Volume 69, Issue 4

Liquid-liquid extraction (LLE) and cloud point extraction (CPE) of vanadium(V) ternary complexes with 4-(2-pyridylazo)resorcinol (PAR) and 2,3,5-triphenyl-2H-tetrazolum chloride (TTC) were investigated. The optimal conditions for vanadium extraction and spectrophotometric determination were identified. The composition (V : PAR : TTC) of the extracted species was 1 : 2 : 3 (optimal conditions; LLE), 2 : 2 : 2 (low reagents concentrations; LLE), 1 : 1 : 1 (short heating time; CPE), and 1 : 1 : 1 + 1 : 1 : 0 (optimal extraction conditions; CPE). LLE, performed in the presence of 1,2-diaminocyclohexane-N,N,N’,N’-tetraacetic acid and NH4F as masking agents, afforded the sensitive, selective, precise, and inexpensive spectrophotometric determination of vanadium. The absorption maximum, molar absorptivity, limit of detection, and linear working range were 559 nm, 1.95 × 105 dm3 mol−1 cm−1, 0.7 ng cm−3, and 2.2-510 ng cm−3, respectively. The procedure thus developed was applied to the analysis of drinking waters and steels. The relative standard deviations for V(V) determination were below 9.4 % (4-6 × 10−7 mass %; water samples) and 2.12 % (1-3 mass %; steel samples).

A novel fluorometric method was developed for the sensitive and selective detection of Pro-Gly (PG) and Pro-Gly-Pro (PGP) using 4-chlorobenzene-1,2-diol (4-CBD) as a fluorogenic reagent. The reaction was performed at 37°C for 30 min in the presence of a borate buffer (pH 7.0) and sodium periodate. The resulting fluorescence intensity was measured using a spectrofluorometer with excitation and emission wavelengths of 450 nm and 535 nm. To obtain a stable fluorescent signal and maximise its intensity, different reaction conditions such as the concentrations of the reagents, the reaction time, and the pH were optimised. Under the optimised conditions, a linear relationship was obtained between fluorescence intensity and peptide concentrations from 1.0-40.0 μmol L -1 with a limit of detection of 1.0 μmol L -1 (S/N = 3). Both PG and PGP generated a strong signal out of all the peptides tested and no other biogenic substances such as amino acids or proteins produced any fluorescence. The reaction thus developed is simple, rapid, selective, and sensitive. It can be applied to the determination of peptides as biomarkers or substrates.

A novel fluorometric method for the determination of adenine was proposed, based on the fluorescence quenching of a nuclear fast red-silver complex as a small molecule optical probe in the presence of adenine. The characteristic spectra of absorption, resonance Rayleigh scattering (RRS) and the fluorescence of the system were analysed. Adenine, Ag + and nuclear fast red formed a sandwichtype complex. The composition of the compound and the mechanisms of fluorescence quenching were discussed. The optimal conditions for the reaction and the effects of co-existing substances were also investigated. The quenched fluorescence intensity was proportional to the concentration of adenine in the range of 0.03-0.90 μg mL -1 , with the limit of detection of 0.023 μg mL -1 . The method was applied satisfactorily to the determination of adenine in synthetic samples, herring sperm DNA, human sera and vitamin B4 tablets with recoveries from 95.3 % to 105 %.

Raman spectroscopy and surface enhanced Raman spectroscopy were used to examine 14 blue inks obtained from commercially available stationery. Standard colouring agents in the inks: β-phase of phtalocyanine blue PB15 and some homologues of the methyl violet class, were identified. Surface enhanced Raman spectra were recorded on a firm heterostructure of silver/nanocrystalline diamond/silicon constituting an active substrate providing the possibility to write directly on the surface. Based on the differences in traditional and surface enhanced Raman spectra, two inks were identified unambiguously, the remaining inks were categorised into three groups exhibiting common spectral features. Despite their similarity, surface enhanced Raman spectra exhibited soft variations enabling discrimination of the inks, thus proving the usefulness of the method.

