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Biomimetic apatite coatings were obtained by soaking chemically treated titanium in SBF with different HCO(3)(-) concentration. XRD, FTIR and Raman analyses were used to characterize phase composition and degree of carbonate substitution. The microstructure, elemental composition and preferred alignment of biomimetically precipitated crystallites were characterized by cross-sectional TEM analyses. According to XRD, the phase composition of precipitated coatings on chemically pre-treated titanium after exposure to SBF was identified as hydroxy carbonated apatite (HCA). A preferred c-axis orientation of the deposited crystals can be supposed due to the high relative peak intensities of the (002) diffraction line at 2theta=26 degrees compared to the 100% intensity peak of the (211) plane at 2theta=32 degrees . The crystallite size in direction of the c-axis of HCA decreased from 26 nm in SBF5 with a HCO(3)(-) concentration of 5 mmol/l to 19 nm in SBF27 with a HCO(3)(-) concentration of 27 mmol/l. Cross-sectional TEM analyses revealed that all distances correspond exactly to the hexagonal structure of hydroxyapatite. The HCO(3)(-) content in SBF also influences the composition of precipitated calcium phosphates. Biomimetic apatites were shown to have a general formula of Ca(10-x-y)Mg(y)(HPO(4))(x-z)(CO(3))(z)(PO(4))(6-x)(OH)(2-x-w)(CO(3))(w/2). According to FTIR and Raman analyses, it can be supposed that as long as the HCO(3)(-) concentration in the testing solutions is below 20 mmol/l, only B-type HCA (0<z<1; w=0) precipitates. At higher HCO(3)(-) concentration, it can be assumed that AB-type HCA (z=1;0<w<1) is formed.
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PMID:Biomimetic apatite coatings--carbonate substitution and preferred growth orientation. 1785 64

In CaCO3, biomineralization nucleation and growth of the crystals are related to the presence of carboxylate-rich proteins within a macromolecular matrix, often with organized beta-sheet domains. To understand the interplay between the organic template and the mineral crystal it is important to explicitly address the issue of structural adaptation of the template during mineralization. To this end we have developed a series of self-organizing surfactants (1-4) consisting of a dodecyl chain connected via a bisureido-heptylene unit to an amino acid head group. In Langmuir monolayers the spacing of these molecules in one direction is predetermined by the hydrogen-bonding distances between the bis-urea units. In the other direction, the intermolecular distance is determined by steric interactions introduced by the side groups (-R) of the amino acid moiety. Thus, by the choice of the amino acid we can systematically alter the density of the surfactant molecules in a monolayer and their ability to respond to the presence of calcium ions. The monolayer films are characterized by surface pressure-surface area (pi-A) isotherms, Brewster angle microscopy, in-situ synchrotron X-ray scattering at fixed surface area, and also infrared reflection absorption spectroscopy (IRRAS) of films transferred to solid substrates. The developing crystals are studied with scanning and transmission electron microscopy (SEM, TEM), selected area electron diffraction (SAED), and crystal modeling. The results demonstrate that although all compounds are active in the nucleation of calcium carbonate, habit modification is only observed when the size of the side group allows the molecules to rearrange and adapt their organization in response to the mineral phase.
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PMID:Template adaptability is key in the oriented crystallization of CaCO3. 1794 71

To investigate the role and importance of nondirectional electrostatic interactions in mineralization, we explored the use of Langmuir monolayers in which the charge density can be tuned using supramolecular interactions. It is demonstrated that, in mixed Langmuir monolayers of bis-ureido surfactants containing oligo(ethylene oxide) and ammonium head groups associated with matching or nonmatching spacers between the two urea groups, the organization is controlled by molecular recognition. These different organizations of the molecules lead to different nucleation behavior in the mineralization of calcium carbonate. The formation of modified calcite and vaterite crystals was induced selectively by different phases of mixed monolayers, and they were characterized by SEM, TEM, and SAED. To understand the influence of the mixed Langmuir monolayers on the crystallization process, we studied the mixtures by means of (pi-A) isotherms and Brewster angle microscopy observations. Infrared reflection-absorption spectroscopy experiments were also performed on Langmuir-Schaefer films. From these results, we conclude that the local organization of the two systems discussed here gives rise to differences in both charge density and flexibility that together determine not only polymorph selection and the nucleation face but also the morphology of the resulting crystals.
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PMID:Molecular recognition controls the organization of mixed self-organized bis-urea-based mineralization templates for CaCO(3). 1797 13

