A study of primary nucleation of calcium oxalate monohydrate: I‐Effect of supersaturation

There are various organic and inorganic constituents in kidney stones. Among them, calcium oxalate monohydrate (COM) is the primary inorganic constituent of kidney stones. However, the mechanisms of formation of kidney stones are not well understood. In this regard, a basic study is carried out for better understanding of nucleation, crystal growth and/or aggregation of formed COM crystals. The primary nucleation of calcium oxalate monohydrate is studied at the laboratory scale using turbidity measurements. Calcium chloride and potassium oxalate solutions are mixed and then added to a Turbidimeter tube for continuous recording of turbidity. Induction time (time to induce formation of detectable crystals) is estimated from time‐turbidity graphs. The effect of some urinary species, such as oxalate and calcium, on nucleation and crystallization characteristics of COM is determined by particle size distribution analysis, measuring weight of crystals and calculation of relative supersaturation. The classical nucleation theory is applied at high supersaturation ratios (SR) ranging from 1.6 to 2.2. The results indicate that nucleation rate increases with increasing supersaturation ratio from 0.81 × 10²⁸ nuclei/cm³.sec at 1.6 SR, to 18.02 × 10²⁸ nuclei/cm³.sec at 2.2 SR. On the other hand, free energy change and radius of critical nucleus are decreased as supersaturation ratio is increased. The nucleation rates are higher than those reported in literature. Such discrepancy is discussed on the bases of differences in experimental techniques. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of primary nucleation of calcium oxalate monohydrate: II. Effect of urinary species

Kidney stones consist of various organic and inorganic compounds. Calcium oxalate monohydrate (COM) is the main inorganic constituent of kidney stones. However, the mechanisms for the formation of calcium oxalate kidney stones are not well understood. In this regard, there are several hypotheses including nucleation, crystal growth and/or aggregation of formed COM crystals. The effect of some urinary species such as oxalate, calcium, citrate, and protein on nucleation and crystallization characteristics of COM is determined by measuring the weight of formed crystals and their size distributions under different chemical conditions, which simulate the urinary environment. Statistical experimental designs are used to determine the interaction effects among various factors. The data clearly show that oxalate and calcium promote nucleation and crystallization of COM. This is attributed to formation of a thermodynamically stable calcium oxalate monohydrate resulting from supersaturation. Citrate, however, inhibits nucleation and further crystal growth. These results are explained on the basis of the high affinity of citrate to combine with calcium to form soluble calcium citrate complexes. Thus, citrate competes with oxalate ion for binding to calcium cations. These conditions decrease the amount of free calcium ions available to form calcium oxalate crystals. In case of protein (mucin), however, the results suggest that no significant effect could be measured of mucin on nucleation and crystal growth. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of essential and non‐essential amino acids on calcium oxalate crystallization

The investigation on the mechanism of nucleation and growth of crystals at organic‐inorganic interfaces is crucial for understanding biological and physiological calcification processes such as the formation of urinary stones. The effects of five different amino acids on the crystallization of calcium oxalate have been investigated at pH 4.5 and 37 °C in aqueous solutions in the batch type crystallizer. The products were characterized by Scanning Electron Microscopy (SEM), Fourier Transfer Infrared Spectroscopy (FT/IR) and X‐Ray diffraction (XRD) analysis. Crystal size distribution (CSD) and filtration rate measurements were done. In order to determine the adsorption characteristics of amino acids on the calcium oxalate crystal surfaces, zeta potential measurements were also done and discussed. The results indicate that in the presence of all investigated amino acids, calcium oxalate monohydrate (COM) crystals were preferentially produced, but the crystal morphology varied with amino acid types and concentrations. Various crystal morphologies such as elongated hexagonal, coffin or platy habits were observed. In the presence of all investigated amino acids, the calcium oxalate crystallized in a monohydrate form. Electrostatic/ionic interaction, different adsorption properties and special functional effects of amino acids led to find different crystal morphology. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of calcium oxalate crystals induced by complex films containing biomolecules

