Volume 64, Issue 4

Single-step microwave digestion methods using four different acidic dissolving reagents were investigated with the main objective to obtain a simple, rapid method for multi-elemental analysis of marine sediment samples by high resolution inductively coupled plasma-mass spectrometry (HRICP-MS), especially for environmental studies. Closed-vessels microwave digestion procedures were carried out using the reagents as follows: HNO3, mixture of HNO3-HCl (φ r = 9: 1), aqua regia, and mixture of HNO3-HCl-HF (φ r = 8: 1: 1). The elements analyzed were: Al, As, Ba, Be, Bi, Cd, Co, Cr, Cu, Fe, K, Li, Mn, Mo, Na, Ni, Pb, Sb, Sn, Sr, Ti, Tl, V, and Zn. Good recoveries were established for many of the metals analyzed even when only nitric acid was employed. However, for a good recovery of Sb and Tl, aqua regia should be employed.

Two simple, sensitive, and selective spectrophotometric methods for the determination of 5-(aminosulfonyl)-4-chloro-2-((2-furanylmethyl)amino)benzoic acid (furosemide, FUR) are described. The methods are based on acid hydrolysis of FUR to free primary aromatic amine and diazotization followed by coupling with N-1-napthylethylene diamine (NEDA) (method A) or 4,5-dihydroxynaphthalene-2,7-disulfonic acid (chromotropic acid, CTA) (method B). The colored reaction product can be measured spectrophotometrically at 520 nm (method A) or 500 nm (method B). Beer’s law is obeyed over the ranges of 1.75–21.0 μg mL−1 and 2.5–30.0 μg mL−1, for method A and method B, respectively. Apparent molar absorptivities and Sandell’s sensitivities (in L mol−1 cm−1 and μg cm−2 per 0.001 absorbance unit, respectively) were 1.34 × 104 and 0.0253 using NEDA as the coupling agent, and 8.5 × 103 and 0.0389 using CTA for the same purpose. Analysis of solutions containing seven different concentrations of FUR gave a correlation coefficient of 0.9979 using NEDA and 0.9984 using CTA, while the slope and the correlation coefficient of the regression equation were calculated. The reaction stoichiometry in both methods was evaluated by the limiting logarithmic method and was found to be 1: 1 (diazotized FUR: NEDA or diazotized FUR: CTA). The methods were successfully applied to the determination of FUR in spiked human urine and in pharmaceutical formulations. The recovery of FUR from spiked urine was satisfactory resulting in the values of (109.4 ± 4.37) % using NEDA and (113.0 ± 4.74) % using CTA. Results of the analysis of pharmaceuticals demonstrated that the proposed procedures are at least as accurate and precise as the official method while a statistical analysis indicated that there was no significant difference between the results obtained by the proposed methods and those of the official method.

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10−6 mol L−1 salicylic acid in 0.1 mol L−1 NH4+/NH3 buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L−1 iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L−1 and the sampling rate was 60 h−1. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).

A liquid chromatographic method for the determination of meloxicam in serum has been developed. The technique includes a solid phase extraction of the serum samples on [poly (divinylbenzeneco-N-vinylpyrrolidone)] as a solid phase extraction sorbent. After conditioning, the cartridge was loaded with 1 mL of acidified serum containing an internal standard. Elution was carried out using 1 mL of water-acetonitrile (φ r = 1: 1) mixture. After evaporation of the eluate to dryness and reconstitution of the residue with 0.1 mL of methanol, the samples were analyzed on a Symmetry C18 column. Mobile phase consisted of 1 % aqueous acetic acid/THF/acetonitrile (φ r = 60: 30: 10) + 0.1 mL of 1-octane sulfonic acid. Detection was carried out using a photodiode array detector. Full validation of the proposed method is provided. Linearity of the method was proven over the range of 0.01–10 φg mL−1 of meloxicam. Meloxicam assay was accurate and reliable with average intra- and inter-day precisions lower than 5.0 % and the intra- and inter-day accuracy higher than 97 %. Limits of detection (LOD) and quantitation (LOQ) found were 0.003 μg mL−1 and 0.01 μg mL−1, respectively. The proposed method was successfully utilized to quantify meloxicam in serum.

