Ústav fyzikální a spotřební chemie

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Soil organic matter interactions along the elevation gradient of the James Ross Island (Antarctica)
(European Geoscience Union, 2024-11-19) Vlček, Vítězslav; Juřička, David; Valtera, Martin; Dvořáčková, Helena; Štulc, Vojtěch; Bednaříková, Michaela; Šimečková, Jana; Váczi, Peter; Pohanka, Miroslav; Kapler, Pavel; Barták, Miloš; Enev, Vojtěch
Around half of the Earth's soil organic carbon (SOC) is presently stored in the Northern Hemisphere permafrost region. In polar permafrost regions, low temperatures particularly inhibit both the production and biodegradation of organic matter. Under such conditions, abiotic factors such as mesoclimate, pedogenic substrate or altitude are thought to be more important for soil development than biological factors. In Antarctica, biological factors are generally underestimated in soil development due to the rare occurrence of higher plants and the short time since deglaciation. In this study, we aim to assess the relationship between SOC and other soil properties related to the pedogenic factors or properties. Nine plots were investigated along the altitudinal gradient from 10 to 320 m in the deglaciated area of James Ross Island (Ulu Peninsula) using a parallel tea-bag decomposition experiment. SOC contents showed a positive correlation with the content of easily extractable glomalin-related soil protein (EE-GRSP; Spearman r = 0.733, P = 0.031) and the soil buffering capacity (expressed as pH; Spearman r = 0.817, P = 0.011). The soil-available P was negatively correlated with altitude (Spearman r = -0.711, P = 0.032), and the exchangeable Mg was negatively correlated with the rock fragment content (Spearman r = -0.683, P = 0.050). No correlation was found between the available mineral nutrients (P, K, Ca and Mg) and SOC or GRSP. This may be a consequence of the inhibition of biologically mediated nutrient cycling in the soil. Therefore, the main factor influencing nutrient availability in these soils does not seem to the biotic environment; rather, the main impact appears to stem from the abiotic environment influencing the mesoclimate (altitude) or the level of weathering (rock content). Incubation in tea bags for 45 d resulted in the consumption and translocation of more labile polyphenolic and water-extractable organic matter, along with changes in the C content (increase of up to +0.53 % or decrease of up to -1.31 % C) and a decrease in the C:N ratio (from 12.5 to 7.1-10.2), probably due to microbial respiration and an increase in the abundance of nitrogen-binding microorganisms. Our findings suggest that one of the main variables influencing the SOC/GRSP content is not the altitude or coarse-fraction content (for which a correlation with SOC/GRSP was not found); rather, we suspect effects from other factors that are difficult to quantify, such as the availability of liquid water.
Effect of Silk Fibroin on the Mechanical and Transport Properties of Agarose Hydrogels
(MDPI, 2024-09-24) Richterová, Veronika; Pekař, Miloslav
In this work, the effect of incorporating silk fibroin, a fibrous biocompatible protein, into physically cross-linked agarose hydrogels was investigated as a simple model study to examine how supramolecular fibrous structures influence the properties of the hydrogels. The rheological and transport properties were studied. Fibroin did not change the general viscoelastic properties of the investigated hydrogels but changed the viscoelastic moduli values and also the mesh size, as calculated from rheometry data. Fibroin influenced the mechanical properties depending on its concentration: at lower concentrations, it increased the mesh size, while at higher concentrations, it acted as a filler, decreasing the mesh size. Similarly, the storage and loss moduli were affected, either increasing or decreasing based on the fibroin concentration. The fibroin effect on the diffusion of two dyes differing in their charge was the result of a combination of structural effects, responsible also for changes in the rheological properties, and a result of electrostatic interactions between the charged groups. For positively charged methylene blue, low fibroin concentrations accelerated diffusion, while higher concentrations slowed it by filling network vacancies. In contrast, for negatively charged eosin-B, fibroin strongly impeded diffusion at all concentrations due to electrostatic repulsion, leading to its accumulation at the hydrogel interface. The findings of this work may contribute to an understanding of the behavior of the extracellular matrix or soft tissues as well as to the development of the tailored design of hydrogel materials.
