Crystallization of calcium carbonates in biologically inspired collagenous matrices

Oriented crystallization of calcite, aragonite and vaterite by means of cross-linked collagenous matrices with entrapped poly-l-aspartate (poly-Asp) or poly-l-glutamate (poly-Glu) is reported. These results suggest that the control of calcium carbonate polymorphism and the architectural assembly of the crystals are related to the modelling of the nucleation sites in terms of polypeptide concentration, local supersaturation and shape. Orientation effect of the calcite has been observed only with entrapped poly-Asp, indicating that the control over the oriented crystallisation is due to the beta structure assumed by the poly-Asp in the presence of calcium ions. The orientation of aragonite and vaterite can be controlled by the uniaxial deformation of the substrate. These results indicate that the local supersaturation in the microenvironment where nucleation and growth occur plays an important role in controlling the deposition of crystalline calcium carbonate polymorphs inside cross-linked gelatin films and that a structured organic scaffold can organize the crystalline units in unusual habitus.     

The crystallization of calcium carbonate on sodium cholate

Recent studies in the bibliography showed that calcium carbonate was the major constituent (77.8%) in gall stones, and the polymorph calcite was at 62.5% of the cases examined. The kinetics of crystallization of calcite on sodium cholate has been studied using the constant composition technique. Analysis of the initial rates as a function of the solution supersaturation, according to the classical nucleation theory, yielded a value of 33 mJ m^-2 for the surface energy of the growing phase and a five-ion cluster, forming the critical nucleus. The apparent order for the calcite crystallization was found to be 4.5±0.7 indicative of a surface nucleation mechanism. The formation of calcite may be initiated through the interaction of Ca²⁺ ions with the negative end of the C=0 bond of the sodium cholate molecule.     

Hydroxyapatite precipitation on a carboxylated vinyl chloride-vinyl acetate copolymer

The kinetics of crystal growth of hydroxyapatite [Ca₅(PO₄)₃OH, HAP], the thermodynamically most stable calcium phosphate phase, on a commercially available carboxylated (1%) vinylchloride (83%) vinyl acetate (13%) copolymer was investigated at relatively low ionic strength, at 37 °C and pH 7.4. Stable supersaturated solutions were seeded with HAP seed crystals as reference and with the polymer in powder form. Well defined induction times preceded the growth of HAP on the polymeric substrate. The induction times measured were inversely proportional to the solution supersaturation. The rates of crystallization both on HAP and on the polymer were measured at conditions of constant supersaturation. HAP growth took place on both substrates and the parabolic dependence of the rates of crystal growth on the relative solution supersaturation suggested a surface diffusion controlled mechanism. The rates of HAP crystal growth on the polymeric substrate were found to depend on the amount of the seed material suggesting selective overgrowth of HAP. A possible explanation for this selectivity is the development of active growth sites through the formation of surface complexes of the calcium ions with the dissociated carboxyl groups.     

In vitro crystallization of octacalcium phosphate on type I collagen: influence of serum albumin

The heterogeneous crystallization of octacalcium phosphate (OCP, Ca₈H₂(PO₄)₆ · 5H₂O) on demineralized Type I collagen has been studied from metastable supersaturated solutions, at 37°C and pH=6.50, using the constant composition crystal growth technique. The induction period, before OCP crystal growth, varied markedly with the degree of supersaturation of the solution. The data obtained allowed us to determine the apparent order for the precipitation and the growth mechanism of OCP on Type I collagen. Infrared spectroscopy analyses indicated the progressive mineralization of collagen and observations by scanning electron microscopy confirmed the development of OCP crystals on the collagen surface. The influence of bovine serum albumin on both the kinetics of OCP nucleation and growth has also been investigated. Because this protein was adsorbed on calcium phosphate nuclei, it exhibited two distinct effects as a function of its concentration in solution. We proposed a mechanism explaining the interaction between albumin and calcium phosphate nuclei or crystals and its incidence on the OCP crystallization kinetics. Observations by scanning electron microscopy revealed a modification of the size and the appearance of crystals grown on collagen due to the adsorption of albumin on the crystal surface. © 1999 Kluwer Academic Publishers     

Effect of Langmuir monolayer of bovine serum albumin protein on the morphology of calcium carbonate

