6 results on '"Damir Kralj"'
Search Results
2. In Vitro Coral Biomineralization under Relevant Aragonite Supersaturation Conditions
- Author
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Damir Kralj, Giuseppe Falini, Zvy Dubinsky, Simona Fermani, Branka Njegić Džakula, Stefano Goffredo, Njegic Dzakula B., Fermani S., Dubinsky Z., Goffredo S., Falini G., and Kralj D.
- Subjects
supersaturation ,coral ,biomineralization ,kinetic ,aragonite ,Artificial seawater ,engineering.material ,010402 general chemistry ,01 natural sciences ,Mineralization (biology) ,Catalysis ,Calcium Carbonate ,Animals ,14. Life underwater ,Growth rate ,Kinetic ,Supersaturation ,Animal ,010405 organic chemistry ,Precipitation (chemistry) ,Chemistry ,Aragonite ,Organic Chemistry ,General Chemistry ,Anthozoa ,0104 chemical sciences ,Kinetics ,Chemical engineering ,Microscopy, Electron, Scanning ,engineering ,Nanoparticles ,Leptopsammia pruvoti ,Crystallization ,Biomineralization - Abstract
The biomineralization of corals occurs under conditions of high and low supersaturation with respect to aragonite, which corresponds to day- or night-time periods of their growth, respectively. Here, in vitro precipitation of aragonite in artificial seawater was investigated at a high supersaturation, allowing spontaneous nucleation and growth, as well as at low supersaturation conditions, which allowed only the crystal growth on the deliberately introduced aragonite seeds. In either chemical systems, soluble organic matrix (SOM) extracted from Balanophyllia europaea (light sensitive) or Leptopsammia pruvoti (light insensitive) was added. The analyses of the kinetic and thermodynamic data of aragonite precipitation and microscopic observations showed that, at high supersaturation, the SOMs increased the induction time, did not affect the growth rate and were incorporated within aggregates of nanoparticles. At low supersaturation, the SOMs affected the aggregation of overgrowing crystalline units and did not substantially change the growth rate. On the basis of the obtained results we can infer that at high supersaturation conditions the formation of nanoparticles, which is typically observed in the skeleton's early mineralization zone may occur, whereas at low supersaturation the overgrowth on prismatic seeds observed in the skeleton fiber zone is a predominant process. In conclusion, this research brings insight on coral skeletogenesis bridging physicochemical (supersaturation) and biological (role of SOM) models of coral biomineralization and provides a source of inspiration for the precipitation of composite materials under different conditions of supersaturation.
- Published
- 2019
3. Polymorphic composition and morphology of calcium carbonate as a function of ultrasonic irradiation
- Author
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Damir Kralj, Jasminka Kontrec, Sanja Sviben, Marko Ukrainczyk, and B. Njegić Džakula
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Calcite ,Supersaturation ,Precipitation (chemistry) ,Sonication ,Aragonite ,General Chemistry ,engineering.material ,Condensed Matter Physics ,Crystallography ,chemistry.chemical_compound ,Calcium carbonate ,chemistry ,Chemical engineering ,Vaterite ,Particle-size distribution ,engineering ,General Materials Science - Abstract
This paper reports on the precipitation of CaCO3 polymorphs, having various crystal morphologies under different conditions. In particular, systems that were subject to ultrasonic irradiation were compared to the corresponding reference systems in the absence of such a treatment. The application of ultrasonic irradiation predominantly resulted in a change of particle size distribution and polymorphic composition of the precipitate, in comparison to the reference systems. Thus, it was found that the supersaturation and temperature influenced the size distribution, in both the reference and sonicated systems. A mixture of calcite, vaterite and aragonite was obtained in all reference systems, at 25 °C. At this temperature, the sonication caused the vaterite content to increase, while aragonite was not detected. In reference and sonicated systems at 80 °C, only aragonite precipitated. The results also indicate that the principle parameter responsible for the morphology of vaterite was the initial supersaturation: at higher supersaturation spherical vaterite particles precipitated, while at lower supersaturation hexagonal platelets were obtained. The morphological investigations also indicated different mechanisms of vaterite formation in the systems in which precipitation was initiated at higher supersaturation: spherulitic growth of vaterite was observed in sonicated systems, while the aggregation of primary particles was predominant in the reference systems. At lower supersaturation, the effect of c(Ca2+)/c(CO32-) on the morphology of hexagonal platelets of vaterite was observed as well. By varying the c(Ca2+)/c(CO32-), significant changes of the polymorphic composition were observed only in the sonicated systems, at 25 ˚C.
