rss_2.0Acta Chimica Slovaca FeedSciendo RSS Feed for Acta Chimica Slovaca Chimica Slovaca 's Cover — materials suitable for respiratory tract protection but a source of nano- and microplastic particles in the environment<abstract> <title style='display:none'>Abstract</title> <p>The paper deals with the formation of nanomaterials (nanoparticles and nanofibers) in the manufacture and use of respiratory protective equipment. It focuses mainly on processes leading to the release of nanoplastics into the workplace and the environment. Based on selected properties of materials used for the manufacture of protective equipment, their stability in the environment is revealed. The paper demonstrates the impact on the environment considering semichronic phytotoxicity of nanoplastics.</p> </abstract>ARTICLE2022-05-16T00:00:00.000+00:00Thermochemistry of antioxidant action of isoflavones and their deprotonated forms in aqueous solution: hydrogen or electron transfer?<abstract> <title style='display:none'>Abstract</title> <p>Isoflavones possessing several weak acidic hydroxyl groups can undergo successive deprotonations in aqueous solutions. Therefore, their antioxidant properties cannot be ascribed only to the neutral forms but also to corresponding phenoxide anions. It was already confirmed that isoflavones prefer the formation of dianions in aqueous solution. For eight isoflavones and their preferred (poly)deprotonated forms, thermochemistry of hydrogen atom transfer and electron abstraction was studied in terms of corresponding reaction enthalpies, i.e., O—H bond dissociation enthalpies and ionization potentials. Our results clearly indicate that the increase in negative charge causes significant drop in ionization potential and bond dissociation enthalpy. On the other hand, proton affinities show the opposite trend. Thus, it is unfeasible to find a generally valid trend for dianions — corresponding reaction enthalpies strongly depend on the structure of isoflavone, especially on the number/positions of OH groups.</p> </abstract>ARTICLE2022-05-16T00:00:00.000+00:00Pre-treatment of lignocellulosic materials by enzymatic mixture to enhance biogas production<abstract> <title style='display:none'>Abstract</title> <p>The aim of this study was to evaluate the effect of an enzymatic mixture on the increase of biogas production from lignocellulosic materials as rapeseed straw, maize waste, and wheat straw. For efficient application of the enzymatic mixture, conditions of its use were optimized regarding 50 °C, pH 7 and an enzyme dose of 0.25 % w/v. Biogas potential test confirmed positive effect of the enzymatic mixture on anaerobic digestion of already thermally and alkali pre-treated lignocellulosic materials, as significantly higher biogas production was observed after the enzymatic mixture addition for all monitored substrates. Addition of the enzymatic mixture to the most used substrate at biogas plants — maize silage, had also positive effect on biogas production during the biogas potential test. This fact was not proven during long-term operations of the reactors as the values of total cumulative biogas productions for the whole monitored period from reactors for anaerobic digestion of maize silage with and without addition of enzymatic mixture did not differ significantly.</p> </abstract>ARTICLE2022-05-16T00:00:00.000+00:00Binary mixtures containing imidazolium ionic liquids: properties measurement<abstract> <title style='display:none'>Abstract</title> <p>Densities and transport properties (dynamic viscosity) of pure imidazolium ionic liquids 1-butyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium dicyanamide and their binary mixtures with water and ethanol were measured within the temperature range of 293.15—333.15 K. Obtained experimental data were used to calculate excess molar volume and viscosity deviation. For the chosen binary mixtures, variations of excess molar volume, partial molar volumes of mixture components and of the viscosity deviation with the binary mixture composition were correlated using the Redlich-Kister equation. In addition, variation of viscosity with the binary mixture composition and temperature was fitted using the Jouyban-Acree model.</p> </abstract>ARTICLE2022-03-24T00:00:00.000+00:00On the energetics of radical adduct formation of OH with phenol analogs and aniline<abstract> <title style='display:none'>Abstract</title> <p>Theoretical studies on aniline, phenol, benzenethiol, benzeneselenol, and their corresponding adducts with hydroxyl radical in possible positions on a hydrocarbon ring are presented. Bond dissociation enthalpies, related to radical scavenging of primary antioxidants, were calculated using the M06–2X/6–311+G** method. Calculated data were compared with available experimental data. Preferable homolytic bond dissociation of the presented molecules with OH<sup>•</sup> through functional groups X—OH followed by the <italic>m</italic>–OH ones has been confirmed. The highest antioxidant activity among the investigated positions is predicted for benzeneselenol. Also, the formation of non-covalent van der Waals structures has been shown as important in radical scavenging.