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Thermal stability, structural evolution pathways, and phase transition mechanisms of the calcium oxalates whewellite (CaC2O4·H2O), weddellite (CaC2O4·(2+x)H2O), and caoxite (CaC2O4·3H2O) have been ...

To study strontium (Sr) incorporation into calcium oxalates (weddellite and whewellite), calcium-strontium oxalate solid solutions (Ca,Sr)[C2O4]∙nH2O (n = 1, 2) are synthesized and studied by a complex of methods: powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Two series of solid solutions, isomorphous (Ca,Sr)[C2O4]&middot, (2.5 &minus, x)H2O) (space group I4/m) and isodimorphous Ca[C2O4]&middot, H2O(sp.gr. P21/c)&ndash, Sr[C2O4]&middot, H2O(sp.gr. P 1 - ), are experimentally detected. The morphogenetic regularities of their crystallization are revealed. The factors controlling this process are discussed.

The crystallization of calcium oxalates (weddellite and whewellite) by interaction of natural and synthetic apatites and fossilized tooth tissue with fungus Aspergillus niger, one of most active acid producers, was studied in vitro. The morphology and the sequence of formation of growing oxalate hydrate crystals were revealed. It was shown that morphogenetic patterns of calcium oxalate crystallization on apatite substrates under the action of Aspergillus niger micromycete are determined by the chemical properties of the crystallization medium, which depends on the solubility of the underlying substrate and on its chemical composition and structural features (dispersity and porosity). The main difference between oxalate crystallization under the influence of Aspergillus niger micromycete on the surface of apatite substrates and on the surface of calcite marble is the predominance of whewellite over weddellite on all stages of growth.

The effect of bacteria that present in the human urine (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus) was studied under the conditions of biomimetic synthesis. It was shown that the addition of bacteria significantly affects both the phase composition of the synthesized material and the position of crystallization boundaries of the resulting phosphate phases, which can shift toward more acidic (struvite, apatite) or toward more alkaline (brushite) conditions. Under conditions of oxalate mineralization, bacteria accelerate the nucleation of calcium oxalates by almost two times and also increase the amount of oxalate precipitates along with phosphates and stabilize the calcium oxalate dihydrate (weddellite). The multidirectional changes in the pH values of the solutions, which are the result of the interaction of all system components and the crystallization process, were analyzed. The obtained results are the scientific basis for understanding the mechanisms of bacterial involvement in stone formation within the human body and the creation of biotechnological methods that inhibit this process.

The presence and study of the species composition of bacterial and fungal colonies in renal stones was determined. It was shown that the presence of microorganisms depends on the phase composition of the renal stone. No microbial colonies were detected in oxalate stones. Under the action of the acid-producing bacterial and fungal colonies, secondary crystallization of calcium oxalates (whewellite and weddellite) on phosphate aggregates can occur.

The work considers the aggregation process of calcium oxalate monohydrate crystals (whewellite) during their crystallization from aqueous solutions. The intensive crystal aggregation during the precipitation is evidenced by a decrease in the bulk concentration against an increase in the crystal size. At the initial stages of crystallization fine particles are mainly captured by larger ones in the form of substance deposition on the initiating centers: organic blobs, dead cells, and so on. During the crystallization the effect of the dominant growth of large aggregates increases; the process develops autocatalytically; fine particles disappear more rapidly than large ones, and the crystal size distribution compresses simultaneously with an increase in the average particle size.

The single-crystal structures of four biomimetic weddellites CaC2O4 · (2 + x)H2O with different contents of zeolitic water (x = 0.10–0.24 formula units) produced by the microscopic fungus Aspergillus niger were refined from X-ray diffraction data (R = 0.029–0.038). The effect of zeolitic water content on the structural stability of weddellite was analyzed. The parameter a was shown to increase with increasing x due to the increase in the distance between water molecules along this direction. The water content and structural parameters of the synthesized weddellites are similar to those of weddellites from biofilms and kidney stones.

