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Rietveld method has been applied to refine the structure of magnesium substituted β-tricalcium phosphate at a magnesium content of about 14 mol%. The results of the refinements, which show a final agreement factor Rwp = 0.12, are in agreement with an almost complete substitution in two of the five crystallo-graphically independent cation sites. The preference of magnesium for these two sites can be explained on the basis of the coordination geometry of the five different cation sites. Furthermore the results allow to interpret the discontinuity found around 10 magnesium mol% in the variation of the c axis as a function of magnesium content.

Poly-L-glutamic (pGlu) and poly-L-aspartic (pAsp) acids, as analogues of naturally occurring soluble acidic proteins, were used to investigate specific interactions between the acidic polypeptides and calcite as a mineral surface. A basic polypeptide (poly-L-lysine, pLys) served as a negative control for testing the role of conformity between the substrate and the adsorbed polypeptides in biomineralization processes. The kinetics of calcite crystal growth was determined in a simplified precipitation model system by inoculating well defined calcite seed crystals into a moderately supersaturated solution containing one of the polypeptides. From the kinetic data, the mode and extent of the calcite/polypeptide interactions were determined. The parabolic rate law was found to be valid for the calcite crystal growth, the integration of ions into the spiral steps at the calcite crystal surface being the rate-determining mechanism. Small amounts of pGlu or pAsp caused an inhibition of calcite crystal growth, the effect being pAsp > pGlu, and the exponential dependence of the growth rate on supersaturation confirmed that surface nucleation was the growth controlling mechanism in the presence of the two acidic polypeptides. The pLys non-selective, weak, electrostatic adsorption at the crystal surface was probably responsible for increasing the calcite growth rate at low concentrations and for inhibiting it at higher concentrations. The strongest interactions between the crystal surfaces and the polypeptides were observed for the calcite/pAsp systems. They could be accounted for by coordinative interactions between the side chain carboxylic groups of the predominantly planar arrangement of the pAsp structure (β -pleated sheet) and Ca2+ ions from the calcite surface.

Since the 1991 discovery of hollow cylindrical carbon-based unidimensional structures, the nanotubular form of matter has been thoroughly investigated leading to a wealth of literature. Their particular features are not limited to graphite but are common in many inorganic highly anisotropic two-dimensional layered compounds. The first non-mineral inorganic nanotubes, constituted of lamellar molybdenum and tungsten disulfides, were synthesized in 1992. Afterwards, a large number of inorganic nanotubes have been synthesized, opening the path to the development of nanoelectronics, due to their dielectric properties. The unique mineral phase that crystallizes with a tubular morphology is chrysotile, which has been tentatively used to prepare ultra-thin wires by filling its hollow nanodimensional core with a conductive material. To overcome its natural heterogeneity in composition, morphology, and structure, synthetic chrysotile-inspired nanotubes have been recently synthesized. These geoinspired nanotubes can be prepared with specific properties, finalized to focused achievements such as preparation of new quantum wires. The existing knowledge on the structural and physicochemical properties of mineral and synthetic chrysotile nanotubes is reviewed, with the aim of emphasizing their potential applications as nonlinear optical and conducting technological devices. Bibliography encompasses over one hundred references.

Integrating carbon nanoparticles (CNPs) with proteins to form hybrid functional assemblies is an innovative research area with great promise for medical, nanotechnology, and materials science. The comprehension of CNP–protein interactions requires the still-missing identification and characterization of the ‘binding pocket’ for the CNPs. Here, using Lysozyme and C60 as model systems and NMR chemical shift perturbation analysis, a protein–CNP binding pocket is identified unambiguously in solution and the effect of the binding, at the level of the single amino acid, is characterized by a variety of experimental and computational approaches. Lysozyme forms a stoichiometric 1:1 adduct with C60 that is dispersed monomolecularly in water. Lysozyme maintains its tridimensional structure upon interaction with C60 and only a few identified residues are perturbed. The C60 recognition is highly specific and localized in a well-defined pocket.

The crystallization of skeletal aragonite by corals takes place in sites whose physical characteristics resemble those of a highly viscous sol or a gel. In these sites, biomolecules are secreted by calicoblast cells of the coral and some of them become entrapped in the skeleton. To explore the biomineralization process, a series of calcium carbonate crystallization experiments were carried out in a counter-diffusion system (CDS) containing a viscous agarose sol with two dissolved intra-skeletal soluble organic matrices (SOM) that were extracted from Balanophyllia europaea, a zooxanthellate coral, and Leptopsammia pruvoti, an azooxanthellate species. The influence of the viscosity of the media and the presence of Mg2+ were investigated in two additional sets of experiments, one using an agarose gel of variable viscosity, and another allowing Mg2+ to diffuse from the cationic reservoir. The main findings are the following: (i) the species-specific molecular composition of the two SOMs has a different impact on the crystallization parameters and morphology of calcium carbonate; (ii) the viscosity of the gelling media, and thus its porosity, is important in regulating the SOM action; (iii) Mg2+ is important in defining specific and sharp limits of supersaturation under which crystallization occurs; (iv) the polymorph distribution is determined by SOM concentration. Thus, through the use of the CDS, it was possible to first study in vitro the biomineralization of zooxanthellate and azooxanthellate corals.