</p> </abstract>ARTICLE2022-03-24T00:00:00.000+00:00Ceylon cinnamon and clove essential oils as promising free radical scavengers for skin care products<abstract> <title style='display:none'>Abstract</title> <p>Due to adverse effects of free radicals on human skin and increasing consumer demand for natural ingredients, essential oils from basil, Ceylon cinnamon bark, clove, juniper, lavender, oregano, rosemary, tea tree, thyme, and ylang-ylang were assessed for their antiradical activity. The oils were evaluated in the concentration range of 5—0.1 mg·mL<sup>−1</sup>, in which the three reference synthetic antioxidants are most often added to mass-produced cosmetics. Among all examined samples, C. cinnamon oil at a concentration of 5 mg·mL<sup>−1</sup> showed the strongest DPPH radical scavenging activity (0.41 mg·mL<sup>−1</sup> IC50), followed by clove oil, BHA, α-tocopherol, and BHT (0.82, 0.84, 0.88 and 0.93 mg·mL<sup>−1</sup> IC50), respectively. At the same concentration, the reduction power of C. cinnamon oil was higher (1.64 mg·mL<sup>−1</sup> Trolox Eq.) than that of α-tocopherol and BHT (1.42 and 0.80 mmol·L<sup>−1</sup> Trolox Eq., respectively) but lower than that of BHA (1.81 mmol·L–1 Trolox Eq.). Antiradical activity of the other eight essential oils was low or negligible. C. cinnamon oil and clove oil are promising antiradical agents for skin care but according to our GC-MS analysis, these oils contain 0.29 % of cinnamaldehyde, 0.03 % of linalool, 0.02 % of D-limonene, and 0.02 % of eugenol or 0.41 % of eugenol and 0.002 % of linalool, respectively, which are monitored contact allergens in cosmetics. Such a product is not be suitable for consumers allergic to these substances but for the vast majority of consumers it does not pose a risk in terms of allergic manifestations.</p> </abstract>ARTICLE2022-03-24T00:00:00.000+00:00Determination of phosphate in water by flow coulometry<abstract><title style='display:none'>Abstract</title><p>In this work, the possibility of flow coulometry application as coulometric titration was studied. The method was used to analyze phosphates in wastewater samples. The principle of the determination consisted in the formation of molybdophosphate and its subsequent one-electron electrolytic reduction. The present method is applicable under optimal conditions in the concentration range of 1.5 × 10<sup>−6</sup> to 5.5 × 10<sup>−5</sup> mol/dm<sup>3</sup>. Detection limit of the method is 3.42 × 10<sup>−7</sup> mol/dm<sup>3</sup>. Mineralization step has been proved a problem in total phosphate content determination. If mineralization was not carried out, only inorganic soluble phosphates were determined. It is a new method characterized by its simplicity of instrumentation and handling, which is a prerequisite for its further use in the field of trace analysis.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Determination of carotenoids in flowers and food supplements by HPLC-DAD<abstract><title style='display:none'>Abstract</title><p>Marigold flowers (<italic>Tagetes patula</italic> and <italic>Calendula officinalis</italic>) were chosen for analysis because they are the most often used source of lutein and its isomer zeaxanthin for the production of food supplements on the Czech market. Direct extraction and extraction with alkaline hydrolysis were compared to detect free or bound carotenoids. For carotenoid separation, C18 and C30 columns were used. A new method for determination of carotenoid content in food supplements in form of capsules has been developed and validated. All matrices were analysed by high-performance liquid chromatography with diode array detection (HPLC-DAD). It has been found that alkaline hydrolysis is required for both Marigold flowers and food supplements to release lutein from ester bonds to fatty acids. In <italic>Calendula officinalis</italic> lutein in the concentration of 807—1472 mg·kg<sup>−1</sup> of dry matter was detected. <italic>Tagetes patula</italic> has been identified as a better lutein source with the content of 5906—8677 mg·kg<sup>−1</sup> of dry matter. It has been found that the content of lutein and zeaxanthin in commercial food supplements (<italic>Lutein Complex Premium</italic> and <italic>Occutein Brillant</italic>) is consistent with the declared quantity. Linearity of the HPLC-DAD method ranged from 0.1—20 μg·mL<sup>−1</sup> with the limit of quantification (LOQ) of 1.7 mg·kg<sup>−1</sup> for lutein in Marigold flowers and 200 mg·kg<sup>−1</sup> in food supplements. Repeatability was 2.3 % for lutein in all tested matrices.