Nucleation and growth of calcium oxalate (CaC₂O₄) crystals induced by films composed of phosphatidylcholine (PC), cholesterol (CS) and human serum albumin (HSA), and of PC, CS and dextran have been carried out. The products obtained were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and ultraviolet‐visible spectroscopy. The results indicate that hexagonal calcium oxalate monohydrate (COM) and club‐shaped calcium oxalate trihydrate (COT) crystals are obtained on the PC/CH/HSA film, and the microstructure and properties of the PC/CH/HSA film depend on the weight ratio of PC to CS. With an increase in the PC‐to‐CS ratio, the number of COM crystals decreases gradually, and finally disappear, suggesting that PC inhibits the growth of COM crystals. On the PC/CS/dextran film, irregular COM and COT crystals are formed. The possible formation mechanisms of CaC₂O₄ on the two complex films are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Bacillus subtilis on the growth of calcium oxalate

The influence of the bacteria Bacillus subtilis (B. subtilis) on the nucleation, growth and aggregation of calcium oxalate (CaOx) crystals in aqueous solution has been studied. The crystals obtained were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X‐ray powder diffractometry. The results show that, in the presence of B. subtilis, quasi‐hexagonal calcium oxalate monohydrate (COM) crystals are obtained after 24 hours of reaction at a temperature of 30°C ± 1K. However, without the presence of the bacteria, irregular CaOx crystals were obtained which contain two crystal phases: COM and calcium oxalate dihydrate (COD). This suggests that B. subtilis may promote the crystallization of COM, the major component of urinary stone. The formation mechanism of CaOx crystals in the presence of B. subtilis is explored, indicating that the cell walls and extracellular proteins of the bacteria may act as templates to induce the nucleation, growth and aggregation of CaOx crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Calcium oxalate crystallization in the presence of amino acids,proteins and carboxylic acids

Reactive crystallization of calcium oxalate was investigated in the presence of amino acids, proteins and carboxylic acids at different pH and temperatures. Average particle size, filtration rates of calcium oxalate crystals obtained in the absence and presence of additives were determined. The influence of pH, temperatures and additives on crystal morphology of calcium oxalate were also investigated and discussed by SEM analysis. TG‐DTA, FT/IR and XRD analysis were carried out for all investigated conditions. Average particle size of calcium oxalate was affected significantly by the additive type and concentration. Variation of crystal morphology depending on type and concentration of the additives affected the filtration characteristics. Majority of calcium oxalate crystals occurred in the form of calcium oxalate monohydrate except those in the presence of tartaric acid. TG‐DTA, FT/IR and XRD analysis proved that calcium oxalate monohydrate and calcium oxalate dihydrate mixtures are formed in the presence of tartaric acid. The effect of all additives on scale formation was also investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Semi-Batch Precipitation of Calcium Oxalate Monohydrate

Calcium oxalate monohydrate (COM) formation on the semi-batch precipitation of CaCl₂ and Na₂C₂O₄ solutions in the stoichiometric ratio carried out at pH = 6 and 37 or 70°C, respectively, was studied. When a certain level of supersaturation in the system is reached, individual COM crystals of a rather uniform size are formed. These crystals then grown and form ‘loose’ agglomerates that later develop into compact and spherical particles. The particle size distribution (PSD) rapidly shifts during early stages of precipitation towards larger sizes as a result of crystal growth and agglomeration. Later the PSD reaches a shape and position on the size axis that remain virtually constant with progressing precipitation. COM agglomerates consisting of mainly intergrown crystals are formed by mechanism of primary and secondary agglomeration. The primary agglomeration can constitute an important factor in urolithiasis.     

Crystal growth of calcium oxalate induced by the extracts of Semen Plantaginis and Folium Pyrrosiae

The crystallization of calcium oxalate (CaOxa) in aqueous solutions of the extracts of Semen Plantaginis and Folium Pyrrosiae has been investigated, focusing on the inhibition mechanism of some herbs on stone formation. It has been shown that in the presence of extracts of above two herbs, calcium oxalate dihydrate (COD) crystals with typical morphologies of tetragonal bipyramids were obtained. This suggests that the extracts of Semen Plantaginis and Folium Pyrrosiae can promote the formation of thermodynamically unstable COD, and inhibit the formation of calcium oxalate monohydrate (COM), a major component of urinary stone. The formation mechanism of COD crystals induced by Semen Plantaginis and Folium Pyrrosiae is also discussed, indicating that the bioorganic molecules in the extracts of the herbs can induce the nucleation and growth of COD crystals. This study can help us make clear the inhibition mechanism of some herbs on stone formation that is in favor of the prevention and treatment of urolithiasis. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

海带硫酸多糖防止草酸钙结石形成的体外模拟

采用扫描电子显微镜、X射线衍射法和红外光谱在草酸钙(CaOxa)结石患者尿液中研究了从海带中提取的硫酸多糖(LSPS)的防石作用.结果表明,LSPS可以抑制一水草酸钙(COM)的成核和聚集,并诱导二水草酸钙(COD)晶体形成.随着ESPS浓度从0增加到0.005, 0.02和0.20 mg/ml,COD的百分含量从0分别增加到22;, 55;和100;.这些结果表明LSPS是抑制CaOxa结石形成的一种潜在药物.     