Two easily-prepared pyridine-based derivatives of (Z)-2-(4-amino-phenyl)-3-(pyridine-4-yl)acrylonitrile (I) and (Z)-2-phenyl-3-(pyridin-4-yl)acrylonitrile (II ) were designed, synthesised and characterised. Due to the formation of a complex with Hg 2+ , hence leading to an enhanced ICT effect, I exhibits a visible colour change from light yellow to orange, rendering it suitable for use as a naked-eye sensor for rapid detection of Hg 2+ in an aqueous ethanol solution. When mixed with Hg 2+ , I interacts with Hg 2+ in a 2 : 1 (Y1-Hg 2+ ) stoichiometry via a coordination bond with an association constant of 7.7 × 10 8 M -2 (R 2 = 0.96). The present probe I exhibits excellent reproducibility, reversibility, sensitivity and selectivity with the presence of low concentration of Hg 2+ (1.74 × 10 -10 M).

A simple, efficient procedure for the preparation of phospho sulfonic acid PO(OSO 3 H) 3 as a Brønsted acidic and recoverable heterogeneous catalyst is described, used for the one-pot synthesis of aryl-14H-dibenzo[a,j ]xanthenes and 1,8-dioxo-octahydro-xanthenes. A cost-effective, simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a,j]xanthenes was developed via a onepot condensation from substituted benzaldehydes and β-naphthol under solvent-free conditions. The one-pot condensation of substituted benzaldehydes and 5,5-dimethyl-1,3-cyclohexanedione (dimedone) under solvent-free conditions leads to 1,8-dioxo-octahydro-xanthenes. These protocols afford a number of advantages, such as: excellent yields, very short reaction times, easy procedure, simple methodology and ease of preparation and regeneration of the catalyst.

Separation of microorganism cells from broth is a very important stage in the recovery of fermentation products. The microfiltration of fermented glycerol solutions was studied. During this process, the filter cake building up on the membrane surface caused an increase of filtration resistances, resulting in the decrease of the permeate flux. In this work, short time reverse flow of permeate was used to remove the fouling layer after each cycle of the filtration. The applied periodical membrane cleaning led to minimization of the observed fouling effects

The impact of electrodialysis module characteristics on mass transfer was examined using the limiting current method. The current-voltage curves of different electrodialysis modules were measured and limiting currents were determined using the derivative method. The mass transfer coefficients were calculated and the parameters of their dependence on linear flow velocity were estimated. From these the impact of spacer thickness, spacer net type, membrane type, and module geometry were evaluated. It was found that the impact of spacer thickness was almost negligible within the examined range, but a decrease in the mass transfer coefficient could be expected in the case of thicker spacers. By contrast, the spacer net type and type of membrane were found to be very important parameters able to significantly influence the mass transfer. By modifying the module geometry, the mass transfer coefficient could also be altered and, only in this case, the exponential parameter of the dependence was changing. The parameters thus determined may be used to calculate the limiting current in a wide range of operational conditions and may help predict the performance of different electrodialysis module types

The presented paper deals with the numerical analysis of pseudo-steady state conditions used in the modelling of the batch dialysis process. First, under specified conditions, time dependences of component concentrations and liquid volumes in both compartments were generated using a rigorous model based on Fick’s second law. From these data, the diffusion coefficient of the component in the membrane was calculated using a simplified model based on Fick’s first law. The specified coefficient was then compared with the calculated one. Numerical analysis revealed that in case of not too thick membranes, sufficiently high values of the diffusion coefficient, high intensity of mixing and considering the concentration and volume data in compartments I and II, the pseudo-steady state conditions can be considered as a good approximation of the real state

Four copper(II) oxime complexes, [Cu(HPPK)(PPK)X] (HPPK = phenyl-2-pyridylketoxime and X = CI − (I ), CF 3 COO− (II ), C 3 F 7 COO− (III ), and [Cu(PPK) 2 ] 2 (IV )), were synthesized and characterized by elemental analysis, infrared spectroscopy (IR), and single-crystal X-ray diffraction (XRD). XRD analysis revealed that I -III contain copper(II) coordinated by four nitrogen atoms from two oxime molecules in the basal plane and one monodentate anion X in the apical position of a distorted square pyramid. Complex IV is dimeric and it is formed by two Cu(PPK) 2 units. Bridges between these units are formed by the two oxygen atoms of the deprotonated oxime groups. Thermal stability of I -IV was investigated by thermogravimetric analysis (TGA) in air and in nitrogen atmosphere, respectively. Evolved gaseous decomposition products were characterized by IR. I -IV decompose via multistep processes. Fluorocarbons and CO 2 were observed to be the most abundant gaseous species evolved. Preliminary ammonolysis experiments were performed to examine the possibility of using II and IV as precursors for the synthesis of copper nitride. Moreover, solutions of IV were spin-coated onto silicon substrates. Surface structure and morphology of the resulting films were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) and layers with island-like distribution of material were observed

