Potentiometric Investigation of Specific Ionic Effects on Interactions between Bovine Serum Albumin and Weak Polyelectrolytes

The effect of salt on the behaviour of bovine serum albumin (BSA) in solution and on the interactions between BSA and the weakly charged polyelectrolytes poly(allylamine hydrochloride) and poly(dimethylaminoethylmethacrylate) was investigated by potentiometric titrations. Titrations of pure BSA solution and of the BSA solution with the addition of polyelectrolyte were performed in the presence of different salts. Three electrolytes having the same anion and a different cation were used, lithium chloride, sodium chloride, and caesium chloride. The corresponding base served as titrant. Experiments were performed at four electrolyte concentrations. The titration curves showed a strong influence of ionic strength and the electrolyte type. The cation effect was found to be in accordance with the Hofmeister series

Crystal Growth Mechanism of Vaterite in the Systems Containing Charged Synthetic Poly(Amino Acids)

Negatively ionisable poly-L-glutamic acid (pGlu) and poly-L-aspartic acid (pAsp), considered as analogues of the naturally occurring acidic macromolecules involved in biomineralization processes, were used as additives in the calcium carbonate precipitation systems in order to investigate their interactions with the vaterite crystallites. Poly-L-lysine (pLys), a positively ionisable poly(amino acid), was also used in order to elucidate the impact of the side chain charge. The growth kinetics of vaterite was found parabolic, indicating that the integration of growth units into the spiral step at the vaterite crystal surfaces is the rate-determining mechanism. The presence of small amounts of pGlu and pAsp inhibited the crystal growth. At the highest concentrations of both acidic macromolecules the exponential rate law was observed, which indicates the surface nucleation as the rate controlling mechanism. The addition of pLys in the range of applied concentrations did not significantly influence the crystal growth of the vaterite. Thus, the kinetic results, corroborated by morphological observations, pointed out to the significance of the negative charge of the side chains of selected polypeptides in the interfacial interactions with mineral planes. This work is licensed under a Creative Commons Attribution 4.0 International License

Green Approach in Synthesis of Bio-Inspired Materials

In this Special Issue, we focus on biomineralization/pathological biomineralization systems and the synthesis of bioinspired materials. This Special Issue promotes the current trend of “green chemistry”, and, as such, in all published papers, only aqueous solutions and eco-friendly additives were used for the production of well-characterized bioinspired materials. This Special Issue contains four papers: three original research papers and one review. Here, a brief introduction of these papers is provided

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

Adsorption of Arsenic on MgAl Layered Double Hydroxide

Groundwater in the Eastern Croatia, as well in the South-eastern Hungary, contains relatively high concentrations of arsenic that can cause chronic toxicity to humans. Therefore, the aim to find an ef-fective composite adsorbent that can be applied for arsenic water remediation by introducing it in the groundwater treatment is very important. The presented results were obtained using layered double hy¬droxide (LDH) as a sorbing system. MgAl LDH samples with a Mg:Al molar ratio of 2:1 were synthe¬sized. Adsorption of arsenic anions from groundwater samples from Eastern Croatia, as well as adsorption of model aquatic arsenic sample solutions, on MgAl layered double hydroxide was investigated. Induc¬tively coupled plasma atomic emission spectrometry (ICP-AES) was used for determination of arsenic concentration after adsorption. It was shown that in both cases the adsorption process could be interpreted in terms of Kroeker adsorption isotherm regardless to the presence of other ions in the groundwater. Addi¬tionally, the influence of phosphate concentration on adsorption of model arsenic samples was examined and it was shown that (at least in examined range of arsenic and phosphate concentration) there is no sig¬nificant influence of phosphate on adsorption of arsenic. (doi: 10.5562/cca2283

The Influence of a Protein Fragment Extracted from Abalone Shell Green Layer on the Precipitation of Calcium Carbonate Polymorphs in Aqueous Media

Many living organisms form mineral phases through biologically controlled processes, known as biomineralization. Thus created materials are composites of both, mineral and organic components. The shell of the gastropod mollusc red abalone (Haliotis rufescens) consists of calcite and aragonite layers, each of them containing characteristic biopolymers responsible for biomineralization. In this work, the effect of interstitial green sheet polypeptide, GP, extracted from the green layer of the mollusc red abalone shell, on the process of spontaneous precipitation of calcium carbonate polymorphs, was investigated. Three precipitation systems, in which the initial mineralogical composition of the precipitate was different, have been studied. Thus, in system (1) calcite appeared, in system (2) a mixture of calcite and vaterite was found, while in system (3), ASW, only aragonite precipitated. However, the precipitation kinetic measurements, X-ray diffraction, FT-IR spectroscopy, and light and scanning electron microscopy indicated that the addition of GP in the model systems caused the inhibition of precipitation and change of morphology of crystals as a consequence of GP adsorption on the crystal surfaces and its entrapment into the mineral structure. (doi: 10.5562/cca2197

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