Modulation of calcium oxalate monohydrate crystallization by citrate through selective binding to atomic steps

The majority of human kidney stones are composed primarily of calcium oxalate monohydrate (COM) crystals. Thus, determining the molecular modulation of COM crystallization by urinary constituents is crucial for understanding and controlling renal stone disease. A comprehensive molecular-scale view of COM shape modification by citrate, obtained through a combination of in situ atomic force microscopy and molecular modeling, is presented here. We find that while the most important factors determining binding strength are coordination between COO- groups on citrate and Ca ions in the lattice, as well as H-bonds formed between the OH group of citrate and an oxalate group, the nonplanar geometry of the steps provides the most favorable environment due to the ability of the step-edge to accommodate all Ca-COO- coordinations with minimal strain. However, binding to all steps and terraces on the (010) face is much less favorable than on the (101) face due to electrostatic repulsion between oxalate and COO- groups. For example, the maximum binding energy, -166.5 kJ mol(-1), occurs for the [101] step on the (101) face, while the value for the [021] step on the (010) face is only -56.9 kJ mol(-1). This high selectivity leads to preferential binding to steps on the (101) face that pins step motion. Yet anisotropy in interaction strength on this face drives anisotropic changes in step kinetics that are responsible for shape modification of macroscopic COM crystals. Thus, the molecular scale growth kinetics and the bulk crystal habit are fully consistent with the simulations.     

Phosphorylation of osteopontin is required for inhibition of calcium oxalate crystallization

Under near-physiological pH, temperature, and ionic strength, a kinetics constant composition (CC) method was used to examine the roles of phosphorylation of a 14 amino acid segment (DDVDDTDDSHQSDE) corresponding to potential crystal binding domains within the osteopontin (OPN) sequence. The phosphorylated 14-mer OPN peptide segment significantly inhibits both the nucleation and growth of calcium oxalate monohydrate (COM), inhibiting nucleation by markedly increasing induction times and delaying subsequent growth by at least 50% at concentrations less than 44 nM. Molecular modeling predicts that the doubly phosphorylated peptide binds much more strongly to both (-101) and (010) faces of COM. The estimated binding energies are, in part, consistent with the CC experimental observations. Circular dichroism spectroscopy indicates that phosphorylation does not result in conformational changes in the secondary peptide structure, suggesting that the local binding of negatively charged phosphate side chains to crystal faces controls growth inhibition. These in vitro results reveal that the interactions between phosphorylated peptide and COM crystal faces are predominantly electrostatic, further supporting the importance of macromolecules rich in anionic side chains in the inhibition of kidney stone formation. In addition, the phosphorylation-deficient form of this segment fails to inhibit COM crystal growth up to concentrations of 1450 nM. However, at sufficiently high concentrations, this nonphosphorylated segment promotes COM nucleation. Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) results confirm that aggregation of the nonphosphorylated peptide segment takes place in solution above 900 nM when the aggregated peptide particles may exceed a well-defined minimum size to be effective crystallization promoters.     

The role of vinyl sulfonic acid homopolymer in calcium oxalate crystallization

In this study, the effect of water soluble homopolymer of vinylsulfonic acid on spontaneous crystallization of calcium oxalate (CaOx) was investigated. CaOx crystals exhibiting different shapes and phase structures were produced in the presence of polymer. While the crystal growth of calcium oxalate was inhibited by homopolymer, the morphology of calcium oxalate transformed from monohydrate to dihydrate. Inhibition of calcium oxalate crystallization was provided by adsorption of homopolymer onto the active growth sites of crystals on account of the charge and hydrophilic effects. Polyelectrolyte effects were interpreted in terms of the adsorption of inhibitors onto the active growth sites on the crystal surface.     

凝胶体系中羧酸对草酸钙结晶的影响

羧酸是泌尿系结石形成的抑制剂。本文采用双扩散法考察凝胶体系中一元羧酸HAc、二元羧酸酒石酸、三元羧酸柠檬酸和四元羧酸EDTA对草酸钙(CaOx)结晶的影响。HAc没有抑制作用。酒石酸和柠檬酸能够改变一水草酸钙(COM)晶体的形貌，并抑制草酸钙晶体二维生长，这种抑制作用随时间的增加而增强。EDTA使COM晶体在长度方向生长更快，而在宽度和厚度上生长更慢。随着结晶温度的降低，形成草酸钙晶体的时间增加，且二水草酸钙(COD)的比例增加。在5℃的低温条件下，添加有二元、三元和四元羧酸的CaOx结晶中，COD成为主要的物相。     

The effects of polyelectrolytes on the inhibition and aggregation of calcium oxalate crystallization

