scholarly journals Nepodceňujme mikrobiální precipitaci oxihydroxidů železa a manganu v životním prostředí

2021 ◽  
Vol 29 (1) ◽  
pp. 115-123
Author(s):  
Dalibor Matýsek ◽  
Jakub Jirásek
Keyword(s):  
Microbial Mats ◽  
Iron Oxidation ◽  
Chemical Precipitation ◽  
X Ray Diffraction ◽  
Minor Admixture ◽  
Similar Materials ◽  
Ca 50 ◽  
A Minor ◽  
Pennate Diatoms

Dolníček (2020) described several occurrences of bog iron (limonite), which according to his article originates in recent streams by chemical precipitation, without the important role of microorganisms on this process. However, similar occurrences of reddish or orange slime, frequently accompanied by oil-like films floating on the water, are according to many papers ascribed to the biogenic iron oxidation by bacteria. To solve the origin of such precipitates, we have sampled similar materials in four places near Ostrava - Hrabová, two close to Řepiště and Staříč, and also two sites in the vicinity of Hulín investigated by Dolníček (2020). In all cases, scanning electron microscopy of dried samples at the low vacuum (ca 50 Pa) revealed a dominant share of tubular sheaths of the Leptothrix-Sphaerotilus group of bacteria. The prevailing diameter of 1.5 to 1 μm should point to genus Leptothrix, while those with a diameter up to 2.5 μm (genus Sphaerotilus) are far less common. Spiral chains of Gallionella were recognized in all samples, as well as rare pennate diatoms. Space between bacterial filaments is predominantly filled with densely stacked particles micrometer to submicrometer in size, sometimes with oval, fibrous, or tabular shape. It might be both decomposed material of previously mentioned genera and some other small-sized bacteria. Energy-dispersive spectroscopy shows dominant content of iron and oxygen, with a minor admixture of Si, Ca, Al, and P. Powder X-ray diffraction of such microbial mats is showing clastic admixtures (quartz, feldspar group minerals, illite-muscovite, and kaolinite) and two broad low-intensity peaks of ferrihydrite. Only sample D from Řepiště locality shows an absence of ferrihydrite and the presence of hematite and magnetite and/or maghemite. Therefore, we demonstrated that bacterially-induced precipitation plays a major role in the genesis of such recent bog iron occurrences and there are ways how to characterize such material by both biological and mineralogical procedures.

FeAs2 biomineralization on encrusted bacteria in hot springs: an ecological role of symbiotic bacteria

2003 ◽  
Vol 40 (11) ◽  
pp. 1725-1738 ◽  
Author(s):  
Kazue Tazaki ◽  
Islam ABM Rafiqul ◽  
Kaori Nagai ◽  
Takayuki Kurihara
Keyword(s):  
Metal Binding ◽  
Microbial Mats ◽  
Hot Springs ◽  
Hot Spring ◽  
Binding Potential ◽  
Resistant Bacteria ◽  
X Ray Diffraction ◽  
Ft Ir ◽  
Ir Analysis

Bacterial FeAs2 mineralization was found in the reddish-brown microbial mats that have grown on the walls of the drainage systems of Masutomi Hot Springs, Yamanashi Prefecture, Japan. The reddish-brown microbial mats, which are mainly composed of bacilliform and coccoid types of bacteria, have been analyzed and observed by microtechniques to interpret the bacterial biomineralization and search for the clues to bioremediation. These bacteria accumulate Fe and As along with other trace elements to form various biominerals. The electron diffraction (ED) pattern of the bacterial capsule identified lollingite (FeAs2) and calcite (CaCO3) on the surface of the cell. Based on Fourier-transform infrared absorbance spectroscopy (FT–IR) analysis, the presence of organic components such as C—H, C=O, CNH, –COOH, and N—H in the reddish-brown microbial mats emphasized the metal-binding potential of the bacteria. X-ray diffraction (XRD) data showed the poorly crystalline character of the precipitates, which consist mainly of hydrous iron oxides (2.7 Å (1 Å = 0.1 nm)). The FeAs2 biominerals form by adsorption onto the bacterial cell wall, as demonstrated by microscopic observations and spectroscopic analysis. These showed that bacteria in the reddish-brown microbial mats have the ability to form biominerals with heavy metals and toxic metalloids like As. Particularly significant in hot spring environments is the role of symbiotic and toxic-resistant bacteria, which have the ability to adapt to high As concentrations. Bacterial FeAs2 mineralization might also be considered a mechanism by which toxic As is removed from the aquatic ecosystem. The results provide evidence for detoxification processes and offer clues to possible methods of bioremediation.

