Enhanced Acetaminophen Electrochemical Sensing Based on Nitrogen-Doped Graphene

Because of the widespread acetaminophen usage and the danger of harmful overdosing effects, developing appropriate procedures for its quantitative and qualitative assay has always been an intriguing and fascinating problem. A quick, inexpensive, and environmentally friendly approach based on direct voltage anodic graphite rod exfoliation in the presence of inorganic salt aqueous solution ((NH₄)₂SO₄–0.3 M) has been established for the preparation of nitrogen-doped graphene (exf-NGr). The XRD analysis shows that the working material appears as a mixture of few (76.43%) and multi-layers (23.57%) of N-doped graphenes. From XPS, the C/O ratio was calculated to be 0.39, indicating a significant number of structural defects and the existence of multiple oxygen-containing groups at the surface of graphene sheets caused by heteroatom doping. Furthermore, the electrochemical performances of glassy carbon electrodes (GCEs) modified with exf-NGr for acetaminophen (AMP) detection and quantification have been assessed. The exf-NGr/GCE-modified electrode shows excellent reproducibility, stability, and anti-interfering characteristics with improved electrocatalytic activity over a wide detection range (0.1–100 µM), with a low limit for AMP detection (LOD = 3.03 nM). In addition, the developed sensor has been successfully applied in real sample analysis for the AMP quantification from different commercially available pharmaceutical formulations.     

Extraction of Fatty Acids from <Emphasis Type=Italic>Boletus edulis</Emphasis> by Subcritical and Supercritical Carbon Dioxide

Mushrooms contain many valuable compounds such as fatty acids, carbohydrates, lycopene, lovastatin, trace elements etc. As they are currently valued for biologically active substances, and as high pressure carbon dioxide fluid extraction has been documented as an effective method for preparing bioactive products from plant materials, subcritical and supercritical carbon dioxide extraction of Boletus edulis mushroom was performed. In the extracts obtained, the fatty acids were determined. Response surface methodology (RSM) was applied to investigate the effect of pressure and extraction time on the extraction yield. The analysis of variance showed that pressure and extraction time had a significant effect on the extraction yield in both investigated process. The interaction between pressure and extraction time had a significant effect only in supercritical extraction process of B. edulis. Higher extraction yields have been obtained by subcritical carbon dioxide, and higher linoleic acid content has been determined in extracts obtained by supercritical carbon dioxide.     

Mathematical Modeling of Ocimum basilicum L. Supercritical CO2 Extraction

The effects of pressure and temperature on supercritical extraction of Ocimum basilicum L. in terms of extraction yield and aromatic compounds were investigated. Linalool, eugenol, and δ‐cadinene were indentified as three main compounds of the prepared extracts. The dominant compound in all investigated supercritical basil extracts was linalool. Within the experimental range the extraction parameters had a significant influence on the extraction yield. The obtained results for the sweet basil total extract, cadinene, and linalool best matched with the Gordillo et al. model, therefore, the solubility of total extract, linalool, and cadinene in supercritical CO₂ at investigated temperatures is described as a function of pressure.     

Effects of supercritical CO2 extraction parameters on soybean oil yield

A series of operational parameters of supercritical fluid extraction of soybean oil (pressure: 300–500 bar, temperature: 40–60 °C, CO₂ mass flow rate: 0.194–0.436 kg/h and characteristic particle size: 0.238–1.059 mm) were investigated in a laboratory scale apparatus. The results show that the extraction yields were significantly affected by applied operational extraction parameters. The increase in pressure, temperature and solvent flow rate improved the extraction yield. The extraction yield increased as the particle size decreased depending on decreasing intra-particle diffusion resistance. To describe the extraction process Sovova's model was used and very good agreement with the experimental results was obtained. Based on the experimental data the internal and external mass transfer coefficients were estimated. To explore the influence of the extractor size on this process, soybean samples were extracted using different extraction basket volumes (0.2 L and 5 L) and related model parameters were examined. The mass transfer coefficient in the fluid phase increased with the increase in extractor size, while the mass transfer coefficient in the solid phase was independent of the extractor size.     

Changes in aromatic profile of fresh and dried fig – the role of pre‐treatments in drying process

The aromatic profile of volatiles in fresh figs (FF), fresh figs frozen in liquid nitrogen (NF) and dried figs (DF) (dark variety Petrova?a Crna) was characterised by HS–SPME followed by GC–MS. Figs were dried in a pilot plant cabinet dryer using different pre‐treatments to preserve the dried fruit: sulphuring and immersion in a solution of citric acid and ascorbic acid (separately). The adaptability of thin‐layer drying models to whole figs was investigated. Fresh figs and fresh figs frozen in liquid nitrogen differed mainly in the amount of aldehydes. The highest abundance of volatile compounds in dried figs was found in figs pre‐treated with sulphur dioxide and the control, compared to samples immersed in the acid solutions. Preservation was the most successful for the group of terpenes and terpenic compounds, quite good for some esters and ketones, whereas aldehydes were not affected by the used pre‐treatment.     

