Food dyes screening using electrochemistry approach in solid state: the case of sunset yellow dye electrochemical behavior

Concerning the importance of the identification and characterization of food dyes in food science, this work presents a screening method using voltammetry of immobilized microparticles for identification in solid state of sunset yellow, tartrazine yellow, brilliant blue, indigotine, and erythrosine in food matrices. Different aqueous supporting electrolyte were investigated for screening purpose and NaCl 0.1 mol L⁻¹ showed to be suitable for evaluating dyes in solid state. By using square wave voltammetry as detection mode was possible to establish qualitative diagnostic criteria for identification of dyes in commercials powder of food dyes samples using both anodic and cathodic scan. Moreover, based on the solid-state electrochemistry profile and due to the lack of information about the electrochemical behavior of these compounds in solid state, some oxi/reduction pathways could be elucidated, and special attention was given to the case of sunset yellow dye.

     

Solid phase microextraction as a powerful alternative for screening of secondary metabolites in actinomycetes

Actinobacteria are one of the most promising producers of medically and industrially relevant secondary metabolites. However, screening of such compounds in actinobacteria growth demands simple, fast, and efficient extraction procedures that enable detection and precise quantification of biologically active compounds. In this regard, solid phase microextraction (SPME) emerges as an ideal extraction technique for screening of secondary metabolites in bacteria culture due to its non‐exhaustive, minimally invasive, and non‐destructive nature: its integrated sample preparation workflow; balanced coverage feature; metabolism quenching capabilities; and superior cleanup, as well as its versatility in configuration, which enables automation and high throughput applications. The current work provides a comparison of micro‐scale and direct immersion SPME (DI‐SPME) for screening of secondary metabolites, describes the optimization of the developed DI‐SPME method, and introduces the developed technique for mapping of target secondary metabolites as well as its direct coupling to mass spectrometry for such applications. The optimized DI‐SPME method provided higher amounts of extracted ions and intensity signals, yielding superior extraction and desorption efficiency as compared with micro‐scale extraction. Studied compounds presented stability on the coating for 24 h at room temperature. The DI‐SPME mapping approach revealed that lysolipin I and the lienomycin analog are distributed along the center and edges of the colony, respectively. Direct coupling of SPME to MS provided a similar ions profile as SPME‐LC‐MS while enabling a significant decrease in analysis time, demonstrating its suitability for such applications. DI‐SPME is herein presented as an alternative to micro‐scale extraction for screening of secondary metabolites in actinobacteria solid medium, as well as a feasible alternative to DESI‐IMS for mapping of biologic radial distribution of secondary metabolites and cell life cycle studies. Lastly, the direct coupling of DI‐SPME to MS is presented as a fast, powerful technique for high throughput analysis of secondary metabolites in this medium.     

Simple and selective spectrophotometric determination of ruthenium after solid phase extraction with some quinoxaline dyes into microcrystalline p-dichlorobenzene

A simple selective and highly sensitive extraction method has been developed for the determination of ruthenium spectrophotometrically after extraction of its 2,3-dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline (I), 2,3-dichloro-6-(2-hydroxy-3,5-dinitrophenylazo)quinoxaline (II) and 2,3-dichloro-6-(2,7-dihydroxy-naphthylazo)quinoxaline (III) complexes into microcrystalline p-dichlorobenzene. The optimization of experimental conditions for the procedure is studied. The solid p-dichlorobenzene containing the ruthenium-reagent (I-III) complexes is separated by filtration and dissolved in N,N-dimethylformamide. The absorbance is measured at lambda(max) 622, 518 and 542 nm against reagents I, II and III, respectively, as blank. Beer's law is obeyed upto 2.5 microg ml(-1) of ruthenium. The molar absorptivity, Sandell sensitivity, detection and quantification limits are calculated, when compared with those parameters without using solid phase extraction method. The interference of various ions has been studied in detail and the statistical evaluation of the experimental results is reported. The proposed methods have been successfully applied for the determination of trace amount of ruthenium in seawater, ore and metallurgy products.     

Physiological changes inPhanerochaete chiysosporium during the onset of ligninolytic activity

In the white-rot basidiomycete,Phanerochaete chrysosporium, ligninolytic activity appears with the transition from primary to secondary metabolism brought on by depletion of fixed nitrogen. To explore changes in cellular physiology during this transition two aspects of cell metabolism have been studied. Firstly, proteins associated with the fungus were separated by twodimensional polyacrylamide gel electrophoresis according to their isoelectric point and molecular weight. Ribosomal, cytoplasmic, and cell wall-associated proteins were separated and the protein patterns compared after growing the fungus under lignin degrading (nitrogen limited) and nonlignin-degrading (nitrogen excess) conditions. We find major differences in the protein populations of nonligninolytic and ligninolytic cultures; in the case of the cytoplasmic proteins there are approximately 20 novel proteins in the latter, but other protein species disappear. Attempts to identify some of the novel secondary phase proteins will be described. The patterns from some mutants of P.chrysosporium defective in ligninolytic activity or other aspects of secondary metabolism will also be discussed. We have also studied the intracellular cyclic AMP levels during the onset of ligninolytic activity. These increased sixfold between days 3 and 5 and were maximal as the culture became ligninolytic. In control cultures (nitrogen excess), there was no ligninolytic activity and cAMP levels merely reflected growth. To determine the effect of added nitrogen on cAMP levels 0.72M glutamate (final conc.) was added to ligninolytic cultures. The level of cAMP was halved between 4 and 8 h after glutamate addition, and ligninolytic activity was also suppressed as expected. Some of the mutants of P.chrysosporium defective in ligninolytic activity showed decreased levels of intracellular cAMP. We thank the Agricultural Research Council and the British Petroleum Venture Research Unit for support.     

