Magister Scientiae - MSc / In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species. / South Africa

Magister Scientiae - MSc / In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE). / South Africa

Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-06-26T00:47:56Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) eliziana_santana_gomes.pdf: 3970415 bytes, checksum: 2481c11516ababe53f6e97ce77e43efc (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-07-18T12:49:10Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) eliziana_santana_gomes.pdf: 3970415 bytes, checksum: 2481c11516ababe53f6e97ce77e43efc (MD5) / Made available in DSpace on 2018-07-18T12:49:10Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) eliziana_santana_gomes.pdf: 3970415 bytes, checksum: 2481c11516ababe53f6e97ce77e43efc (MD5) Previous issue date: 2017 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / O estriol (C18H24O3, denominado E3) ? o principal esteroide estrog?nico produzido na gravidez. O uso do estriol ? comum para o tratamento da menopausa como alternativa ao 17?- estradiol, estrona ou a uma combina??o destes dois f?rmacos. O principal objetivo deste trabalho foi estudar o perfil voltam?trico do estriol utilizando a voltametria c?clica e desenvolver uma metodologia para a sua determina??o em comprimidos e urina utilizando a voltametria de pulso diferencial (DPV) e o eletrodo de carbono v?treo modificado com um filme de polimetionina e cobalto. Os resultados mostraram que em solu??o de tamp?o fosfato a 0,1 mol L-1 (pH 7,0) o E3 oxidou irreversivelmente no potencial de +0,58V, apresentando uma boa defini??o do pico. A curva anal?tica para o E3 foi linear no intervalo de concentra??o de 0,60 ?mol L-1 ? 4,76 ?mol L-1 (R2 = 0,996) e 5,66 ?mol L-1 ? 9,90 ?mol L-1 (R2 = 0,994), com limites de detec??o e de quantifica??o iguais a 3,40x10-8 mol L-1 e 1,13 x 10-7 mol L-1, respectivamente. A precis?o foi avaliada atrav?s de an?lises voltam?tricas do estriol realizadas em um mesmo dia e em dias diferentes e apresentaram desvios padr?es relativos (RSD) inferiores a 5,0%, mostrando que o m?todo desenvolvido ? preciso. Os estudos sobre interferentes mostraram que as subst?ncias presentes nas amostras de comprimido (lactose, estearato de magn?sio e amido) ou urina (?cido ?rico, ?cido asc?rbico e ?cido c?trico) n?o interferiram de maneira significativa na determina??o do E3. Al?m disso, o m?todo desenvolvido foi comparado estatisticamente com um m?todo citado na farmacop?ia atrav?s do teste-t e do teste-F. Os resultados mostraram que os valores de t e F calculados foram menores do que os valores de t e F cr?ticos, indicando que n?o houve diferen?a estat?stica significativa entre os m?todos. A exatid?o do m?todo foi avaliada tamb?m por estudos de adi??o e recupera??o. As recupera??es do E3 variaram de 97,7 ? 100,9% para a formula??o farmac?utica e 99,0 ? 100,9% para a urina, indicando que n?o houve efeitos de interfer?ncia de matriz significativos e que o m?todo apresenta boa exatid?o. Desta forma, a valida??o da metodologia desenvolvida demonstrou que o m?todo proposto pode ser aplicado com sucesso na determina??o do E3 em medicamentos e urina humana. / Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Ci?ncias Farmac?uticas, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / The estriol (C18H24O3, named as E3) is the main estrogenic steroid produced during pregnancy. The E3 is used to treatment of menopause as an alternative for 17?-estradiol, estrone or a combination of both. The main goal of this work was to study the voltammetric profile of E3 using cyclic voltammetry in order to develop a methodology for its determination in tablets and urine using differential pulse voltammetry (DPV) and the glass carbon electrode modified with a film of polymethionine and cobalt. The results showed that the E3 was oxidized at + 0.58V in a 0.1 molL-1 phosphate buffer solution (pH 7.0), giving a good peak definition. The analytical curve for E3 was linear in the concentration range of 0.60 ?molL-1 ? 4.76 ?molL-1 (R2 = 0.996) and 5.66 ?molL-1 ? 9.90 ?molL- 1 (R2 = 0.994 with lmits of detection and quantification of 3.40x10-8 molL-1 and 1.13x10-7 molL-1, respectively. The precision was evaluated by recording voltammograms of E3 on the same or different day. The relative standard deviations were lower than 5.0% for each test, indicating that the developed method has good precision. The interfering study showed that the tested substances do not interfered significantly in the determination of E3, as for both tablets (lactose, magnesium stearate and starch) or urine test (uric acid, ascorbic acid and citric acid). Furthermore, the developed method was compared to the suggested method from American Pharmacopoeia using the t-test and the F-test. The results showed that the calculated values of t and F were lower than their critical values, indicating no significant statistical difference between the methods. The accuracy of the method was also evaluated by studies of addition and recovery. The recovery of E3 ranged from 97.7 ? 100.9% for the pharmaceutical formulation and 99.0 ? 100.9% for the urine, indicating no significant effects of matrix interference and that the developed method presented accuracy. Thus, the validation of the developed methodology demonstrated that the proposed method can be applied successfully to the determination of E3 in drugs and human urine.