4-Nitro-o-xylene was selectively oxidized to 2-methyl-4-nitrobenzoic acid using dilute nitric acid as the oxidizing agent under atmospheric pressure. The oxidation of 4-nitro-o-xylene was effectively promoted by an addition of radical initiators. Under reflux, 2-methyl-4-nitrobenzoic acid was afforded in high yield using nitric acid combined with N-hydroxyphthalimide, cobalt dichloride (CoCl 2 · 6H 2 O), manganese acetate (Mn(OAc) 2 · 4H 2 O) and phase transfer catalyst

An efficient ionic liquid with both Brønsted acidic and Lewis basic sites, namely 1,4-dimethyl-1- (4-sulphobutyl)piperazinium hydrogen sulphate (IL1), was synthesised and characterised. IL1 is a “green”, homogeneous and reusable catalyst for: i) the synthesis of pyranopyrazoles (Va-Vj) and benzopyrans (VIa-VIj and VIIa-VIIf) at ambient temperature under solvent-free conditions and ii) the synthesis of amino-2-chromenes (VIIIa-VIIIi and IXa-IXi) and dihyropyrano[c]chromenes (Xa- Xi) at 80◦C under solvent-free conditions. The reactions were rapid with excellent product yields. In addition, the double Brønsted acid, 1,4-dimethyl-1,4-bis(4-sulphobutyl)piperazinium hydrogen sulphate (IL2), was prepared to evaluate the cooperation efficiency of their Brønsted acidic and Lewis basic sites as compared with the double Brønsted acidic sites in IL1

The conjugate hydrocyanation of α-cyanoacrylates through chemoselective 1,4-addition to synthesise α,β-dicyanopropanoates by one-pot two-step procedure using potassium hexacyanoferrate(II) as an eco-friendly cyanide source, benzoyl chloride as a promoter and potassium carbonate as a catalyst is described. The advantages of this protocol are use of a non-toxic, non-volatile and inexpensive cyanating reagent, high product yields and simple working procedure

The morphological orders of spherulitic crystal patterns in a Belousov-Zhabotinsky-type oscillatory reaction system were studied. The experiments showed that the morphology of crystal patterns were highly dependent on the reaction temperature. The reaction was initially carried out at 30°C, leading to the growth of multi-centred spherulitic patterns. The single-centred spherulitic patterns with fairly large crystal fibrils were obtained at 35°C. A number of undersized crystal assemblies with fractal geometry were also investigated at 25°C. The gross morphology of the crystal patterns was examined using optical microscopy and a scanning electron microscope which revealed the fibrous organisations. A particle-mediated self-assembly scheme was proposed for the growth of the spherulitic patterns. The insight into the nucleation mechanism, growth behaviour, and morphological orders of the growing patterns is discussed in detail. The crystal phases, ordering of textures, and composition of the crystals were characterised by thermal and X-ray diffraction techniques

The molecular structures of a series of selenocysteine-containing dipeptides in their zwitterionic forms were studied using the B3LYP/6-311++G(d,p) level in the aqueous phase. The B3LYP and BHandHLYP functionals in combination with 6-311++G(d,p) and LANL2DZ basis sets were used to investigate the effects of metal coordination on the structural and molecular properties of the dipeptides by complexing them with bivalent copper ions. The results from this DFT study provide valuable insights into the interaction enthalpies (metal ion-binding affinities) and free energies, the influence of the C-terminal moiety on the backbone structural features, the existence of various types of intramolecular H-bond interactions, harmonic vibrational frequencies, along with various other electronic properties pertaining to the zwitterions of the dipeptide molecules as well as their metallic complexes. Metal coordination via the carboxylate groups tends to enhance the planarity of the amide planes. The participations of the N- and C-terminal side-chain moieties in metal-binding markedly enhance the thermodynamic stability of the metalated dipeptides. The theoretical λmax values, calculated using the TD/DFT level for all the systems, well represent the occurrence of d-d transitions in the Cu-dipeptide complexes