Orientador: Pedro Paulo Corbi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-25T01:00:34Z (GMT). No. of bitstreams: 1 Paiva_RaphaelEnoqueFerrazde_M.pdf: 15807547 bytes, checksum: e13f0a8a3bbde08ba558ac7cdb13c9a5 (MD5) Previous issue date: 2014 / Resumo: Complexos metálicos têm sido estudados quanto as suas propriedades medicinais há décadas. Neste trabalho, dois complexos inéditos de Ag(I) e Pt(II) foram sintetizados com o anti-inflamatório nimesulida (NMS), e avaliados como agentes antibacterianos e antitumorais. O complexo Ag-NMS (AgC13H11N2O5S) apresenta o ligante em uma coordenação bidentada à prata pelos átomos de N e O do grupo sulfonamida. A estrutura proposta foi confirmada por DFT. Devido à baixa solubilidade em água, foi preparado um complexo de inclusão de Ag-NMS em b-CD, pelo método de co-evaporação. Utilizando o método de Scatchard, foi determinado o valor de Ka = 370 2 L mol. Estudos de RMN por correlação H-H através do espaço mostram que a inclusão ocorre pelo grupo fenoxi da NMS. Já o complexo Pt-NMS (PtC26H22N4O10S2) apresenta dois ligantes, coordenados pelos átomos de N e O do grupo sulfonamida, para cada Pt(II). A DFT indica que o isômero N, O trans é o mais estável. O complexo Ag-NMS apresentou valores de MIC na faixa de 15,0-120 mmol L sobre cepas de Pseudomonas aeruginosa, Escherichia col e Staphylococcus aureus. O CE-[(Ag-NMS)·b-CD], embora mais solúvel em água do que o Ag-NMS, não apresentou atividade antibacteriana nas concentrações testadas. Os complexos Ag-NMS e Pt-NMS mostraram-se citotóxicos sobre células normais (Balb/c 3T3) e tumorais (SK-Mel 103 e Panc-1), porém o Pt-NMS foi significativamente mais seletivo contra as linhagens tumorais. Os ensaios de intercalação com EtBr e a avaliação da estrutura do DNA por dicroísmo circular indicam que o DNA não é um alvo biológico para o complexo Pt-NMS, indicando um mecanismo de ação diferente da cisplatina / Abstract: Metal complexes have been studied regarding its medicinal properties for decades. In this work, novel complexes of Ag(I) and Pt(II) with the anti-inflammatory nimesulide were synthesized and evaluated regarding their antibacterial and antitumoral properties. The Ag-NMS complex (AgC13H11N2O5S) shows the ligand in a bidentate coordination mode, bound to silver through the N and O atoms of the sulfonamide group. The proposed structure was confirmed by DFT. Due to its poor solubility in water, the Ag-NMS complex was included in b-CD, by co-evaporation. The Ka = 370 2 L mol was determined using the Scatchard method. Studies by H-H NMR correlation through space shows the inclusion of NMS by the fenoxi group. The Pt-NMS complex (PtC26H22N4O10S2) contain two ligands, coordinated through the N and O atoms of the sulfonamide group, for each Pt(II). DFT studies indicate that the N,O trans isomer is the most stable. The Ag-NMS complex presents MIC values in the range 15.0-120 mmol L over Pseudomonas aeruginosa, Escherichia coli e Staphylococcus aureus. The inclusion complex CE-[(Ag-NMS)·b-CD], although more soluble in water than Ag-NMS, shows no antibacterial activity in the tested concentrations. Both complexes were cytotoxic against normal (Balb/c 3T3) and tumor (SK-Mel 103 and Panc-1) cells, but the Pt-NMS complex was significantly more selective against tumor cells. The EtBr competitive intercalation assay and the evaluation of CT-DNA structure using circular dichroism show that DNA is not a biological target for the Pt-NMS complex, indicating a mechanism of action different of the cisplatin one / Mestrado / Quimica Inorganica / Mestre em Química

No description available.

