Band 63, Heft 6

A simple, selective, highly sensitive and accurate procedure for the determination of trace amounts of copper has been developed based on solid-phase spectrophotometry. Copper reacts with 5-(2-benzothiazolylazo)-8-hydroxyquinoline (BTAHQ) to give a complex with high molar absorptivity (3.17 × 107 L mol−1 cm−1, 3.07 × 108 L mol−1 cm−1, 1.22 × 109 L mol−1 cm−1, and 1.80 × 109 L mol−1 cm−1), fixed on a Dowex 1-X8 type anion-exchange resin for 10 mL, 100 mL, 500 mL, and 1000 mL, respectively. The absorbance at 667 nm and 800 nm packed in a 1.0 mm cell was measured directly. Calibration is linear over the range 0.2–3.7 µg L−1 with RSD of < 1.28 % (n = 10). The detection and quantification limits of the 500 mL sample method are 79 ng L−1 and 260 ng L−1 when using 60 mg of Dowex 1-X8. For a 1000 mL sample, the detection and quantification limits are 67 ng L−1 and 220 ng L−1 using 60 mg of the exchanger. Increasing the sample volume can enhance the sensitivity. The proposed method was applied to the determination of copper in different environmental water samples (tap, pit, spring, and river), food products (rice, corn flour, and tea), and mushrooms, using the standard addition technique.

A pre-column derivatized high-performance liquid chromatographic (HPLC) method with ultraviolet-visible detection was developed to measure the concentrations of spectinomycin in fermentation broth. Derivatization reagents, 2,4-dinitrophenylhydrazine in acetonitrile (5 mg mL−1) and trifluoroacetic acid in acetonitrile (0.8 mol L−1), were added to an aliquot of the fermentation broth, and the mixture was incubated for 60 min at 70°C. The resulting derivative was separated from other compounds by isocratic elution in a reversed-phase column Zorbax SB-C18 (250 mm × 4.6 mm, 5 µm). Mobile phase consisted of acetonitrile, tetrahydrofuran, and water (φ r = 40: 35: 25) and the flow rate was 1.0 mL min−1. The detection wavelength was 415 nm. The standard curve for spectinomycin sulfate was linear with correlation coefficients of 0.9997 in the range of 25 µg mL−1 to 600 µg mL−1. The relative standard deviation values ranged from 0.43 % to 2.18 % depending on the concentration of samples. The average recovery was 101.5 %. The limit of detection was 50 ng mL−1.

A novel amperometric sensor for uric acid based on ordered mesoporous carbon modified pyrolytic graphite electrode was developed. Uric acid oxidation was easily catalyzed by this electrode in a phosphate buffer solution at pH 7.0, with an anodic potential decrease about 140 mV compared to bare pyrolytic graphite electrode. The uric acid level was determined by the amperometric method, at a constant potential of 0.31 mV, the catalytic current of uric acid vs. its concentration showed a good linearity in the range of 1.0 × 10−6−1.0 × 10−4 mol L−1, with a correlation coefficient of 0.999. The detection limit was 4.0 × 10−7 mol L−1. The proposed method could be effectively used for uric acid amperometric sensing in human urine.

A simple, sensitive and accurate spectrophotometric method for the determination of sulphonamides (sulphamethoxazole (SMZ), sulphaguanidine (SGD), sulphaquinoxaline sodium (SQX), sulphametrole (SMR), and sulphadimidine sodium (SDD)) has been developed. The charge-transfer reactions between sulphonamides as n-electron donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, p-CLA) as π-acceptors resulting in highly coloured complexes were studied. Experimental conditions for these CT reactions were carefully optimised. Beer’s law is valid over the concentration ranges from 4–280 µg mL−1, 4–260 µg mL−1, 4–200 µg mL−1, and 4–200 µg mL−1 of SMZ, SGD, SQX, and SDD using DDQ reagent, respectively. While the calibration curves are linear in the concentration ranges from 4–180 µg mL−1, 4–80 µg mL−1, 4–60 µg mL−1, 4–180 µg mL−1, and 4–60 µg mL−1 of SMZ, SGD, SQX, SMR, and SDD, respectively, using TCNQ reagent and from 4–380 µg mL−1 and 4–300 µg mL−1 of SQX and SDD, respectively, using p-CLA reagent, respectively. Different analytical parameters, namely molar absorptivity (ε), standard deviation, relative standard deviation, correlation coefficient, limit of detection, and limit of quantification, were calculated. The results obtained by the proposed methods are in good agreement with those obtained by the official method as indicated by the percent recovery values.

Tumor suppressor protein p53 becomes inactive due to mutation on its DNA binding core domain leading to misbehavior of this protein and preventing its interaction with DNA. In the present study, changes of the protein conformation by five hot spot mutations of T-p53C were assessed preventing the mutants wild-type (WT) behavior. While studies of this nature were undertaken both experimentally and theoretically, the focus is fundamentally on the effects of the mutation on the dynamics of the protein. Hence, the basic concept underlying this study is the change in flexibility or rigidity of the protein. It was found that stable variant T-p53C (PDB-ID: 1uol) that is structurally and functionally very close to wild-type p53 is the most rigid structure and each single carcinogenic mutation on it makes the structure more flexible. We hypothesize that these changes of the molecule’s flexibility disrupt the network of hydrogen bonds associated with the interaction of WT not only at interaction but in the internal structures of the mutants as well, which prevents them from interacting in the WT fashion loosing the anti-cancer properties of WT.