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Carbon family nanomaterials — new applications and technologies<abstract><title style='display:none'>Abstract</title><p>Research on carbon-based nanomaterials (CBNMs) and their development is one of the major scientific disciplines of the last century. This is mainly because of their unique properties which can lead to improvements in industrial technology or new medical applications. Therefore, it is necessary to examine their properties such as shape, size, chemical composition, density, toxicity, etc. This article focuses on the general characteristics of nanomaterials (NMs) and their behavior when entering the environment (water and soil). In addition, it presents individual members of the graphene family including porous ecological carbon (biochar). The article mainly deals with the new potential technologies of CBNMs considering their possible toxic and genotoxic effects. This review also highlights the latest developments in the application of self-propelled micromotors for green chemistry applications. Finally, it points to the potential biomedical applications of CBNMs.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Inclination to self-ignition and analysis of gaseous products of wood chips heating<abstract><title style='display:none'>Abstract</title><p>This paper focuses on the assessment of the inclination to self-ignition of various types of wood chips according to the methodology of European standard EN 15188. The study also assesses the effect of heating temperatures on the composition and quantity of gaseous products of heating. Gases were analysed using an infrared spectrometer with Fourier transformation. From the measured results it was found that the inclination to self-ignition differs for various samples of wood chips. The paper discusses certain parameters assumed to affect the inclination of biomass to self-ignite. When assessing the effect of temperature on the composition of gaseous products, a sample of forest wood chips heated at temperatures from 50 to 150 °C resulted in the following gaseous products: carbon dioxide, carbon monoxide, water and aliphatic hydrocarbons; their concentrations increase with the increasing temperature. Carbon oxides have been proposed as indicators of the state of stored materials self-heating. Observations presented in this paper can be used as data for elaborating safety instructions for storage of fuels based on solid biomass.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Apiin-induction of -apiosidase production by sp. strains<abstract><title style='display:none'>Abstract</title><p><italic>β</italic>-Apiosidase is a rare glycosidase applied in winemaking for flavour enhancement. This enzyme is involved in the release of volatile terpenes by hydrolysis of their odourless glycosidic precursors. It is found as a minor component in commercial pectinase/cellulase preparations. Microbial production of <italic>β</italic>-apiosidase by two <italic>Aspergillus</italic> sp. strains was investigated. Apiin-induced production of this extracellular glycosidase was confirmed only during the cultivation of <italic>Aspergillus niger</italic> CBS 554.65 but the high productivity value reported in the work of Dupin et al. (1992) J. Agric. Food Chem. 40(10): 1886—1891 could not be reproduced. The achieved productivity was by far not satisfactory considering the apiin cost. Commercial enzyme preparations with <italic>β</italic>-apiosidase side-activity thus remain a better alternative as the enzyme source for biocatalytic applications.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Influence of catecholic ring torsion on hydroxyflavones<abstract><title style='display:none'>Abstract</title><p>Systematic quantum chemical investigation of quercetin and selected eight mono- and bihydroxyflavonols is presented. Structural analysis based on the Density Functional Theory showed that the energetically preferred conformation of flavonols substituted at the C5 and C3 atoms by a hydroxyl group is stabilised via intramolecular hydrogen bonds occurring between the (C4)O···HO(3 or 5) atomic pairs. Depending on the hydroxyl group positions, energetically preferred torsional orientation of the phenyl ring with respect to the planar benzo-γ-pyrone moiety changed from 0 to 180 degrees. Gas-phase electron transitions were investigated using the time-dependent DFT treatment. The dependence of maximal wavelengths on the torsional deformation of the phenyl ring is of a similar shape, i.e. minima observed for the perpendicular orientation and maxima for the planar one. Shape and energies of the Highest Occupied (HOMO) and Lowest Unoccupied (LUMO) Molecular Orbitals were compared. The obtained theoretical results were compared with available experimental data.