A growing number of classes of organic (macro)molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites. © The Royal Society of Chemistry 2013.

Many mineralization processes occur in convection-free conditions. Understanding these processes requires knowledge of crystal nucleation and growth processes in gels or high viscous sol systems. In this work, the crystallization parameters of calcium carbonate in an agarose viscous sol using counterdiffusion crystallization were monitored as a function of time. Additionally, by comparing the precipitation parameters in the high viscous sol entrapping charged polypeptides, namely, poly-l-lysine (pLys), poly-l-aspartate (pAsp), and poly-l-glutamate (pGlu), it was possible to establish the polypeptide capability to inhibit, or eventually promote, the calcium carbonate nucleation and/or crystal growth processes. The polymorphism and morphology of the precipitates indicate that pLys only influences the growth mechanism of calcium carbonate without affecting the nucleation process. On the contrary, pAsp and, to a minor extent, pGlu affect both nucleation and growth. The application of this analysis can be extended to other additives and macromolecules able to affect crystallization processes.

Acid catalysts were prepared by sulfonation of carbon materials obtained from the pyrolysis of sugar beet molasses, a cheap, viscous byproduct in the processing of sugar beets into sugar. Conditions for the pyrolysis of molasses (temperature and time) influenced catalyst performance; the best combination came from pyrolysis at low temperature (420 °C) for a relatively long time (8-15 h), which ensured better stability of the final material. The most effective molasses catalyst was highly active in the esterification of fatty acids with methanol (100 % yield after 3 h) and more active than common solid acidic catalysts in the transesterification of vegetable oils with 25-75 wt % of acid content (55-96 % yield after 8 h). A tandem process using a solid acid molasses catalyst and potassium hydroxide in methanol was developed to de-acidificate and transesterificate algal oils from Chlamydomonas reinhardtii, Nannochloropsis gaditana, and Phaeodactylum tricornutum, which contain high amounts of free fatty acids. The amount of catalyst required for the de-acidification step was influenced by the chemical composition of the algal oil, thus operational conditions were determined not only in relation to free fatty acids content in the oil, but according to the composition of the lipid extract of each algal species.

In protein crystallization trials there is always some ambiguity in defining if the nucleation event occurred by a homogeneous or a heterogeneous process. One of the reasons comes from the difficulty to compare experiments with or without a heterogeneous nucleant under the same chemical conditions. The outcome is that it is difficult to figure out the values of supersaturation addressing homo- versus heterogeneous nucleation. Recently it has been shown that the crystallization mushroom allows performance of sitting drop vapor diffusion experiments under identical physical-chemical conditions and that functionalized surfaces are favorable heterogeneous substrates for protein crystallization. With the aim to discriminate between nucleation processes, three model proteins, lysozyme, glucose isomerase, and thaumatin, have been crystallized at different starting concentrations, using positively and negatively charged surfaces, in the crystallization mushroom. The results show that (i) the heterogenenous nucleation does not crucially affect the nucleation process under conditions of high supersaturation and that (ii) the nucleating action of the fianctionalized surfaces is mainly related to their superficial charge distribution more than to their absolute charge, according to both classical and colloidal nucleation theories.

Precipitation of calcium carbonate in different carrageenan gelling environments was initiated by fast mixing of calcium chloride and sodium carbonate solutions. Carrageenan concentration and the gelling mechanism, controlled by the addition of different cross-linking cations, calcium or sodium, were varied in order to elucidate the mechanism and dynamic of solid phase formation in highly supersaturated precipitation systems in which initial formation of three calcium carbonate polymorphs and amorphous calcium carbonate is possible. The analysis of the samples isolated 5 days after initiating the precipitation showed that calcite was the only solid phase obtained in the whole range of carrageenan concentrations investigated. At lower carrageenan concentrations, the calcite aggregates were observed, while at higher concentrations rhombohedral crystals of uniform size distribution were found. Spherical imprints on the surfaces of calcite particles precipitated at lower gel concentrations were observed, thus pointing out the initial and simultaneous precipitation of stable calcite and metastable calcium carbonate phases, vaterite and possibly amorphous calcium carbonate. Time resolving precipitation experiments within gelling media of low concentration confirmed such an assumption and implied the solution mediated mechanism of transformation of metastable vaterite, which was in close contact with calcite crystals. Reference precipitation systems, performed at apparently similar initial supersaturation and hydrodynamic conditions but without the presence of carrageenan, showed a comparable pattern of stepwise solution mediated transformation of metastable amorphous calcium carbonate and vaterite into calcite

The synthesis of the small pseudopeptide Boc-L-Phe-D-Imz-OBn (Imz = imidazolidin-2-one-4-carboxylate) is reported. Crystallization of this peptide from methanol, ethanol, and isopropanol leads to isostructural solvates when the solvent is methanol or ethanol with a peptide/solvent ratio of 2:1 and to an unsolvated polymorph in the case of isopropanol. The solvate peptide crystallizes forming infinite chains with the monomers in parallel orientation connected by a single hydrogen bond. The chains are arranged in antiparallel direction and cross-linked through the NH group of the imidazolidin heterocycle with formation of a stable 2D network. Crystals from isopropanol form a different 2D network. The degree of order in the crystal assembly decreases from methanol and ethanol solvates to the unsolvated pseudopeptide grown from isopropanol. Quantum chemical calculations at the HF/6-31G* level of ab initio MO theory, carried out on the two different packings, show a slight preference for the unsolvated packing.

