Spectroelectrochemical Behavior of Polycrystalline Gold Electrode Modified by Reverse Micelles

The increasing demand for raising the reliability of electronic contacts has led to the development of methods that protect metal surfaces against atmospheric corrosion agents. This severe problem implies an important economic cost annually but small amounts of corrosion inhibitors can control, decrease or avoid reactions between a metal and its environment. In this regard, surfactant inhibitors have displayed many advantages such as low price, easy fabrication, low toxicity and high inhibition efficiency. For this reason, in this article, the spectroelectrochemical behavior of polycrystalline gold electrode modified by reverse micelles (water/polyethyleneglycol-dodecylether (BRIJ 30)/n-heptane) is investigated by atomic force microscopy (AFM), potentiodynamic methods and electrochemical impedance spectroscopy (EIS). Main results indicate a strong adsorption of a monolayer of micelles on the gold substrate in which electron tunneling conduction is still possible. Therefore, this method of increasing the corrosion resistance of gold contacts is usable only in conditions of long-term storage but not in the operation of devices with such contacts. In this regard, the micelle coating must be removed from the surface of the gold contacts before use. Finally, the aim of the present work is to understand the reactions occurring at the surfactant/metal interface, which may help to improve the fabrication of novel electrodes.     

Monitoring of the non-steroid anti-inflammatory drug indomethacin: development of immunochemical methods for its purification and detection

The present research focused on the development of an immunoassay and an immunochemical sol–gel-based immunoaffinity purification (IAP) method for purification and detection of the non-steroid anti-inflammatory drug (NSAID) indomethacin (IMT). A polyclonal antibody (Ab) for IMT was generated, and two sensitive microplate assays for the detection of IMT were developed (termed OV and HRP formats), based on the enzyme-linked immunosorbent assay (ELISA) method. The limits of detection of the assays were 15 ± 1.25 ng mL⁻¹ (n = 50) and 12 ± 0.17 ng mL⁻¹ (n = 4) for the OVA and HRP formats, respectively. The Abs exhibited slight cross-reactivity with other NSAIDs. The Abs were also used to develop a sol–gel-based IAP method for clean-up and concentration of IMT. Several sol–gel formats with various amounts of antibodies were examined; the best and most reproducible format was at a TMOS:HCl molar ratio of 1:6 in which 120 μL of IMT Abs was entrapped. The binding capacity under these conditions was ca. 100 to 250 ng of IMT with very low non-specific binding (less than 5% of the applied amount). The sol–gel IAP method, combined with solid-phase extraction, successfully eliminated serum interference to a degree that enabled analysis of spiked serum samples by ELISA. The method was also found to be fully compatible with subsequent chemical analytical methods, such as liquid chromatography followed by mass spectrometry. The approaches developed in this study form a basis for analysis of IMT in biological samples in order to monitor their pharmacokinetic properties, and may be further used to study population exposure to IMT, and to monitor the occurrence of IMT contamination in water samples.     

Nanoscale inhomogeneities in thermoresponsive triblock copolymers

We present continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy data of the spin probe 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in aqueous solutions of poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers (Pluronic or Poloxamer). TEMPO is notably smaller than the spin probes conventionally used in the context of polymer science and reveals the early emergence of small hydrophobic cavities when PPO strands of several molecules aggregate and collapse upon temperature increase. The occurrence of hydrophobic cavities appears independent of the overall molecular weight of the Pluronics, but clearly depends on the relative PPO/PEO contents. In all the cases studied, the volume fraction of hydrophobic cavities increases in a broad temperature range of ≥40 °C. The appearance of the hydrophobic regions does not seem to be directly correlated to micellization of the polymers. A decrease of the relative PPO amount in the polymers not only hinders collapse of the PPO strands, it can also be described as a site exchange of the spin probes between hydrophobic cavities and the surrounding medium. On the other hand, in cases of high PPO contents, spin probe exchange could not be observed. This suggests that one may potentially control the diffusion of small molecules between the micellar cores and the surrounding medium by adjusting the PEO/PPO ratio of the used Pluronics.     

