Chalcogen S∙∙∙S Bonding in Supramolecular Assemblies of Cadmium(II) Coordination Polymers with Pyridine-Based Ligands

Two cadmium(II) coordination polymers, with thiocyanate and pyridine-based ligands e.g., 3- acetamidopyridine (3-Acpy) and niazid (nicotinic acid hydrazide, nia), namely one- dimensional {; ; [Cd(SCN)2(3-Acpy)]}; ; n (1) and two- dimensional {; ; [Cd(SCN)2(nia)]}; ; n (2), are prepared in the mixture of water and ethanol. The adjacent cadmium(II) ions in 1 are bridged by two N, S-thiocyanate ions and an N, O-bridging 3-Acpy molecule, forming infinite one- dimensional polymeric chains, which are assembled by the intermolecular N–H∙∙∙S hydrogen bonds in one direction and by the intermolecular S∙∙∙S chalcogen bonds in another direction. Within the coordination network of 2, the adjacent cadmium(II) ions are bridged by N, S-thiocyanate ions in one direction and by N, O, N’-chelating and bridging nia molecules in another direction. The coordination networks of 2 are assembled by the intermolecular N–H∙∙∙S and N–H∙∙∙N hydrogen bonds and S∙∙∙S chalcogen bonds. Being the only supramolecular interactions responsible for assembling the polymer chains of 1 in the particular direction, the chalcogen S∙∙∙S bonds are more significant in the structure of 1, whilst the chalcogen S∙∙∙S bonds which act in cooperation with the N–H∙∙∙S and N–H∙∙∙N hydrogen bonds are of less significance in the structure of 2

Effect of pH and Type of Stirring on the Spontaneous Precipitation of CaCO3 at Identical Initial Supersaturation, Ionic Strength and a(Ca2+)/a(CO32−) Ratio

CaCO3 precipitation is physical-chemical basis of biomineral formation of hard tissue (shells, skeletons) in marine calcifying organisms (=biomineralization). Processes controlling biomineralization are still not fully clarified, so the study of influence of pH on basic processes of CaCO3 precipitation should contribute to better understanding of biomineralization under climate change. This paper reports on the effect of initial pH (pH0) and type of stirring (mechanical and magnetical) on spontaneous precipitation and phase composition, size and morphology of spontaneously precipitated CaCO3 formed at the identical initial supersaturation, ionic strength and a(Ca2+)/a(CO3 2-) ratio. The initial pH varied in a range 8.50 ≤ pH0 ≤ 10.50 and included values relevant for mimicking the conditions related to biomineralization in marine organisms. In all systems two CaCO3 polymorphs were found: calcite and/or vaterite. The increase of pH0 favoured the formation of rhombohedral calcite no matter the type of stirring. This was exclusively influenced by the systems’ pH0 (other relevant initial parameters were identical). Furthermore, increase of pH0 caused change of vaterite morphology from cauliflower-like spheroids to regular spherulites. The mechanically stirred systems produced larger calcite and vaterite particles and higher content of calcite

Role of Hydrodynamics, Li+ Addition and Transformation Kinetics on the Formation of Plate-Like {001}; Calcite Crystals

Plate-like calcite crystals with expressed unstable {; ; ; 001}; ; ; planes are interesting research model for investigations of interfacial interactions of different additive molecules, but also the crystal growth mechanisms. The aim of this study is to reproducibly prepare a significant amount of well- defined plate-like calcite crystals and to investigate the critical experimental parameters. Thus, in precipitation system c(NaHCO3) = c(CaCl2) = 0.1 mol dm−3, the influence of hydrodynamic parameters (mode of mixing of the reaction components) and a presence of lithium ions Li+ within a wide range of concentrations, 0.0 mol dm−3 < c(Li+) < 1.0 mol dm−3, have been studied. In addition, the kinetics of the solution mediated transformation of the initially formed metastable polymorph, vaterite, were followed in order to reproducibly describe the formation of stable calcite with expressed unstable morphology. The results indicate that the plate-like calcite is formed predominantly when the ultrasound irradiation is applied at c(Li+) ≥ 0.3 mol dm−3. On the other hand, when the magnetic and mechanical stirring are applied at higher Li+ concentrations, truncated rhombohedral crystals in a mixture with plate-like crystals are obtained. It was also found that the Li+ addition significantly prolonged the transformation, mainly by inhibiting the crystal growth of calcite

Calcium oxalate and gallic acid: structural characterization and process optimization toward obtaining high contents of calcium oxalate monohydrate and dihydrate

