The Effect of Organic Macromolecules on the Vateritet to Calcite Transformation

1993 ◽  
Vol 330 ◽  
Author(s):  
Liisa Kuhn Spearing ◽  
S. Sarig ◽  
D. J. Fink ◽  
A. H. Heuer
Keyword(s):  
Crystal Growth ◽  
Calcium Carbonate ◽  
Close Association ◽  
Nucleation And Growth ◽  
Mineral Phase ◽  
Aqueous Suspensions ◽  
Crystal Product

ABSTRACTSmall quantities of acidic macromolecules were added to crystallizing calcium carbonate in an attempt to engineer crystal growth. The additives are simple analogs to those molecules found in close association with the mineral phase in biological ceramics. When 5 or 10 ppm of the four additives (poly-L-glutamate, poly-L-aspartate, polyacrylate and polymaleate) were added to aqueous suspensions of metastable vaterite, the transformation to calcite was markedly retarded, and the morphology of the final crystal product was altered. The two polypeptides were most effective in inhibiting calcite nucleation and growth; they also promoted vaterite aggregation, and caused the formation of large calcite crystals.

A TEM study of the microstructure of avian eggshells

1992 ◽  
Vol 50 (2) ◽  
pp. 1102-1103
Author(s):  
S. Q. Xiao ◽  
S. Baden ◽  
A. H. Heuer
Keyword(s):  
Electron Microscope ◽  
Calcium Carbonate ◽  
Nucleation And Growth ◽  
Growth Mechanisms ◽  
Shell Surface ◽  
Thin Sections ◽  
Polycrystalline Metals ◽  
Transmission Electron ◽  
Nucleation And Growth Mechanisms

The avian eggshell is one of the most rapidly mineralizing biological systems known. In situ, 5g of calcium carbonate are crystallized in less than 20 hrs to fabricate the shell. Although there have been much work about the formation of eggshells, controversy about the nucleation and growth mechanisms of the calcite crystals, and their texture in the eggshell, still remain unclear. In this report the microstructure and microchemistry of avian eggshells have been analyzed using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS).Fresh white and dry brown eggshells were broken and fixed in Karnosky's fixative (kaltitanden) for 2 hrs, then rinsed in distilled H2O. Small speckles of the eggshells were embedded in Spurr medium and thin sections were made ultramicrotome.The crystalline part of eggshells are composed of many small plate-like calcite grains, whose plate normals are approximately parallel to the shell surface. The sizes of the grains are about 0.3×0.3×1 μm3 (Fig.l). These grains are not as closely packed as man-made polycrystalline metals and ceramics, and small gaps between adjacent grains are visible indicating the absence of conventional grain boundaries.

Phase separation in undercooled molten Pd80Si20: Part I

1999 ◽  
Vol 14 (9) ◽  
pp. 3653-3662 ◽  
Author(s):  
K. L. Lee ◽  
H. W. Kui
Keyword(s):  
Growth Rate ◽  
Phase Separation ◽  
Crystal Growth ◽  
Grain Refinement ◽  
Crystallization Temperature ◽  
Sharp Decrease ◽  
Nucleation And Growth ◽  
Crystal Growth Rate ◽  
Large Undercooling ◽  
Kinetic Crystallization

Three different kinds of morphology are found in undercooled Pd80Si20, and they dominate at different undercooling regimens ΔT, defined as ΔT = T1 – Tk, where T1 is the liquidus of Pd80Si20 and Tk is the kinetic crystallization temperature. In the small undercooling regimen, i.e., for ΔT ≤ 190 K, the microstructures are typically dendritic precipitation with a eutecticlike background. In the intermediate undercooling regimen, i.e., for 190 ≤ ΔT ≤ 220 K, spherical morphologies, which arise from nucleation and growth, are identified. In addition, Pd particles are found throughout an entire undercooled specimen. In the large undercooling regimen, i.e., for ΔT ≥ 220 K, a connected structure composed of two subnetworks is found. A sharp decrease in the dimension of the microstructures occurs from the intermediate to the large undercooling regimen. Although the crystalline phases in the intermediate and the large undercooling regimens are the same, the crystal growth rate is too slow to bring about the occurrence of grain refinement. Combining the morphologies observed in the three undercooling regimens and their crystallization behaviors, we conclude that phase separation takes place in undercooled molten Pd80Si20.

Crystal growth of calcium carbonate. A controlled composition kinetic study

1982 ◽  
Vol 86 (1) ◽  
pp. 103-107 ◽  
Author(s):  
T. F. Kazmierczak ◽  
M. B. Tomson ◽  
G. H. Nancollas
Keyword(s):  
Crystal Growth ◽  
Calcium Carbonate ◽  
Kinetic Study

scholarly journals In situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated Ce(IV)-based Metal-Organic Frameworks with UiO-66 and MIL-140 architectures

2020 ◽  
Author(s):  
Stephen Shearan ◽  
Jannick Jacobsen ◽  
Ferdinando Costantino ◽  
Roberto D’Amato ◽  
Dmitri Novikov ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Metal Organic Frameworks ◽  
Building Blocks ◽  
Nucleation And Growth ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rate Determining Step ◽  
Wide Range ◽  
Metal Organic

