, the described strategy is demonstrated advantageous for characterizing physicochemical aspects of heterogeneous nucleation processes in a simple and accessible manner, which could be potentially explored to study more complex nucleation phenomena.

Current developments in nanotechnology have increased the demand for nanocrystal assemblies with well-defined shapes and tunable sizes. DNA is a particularly well-suited building block in nanoscale assemblies because of its scalable sizes, conformational variability, and convenient self-assembly capabilities viabase pairing. In hybrid materials, gold nanoparticles (AuNPs) can be assembled into nanoparticle structures with programmable interparticle distances by applying appropriate DNA sequences. However, the development of stoichiometrically defined DNA/NP structures is still challenging since product mixtures are frequently obtained and their purification and characterization is the rate-limiting step in the development of DNA–NP hybrid assemblies. Improvements in nanostructure fractionation and characterization techniques offer great potential for nanotechnology applications in general. This study reports the application of analytical ultracentrifugation (AUC) for the characterization of anisotropic DNA-linked metal–crystal assemblies. On the basis of transmission electron microscopy data and the DNA primary sequence, hydrodynamic bead models are set up for the interpretation of the measured frictional ratios and sedimentation coefficients. We demonstrate that the presence of single DNA strands on particle surfaces as well as the shape factors of multiparticle structures in mixtures can be quantitatively described by AUC. This study will significantly broaden the possibilities to analyze mixtures of shape-anisotropic nanoparticle assemblies. By establishing insights into the analysis of nanostructure mixtures based on fundamental principles of sedimentation, a wide range of potential applications in basic research and industry become accessible.

In the purple sea urchin Strongylocentrotus purpuratus, the formation and mineralization of fracture-resistant skeletal elements such as the embryonic spicule require the combinatorial participation of numerous spicule matrix proteins such as the SpSM30A–F isoforms. However, because of limited abundance, it has been difficult to pursue extensive biochemical studies of the SpSM30 proteins and deduce their role in spicule formation and mineralization. To circumvent these problems, we expressed a model recombinant spicule matrix protein, rSpSM30B/C, which possesses the key sequence attributes of isoforms “B” and “C”. Our findings indicate that rSpSM30B/C is expressed in insect cells as a single polypeptide containing variations in glycosylation that create microheterogeneity in rSpSM30B/C molecular masses. These post-translational modifications incorporate O- and N-glycans and anionic mono- and bisialylated and mono- and bisulfated monosaccharides on the protein molecules and enhance its aggregation propensity. Bioinformatics and biophysical experiments confirm that rSpSM30B/C is an intrinsically disordered, aggregation-prone protein that forms porous protein hydrogels that control the in vitromineralization process in three ways: (1) increase the time interval for prenucleation cluster formation and transiently stabilize an ACC polymorph, (2) promote and organize single-crystal calcite nanoparticles, and (3) promote faceted growth and create surface texturing of calcite crystals. These features are also common to mollusk shell nacre proteins, and we conclude that rSpSM30B/C is a spiculogenesis protein that exhibits traits found in other calcium carbonate mineral modification proteins.

Given a certain binary phase, its crystal structure can usually be rationalized by thermodynamics and packing rules. However, there is still no fundamental understanding of how metastable solids form and how this is influenced by kinetic factors. Furthermore, the very early stages of crystallization remain vague. We present an experimental study using a binary mixture of colloidal particles as a model. Particle assembly is provoked by centrifugation, and the degree of separation can be adjusted precisely. Between the scenarios of random mixture (glassy state) and complete phase separation, conditions could be realized to facilitate the occurrence of various periodic structures in a single experiment. Some of these structures can only be explained by a dynamic, nonequilibrium and dissipative state. Eventually, the formation of certain metastable lattices can be interpreted as an emergent, systemic phenomenon. Thus, centrifugation can be used for studying the chaos–order transition in complex particle systems.