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Absorption removal of hydrogen sulfide from recirculated biogas<abstract><title style='display:none'>Abstract</title><p>This study is focused on the effect of biogas recirculation with hydrogen sulfide removal on anaerobic treatment of sulfur-enriched synthetic wastewater in a UASB reactor. The presence of hydrogen sulfide in biogas causes problems in its further energy recovery while sulfides inhibit the anaerobic process. The reactor was gradually loaded with sulfates and their effect on the reactor operation was monitored. At the same time, external absorption of hydrogen sulfide from biogas with absorbent regeneration was operated. The results show that low concentrations of added sulfates support biogas production. At the sulfate concentration of 125 mg l<sup>−1</sup>, biogas production increased by approximately 2 l d<sup>−1</sup>. However, further increasing of the amount of sulfates in the substrate led to the opposite effect. At twice the amount of sulfates, the biogas production decrease by 1 l d<sup>−1</sup> and its adverse effects on the removal of N-NH<sub>4</sub>, N<sub>C</sub> and P-PO<sub>4</sub> were observed. Biogas recirculation through the absorption column ensured a decrease in the hydrogen sulfide concentration from 19 960 ppm to 4 030 ppm and an increase in the methane content from 59.2 % to 83 % and also a decrease in the sulfides concentration in the reactor. From the measured data it can be concluded that this method reduces sulfides inhibition.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00 — recombinant enzyme producent for environment treatment — review<abstract><title style='display:none'>Abstract</title><p>Since environmental pollution is increasing, scientists try to find a sustainable way for its clean up and for environment protection. Due to increasing knowledge of genetics and recombinant technologies, recombinant enzymes have been increasingly applied for these purposes. This article deals with the possibilities of environmental treatment with different types of enzymes produced by <italic>P. pastoris.</italic> Environment is polluted mostly with pesticides, wastewaters, phenol compounds, plastics, toxic compounds, wastes from medical treatment, etc. All these compounds have to be eliminated considering the deteriorating biodiversity, human health, and condition of plants. Enzymes are an environmentally friendly way of such treatment.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Antibiotic resistant bacteria in surface waters in Slovakia<abstract><title style='display:none'>Abstract</title><p>This work deals with the occurrence of selected antibiotic resistant bacteria in Slovak surface waters. Total and antibiotic resistant coliform bacteria, enterococci and coagulase positive staphylococci were determined in 34 samples of surface water from rivers and still waters (dams, natural lakes, thermal bath) some of them used for recreational swimming. Sampling was performed during summer season 2017 (July and August). The number of total coliforms ranged from 1.74 log CFU/10 mL to 3.69 log CFU/10 mL. Coliform bacteria were registered in each tested sample. The highest number was observed in the sample from river Hron. Majority of samples contained ampicillin and tetracycline resistant bacteria. Enterococci were determined in 70 % of samples ranging from 0.78 log CFU/10 mL to 3.81 log CFU/10 mL. The highest number of enterococci was observed in river Váh. Ampicillin and vancomycin resistance prevailed over ciprofloxacin and gentamicin resistance. Coagulase positive staphylococci were present in 91 % of samples in the range of 0.70—3.03 log CFU/10 mL. Antibiotic resistant coagulase positive staphylococci were observed only in 32 % of samples, predominantly from rivers. In these samples, chloramphenicol resistance predominated. In three samples of water used for recreational purposes, the limit value for enterococci and <italic>E. coli</italic> according to Slovak legislation (Decree no. 308/2012 Coll.) for the quality of water in natural swimming pools during bathing season was exceeded.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Control of heat exchangers in series using neural network predictive controllers<abstract><title style='display:none'>Abstract</title><p>The paper reveals three applications of neural network predictive control (NNPC) to a system of four heat exchangers (HEs) in series with counterflow configuration to save energy expressed by cooling water in the system of HEs cooling the distillation product. Neural networks (NNs) are used at first in conventional NNPC and subsequently, neural network predictive controllers (NNPCLs) are employed as a master controller in a cascade control, and as a feedback controller in the control system with disturbance measurement. Neural-network-predictive-control-based (NNPC-based) feedback control systems are compared with PI controller based feedback control loop. Series of simulation experiments were done and the results showed that using NNPC-based cascade control reduced cooling water consumption. This control system also significantly reduced the settling time and overshoots in the control responses and provided the best assessed integral quality criteria compared to other control systems. NNPC-based cascade control can also be interesting for industrial use. Generally, simulation results proved that NNPC-based control systems are promising means for the improvement of HEs control and achievement of energy saving.