Supramolecular chemosensor for selective detection of iron in aqueous medium

We have successfully developed a ‘turn-on’ colorimetric chemosensor for Fe³⁺ based on 1,10-phenanthroline. An amide derivative of 1,10-phenanthroline 4 was developed for the selective recognition of Fe³⁺ over Co²⁺, Cr³⁺, Cu²⁺, Mn²⁺, Ni²⁺, Ag⁺ and Zn²⁺ and could measure Fe³⁺ concentration in the range of 15–210 μM by UV–vis spectroscopy. Moreover, the addition of Fe³⁺ to a colourless solution of 4 turned its colour to light pink, indicating that 4 is capable of detecting Fe³⁺ by the naked eye. Compound 4 exhibits a major absorption band centred at 268 which shifted to 278 nm after addition of Fe³⁺, and a shoulder band around 514 nm was also observed. The complexation of Fe³⁺ with 4 was analysed at a different pH and favourable binding was observed at pH 6.2.     

Efficient solid phase strategy for preparation of modified xanthene dyes for biolabelling

An efficient solid phase strategy for the versatile functionalisation of xanthene dyes for conjugation and labelling of biomolecules is presented. The low cost, high purity and excellent spectral properties of the obtained materials provide an attractive alternative for the labelling of a wide range of molecules.     

Organic synthesis in solid media. Silica gel as an effective and reusable medium for the selective allylation of aldehydes with tetraallyltin

Wet silica gel promotes the chemoselective and almost complete allylation of aldehydes with 0.25-0.30 molar equivalents of tetraallyltin without an organic solvent, leaving no organotin compounds, requiring neither extraction nor chromatographic separation after the reaction, and enabling the repeated use of the silica gel.     

Lignin selective dyes: quantum-mechanical study of their characteristics

The mechanism of dye-bonding to the lignin component of the fibre was checked using the quantum-mechanical and crystallographic approach. The calculated data support the conclusion that for the selectivity of cationic dyes for lignin, a high partial negative charge on accessible substituents on the periphery of the molecule is the most important, but not an exclusive factor. Besides the delocalized positive charge, what is also important for the interaction of a dye with hemicellulose, is the dye’s ability to be involved in hydrogen bonds, whereas for the interaction with lignin also its ability of stacking to it.     

Use of intercalated clays in oxidation of organic dyes

Intercalated materials based on natural montmorillonite and Fe- and mixed Fe/Al-polyhydroxo complex were obtained and their texture properties were studied. The catalytic properties of these materials were examined in the reaction of oxidation of an organic dye, Direct Pure Blue, with hydrogen peroxide in aqueous solutions. The optimal conditions of oxidation of azo dyes in the presence of intercalated clays were determined. In these conditions, a 100% oxidation of dye solutions can be achieved, with the stability of catalysts preserved.     

Disposable solid state probe for optical screening of chlorpromazine

We are presenting a simple, low-cost and rapid solid-state optical probe for screening chlorpromazine (CPZ) in aquacultures. The method exploits the colourimetric reaction between CPZ and Fe(III) ion that occurs at a solid/liquid interface, the solid layer consisting of ferric iron entrapped in a layer of plasticized PVC. If solutions containing CPZ are dropped onto such a layer, a colour change occurs from light yellow to dark pink or even light blue, depending on the concentration of CPZ. Visual inspection enables the concentration of CPZ to be estimated. The resulting colouration was also monitored by digital image collection for a more accurate quantification. The three coordinates of the hue, saturation and lightness system were obtained by standard image processing along with mathematical data treatment. The parameters affecting colour were assessed and optimized. Studies were conducted by visible spectrophotometry and digital image acquisition, respectively. The response of the optimized probe towards the concentration of CPZ was tested for several mathematical transformations of the colour coordinates, and a linear relation was found for the sum of hue and luminosity. The limit of detection is 50???M (corresponding to about 16???g per mL). The probe enables quick screening for CPZ in real water samples with prior sample treatment.

Hydrogels formed by l-histidine derivatives with highly selective release for charged dyes

Hydrogels formed by UIPCA with CA could selectively release anionic dyes, chrome azurol S (A) and cationic dyes, methyl violet (B), showing excellent separating ability for differently charged dyes.     