The worldwide trend in nanoparticle technology toward increasing complexity must be directly linked to more advanced characterization methods of size, shape and related properties, applicable to many different particle systems in science and technology. Available techniques for nanoparticle characterization are predominantly focused on size characterization. However, simultaneous size and shape characterization is still an unresolved major challenge. We demonstrate that analytical ultracentrifugation with a multiwavelength detector is a powerful technique to address multidimensional nanoparticle analysis. Using a high performance optical setup and data acquisition software, information on size, shape anisotropy and optical properties were accessible in one single experiment with unmatched accuracy and resolution. A dynamic rotor speed gradient allowed us to investigate broad distributions on a short time scale and differentiate between gold nanorod species including the precise evaluation of aggregate formation. We report how to distinguish between different species of single-wall carbon nanotubes in just one experiment using the wavelength-dependent sedimentation coefficient distribution without the necessity of time-consuming purification methods. Furthermore, CdTe nanoparticles of different size and optical properties were investigated in a single experiment providing important information on structure–property relations. Thus, multidimensional information on size, density, shape and optical properties of nanoparticulate systems becomes accessible by means of analytical ultracentrifugation equipped with multiwavelength detection.

Biomimetic composite materials consisting of vanadium pentoxide (V2O5) and a liquid crystal (LC) “gluing” polymer were manufactured exhibiting six structural levels of hierarchy, formed through LC phases. The organic matrix was a polyoxazoline with pendant cholesteryl and carboxyl units, forming a lyotropic phase with the same structural orientation extending up to hundreds of micrometers upon shearing, and binding to V2O5viahydrogen bridges. Composites consisting of V2O5–LC polymer hybrid fibers with a pronounced layered structuring were obtained. The V2O5–LC polymer hybrid fibers consist of aligned V2O5ribbons, composed of self-assembled V2O5sheets, encasing a chiral nematic polymer matrix. The structures of the V2O5–LC polymer composites strongly depend on the preparation method, i.e., the phase-transfer method from aqueous to organic medium, in which the polymer forms LC phases. Notably, highly defined micro- and nanostructures were obtained when initiating the synthesis using V2O5tactoids with preoriented nanoparticle building units, even when using isotropic V2O5dispersions. Shear-induced hierarchical structuring of the composites was observed, as characterized from the millimeter and micrometer down to the nanometer length scales using complementary optical and electron microscopy, SAXS, μCT, and mechanical nanoindentation.

In this study, the effect of centrifugal force on the assembly and crystallization of binary colloidal mixtures is demonstrated. Monolithic pieces have been prepared which are characterized by a structural gradient along the direction of the centrifugal force. For a given number ratio of monodisperse 154 and 300 nm latex spheres, the absolute latex concentration was varied and with it the sedimentation velocity of the individual particle species. For three different concentrations it has been demonstrated that the structure of the binary colloidal assembly obtained after centrifugation is affected significantly. For the largest initial latex absolute concentrations, the structural variation along the packed latex column in the ultracentrifuge tube is minimal, while a decrease in the absolute concentrations leads to crystalline packing in defined regions of the column. The observation of the thermodynamically favored structure resembling NaCl, but also of the aluminum boride AlB2analog as well as unordered, glass-like packing depending on the mutual latex concentration under unchanged particle number and size ratio, shows that by centrifugation kinetically favored states can be realized. This result implies that centrifugation of binary latex mixtures is a promising route for investigating the self-organization of binary colloidal systems since the sedimentation velocities of the two particle species are different, and thus the local concentrations and mixing ratios vary continuously also enabling rare packing motifs.

AbstractIt is demonstrated that magnesium and carbonate ions can form pre-nucleation clusters in analogy to calcium carbonate. If a mixed calcium and magnesium solution is brought in contact with carbonate ions, mixed pre-nucleation clusters form. The equilibrium constants for their formation are reported revealing that over the entire range of possible cation mixing ratios, calcium gets enriched over magnesium in the pre-nucleation clusters. This can explain high magnesium contents in amorphous calcium carbonate. However, this enrichment alone is not sufficient to explain the magnesium content of less than 41 mol% which is found in magnesium calcite biominerals nucleated from seawater.

