Experimental-computational approach to investigate elastic properties of struvite.

The research presented in the paper concerns the elastic properties of struvite. The article combines theoretical and experimental research. Experimental studies were carried out on struvite single crystals grown in sodium metasilicate gel by single diffusion. This unique method leads to obtaining crystals of sufficiently large size to conduct, for the first time, experimental measurement of elastic properties of monocrystalline struvite. Using the nanoindentation method, the Ez = 29.1 ± 0.7 GPa value of the component of Young's modulus was determined for a struvite single crystal. In addition, the elastic constants C11, C22, and C33 were determined using micro-Brillouin spectroscopy. Theoretical calculations of the abovementioned properties have been carried out by employing density functional theory methods. Scaling of the theoretical elastic constants leads to obtaining good agreement with the experimental values. Values of the Ex and Ey components of the Young's modulus, not available from the experimental nanoindentation technique, have been determined theoretically as 23 GPa and 27 GPa, respectively. Differences in the values of elastic components and Young's modulus components are related to the layered crystal structure of struvite and directional character of the hydrogen-bonding pattern.

Structural and Optical Properties of Struvite. Elucidating Structure of Infrared Spectrum in High Frequency Range.

Study of structure and optical properties of magnesium ammonium phosphate hexahydrate crystal known as struvite is presented. Experimentally determined infrared (IR) and ultraviolet-visible (UV-vis) spectra are compared with the theoretical predictions of density functional methods. Examination of the interatomic bond lengths, Mulliken atomic charges, and binding energies of water in the magnesium hexahydrate cation, together with the analysis of the hydrogen bond pattern have allowed us to explain a special feature of the IR spectrum of struvite, a blueshift of the band corresponding to the O-H stretching mode. This mode has been assigned to a "dangling" hydroxyl group in one of the water molecules in magnesium hexahydrate. Using experimentally obtained UV-vis spectrum and performing Tauc plots analysis, optical bandgap of struvite has been narrowed to a range from 5.92 to 6.06 eV.

Understanding the role of zinc ions on struvite nucleation and growth in the context of infection urinary stones.

Taking into account that in recent decades there has been an increase in the incidence of urinary stones, especially in highly developed countries, from a wide range of potentially harmful substances commonly available in such countries, we chose zinc for the research presented in this article, which is classified by some sources as a heavy metal. In this article, we present the results of research on the influence of Zn2+ ion on the nucleation and growth of struvite crystals-the main component of infection urinary stones. The tests were carried out in an artificial urine environment with and without the presence of Proteus mirabilis bacteria. In the latter case, the activity of bacterial urease was simulated chemically, by systematic addition of an aqueous ammonia solution. The obtained results indicate that Zn2+ ions compete with Mg2+ ions, which leads to the gradual replacement of Mg2+ ions in the struvite crystal lattice with Zn2+ ions to some extent. This means co-precipitation of Mg-struvite (MgNH4PO4·6H2O) and Znx-struvite (Mg1-xZnxNH4PO4·6H2O). Speciation analysis of chemical complexes showed that Znx-struvite precipitates at slightly lower pH values than Mg-struvite. This means that Zn2+ ions shift the nucleation point of crystalline solids towards a lower pH. Additionally, the conducted research shows that Zn2+ ions, in the range of tested concentrations, do not have a toxic effect on bacteria; on the contrary, it has a positive effect on cellular metabolism, enabling bacteria to develop better. It means that Zn2+ ions in artificial urine, in vitro, slightly increase the risk of developing infection urinary stones.

Insights into the physical and chemical properties of struvite crystal surfaces in terms of the effectiveness of bacterial adhesion.

In this paper, we present the results of research on the physicochemical properties of two selected faces of the struvite crystal, which is the main component of infectious urinary stones. Two main faces, (001) and ([Formula: see text]), ending the c-axis, were selected for the study. These faces are not related by symmetry relations, which means, among other things, that they should have a different atomic structure, which was confirmed experimentally. In addition, the studies show that the tested surfaces have hydrophilic properties, however, the ([Formula: see text]) face is more hydrophilic compared to the (001) face. The physicochemical properties of the crystal as a whole, as well as the physicochemical properties of these faces influence the magnitude of adhesion. The adhesive force in both water and artificial urine is greater for face ([Formula: see text]) compared to face (001). The assessment of the adhesion of Proteus mirabilis bacteria in artificial urine also shows that the adhesion is greater for face ([Formula: see text]) than for face (001). The adhesion of bacteria to the examined faces of the struvite crystal, and in particular the increased adhesion of bacteria to the face ([Formula: see text]), may be the first stage of biofilm formation, which may result in a high rate of recurrence of infectious urinary stones after treatment.

Unique surface and internal structure of struvite crystals formed by Proteus mirabilis.