Characteristics of the electroosmotic flow of electrolyte systems for nonaqueous capillary electrophoresis

Nonaqueous capillary electrophoresis (NACE) is a powerful tool for the analysis of surface-active substances, which represent a broad class of analytes containing cationic and anionic species, such as surfactants, phosphoric acid esters, and amines. In order to conduct an efficient method development in NACE, the influence of the electrolyte composition on the electroosmotic flow (EOF) of organic separation systems was systematically investigated. Background electrolytes and background chromophores appropriate for direct and indirect UV-detection were considered, as the majority of surface-active substances do not absorb UV-light. It was found that theoretical models developed to describe the EOF in aqueous electrolyte systems are insufficient for organic electrolyte systems. Experimental data on electroosmosis in a variety of organic solvents and mixtures of methanol and acetonitrile applying different background chromophores and basic or acidic additives are given. Differences between them are discussed with relation to the physicochemical properties of the organic solvents.     

Spectral graph features for the classification of graphs and graph sequences

In this paper, the classification power of the eigenvalues of six graph-associated matrices is investigated. Each matrix contains a certain type of geometric/ spatial information, which may be important for the classification process. The performances of the different feature types is evaluated on two data sets: first a benchmark data set for optical character recognition, where the extracted eigenvalues were utilized as feature vectors for multi-class classification using support vector machines. Classification results are presented for all six feature types, as well as for classifier combinations at decision level. For the decision level combination, probabilistic output support vector machines have been applied, with a performance up to 92.4 %. To investigate the power of the spectra for time dependent tasks, too, a second data set was investigated, consisting of human activities in video streams. To model the time dependency, hidden Markov models were utilized and the classification rate reached 98.3 %.     

Determination of T-2 toxin in cereal grains by liquid chromatography with fluorescence detection after immunoaffinity column clean-up and derivatization with 1-anthroylnitrile

1-Anthroylnitrile (1-AN) has been shown to be an efficient labelling reagent for the determination of T-2 toxin (T-2) by high-performance liquid chromatography (HPLC)-fluorescence detection. This reaction has been used to develop a sensitive, reproducible and accurate method for the determination of T-2 in wheat, corn, barley, oats, rice and sorghum. The method uses immunoaffinity columns containing antibodies specific for T-2 for extract clean-up, pre-column derivatization with 1-AN and HPLC with fluorescence detection for toxin determination. Ground cereal samples were extracted with methanol-water (80:20, v/v), the extracts were purified by immunoaffinity columns and the toxin was quantified by reversed-phase HPLC with fluorometric detection (excitation wavelength 381 nm, emission wavelength 470 nm) after derivatization with 1-AN. Recoveries from the different cereals spiked with T-2 at levels ranging from 0.05 to 1.5 microg/g were from 80 to 99%, with relative standard deviations of less than 6%. The limit of detection was 0.005 microg/g, based on a signal-to-noise ratio of 3:1.     

Near-infrared photosensitizer based on a cycloimide derivative of chlorin p6: 13,15-N-(3'-hydroxypropyl)cycloimide chlorin p6

The 13,15-N-(3'-hydroxypropylcycloimide) chlorin p6 (CIC), which absorbs at 711 nm, possesses considerable photoinduced cell-killing activity. It is 43-, 61- and 110-fold more active than chlorin p6, 3-formyl-3-devinyl chlorin p6 and Photogem, respectively, and has no cytotoxicity without irradiation as estimated on A549 human adenocarcinoma cells. To attain the highest intracellular penetration and activity the monomeric form of CIC should be stabilized. This stabilization in an aqueous environment can be achieved using 0.002-0.005% of Cremophor EL emulsion (polyoxyethylene derivative of hydrogenated castor oil). The intracellular accumulation of CIC occurs in cytoplasm in a monomeric form bound to cellular membranes. This form of the dye is characterized by a high quantum yield of singlet oxygen generation (0.66 +/- 0.02). Besides diffuse staining of intracellular membranous structures, CIC accumulates 3- to 4-fold more intensely in mitochondria and Golgi apparatus, thus indicating these organelles to be the initial targets of its photodynamic action. The incubation time providing 50% accumulation level of CIC in cells is 30 +/- 5 min. The time for 50% release of CIC from the cells is 60 +/- 10 min. A 10-fold decrease in CIC intracellular penetration at 22 degrees C proves that temperature-sensitive mechanisms of transport, rather than diffusion, are responsible for the dye uptake. The average cytoplasmic concentration of CIC was seven times the extracellular concentration in the 0.2-1.6 microM range, used for the photodynamic activity measurements. The concentration of CIC and the light dose that correspond to ca 50% level of phototoxicity induce predominantly an apoptotic-type of cell death, whereas the conditions providing 100% level of phototoxicity induced necrosis. The results obtained indicate that cycloimide derivatives of chlorin p6 may serve as a base for the development of an efficient near-IR photosensitizer.     