The search for an efficient drug or inhibitor in the formation process of kidney stones has been a promising research topic towards reducing the risks of the formation of disease. However, several challenges have been faced in investigating the most common constituents of kidney stones, calcium oxalate and its hydrate forms (COM, COD and COT). This study focuses on the preparation and structural characterization (TG, XRD, FTIR, SEM) of calcium oxalate hydrates in the presence of gallic acid (GA) and by varying operating parameters such as temperature (25 °C, 36.5 °C and 48 °C), pH (5.6, 6.5 and 7.5) and amount of added GA (ranging from 100 mg to 1000 mg). Response surface methodology was applied in order to evaluate the effects of operating parameters in the formation of COM and COD, and for the process optimization towards maximizing their content in samples. The results indicated that GA inhibited the formation of COM (0–100%) and promoted the formation of COD (0 ≤ 99%), while a medium pH and the amount of added GA showed a significant effect in the process of COD formation. In order to investigate the interactions established in the formation process and the possible adsorption between GA and the formed crystals, electrochemical measurements were performed

Precipitation of Calcium Oxalate Monohydrate Under Nearly the Same Initial Supersaturation

Spontaneous precipitation of calcium oxalate monohydrate (COM) in additive-free systems with nearly the same initial supersaturation has been investigated. The influence of thermodynamic parameters such as: temperature (t = 25, 36.5 and 48 °C), calcium concentration range of 5 mmol dm−3 ≤ ci(Ca2+) ≤ 10 mmol dm−3 and pH (5.6, 6.5 and 7.5), on the potential changes in structure, morphology and crystal size of COM have been studied. The values of the initial parameters were varied in a wide range and included values relevant for mimicking the physiological conditions related to those in biological systems and kidney stone formation. The results contributed to the knowledge about the influence of the selected individual parameters as well as their interplay influence on in vitro precipitation of COM. The findings have indicated that COM was the only precipitated phase exhibiting predominant dendritic morphology. The effects on crystal size, structure and morphology are more pronounced at higher temperature, pH and calcium concentration. These results provide basis for future studies of overall mechanism of COM formation and the future studies of kidney stone prevention

Comparison of the effect of the amino acids on spontaneous formation and transformation of calcium phosphates

Understanding the effect that specific amino acids (AA) exert on calcium phosphate (CaPs) formation is proposed as a way of providing deeper insight into CaPs’ biomineralization and enabling the design of tailored-made additives for the synthesis of functional materials. Despite a number of investigations, the role of specific AA is still unclear, mostly because markedly different experimental conditions have been employed in different studies. The aim of this paper was to compare the influence of different classes of amino acids, charged (aspartic acid, Asp and lysine, Lys), polar (asparagine, Asn and serine, Ser) and non-polar (phenylalanine, Phe) on CaPs formation and transformation in conditions similar to physiological conditions. The precipitation process was followed potentiometrically, while Fourier transform infrared spectroscopy, powder X-ray diffraction, electron paramagnetic spectroscopy (EPR), scanning and transmission electron microscopy were used for the characterization of precipitates. Except for Phe, all investigated AAs inhibited amorphous calcium phosphate (ACP) transformation, with Ser being the most efficient inhibitor. In all systems, ACP transformed in calcium-deficient hydroxyapatite (CaDHA). However, the size of crystalline domains was affected, as well as CaDHA morphology. In EPR spectra, the contribution of different radical species with different proportions in diverse surroundings, depending on the type of AA present, was observed. The obtained results are of interest for the preparation of functionalized CaPs’, as well as for the understanding of their formation in vivo

A Comparative EPR Study of Non-Substituted and Mg- Substituted Hydroxyapatite Behaviour in Model Media and during Accelerated Ageing

To assess the application potential of novel biomaterials, their behaviour in model media and upon sterilization should be investigated, as well as the stability related to their storage conditions. Such data are lacking for Mg- substituted HAP (Mg-HAP). Therefore, the changes in the local structure of non-substituted and Mg- HAP after irradiation and immersion in corrected simulated fluid and saline solution for 28 days were followed by electron paramagnetic resonance (EPR) spectroscopy for the first time. To better understand the stability of radical species induced by sterilization, EPR spectra of samples kept for 2 h at temperatures up to 373 K were recorded to provide an insight into the stability of the sample storage conditions by the accelerated aging method. Samples were characterized by PXRD, FTIR, SEM, EDS, AAS and TGA. Results confirmed that irradiation does not induce changes in the composition or the structure of any of the investigated materials. Fading or the complete disappearance of radical signals in the EPR spectra after immersion in both media was accompanied by the disappearance of other phases formed as a minor byproduct in the synthesis of substituted HAP, as confirmed by PXRD and FTIR analysis. Obtained results confirm the great potential of Mg-HAPs for biomedical applications, although closer attention should be given to the processes related to sample storage stability at different temperatures

Precipitation of Calcium Phosphates and Calcium Carbonates in the Presence of Differently Charged Liposomes