The influence of polyelectrolytes with different architecture on spontaneous batch crystallization of calcium oxalate was investigated. A series of acidic acrylate block copolymers were been made, by radical polymerization, with defined molecular weight and structure. Radical polymerization of acrylic acid (AA) was carried out in the presence of α‐thiopolyethylene glycol monomethylether as a chain transfer agent to produce poly(ethylene glycolblockacrylic acid) copolymers. Poly(ethylene glycol) (PEG) block length in the copolymers was controlled by using three different molecular weight chain transfer agents (M_n = 350, 750 and 2000 g/mol). The presence of copolymers inhibited the crystal growth of calcium oxalate possibly through adsorption onto the active growth sites for crystal growth due to the charge and hydrophilic effects. Copyright © 2006 John Wiley & Sons, Ltd.     

柠檬酸钾和pH对单分子膜诱导草酸钙晶体生长的影响

研究了柠檬酸钾(K3cit)和pH对硬脂酸(SA)单分子膜诱导下一水草酸钙(COM)晶体生长的影响。当K3cit浓度c(K3cit)≤0．03mmol／L时，表面压(π)减小使COM尺寸变大；c(K3cit)=0．1mmol／L时，π压变化对COM尺寸影响不大，表明在较高的K3cit浓度下COM生长过程中晶格匹配不是主要控制因素。当c(K3cit)≤0．03mmol／L时，随着K3cit浓度增大，单分子膜下COM变薄。当c(K3cit)≥0．3mmol／L时，K3cit强烈地抑制COM的生长。pH的变化改变了柠檬酸不同物种的分布情况，从而影响COM晶面的生长。在pH=12时诱导了二水草酸钙(COD)晶体的生长，归因于K3cit对COD的诱导作用和高pH条件下SA单分子膜／水界面高的Ca^2 ／Oxa^2-摩尔比。     

In vitro effect of wheat bran (Triticum aestivum) extract on calcium oxalate urolithiasis crystallization

Urolithiasis can lead to the loss of renal function in some cases. In this study, we tested the inhibiting effect of wheat bran (Triticum aestivum L) extract on calcium oxalate crystallization in a turbidimetric model, by FTIR spectroscopy, and polarized microscopy. The results show that this plant extract has a major inhibitory effect on calcium oxalate crystallization.     

二维琼脂凝胶体系中过渡金属离子对草酸钙晶体生长和周期性沉淀的影响

在二维凝胶圆盘体系中,研究过渡金属离子对草酸钙晶体生长和周期性环状沉淀的影响,并对其形成机理进行探讨.结果表明:在一定浓度的Fe3 存在下,体系中出现了周期性环状沉淀现象.同时发现在此条件下抑制了一水合草酸钙(COM)晶型生成.此外,加入Zn2 、Co2 、Ni2 体系中的晶体都以二水合草酸钙(COD)为主;而加Cu2 离子的圆盘中,三水合草酸钙(COT)占据了主要的成分,这说明不同的过渡金属离子对三种草酸钙晶型的生成影响不同.另外,还对出现的与尿结石有关的特殊现象(白斑和放射状的条纹)进行了探讨.     

The kinetics of crystallization and dissolution of barium oxalate dihydrate and cadmium oxalate trihydrate

The kinetics of crystallization and dissolution of barium oxalate dihydrate and cadmium oxalate trihydrate have been studied at 25°C by following the changes in conductivity when supersaturated or subsaturated solutions are inoculated with seed crystals. In additive-free solutions, the growth of barium oxalate dihydrate seed crystals follows a rate law second order with respect to supersaturation, and a surface-controlled reaction is proposed. The same kinetic equation may be used to interpret the growth of this salt from supersaturated solutions containing a variety of phosphonate additives. However in these experiments the reaction is preceded by an initial fast surge in the concentration—time profiles. The rate of growth of cadmium oxalate trihydrate crystals varies linearly with supersaturation and this can be explained in terms of a surface diffusion model for growth. The dissolutions of both barium oxalate dihydrate and cadmium oxalate trihydrate follows a rate law in which the rate of reaction is proportional to the undersaturation and evidence is presented for a liquid transport rate-determining step for the dissolution reactions. Although both the crystallization and dissolution of cadmium oxalate trihydrate follow similar first order kinetic equations the appreciable differences in the values of the rate constants suggest that they are not reciprocal processes.     

Synthesis of different polymorphic modifications of calcium oxalate by electrodeposition

Different hydrates of calcium oxalate have been electrodeposited by electrogeneration of acid at the anode from an EDTA-stabilized calcium nitrate bath containing dissolved oxalate ions. The deposition is controlled by varying the bath pH, temperature, and current density. Formation of metastable CaC₂O₄·2H₂O is favored at high current densities at ambient temperature, whereas the thermodynamically stable CaC₂O₄·H₂O is formed at elevated bath temperatures. Both the polymorphs show oriented growth with respect to the substrate normal under different deposition conditions.     