Synthesize and Characterization of Hollow Hydroxyapatite Nanopowders with Different Morphologies: Role of Cationic and Non-Ionic Surfactants

2013 ◽  
Vol 829 ◽  
pp. 268-273 ◽  
Author(s):  
Amir Seyfoori ◽  
Hamideh Mahmoodzadeh Hosseini ◽  
Abbas Ali Imani Fooladi ◽  
Mohammad Reza Nourani
Keyword(s):  
Protein Delivery ◽  
Nitrogen Adsorption ◽  
Chemical Precipitation ◽  
Precipitation Method ◽  
Live Cells ◽  
X Ray Diffraction ◽  
Hollow Structures ◽  
Average Surface Area

Today, hydroxyapatite hollow nanopowders have attracted the attention of researchers as a reliable option for drug and protein delivery systems. In this study, nanohydroxyapatite powders with different morphologies were successfully synthesized via wet chemical precipitation method. Elongated rice-shape and semi-spherical nanopowders with hollow structures were synthesized using CTAB and the mixture of cetyltrimethylammonium bromide (CTAB) and polyethylene glycol (PEG) as surfactants respectively. The properties of these nanopowders were charecterized by means of scanning electron microscopy, x-ray diffraction, fourier transform infrared spectroscopy and nitrogen adsorption experiments. The results showed that using CTAB as a surfactant not only can alter the morphology of the HAp nanopowders but also it can have a significant effect on the structure of them, so that by using CTAB and mixture of CTAB and PEG, nanoporous HAp nanopowders were acquired. Moreover, the analysis of nitrogen adsorption showed a higher average surface area for CTAB synthesized HAp in comparison to CTAB/PEG synthesized nanopowder. The amount of live cells adjacent to the HAp suspensions in PBS (50, 100, 200 mg/L) was evaluated by MTT experiment. The results of MTT assay showed the ascending cell proliferation trend for spherical nanopowders by an increment in suspension concentration, while this trend was descending for rice-shape nanopwders.

scholarly journals Role of annealing temperature on the properties of SrO nanoparticles by precipitation method

2020 ◽  
Vol 1 (1) ◽  
pp. 18-23
Author(s):  
Suresh R ◽  
◽  
Indira Priyadharshini T ◽  
Thirumal Valavan K ◽  
Justin Paul M ◽  
...  
Keyword(s):  
Single Phase ◽  
Annealing Temperature ◽  
Surface Defects ◽  
Visible Region ◽  
Chemical Precipitation ◽  
Precipitation Method ◽  
X Ray Diffraction ◽  
Crystalline Nature ◽  
Diffraction Peaks

Strontia nanoparticles are successfully prepared by chemical precipitation method. The SrO nanoparticles are characterized by XRD, UV-DRS and I-V analysis. X-ray diffraction peaks reveal the single-phase polycrystalline tetragonal structure with preferential orientation along (2 0 2) direction. Influence of annealing temperature strongly induce the growth of peak which indicates the increased intensity of (202) peak. The heat treatment strongly distresses the growth of triplet peaks (002), (101) and (110) whereas the same augment the growth of (202) and (310). Strontium oxide nanoparticles would allow more light for absorption in UV region due to its rough surface whereas the same would allow moderate light absorption in visible region due to its high packing density. The expansion and contraction of Sr-O bonds leads to a high crystalline nature with its purity at 322 nm. It is proposed that strain and surface defects in SrO nanocrystal take place due to different absorption edge.