Nanocrystalline Lu2O3:Eu3+ was prepared by co-precipitation method using ammonium hydrogen carbonate and ammonium oxalic acid as precipitants, respectively. The crystal structure and morphology were analyzed by means of XRD and TEM. The resultant powders were sintered into transparent ceramics in vacuum and then in nitrogen without any additive. The surface morphology of the unpolished sintered specimens was characterized using SEM. The effect of different precipitants on microstructure of the nanopowders and transparency of the ceramics are compared. The excitation and emission spectra of Lu2O3:Eu3+ powders and ceramics were measured at room temperature by using synchrotron radiation as the light source. The fluorescence decay times of all specimens were analyzed. Luminescence of the ceramics decays faster than the corresponding nanopowders.
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PMID:Effects of precipitant on microstructure and luminescent properties of Lu2O3:Eu3+ nanopowders and ceramics. 1798 Oct 80

Calcium carbonate biomineralization uses complex assemblies of macromolecules that control the nucleation, growth, and positioning of the mineral with great detail. To investigate the mechanisms involved in these processes, for many years Langmuir monolayers have been used as model systems. Here, we descibe the use of cryogenic transmission electron microscopy in combination with selected area electron diffraction as a quasi-time-resolved technique to study the very early stages of this process. In this way, we assess the evolution of morphology, polymorphic type, and crystallographic orientation of the calcium carbonate formed. For this, we used a self-assembled Langmuir monolayer of a valine-based bisureido surfactant (1) spread on a CaCl2-containing subphase and deposited on a holey carbon TEM grid. In a controlled environment, the grid is exposed to an atmosphere containing NH3 and CO2 (the (NH4)2CO3 diffusion method) for precisely determined periods of time (reaction times 30-1800 s) before it was plunged into melting ethane. This procedure allows us to observe amorphous calcium carbonate (ACC) particles growing from a few tens of nanometers to hundreds of nanometers and then crystallizing to form [00.1] oriented vaterite. The vaterite in turn transforms to yield [10.0] oriented calcite. We also performed the reaction in the absence of monolayer or in the presence of a nondirective monolayer of surfactant containing an oligo(ethylene oxide) 2 head group. Both experiments also showed the formation of a transient amorphous phase followed by a direct conversion into randomly oriented calcite crystals. These results imply the specific though temporary stabilization of the (00.1) vaterite by the monolayer. However, experiments performed at higher CaCl2 concentrations show the direct conversion of ACC into [10.0] oriented calcite. Moreover, prolonged exposure to the electron beam shows that this transformation can take place as a topotactic process. The formation of the (100) calcite as final product under different conditions shows that the surfactant is very effective in directing the formation of this crystal plane. In addition, we present evidence that more than one type of ACC is involved in the processes described.
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PMID:A quasi-time-resolved CryoTEM study of the nucleation of CaCO3 under langmuir monolayers. 1830 94

Recently, we reported a temperature-sensitive biodegradable diblock copolymer of monomethoxy-poly(ethylene glycol)-b-poly(trimethylene carbonate) (mPEG-PTMC; Macromolecules 2007, 40, 5519-5525). In this paper, we report the detailed morphological transition of the polymer in water as a function of polymer concentration and temperature, using cryo-transmission electron microscopy (cryo-TEM). At a low polymer concentration (0.05 wt %), the mPEG-PTMC diblock copolymers formed vesicles in water. On the other hand, vesicle-to-micelle transition was observed as the polymer concentration increased. The polymer predominantly formed micelles above 2.0 wt %. In the 2.0 wt % polymer solution, the mPEG-PTMC underwent spherical micelle-to-tubular nanostructure transition as the temperature increased from 10 to 40 degrees C, and the transition accompanied an increase in turbidity of the polymer aqueous solution due to the increase in the apparent size of the polymer aggregates. Here, we report that the morphology of vesicles, spherical micelles, and tubular nanostructures is reversibly controlled by a thermosensitive polymer of mPEG-PTMC and the variation of the morphology can be carefully traced by using cryo-TEM. This paper will not only provide an important method for morphological control of an amphiphilic polymer but also improve our understanding of a temperature-sensitive transition mechanism of the polymer.
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PMID:Vesicle-to-spherical micelle-to-tubular nanostructure transition of monomethoxy-poly(ethylene glycol)-poly(trimethylene carbonate) diblock copolymer. 1852 76

