64 research outputs found
Study of the electrochemical reduction of amoebicide Teclozan and its amperometric determination in pharmaceutical formulations
Neste trabalho, a redução eletroquĂmica do amebicida Teclozan (TEC) foi estudada sobre um eletrodo de carbono vĂtreo em meio de acetonitrila. EletrĂłlises com potencial controlado foram realizadas visando, tanto a determinação do nĂșmero de elĂ©trons envolvidos na redução do fĂĄrmaco, quanto a identificação dos produtos eletrogerados, os quais foram isolados por extração lĂquido-lĂquido e caracterizados por 1H RMN. Foi verificado que o TEC apresenta dois picos voltamĂ©tricos, cada um associado Ă quebra redutiva de duas ligaçÔes C-Cl. Em presença de um doador de prĂłtons, foi observado que o primeiro pico voltamĂ©trico em â1,8 V corresponde principalmente Ă redução dos grupamentos -CHCl2 a -CH2Cl; enquanto o segundo pico em â2,2 V Ă© responsĂĄvel pela redução dos grupos -CH2Cl a CH3, fornecendo como Ășnico produto o derivado totalmente desalogenado do TEC, com rendimentos entre 82 e 97%. Este trabalho descreve tambĂ©m o desenvolvimento de um mĂ©todo eletroanalĂtico baseado na detecção amperomĂ©trica do TEC em condiçÔes hidrodinĂąmicas, o qual forneceu um limite de detecção de 8,9 Ă 10-6 mol L-1.The electrochemical reduction of amoebicide Teclozan (TEC) was studied on a glassy carbon electrode in acetonitrile. Controlled-potential electrolyses were performed for coulometric and preparative purposes. The electrogenerated products were isolated by liquid-liquid extraction and characterized by 1H NMR. It was observed that TEC presents two voltammetric peaks, each one associated with the cleavage of two C-Cl bonds. In presence of a proton donor it was observed that the first peak at â1.8 V promotes mainly the reduction of the groups CHCl2 to CH2Cl and the second one at â2.2 V promotes the reduction of the groups CH2Cl to CH3 giving as the sole product the completely dechlorinated TEC derivative with yields between 82 and 97%. In addition, a comparative study between the analytical performance of voltammetric techniques and amperometric detection of TEC in hydrodynamic conditions was performed. The amperometric detection was more sensitive than all evaluated voltammetric techniques, providing a detection limit of 8.9 Ă 10-6 mol L-1.FAPESP; CAPES; FC
Electrochemical reduction and voltammetric determination of diloxanide furoate in non-aqueous medium
Determinação VoltamĂ©trica de Nitrito Empregando o Ăon [Fe(CN)6]3- como Mediador EletroquĂmico
In this work, a voltammetric method for determination of nitrite in tap and mineral waters samples was developed. The method is based on the reduction of nitrite catalyzed by the electrochemical mediator [Fe(CN)6]3-. A carbon paste electrode (CPE) prepared with solid paraffin as binder agent was used as working electrode and cyclic voltammetry was the voltammetric technique employed for nitrite quantification. All parameters of the analytical method were optimized and the best conditions obtained were: BR buffer 0.04 mol L-1 pH = 1.0 as supporting electrolyte and 0.7 mmol L-1 of Fe(CN)6] 3- in the electrochemical cell. Under these optimized conditions, the method presented a linear range from 0.05 to 2.5 mmol L-1 of nitrite, with limits of detection and quantification equal to 22 and 75 Όmol L-1, respectively. Spiked samples of mineral and tap water were analyzed by the proposed method and recovery percentages close to 100 % were obtained for all analyzed samples. Moreover, the method has presented a satisfactory precision since low values of relative standard deviation (RSD) were always obtained. These results indicate that the method allow the reliable determination of nitrite in water samples in a simple and inexpensive way.
DOI:Â http://dx.doi.org/10.17807/orbital.v7i1.67
Value of MRI and diffusion-weighted MRI for the diagnosis of locally recurrent rectal cancer
OBJECTIVES: To evaluate the accuracy of standard MRI, diffusion-weighted MRI (DWI) and fusion images for the diagnosis of locally recurrent rectal cancer in patients with a clinical suspicion of recurrence. METHODS: Forty-two patients with a clinical suspicion of recurrence underwent 1.5-T MRI consisting of standard T2-weighted FSE (3 planes) and an axial DWI (b0,500,1000). Two readers (R1,R2) independently scored the likelihood of recurrence; [1] on standard MRI, [2] on standard MRI+DWI, and [3] on T2-weighted+DWI fusion images. RESULTS: 19/42 patients had a local recurrence. R1 achieved an area under the ROC-curve (AUC) of 0.99, sensitivity 100% and specificity 83% on standard MRI versus 0.98, 100% and 91% after addition of DWI (p = 0.78). For R2 these figures were 0.87, 84% and 74% on standard MRI and 0.91, 89% and 83% with DWI (p = 0.09). Fusion images did not significantly improve the performance. Interobserver agreement was kappa0.69 for standard MRI, kappa0.82 for standard MRI+DWI and kappa0.84 for the fusion images. CONCLUSIONS: MRI is accurate for the diagnosis of locally recurrent rectal cancer in patients with a clinical suspicion of recurrence. Addition of DWI does not significantly improve its performance. However, with DWI specificity and interobserver agreement increase. Fusion images do not improve accuracy
Molecular Structure of Amyloid Fibrils Controls the Relationship between Fibrillar Size and Toxicity
According to the prevailing view, soluble oligomers or small fibrillar fragments are considered to be the most toxic species in prion diseases. To test this hypothesis, two conformationally different amyloid states were produced from the same highly pure recombinant full-length prion protein (rPrP). The cytotoxic potential of intact fibrils and fibrillar fragments generated by sonication from these two states was tested using cultured cells.For one amyloid state, fibril fragmentation was found to enhance its cytotoxic potential, whereas for another amyloid state formed within the same amino acid sequence, the fragmented fibrils were found to be substantially less toxic than the intact fibrils. Consistent with the previous studies, the toxic effects were more pronounced for cell cultures expressing normal isoform of the prion protein (PrP(C)) at high levels confirming that cytotoxicity was in part PrP(C)-dependent. Silencing of PrP(C) expression by small hairpin RNAs designed to silence expression of human PrP(C) (shRNA-PrP(C)) diminished the deleterious effects of the two amyloid states to a different extent, suggesting that the role of PrP(C)-mediated and PrP(C)-independent mechanisms depends on the structure of the aggregates.This work provides a direct illustration that the relationship between an amyloid's physical dimension and its toxic potential is not unidirectional but is controlled by the molecular structure of prion protein (PrP) molecules within aggregated states. Depending on the structure, a decrease in size of amyloid fibrils can either enhance or abolish their cytotoxic effect. Regardless of the molecular structure or size of PrP aggregates, silencing of PrP(C) expression can be exploited to reduce their deleterious effects
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