The Effect of Path Length and Display Size on Memory for Spatial Information

2012 ◽  
Vol 59 (3) ◽  
pp. 147-152 ◽  
Author(s):  
Katherine Guérard ◽  
Sébastien Tremblay
Keyword(s):  
Path Length ◽  
Potential Role ◽  
Spatial Information ◽  
Recall Performance ◽  
Minor Role ◽  
Length Effect ◽  
Serial Memory ◽  
Fixed Reference ◽  
A Minor

In serial memory for spatial information, some studies showed that recall performance suffers when the distance between successive locations increases relatively to the size of the display in which they are presented (the path length effect; e.g., Parmentier et al., 2005) but not when distance is increased by enlarging the size of the display (e.g., Smyth & Scholey, 1994). In the present study, we examined the effect of varying the absolute and relative distance between to-be-remembered items on memory for spatial information. We manipulated path length using small (15″) and large (64″) screens within the same design. In two experiments, we showed that distance was disruptive mainly when it is varied relatively to a fixed reference frame, though increasing the size of the display also had a small deleterious effect on recall. The insertion of a retention interval did not influence these effects, suggesting that rehearsal plays a minor role in mediating the effects of distance on serial spatial memory. We discuss the potential role of perceptual organization in light of the pattern of results.

THE ROLE OF ANTHROPONYMS IN THE SEMANTIC FIELD OF ARTISTIC WORKS

2019 ◽  
Vol 2019 (29) ◽  
pp. 66-77
Author(s):  
Lidiya Derbenyova
Keyword(s):  
Literary Work ◽  
Main Theme ◽  
Semantic Field ◽  
New Meanings ◽  
Minor Part ◽  
The One ◽  
A Minor ◽  
And Storage ◽  
Horizon Of Expectations

The article explores the role of antropoetonyms in the reader’s “horizon of expectation” formation. As a kind of “text in the text”, antropoetonyms are concentrating a large amount of information on a minor part of the text, reflecting the main theme of the work. As a “text” this class of poetonyms performs a number of functions: transmission and storage of information, generation of new meanings, the function of “cultural memory”, which explains the readers’ “horizon of expectations”. In analyzing the context of the literary work we should consider the function of antropoetonyms in vertical context (the link between artistic and other texts, and the groundwork system of culture), as well as in the context of the horizontal one (times’ connection realized in the communication chain from the word to the text; the author’s intention). In this aspect, the role of antropoetonyms in the structure of the literary text is extremely significant because antropoetonyms convey an associative nature, generating a complex mechanism of allusions. It’s an open fact that they always transmit information about the preceding text and suggest a double decoding. On the one hand, the recipient decodes this information, on the other – accepts this as a sort of hidden, “secret” sense.

Tuning the mechanical and dielectric properties of zinc incorporated hydroxyapatite

2020 ◽  
Vol 16 ◽  
Author(s):  
Alliya Qamar ◽  
Rehana Zia ◽  
Madeeha Riaz
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Bone Growth ◽  
Healing Process ◽  
Secondary Phase ◽  
Chemical Precipitation ◽  
Hexagonal Structure ◽  
Precipitation Method ◽  
Low Frequencies ◽  
A Minor

