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)     

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)     

Crystallization of silicalite‐1 from clear synthesis solutions: Effect of template concentration on crystallization rate and crystal size

Synthesis of silicalite‐1 powders and membranes from initially clear solutions with different tetrapropylammonium hydroxide or bromide concentrations was studied. While tetrapropylammonium bromide acts only as template, tetrapropylammonium hydroxide provides both the template and hydroxyl ions to the synthesis medium. The effects of template and hydroxyl ion concentration on the product yield, crystallization rate and crystal size were investigated. Pure and highly crystalline silicalite‐1 was obtained with all compositions. The nucleation time decreases from 100 h to 20 h and the crystal size decreases from 3.5 μm to 0.35 μm as the template amount x is increased from 5 to 30 moles at a batch composition of 80SiO₂.xTPAOH.1500H₂O at 95 °C. Yield of silicalite‐1 passes through a maximum at intermediate TPA concentration. (© 2009 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)     

Preparation and structure of calcium peroxide‐templated porous calcium carbonate crystals

Crystalline calcium carbonate with randomly dispersed porous structure was prepared through co‐ crystallization with calcium peroxide and the following template elimination by a post heating treatment and washing with water. The artificial CaCO₃ possess abundant macro‐mesopores structures and high surface area. This approach may open a new general route for the preparation of crystals with high porosity and structure specialty. (© 2011 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)     

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)     

Formation of oxygen deficient BaPbO3‐x by oxalate decomposition

BaPbO₃ is assumed to be oxygen deficient but the exact determination has never been reported. The aim of this study is to investigate the correlation between synthetic conditions and the resulting oxygen deficiency of BaPbO_3‐x. The formation of BaPbO_3‐x by decomposition of barium‐ and lead oxalate up to 850 °C is significantly faster compared to conventional high temperature solid state reactions of oxide compounds. The discrete reaction steps were studied by simultaneous thermal analysis and X‐ray powder diffraction. The oxygen content was determined by temperature‐programmed reduction analysis. It is shown that the formation process is very sensitive to the chosen starting materials leading to different oxygen deficits caused by partial oxidation from Pb²⁺ to Pb⁴⁺. The resulting perovskites show chemical compositions of BaPbO_2.74 and BaPbO_2.82. The varying oxygen deficits should have an effect on structural properties. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Syntheses and X‐Ray crystal structures of aminated 4,4'‐Bi‐1,2,4‐triazole salts

3‐Amino‐4,4'‐bi‐1,2,4‐triazole hydrochlorate and 3,3'‐diamino‐4,4'‐bi‐1,2,4‐triazole ditosylate were obtained with the reduction of 3,3',5,5'‐tetraazide‐4,4'‐bi‐1,2,4‐triazole (TABT) by (Ph)₃P/H₂O and the followed salt forming reaction with concentrated HCl and aqueous TsOH, respectively. Their structures were characterized with elemental analyses, IR, MS, ¹H and ¹³C NMR spectra. The single crystals were cultivated and determined with X‐ray diffraction, test results reveal that H⁺ combines with electron‐rich N atom in triazole ring to form ionic salts, two N,N‐linked triazoles are almost perpendicular to each other due to lower steric hindrance. The aromatic π…π stacking interactions and hydrogen bonds between molecules are observed. These two novel salts and their derivatives may be applied in coordination chemistry, medicinal chemistry and energetic materials.     

Effect of monovalent salts on morphology of calcium carbonate crystallized in Couette‐Taylor reactor

Monovalent ionic additives, Na⁺, K⁺ and NHequation/tex2gif-stack-1.gif impact on the morphology and agglomeration of CaCO₃ crystals. As increasing the additive concentration, the regular shaped crystals such as rhombohedron and spindle are changed to irregular one due to the inclusion of Na⁺ and K⁺ into the crystal structure. The inclusion of Na⁺ and K⁺ is detected using ICP‐AES. The partition of coefficients of Na⁺ and K⁺ are estimated as 9.74 × 10^–4, 9.73×10^–4, respectively and the amount of inclusion in the crystals is about 2×10³ ppm. However, the inclusion of ions does not modify a crystal structure of calcite. Since NH₄⁺ is large in radius, it is not included in crystal but shifts the spindle shape of crystal to the rhombohedral one. It is interesting to find that such modification of crystal morphology begins to appear at high additive concentration (0.05 M). In addition, the crystal agglomeration is promoted because the electric repulsive charge is reduced as increasing the additive concentration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase‐manipulable synthesis of Cu‐based nanomaterials using ionic liquid 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate

Using the ionic liquid (IL), 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate, and the precursor Cu₇Cl₄(OH)₁₀·H₂O, series of phase‐manipulable Cu‐based nanomaterials were synthesized by hydrothermal and microwave assisted routes, respectively. The structural characters of the as‐prepared CuO, CuO/Cu₂O composites and pure Cu nanoparticles were investigated by XRD, SEM, TEM and HRTEM, and their surface photovoltaic properties were studied by surface photovoltage spectra. Via hydrothermal route Cu²⁺ ions were found to be reduced gradually into Cu⁺ and subsequently Cu⁰ with increasing the IL, and various phase ratio of CuO, Cu₂O and Cu composite nanosheets and pure Cu nanoparticles were obtained. This implies that the IL could function as both a reductant in the oxygen‐starved condition and a template for the nanosheet products. The ¹H‐NMR result of the IL supports it being a reductant. In microwave assisted route, however, only monoclinic single crystalline CuO nanosheets were obtained, which indicates the IL being a template only in oxygen‐rich condition. Therefore, the crystal phase, composition and morphology of the Cu‐based products could be controlled by simply adjusting the quantity of the IL and oxygen in solution routes. The molecular structure of the IL after oxidation reactions was investigated by ¹H‐NMR and a possible reaction mechanism was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of high purity calcium carbonate micro‐ and nano‐structures on polyethylene glycol templates using dolomite

This research paper describes the synthesis of nano‐ and micro‐structures of high purity precipitated calcium carbonate (PCC) on poly(ethylene glycol)(PEG) templates for broad‐range industrial applications, using readily available and cheap impure dolomitic marbles. In the method, calcium components of impure dolomitic marbles are extracted as calcium sucrate which is then bubbled with carbon dioxide gas using a carbonation column in the presence of PEG. The effects of concentration of PEG, pH of calcium sucrate solution and temperature on the final yield, morphology and polymorphism of PCC have been studied. Vaterite and calcite are the crystalline forms of calcium carbonate found in final PCC products. The vaterite is observed as hollow spheres with particle diameter of 1.5‐2 μm which is formed by aggregation of vaterite nanoparticles with particle size of 20 nm on PEG templates. Optimum conditions for the highest PCC yield of 79.94% are 0.4 mol dm⁻³ of PEG, pH of 6.5 and temperature of 80 °C. The purity of PCC products is about 99%. Therefore, the synthesized PCC products are of required purity and quality for industrial applications.     

Diamagnetic and photoabsorption characterisation of gel‐grown cadmium oxalate single crystals

Perfect single crystals of cadmium oxalate trihydrate have been grown using the slow and controlled reaction between Cd⁺² and (C₂O₄)^‐2 ions in agar‐agar gel, resulting in the formation of insoluble product Cd(COO)₂.3H₂O. The optimum growth parameters have been determined. The variation of magnetic moment of the grown crystals under an applied static magnetic field is studied and the material is found to be diamagnetic. The polarizability is found sensitive to optical band gap. An empirical relation between magnetic susceptibility and electronic polarizability has been established. Optical absorption spectra of the sample recorded in the range 200‐2500 nm reveal transitions involving absorption and emission of phonons. The detailed study supports the existence of allowed direct and indirect allowed gaps in the material. The direct allowed transition prevails in the region of relatively higher photon energy. Some feeble disorder in the crystal is conceived to be present. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis and structure of a 2D supramolecular framework with right‐ and left‐helices based on mixed ligands

An exploration of the cobalt‐OH‐BDC‐bpp system under hydrothermal conditions, has led to the isolation of a novel framework [Co(OH‐BDC)(bpp)_0.5(H₂O)]_n (OH‐BDC = 5‐hydroxyisophthalic acid, bpp = 1,3‐bi(4‐pyridyl)propane). Single‐crystal X‐ray analysis reveals that it crystallizes in the monoclinic space group P2₁/n. a = 10.235(8) Å, b =17.882(14) Å, c = 14.291(11) Å, β = 92.107(9)°.The cobalt ions are linked into an extended helical chain via OH‐BDC and mono‐coordinated bpp ligands through hydrogen‐bonding interactions. Further these helical chains are united together through the bridging bpp to form a 2D layer and the adjacent chains possess the opposite chirality. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of calcium sulfate dihydrate at different supersaturation ratios and different free sulfate concentrations