Crystallization of struvite from artificial urine in the presence of Proteus mirabilis microorganisms depends strongly on pH value. At small value of pH, struvite yields crystals of coffin-like habit with very specific structure. The analysis using scanning electron microscopy shows that the crystals possess well-defined faces, but higher magnifications show very specific structuration as if the crystals were built from small three-dimensional subunits. The possible role of microorganisms in the formation of such a structuration is analyzed. At higher pH value, the crystals exhibit dendritic growth with main trunk and branches. Although the formation mechanism of the specific structuration as well as dendritic structures is unknown, the nature of forces for such an alignment is analyzed. The revealed porous internal structure of struvite is also analyzed. The investigations provide evidence for the importance of biological regulation in crystallization process.

Effect of Curcumin Against Proteus mirabilis During Crystallization of Struvite from Artificial Urine.

We investigated the activity of curcumin against Proteus mirabilis and the struvite crystallization in relation to urinary stones formation. In order to evaluate an activity of curcumin we performed an in vitro experiment of struvite growth from artificial urine. The crystallization process was induced by Proteus mirabilis to mimic the real urinary tract infection, which usually leads to urinary stone formation. The results demonstrate that curcumin exhibits the effect against Proteus mirabilis inhibiting the activity of urease-an enzyme produced by these microorganisms. Addition of curcumin increases the induction time and decreases the efficiency of growth of struvite compared with the absence of curcumin. Interestingly, the addition of curcumin does not affect the crystal morphology and habit. In conclusion, curcumin has demonstrated its significant potential to be further investigated for its use in the case of struvite crystallization induced for the growth by Proteus mirabilis in relation to urinary stone formation.

The fascinating world of biogenic crystals.

The diverse properties of these crystals may lead to a variety of applications.

Consumption of soft drinks rich in phosphoric acid versus struvite crystallization from artificial urine.

In recent years, there has been a continuous increase in the incidence of urolithiasis, especially in highly developed countries. Therefore, the question arises which factors specific to these countries may be responsible for the increase in the incidence of this disease. In this article, we try to assess the effect of phosphoric acid, a component of various carbonated drinks, including Coca-Cola, on the nucleation and growth of struvite crystals, which are the main component of infectious urinary stones. The research was carried out in the environment of artificial urine with and without the presence of Proteus mirabilis bacteria. In the latter case, the activity of bacterial urease was simulated by adding an aqueous ammonia solution. The obtained results indicate that phosphoric acid present in artificial urine causes the nucleation of struvite to shift towards a lower pH, which means that struvite nucleates earlier in artificial urine compared to the control test. The amount of struvite formed is the greater the higher the concentration of phosphoric acid. At the same time, as the concentration of phosphoric acid increases, the growing struvite crystals are larger, which is disadvantageous because they are more difficult to remove from the urinary tract along with the urine. For the highest levels of phosphoric acid tested, large dendrites are formed, which are particularly undesirable as they can damage the epithelium of the urinary tract. The effect of phosphoric acid on the nucleation and growth of struvite is explained in base of chemical speciation analysis. This analysis indicates that the MgHCit and MgCit- complexes have the main influence on the nucleation and growth of struvite in artificial urine in the presence of phosphoric acid. It should be keep in mind that all these effects of phosphoric acid are possible when the urinary tract is infected with urease-positive bacteria. In the absence of infection, phosphoric acid will not cause struvite to crystallize.

First experimental evidence of the piezoelectric nature of struvite.

In this paper, we present the first experimental evidence of the piezoelectric nature of struvite (MgNH4PO4·6H2O). Using a single diffusion gel growth technique, we have grown struvite crystals in the form of plane parallel plates. For struvite crystals of this shape, we measured the piezoelectric coefficients d33 and d32. We have found that at room temperature the value of piezoelectric coefficient d33 is 3.5 pm/V, while that of d32 is 4.7 pm/V. These values are comparable with the values for other minerals. Struvite shows stable piezoelectric properties up to the temperature slightly above 350 K, for the heating rate of 0.4 K/min. For this heating rate, and above this temperature, the thermal decomposition of struvite begins, which, consequently, leads to its transformation into dittmarite with the same non-centrosymmetric symmetry as in case of struvite. The struvite-dittmarite transformation temperature is dependent on the heating rate. The higher the heating rate, the higher the temperature of this transformation. We have also shown that dittmarite, like struvite exhibits piezoelectric properties.

Density functional theory determination of structural and electronic properties of struvite.