Les métaux sont impliqués dans de nombreux processus biologiques essentiels pour le vivant. Ils interviennent au sein de métallo-enzymes sélectives et efficaces, qui catalysent des réactions chimiques dans des conditions douces. Les plus illustres sont les RiboNucléotide Réductases (RNR), essentiels à la synthèse de l'ADN, ou bien encore la Méthane MonoOxygènase (MMO) capable à partir du méthane de former le méthanol, molécule à fort potentiel énergétique. Ces métallo-enzymes fonctionnent au travers d'un site actif contenant deux fers. Récemment, un nouveau membre de cette famille a été isolé et présente un nouveau site actif hétérodinucléaire à fer et manganèse. Le potentiel chimique de ces enzymes commence juste a être caractérisé, mais les premières études suggèrent une réactivité semblable aux enzymes homodinucléaires à fer. Puisque le comportement de l'ion métallique dans les protéines n'est pas très différent de la chimie fondamentale du métal, l'étude de petits analogues synthétiques de site actif est particulièrement utile. Nous proposons la synthèse de complexes dinucléaires à Fe-Mn pour étudier la réactivité et les propriétés électroniques de ce nouveau site actif. Par une étude physicochimique approfondie et des études de réactivités, nous avons apporté une meilleure compréhension sur la réactivité de ce nouveau système enzymatique. / Nonheme enzymes possessing a dinuclear active site are performing many essential functions such as Ribonucleotide reductase (RNR) in DNA production and Methane oxygenation (MMO) to convert gas toxic methane in combustible methanol. While most of these enzymes have been shown to possess a diiron active site, new members of this protein family were recently isolated from bacteria and found to possess instead a heterodinuclear Fe-Mn active site. The chemical potential of the heterodinuclear metal site is just starting to be evaluated, but available data suggest that it may have capabilities for similarly versatile chemistry as the extensively studied diiron-carboxylate cofactor. In recent years, the study of models based on simple dinuclear metal complexes has became an important tool for gaining insight into the biological functions of such bimetallic cores. The design of binucleating ligands capable of providing asymmetric dinuclear complexes is a subject of great interest. We propose to synthesize dinuclear Fe-Mn complexes to investigate the reactivity and the electronic properties of this new active site. By combining spectroscopic and electronical studies we have gain a better understanding on the reactivity of this new enzymatic system.

No description available.

Metabolism is a subset of chemistry that allows cells to defy thermodynamic equilibrium, a fundamental process that must have been in place from the very beginning of biology. Before evolution produced efficient catalysts in the form of complex protein machinery, short metal binding peptides might have preceded modern metalloproteins. Such prebiotic, metal-binding motifs have been hypothesized to have existed through analyses of extant protein sequences. However, it is unclear how metal-binding motifs might have evolved in the harsh prebiotic environment. Here, we show how certain environments, in particular seawater-like environments rich in divalent cations and especially Mg2+, support the survival of short peptides upon extreme temperatures as high as 150 °C. Moreover, while Mg2+ does not offer the same protection from UV light, peptides are protected from both heat and irradiation when bound to a metal ion. The results suggest that specific environments rich in metal ions may be better suited for the emergence of complex systems in the path toward life. Additionally, the conditional degradation of peptides depending on their ability of binding metals might have enabled a selection mechanism that would favor the survival of metal-binding motifs which resemble the motifs found in modern proteins. These short sequences could have acted as early, simple catalysts able to facilitate a restricted set of chemical reactions, which would shape the emergence and biology of the Last Universal Common Ancestor.

No description available.