Bovine serum albumin (BSA) Langmuir monolayer, as a model of biomineralization-associated proteins, was used to study its effect on regulated biomineralization of calcium carbonate. The effects of the BSA Langmuir monolayer and the concentration of the subphase solution on the nucleation and growth processes and morphology of the calcium carbonate crystal were investigated. The morphology and polymorphic phase of the resulting calcium carbonate crystals were characterized by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). Moreover, the interaction mechanisms of the subphase solution with the BSA Langmuir monolayer were discussed. It was found that BSA Langmuir monolayer could be used as a template to successfully manipulate the polymorphic phase and crystal morphology of calcium carbonate and had obvious influence on the oriented crystallization and growth. The final morphology or aggregation mode of the calcite crystal was closely dependent on the concentration of calcium bicarbonate solution. It is expected that this research would help to better understand the mechanism of biomineralization by revealing the interactions between protein matrices and crystallization of calcium carbonate crystal.     

Formation of cytochrome C–apatite composite layer on NaOH- and heat-treated titanium

A cytochrome C (cyt C) and apatite composite layer was formed on a NaOH- and heat-treated titanium substrate (Ti substrate) by immersing the Ti substrate for one day at 25 °C in supersaturated calcium phosphate solutions obtained by mixing infusion fluids. When the initial supersaturation level of the calcium phosphate solution was increased, the total amount of cyt C and apatite deposited on the Ti substrate increased. On the other hand, the cyt C content in the composite layer decreased with an increase in initial supersaturation level. The morphology of the composite layer markedly changed depending on the initial supersaturation level. Therefore, the initial supersaturation level affected the formation of the cyt C and apatite composite layer. It is expected that fibroblast growth factor-2 can be immobilized on NaOH- and heat-treated titanium substrates using the same method.     

In vitro growth of calcium carbonate crystals on bivalve shells: Application of two methods of synthesis

The classic ammonium carbonate vapor diffusion method (VDM) and the coprecipitation method (CM) in its modified form were applied for in vitro growth of calcium carbonate crystals on glass substrate and on calcitic and aragonitic shell layers of blue mussel Mytilus edulis (L.) and Iceland scallop Chlamys islandica (M.). The experiments were carried out using large volumes of growth medium (250 ml and 1000 ml). Crystallization using the VDM is relatively slow, but faster with the CM. The formation of calcium carbonate polymorphs is strongly influenced by the mineralogical phase in the uppermost layer of the shell substrate bathed in the experimental solution, even if magnesium ions are added to solution with the CM. The morphology of calcium carbonate crystals clearly differs between methods, and is influenced by the type of substrate. The effect of biomacromolecules released from the shell substrate on morphology and organization of calcium carbonate crystals is clearly observed with both methods of crystallization.     

Effect of crystallization parameters and presence of aqueous extract of Nigella Sativa on growth inhibition of calcium oxalate monohydrate particles

For the first time, nucleation kinetics, crystal growth and agglomeration of calcium oxalate monohydrate (COM) are studied as a crystal growth inhibitor with and without Nigella Sativa(NS) extract. The induction period was determined under different supersaturation ratios ranging from 1.63 to 4.51 at 37°C using the conductivity method. Based on the classical homogeneous nucleation theory; the critical nucleation parameters were evaluated at higher supersaturation ratio. The calculated surface energy was increased from 7.97?mJ/m² without additive to 10.31?mJ/m² with NS extract. However, the nucleation rate at a supersaturation ratio of 3.26 corresponding to 5.44 with the NS extract was decreased from 3.9?×?10²⁹ nuclei/cm³.s (without additive) to 1.3?×?10²⁹ nuclei/cm³.s with NS extract addition. The number of molecules required for the formation of a stable nucleus was calculated with and without NS extract at different supersaturation ratios. The crystallite sizes of the formed crystals without and with the additive are 93 and 51?nm, respectively. Scanning electron microscopy (SEM) photomicrographs show the formation of small crystals and less aggregated with the NS inhibitor compared with the baseline (without the inhibitor). This study can help us with a clear understanding of the inhibition mechanism of an aqueous NS extract on COM crystals.     