Intestine proteases of Nile tilapia (Oreochromis niloticus) were partially purified by heat treatment (purification factor of 3.5, enzyme activity remained almost constant) to reach the maximum activity and stability within an alkaline pH range of 7.2–11.0. The optimum temperature and stability over a 120 min period were found to be at 55°C and at 35–45°C, respectively. The proteases’ activity was not affected by a 1 vol. % saponin surfactant, inactivated by 0.01 g mL−1 sodium dodecylsulphate after 120 min, and it remained stable for 30 min in a 5 vol. % and 10 vol. % hydrogen peroxide solutions. The proteases were slightly activated by Ca2+, Mg2+, and K+ and the substrate most effectively hydrolysed was casein (40.0 U mg−1). A 24 full factorial design used to evaluated the influence of independent variables showed that the enzyme extract, detergent concentration and the incubation time had a significant influence on the enzymatic activity. The best conditions to be used concerning detergent additive were found with 0.3 mg mL−1 of protein and 3.0 mg mL−1 of detergent for 30 min in the presence of Astrus® detergent.

The dependence of crystalline structure and optical properties of pulp on anthraquinone (AQ) added to the soda process at different cooking times was determined in this study. Wheat (Triticum aestevum L.) straw was used as the raw material for pulp. Soda and soda-AQ processes were selected for pulping at 80 min and 120 min. The soda-AQ process improved the yield and viscosity of pulp delignification ratio for pulping in comparison with the soda process. Crystallinity of pulp samples decreased by adding anthraquinone to the soda process because of stabilized less ordered cellulose and amorphous hemicelluloses in pulp. It was determined that crystallinity of pulp samples decreased with longer cooking time, from 80 min to 120 min, in both soda and soda-AQ processes. Monoclinic structure was dominant in pulp samples; however, the triclinic structure ratio increased in both soda and soda-AQ processes compared to raw material. It was found that brightness and lightness values in pulp samples decreased when using anthraquinone depending on the changes of the crystalline structure.

The goal of the study was to find the most accurate and sensitive method for the determination of activity of pectinolytic enzymes in complex mixtures obtained from fruit materials such as raw cloudberry and raspberry juices. Several assay methods based on enzymatic reactions using viscometric, colourimetric, spectrophotometric, or pH-titration detection of the reaction products were tested. Problems with the application of the selected methods, such as very low detection signal or very large background signal, were observed. Among the tested methods, only a modified method based on the continuous recording of the released carboxyl groups titration allowed to assay the activity of exogenous pectin methylesterase with a good linearity, sensitivity, accuracy, and minimised the interference of other fruit components.

Poly(γ-benzyl l-glutamate)-graft-poly(ethylene glycol) (PBLG-graft-PEG) copolymer was synthesized by the ester exchange reaction of the PBLG homopolymer with PEG. NMR spectroscopy was used to confirm the composition of the PBLG-graft-PEG copolymer. FTIR spectroscopy was used to characterize the chain conformation of polypeptide segments in the PBLG-graft-PEG copolymer in solid state. The self-assembly behavior of PBLG-graft-PEG and its mixtures with PBLG in ethanol were investigated by transmission electron microscopy (TEM) and viscometry. Experimental results showed that the PBLG-graft-PEG copolymer can self-assemble to form polymeric micelles with a core-shell structure of a thin shuttle-like shape. The introduction of the PBLG homopolymer into the mixed system not only decreases the critical micelle concentration (CMC) but also changes the morphology of the micelles from their shuttle-like shape to cylindrical shape. The effects of test temperature on the critical micelle concentration of PBLG-graft-PEG were also studied.

In the synthesis of mesoporous molecular sieves of the type MCM-41, different cationactive surfactants and sources of silicon were used. Moreover, Al-MCM-41 samples with different content of aluminium were synthesized. MCM-41 and Al-MCM-41 were synthesized at elevated temperature in stainless-steel autoclaves. Prepared mesoporous molecular sieves were characterized by powder X-ray diffraction (XRD), physical adsorption of nitrogen at the temperature of −197°C, sorption capacity of benzene, and by infrared spectroscopy (FTIR). Acidity was measured for Al-MCM-41 by temperature programmed desorption of ammonia (TPDA) and by FTIR of adsorbed pyridine. Acid catalytic activity of Al-MCM-41 was tested by isomerization of o-xylene. Influence of the synthesis reproducibility, surfactant used, source of silicon, synthesis time, source of aluminium, and Si to Al mole ratio on the properties of mesoporous molecular sieves were evaluated.