Neste trabalho sintetizaram-se novos complexos imínicos e diimínicos de Cu(II) derivados da isatina, um indol endógeno, que foram então extensivamente caracterizados por análise elementar, medidas de condutividade molar, técnicas espectroscópicas: IV, UV/Vis e EPR, e por espectrometria de massa, ESI-MS. Estes compostos apresentaram equilíbrio ceto-enólico em solução, variando a geometria ao redor do íon Cu(II), ao se alterar o pH do meio, indo de tetraédrico em meio ácido à tetragonal em meio básico. Para a elucidação do papel do cobre no mecanismo de oxidação de carboidratos pelo oxigênio molecular, realizaram-se estudos cinéticos tendo como catalisadores estes complexos de cobre. Determinou-se a uma lei cinética global mais abrangente para estas reações, incluindo uma etapa dependente do cobre (a concentrações bem baixas), seguida de outra independente do metal. As etapas no mecanismo proposto, sob condições de pseudo-primeira ordem, combinam transferência eletrônica intramolecular, com provável redução do íon de cobre pelo substrato, levando a espécies muito reativas (OH•-, O2•-, H2O2, CO2•-), responsáveis pelo processo de iniciação e propagação, e a formação de produtos carbonílicos de cadeia curta (glicolato, glicerato e formiato). Para o estudo da interação metal-carboidrato, importante para se entender melhor o papel do cobre frente a este ligante biológico, complexos de Cu(II) com monossacarídeos foram sintetizados e caracterizados por análise elementar e termogravimétrica, medidas de condutividade molar, espectroscopias UV/Vis, IV e EPR, além da espectroscopia Raman, através da qual investigou-se o modo de ligação do carboidrato ao metal em cada um destes complexos. Foram ainda preparados e caracterizados por análise elementar, medidas de condutividade molar, espectroscopias UV/Vis, IV, EPR, ESI-MS e CD dois novos complexos imínicos quirais de Cu(II), com ligantes do tipo aminocarboidrato, e que também foram utilizados para estudos biológicos. Estudos de atividade biológica foram feitos in vitro, usando as linhagens celulares tumorais promonocítica sanguínea U937 e neuroblastoma SH-SY5Y, com os complexos imínicos de cobre, principalmente aqueles derivados da isatina. As células tratadas com os complexos mais ativos sofreram apoptose, verificada por ensaios citofluorimétricos, em que os complexos agiram em diferentes fases do ciclo celular de cada linhagem (fase G1, S ou G2/M). Através da técnica citofluorimétrica foi observada também a geração de radicais livres na célula e, através de ensaios imunológicos, determinou-se a quantidade de proteínas citoplasmáticas carboniladas e glicosiladas, geradas após os tratamentos com os compostos, em diferentes tempos de incubação. De uma maneira geral, estes estudos indicaram modulação da atividade biológica, com um comportamento antiproliferativo muito diferente, indo de baixa eficácia até alta eficiência. Dentre os compostos mais ativos, pode ser observada uma especificidade diferente, tanto com relação ao tipo de célula quanto ao seu modo de ação, evidenciando sua potencial aplicação como agentes antitumorais. / In this work, novel imine and diimine copper(II) complexes with ligands derived from isatin, an endogenous indol, were synthesized, and extensively characterized by elemental analysis, conductivity measurements, spectroscopic techniques (IR, UV/Vis, and EPR), and electrospray mass spectrometry (ESI-MS/MS). These compounds showed a keto-enolic equilibrium in solution, with variations in the geometry around the copper ion with increasing pH, varying from a more tetrahedral configuration in acidic medium to a tetragonal one in basic solution. In order to elucidate the role of copper in the carbohydrate oxidation by molecular oxygen, kinetic studies were performed using these complexes as catalysts. A more comprehensive global rate law was determined for this process, including a copper-dependent pathway (at very low concentrations), in addition to an independent one, both influenced by alkaline medium. The proposed mechanism, under pseudo-first order conditions, combine intramolecular electronic transfer with reduction of the copper ion by the substrate, leading to the formation of intermediary reactive species (OH•-, O2•-, H2O2, CO2•-), responsible for initiation and propagation steps, and of short chain carbonylic products (glycolate, glycerate and formiate ions). To better understanding metal-carbohydrate interactions, copper(II) complexes with simple monosacharides were isolated, and characterized by elemental and thermogravimetric analyses, and spectroscopic techniques (IR, UV/Vis, and EPR), besides Raman spectroscopy, used to investigate the binding mode of the carbohydrate moiety to the copper ion, in each one of these complexes. Additionally, two novel chiral imine copper(II) complexes, derived from aminocarbohydrate ligands, were prepared and characterized by elemental analysis, conductivity measurements, and spectroscopic techniques (IR, UV/Vis, EPR, ESI-MS and CD), and one of them was also used in biological studies. Biological activity studies were carried out with the imine and diimine copper(II) complexes derived from isatin, verifying antiproliferative effect toward some tumor cell lines (promonocite U937 and neuroblastoma SH-SY5Y). Cells treated with the most active complexes were committed by the apoptotic program, as verified by citofluorimetric assays, with the complexes interfering the cell cycle in different ways (G1, G2/M or S phase. Formation of free radicals was detected, and citoplasmatic carbonylated and glycosilated proteins inside the treated cells were determined by imunologic assays. In conclusion, these studies indicated modulation of the biological activity by the imine ligand in the copper(II) complexes, with very different antiproliferative behavior, going from undetectable activity to high efficacy. Among the most active compounds, a different specificity and action mode in both cell type could be observed, evidencing their potential application as antitumoral agents.