Probing crystallization of calcium oxalate monohydrate and the role of macromolecule additives with in situ atomic force microscopy

Kidney stones are crystal aggregates, most commonly containing calcium oxalate monohydrate (COM) microcrystals as the primary constituent. Macromolecules, specifically proteins rich with anionic side chains, are thought to play an important role in the regulation of COM growth, aggregation, and attachment to cells, all key processes in kidney stone formation. The microscopic events associated with crystal growth on the [010], [121], and [100] faces have been examined with in situ atomic force microscopy (AFM). Lattice images of each face reveal two-dimensional unit cells consistent with the COM crystal structure. Each face exhibits hillocks with step sites that can be assigned to specific crystal planes, enabling direct determination of growth rates along specific crystallographic directions. The rates of growth are found to depend on the degree of supersaturation of calcium oxalate in the growth medium, and the growth rates are very sensitive to the manner in which the growth solutions are prepared and introduced to the AFM cell. The addition of macromolecules with anionic side chains, specifically poly(acrylic acid), poly(aspartic acid), and poly(glutamic acid), results in inhibition of growth on the hillock step planes. The magnitude of this effect depends on the macromolecule structure, macromolecule concentration, and the identity of the step site. Poly(acrylic acid) was the most effective inhibitor of growth. Whereas poly(aspartic acid) inhibited growth on the (021) step planes of the (100) hillocks more than poly(glutamic acid), the opposite was found for the same step planes on the (010) hillocks. This suggests that growth inhibition is due to macromolecule binding to both planes of the step site or pinning of the steps due to binding to the (100) and (010) faces alone. The different profiles observed for these three macromolecules argue that local binding of anionic side chains to crystal surface sites governs growth inhibition rather than any secondary polymer structure. Growth inhibition by cationic macromolecules is negligible, further supporting an important role for proteins rich in anionic side chains in the regulation of kidney stone formation.     

Vibrational studies of calcium oxalate monohydrate (whewellite) and an anhydrous phase of calcium oxalate

The IR spectrum of calcium oxalate monohydrate is re-analysed, and the Raman spectrum presented for the first time. The IR and Raman spectra of an anhydrous phase of calcium oxalate are discussed in relation to the effects of dehydration and compared with the monohydrate.     

Precipitation of calcium oxalate from homogeneous solution by cation release

Calcium oxalate can be precipitated from homogeneous solution by oxidation of the calcium/EDTA complex with hydrogen peroxide in boiling solution, in the presence of oxalate ion, at pH 6-8. The method gives large crystals and enables calcium to be determined in the presence of lead, which remains complexed.     

Biogenic synthesis of calcium oxalate crystal by reaction of calcium ions with spinach lixivium

In this paper, we report a biogenic synthesis protocol for preparation of calcium oxalate (CaC₂O₄, CaOx) crystal at room temperature by a simple protein-mediated reaction of aqueous Ca²⁺ ions with the C₂O₄²⁻ ions spontaneously released from spinach. The aggregation of calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) with a rod-like morphology was mainly formed in the spinach root lixivium, and the proportion of COM crystal in the aggregation increased with the concentration of Ca²⁺ ions increasing, however, spindle-shaped crystal was mainly obtained in the spinach leaf lixivium and the content of COM in the product was higher than that obtained in the root lixivium with the similar concentration of Ca²⁺ ions. COM phase disappeared and only COD crystal with morphology of tetragonal bipyramidal prisms presented in the product when the leaf lixivium was replaced by the leaf broth. The biomolecules such as proteins with molecular weight of 31 kDa liberated from the spinach root are negative-charged, which played important roles for the control of CaOx crystal growth in the root lixivium corresponding to the changes of protein secondary structures after reaction with Ca²⁺ ions. This research was potentially important for unraveling the biomineralization mechanism of CaOx crystal.     

Circular patterns of calcium oxalate crystals induced by defective Langmuir-Blodgett film

The injury of the renal epithelial cell membrane can promote the nucleation of nascent crystals, as well as adhesion of crystals on it. It thus accelerates the formation of renal calculi. In this paper, the defective Langmuir-Blodgett (LB) films were used as a model system to simulate the injured renal epithelial cell membrane. The microcosmic structure of the defective LB film and the molecular mechanism of the effect of this film on nucleation, growth, deposited patterns and adhesion of calcium oxalate monohydrate (COM) were investigated. The circular defective domains were formed in dipalmitoylphosphatidylcholine (DPPC) LB film after the film was treated by potassium oxalate. These domains could induce ring-shaped patterns of COM crystals. In comparison, the LB film without pretreatment by potassium oxalate only induced random growth of hexagonal COM crystals. As the crystallization time increased, the size of COM crystals in the patterns increased, the crystal patterns changed from empty circles to solid circles, and the number of the circular patterns with small size (5-20 μm) increased. The results would shed light on the molecular mechanism of urolithiasis induced by injury of the renal epithelial membrane at the molecular and supramolecular level.     