Nucleation of solid solutions crystallizing from aqueous solutions

The study of nucleation and growth mechanisms of salts from aqueous solutions, as a function of supersaturation, is described using both macroscopic and microscopic experiments. In situ observations in a fluid cell in an atomic force microscope (AFM) reveal phenomena not accounted for in standard crystal-growth theories, specifically on the role of the crystal structure of the substrate in controlling spiral growth and two-dimensional nucleation. As a model example, the crystallization of two isostructural salts, BaSO(4) and SrSO(4), is described. The growth of solid-solution crystals is considerably more complex. The supersaturation of a given aqueous solution relative to a solid solution is different with respect to each solid composition, and it leads to the possibility that different compositions can simultaneously grow by different mechanisms on the same crystal face. Oscillatory compositional zoning is another consequence of the interplay between the thermodynamics and the kinetics of nucleation. The factors which control nucleation and growth of the solid solution (Ba,Sr)SO(4) from an aqueous solution are described. The predictions made from the theory are compared with direct observations of crystal growth in an AFM.     

Synthesis of nanocrystals of gadolinium carbonate by reaction crystallization

The formation of nano-sized crystals of gadolinium carbonate via reaction crystallization was studied in a semi-batch crystallizer using gadolinium chloride and ammonium hydrogen carbonate as the reactants. The gadolinium carbonate crystals were formed by the aggregation of primary particles sized about 5 nm. Thereby, the crystallization parameters acting directly on the aggregation of the primary particles, such as the reactant concentrations, non-stoichiometry of the reactants, solution pH, acoustic energy, and agitation speed, were mechanistically investigated. As such, increasing the reactant concentrations enhanced the crystal size due to higher nucleation of the primary particles for the aggregation. Non-stoichiometric reactant concentrations resulted in a significant reduction of the crystal size, due to the adsorption of the excess species on the primary particles. Similarly, the surface charge of the primary particles depended on the solution pH. Thus, the crystal size was reduced when the pH deviated from the neutral point. The acoustic cavitation of the ultrasound was much more effective than the turbulent fluid motion of the agitation in inhibiting the primary particle aggregation. Thus, the crystal size was remarkably reduced, even at a low acoustic energy of 6 watts.     

SiO2-Al2O3-MgO-K2O-(F,Cr2O3)玻璃陶瓷的析晶

为了研究形核剂氟化物、氧化铬及其复合作用对SiO2-Al2O3-MgO-K2O系玻璃陶瓷形核和析晶的影响,采用高温熔融法制备了不同氟化物和氧化铬含量的基础玻璃,并对该基础玻璃进行了差热分析、显微分析和X射线衍射分析.结果表明:在所研究的玻璃体系中,氟化物或氧化铬的加入,都不同程度地削弱了玻璃体的结构,降低了玻璃的转变温度;当基础玻璃只含有氟化物时,玻璃在表面析出云母晶体,内部发生分相现象,而玻璃中仅含有氧化铬时,玻璃中发生整体析晶;没有氟化物的存在,不能析出云母晶体;当同时加入两种元素的物质后,对玻璃体析晶的影响不是简单的加合,复合的作用更为突出,进一步降低了玻璃的转变温度和析晶温度,整体均匀析出云母晶体.     

用于蛋白质结晶的形核剂研究综述

获取蛋白质晶体是蛋白质三维结构解析、医疗药品生产、自组装纳米体系构建等过程中重要的步骤。例如,利用X射线衍射技术对蛋白质进行三维结构解析时,首先需要通过结晶条件筛选,获得质量较高的蛋白质晶体,进而进行衍射得到蛋白质结构相关信息。蛋白质结晶需要经历从未饱和区经亚稳区至形核区的形核过程以及从形核区到亚稳区的生长成熟过程。在整个蛋白质结晶过程中,形核过程是至关重要的一步。均相形核过程中,结晶体系中各个部分形核概率相同,当蛋白质结晶体系中溶液的过饱和度足够克服形核势垒时,在形核区发生成核,因而在低浓度的结晶溶液体系中,均相形核存在一定的局限性。形核剂的添加使蛋白质晶体异相形核,相较于均相形核其需要克服的阻力小,形核势垒低。因而形核剂的使用对于难结晶蛋白或者起始浓度过低的蛋白质结晶具有重要意义。随着结构生物学的发展,形核剂在蛋白质结晶中的研究仍是结晶方法学领域的热点问题。多孔微球对蛋白质分子的吸附作用有利于无序蛋白质分子团簇的形成,进而促进蛋白质形核。添加多孔微球不但可以增加结晶条件筛选数,也可以提高晶体质量。促进蛋白质分子有序排列的形核剂籽晶的使用,使晶体的形核生长过程始终处于结晶体系溶液浓度较低的状态,而交联的籽晶因为稳定性更高而更有应用前景。新型交互扩散结晶板中,蛋白质结晶体系通过一个较缓慢的交互扩散过程实现蛋白质结晶溶液浓度的变化,并且结晶体系可达到共平衡,因而能显著提高蛋白质晶体结晶条件筛选数和晶体质量:蛋白酶K结晶条件数由39个提升至47个,分辨率由1.66提升至1.54。利用基底材料的一些特性,如静电作用、疏水作用和氢键,可以起到促进蛋白质分子聚集的功能,从而促进形核。本文从物理作用和化学作用两个角度详细总结了形核剂对蛋白质结晶的影响,并展望了该领域的发展前景及研究方向。     