Neste trabalho sintetizaram-se novos complexos imínicos e diimínicos de Cu(II) derivados da isatina, um indol endógeno, que foram então extensivamente caracterizados por análise elementar, medidas de condutividade molar, técnicas espectroscópicas: IV, UV/Vis e EPR, e por espectrometria de massa, ESI-MS. Estes compostos apresentaram equilíbrio ceto-enólico em solução, variando a geometria ao redor do íon Cu(II), ao se alterar o pH do meio, indo de tetraédrico em meio ácido à tetragonal em meio básico. Para a elucidação do papel do cobre no mecanismo de oxidação de carboidratos pelo oxigênio molecular, realizaram-se estudos cinéticos tendo como catalisadores estes complexos de cobre. Determinou-se a uma lei cinética global mais abrangente para estas reações, incluindo uma etapa dependente do cobre (a concentrações bem baixas), seguida de outra independente do metal. As etapas no mecanismo proposto, sob condições de pseudo-primeira ordem, combinam transferência eletrônica intramolecular, com provável redução do íon de cobre pelo substrato, levando a espécies muito reativas (OH•-, O2•-, H2O2, CO2•-), responsáveis pelo processo de iniciação e propagação, e a formação de produtos carbonílicos de cadeia curta (glicolato, glicerato e formiato). Para o estudo da interação metal-carboidrato, importante para se entender melhor o papel do cobre frente a este ligante biológico, complexos de Cu(II) com monossacarídeos foram sintetizados e caracterizados por análise elementar e termogravimétrica, medidas de condutividade molar, espectroscopias UV/Vis, IV e EPR, além da espectroscopia Raman, através da qual investigou-se o modo de ligação do carboidrato ao metal em cada um destes complexos. Foram ainda preparados e caracterizados por análise elementar, medidas de condutividade molar, espectroscopias UV/Vis, IV, EPR, ESI-MS e CD dois novos complexos imínicos quirais de Cu(II), com ligantes do tipo aminocarboidrato, e que também foram utilizados para estudos biológicos. Estudos de atividade biológica foram feitos in vitro, usando as linhagens celulares tumorais promonocítica sanguínea U937 e neuroblastoma SH-SY5Y, com os complexos imínicos de cobre, principalmente aqueles derivados da isatina. As células tratadas com os complexos mais ativos sofreram apoptose, verificada por ensaios citofluorimétricos, em que os complexos agiram em diferentes fases do ciclo celular de cada linhagem (fase G1, S ou G2/M). Através da técnica citofluorimétrica foi observada também a geração de radicais livres na célula e, através de ensaios imunológicos, determinou-se a quantidade de proteínas citoplasmáticas carboniladas e glicosiladas, geradas após os tratamentos com os compostos, em diferentes tempos de incubação. De uma maneira geral, estes estudos indicaram modulação da atividade biológica, com um comportamento antiproliferativo muito diferente, indo de baixa eficácia até alta eficiência. Dentre os compostos mais ativos, pode ser observada uma especificidade diferente, tanto com relação ao tipo de célula quanto ao seu modo de ação, evidenciando sua potencial aplicação como agentes antitumorais. / In this work, novel imine and diimine copper(II) complexes with ligands derived from isatin, an endogenous indol, were synthesized, and extensively characterized by elemental analysis, conductivity measurements, spectroscopic techniques (IR, UV/Vis, and EPR), and electrospray mass spectrometry (ESI-MS/MS). These compounds showed a keto-enolic equilibrium in solution, with variations in the geometry around the copper ion with increasing pH, varying from a more tetrahedral configuration in acidic medium to a tetragonal one in basic solution. In order to elucidate the role of copper in the carbohydrate oxidation by molecular oxygen, kinetic studies were performed using these complexes as catalysts. A more comprehensive global rate law was determined for this process, including a copper-dependent pathway (at very low concentrations), in addition to an independent one, both influenced by alkaline medium. The proposed mechanism, under pseudo-first order conditions, combine intramolecular electronic transfer with reduction of the copper ion by the substrate, leading to the formation of intermediary reactive species (OH•-, O2•-, H2O2, CO2•-), responsible for initiation and propagation steps, and of short chain carbonylic products (glycolate, glycerate and formiate ions). To