The search for new antioxidants of natural origin derived from plants and seaweeds is still very important at present. In our study, the acetone extract of A. nodosum was investigated for its potential use as a natural antioxidant, natural feed additive with antibacterial activity and as a tyrosinase inhibitor. This study could be useful in the context of improved utilization of the A. nodosum extract in the food and cosmetics industry, being not only economically advantageous but also environmentally friendly. Extracts showed antioxidant activity with application of different methodologies: 1,1-diphenyl-2-picrilhydracil DPPH· radicals scavenging (39 %, 4 mg of freeze-dried sample), β-carotene-linoleic acid antioxidant assay (11 %, 4 mg of freeze-dried sample), O2· radicals scavenging activity (IC50 0.43 mg mL−1), OH· radicals scavenging activity (IC50 1.55 mg mL−1), and iron chelation ability (IC50 0.56 mg mL−1). The extract showed considerable antibacterial activity being more effective against gram-positive bacteria (Micrococcus luteus, Staphylococcus aureus) than against gram-negative bacteria (Escherichia coli, Enterococcus aerogenes). Results of tyrosinase assay for the acetone extract of Ascophyllum nodosum presented 65.6 % inhibition of tyrosinase activity at the IC50 value of 0.1 mg mL−1. The outcomes of our study support potential utilization of this brown seaweed as a source of natural antioxidants. Antioxidant activity of the studied seaweed can be apparently explained by the free radicals scavenging activity, particularly related to the mechanisms of O2−· radicals scavenging activity, OH· radicals inactivation, and iron chelation ability.

The transesterification-active enzyme bacillolysin was extracted into organic solvents such as isooctane by enzyme-AOT (bis (2-ethylhexyl) sulfosuccinate) ion-pairing preserving its natural second structure and catalytic activity. Extraction efficiency was affected by the interaction mode of the two phases, ionic strength, and pH of aqueous phase, surfactant and enzyme concentration. Magnetic stirring with phase mixing was favorable for the enzyme extraction. Optimal ionic strength and pH were 8 mM CaCl2 and 5.0, respectively. Critical number of AOT molecule for an enzyme molecule to be extracted into isooctane was 89. Optimal initial enzyme concentration in the aqueous phase was 7 mg mL−1 while the initial AOT concentration in isooctane was 3 mM. Within CMC (critical micellar concentration) of AOT in isooctane, the increase of initial AOT concentration enhanced the extraction efficiency.

Optimal operation of a chemical reactor according to various performance criteria often drives the system towards critical boundaries. Thus, precise evaluation of runaway limits in the parametric space becomes a crucial problem not only for the reactor’s safe operation, but also for over-designing the system. However, obtaining an accurate estimate for operating limits is a difficult task due to the limited validity of kinetic models describing complex processes, as well as the inherent fluctuations of the system’s properties (catalyst, raw-material quality). This paper presents a comparison of several effective methods of deriving critical conditions for the case of a tubular fixed-bed catalytic reactor used for aniline production in the vapour phase. Even though the methods being compared are related to one another, the generalised sensitivity criterion of Morbidelli-Varma (MV) seems to be more robust, not depending on a particular parameter being perturbed, when compared to the criteria that detect an incipient loss of system stability in the critical region (i.e., div-methods based on the system’s Jacobian and Green’s function matrix analysis). Combined application of div- and MV criteria allows for an accurate evaluation of the distance from the reactor’s nominal conditions to the safety limits.