The two epimers Boc-l-Phe-d-Oxd-(S)-β3-hPhg-OBn (1) and Boc-l-Phe-d-Oxd-(R)-β3-hPhg-OBn (2) have been prepared by standard methods in solution, and their conformation was analyzed both in solution ...

The effectiveness of some seawater components, such as magnesium, potassium, sodium, sulfate and chloride ions, and humic acid, in the control of calcium carbonate composition, morphology, and phase distribution was studied. These components were tested singularly, in pairs, and all together. It was observed that magnesium ions phase distribution control is influenced by the presence of other ions and that in the presence of a high content of magnesium ions monohydrocalcite precipitates. Moreover, in the presence of magnesium or potassium ions the calcite crystals show modified rhomohedral morphologies, while the presence of sulfate ions favors their aggregation. Humic acids have an inhibition effect on calcium carbonate precipitation, induce the formation of empty spheres of vaterite, and modify the calcium carbonate phase distribution. The isomorphic substitution of magnesium to calcium in the calcite structure is favored by some seawater ions and enhanced by the presence of humic acids.

Comb-like polymers have an important application in cement industries, where they are referred to as polymeric admixtures/superplasticizers. They are used to increase the workability of fresh cementitious mixtures as well as to improve the strength and durability of the hardened state. So far, the interaction of polymer/Portland-limestone cement particles has been poorly investigated. This paper describes the overgrowth of calcite on Portland-limestone cement particles, a mixture of ground clinker and calcite, in the presence of comb-like polymers. The morphological and aggregational variation of overgrown calcite crystals is used as a model to evaluate the interaction occurring between cement particles and polymeric admixtures. Rhombohedral, spherulitic, microtrumpet, or fibrous calcite crystals were observed as a function of the kind of cement particles and comb-like polymers used. These results suggest that comb-like polymers may assume diverse conformations when associated with the different particles that constitute Portland-limestone cement.

The chemical conjugation of bisphosphonates (BPs), specifically alendronate, to hydroxyapatite could be an effective means to impart to it fine-tuned bioactivity. Horse heart myoglobin (Mb), a well-characterized protein, has been adsorbed onto biomimetic hydroxyapatite nanocrystals (nHA) and onto the nHA/alendronate conjugate powdered samples. The obtained materials have potential use in bone implantation and as prospective drug-delivery devices. The kinetic absorption of Mb onto nHA is dramatically affected by its functionalization with alendronate. The covering of the nHA surface by alendronate inhibits the adsorption of myoglobin. The adsorption mechanisms of the protein were studied by spectroscopic techniques (UV−vis and surface-enhanced Raman spectroscopy). The results indicate that the protein changes conformation upon adsorption on the inorganic substrate. In particular, the interaction with nHA alters the coordination state of the iron in the heme through the formation of a hexacoordinated low-spin Mb heme, possibly involving the distal histidine. Instead, the covering of the nHA surface by alendronate does not adsorb the protein but preserves the coordination state of the heme moiety. This study could be of significance either in the field of biomaterials science, in particular, to fine tune a bone-specific drug delivery device and to test nHA as a new support for heterogeneous catalysis, improving the understating of enzyme immobilization.

In the cement industries the use of plasticizer additives, referred to as admixtures, to increase the material workability is of growing interest. Polymeric admixtures are sulfonate or carboxylate polyelectrolytes, the last had been recently also grafted with methoxy poly(ethylene glycol) chains. Their structure and chemical composition recall the acidic macromolecules hosted by several mineralized tissues. The mechanism of action of the polymeric admixtures on cement hydration and carbonation is still poorly understood. Here, we report a study on the variations in the calcium carbonate morphology and polymorphism induced by the presence of commercial polymeric admixtures, since calcium carbonate is one of the products of cement carbonation. We found that the conformation of the polymeric admixtures, the kind of charged functional groups and the presence of grafted chains are the crucial parameters for the specific control of the calcite crystals size and morphology. The formation of crystalline faces already observed in biogenic calcites, as function of the presence of carboxylate or sulfonate groups in the polymeric chain, was obtained. This work evidences an analogy between the polymeric admixtures and the acid macromolecules with respect to calcium carbonate crystallization and the gained information are of interest both for the cement industries and to the understanding of the biomineralization processes.