better understanding metal-carbohydrate interactions, copper(II) complexes with simple monosacharides were isolated, and characterized by elemental and thermogravimetric analyses, and spectroscopic techniques (IR, UV/Vis, and EPR), besides Raman spectroscopy, used to investigate the binding mode of the carbohydrate moiety to the copper ion, in each one of these complexes. Additionally, two novel chiral imine copper(II) complexes, derived from aminocarbohydrate ligands, were prepared and characterized by elemental analysis, conductivity measurements, and spectroscopic techniques (IR, UV/Vis, EPR, ESI-MS and CD), and one of them was also used in biological studies. Biological activity studies were carried out with the imine and diimine copper(II) complexes derived from isatin, verifying antiproliferative effect toward some tumor cell lines (promonocite U937 and neuroblastoma SH-SY5Y). Cells treated with the most active complexes were committed by the apoptotic program, as verified by citofluorimetric assays, with the complexes interfering the cell cycle in different ways (G1, G2/M or S phase. Formation of free radicals was detected, and citoplasmatic carbonylated and glycosilated proteins inside the treated cells were determined by imunologic assays. In conclusion, these studies indicated modulation of the biological activity by the imine ligand in the copper(II) complexes, with very different antiproliferative behavior, going from undetectable activity to high efficacy. Among the most active compounds, a different specificity and action mode in both cell type could be observed, evidencing their potential application as antitumoral agents.

Thyroxine (T4), the main secretory hormone of the thyroid gland, is produced on thyroglobulin by thyroid peroxidase (TPO)/hydrogen peroxide/iodide system. The synthesis of T4 by TPO involves two independent steps: iodination of tyrosine and phenolic coupling of the resulting iodotyrosine residues. The prohormone T4 is then converted to its biologically active form T3 by a selenocysteine-containing iodothyronine deiodinase (ID-I), which is present in highest amounts in liver, kidney, thyroid and pituitary. The 5'-deiodination catalyzed by ID-I is a ping-pong, bisubstrate reaction in which the selenol (or selenolate) group of the enzyme (E-SeH or E-Se-) first reacts with thyroxine (T4) to form a selenenyl iodide (E-SeI) intermediate. Subsequent reaction of the selenenyl iodide with an as yet unidentified intracellular cofactor completes the catalytic cycle and regenerates the selenol. Although the deiodination reactions are essential for the function of thyroid gland, the activation of thyroid stimulating hormone (TSH) receptor by auto-antibodies leads to an overproduction of thyroid hormones. In addition, these antibodies stimulate ID-I and probably other deiodinases to produce relatively more amount of T3. Figure 1. Synthesis of thyroid hormones by heme-containing Thyroid Peroxidase(TPO)(Refer PDF File) As these antibodies are not under pituitary feedback control system, there is no negative influence on the thyroid activity and, therefore, the uncontrolled production of thyroid hormones leads to a condition called “hyperthyroidism”. Under these conditions, the overproduction of T4 and T3 can be controlled by specific inhibitors, which either block the thyroid hormone biosynthesis or reduce the conversion of T4 to T3. A unique class of such inhibitors is the thiourea drugs, methimazole (1, MMI), 6-n-propyl-2-thiouracil (3, PTU), and 6-methyl-2-thiouracil (5, MTU). Although these compounds are the most commonly employed drugs in the treatment of hyperthyroidism, the detailed mechanism of their action is still not clear. According to the initially proposed mechanism, these drugs may divert oxidized iodides away from thyroglobulin by forming stable electron donor-acceptor complexes with diiodine, which can effectively reduce the thyroid hormone biosynthesis. It has also been proposed that these drugs may block the thyroid hormone synthesis by coordinating to the metal center of thyroid peroxidase (TPO). After the discovery that the ID-I is responsible for the activation of thyroxine, it has been reported that PTU, but not MMI, reacts with the selenenyl iodide intermediate (E-SeI) of ID-I to form a selenenyl sulfide as a dead end product, thereby blocking the conversion of T4 to T3 during the