•In the model precipitation system a mixture of calcite and vaterite precipitate.•The amino acids with charged side groups strongly change the precipitate.•The influence of amino acids with non-polar ...side groups is weak.•The effect of amino acids with polar side groups is similar to effect of charged AA.
Spontaneous precipitation of CaCO3 polymorphs in the presence of selected amino acids (AA) has been investigated. The l-aspartic acid (Asp), l-lysine (Lys), l-asparagine (Asn), l-tyrosine (Tyr), l-phenylalanine (Phe), l-serine (Ser) and l-alanine (Ala) were selected because of different charge and polarity of their side chains at applied experimental conditions. The investigated AA are building units of soluble macromolecules, putatively responsible for biomineralization of molluscs’ exoskeletons. It was assumed that not only the acidic, but also the polar (hydrogen bonding) AA might contribute to macromolecules’ interactions with the mineral surfaces. The mineralogical composition, structure and morphology of precipitates formed in the presence of wide range of concentrations of AA have been determined by XRD, FT-IR and EPR spectroscopy, HPLC-MS and SEM. In the reference system, without AA addition, a mixture of typical calcite rhombohedral crystals and vaterite spherulites has been observed, while AA with negatively charged or polar side chains (Asp, Tyr, Lys, Asn, Ser) significantly changed the morphology, phase composition and crystal structure of the precipitates. The effects of nonpolar AA (Phe, Ala) on the structural and morphological properties of precipitates are less pronounced. The stronger impact observed for polar AA and particularly negatively charged Asp, may be correlated with the additional electrostatic interactions of side-chain groups with mineral surfaces.
The aim of this study is to contribute to understanding the mechanisms underlying the formation of biologically relevant minerals by comparing the properties of solid phases formed in calcium ...phosphate (CaP) or calcium carbonate (CaCO3) precipitation systems, at defined initial experimental conditions: supersaturation, constituent ions ratio, ionic strength, and/or presence of relevant inorganic ions. Thus, three systems of different chemical complexities were investigated: (a) system containing constituent ions, (b) system containing additional co-ions, and (c) system with higher ionic strength and addition of Mg2+. The respective precipitation diagrams were constructed, and supersaturation domains of different CaP and CaCO3 solid phases formation were identified. The obtained results may have implications not only for biomineralization and geochemistry, but also for materials science in general.
•Lysozyme–PSS complexation was examined at various pH and reactant concentrations.•At lower charge ratios of reactants stable colloid particles were formed.•At higher charge ratios larger particles ...(floccules) appeared.•Complexation resulted in negative enthalpy changes.
It is well-known that mixing of aqueous solutions of oppositely charged proteins and polyelectrolytes leads to the formation of aggregates often called protein–polyelectrolyte complexes. In this study, we investigated the interactions between aqueous solutions of lysozyme and sodium poly(styrenesulfonate) (PSS) as the model system for investigating protein–polyelectrolyte complexation processes. The experimental methods used in this study were isothermal titration microcalorimetry, electrophoretic mobility (i.e. zeta potential determination) and particle size (i.e. hydrodynamic radius) measurements. The effect of pH, reactant (protein and polyelectrolyte) concentration and titration direction (addition order) on lysozyme–PSS complexation was investigated at θ=25°C and at ionic strength Ic=10−2moldm−3.
At all three examined pH values (pH=3.1, 4.6 and 7.5) at low charge ratios a stable colloidal suspension was obtained in which charged colloid particles, whose sign of charge corresponds to that of the titrand, were present. On the other hand, at higher charge ratios large particles (floccules) appeared (with the hydrodynamic radius in the range 2–7μm). These floccules were also charged and, at first, their charge sign was equal to that of the titrand (|ζ|=30–50mV). However, upon further addition of the titrant the charge of the floccules reversed as a result of the surplus of titrant molecules in the corona.
The change in pH leads to the significant change in charge ratios at which the onset of flocculation is observed. In all examined cases the charge ratio at which zeta potential starts to change corresponds to the onset of flocculation determined by DLS. The reaction heat effects were determined and it was shown that in all examined cases complexation resulted in measurable negative enthalpy changes.
With the ever growing use of nanoparticles in a broad range of industrial and consumer applications there is increasing likelihood that such nanoparticles will enter the aquatic environment and be ...transported through freshwater systems, eventually reaching estuarine or marine waters. Due to silver's known antimicrobial properties and widespread use of silver nanoparticles (AgNP), their environmental fate and impact is therefore of particular concern. In this context we have investigated the species-specific effects of low concentrations of 60 nm AgNP on embryonal development in Mediterranean sea urchins Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis. The sensitivity of urchin embryos was tested by exposing embryos to nanoparticle concentrations in the 1–100 μg L−1 range, with times of exposure varying from 30 min to 24 h (1 h–48 h for S. granularis) post-fertilisation which corresponded with fertilized egg, 4 cell, blastula and gastrula development phases. The most sensitive species to AgNP was A. lixula with significant modulation of embryonal development at the lowest AgNP concentrations of 1–10 μg L−1 with high numbers of malformed embryos or arrested development. The greatest impact on development was noted for those embryos first exposed to nanoparticles at 6 and 24 h post fertilisation. For P. lividus, similar effects were noted at higher concentrations of 50 μg L−1 and 100 μg L−1 for all times of first exposure. The S. granularis embryos indicated a moderate AgNP impact, and significant developmental abnormalities were recorded in the concentration range of 10–50 μg L−1. As later post-fertilisation exposure times to AgNP caused greater developmental changes in spite of a shorter total exposure time led us to postulate on additional mechanisms of AgNP toxicity. The results herein indicate that toxic effects of AgNP are species-specific. The moment at which embryos first encounter AgNP is also shown to be an important factor in the development of abnormalities, and future applications of the sea urchin embryo development test for nanoparticle toxicity testing should carefully address the specific phase of development of embryos when nanoparticles are first introduced.
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•AgNP effects on sea urchin embryo development is species specific.•Time-point of first exposure to AgNP has a significant impact on embryo development.•Sensitivity to AgNP increases from Paracentrotus lividus to Sphaerechinus granularis to Arbacia lixula embryos.•Effect of AgNP compared to equal mass of Ag+ shows additional mechanism of toxicity.
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