柠檬酸钾对尿石患者和正常人尿液凝胶中草酸钙晶体生长的影响

采用扫描电子显微镜(SEM)和X射线衍射(XRD)方法,比较研究了防石药物柠檬酸钾(K3cit)在尿石患者尿液和正常人尿液制备的凝胶中对草酸钙(CaOxa)晶体生长的影响.没有加入K3cit时,CaOxa晶体均以一水草酸钙(COM)为主要晶相,加入K3cit后,不但COM晶体变得圆钝,比表面积减小,而且诱导了二水草酸钙(COD)生成.随着K3cit浓度从0.10增加到0.20 mol/L,在正常人尿液凝胶中COD晶体的百分含量从20;增加到45;,而在CaOxa结石患者尿液凝胶中,不但COD含量从10;增加到25;,而且K3cit可诱导草酸钙成核,从而产生大量的小尺寸草酸钙晶体,这有利于阻止草酸钙晶体变大形成尿石.本结果可为临床上治疗CaOxa结石提供启示.     

不同晶相草酸钙晶体的选区电子衍射和X射线衍射比较分析

在卵磷脂-水脂质体中制备了一水草酸钙(COM)、二水草酸钙(COD)和三水草酸钙(COT).并对它们分别进行了透射电镜(TEM)、选区电子衍射分析(SAED)和X射线衍射(XRD)分析.TEM结果表明,COM、COD和COT均为泡状,粒径约80～150nm.将SAED结果与XRD结果对比分析,发现将SAED图谱指标化后所得的衍射数据与XRD的特征峰值基本相符,但在相对强度上存在差别.本实验结果表明,将TEM、SAED和XRD技术联合分析纳米级草酸钙晶体,不但可以观察纳米级草酸钙的形貌,而且能对其晶相、单晶和多晶等进行深入的了解.     

Inhibition of Calcium Oxalate Monohydrate Crystal Growth in High and Low Ionic Strength Solutions

The effect of additives on the kinetics of growth of calcium oxalate monohydrate crystals has been studied. Conductivity and potentiometry measurements have been compared. Growth rates were calculated from precipitate curves by a cubic spline method. An approach consisting on the calculation of rate constants and orders of reaction from logarithmic plots of growth rate versus supersaturation has been followed to study crystal growth kinetics. This method revealed that the presence of additives is causing not only a decrease on the rate constant but an increase on the order of reaction as well. The effect of additives (EDTA, citrate and phytate) was considerably weaker in high ionic strength media. Phytate produced a complete blockage of crystal growth in concentrations as low as 2 × 10^—6 mole/L in both methods.     

Growth aspects of barium oxalate monohydrate single crystals in gel medium

Single crystals of barium oxalate monohydrate (BaC₂O₄.H₂O, BOM) were grown in pure form by controlled diffusion of Ba²⁺ using the gel technique at different temperatures. Starting from aqueous Ba²⁺ chloride (BaCl₂) and acetic acid (C₂H₂O₄) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Calcium Oxalate Monohydrate Crystal Growth

The growth rate of calcium oxalate monohydrate seed representing aggregates of highly irregular crystals from solutions of the stoichiometric composition with I = 100 mol m⁻³ in the range of supersaturation Δc = 0.056 to 0.353 mol m⁻³ was measured at 37 °C by the constant composition method. The crystal growth rate decreased during the initial period of experiment, then reached a value constant over a considerable time and later increased again. The initial decrease of the growth rate resulted from crystal perfection whereas the later increase was caused by formation of new crystals by secondary nucleation. The supersaturation dependence of the kinetic growth rate satisfied the power law with the growth order equal to 2 and 4 at supersaturations lower and higher than about Δc = 0.150 mol m⁻³, respectively.     