The Effect of Biochar Particle Size on the Leaching of Organic Molecules and Macro- and Microelements
(MDPI, 2024-10-11) Bačovská, Šárka; Mravcová, Ludmila; Pořízka, Jaromír; Kubíková, Leona; Kalina, Michal
Biochar is a carbon-rich material that has recently received attention due to its increasing agronomical potential. The agricultural utilization of biochar relates to its potential to act in the soil as a soil conditioner; nevertheless, complex information on the direct dependence of biochar’s physical properties (texture, particle size) and corresponding leaching and availability of organic molecules (e.g., the polycyclic and heterocyclic organic compounds) and inorganic mineral salts (based on micro- and macroelements) is still inconsistent. Multi-elemental analysis by using inductively coupled plasma atomic emission spectroscopy (ICP-OES) was used to assess the information on the contents and availability of macro- and microelements in studied commercial biochar samples. The results showed a statistically significant indirect relation between an increase in the size fraction of biochar and the content of aqueous-extractable K and Na and the direct relation with the aqueous-extractable Ca, Mg, and P. Compared to the macroelements, the detected contents of aqueous-extractable microelements were almost three orders lower, and the dependence on fraction size was not consistent or statistically significant. In addition, gas chromatography (GC) coupled with mass spectroscopy (MS) was further used to reveal the concentrations of available polycyclic aromatic and heterocyclic compounds in biochar samples. The detected concentrations of these types of organic compounds were far below the certified limits, and a statistically significant indirect correlation with particle size was also observed for all the studied biochar samples. The proposed methodological concept could provide the necessary insights into the description of biochar mineral content and its connection to biochar texture, the physicochemical properties, and the potential of biochar to release nutrients into the soil. These findings could help in the further assessment of biochar as a soil conditioner in modern agriculture.
Specific buffer effects on the formation of BSA protein corona around amino-functionalized mesoporous silica nanoparticles
(Elsevier, 2024-08-05) Mura, Monica; Carucci, Cristina; Caddeo, Elena; Bačovská, Šárka; Piludu, Marco; Pekař, Miloslav; Jachimska, Barbara; Parsons, Drew Francis; Salis, Andrea
The effect of buffer species on biomolecules and biomolecule-nanoparticle interactions is a phenomenon that has been either neglected, or not understood. Here, we study the formation of a BSA protein corona (PC) around amino-functionalized mesoporous silica nanoparticles (MSN-NH2) 2 ) in the presence of different buffers (Tris, BES, cacodylate, phosphate, and citrate) at the same pH (7.15) and different concentrations (10, 50, and 100 mM). We find that BSA adsorption is buffer specific, with the adsorbed amount of BSA being 4.4 times higher in the presence of 100 mM Tris (184 +/- 3 mg/g) than for 100 mM citrate (42 +/- 2 mg/g). That is a considerable difference that cannot be explained by conventional theories. The results become clearer if the interaction energies between BSA and MSN-NH2, 2 , considering the electric double layer (EEDL) EDL ) and the van der Waals (EvdW) vdW ) terms, are evaluated. The buffer specific PC derives from buffer specific zeta potentials that, for MSN-NH2, are positive with Tris and negative with citrate buffers. A reversed sign of zeta potentials can be obtained by considering polarizability-dependent dispersion forces acting together with electrostatics to give the buffer specific outcome. These results are relevant not only to our understanding of the formation of the PC but may also apply to other bio- and nanosystems in biological media.
Effect of calcium, magnesium, and iron on migration of copper in humic systems
(Springer, 2024-08-21) Klučáková, Martina; Enev, Vojtěch
The mobility of heavy metals in natural soil systems can be affected by the properties and compositions of those systems: the content and quality of organic matter as well as the character of inorganic constituents. In this work, the diffusion of copper(II) ions in humic hydrogels with incorporated calcium(II), magnesium(II), and iron(III) ions was investigated. The methods of instantaneous planar source and of constant source were used. Experimental data yielded the time development of the concentration in hydrogels and the values of effective diffusion coefficients. The coefficients include both the influence of the hydrogel structure and the interaction of diffusing particles with the hydrogel. Our results showed that the presence of natural metal ions such as calcium, magnesium, or iron can strongly affect the diffusivity of copper in humic systems. They indicate that the mobility of copper ions depends on their concentration. The mobility can be supported by higher contents of copper in the system. While the incorporation of Ca and Mg resulted in the decrease in the diffusivity of copper ions, tThe incorporation of Fe(III) into humic hydrogel resulted in an increase in the diffusivity of Cu(II) in the hydrogel in comparison with pure humic hydrogel.

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