Simulation of calcium oxalate stone in vitro

Urolithiasis constitutes a serious health problem that affects a significant section of mankind. Between 3% and 14% of the population, depending on the geographical region, suffer from this illness[1]. For example, the incidence of urolithiasis in Florida in the United States of America was 15.7 in 100000 people and increased to 20.8 in 1996. Urolithiasis remains a major medical prob-lem in China, especially in Guangdong Province. A survey in 1997 in Shenzhen City, the most southern city i…     

Alginate hydrogel-mediated crystallization of calcium carbonate

We documented a specific method for combining calcium ions and alginate molecules slowly and continuously in the mineralization system for the purpose of understanding the mediating function of alginate on the crystallization of calcium carbonate. The alginate was involved in the nucleation and the growth process of CaCO₃. The crystal size, morphology and roughness of crystal surface were significantly influenced by the type of the alginate, which could be accounted for by the length of the G blocks in alginate. A combination of Fourier transform infrared spectroscopy and thermogravimetric analysis showed that there were the chemical interactions between the alginate and the mineral phase. This strategic approach revealed the biologically controlled CaCO₃ mineralization within calcium alginate hydrogels via the selective nucleation and the confined crystallization of CaCO₃. The results presented here could contribute to the understanding of the mineralization process in hydrogel systems.     

Thermal decomposition of calcium oxalate: beyond appearances

The goal of this study is twofold: to take a fresh look at the decomposition of calcium oxalate and to warn users of thermogravimetric analysis against the hasty interpretation of results obtained. Since the pioneer work of Duval 70 years ago, the scientific community has agreed unanimously as to the decomposition of anhydrous calcium oxalate (CaC₂O₄) into calcium carbonate (CaCO₃) and CO gas, and that of the calcium carbonate into calcium oxide (CaO), and CO₂ gas. We will demonstrate how these reactions, simple in appearance, in fact result from a succession of reactive phenomena involving numerous constituents both solid (CaCO₃, free carbon) and gaseous (CO₂ and CO) produced by intermediary reactions. The mass losses evaluated in the two distinct domains correspond closely to the molar masses of CO and CO₂, respectively. The simple mathematical calculation of that mass loss has simply concealed the existence of other reactions, and, most particularly the Boudouard reaction and that of solid phases between CaCO₃ and C. It just goes to show that appearances can be deceiving.

     

Metal-ligand-coordinated vesicles and vesicle-assisted preparation of calcium oxalate

A Ca(2+) -ligand-coordinated vesicle phase was prepared from a mixture of tetradecyldimethylamine oxide (C14DMAO) and calcium tetradecylamidomethyl sulfate [(CH3(CH2)13NHCOCH2OSO3)2Ca] in aqueous solution. At the appropriate mixing ratios, Ca(2+) -ligand coordination results in the formation of molecular bilayers because Ca(2+) can firmly bind to the head groups of C14DMAO and (CH3(CH2)13NHCOCH2OSO3)2Ca by complexation which reduces the area of head group. In this system, no counterions in aqueous solution exist because of the Ca(2+) -ligand coordination, and the bilayer membranes are not shielded by salts, i.e., a salt-free but charged molecular bilayer. The structures of the birefringent solutions of (CH3(CH2)13NHCOCH2OSO3)2Ca and C14DMAO mixtures were determined by transmission electron microscopy (TEM) images and rheological measurements, demonstrating that the birefringent sample solutions consist of vesicles. The Ca(2+) -ligand complex vesicle phase was used as a microreactor to prepare calcium oxalate (CaC2O4) crystals. Dimethyl oxalate, as a precursor, can hydrolyze to oxalic acid and methanol. Oxalic acid should precipitate Ca(2+) ions binding to the head groups of C14DMAO and (CH3(CH2)13NHCOCH2OSO3)2Ca to produce CaC2O4 crystals (Ca(2+) + H2C2O4 --> CaC2O4 (downward arrow) + 2H+). The obtained particles were CaC2O4 monohydrate, which were dominated by (020) faces. CaC2O4 precipitates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) analysis. After removal of CaC2O4 precipitates, a new cationic and anionic (catanionic) vesicle phase was constructed through electrostatic interaction between cationic C14DMAOH+ (C14DMAO + H+ --> C14DMAOH+) and anionic CH3(CH12)13 NHCOCH2OSO3-.