Liposomes (lipid vesicles) are often considered to be a versatile tool for the synthesis of ad-vanced materials, as they allow various control mechanisms to tune the materials’ properties. Among diverse materials, the synthesis of calcium phosphates (CaPs) and calcium carbonates (CaCO3) using liposomes has attracted particular attention in the development of novel (bio)materials and biomineralization research. However, the preparation of materials using liposomes has not yet been fully exploited. Most of the liposomes used have been anionic and/or zwitterionic, while data on the influence of cationic liposomes are limited. Therefore, the aim of this study was to investigate and compare the influence of differently charged liposomes on CaPs and CaCO3 formation. Zwitterionic 1, 2-dimyristoyl-sn- glycero-3-phosphocholine (DMPC), negatively charged 1, 2-dimyristoyl-sn-glycero-3-phospho-L- serine (DMPS), and positively charged 1, 2- dioleoyl-sn-glycero-3-ethylphosphocholine (EPC) lipids were used to prepare the respective liposomes. The presence of liposomes during the spontaneous precipitation of CaPs and CaCO3 affected both the precipitation and transformation kinetics, as well as the morphol-ogy of the precipitates formed. The most prominent effect was noted for both materials in the presence of DMPS liposomes, as (nano) shell structures were formed in both cases. The obtained results indicate possible strategies to fine-tune the precipitation process of CaPs and CaCO3, which may be of interest for the production of novel materials

The effect of selected environmental and anthropogenic molecules on calcium carbonate precipitation in artificial karst water

U ovom radu sustavno su, kroz dulji period, provedene fizičko-kemijske analize krške vode i sedre na odabranim lokacijama Nacionalnog parka Plitvička jezera. Zbog intenzivne mineralizacije, visokog pH i prezasićenosti kemijski sastav krške vode na jezeru Novakovića brod odabran je kao najreprezentativniji za usporedbu taloženja u prirodi te u laboratorijskim uvjetima, u umjetnoj krškoj vodi. Korištenjem standardnog laboratorijskog modela taloženja kalcijeva karbonata (CaCO3), sustavno je istražen utjecaj okolišnih molekula (huminska kiselina, HA i fulvinska kiselina, FA) i antropogenih iona (fosfat, PO43− i polifosfat, (PO3−)n) na taloženje CaCO3. Pokusima spontanog taloženja u rasponu temperatura, 10 °C (FA ≈ HA) > PO43−. Pri nižim temperaturama taloži manja količina CaCO3, a uz dodatak viših koncentracija PO43− i (PO3−)n taloženje CaCO3 je u potpunosti inhibirano. Za istraživanja mehanizma rasta kristala također je korištena umjetna krška voda, kao i prethodno pripravljeno kristalno sjeme romboedarskog {104} kalcita te pločastog kalcita s dominantnim {001} plohama. Analizom kinetičkih mjerenja, θ = 20 °C, utvrđeno je da se rast kristala {104} kalcita i {001} kalcita zbiva na spiralnoj dislokaciji te da je rast {104} kalcita znatno brži od rasta {001} kalcita. Okolišni i antropogeni aditivi uzrokuju inhibiciju rasta, kako {104} tako i {001} kalcita u nizu: (PO3−)n > (FA ≈ HA) > PO43−. Također, uz dodatak aditiva mijenja se mehanizam procesa rasta kristala kalcita te on postaje kontroliran procesom površinske nukleacije.In this disertation, the physico-chemical analyzes of karst water and travertine were performed in the Plitvice Lakes National Park. Due to the most intensive mineralization, high pH and supersaturation the chemical composition of water on the Lake Novakovića brod was chosen for comparison of precipitation in nature and in laboratory conditions in artificial karst water. Using a laboratory model of calcium carbonate (CaCO3) precipitation the influence of environmental molecules (humic acid, HA and fulvic acid, FA) and anthropogenic ions (phosphate, PO43− and polyphosphate, (PO3−)n) were investigated. Spontaneous precipitation experiments, in the range 10 ° C (FA ≈ HA) > PO43−. Lower temperatures cause the formation of smaller amounts of CaCO3 and with the addition of the high concentrations of additives, the precipitation of CaCO3 is completely inhibited. Rhombohedral {104} calcite and plate-like {001} calcite were used for crystal growth experiments in artificial karst water. Analysis of kinetic measurements showed that the growth of {104} calcite and {001} calcite crystals in artificial karst water, θ = 20 ° C, occurs on a spiral dislocation and that the growth of {104} calcite is much faster than the growth of {001} calcite. The addition of additives causes inhibition of {104} and {001} calcite growth: (PO3−)n > (FA ≈ HA) > PO43−. The applied additives cause a change in the growth mechanism, which becomes controlled by surface nucleation