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Application of selective polymeric sorbents for simple coumarins extraction from deodorant samples<abstract><title style='display:none'>Abstract</title><p>Coumarins (2H-1-benzopyran-2-coumarin derivatives) are derivatives of cinnamic acid naturally occurring in many plants, fungi, and fruits. They are used as ingredients in cosmetics to enhance the aroma and other biological effects. In this work, cosmetic samples (deodorants) were treated by solid phase extraction prior to high performance liquid chromatography determination of coumarins. Traditional sorbent (C18) and selective polymer-based sorbents (laboratory prepared and commercial) were used for solid phase extraction. Recovery values were above 85 % (RSDs below 6 %) except for esculin, where the recovery was lower. Core-shell column of C18 type and gradient of mobile phase methanol—1 % acetic acid were used for high performance liquid chromatography analysis of extracts. Limits of quantitation were 0.5 µg mL<sup>−1</sup> for coumarin (ultraviolet detection) and below 12 ng mL<sup>−1</sup> for esculin, umbelliferonene, scoparone, 4-methylumbelliferone, herniarin (fluorescence detection). In the tested samples, no coumarins were detected.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Dechloromethylation of the berberine to berberrubine — tricks to obtain pure product<abstract><title style='display:none'>Abstract</title><p>Berberine (<bold>1</bold>), as a compound with interesting biological activities, can be modified at various positions to obtain more potent substances. Modifications at position 9 are based on demethylation with simultaneous dechloration resulting in berberrubine. The most frequent process is thermal dechloromethylation and this work describes this method with detailed tricks to obtain almost pure product in high yield.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Influence of -polyoctylene rubber content on styrene-butadiene rubber properties<abstract><title style='display:none'>Abstract</title><p>The study was focused on the investigation of <italic>trans</italic>-polyoctylene (TOR) influence on cross-linking as well as mechanical and rheological properties of rubber compounds based on styrene-butadiene rubber (SBR). SBR was compounded with different proportions of TOR in the concentration range from 0 to 30 phr. Integration of TOR into rubber leads to the prolongation of the optimum curing time and scorch time and thus the decrease of the curing rate. Higher content of TOR led to less viscous rubber due to the plasticizing effect. Cross-link density of vulcanizates was reduced, which correlates with higher elongation at break. Tensile strength and hardness of vulcanizates increased with the increasing TOR content, probably due to the increasing amount of the crystalline phase.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00Sample matrix influence on microdrop hold-up in single drop microextraction<abstract><title style='display:none'>Abstract</title><p>Single drop microextraction has become a widespread liquid/liquid microextraction technique owing to its simplicity, high preconcentration factor and low consumption of organic solvents in the extraction due to direct introduction of the very low volume of extract into the analytical system. Crucial features ensuring excellent repeatability of single drop microextraction include: solvent volume, solvent type, sample agitation, salts addition, and pH. The influence of sample quality on the microdrop volume and agitation type was studied. Effect of the sample matrix, such as water, acid content samples (orange juice), sample containing alcohol (plum brandy) and protein content sample (milk), on the microdrop hold-up was also investigated. For water analysis, several organic solvents such as chloroform, dichloromethane, tetrachloromethane, tetrachloroethane and chlorobenzene were tested; last three mentioned were suitable for SDME experiments. For milk samples analysis, chlorobenzene microdrop was found to be optimal; advantage of salt addition has been reported. For orange samples, 1:10 dilution was suggested with stable microdrop volumes (toluene) of up to 6 µL for lower stirring rates (100 rpm and 250 rpm). For alcohol-content samples, the change of alcohol percentage of real-life samples had to be considered. A strong influence of the matrix quality on the microdrop stability has been proven.</p></abstract>ARTICLE2020-06-29T00:00:00.000+00:00en-us-1