Growth of calcium carbonate on non-covalently modified carbon nanotubes

The crystallization of calcium carbonate was investigated on pristine and non-covalently modified carbon nanotubes (CNTs) using the vapor diffusion technique in a calcium chloride solution. Non-covalent modification was accomplished by treating the carbon nanostructures with the amphiphilic copolymer poly(isoprene-b-acrylic acid). Calcium carbonate crystals grown on the surface and in the interstitial channels of CNT buckypapers were observed in both cases. Scanning electron microscopy analysis of the untreated CNTs showed the characteristic rhombohedral morphology of calcite crystals, while in the case of modified material spherical and ellipsoidal crystals, consisted of nanocrystallites, were observed. X-ray diffraction analysis showed the presence of calcite crystals in both cases.     

On the morphology of SrCO<Subscript>3</Subscript> crystals grown at the interface between two immiscible liquids

In this paper we report on the growth of strontianite crystals at the interface between an aqueous solution of Sr²⁺ ions and organic solutions of chloroform and hexane containing fatty acid/fatty amine molecules by reaction with sodium carbonate. When fatty acid was used as an additive at the interface, the crystals grown were self-assembled needle shaped strontianite crystallites branching out from the seed crystal via secondary nucleation. Under identical conditions of supersaturation, the presence of fatty amine molecules at the liquid-liquid interface resulted in needle shaped strontianite crystals with spherical crystallites arranged around central needles. This clearly indicates that the functionality of the head group of the amphiphiles at the liquid-liquid interface affects the morphology of the strontium carbonate crystals formed. The use of interfacial effects such as dielectric discontinuity, polarity and finite solubility of the two solvents etc opens up exciting possibilities for tailoring the morphology of crystals at the liquid-liquid interface and is currently not possible in the more popular crystal growth with similar amphiphiles at the air-water interface.     

Hexagonal AlN Layers Grown on Sulfided Si(100) Substrate

We have studied the influence of sulfide passivation on the initial stages of aluminum nitride (AlN)-layer nucleation and growth by hydride vapor-phase epitaxy (HVPE) on (100)-oriented single-crystalline silicon substrates. It is established that the substrate pretreatment in (NH₄)₂S aqueous solution leads to the columnar nucleation of hexagonal AlN crystals of two modifications rotated by 30° relative to each other. Based on the sulfide treatment, a simple method of oxide removal from and preparation of Si(100) substrate surface is developed that can be used for the epitaxial growth of group-III nitride layers.     

Growth of monocrystalline CdS films on mica surfaces through amorphous interfacial layers of silicon monoxide and carbon by chemical transport reactions

The oriented crystallization of CdS through amorphous interfacial layers of silicon monoxide and carbon by the method of chemical transport reactions has been studied. Cleaved mica (muscovite) single crystals were used as substrates. The interfacial layer thicknesses ranged from 70 to 150 Å. The informative ability of the interfacial layers was checked using the method of decoration with anthraquinone. Epitaxial CdS films 3–15 μm thick were obtained on top of the amorphous interfacial layers, with the (0001) CdS plane parallel to the (001) cleavage plane of mica and the direction [10$\text{1}$0]_CdS coinciding with [110]_mica, which corresponds to the orientation of CdS films prepared directly on the mica surface. The structural perfection of CdS films obtained through interfacial silicon monoxide and carbon layers was practically the same as that of films grown on the mica surface with no interfacial layers. For interfacial layer thicknesses exceeding 120 Å for SiO and 100 Å for carbon, the informative properties of the layers vanished and the CdS films were polycrystalline. The suggestion is made that chemical transport reactions leading to oriented crystallization can proceed without direct contact of the reacting components with the surface of the single-crystal substrates.     