monodeiodination reaction. The mechanism of anti-thyroid activity is further complicated by the fact that the gold-containing drugs such as gold thioglucose (GTG) inhibit the deiodinase activity by reacting with the selenol group of the native enzyme. Recently, the selenium analogues 2 (MSeI), 4 (PSeU) and 6 (MSeU) attracted considerable attention because these compounds are expected to be more nucleophilic than their sulfur analogues and the formation of an –Se–Se– bond may occur more readily than the formation of an –Se–S– bond with the ID-I enzyme. However, the data derived from the inhibition of TPO by selenium compounds show that these compounds may inhibit the TPO activity by a different mechanism. Therefore, further studies are required to understand the mechanism by which the selenium compounds exert their inhibitory action. Our initial attempts to isolate 2 were unsuccessful and the final stable compound in the synthesis was characterized to be the diselenide (8). In view of the current interest in anti-thyroid drugs and their mechanism, we extended our approach to the synthesis and biological activities of a number of sulfur and selenium derivatives bearing the methimazole pharmacophore. The thesis consists of five chapters. The first chapter gives a general introduction to thyroid hormone synthesis and anti-thyroid drugs. In this chapter, the biosynthesis of thyroid hormones, structure and function of heme peroxidases, activation of thyroid hormones by iodothyronine deiodinases are discussed. This chapter also gives a brief introduction to some common problems associated with the thyroid gland, with a particular emphasis on hyperthyroidism. The structure and activity of some commonly used anti-thyroid drugs and the role of selenium in thyroid are discussed. The literature references related to this work are provided at the end of the chapter. The second chapter deals with the synthesis and characterization of the selenium analogue (MSeI) of anti-thyroid drug methimazole and a series of organoselenium compounds bearing N-methylimidazole pharmacophore are described. The clinically employed anti-thyroid drug, methimazole (MMI), exists predominantly in its thione form, which is responsible for its anti-thyroidal activity. The selenium analogue MSeI, on the other hand, is not stable in air and spontaneously oxidizes to the corresponding diselenide (MSeIox). Experimental and theoretical studies on MSeI suggest that this compound exists in a zwitterionic form in which the selenium atom carries a large negative charge. The structure of MSeI was studied in solution by NMR spectroscopy and the 77Se NMR chemical shift shows a large upfield shift (-5 ppm) in the signal as compared to the true selones for which the signals normally appear in the downfield range (500-2500 ppm). This confirms that MSeI exists predominantly in its zwitterionic form in solution. Our theoretical studies show that the formation of the diselenide (MSeIox) from selenol tautomer is energetically more favored than the formation of the disulfide (MMIox) from the thiol tautomer of MMI. This study also shows that the replacement of the N−H group in MSeI by an N-methyl or N-benzyl substituent does not affect the nature of C−Se bond. In the third chapter, the inhibition of lactoperoxidase-catalyzed oxidation of ABTS by anti-thyroid drugs and related derivatives is described. The commonly used anti-thyroid agent methemazole (MMI) inhibits the lactoperoxidase (LPO) with an IC50 value of 7.0 µM which is much lower than that of the other two anti-thyroid drugs, PTU and MTU. The selenium analogue of methimazole (MSeI) also inhibits LPO with an IC50 value of 16.4 µM, which is about 4-5 times lower than that of PTU and MTU. In contrast to thiones and selones, the S- and Se-protected compounds do not show any noticeable inhibition under identical experimental conditions. While the inhibition of LPO by MMI cannot be reversed by increasing the hydrogen peroxide concentration, the inhibition by MSeI can be completely reversed by increasing the peroxide concentration. Some of the selenium compounds in the present study show interesting anti-oxidant activity in addition to their inhibition propertities. In the presence of glutathione (GSH), MSeI constitutes a redox cycle involving a catalytic reduction of H2O2 and thereby mimics the glutathione peroxidase (GPx) activity in