The influence of ionic strength on the adsorption capacity of seven commercial adsorbents used in downstream processing of monoclonal antibodies was examined. Affinity (MabSelect, Poros 50A High Capacity, ProSep-vA High Capacity), hydrophobic charge-induction (MEP HyperCel), and cation exchange adsorbents (FractoGel EMD SE Hicap (M), SP Sepharose Fast Flow, Ceramic HyperD F) were used to study the adsorption of polyclonal human immunoglobulin G at optimal pH values. The ionic strength, adjusted by sodium chloride concentrations in the range of 0–225 mM, strongly decreased the adsorption capacity of the cation exchangers. Equilibrium data were described in the form of the dependence of the ratio of protein concentrations in the solid and liquid phases on the total concentration of cation counter ions. They were successfully fitted and interpreted through a stoichiometric ion-exchange model.

HY-zeolite and its deep-bed dealuminated and EFAL-extracted forms were tested in liquid phase alkylation of benzene with 1-hexadecene in a batch reactor at 120°C. Deep-bed dealumination of the HY-sample at 560 °C followed by careful selective extraction of extra-framework aluminium by hydrochloric acid increased the catalytic activity as well as oxidative regenerability of Y-zeolite.

Policaju-based coatings were applied on “Tommy Atkins” mangoes and the effects of four different treatments on mango shelf-life were evaluated under storage condition at 4°C and 82 % of relative humidity over 28 days. The surface tension of mangoes was found to be 29.04 mN m−1; the dispersive and polar components were 27.57 mN m−1 and 1.47 mN m−1, respectively, and the critical surface tension was 22.7 mN m−1. A significantly lower mass loss was observed in all mangoes treated with Policaju-based coatings. For all applied treatments, no significant variation in the total soluble solids and pH was detected over the experimental storage time. The results show that Policaju-based coatings have a positive effect on the shelf-life extension of mangoes at low storage temperatures (4°C).

In this study, bioactivity of glass in the system SiO2-CaO-Al2O3-P2O5-Na2O-MgO-CaF2 was investigated. For this purpose, a glass sample was prepared by the traditional melting method. Crystallization behavior of bioactive glass was also investigated using differential thermal analyses. The Avrami constant of bioactive glass sample calculated according to the Ozawa equation was 3.72 ± 0.4, which indicates bulk crystallization. Using the Matusita-Sakka and the Kissinger equations, activation energy of crystal growth was determined as (394 ± 17) kJ mol−1 and (373 ± 12) kJ mol−1, respectively. These results indicate that the crystallization activation energy data of bioactive glass obtained in this study are accurate and reliable. Bioactivity of the resultant glass sample was analyzed by immersion in simulated body fluid. Scanning electron microscopy, thin film X-ray diffraction, ultraviolet spectroscopy and inductively coupled plasma techniques were used to monitor changes in the glass surface and the simulated body fluid composition. The results revealed that a hydroxyapatite layer was formed on the glass surface after 21 days of immersion in SBF. Formation of the hydroxyapatite layer confirmed the bioactivity of the glass in the system SiO2-CaO-Al2O3-P2O5-Na2O-MgO-CaF2. In addition, physical and mechanical properties of the sample were measured to determine changes in the properties with the immersion time. The results show that bioactive glass maintained its strength during the immersion in a simulated body fluid solution.

Phase pure, stable nanocrystalline brushite particles with average diameter in the range of 23–87 nm were obtained by the reverse microemulsion technique employing a mixture of surfactants (Aliquat 336 & Tween 80) as template directing agents, and calcium nitrate tetrahydrate and biammonium hydrogen phosphate as precursors. Particle sizes and morphologies were tuned by adjusting the reaction parameters, precursor concentration and temperature. FTIR, TEM, and XRD were used to characterize morphological changes of as synthesized nanoparticles. FTIR and XRD analyses confirmed the formation of brushite nanoparticles. Variations in the reaction temperature resulted in changes in the particle morphology and distribution. At high temperatures (60°C), the sample exhibited high monodispersity and spherical morphology with the average grain size of 42 nm. At low temperatures (6°C), nanoflakes were formed. The results suggest that a reverse microemulsion system provides facile media for control of the phase and morphology of nanoscale calcium phosphate biominerals. A mechanism providing an insight into the formation of brushite particles has also been proposed.