Aqueous interfaces are of paramount importance in the study of biological systems as well as in the biomedical sciences. To study these interfaces at the nanometer level it is of interest to develop methods that allow their observation with cryogenic transmission electron microscopy (cryo-TEM). Prevention of dehydration to preserve the "native" state during sample preparation prior to vitrification is often one of the most important parameters to control in cryo-TEM experiments. For the preparation of these types of samples, we felt the need for an extended workspace with temperature and humidity control; a 'glove-box' that seamlessly connects to the vitrification instrument, the Vitrobot. In this paper we describe the use of the glove-box in the 2D and 3D cryo-TEM study of DNA adsorption and calcium carbonate mineralization to Langmuir films. The data presented illustrates the necessity of a humidity-controlled environment to preserve the original "native" state of the monolayer system.
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PMID:The development of a glove-box/Vitrobot combination: air-water interface events visualized by cryo-TEM. 1869 18

The Langmuir monolayer is widely regarded as a model for investigating biomineralization on biological membranes, but so far the crystallization process has been elusive. In this work, we study the crystallization process of CaCO(3) on a stearic acid monolayer at the air-water interface by in situ Brewster angle microscopy and ex situ electron microscopy. It is shown that the final CaCO(3) crystals are transformed from a particle precursor rather than directly from the solvated ions under the compressed stearic acid monolayer. SEM and TEM images reveal that the precursors are uniform spherical particles of amorphous calcium carbonate (ACC) with sizes smaller than 100 nm. The amorphous particles are produced in an early stage of mineralization and can be stabilized for at least 0.5 h. Subsequently, the ACC particles tend to aggregate with increasing population and are eventually transformed into the crystalline calcite phase with the elapse of time. This work is the first to clarify the crystallization process of calcium carbonate under the monolayer at the air-water interface by a direct observation of the ACC and therefore establish the roles of stearic acid in the process.
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PMID:Observation of an amorphous calcium carbonate precursor on a stearic acid monolayer formed during the biomimetic mineralization of CaCO(3). 1909 53

The initial formation and subsequent development of larval shells in marine bivalve, Crassostrea nippona were investigated using the FIB-TEM technique. Fourteen hours after fertilization (the trochophore stage), larvae form an incipient shell of 100-150nm thick with a columnar contrast. Selected-area electron diffraction analysis showed a single-crystal aragonite pattern with the c-axis perpendicular to the shell surface. Plan-view TEM analysis suggested that the shell contains high density of {110} twins, which are the origin of the columnar contrast in the cross-sectional images. 72h after fertilization (the veliger stage), the shell grows up to 1.2-1.4mum thick accompanying an additional granular layer between the preexisting layer and embryo to form a distinctive two-layer structure. The granular layer is also composed of aragonite crystals sharing their c-axes perpendicular to the shell surface, but the crystals are arranged with a flexible rotation around the c-axes and not restricted solely to the {110} twin relation. No evidence to suggest the existence of amorphous calcium carbonate (ACC) was found through the observation. The well-regulated crystallographic properties found in the present sample imply initial shell formation probably via a direct deposition of crystalline aragonite.
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PMID:Microtexture of larval shell of oyster, Crassostrea nippona: a FIB-TEM study. 1961 99

C.I. Basic Red 46, commonly used as a textile dye, was photocatalytically removed using supported TiO2 nanoparticles irradiated by a 30 W UV-C lamp in a batch reactor. The investigated photocatalyst was industrial Degussa P25 (crystallite mean size 21 nm) immobilized on glass beads by a heat attachment method. The catalyst was characterized by XRD, SEM, TEM and BET techniques. The process of the dye decolorization in the presence of TiO2 nanoparticles was experimentally studied through changing the initial dye concentration, UV light intensity and initial pH. The influence of inorganic anions such as chloride, sulphate, bicarbonate, carbonate and phosphate on the photocatalytic decolorization of BR46 was investigated. The decolorization of BR46 follows the pseudo-first-order kinetic according to the Langmuir-Hinshelwood model (k1 = 0.273 mg L(-1) min(-1), 2 = 0.313 (mg L(-1))(-1)). The efficiency parameters such as apparent quantum yield and electrical energy per order (EEO) were estimated. An artificial neural network model (ANN) was developed to predict the photocatalytic decolorization of BR46 solution. The findings indicated that the ANN provided reasonable predictive performance (R2 = 0.96). The influence of each parameter on the variable studied was assessed: initial concentration of the dye being the most significant factor, followed by the initial pH and reaction time.
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PMID:Photocatalytic removal of C.I. Basic Red 46 on immobilized TiO2 nanoparticles: artificial neural network modelling. 1994 46


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