Uso da RMN como um sensor online em processos industriais

Nuclear magnetic resonance (NMR) is one of the most versatile analytical techniques for chemical, biochemical and medical applications. Despite this great success, NMR is seldom used as a tool in industrial applications. The first application of NMR in flowing samples was published in 1951. However, only in the last ten years Flow NMR has gained momentum and new and potential applications have been proposed. In this review we present the historical evolution of flow or online NMR spectroscopy and imaging, and current developments for use in the automation of industrial processes.

Influência do pH nas propriedades físico-químicas, térmicas e mecânicas de filmes de poli(vinil álcool)/poli(ácido acrílico)/aciclovir

Drug-loaded films represent an alternative method for the treatment of skin lesions caused by Herpes simplex, since they facilitate delivery of the drug directly at the site of lesion. The objective of this work was to prepare PVA/PAA films containing AC at pH 2.0 and 4.0. The results show that the pH of the film preparations influences the polymer¾drug interaction kinetic order and the degree of swelling. The mechanism of release of AC from the films obtained at pH 4.0 was anomalous, whereas for the films prepared at pH 2.0 the release followed zero-order kinetics.

Preparative separation of C19-diterpenoid alkaloids from Aconitum carmichaelii Debx by pH‑zone-refining counter-current chromatography

The technique of pH-zone-refining counter-current chromatography was successfully applied to preparatively separate three C19-diterpenoid alkaloids from the crude extracts of Aconitum carmichaelii for the first time using a two-phase solvent system of petroleum ether-ethyl acetate-methanol-water (5:5:1:9, v/v/v/v). Mesaconitine (I), hypaconitine (II), and deoxyaconitine (III) were obtained from 2.5 g of the crude alkaloids in a one-step separation; the yields were 4.16%, 16.96%, and 5.05%, respectively. The purities of compounds I, II, and III were 93.0%, 95%, and 96%, respectively, as determined by HPLC. The chemical structures of the three compounds were identified by electrospray ionization mass spectrometry (ESI-MS) and NMR.

Registrador portátil de odorantes basado en la modulación de temperatura de un sensor mos comercial

A simple, portable and low-cost system for odor detection was developed using a single MOS commercial sensor and a microcontroller. The temperature modulation technique was implemented applying a DC signal pulse to the sensor heater by a bipolar transistor. Two odorant profiles, ethanol and acetic acid vapors, were obtained and distinguished based on their amplitude versus time responses. Response for acetic acid was not reported by the sensor manufacturer. An ethanol vapor calibration curve was also obtained. Experimental data showed a potential behavior according to the theoretical equation of the MOS sensors. Values of logK=0.457 and α=-0.213 for a 95% confidence level were obtained.

Adsorção de alfa-lactalbumina do soro de leite em hidroxiapatita: efeito do pH e da temperatura e análise termodinâmica

The nutritional and functional benefits offered by whey protein α-lactalbumin justify the great interest in its manufacture in large quantities at a high purity level. Hydroxyapatite is a calcium phosphate material able to adsorb proteins and can be synthesized at low production cost. Therefore, this work evaluated the adsorption of α-lactalbumin on hydroxyapatite using solid-liquid phase equilibrium data reported as adsorption isotherms. Van't Hoff's thermodynamics analysis showed that the adsorption process is entropically driven.

Potentiometric determination of Nickel (II) ion using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electroactive material

A potentiometric Nickel sensor was prepared using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electro-active material and epoxy resin as a binding material. A membrane composed of 40% Schiff's base and 60% epoxy resin exhibited the best performance. The membrane showed excellent response in the concentration range of 0.15 ppm to 0.1 mol L- 1 Ni+2 ions with non-Nernstian slope of 22.0 mV/decade, had a rapid response time (less than 10 s), and can be used for three months without any considerable loss of potential. The sensor was useful within the pH range of 1.3 to 9.6, and was able to discriminate between Ni2+ and a large number of alkaline earth and transition metal ions. The practical utility of the sensor has been demonstrated by using it successfully as an indicator electrode in the potentiometric titration of Ni2+ with EDTA and oxalic acid.

Final chlorine dioxide stage at near-neutral pH for bleaching eucalypt pulp

It is well known that pH is an important parameter for controlling the eucalyptus pulp bleaching when using the final chlorine dioxide stage, since it affects the effectiveness of the process. Recommendations found in the literature for operating are in the 3.5 to 4.0 range. However, in this paper it was shown that final chlorine dioxide has better performance, with significant brightness gain while also preserving pulp quality, when it is operated at near neutral pH. This result can be explained by the generation of sodium bicarbonate in situ upon adding carbon dioxide at this stage.

O USO DE UM SENSOR DE LUZ LINEAR COMO RECURSO DIDÁTICO PARA DEMONSTRAR PRINCÍPIOS DE DIFRAÇÃO E ESPECTROSCOPIA

This article presents a discussion on light diffraction by slits and grids as well as the development of an experimental apparatus which provides quantitative observation of the phenomenon. We conducted a brief historical survey on the evolution of the wave theory of light and the role of diffraction in the context of optical spectroscopy. We also reviewed the use of Huygens’ principle to calculate the intensity pattern obtained when light is diffracted by slits and compared the predictions with experimental results obtained using the apparatus developed. Finally, the use of the apparatus in an optical spectroscopy experiment was demonstrated.