Background: Hydroxyapatite is similar to bone mineral in chemical composition, has good biocompatibility with host tissue and bone. Objective: This work aims to tailor the mechanical and dielectric properties of hydroxyapatite with zinc sudstitution, to improve wearability of implant and accelerate the healing process. Method: Pure and zinc incorporated hydroxyapatite Ca10(PO4)6(OH)2 samples have been successfully prepared by means of the chemical precipitation method. Results: The results showed that hydroxyapatite(Hap) having hexagonal structure was the major phase identified in all the samples. It was found that secondary phase of β-tricalcium phosphate (β-TCP) formed due to addition of Zinc resulting in biphasic structure BCP (Hap + β-TCP). A minor phase of ZnO also formed for higher concentration of Zn (Zn ≥ 2mol%) doping. It was found that the Zn incorporation to Hap enhanced both mechanical and dielectric properties without altering the bioactive properties. The microhardness increased upto 0.87 GPa for Zn concentration equal to 1.5mol%, which is comparable to the human bone ~0.3 - 0.9 GPa. The dielectric properties evaluated in the study showed that 1.5 mol% Zn doped hydroxyapatite had highest dielectric constant. Higher values of dielectric constant at low frequencies signifies its importance in healing processes and bone growth due to polarization of the material under the influence of electric field. Conclusion: Sample Z1.5 having 1.5 mol% Zn doping showed the most optimized properties suitable for bone regeneration applications.

Effects of Myo-inositol Alone and in Combination with Seleno-Lmethionine on Cadmium-Induced Testicular Damage in Mice

2019 ◽  
Vol 12 (4) ◽  
pp. 311-323 ◽  
Author(s):  
Salvatore Benvenga ◽  
Antonio Micali ◽  
Giovanni Pallio ◽  
Roberto Vita ◽  
Consuelo Malta ◽  
...  
Keyword(s):  
Structural Changes ◽  
Natural Antioxidants ◽  
Minor Role ◽  
Positive Role ◽  
Testosterone Levels ◽  
Tnf Α ◽  
Testicular Lesions ◽  
A Minor ◽  
Immunohistochemical Analyses

Background: Cadmium (Cd) impairs gametogenesis and damages the blood-testis barrier. Objective: As the primary mechanism of Cd-induced damage is oxidative stress, the effects of two natural antioxidants, myo-inositol (MI) and seleno-L-methionine (Se), were evaluated in mice testes. Methods: Eighty-four male C57 BL/6J mice were divided into twelve groups: 0.9% NaCl (vehicle; 1 ml/kg/day i.p.); Se (0.2 mg/kg/day per os); Se (0.4 mg/kg/day per os); MI (360 mg/kg/day per os); MI plus Se (0.2 mg/kg/day); MI plus Se (0.4 mg/kg/day); CdCl2 (2 mg/kg/day i.p.) plus vehicle; CdCl2 plus MI; CdCl2 plus Se (0.2 mg/kg/day); CdCl2 plus Se (0.4 mg/kg/day); CdCl2 plus MI plus Se (0.2 mg/kg/day); and CdCl2 plus MI plus Se (0.4 mg/kg/day). After 14 days, testes were processed for biochemical, structural and immunohistochemical analyses. Results: CdCl2 increased iNOS and TNF-α expression and Malondialdehyde (MDA) levels, lowered glutathione (GSH) and testosterone, induced testicular lesions, and almost eliminated claudin-11 immunoreactivity. Se administration at 0.2 or 0.4 mg/kg significantly reduced iNOS and TNF-α expression, maintained GSH, MDA and testosterone levels, structural changes and low claudin-11 immunoreactivity. MI alone or associated with Se at 0.2 or 0.4 mg/kg significantly reduced iNOS and TNF-α expression and MDA levels, increased GSH and testosterone levels, ameliorated structural organization and increased claudin-11 patches number. Conclusion: We demonstrated a protective effect of MI, a minor role of Se and an evident positive role of the association between MI and Se on Cd-induced damages of the testis. MI alone or associated with Se might protect testes in subjects exposed to toxicants, at least to those with behavior similar to Cd.

Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol

1993 ◽  
Vol 58 (7) ◽  
pp. 1591-1599 ◽  
Author(s):  
Abd El-Aziz A. Said
Keyword(s):  
Active Sites ◽  
Isopropyl Alcohol ◽  
Oxide Catalyst ◽  
Flow System ◽  
Charge Carriers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Catalyst Composition ◽  
Surface Active

Molybdenum oxide catalyst doped or mixed with (1 - 50) mole % Fe3+ ions were prepared. The structure of the original samples and the samples calcined at 400 °C were characterized using DTA, X-ray diffraction and IR spectra. Measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on increasing the content of Fe3+ ions up to 50 mole %. The activation energies of charge carriers were determined in presence and absence of the alcohol. The catalytic dehydration of isopropyl alcohol was carried out at 250 °C using a flow system. The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation. However, the catalyst containing 40 mole % Fe3+ ions exhibited the highest activity and selectivity. Correlations were attempted to the catalyst composition with their electronic and catalytic properties. Probable mechanism for the dehydration process is proposed in terms of surface active sites.

Introduction to geomicrobiology

2018 ◽  
Author(s):  
David L. Kirchman
Keyword(s):  
Fossil Fuels ◽  
Solid Phase ◽  
Direct Reduction ◽  
Iron Oxidation ◽  
Mineral Dissolution ◽  
Precipitation Process ◽  
Soluble Ions ◽  
Chemolithoautotrophic Bacteria ◽  
The Impact

Geomicrobiology, the marriage of geology and microbiology, is about the impact of microbes on Earth materials in terrestrial systems and sediments. Many geomicrobiological processes occur over long timescales. Even the slow growth and low activity of microbes, however, have big effects when added up over millennia. After reviewing the basics of bacteria–surface interactions, the chapter moves on to discussing biomineralization, which is the microbially mediated formation of solid minerals from soluble ions. The role of microbes can vary from merely providing passive surfaces for mineral formation, to active control of the entire precipitation process. The formation of carbonate-containing minerals by coccolithophorids and other marine organisms is especially important because of the role of these minerals in the carbon cycle. Iron minerals can be formed by chemolithoautotrophic bacteria, which gain a small amount of energy from iron oxidation. Similarly, manganese-rich minerals are formed during manganese oxidation, although how this reaction benefits microbes is unclear. These minerals and others give geologists and geomicrobiologists clues about early life on Earth. In addition to forming minerals, microbes help to dissolve them, a process called weathering. Microbes contribute to weathering and mineral dissolution through several mechanisms: production of protons (acidity) or hydroxides that dissolve minerals; production of ligands that chelate metals in minerals thereby breaking up the solid phase; and direct reduction of mineral-bound metals to more soluble forms. The chapter ends with some comments about the role of microbes in degrading oil and other fossil fuels.

scholarly journals X-ray and Neutron Study on the Structure of Hydrous SiO2 Glass up to 10 GPa

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 84 ◽  
Author(s):  
Satoru Urakawa ◽  
Toru Inoue ◽  
Takanori Hattori ◽  
Asami Sano-Furukawa ◽  
Shinji Kohara ◽  
...  
Keyword(s):  
Oxide Glasses ◽  
Void Space ◽  
X Ray Diffraction ◽  
Amorphous Sio2 ◽  
Sio2 Glass ◽  
X Ray ◽  
X Ray Scattering ◽  
Medium Range ◽  
Two Phases ◽  
A Minor

The structure of hydrous amorphous SiO2 is fundamental in order to investigate the effects of water on the physicochemical properties of oxide glasses and magma. The hydrous SiO2 glass with 13 wt.% D2O was synthesized under high-pressure and high-temperature conditions and its structure was investigated by small angle X-ray scattering, X-ray diffraction, and neutron diffraction experiments at pressures of up to 10 GPa and room temperature. This hydrous glass is separated into two phases: a major phase rich in SiO2 and a minor phase rich in D2O molecules distributed as small domains with dimensions of less than 100 Å. Medium-range order of the hydrous glass shrinks compared to the anhydrous SiO2 glass by disruption of SiO4 linkage due to the formation of Si–OD deuterioxyl, while the response of its structure to pressure is almost the same as that of the anhydrous SiO2 glass. Most of D2O molecules are in the small domains and hardly penetrate into the void space in the ring consisting of SiO4 tetrahedra.

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