不同化学官能团对无机相碳酸钙晶体的调控

选择了具有代表性的化学官能团, 羟基(—OH)、 氨基(—NH₂)、 羧基(—COOH)和甲基(—CH₃), 通过在单晶硅片上进行接枝改性, 并在改性后的硅基底上进行碳酸钙体外矿化模拟实验, 以研究这些官能团对碳酸钙矿化的影响。利用接触角实验对接枝效果进行了分析, 结果显示接枝成功。根据拉曼光谱(Raman)确定了碳酸钙的晶型; 采用扫描电子显微镜(SEM)获得了碳酸钙的形貌、 尺寸、 数量和取向信息。结果显示羟基化硅基底上出现了方解石的聚集; 氨基化硅基底和羧基化硅基底上均出现一定量的球文石, 但形貌各异; 甲基化硅基底上晶体数目较少。通过对结果的对比分析, 认为羟基和甲基对碳酸钙的晶型选择无明显影响, 氨基和羧基能通过对碳酸根离子或钙离子的吸附而诱导球文石结晶。      

Formation of three-dimensional lead telluride nanoislands on strained barium fluoride (111) surface

The nucleation and growth of three-dimensional lead telluride (PbTe) nanoislands from vapor phase on BaF₂(111) substrates strained by an external load under conditions close to thermodynamic equilibrium have been studied. Evolution of the shape of nanoislands was traced and their size distribution was statistically analyzed as dependent on the character of straining of the substrate. Homogeneous arrays of faceted PbTe nanoislands with an ultrahigh surface number density (above 10¹¹ cm^?2) and an average height of h ₁ ～ 3.5 nm (at a 8–9% rms deviation) are obtained for the first time on elastoplastically strained BaF₂(111) substrates under the conditions of small vapor supersaturation in the condensation zone. The formation of nanoisland arrays with such parameters is possible due to (i) the heterogeneous nucleation of PbTe nanoislands at the surface monatomic slip steps aligned in the 〈110〉 direction and (ii) the influence of straining on the kinetic processes on the substrate surface.     

The effect of mica surface “dehydroxylation” on particulate palladium vapor deposits

Electron energy loss spectroscopy (ELS) and palladium nucleation were used to study the influence of pre-and post-cleavage annealing on some surface properties of muscovite mica. Two ELS features at 28 eV and 16 eV indicate OH molecules on the mica surface and in the near-surface bulk respectively. On post-cleavage heating of the mica to temperatures above 400°C the two surface losses disappear, causing the simultaneous liberation of water, which is explained by a dehydration of the AlO(OH) layer of the mica lattice. The palladium nucleation and growth behavior is strongly influenced by the state of “dehydroxylation” of the mica surface. On “dehydroxylated” mica the particle number density of palladium is increased and the mean particle size decreased owing in principle to stronger interaction between the mica substrate and the palladium deposit.     

Zeolite synthesis using a semicontinuous reactor,Part 1: Controlled nucleation and growth of ZSM-5 crystals having well-defined morphologies

ZSM-5 has been synthesized at 90 and 130°C in reactor systems in which reagents were supplied continuously, and homogeneous product slurry was withdrawn semicontinuously. In some cases, precursor crystals were nucleated in situ, whereas other preparations started from dispersions of seed crystals. Guided by a simple mathematical model, conditions were chosen to give a steady, near-linear crystal growth regime. The crystals grew from solution in a medium free of solid gel in which the predominant source of nutrient silica was the monomeric monoanion [(HO)₃SiO]⁻. The products were well formed, of high crystallinity, and of narrow crystal size distribution. By providing a means for regulating solution composition and effective supersaturation, the experimental method allowed direct control over nucleation and growth processes and of the radial composition of the resulting crystals. Continuous methods of zeolite synthesis provide a versatile preparative tool and a powerful technique for studying crystallization behavior.