Optimisation of supercritical CO2 extraction of grape seed oil using response surface methodology

The aim of this study was to use waste from the wine production process with special accent on grape seeds and new green technology. Supercritical CO₂ was considered as a green solvent in extraction of grape seed oil. The effects of different extraction process parameters on oil yield and antioxidant activity were investigated. Extraction optimisation was conducted using response surface methodology (RSM). Extraction pressure has proven to be the most significant factor influencing oil yield and antioxidant activity (P < 0.0001). The optimal conditions for obtaining the highest oil yield and antioxidant activity within the experimental range of the variables studied were at extraction pressure of 400 bar and temperature of 41 °C. Under these optimal conditions, the predicted extraction oil yield was 14.49% and DPPH 37.07%. Applying this green extraction method, the oil from grape seeds was totally extracted. The produced oil was of satisfactory quality, and the content of α‐tocopherol in obtained grape seed oil at optimal extraction conditions was 36.05 mg kg^?1.     

On transitive parallelisms of PG(3,4)

A parallelism in $PG(n,q)$ P G ( n , q ) is transitive if it has an automorphism group which is transitive on the spreads. A parallelism is regular if all its spreads are regular. In $PG(3,4)$ P G ( 3 , 4 ) no examples of transitive and no regular parallelisms are known. Transitive parallelisms in $PG(3,4)$ P G ( 3 , 4 ) must have automorphisms of order 7. That is why we construct all 482 parallelisms with automorphisms of order 7 and establish that there are neither transitive, nor regular ones among them. We conclude that there are no transitive parallelisms in $PG(3,4)$ P G ( 3 , 4 ) . The investigation is computer-aided. We use GAP (Groups, Algorithms, Programming—a System for Computational Discrete Algebra) to find a subgroup of order 7 and its normalizer in the automorphism group of $PG(3,4)$ P G ( 3 , 4 ) . For all the other constructions and tests we use our own software written in C++.     

Polyelectrolyte complexes IV. Interpolyelectrolyte complexes between some polycations with N,N-dimethyl-2-hydroxypropyleneammonium chloride units and poly(sodium styrenesulfonate) in dilute aqueous solution

We report first on the interpolyelectrolyte complex formation (PEC) between one polycation of integral type having about 95 mol% of N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the backbone (PCA₅) and poly(sodium styrenesulfonate) (NaPSS), in dependence on the polyion concentrations and the mixing order. The PEC formation was qualitatively followed by viscometry, conductometry and UV-spectroscopy. Quasi-soluble PECs could be formed in the polyion concentration range of 0.1-1.0 unit mM. A complex stoichiometry close to 1:1 was found by both the qualitative measurements on the formation of quasi-soluble PEC in dilute aqueous solutions (when PCA₅ concentration was lower than the overlap concentration, C<C^∗) and elemental analyses of the insoluble PEC formed at the high polycation concentration (50 unit mM, C?C^∗). The influence of the ionic strength on the PECs stability was followed by the subsequent addition of NaCl up to an ionic strength of 3.5 M on the reaction mixture, after the PECs formation with three polycations different by both the content of quaternary ammonium salt groups in the backbone and the degree of branching (PCA₅, PCA₂₀ and PCT₂₀). No dissociation of PECs into the original components was evidenced irrespective of the polycation structure and the mixing order.     

Investigation of Electrochemical Properties of Carbon Nanofibers Prepared by CCVD Method

Carbon nanofibers, with diameters between 80 and 290 nm and specific area of 242 m²g^-1, have been prepared by the catalytic chemical vapor deposition method. After preparation, the powder was mixed with silicon oil in order to create a paste electrode. The electrochemical behavior of this type of electrode was investigated by cyclic voltammetry, using a solution of 10^-3 M ferrocenecarboxylic acid as mediator. The redox process is quasi-reversible, and it involves the transfer of electrons between Fe(II) and Fe(III).

The same mediator was used for the construction of a second-generation glucose biosensor. The mediator was co-immobilized with the enzyme in the carbon nanofibers paste. The sensor linearly responded to glucose, in the concentration range of 1.7 to 7 mM. A time of around 30 seconds was required to reach 95% of the maximum steady-state current.

Also, the oxidation of calf thymus DNA at the carbon nanofiber paste electrode was investigated by differential pulse voltammetry (DPV). A clear signal, due to guanine oxidation, was obtained in the case of single-stranded DNA.