2009-08-10, Perriman, Adam W., Cölfen, Helmut, Hughes, Roy W., Barrie, Claire L., Mann, Stephen

Molten proteins: Warming a freeze-dried powder of a stoichiometric ferritin–polymer ionic construct produces a solvent-free liquid protein that exhibits viscoelastic and thermotropic liquid-crystalline properties at 30 °C (see polarized-light micrograph), and transforms into a Newtonian fluid above 40 °C.

2009-07-10, Ma, Yurong, Mehltretter, Gerald, Plüg, Carsten, Rademacher, Nadine, Schmidt, Martin U., Cölfen, Helmut

Organic pigments are important crystalline substances, and their properties and applications rely on size and shape control. Pigment Yellow 181 (PY181) is an industrial azo pigment that is light and weatherfast and suitable for high temperature processing. One disadvantage is its needle-like shape in the default β-phase, which makes the pigment difficult to process in industry, e.g., in polymer melts, where a spherical structure would be ideal. Here, we show for the first time, that polymer-induced liquid precursor structures can be formed even in association to a chemical reaction. Furthermore, it is demonstrated that biomineralization principles can be exploited for the generation of advanced functional materials, such as pigments with novel complex morphology and different properties. Stable PY181 microspheres of nanoplates in the β-phase were obtained in mixed solvents of water and isopropanol by direct azo coupling under the directing influence of a designed copolymer additive aminobenzoylaminobenzamide-acetoacetyl-poly(ethylene imine)-block-poly(ethylene glycol) (ABABA-acetoacetyl-PEI-b-PEG).

2009-01-02, Song, Rui-Qi, Xu, An-Wu, Antonietti, Markus, Cölfen, Helmut

A Platonic relationship: Calcite single and mesocrystals with two platonic shapes and minimal surfaces are formed by a unified polymer-controlled nanoparticle aggregation. The shapes of the crystals (see picture for example) are tuned by the reactant concentration. The morphogenesis follows a nonclassical mechanism. A rhombohedral primitive minimal surface was observed for the first time in a synthetic crystallization of micrometer-sized particles.

2009, Gebauer, Denis, Verch, Andreas, Börner, Hans G., Cölfen, Helmut

Calcium carbonate is an abundant biomineral with fascinating shapes and properties. Much effort is spent to study how creatures can control mineral formation. We present a quantitative study of the early stage of calcium carbonate precipitation in the presence of artificial peptide additives, the sequences of which were derived in phage assays to have aragonite binding affinity. A novel crystallization assay shows that the peptide additives inhibit nucleation of calcite. Analysis of the precipitated particles and comparison with nucleation inhibition confirm our recent findings, which suggest that calcitic and vateritic short-range order is already preformed in stable prenucleation clusters, which form amorphous intermediates after nucleation reflecting similar structures and finally become crystalline. In the long run, this process facilitates the control of polymorph formation by the design of the binding affinity of additives to different polymorphs (i.e., the polymorph bound weakest by the additive is to be formed as its formation is least inhibited). These findings facilitate a novel understanding of mineralization control and provide a basis for the analysis of biological peptide sequences and for the analysis of their role in biomineralization processes.

2009-08-03, Salwiczek, Mario, Samsonov, Sergey, Vagt, Toni, Nyakatura, Elisabeth, Fleige, Emanuel, Numata, Jorge, Cölfen, Helmut, Pisabarro, M. Teresa, Koksch, Beate

Systematic model investigations of the molecular interactions of fluorinated amino acids within native protein environments substantially improve our understanding of the unique properties of these building blocks. A rationally designed heterodimeric coiled coil peptide (VPE/VPK) and nine variants containing amino acids with variable fluorine content in either position a16 or d19 within the hydrophobic core were synthesized and used to evaluate the impact of fluorinated amino acid substitutions within different hydrophobic protein microenvironments. The structural and thermodynamic stability of the dimers were examined by applying both experimental (CD spectroscopy, FRET, and analytical ultracentrifugation) and theoretical (MD simulations and MM-PBSA free energy calculations) methods. The coiled coil environment imposes position-dependent conformations onto the fluorinated side chains and thus affects their packing and relative orientation towards their native interaction partners. We find evidence that such packing effects exert a significant influence on the contribution of fluorine-induced polarity to coiled coil folding.