Free Sulfate is a major parameter affecting gypsum crystallization during phosphoric acid production. Gypsum crystal size, shape and filtration rate are significantly affected by the concentration of free sulfate. It is, therefore, important to evaluate the effectiveness of different sulfate levels from 1.5% to 3.5% on induction time and gypsum morphology. The crystallization of gypsum was carried out under simulated conditions of phosphoric acid production by the dihydrate process. Calcium hydrogen phosphate and sulfuric acid were mixed with dilute phosphoric acid at 80 °C, and the turbidity of the reaction mixture was measured at different time periods to calculate the induction time of gypsum crystals formation. With increasing free sulfate concentration, the induction time was significantly decreased. Chemical processing of Central and South Florida phosphate concentrates under different concentrations of free sulfate from 1.5% to 5.5% was carried out. The change on crystal size distribution and filtration rate were traced with free sulfate concentrations. The results show that, filtration rate of phosphogypsum was correlated to the mean diameter of crystals. In addition, induction time and co‐crystallized (lattice) P₂O₅ % in gypsum are decreased with increasing free sulfate content from 1.5% to 3.5%. Morphology of formed gypsum crystals at different sulfate contents and different supersaturation ratios are investigated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

One‐step synthesis of ZnO/MgO core‐sheath structures

A kind of ZnO/MgO core‐sheath structure has been prepared directly by the pyrolysis of a mixture of polyvinyl alcohol, magnesium acetate, and zinc chloride coating on glass fiber mats at 450 °C for 60 min. The growing process and effect of the anions on the morphology of ZnO/MgO structures have been preliminarily discussed. The results indicate that ZnCl₂ will transform to ZnO crystal through an intermediate of zinc hydroxide chloride. ZnO crystal act as the core of the micorod, and MgO lamellas act as the sheath. The concurrence of chloride and acetate anions in the precursor is necessary for the growth of ZnO/MgO core‐sheath structures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase‐controlled crystallization of amorphous calcium carbonate in ethanol‐water binary solvents

The evolution of amorphous calcium carbonate (ACC) into crystals in ethanol/water binary solvents under ambient temperature was investigated, and it was found to depend on the volume ratio of ethanol to water (R). Calcite remained dominant when the amount of water was high (R = 1/3). A slight change in the amount of ethanol (R = 3/1) could lead to a dramatic change in the polymorph from calcite to aragonite. However, when poly (allylamine hydrochloride) (PAH) was added at R = 3/1, almost pure vaterite could be obtained, which has a specific morphological variation (from hollow microspheres to cloud‐like). This study provides an alternative polymorphic route for the CaCO₃ mineral by using the evolution of ACC in different solvent environments, which provides some useful clues for understanding the importance of kinetic control of the morphologies and polymorphs of a wide range of inorganic materials. In addition, this simple mild phase‐controlled synthetic method could be scaled up as a green chemistry route for the industrial production of different polymorphs of CaCO₃.     

Crystallization of potassium sulfate by cooling and salting‐out using 1‐propanol in a calorimetric reactor

A study was made on a isothermal process for the crystallization of potassium sulfate as an alternative to the cooling process. The process employs addition of 1‐propanol to aqueous salt solutions to achieve the “saltingout” of the K₂SO₄. This work was carried out using an automated Mettler Toledo model RC1 reactorcrystallizer with 800 ml capacity, and controlled isothermally at 25 °C to test the crystallization of K₂SO₄ by addition of the alcohol, and from 50 to 10 °C for the cooling crystallization. In both systems, the line of nucleation points was shown to be approximately parallel to the saturation curve, with an average width of 13°C or 3 % mass for crystallization by cooling, compared with 0.2 to 1 % by salting‐out. In experiments on crystallization by cooling, the K₂SO₄ crystals were 0.27 mm in mean size, showed 7 % agglomeration, and contained 8.5 % moisture. Crystals obtained by salting‐out had a mean size of 0.79 mm, 28 % agglomeration, and 9‐10 % moisture content. A crystal shape factor of approximately of 0.7 was obtained in both systems, apart from the agglomeration.     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polychloro‐alkanes used as templates in solvothermal synthesis of selenium microrods

Polychloro‐alkanes, including dichloromethane (CH₂Cl₂), chloroform (CHCl₃) and tetrachloromethane (CCl₄), were first introduced to synthesize trigonal selenium (t‐Se) microrods as a new kind of coordinating solvent, which played two important roles in the formation of Se nuclei and templated effect of Se microrods. The possible formation mechanism of t‐Se microrods was proposed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)