AbstractProteins have found their way into many of Nature’s structures due to their structural stability, diversity in function and composition, and ability to be regulated as well as be regulators themselves. In this study, we investigate the constitutive amino acids that make up some of these proteins which are involved in CaCO3mineralization – either in nucleation, crystal growth, or inhibition processes. By assaying all 20 amino acids with vapor diffusion and in situ potentiometric titration, we have found specific amino acids having multiple effects on the early stages of CaCO3crystallization. These same amino acids have been independently implicated as constituents in liquid-like precursors that form mineralized tissues, processes believed to be key effects of biomineralization proteins in several biological model systems.

Biominerals are complex inorganic‐organic structures that often show excellent mechanical properties. Here a bio‐inspired study of a remarkably simple synthetic system is presented in which only one charged polymer additive (poly(sodium 4‐styrenesulfonate)) is able to induce hierarchical structuring of calcite similar to biominerals. The interaction of the negatively charged polymer with the nucleation and growth of the mineral, in particular via selective adsorption to internal and external (001) facets of the calcite lattice, implies structural features from the micrometer down to the nanometer level. The crystals exhibit a distinct rounded morphology and a controlled orientation. Moreover, the polymer molecules are occluded within the crystals with different concentrations in well‐defined regions. This leads to the induction of a mesoscale structure based on 100 nm sized mineral building blocks with granular substructure and rough surface, as well as small modifications of the crystallographic structure. Such a combination of hierarchically organized structural features has previously only been reported for biogenic calcite, which is typically grown in a complex process involving multiple organic additives. It is also shown that the organic occlusions in the calcite‐PSS hybrid crystals strongly affect the mechanical performance, as known for some biominerals.

Calcium carbonate precipitation proceeds via a complex multistage scenario involving neutral ion clusters as precursors and amorphous phases as intermediates, which finally transform to crystals. Although the existence of stable clusters in solution prior to nucleation has been demonstrated, the molecular mechanisms by which they precipitate are still obscure. Here, direct insight into the processes that drive the transformation of individual clusters into amorphous nanoparticles is provided by progressive colloidal stabilization of different transient states in silica‐containing environments. Nucleation of calcium carbonate in the presence of silica can only take place via cluster aggregation at low pH values. At higher pH, prenucleation clusters become colloidally stabilized and cannot aggregate. Nucleation through structural reorganization within the clusters is not observed under these conditions, indicating that this pathway is blocked by kinetic and/or thermodynamic means. The degree of stabilization against nucleation is found to be sufficient to allow for a dramatic enrichment of solutions with prenucleation clusters and enable their isolation into the dry state. This approach renders direct analyses of the clusters by conventional techniques possible and is thus likely to facilitate deeper insight into the chemistry and structure of these elusive species in the future.

Vanadium pentoxide mesocrystals were synthesized from a mineral liquid crystalline precursor phase, a so-called tactosol. For comparative evaluation of solid formation from that phase, the distance between the vanadium pentoxide particles was lowered by three different modes: (a) by adding a 0.1 M NaCl solution, the electric double layer was compressed and controlled particle aggregation was induced; (b) application of external pressure by ultracentrifugation resulted in particle compression and final crystallization; (c) an acrylic acid/sulfonic acid copolymer was added to introduce polymer-mediated particle alignment and densification. In all three cases, the preorientation of the particles within the liquid crystal remained, and different mesocrystals were formed. This was demonstrated by comparative analysis of the resulting structures by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and polarization microscopy.

Europium(III) fluoride mesocrystals were synthesised in an organic matrix. This matrix is a gel formed by Eu3+ions and a polycarboxylate/sulfonate copolymer, ACUSOL 588G. In the gel phase, the local amount of europium ions is very high since Eu3+acts as a crosslinker, and crystallisation occurs upon addition of F–. Nucleated seed crystals in the gel phase grow by further ion attachment and form mesocrystals by mutual orientation of the EuF3particles in the gel. We propose a dipole field as reason for this alignment and that the dipolar character of the particles originates from adsorption of the polyelectrolyte on charged crystal faces.

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