Difluorobora-s-diazaindacene dyes as highly selective dosimetric reagents for fluoride anions

Difluorobora-s-diazaindacene derivatives are shown to report fluoride ions selectively in acetone solutions; both absorption and emission characteristics are drastically altered, and as a result, this hitherto unknown reaction transforms the BODIPY^® class of dyes into highly selective chromogenic and dual channel fluorogenic reagents for fluoride.     

Electrochemical analysis of natural solid organic dyes and pigments

Square-wave voltammetry of solid naphthoquinone, anthraquinone, and flavone dyes, carmine, cochineal red, indigo, and Prussian blue, was compared to microanalysis (sample consumption <1 mg) of traditional painting pigments and dyes without their preliminary dissolution. Electrochemical analysis was also performed after the samples' hydrolysis simultaneously with thin-layer chromatography. Anthraquinone-based pigments and Prussian blue are reversibly reduced, cochineal red and lac dyes are irreversibly reduced, flavones are mostly reversibly oxidized, dragon's blood is irreversibly oxidized and reduced, and indigo yields both reversible oxidation and reduction. The potential window of these reactions is about 1.4 V wide. This variability permits identification of the kind of pigment or dye, and directly distinguishes, for example, alizarin and purpurin; luteolin and quercetin; or indigo and Prussian blue.     

A novel solid phase for selective separation of flavonoid compounds

A novel straightforward approach to selective separation for flavonoid compounds was reported. The solid phase material was prepared by copolymerization using allyl-bromide-modified chitosan as macromonomer, and ethylene glycol dimethacrylate as cross-linker. The material was evaluated by chromatographic analysis; it exhibited high selectivity separation for quercetin and its structural analogues using different mobile phases. The material could directly trap a specific class of compounds including quercetin and kaempferol from the hydrolyzate of Ginkgo biloba extract. These results demonstrated the possibility of direct extraction of certain constituents from herb using this material.     

Evolutionary screening of biomimetic coatings for selective detection of explosives

Susceptibility of chemical sensors to false positive signals remains a common drawback due to insufficient sensor coating selectivity. By mimicking biology, we have demonstrated the use of sequence-specific biopolymers to generate highly selective receptors for trinitrotoluene and 2,4-dinitrotoluene. Using mutational analysis, we show that the identified binding peptides recognize the target substrate through multivalent binding with key side chain amino acid elements. Additionally, our peptide-based receptors embedded in a hydrogel show selective binding to target molecules in the gas phase. These experiments demonstrate the technique of receptor screening in liquid to be translated to selective gas-phase target binding, potentially impacting the design of a new class of sensor coatings.     

Highly selective adsorption of organic dyes onto tungsten trioxide nanowires

Research on Chemical Intermediates - The strong selective adsorption property of monoclinic tungsten trioxide nanowires (WO3NWs) towards organic dyes was reported in this paper. The effects of pH,...     

Molecularly imprinted solid phase extraction for rapid screening of metformin

A molecularly imprinted solid phase extraction (MISPE) method has been developed for the rapid screening of metformin. Newly synthesized molecularly imprinted polymer (MIP) particles were slurry-packed into a micro-column for selective solid phase extraction (SPE) of metformin. With CH₃CN flowing at 0.5 ml/min, a total binding capacity of 1600 ng metformin was determined for the 20 mg of MIP particles. A broad range of MISPE conditions was evaluated with respect to sample solvent, pH, and buffer compositions. A 95±2% binding could be achieved from one 20-μl injection of sample solution in acetonitrile plus phosphate buffer, up to 1200 ng of metformin. However, the micro-column interacted indiscriminately with phenformin, a structural analogue, to attain 49±2% binding. Separation of phenformin from metformin was ultimately achieved, using differential pulsed elution (DPE) with 1 M trifluoromethacrylic acid in acetonitrile. Final pulsed elution (FPE) using 3% trifluoroacetic acid in methanol was good for the quantitative elution of metformin. The MISPE–DPE–FPE method, with UV detection at 240 nm, afforded a detection limit of 0.8 μg/ml (or 16 ng) for metformin. Each MISPE–DPE–FPE analysis required less than 5 min to complete.     

Quadrupolar coupling selective cross-polarization in solid state NMR

A new strategy is presented for achieving selective heteronuclear polarization transfers from half-integer quadrupolar spins in magic-angle spinning (MAS) NMR. By combining cross-polarization with a recently introduced RAPT pulse sequence that selectively excites the signal of a half-integer quadrupolar nucleus based on its quadrupolar coupling constant magnitude, we demonstrate that hetero-nuclei in its close proximity may be selectively excited. Selective 23Na --> 1H polarization transfers are demonstrated in Na2MoO4 x 2 H2O, Na2HPO4 x 2 H2O and a mixture of NaHCO3 and Na2HPO4 x 2 H2O.