ZnO nano-tubes (ZNTs) have been successfully synthesized via a simple hydrothermal-etching method, and characterized by X-ray diffraction, field emission scanning electron microscopy and room temperature photoluminescence measurement. The as-synthesized ZNTs have a diameter of 500 nm, wall thickness of 20–30 nm, and length of 5 µm. Intensity of the plane (0002) diffraction peak, compared with that of plane (10$$ \bar 1 $$0) of ZNTs, is obviously lower than that of ZnO nano-rods. This phenomenon can be caused by the smaller cross section of plane (0002) of the nano-tubes compared with that of other morphologies. On basis of the morphological analysis, the formation process of nano-tubes can be proposed in two stages: hydrothermal growth and reaction etching process.

The presented work is aimed at the development of nontoxic nanocrystalline silicon fluorescence labels, biodegradable in living body and long-term stable, and of fluorescent nanodiamonds mainly for in vitro use. These novel fluorescence labels could be very good substitutes for commercially used quantum dots (e.g. cadmium compound quantum dots) which can be toxic according to the latest results. In this work, manufacturing of porous nanocrystalline silicon (por-Si) is described, several basic optical properties of por-Si are presented and the influence of Si nanocrystals, nanodiamonds, and milled silicon on the growth of a cell culture of L929 mouse fibroblast and HeLa cells is compared. Bio-interaction of nanoparticles was studied by optical transmission microscopy, time-lapse microphotography of cell culture evolution, fluorescence microscopy, fluorescence microspectroscopy, and scanning electron microscopy. The size and shape of nanocrystals were determined using atomic force microscopy (AFM).

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F− over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by 1H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10−5 mol dm−3 of the receptor and host.

A spectrophotometric procedure for the determination of sertraline hydrochloride (Sert) and/or clidinium bromide (Clid) in bulk sample and in dosage forms was developed. The purpose of this work was to develop a rapid, simple, inexpensive, precise, and accurate visible spectrophotometric method. The procedure is based on formation of an ion-pair complex by their reaction with bromocresol green (BCG), bromophenol blue (BPB), and bromothymol blue (BTB) in buffered aqueous solution at pH 3. The colored products are extracted into a polar solvent and measured spectrophotometrically at the optimum λmax for each complex. Optimization of different experimental conditions is described. Regression analysis of Beer-Lambert plots showed good correlation in the concentration range of 1–30 µg mL−1. The apparent molar absorptivity, Sandell sensitivity, detection and quantification limits were calculated. For more accurate analysis, Ringbom optimum concentration range of 2–27 µg mL−1 was used. The developed methods were successfully applied for the determination of sertraline hydrochloride and clidinium bromide in bulk in pharmaceutical formulations without any interference from common excipients. The procedure has the advantage of being highly sensitive and simple for the determination of the studied drugs, weak UV-absorbing compounds.

Enduring pandemic nature of tuberculosis urges to explore novel antimycobacterial agents with different mechanism of actions. Plant containing 1,4-naphthoquinone derivatives showed promising antitubercular activity with novel mode of action and their synthetic/semi-synthetic derivatives devoid of toxicity. Structural requirements of naphthalene-1,4-dione derivatives towards antitubercular activity and cytotoxicity were explored using a mathematical model in order to understand their physicochemical parameters. A quantitative structure activity relationship study furnished some important structural insights for antitubercular activity, i.e. average connectivity index, information content index of neighborhood symmetry, aromatic ratio, and path/walk 3 Randic shape index. Similarly it also provides drivers for the cytotoxicity of compounds. These drivers will be helpful in further development of safer and potent 1,4-naphthoquinone derivatives.

Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK HL = 9.65 ± 0.04, pK H2L = 4.18 ± 0.04), adenosine (pK H2L = 3.59 ± 0.05), cytosine (pK H2L = 4.56 ± 0.01), cytidine (pK H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH 0 = (−17 ± 4) kJ mol−1, ΔS 0 = (23 ± 13) J K−1 mol−1), cytosine (ΔH 0 = (−22 ± 1) kJ mol−1, ΔS 0 = (13 ± 5) J K−1 mol−1) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)3, 5′AAA-CCC-CCC3′ = A3C6, 5′CCC-AAA-CCC3′ = C3A3C3) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning (C+-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature.

Rheological properties of doughs prepared from wheat flour with buckwheat and quinoa flour addition (2.5 mass %, 5.0 mass %, 7.5 mass %, and 10 mass %) were investigated using a farinograph and compared with those of standard dough (without addition of pseudocereals). The following characteristics were determined: water absorption capacity, water consumption, dough growth time, level of dough softening, dough stability, mechanical resistance, and dough elasticity. Dough stability showed a linear decrease with the increasing content of pseudocereals. Doughs containing quinoa flour were more stable than those with buckwheat flour addition. Dough growth time was reduced with increasing amounts of buckwheat flour but it was not affected in the case of quinoa flour addition. From the comparison of the studied characteristics it can be concluded that an addition of lower amounts of quinoa (up to 5.0 mass %) to wheat flour will not significantly impair rheological properties of the dough but provides for enhanced nutritional value of the prepared bakery products.

After the synthesis and isolation of methylated bismuth cysteine, its initial identification by IR-spectroscopy was performed, whereas for definitive identification, high resolution mass spectrometry (ESI-TOF-MS and LTQ Orbitrap) was carried out.