The refinement of the structures of 17 weddellite crystals [Ca(C 2 O 4 )·(2+ x )H 2 O, I 4/ m , a = 12.329–12.378 A, c = 7.345–7.366 A, V = 1117.8–1128.6 A 3 ], which were taken from the oxalic renal stones of the St. Petersburg (Russian Federation) citizens of both sexes aged from 24 to 65 years, has been carried out by the means of single-crystal X-ray diffraction ( R 1 = 0.024–0.057). According to the results of the study, the amount of “zeolitic” water molecules ( x ) in the structure of weddellite varies from 0.13 to 0.37 pfu. A significant positive correlation between the amount of “zeolitic” water in the structure of weddellite and the closest interatomic distance between coordination water molecules in the large channels (OW1-OW1) was found as well as positive correlation between the value of the a parameter and the average distance of in Ca polyhedron. Obtained linear regression equation: x = 5.43 a – 66.80, can be used for determination of the “zeolitic” water amount using the known unit-cell a parameter with mean-root-square error ±0.03 pfu. It was found that the x value for the crystals selected from the “mono-weddellite” stones ( x = 0.13–0.24) are at the bottom of the range, thus we can assume that weddellite crystals with fewer “zeolitic” water amounts would be relatively stable. This work expands the knowledge of pathogenic crystal growth processes in living organisms and the development of the theory of oxalate stone formation in humans and animals, and may provide a building block for biomolecular technologies that approach the prevention and treatment of diseases associated with lithiasis.

The pattern of ion substitutions and non-stoichiometry of oxalate and phosphate human body minerals (weddellite, whewellite, hydroxyapatite, struvite, and brushite) and their synthetic analogs was investigated by complex X-ray diffraction, spectroscopic, and chemical methods. All the studied biological minerals are characterized by variable non-stoichiometry composition that reflects the non- stationarity of formation conditions. Non-stoichiometry of calcium oxalates results from variations in quantities of disorderly distributed water molecules. The water amount in weddellite significantly influences the crystal structure parameters. In particular, there is positive correlation between the value of a parameter and the occupancy of “zeolitic” water sites. Variations in composition of calcium and magnesium phosphates are caused by substitutions at all the crystallographic sites. Ion replacements in apatite and struvite are more prominent in comparison with those in brushite. Non-stoichiometry of apatite and brushite is due to the presence of vacancies at the Ca-sites, and that of struvite is due to the vacancies at the Mg-site. Two types of non-stoichiometry in carbonated apatites of B-type realize due to replacements PO4 3− ← CO3 2− or OH− ← H2O. Maximum concentrations of impurity ions in magnesium and calcium phosphates are mainly limited by the content of these ions in the physiological solution. In case of Mg replacement with Ca in struvite and Ca with K in brushite and apatite, it is also essentially limited by the size differences of the host and admixture ions.

Urolithiasis is rather widespread disease. However, till now there are no reliable methods of treatment and preventive maintenance for this illness, despite significant efforts. Moreover, it is completely not clear how renal stones are forming. The majority of renal stones consist of calcium oxalates – monohydrated whewellite CaC2O4·H2O and dihydrated weddellite CaC2O4·2H2O. Weddellite is a metastable phase under crystallizing conditions, and usually its crystals are substituted with small-grained whewellite. At the same time, about 38% of oxalate renal stones are made of weddellite. The purpose of this work is to examine the influence of crystallizing conditions on the calcium oxalates phase formation in the renal stones. Our modeling experiments were carried out with the variation of crystallizing conditions (temperature, pH, proportion of calcium and oxalate, organic and inorganic species in the physiological solution, amount of micromycetes and bacterial–viral associates, and time of crystallization). Experimental data show that the presence of peptides, bacteria, micromycetes and viruses, Mg2+, and CO3 2− ions in the solution stabilizes the calcium oxalate dehydrate crystallization.