Preparation of Dry Extract of<em> Mikania glomerata</em> Sprengel (Guaco) and Determination of Its Coumarin Levels by Spectrophotometry and HPLC-UV

Guaco (Mikania glomerata Sprengel) syrup is one of the most popular herbal medicines used to treat the symptoms of asthmatic bronchitis, cough and hoarseness. The coumarin 2H-1-benzopyran-2-one, is one of the major constituents of Guaco and contributes to its pharmacological effects. The pharmaceutical capsule form of dry extract of Guaco is recommended by the Brazilian Program of Medicinal Plants and Herbal Medicines and used in primary health care. In order to identify a new protocol to obtain the raw material for Guaco capsule production we evaluated two methods, including a freeze-drying process (lyophilization) and the spray-dryer technique, as well as the use of two adjuvants, Maltodextrins and Aerosil^?, in different concentrations. The coumarin levels of the dried extracts were analyzed by UV-spectrophotometry and HPLC-UV/DAD. The adjuvant Aerosil^? 8% showed better dry powder physical appearance. Lyophilization was observed to be the best process to obtain the dry extract of Guaco based on the measured coumarin levels.     

Bisphosphonate metal complexes as selective inhibitors of Trypanosoma cruzi farnesyl diphosphate synthase

In the search for a pharmacological answer to treat Chagas disease, eight metal complexes with two bioactive bisphosphonates, alendronate (Ale) and pamidronate (Pam), were described. Complexes of the formula [M(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O, with M = Cu, Co, Mn, Ni, and ([CuPam]·H(2)O)(n) as well as [M(II)(Pam)(2)(H(2)O)(2)]·3H(2)O, with M = Co, Mn and Ni, were synthesized and fully characterized. Crystal structure of [Cu(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O, [Co(II)(Pam)(2)(H(2)O)(2)] and [Ni(II)(Pam)(2)(H(2)O)(2)] were solved by X-ray single crystal diffraction methods and the structures of [M(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O complexes M = Co, Mn and Ni were studied by X-ray powder diffraction methods. All obtained complexes were active against the amastigote form of Trypanosoma cruzi (T. cruzi), etiological agent of Chagas disease. Most of them were more active than the corresponding free ligands showing no toxicity for mammalian cells. The main mechanism of the antiparasitic action of bisphosphonates, inhibition of parasitic farnesyl diphosphate synthase (TcFPPS), remains in the obtained metal complexes and an increase in the inhibiting enzyme levels was observed upon coordination. Observed enzymatic inhibition was selective for TcFPPS as the metal complexes showed no or little inhibition of human FPPS. Additionally, metal complexation might improve the bioavailability of the complexes through the hindrance of the phosphonate group's ionization at physiological pH and, eventually, through the ability of plasma proteins to work as complex transporters.     

Accurate whole-spectrum measurements of intracellular pH and [Na+]

Fluorescent measurements of intracellular H⁺ and Na⁺ are improved by using whole spectra of the fluorescent indicators BCECF and SBFI, respectively. The extra data in whole spectra enable both an accurate calibration and a ready detection of artifacts which are not possible to identify using a more conventional data analysis that relies upon only two wavelength windows in the fluorescence spectra. The whole-spectrum technique is applicable to cell suspensions in a conventional fluorimeter (as is reported here with SBFI), as well as to attached cells using a fluorimeter combined with an inverted epifluorescence microscope. The spectral method was highly reproducible in that pairs of successive pH measurements differed, on average, by only 0.01±0.02 U. Random uncertainty from sample to sample was estimated numerically from the standard deviation of measurements on ionophore-treated cells. When full-spectrum analysis was employed, this scatter showed a two-fold improvement over results obtained using the two-wavelength ratio method. Because SBFI has a relatively narrow dynamic range, whole-spectrum analysis has been applied to improve the accuracy of sodium determinations. The calibrated system measured [Na⁺]_i with excellent linearity over the range 2–150 mM and with an accuracy of approximately 5 mM.