We report on the results of a thorough <i>in situ</i> synchrotron powder X-ray diffraction study of the crystallisation in aqueous medium of two recently discovered perfluorinated Ce(IV)-based metal-organic frameworks (MOFs), analogues of the already well investigated Zr(IV)-based UiO-66 and MIL-140A, namely, F4_UiO-66(Ce) and F4_MIL-140A(Ce). The two MOFs were originally obtained in pure form in similar conditions, using ammonium cerium nitrate and tetrafluoroterephthalic acid as building blocks, and small variations of the reaction parameters were found to yield mixed phases. Here, we investigate the crystallisation of these compounds <i>in situ</i> in a wide range of conditions, varying parameters such as temperature, amount of the protonation modulator nitric acid (HNO<sub>3</sub>) and amount of the coordination modulator acetic acid (AcOH). When only HNO<sub>3</sub> is present in the reaction environment, F4_MIL-140A(Ce) is obtained as a pure phase. Heating preferentially accelerates nucleation, which becomes rate determining below 57 °C, whereas the modulator influences nucleation and crystal growth to a similar extent. Upon addition of AcOH to the system, alongside HNO<sub>3</sub>, mixed-phased products, consisting of F4_MIL-140A(Ce) and F4_UiO-66(Ce), are obtained. In these conditions, F4_UiO-66(Ce) is always formed faster and no interconversion between the two phases occurs. In the case of F4_UiO-66(Ce), crystal growth is always the rate determining step. An increase in the amount of HNO<sub>3</sub> slows down both nucleation and growth rates for F4_MIL-140A(Ce), whereas nucleation is mainly affected for F4_UiO-66(Ce). In addition, a higher amount HNO<sub>3</sub> favours the formation of F4_MIL-140A(Ce). Similarly, increasing the amount of AcOH leads to slowing down of the nucleation and growth rate, but favours the formation of F4_UiO-66(Ce). The pure F4_UiO-66(Ce) phase could also be obtained when using larger amounts of AcOH in the presence of minimal HNO<sub>3</sub>. Based on these <i>in situ</i> results, a new optimised route to achieving a pure, high quality F4_MIL-140A(Ce) phase in mild conditions (60 °C, 1 h) is also identified.

Functional analyses of chitinolytic enzymes in the formation of calcite prisms inPinctada fucata

2019 ◽  
Author(s):  
Hiroyuki Kintsu ◽  
Alberto Pérez-Huerta ◽  
Shigeru Ohtsuka ◽  
Taiga Okumura ◽  
Shinsuke Ifuku ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Crystal Growth ◽  
Calcium Carbonate ◽  
Small Angle ◽  
Organic Matrix ◽  
Pinctada Fucata ◽  
Prismatic Layer ◽  
Chitinolytic Enzymes ◽  
Organic Matrices

Abstract Background: The mollusk shells present distinctive microstructures that are formed by small amounts of organic matrices controlling the crystal growth of calcium carbonate. These microstructures show superior mechanical properties such as strength or flexibility. The shell of Pinctada fucata has the prismatic layer consisting of prisms of single calcite crystals. These crystals contain small-angle grain boundaries caused by a dense intracrystalline organic matrix network to improve mechanical strength. Previously, we identified chitin and chitinolytic enzymes as components of this intracrystalline organic matrix. In this study, we analyzed the function of those organic matrices in calcium carbonate crystallization by in vitro and in vivo experiments.Results: We analyzed calcites synthesized in chitin gel with or without chitinolytic enzymes by using transmission electron microscope (TEM) and atom probe tomography (APT). TEM observations showed that grain boundary was more induced as concentration of chitinolytic enzymes increased and thus, chitin became thinner. In an optimal concentration of chitinolytic enzymes, small-angle grain boundaries were observed. APT analysis showed that ion clusters derived from chitin were detected. In order to clarify the importance of chitinolytic enzymes on the formation of the prismatic layer in vivo , we performed the experiment in which chitinase inhibitor was injected into a living Pinctada fucata and then analyzed the change of mechanical properties of the prismatic layer. The hardness and elastic modulus increased after injection of chitinase inhibitor. Electron back scattered diffraction (EBSD) mapping data showed that the spread of crystal orientations in whole single crystal also increased by the effect of inhibitor injections.Conclusion: Our results suggested that chitinolytic enzymes may function cooperatively with chitin to regulate the crystal growth and mechanical properties of the prismatic layer, and chitinolytic enzymes are essential for the formation of the normal prismatic layer of P. fucata.

Organic-Inorganic Nanocomposites Based on Iron Containing Clusters and Biomolecules

1995 ◽  
Vol 48 (4) ◽  
pp. 783 ◽  
Author(s):  
P Chan ◽  
W Chuaanusorn ◽  
M Nesterova ◽  
P Sipos ◽  
TG Stpierre ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Chondroitin Sulfate ◽  
Iron Sulfide ◽  
Nucleation And Growth ◽  
Protein Cage ◽  
Structural Order ◽  
Nucleation Sites ◽  
Inorganic Nanocomposites ◽  
Higher Temperature ◽  
Inorganic Clusters

Biopolymers, such as the protein ferritin and the polysaccharides chondroitin sulfate and chitosan, have been used to control the nucleation and growth of nanoscale iron(III) hydroxide clusters. The biopolymers can provide nucleation sites, that in some cases are spatially defined by the shape of the polymer, and/or defined volumes within which crystal growth of the iron(III) hydroxide can proceed. The product inorganic clusters are bound to the organic polymers which both keep them in solution and prevent aggregation. The morphology of the clusters (spheres or rods) and the uniformity of their dimensions are determined by the biopolymer chosen. The temperature of formation is shown to have an effect on the structure of the clusters, a higher temperature resulting in larger inorganic clusters with a higher degree of structural order. Iron(III) hydroxide clusters in ferritin cages can be partially transformed to iron sulfide by reaction with H2S gas while remaining in the protein cage.

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