Magister Scientiae - MSc (Dept. of Chemistry) / This study reports the synthesis of graphene by oxidizing graphite to graphite oxide using H2SO4 and KMnO4 and reducing graphene oxide to graphene by using NaBH4. Graphene was then characterized using FT-IR, TEM, AFM, XRD, Raman spectroscopy and solid state NMR. Nafion-Graphene in combination with a mercury film electrode, bismuth film electrode and antimony film electrode was used as a sensing platform for trace metal analysis in 0.1 M acetate buffer (pH 4.6) at 120 s deposition time, using square-wave anodic stripping voltammetry (SWASV). Detection limits were calculated using 3σblank/slope. For practical applications recovery studies was done by spiking test samples with known concentrations of metal ions and comparing the results to inductively coupled plasma mass spectrometry (ICPMS). This was then followed by real sample analyses. / South Africa

Electrochemical oxidation of acyclovir at glassy-carbone electrode and boron-doped diamond electrode gives one pH-dependent oxidation signal; the corresponding electrode reaction is controlled by diffusion. It is followed by a second indistinctive signal in the pH range 2,0 - 9,0. Further, optimization of conditions was carried out for determination of acyclovir using DC and DP voltammetry. The calibration dependence on GC electrode in B−R buffer (pH = 6,0) is linear only in the concentration range from 2 to 10 μmol∙l−1 for DCV with limit of detection 0,38 μmol∙l−1; for DPV it is not linear. BDD electrode has to be activated to prevent its passivation. Anodic activation at +2,4 V for 15 s with simultaneous stirring of solution results in relative standard deviation of 0,9% for acyclovir concentration of 1∙10−4 mol∙l−1. Using DCV and DPV methods linear concentration dependences were obtained in 0,1 mol∙l-1 nitric acid and in pH 6,0 B−R buffer. The lowest limit of detection and limit of quantification (LOD = 0,47 μmol∙l−1 a LOQ = 1,55 μmol∙l−1) and linear range from 0,6 to 100 μmol∙l−1 was reached in pH 6,0 B−R buffer. Further, standard addition method was used to quantify acyclovir in Zovirax tablets. Satisfactory recoveries of 101,1 ± 2,3 % using DCV and 98,8 ± 2,2 % using DPV at BDD (compared with the...

The aim of this diploma thesis was to develop an electrochemical method for three phytosterols, namely stigmasterol β-sitosterol and ergosterol using voltammetry techniques on glassy carbon electrode and boron doped diamond electrode. The work builds on previous results, where it was shown that the electrochemical oxidation of phytosterols requires perchloric acid in acetonitrile. When this acid is used, a dehydration reaction occurs. Calibration dependences were measured here for all phytosterols in an environment with a water content of 0.43%. The stability of the signal with increasing distilled water content was further investigated. Then the calibration dependences in the increased water content were measured again. If we want to use HPLC-type separation techniques, we must first find out how the phytosterols will behave in this environment, and therefore the signal stability on the buffer content was investigated. The buffers used were phosphate and acetate buffer. Subsequently, the concentration dependence was measured in an environment with a higher content of phosphate buffer. Furthermore, the possibility of detecting two phytosterols at once was investigated. Key words: dehydration, glassy carbon electrode, boron doped diamond electrode, oxidation, phytosterols, voltammetry