Crystallographic structure, total energy, electronic structure, and the most important elastic properties of struvite, NH(4)MgPO(4).6H(2)O, the main component of infectious urinary stones, are presented. The calculations were performed using ab initio full-electron calculations within the density functional theory-generalized gradient approximation (DFT-GGA) framework. The obtained crystallographic symmetry and the calculated lattice parameters and also the elastic constants are in good agreement with the experimental data. The elastic properties are essential for establishing an optimal response of urinary stones during shock-wave lithotripsy. The calculated electronic charge distribution confirms the layered structure of the struvite crystals. The polar character of the crystal, well-known from crystal growth experiments, was also confirmed by the magnitude of spontaneous polarization which was obtained from direct determination of the electrical dipole density. The calculated value of spontaneous polarization is equal to -8.8 microC cm(-2). This feature may play a key role in struvite crystallization, electrically binding the charged active impurities and other active species, and consequently determining urinary stone formation. We also present the results of our own experiment of the mineralization of struvite induced to growth by Proteus bacteria which are mainly isolated from infectious urinary stones.

Publisher Correction: Aggregation of poorly crystalline and amorphous components of infectious urinary stones is mediated by bacterial lipopolysaccharide.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Aggregation of poorly crystalline and amorphous components of infectious urinary stones is mediated by bacterial lipopolysaccharide.

Poorly crystalline and amorphous precipitate (PCaAP) is one of the components of the so-called infectious urinary stones, which are the result of the activity of urease-producing microorganisms, mainly from the Proteus species, in particular Proteus mirabilis. The main component of this kind of stones is crystalline struvite (MgNH4PO4∙6H2O). Bacteria can build into the structure of the urinary stone and, in this way, they are one of the components of the urinary stone. From these three components - PCaAP, struvite and Proteus mirabilis - PCaAP exhibits the greatest ability to aggregate. The present study focuses on the aggregation of PCaAP. In particular, an influence of lipopolysaccharide (LPS) isolated from Proteus mirabilis on aggregation of PCaAP is presented. An aggregation of PCaAP is characterized by cross-sectional area of aggregates and zeta potential. The results demonstrate that, in artificial urine, the influence of freely suspended LPS on aggregation of PCaAP depends on the concentrations of LPS. Small concentrations of freely suspended LPS enhance the aggregation of PCaAP compared to the control test. For high concentrations of freely suspended LPS the formation of aggregates of PCaAP is inhibited. LPS, which is not freely suspended, but covers polystyrene latex beads, has no such properties. The investigations provide evidence for the importance of biological regulation in the PCaAP aggregation process.

Bacterially Induced Formation of Infectious Urinary Stones: Recent Developments and Future Challenges.

Infectious urinary stones make a serious medical problem concerning up to 20% of population. Additionally, recurrence after treatment reaches 50%. The formation of infectious urinary stones is connected with urinary tract infection with various bacteria. These are mainly the bacteria from Proteus species which have been isolated in 70% of bacteriainduced urinary stone cases. These microorganisms produce urease - a bacterial enzyme which plays a principal role in the crystallization process and is one of the main virulence parameters of these bacteria. The most common solid components of infectious urinary stones are the crystals of struvite and amorphous carbonate apatite. The formation of this kind of stones involves two main processes. The first one is the nucleation process of solid phases and the second is the aggregation of the precipitated phases, both crystalline and amorphous. In recent years, both these processes have been deeply investigated. In particular, different active compounds have been reported as potentially novel therapeutic agents to prevent or inhibit the formation of infectious urinary stones. In addition, there is rich scientific evidence regarding the chemical mechanisms of inhibitory effect of these active compounds. In recent years, specific interior and exterior structure of struvite and its porous nature have also been reported. In this article, we summarize and discuss recent development in this field of research. The paper concludes with future goals and challenges.

Temperature-dependent µ-Raman investigation of struvite crystals.

The effect of temperature on the vibrational properties of struvite crystals grown from silica gels was systematically studied by µ-Raman spectroscopy. The time-dependent Raman spectra recorded in the process of long time annealing of struvite crystal at 353 K do not indicate structural changes in the struvite crystal with the time of annealing. The temperature-dependent Raman spectra recorded in the range 298-423 K reveal a phase transition in struvite at about 368 K. Above this characteristic temperature, some of bands assigned to vibrations of the PO4 and NH4 tetrahedra and water molecules observed in the Raman spectra in low temperatures (orthorhombic phase) change their spectral parameters or disappear, which indicates a transition to a higher symmetry structure of struvite in the range of high temperatures.

Ab initio predictions of structural and elastic properties of struvite: contribution to urinary stone research.

In the present work, we carried out density functional calculations of struvite--the main component of the so-called infectious urinary stones--to study its structural and elastic properties. Using a local density approximation and a generalised gradient approximation, we calculated the equilibrium structural parameters and elastic constants C(ijkl). At present, there is no experimental data for these elastic constants C (ijkl) for comparison. Besides the elastic constants, we also present the calculated macroscopic mechanical parameters, namely the bulk modulus (K), the shear modulus (G) and Young's modulus (E). The values of these moduli are found to be in good agreement with available experimental data. Our results imply that the mechanical stability of struvite is limited by the shear modulus, G. The study also explores the energy-band structure to understand the obtained values of the elastic constants.