- Published
- 2014
4. Structural Changes in a Protein Fragment from Abalone Shell during the Precipitation of Calcium Carbonate
- Author
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Giuseppe Falini, Luca Prodi, Damiano Genovese, Natalia Calonghi, Branka Njegić Džakula, Daniele Fabbri, Sara Bonacchi, Simona Fermani, Giorgio Sartor, Marco Montalti, Damir Kralj, and Alessio Adamiano
- Subjects
protein structures KeyWords Plus:CRYSTAL-GROWTH ,Mineralized tissues ,PHASE ,Gastropoda ,010402 general chemistry ,01 natural sciences ,Catalysis ,03 medical and health sciences ,chemistry.chemical_compound ,Protein structure ,biomineralization ,calcium carbonate ,conformation analysis ,fluorescence ,BIOMINERALIZATION ,CRYSTALLIZATION ,FLUORESCENCE ,PEPTIDES ,STATES ,PROBE ,Phase (matter) ,Animals ,Fluorescent Dyes ,030304 developmental biology ,0303 health sciences ,Precipitation (chemistry) ,Organic Chemistry ,Proteins ,General Chemistry ,0104 chemical sciences ,Crystallography ,Spectrometry, Fluorescence ,Calcium carbonate ,chemistry ,protein structures ,Biophysics ,Macromolecule ,Biomineralization ,Fluorescent tag - Abstract
Mineralized tissues grow through biologically controlled processes in which specific macromolecules are involved. Some of these molecules, which are present in very low concentrations and are difficult to localize and characterize, become entrapped inside the mineralized tissue. Herein, a protein fragment, GP, which was obtained by the alkaline digestion of the green sheet of the abalone shell, is used as a probe to study the changes in molecular structure that occur during the precipitation of calcium carbonate. This important goal was achieved by exploiting a fluorescent tag in GP. The experimental results that were obtained by using spectroscopic-, chromatographic-, and microscopic techniques indicate that GP controls the precipitation kinetics and morphology of calcium carbonate crystals, and that it only undergoes structural reorganization when entrapped inside calcium carbonate crystals. To the best of our knowledge, this report represents one of the first studies on the conformational changes of a protein fragment that is involved in biomineralization processes on moving from the solution phase into the mineral phase.
- Published
- 2012
5. Precipitation and characterization of hollow calcite nanoparticles
- Author
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Damir Kralj, Marko Ukrainczyk, Branka Njegić Džakula, and Jasminka Kontrec
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Calcite ,Supersaturation ,Materials science ,Precipitation (chemistry) ,Carbonation ,Nucleation ,Mineralogy ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Amorphous calcium carbonate ,0104 chemical sciences ,chemistry.chemical_compound ,Calcium carbonate ,chemistry ,Chemical engineering ,General Materials Science ,0210 nano-technology ,Dissolution - Abstract
A method for preparation of significant amount of hollow rhombohedral calcite nanoparticles, based on carbonation of calcium hydroxide suspension, is described. The mineralogical and morphological analyses of the precipitate confirmed the existence of exclusively stable polymorphic modification, calcite, with the mean particle size of about 100 nm and the diameter of the holes observed at the surfaces that are about 50 nm. The analysis of carbonation kinetics pointed out to a complex mechanism of hollow particles formation at high initial supersaturation, that assumed nucleation of amorphous precursor calcium carbonate phase and its solution mediated transformation into nanosized crystalline calcite. The holes obtained at the calcite surfaces are most probably the imprints remained after the dissolution of amorphous calcium carbonate particles.
- Published
- 2013
6. ChemInform Abstract: On Calcium Carbonates: From Fundamental Research to Application
- Author
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Ljerka Brečević and Damir Kralj
- Subjects
Calcite ,chemistry.chemical_compound ,Calcium carbonate ,chemistry ,Precipitation (chemistry) ,Vaterite ,Inorganic chemistry ,chemistry.chemical_element ,General Medicine ,Solubility ,Calcium ,Amorphous calcium carbonate ,Biomineralization - Abstract
Appearance of a solid phase from aqueous solution, known as precipitation, is responsible for the formation of numerous natural materials and technological products. Therefore, the knowledge on mechanisms of elementary processes involved in precipitation should be considered in the areas such as geology, oceanology, biomineralization, medicine, basic chemical and pharmaceutical industries, analytical and materials chemistry in particular. Calcium carbonates are a very suitable model system for investigations of these processes. Owing to their low solubility, a wide range of initial supersaturations can be achieved that direct to different conditions under which a particular process dominates. Calcium carbonates can precipitate in the form of six modifications (polymorphic or hydrated). In the Laboratory for Precipitation Processes, systematic investigations of the conditions for formation, crystal growth and transformation of amorphous calcium carbonate, calcium carbonate hexahydrate, calcium carbonate monohydrate, vaterite and calcite have been performed during the last nearly twenty years. An overview of these studies is presented.
- Published
- 2008
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