1,2-Diketone moiety-bearing monomer 1-phenylbut-3-ene-1,2-dione, an analogue of phenyl vinyl ketone, was synthesized from 4-chlorobutyryl chloride in a 29 % overall yield in five steps. Following acylation of benzene with 4-chlorobutyryl chloride, the resulting α-methylene group was oxidized to 1,2-diketone in three steps: successive bromination, substitution with lithium hydroxide, and oxidation of α-hydroxyketone with potassium dichromate. The final step was dehydrochlorination of 4-chloro-1-phenyl-butane-1,2-dione. The attempted copolymerization of this monomer with styrene, using AIBN as the initiator, was unsuccessful.

Possible stable conformers of the 1-(4-pyridyl)piperazine (1-4pypp) molecule were experimentally and theoretically studied by FT-IR and Raman spectroscopy. FT-IR and Raman spectra were recorded in the region of 4000–200 cm−1. Optimized geometric structures related to the minimum on the potential energy surface were investigated by the B3LYP hybrid density functional theory method using the 6-31G(d) basis set. Comparison of the experimental and theoretical results indicates that the density functional B3LYP method provides satisfactory results for the prediction of vibrational wavenumbers and structural parameters and equatorial-equatorial (e-e) isomer is supposed to be the most stable form of the 1–4pypp molecule.

Binding affinities of a cyclic β-peptoid to amino acids were studied using the density functional theory (DFT) at the B3LYP/6-311G(d,p) level after the basis set superior error (BSSE). The host molecule possesses binding ability to amino acids since the binding energies of the complexes formed are negative. The complexes were stabilized via hydrogen bonds between the host and the guest molecules. Based on the B3LYP/6-31G(d) optimized geometries, electronic spectra of the complexes were calculated using the INDO/CIS method. 13C NMR spectra and nucleus-independent chemical shift (NICS) values of the complexes were computed at the B3LYP/6-31G(d) level. Carbon atoms in the carboxyl groups of the complexes are shifted downfield relative to those of the host. Some complexes exhibit aromaticity although the host shows anti-aromaticity. Formation of hydrogen bonds leads to cyclic current formation in these complexes.

The azo coupling reaction with 2-aminonaphthalene-4,8-disulfonic acid (I) was used to develop a new cheap and rapid method of triclosan (II) determination in hygiene products. The calibration graph was linear in the range of 2.0−100 × 10−6 mol L−1. The detection limit was 2.0 μmol L−1.

In this study, a new source of ellagic acid (EA) is reported. Euphorbia antisyphilitica or “candelilla” was used to extract phenolic dilactone. Cereous layers and fibrous tissue were analyzed. A completely randomized experimental design with a treatment factorial arrangement was employed. The factors considered were: plant/extracting agent ratio, extraction temperature and time. Candelilla wax does not contain EA. Temperature and the ratio plant/extracting agent were determinant during the EA extraction process. Around 20 mg of free EA per gram of fibrous tissue were found. Residues of candelilla are a good source of EA.

Ritter reaction of podophyllotoxins with chloroacetonitrile and subsequent cleavage of the chloroacetyl group in the resulting chloroacetamide with thiourea under both classical heating and ultrasonic conditions is an efficient procedure for the synthesis of 4β-aminopodophyllotoxins. In general, significant improvements in the rates of reaction and yields of the sonochemical reactions relative to the classical heating reactions were observed.

A novel and simple method for the N-alkylation of amines with different ethers as alkylating reagents has been developed, using cheap γ-Al2O3 as the catalyst at atmospheric pressure in the temperature range of 260–320°C. For example, the reaction of equimolar amounts of morpholine and diethyl ether gave N-ethylmorpholine quantitatively. The present catalytic system is applicable to the N-alkylation of both primary and secondary amines. Since only water is generated as byproduct, the protocol proved to be eco-friendly and atom-economic.