ASYMMETRIC SULFOXIDATION OF ALBENDAZOLE TO RICOBENDAZOLE BY FUNGI: EFFECT OF pH

Albendazole (ABZ) is an anthelmintic drug used for the treatment of infectious diseases in veterinary and human medicine. This drug is a prochiral drug that after administration, is rapidly oxidized in the pharmacologically active sulfoxide metabolite, which is also known as ricobendazole (ABZSOX). ABZSOX has a stereogenic center and possibly two enantiomers, (+)-ABZSOX and (-)-ABZSOX. In the present work, we investigate the pH effect on the asymmetric stereoselective sulfoxidation of ABZ into ABZSOX by employing the fungi Nigrospora sphaerica, Papulaspora immera Hotson, and Mucor rouxii. The results show a possibility of obtaining the pure enantiomers of the ricobendazole drug using fungi as biocatalytic agents. The three fungi showed a high degree of enantioselectivity expressed by enantiomeric excess. In addition, M. rouxii can be used as an alternative to obtain the (+)-ABZSOX enantiomer (ee 89.8%).

ELETRODOS DE FTO MODIFICADOS POR ELETRODEPOSIÇÃO DIRETA DE OURO: PRODUÇÃO, CARACTERIZAÇÃO E APLICAÇÃO COMO SENSOR ELETROQUÍMICO

Chemically modified electrodes have been studied to obtain new and better electrochemical sensors. Transparent conductive oxides, such as fluorine-doped tin-oxide (FTO), shows electrical conductivity comparable to metals and are potential candidates for new sensors. In this work, FTO was modified by gold electrodeposition from chlorine-auric acid solution using cyclic voltammetry (CV) technique. A set of different materials were produced, varying the scan number. Scanning electron microscopy and electrochemical impedance spectroscopy were performed for the characterization of electrodes surfaces. From this analysis was possible to observe the resistive, capacitive and difusional aspects from all kind of modified electrodes produced, establishing a relationship between this parameters and the scan number. The electrode with 100 scans of CV presented better characteristics for an electrochemical sensor; it has the lowest global impedance and rising of capacitive behavior (related to electrical double layer formation) at lower frequencies. This electrode was tested for paracetamol and caffeine detection. The results showed a high specificity, decreased oxidation potential (0.58 V and 0.97 Vvs. SCE, for paracetamol and caffeine, respectively) and low detection limits (0.82 and 0.052 µmol L-1).

Métodos de preservação e crescimento de Xanthomonas campestris pv. viticola em meio de cultura variando temperatura, pH e concentração de NaCl

A bactéria fitopatogênica Xanthomonas campestris pv. viticola (Xcv) causa o cancro bacteriano da videira (Vitis vinifera), que ocasiona grandes prejuízos à viticultura no Brasil. Os métodos de dessecação em papel de filtro (DPF), repicagens periódicas (RP), água destilada esterilizada (ADE) e folhas herborizadas (FH) foram utilizados para preservar duas estirpes de Xcv durante 12 meses. As variáveis viabilidade e patogenicidade foram avaliadas mensalmente e estimadas pela obtenção de crescimento bacteriano e área abaixo da curva de incidência da doença (AACID). Tanto o método de DPF como o de ADE propiciaram viabilidade constante de 100% durante 11 meses e os maiores valores de AACID. No método de RP não houve crescimento das estirpes já aos 30 dias, enquanto que, em FH, Xcv foi isolada até cinco meses. o crescimento das estirpes de Xcv em meio de cultura líquido variando temperatura (0, 5, 10, 15, 20, 25, 27, 28, 29, 30, 35, 40 e 45 °C), pH (5,0; 5,5; 6,0; 6,5; 7,0; 7,5; 8,0; 8,5 e 9,0) e concentração de NaCl (1, 2, 3, 4, 5, 6 e 7%) foi avaliado em fotocolorímetro. O crescimento de Xcv foi observado no intervalo de 5 até 35 °C, enquanto que o crescimento ótimo ocorreu de 27 a 29 °C. A Xcv não cresceu a zero e 40 °C. O pH ótimo para o crescimento desta bactéria foi 7,5. O crescimento de Xcv decresceu a partir de 3,0% de NaCl, com concentração letal de 6,0%.

Electrometric studies on uranyl molybdates as a function of pH

The formation and composition of uranyl molybdates obtained by the interaction of uranyl acetate and sodium molybdate at specific pH levels 7.6, 5.5 and 4.1 have been studied by employing electrometric techniques involving pH and conductometric titrations. The results provide cogent evidence for the formation of three uranyl molybdates having the molecular formulae UO2O.MoO3, 3UO2O.7MoO3 and 2UO2O.8MoO3 in the vicinity of pH 5.7, 4.6 and 3.8, respectively. Analytical investigations of the compounds have also been carried out which substantiate the results of electrometric study.

Electrometric investigations on the formation of cerium(III) tungstates as a function of PH

The course of reaction between cerium(III) nitrate and different sodium tungstates (Na2WO4, Na10W12O41 and Na6W12O39) has been followed by means of pH and conductometric titrations between the reactants at different pH levels, in aqueous and alcoholic media, with each of the reagents alternatively used as titrant. The electrometric experiments provide definite evidence of the formation of normal-Ce2O3.3WO3 and para- 5Ce2O3.36WO3 tungstates of cerium in the vicinity of pH 6.2 and 5.3. The formation of normal tungstate is almost quantitative and the pH titrations offer a simple means for determination of cerium(III) or tungstate solutions at suitable concentrations and pH range.

Influência do pH na estabilidade dos coacervatos de prata como precursores vítreos

Neste trabalho, usando o processo de coacervação, foi estudado o sistema NaPO3/AgNO3/H2O. Determinou-se o domínio de coacervação a partir de diferentes concentrações de NaPO3 e AgNO3 e a influência do pH na estabilização do coacervato foi determinada. Os coacervatos obtidos em pH ~ 5 apresentam maior região de estabilidade.