Synthesis of Janus compounds for the recognition of G-U mismatched nucleobase pairs

The design and synthesis of two Janus-type heterocycles with the capacity to simultaneously recognize guanine and uracyl in G-U mismatched pairs through complementary hydrogen bond pairing is described. Both compounds were conveniently functionalized with a carboxylic function and efficiently attached to a tripeptide sequence by using solid-phase methodologies. Ligands based on the derivatization of such Janus compounds with a small aminoglycoside, neamine, and its guanidinylated analogue have been synthesized, and their interaction with Tau RNA has been investigated by using several biophysical techniques, including UV-monitored melting curves, fluorescence titration experiments, and 1H NMR. The overall results indicated that Janus-neamine/guanidinoneamine showed some preference for the +3 mutated RNA sequence associated with the development of some tauopathies, although preliminary NMR studies have not confirmed binding to G-U pairs. Moreover, a good correlation has been found between the RNA binding affinity of such Janus-containing ligands and their ability to stabilize this secondary structure upon complexation.

Rapid analysis of multiclass antibiotic residues and some of their metabolites in hospital, urban wastewater and river water by ultra-highperformance liquid chromatography coupled to quadrupole-linear ion trap tandem mass spectrometry

The present work describes the development of a fast and robust analytical method for the determination of 53 antibiotic residues, covering various chemical groups and some of their metabolites, in environmental matrices that are considered important sources of antibiotic pollution, namely hospital and urban wastewaters, as well as in river waters. The method is based on automated off-line solid phase extraction (SPE) followed by ultra-high-performance liquid chromatography coupled to quadrupole linear ion trap tandem mass spectrometry (UHPLC–QqLIT). For unequivocal identification and confirmation, and in order to fulfill EU guidelines, two selected reaction monitoring (SRM) transitions per compound are monitored (the most intense one is used for quantification and the second one for confirmation). Quantification of target antibiotics is performed by the internal standard approach, using one isotopically labeled compound for each chemical group, in order to correct matrix effects. The main advantages of the method are automation and speed-up of sample preparation, by the reduction of extraction volumes for all matrices, the fast separation of a wide spectrum of antibiotics by using ultra-high-performance liquid chromatography, its sensitivity (limits of detection in the low ng/L range) and selectivity (due to the use of tandem mass spectrometry) The inclusion of β-lactam antibiotics (penicillins and cephalosporins), which are compounds difficult to analyze in multi-residue methods due to their instability in water matrices, and some antibiotics metabolites are other important benefits of the method developed. As part of the validation procedure, the method developed was applied to the analysis of antibiotics residues in hospital, urban influent and effluent wastewaters as well as in river water samples

X-ray fluorescence determination of adsorbed copper on activated charcoal after glycerin complexation

X-This work shows an alternative method to copper determination by X-Ray Fluorescence (XRF). Since copper concentration in natural waters is not enough to reach XRF detection limit, a liquid-solid preconcentration procedure was proposed. Glycerin was used to complex the metal increasing its adsorption on activated charcoal. The solid phase was used to XRF determination. Several parameters were evaluated, such as, the complexation pH, the charcoal adsorption limit and the glycerin concentration. The interferences are lead and bismuth and the sensitivities decreased in the order Cu2+, Bi3+ and Pb2+. The advantages of the method are its simplicity, low cost and low spectral interference.

Determinação de pesticidas organofosforados em água usando microextração em fase sólida e CGAR-EM

Solid-phase microextraction (SPME) has been applied to direct extraction of 11 organophosphorus pesticides in water using a 100 mm fiber polydimethylsiloxane. The method was evaluated with respect time of exposure, detection limits (LODs), linearity and precision. The detection limits (S/N = 3) depend of each pesticide and varie about ng/L levels. The linearity was satisfactory with coefficients of correlation usually greater than 0.993. The precision of the method was determined by extraction from 4.0 mg/L aqueous standard with coefficients of variation between 5.7 to 17.2%.

Comparison of three analytical methods for the determination of quinolones in pig muscle samples

This work presents a comparison between three analytical methods developed for the simultaneous determination of eight quinolones regulated by the European Union (marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin, difloxacin, sarafloxacin, oxolinic acid and flumequine) in pig muscle, using liquid chromatography with fluorescence detection (LC-FD), liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The procedures involve an extraction of the quinolones from the tissues, a step for clean-up and preconcentration of the analytes by solid-phase extraction and a subsequent liquid chromatographic analysis. The limits of detection of the methods ranged from 0.1 to 2.1 ng g−1 using LC-FD, from 0.3 to 1.8 using LC-MS and from 0.2 to 0.3 using LC-MS/MS, while inter- and intra-day variability was under 15 % in all cases. Most of those data are notably lower than the maximum residue limits established by the European Union for quinolones in pig tissues. The methods have been applied for the determination of quinolones in six different commercial pig muscle samples purchased in different supermarkets located in the city of Granada (south-east Spain).