The analysis of literature data has shown that the methods used in laboratory diagnostics for determining the concentration of glucose and hydrogen peroxide have a number of disadvantages, for the elimination of which it is proposed to use electrochemical methods of determination. The electrochemical properties of complex oxides with a perovskite-like structure were studied using voltammetry and chronoamperometry. It has been established that all the complex oxides studied exhibit electrocatalytic activity with respect to glucose and hydrogen peroxide. It is shown that the scanning speed and the time of ultrasonic treatment of oxides have no significant effect on the process. Compounds that can be used as catalysts for creating sensors for determining glucose and hydrogen peroxide are proposed. / Анализ литературных данных показал, что применяемые в лабораторной диагностике методы для определения концентрации глюкозы и пероксида водорода имеют ряд недостатков, для устранения которых предлагается использовать электрохимические методы определения. Изучены электрохимические свойства сложных оксидов с перовскитоподобной структурой с применением вольтамперометрии и хроноамперометрии. Установлено, что все исследованные сложные оксиды проявляют электрокаталитическую активность по отношению к глюкозе и пероксиду водорода. Показано, что скорость сканирования и время ультразвуковой обработки оксидов не оказывает существенного влияния на процесс. Предложены соединения, которые могут быть использованы в качестве катализаторов для создания сенсоров для определения глюкозы и пероксида водорода.

2-Nitrofluorene is a model representative of nitrated polycyclic aromatic hydrocarbons (NPAH) which belongs to a group of mutagens and carcinogens. Interaction of DNA with genotoxic 2-nitrofluorene was monitored by an electrochemical DNA biosensor made of a glassy carbon electrode (GCE) and low molecular weight DNA from salmon sperm. Techniques used are electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square-wave voltammetry (SWV). Using the EIS technique, no damage to DNA, which would cause strand breaks in DNA, was observed, whereas using the CV technique, the intercalation of NF to the structure of DNA was observed, leading to the formation of a NF-DNA complex. The intercalation results in a reduction of electroactive sites which can be oxidized. It was verified using the SWV technique, by which a decrease of the peak heights of adenosine and guanosine was observed. Because of the dangerous effect of NF on the structure of DNA, an electroanalytical method for its determination was developed. An applicability of the method was successfully tested on a model sample of sand. For the development of the technique, differential pulse voltammetry (DPV) was used in a mixture of the Britton-Robinson buffer of pH 7.0 and ethanol in a ratio of 7:3 (v/v) and with a periodic...

This work was focused on study of a behaviour of the food additivum butylated hydroxyanisole on modified carbon electrodes by the voltammetric techniques - cyclic and differential pulse voltammetry. Glassy carbon and carbon paste electrode were used. Multiwalled carbon nanotubes (MWCNT) in combination with three different binders (acetonitrile, nafione or chitosane) were employed for the electrode modification. Carbon paste electrode was unable to modificate with film containing carbon nanotubes and acetonitrile, its active surface was treated only with nafione and chitosane film. All three mentioned modifications were applied in case of glassy carbon electrode. Butylated hydroxyanisole provided a significantly higher signal using electrodes modified with carbon nanotubes with all three binders in contrast to electrodes without any surface modification. The glassy carbon electrode with carbon nanotube / acetonitrile film on its surface appeared to be the most effective for analytical purposes. Voltammetric determination of butylated hydroxyanisole using this electrode provided a better defined and higher analytical signal and lower relative standard deviations in comparison with other ways of modification. The limit of detection of butylated hydroxyanisole obtained by cyclic voltammetry on glassy...

Differential pulse voltammetry (DPV) was used for developing a method for the determination of phenothiazine derivatives, namely chlorpromazine (CHP) and levomepromazine (LMP), using a glassy carbon electrode (GCE) and a graphite electrode, both with a 2 mm disc diameter. Comparison of quantification limits (LQ) for both substances on both electrodes was performed. After optimizing and processing the results, the optimal conditions for measuring calibrations were as follows: Britton- Robinson (BR) buffer at pH 4.0. Calibration dependences were measured inthe concentration range from 1·10-7 to 1·10-4 mol·dm-3 . There was no need for electrochemical electrode regeneration or matrix pretreatment. The results showed higher measurement sensitivity for CHP, and the graphite electrode also showed higher sensitivity. Although there were measured lower concentrations with the graphite electrode in comparison to the GCE, because of the low repeatability of the measurements in the lower concentration range 1-10·10-7 mol·dm-3 , the LQ is comparable to the results reached on the GCE. Besides to the BR buffer, measurements in other matrices (drinking water and river water) were also made. The following LQ values were achieved: 1.0·10-6 mol·dm-3 (in BR buffer), 1.1·10-6 -1.4·10-6 mol·dm-3 (in drinking water) and...