Effect of Supersaturation and Temperature on the Growth Morphology of Ammonium Oxalate Monohydrate Crystals Obtained from Aqueous Solutions

The experimental results of a study of the effect of supersaturation and temperature on the growth morphology of ammonium oxalate monohydrate [(NH₄)₂C₂O₄H₂O; AO] single crystals obtained from aqueous solutions at 30 and 40 °C and supersaturation up to 9% are presented. The observations are analysed in terms of theoretical morphology, growth models and attachment energy for growth units in steps of growing faces.     

Study of the Growth Morphology of Ammonium Oxalate Monohydrate Crystals Obtained from Aqueous Solutions

The experimental results of the growth morphology of ammonium oxalate monohydrate [(NH₄)₂C₂O₄ · H₂O; AO] single crystals obtained from aqueous solutions at 30 and 40 °C and supersaturation up to 9% are presented. The observations are compared with the theoretical morphology predicted by PBC analysis and Braivais-Donnay-Harker law.     

On the origin of supersaturation barriers during the growth of single crystals from aqueous solutions containing impurities – a review

A generalised treatment of the appearance of supersaturation barriers σ_d, σ* and σ** during the growth of single crystals is outlined from the standpoint of well‐defined critical values of relative step velocities on a face. The final theoretical expressions are based on the premise that: (1) there are critical values of the relative step velocities associated with different average distances between adsorbed impurity particles during instantaneous, time‐dependent and time‐independent adsorption of the impurity on the growing surface, (2) the growth rate of a face is proporptional to velocity of steps on the growing face, and (3) Freundlich and Langmuir adsorption isotherms apply for different impurities. The theoretical expressions are then used to critically analyse the experimental data on supersaturation barriers observed during the growth of ammonium oxalate monohydrate and potassium dihydrogen phosphate single crystals from aqueous solutions containing different impurities. It was found that: (1) Langmuir adsorption isotherm is more practical for the analysis of the experimental data of the dependence of supersaturation barriers σ_d, σ* and σ** on the concentration c_i of an impurity, and (2) the ratios σ_d/σ* and σ*/σ** of successive supersaturation barriers for an impurity either increases or remains constant with an increase in impurity concentration c_i, and may be explained in terms of the mechanism of adsorption of impurity particles. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Peculiarities of the micromorphology of the CaC2O4 · H2O crystal faces

Crystallography Reports - Peculiarities of the faceted microrelief formed during the growth of CaC2O4 · H2O calcium oxalate monohydrate (whewellite) crystals are investigated to gain insight...     

The mechanism of biological mineralization

The control of supersaturation and the nucleation and growth of crystals in calcium phosphate systems are important in relation to the physiological deposition of bone and tooth. Other calcium salts such as the carbonate and oxalate hydrates are significant components of pathological mineral deposits. The use of a highly reproducible seeded growth technique has enabled kinetic studies to be made of the crystal growth of these minerals. Under conditions of relatively high supersaturation, secondary nucleation may be induced upon the surface of the seed crystals. In the case of the calcium phosphates, temperature, supersaturation, surface concentration, pH, ionic strength and presence of foreign ions are very important in determining the nature of the phase which grows upon the added seed crystals. Kinetic considerations are of overriding importance in determining the course of the reactions. It is not possible to predict the phase which forms purely on the basis of thermodynamic solubility data. Thus, in solutions appreciably supersaturated with respect to both dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAP), the addition of low concentrations of HAP seed results in the exclusive formation of DCPD whereas this phase is absent when the seed concentration is increased. The kinetic results for calcium oxalate and phosphates are discussed in terms of the important problems relating to tooth mineralization and the origin and growth of renal calculi.     

The influence of crystallization conditions on the onset of dendritic growth of calcium carbonate

Understanding the crystallization of calcium carbonate is relevant in numerous fields like biomineralization, geology and industrial applications where calcium carbonate forms. In order to enhance the knowledge about the formation of calcium carbonate with focus on the vaterite polymorph, in this work calcium carbonate has been crystallized in aqueous solutions at temperatures from 5 °C to 90 °C. Special attention has been directed to higher temperatures for which the effect of the initial supersaturation on the resulting crystal morphologies and the onset of dendritic growth have been studied. In analogy to snow crystal formation, it has been found that in a certain temperature range hexagonal plate‐like crystals form at low supersaturation whereas dendritic patterns start to appear at higher supersaturation. The symmetrical branches characteristic for dendritic growth get less pronounced as the temperature is decreased. The results reported here related to the interdependence between supersaturation, crystal morphology and growth mechanisms, can be used in future works to predict particle formation and to design crystal architectures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)