Convergent Approaches for the Synthesis of the Anti-tumoral Peptide, Kahalalide F. Study of Orthogonal Protecting Groups

Kahalalide compounds are peptides that are isolated from a Hawaiian herbivorous marine species of mollusc, Elysia rufescens, and its diet, the green alga Bryopsis sp. Kahalalide F and its synthetic analogues are the most promising compounds of the Kahalalide family because they show anti-tumoral activity. Linear solid-phase syntheses of Kahalalide F have been reported. Here we describe several new improved synthetic routes based on convergent approaches with distinct orthogonal protection schemes for the preparation of Kahaladide analogues. These strategies allow a better control and characterization of the intermediates because more reactions are performed in solution. Five derivatives of Kahalalide F were synthesized using several convergent approaches.

Construção de uma cela de fluxo para medidas por espectrofotometria em fase sólida

A simple and low cost flow cell is proposed for measurements by solid-phase spectrophotometry employing a conventional spectrophotometer. The flow cell geometry allows the employment of a large amount of the solid support without causing both excessive attenuation of the radiation beam and increasing of the back-pressure. The adaptation of the flow cell in the optical path of the spectrophotometer in order to increase the precision is discussed. The flow cell characteristics were demonstrated by measurements of Co(II), employing 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C18 bonded silica as solid support. The apparent molar absorptivity and coefficient of variation were estimated as 1.86 x 10(5) L mol-1 cm-1 and 1.4 % (n=15). A sample throughput of 40 determinations per hour and a detection limit of 15 mug L-1 (99.7 % confidence level) were achieved.

Determinação espectrofotométrica de aspartame em adoçantes por injeção em fluxo usando um reator em fase sólida contendo fosfato de zinco imobilizado

A flow injection spectrophotometric method was developed for determining aspartame in sweeteners. Sample was dissolved in water and 250 µL of the solution was injected into a carrier stream of 5.0 x 10-5 mol L-1 sodium borate solution. The sample flowed through a column (14 cm x 2.0 mm) packed with Zn3(PO4)2 immobilized in a polymeric matrix of polyester resin and Zn(II) ions were released from the solid-phase reactor by formation of the Zn(II)-aspartame complex. The mixture merged with a stream of borate buffer solution (pH 9.0) containing 0.030 % (m/v) alizarin red S and the Zn(II)-alizarin red complex formed was measured spectrophotometrically at 540 nm. The calibration graph for aspartame was linear in the concentration range from 10 to 80 µg mL-1 with a detection limit of 4 µg mL-1 of aspartame. The RSD was 0.3 % for a solution containing 40 µg mL-1 aspartame (n = 10) and seventy results were obtained per hour. The proposed method was applied for determining aspartame in commercial sweeteners.

Microextração por fase sólida

Fundamental aspects of Solid Phase Micro-Extraction (SPME) are discussed in the present paper. The application of SPME as a microtechnique of sample preparation for gas chromatographic analysis is considered and related to existing theoretical models. Both research prototypes and commercial SPME devices are considered.

Morfologia e cristalinidade de hidroxicarbonato de zinco obtido via precipitação homogênea: influência dos ânions cloreto e nitrato

The effects of chloride and nitrate anions and their respective concentrations, as well as urea presence, on solid phase morphologies were investigated. Zinc hydroxide carbonate was prepared by aging diluted zinc salt solution in presence of urea at 90ºC. Samples were identified by X-ray powder diffractograms showing the characteristic patterns of hydrozincite. The crystallinity was correlated with the concentrations of reagents. Spherulitic-type aggregates and single acicular particles were obtained from diluted chloride and nitrate solutions while porous aggregates of uniform size were formed from solutions with high chloride and urea concentrations.

Métodos de extração e/ou concentração de compostos encontrados em fluidos biológicos para posterior determinação cromatográfica

When organic compounds present in biological fluids are analysed by chromatographic methods, it is generally necessary to carry out a prior sample preparation due the high complexity of this type of sample, especially when the compounds to be determinated are found in very low concentrations. This article describes some of the principal methods for sample preparation in analyses of substances present in biological fluids. The methods include liquid-liquid extraction, solid phase extraction, supercritical fluid extraction and extraction using solid and liquid membranes. The advantages and disadvantages of these methods are discussed.

