PAA-PAMPS copolymers as an efficient tool to control CaCO3 scale formation.

Scale formation, the deposition of certain minerals such as CaCO3, MgCO3, and CaSO4·2H2O in industrial facilities and household devices, leads to reduced efficiency or severe damage. Therefore, incrustation is a major problem in everyday life. In recent years, double hydrophilic block copolymers (DHBCs) have been the focus of interest in academia with regard to their antiscaling potential. In this work, we synthesized well-defined blocklike PAA-PAMPS copolymers consisting of acrylic acid (AA) and 2-acrylamido-2-methyl-propane sulfonate (AMPS) units in a one-step reaction by RAFT polymerization. The derived copolymers had dispersities of 1.3 and below. The copolymers have then been investigated in detail regarding their impact on the different stages of the crystallization process of CaCO3. Ca(2+) complexation, the first step of a precipitation process, and polyelectrolyte stability in aqueous solution have been investigated by potentiometric measurements, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). A weak Ca(2+) induced copolymer aggregation without concomitant precipitation was observed. Nucleation, early particle growth, and colloidal stability have been monitored in situ with DLS. The copolymers retard or even completely suppress nucleation, most probably by complexation of solution aggregates. In addition, they stabilize existing CaCO3 particles in the nanometer regime. In situ AFM was used as a tool to verify the coordination of the copolymer to the calcite (104) crystal surface and to estimate its potential as a growth inhibitor in a supersaturated CaCO3 environment. All investigated copolymers instantly stopped further crystal growth. The carboxylate richest copolymer as the most promising antiscaling candidate proved its enormous potential in scale inhibition as well in an industrial-filming test (Fresenius standard method).

Ab†Initio structure determination of vaterite by automated electron diffraction.

"This is a mineral about which there has been much discussion" is a typical statement about vaterite in older standard textbooks of inorganic chemistry. This polymorph of CaCO(3) was first mentioned by H. Vater in 1897, plays key roles in weathering and biomineralization processes, but occurs only in the form of nanosized crystals, unsuitable for structure determination. Its structure could now be solved by automated electron diffraction tomography from 50 nm sized nanocrystals.

Transformation of vaterite nanoparticles to hydroxycarbonate apatite in a hydrogel scaffold: relevance to bone formation.

Biomimetic materials have been gaining increasing importance for use as bone biomaterials, because they may provide regenerative alternatives for the use of autologous tissues for bone regeneration. We demonstrate a promising alternative for the use of biomimetic materials based on a biodegradable PEG hydrogel loaded with vaterite nanoparticles as mineral storage. Vaterite, the least stable CaCO3 polymorph, is stable enough to ensure the presence of a potential ion buffer for bone regeneration, but still has sufficient reactivity for the transformation from CaCO3 to hydroxyapatite (HA). A combination of powder X-ray diffraction (PXRD), electron microscopy, and Fourier-transform infrared (FT-IR) and Raman spectroscopy showed the transformation of vaterite nanoparticles incorporated in a PEG-acetal-DMA hydrogel to hydroxycarbonate apatite (HCA) crystals upon incubation in simulated body fluid at human body temperature within several hours. The transformation in the PEG-acetal-DMA hydrogel scaffold in simulated body fluid or phosphate saline buffer proceeded significantly faster than for free vaterite. The vaterite-loaded hydrogels were free of endotoxin and did not exhibit an inflammatory effect on endothelial cells. These compounds may have prospects for future applications in the treatment of bone defects and bone degenerative diseases.

Designed peptides for biomineral polymorph recognition: a case study for calcium carbonate.

With their unique ability for substrate recognition and their sequence-specific self-assembly properties, peptides play an important role in controlling the mineralization of inorganic materials in natural systems and in controlling the assembly of soft materials into complex structures required for biological functions. Here we report the use of an engineered heptapeptide that can differentiate between the crystalline anhydrous polymorphs of calcium carbonate. This peptide contains the positively charged amino acid arginine as well as proline rather than the prototypical negatively charged aspartate or glutamate units. Its affinity to vaterite compared to aragonite was demonstrated by fluorescence microscopy using biotinylated peptides. Crystallization experiments in the presence of the vaterite-affine peptide afforded only vaterite, whereas a mutant peptide, where a proline residue was replaced by glycine, exclusively leads to the formation of calcite.

Versatile wet-chemical synthesis of non-agglomerated CaCO3 vaterite nanoparticles.

Calcium carbonate (vaterite) nanoparticles of 20-60 nm size were obtained without stabilizing tensides by heating a dispersion of calcium bicarbonate (CaHCO(3)) in ethylene glycol for 30 minutes at 40 to 100 °C.