2009-05-15, Dieckmann, Yvonne, Cölfen, Helmut, Hofmann, Heinrich, Petri-Fink, Alke

We performed particle size and particle size distribution measurements for L-cysteine-stabilized ZnS/Mn nanoparticles in the size region below 10 nm. For this we applied transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), dynamic light scattering (DLS), and asymmetric flow field flow fractionation (aF-FFF) measurements, and we calculated particle sizes with the help of X-ray diffraction (XRD) patterns and the shift of the band gap absorption in the UV-vis spectrum. The different methods are explained, and their limitations are discussed, with the conclusion that only a combination of different techniques can yield a realistic and complete picture about the size distribution of the sample. From these methods TEM, AUC, DLS, and aF-FFF measure the actual particle size distribution either in dispersion or after drying of the sample, whereas the particle size obtained from XRD patterns and with the help of the band gap widening corresponds to the average size of the crystal domains within the particles. We obtained particle size distributions with their maximum between 3 and 7 nm and a mean crystallite size of 3.5-4 nm.

2009, Zhu, Jian-Hua, Yu, Shu-Hong, Xu, An-Wu, Cölfen, Helmut

A facile biomimetic method is reported for the synthesis of novel BaCO₃ nanofibres with double-stranded and cylindrical helical morphologies via a phosphonated block co-polymer -controlled mineralization process.

2009-07-28, Song, Rui-Qi, Cölfen, Helmut, Xu, An-Wu, Hartmann, Jürgen, Antonietti, Markus

Besides the classical atom/ion/molecule based mechanism, nonclassical crystallization provides a nanoparticle-based crystallization pathway toward single crystals. However, there is a lack of experimentally established strategies for engineering a range of crystalline microstructures from common nanoparticles by nonclassical crystallization. We demonstrate that a commercial random copolymer polyelectrolyte poly(4-styrene sulfonate)-co-(maleic acid) (PSS-co-MA) considerably guides crystallization of calcium carbonate (CC) with a high versatility. The bioinspired nonclassical crystallization protocol yielded a series of calcite microstructures. Calcite single crystals obtained at low supersaturation show a pseudo-dodecahedral shape with curved faces, whereas increasing supersaturation generated calcite mesocrystals with pseudo-octahedral shapes and scalloped surfaces. Further increase of supersaturation induced the formation of polycrystalline multilayered and hollow spheres. In the initial growth stage of all these microstructures, amorphous CC nanoparticles formed as the early product. Remarkably, microparticles with minimal primitive (P)-surface were captured as the prominent intermediate indicative of liquidlike behavior. Moreover, nanogranular structures exist broadly in the as-synthesized crystals. These results demonstrate that the polyelectrolyte can effectively stabilize the amorphous CC nanoparticle precursors, impart control over the evolution from amorphous precursors via a liquid aggregate through P-surface intermediates to the final crystals, and thus allow the morphogenesis. Simple variation of calcium and polyeletrolyte concentrations enables a systematic control over the size and morphology of particles among pseudo-dodecahedra, pseudo-octahedra, multilayered spheres, and hollow spheres, which are expressed in a morphology diagram. A unifying nanoparticle aggregation formation mechanism was suggested to explain the morphogenesis by the combination of nonclassical crystallization and surface area minimization principles.

2009-01-02, Song, Rui-Qi, Xu, An-Wu, Antonietti, Markus, Cölfen, Helmut

Durch polymerkontrollierte Nanopartikelaggregation wurden Calciteinkristalle und -mesokristalle mit zwei platonischen Formen und Minimaloberflächen hergestellt. Die Kristallform wurde über die Reaktantenkonzentration eingestellt (Beispiel siehe Bild). Die Morphogenese erfolgte über eine nichtklassische Kristallisation. Erstmals wurde eine rhomboedrische primitive Minimaloberfläche bei einer synthetischen Kristallisation mikroskaliger Partikel beobachtet.

2009, Wang, Tongxin, Verch, Andreas, Börner, Hans G., Cölfen, Helmut, Antonietti, Markus

A family of calcite nanocrystal superstructures with unusual morphology were obtained from crystallization of calcite by the CO₂ gas diffusion technique in the presence of a bioinspired double hydrophilic block copolymer, polyethyleneglycol-block-poly (L-aspartic acid). From the typical calcite rhombohedra as a starting situation, the morphology can be systematically varied via various unusual porous mesocrystal morphologies to hemispheres composed of fine calcite triangles. The formation of mesocrystals is starting at a polymer concentration of only 10^-3 g/L and shows two remarkable results: (a) the reported bio-inspired block copolymer is the so far most active polymer for mesocrystal formation reported to our knowledge, and (b) the data prove that nucleation promoters exist, which can form nanocrystals for mesocrystal formation even without enhanced colloidal stabilization. This gives mesocrystal formation a much broader operation range than previously assumed.