Nanoparticle Labels in Bioaffinity Assays

Nanoparticles offer adjustable and expandable reactive surface area compared to the more traditional solid phase forms utilized in bioaffinity assays due to the high surface to-volume ratio. The versatility of nanoparticles is further improved by the ability to incorporate various molecular complexes such as luminophores into the core. Nanoparticle labels composed of polystyrene, silica, inorganic crystals doped with high number of luminophores, preferably lanthanide(III) complexes, are employed in bioaffinity assays. Other label species such as semiconductor crystals (quantum dots) or colloidal gold clusters are also utilized. The surface derivatization of such particles with biomolecules is crucial for the applicability to bioaffinity assays. The effectiveness of a coating is reliant on the biomolecule and particle surface characteristics and the selected coupling technique. The most critical aspects of the particle labels in bioaffinity assays are their size-dependent features. For polystyrene, silica and inorganic phosphor particles, these include the kinetics, specific activity and colloidal stability. For quantum dots and gold colloids, the spectral properties are also dependent on particle size. This study reports the utilization of europium(III)-chelate-embedded nanoparticle labels in the development of bioaffinity assays. The experimental covers both the heterogeneous and homogeneous assay formats elucidating the wide applicability of the nanoparticles. It was revealed that the employment of europium(III) nanoparticles in heterogeneous assays for viral antigens, adenovirus hexon and hepatitis B surface antigen (HBsAg), resulted in sensitivity improvement of 10-1000 fold compared to the reference methods. This improvement was attributed to the extreme specific activity and enhanced monovalent affinity of the nanoparticles conjugates. The applicability of europium(III)-chelate-doped nanoparticles to homogeneous assay formats were proved in two completely different experimental settings; assays based on immunological recognition or proteolytic activity. It was shown that in addition to small molecule acceptors, particulate acceptors may also be employed due to the high specific activity of the particles promoting proximity-induced reabsorptive energy transfer in addition to non-radiative energy transfer. The principle of proteolytic activity assay relied on a novel dual-step FRET concept, wherein the streptavidin-derivatized europium(III)-chelate-doped nanoparticles were used as donors for peptide substrates modified with biotin and terminal europium emission compliant primary acceptor and a secondary quencher acceptor. The recorded sensitized emission was proportional to the enzyme activity, and the assay response to various inhibitor doses was in agreement with those found in literature showing the feasibility of the technique. Experiments regarding the impact of donor particle size on the extent of direct donor fluorescence and reabsorptive excitation interference in a FRET-based application was conducted with differently sized europium(III)-chelate-doped nanoparticles. It was shown that the size effect was minimal

Extração em fase sólida (SPE) e micro extração em fase sólida (SPME) de piretróides em água

The pyrethroids bifenthrin, permethrin, cypermethrin and deltamethrin were extracted by solid phase extraction (SPE) and solid phase microextraction (SPME). The analysis were performed on a gas chromatograph with electron capture detection (GC-ECD). Octadecil Silano-C18, Florisil and Silica stationary phases were studied for SPE. Better results were obtained for Florisil which gave recoveries from 80% to 108%. Pyrethroids extraction by SPME showed a linear response and a detection limit of 10 pg ml-1. Although the data showed that the two extraction methods were able to isolate the pesticide residues from water samples, the best results were obtained by using SPME which is more sensitive, faster, cheeper, being a more useful technique for the analysis of pyrethroids in drinking water.

Estudo de compostos orgânicos em lixiviado de aterros sanitários por EFS e CG/EM

The main purpose of this work was the qualitative study of organic compounds in landfill leachate. The samples were collected from a sanitary landfill located at Gravataí, a southern Brazilian city, that receive both, industrial and domestic refuse. The samples were submitted to solid phase extraction (SPE) with XAD-4 resin as the stationary phase. The instrumental analysis was performed by Gas Chromatography with a Mass Spectrometry Detector (GC/MSD). The compounds achieved in the SPE extracts were tentatively identified by the GC/MS library. It was found several oxygen and nitrogen compounds like carboxylic acids, ketones, amines and amides. Sulfur compounds and phthalate esters are also identified.

Desenvolvimento de um método de MEFS com CG-DIC para determinação de 1,4 dioxana em amostras de cosméticos

A headspace solid-phase microextraction (HS-SPME) for the determination of 1,4 dioxane in cosmetics by gas chromatography is described. A manual SPME holder with 85 µm polyacrylate coating is utilized. The method is determined to have good resolution, satisfactory linerity (correlation coefficient r=0.997 for 0.20-10.00 mg Kg-1 range), a relative standard deviation of 6.3% and a detection limit of 5.00 µg Kg-1. Some cosmectic products were analyzed.