vitro. These studies reveal that the degradation of the intracellular H2O2 by the selenium analogues of anti-thyroid drugs may be beneficial to the thyroid gland as these compounds may act as antioxidants and protect thyroid cells from oxidative damage. Because the drugs with an action essentially on H2O2 can reversibly inhibit thyroid peroxidase, such drugs with a more controlled action could be of great importance in the treatment of hyperthyroidism. Figure 2. (A) Concentration-inhibition curves for the inhibition of LPO-catalyzed oxidation of ABTS by MMI and MSeI at pH 7.0 and 30 °C. (B) Plot of initial rates (vo) for the LPO-catalyzed oxidation of ABTS vs concentration of H2O2. (a) Control activity, (b) 40 µM of MSeI, (c) 40 µM of MSeIox, (d) 80 µM of PTU, (e) 80 µM of MTU, (f) 40 µM of MMI. The incubation mixture contained 6.5 nM LPO, 1.4 mM ABTS, 0.067 M phosphatebuffer(pH7).(Refer PDF File) The fourth chapter describes the inhibition of lactoperoxidase (LPO)-catalyzed iodination of L-tyrosine by anti-thyroid drug methimazole (MMI) and its selenium analogue (MSeI). These inhibition studies show that MSeI inhibits LPO with an IC50 value of 12.4 µM, which is higher than that of MMI (5.2 µM). The effect of hydrogen peroxide on the inhibition of LPO by MMI and MSeI is also discussed. These studies also reveal that the inhibition of LPO-catalyzed iodination by MSeI can be completely reversed by increasing the peroxide concentration. On the other hand, the inhibition by MMI cannot be reversed by increasing the concentration of the peroxide. To under stand the nature of compounds formed in the reactions between anti-thyroid drugs and iodine, the reactions of MSeI with molecular iodine is described. MSeI reacts with I2 to produce novel ionic diselenides, and the nature of the species formed in this reaction appears to be solvent dependent. The formation of ionic species (mono and dications) in the reaction is confirmed by UV-Vis, FT-IR and FT-Raman spectroscopic investigations and single crystal x-ray studies. The major conclusion drawn from this study is that MSeI reacts with iodine, even in its oxidized form, to form ionic diselenides containing iodide or polyiodide anions, which might be possible intermediates in the inhibition of thyroid hormones. Dication X-ray crystal structure of the monocation X-ray crystal structure of the dication In the fifth chapter, the synthesis and characterization of several thiones and selones having N,N-disubstituted imidazole moiety are described. Experimental and theoretical studies were performed on a number of selones, which suggest that these compounds exist as zwitterions in which the selenium atom carries a large negative charge. The structures of selones were studied in solution by NMR spectroscopy and the 77Se NMR chemical shifts for the selones show large upfield shifts in the signals, confirming the zwitterionic structure of the selones in solution. The thermal isomerization of some S- and Se-substituted methyl and benzyl imidazole derivatives to produce the thermodynamically more stable N-substituted derivatives is described. A structure–activity correlation was attempted on the inhibition of LPO-catalyzed oxidation and iodination reactions by several thiouracil compounds, which indicates that the presence of an n-propyl group in PTU is important for an efficient inhibition. In contrast to the S- and Se-substituted derivatives, the selones produced by thermal isomerization exhibited efficient inhibition, indicating the importance of reactive selone (zwitterionic) moiety in the inhibition. The inhibition data on another well-known anti-thyroid agent carbimazole (CBZ) support the assumption that CBZ acts as a prodrug, requiring a conversion to methimazole (MMI) for its inhibitory action on thyroid peroxidase. (Refer pdf file/original thesis)

Biological processes at the cellular level take place in heterogeneous environments, and usually involve only a small number of molecules. They tend to exhibit strong time dependent fluctuations, as a result, and are, therefore, intrinsically stochastic. The present thesis describes some of the efforts I have made during the course of my research work to develop simple, analytically tractable models of a selection of biologically-inspired problems in which this kind of stochasticity is a central ingredient. These problems are: (i) single molecule enzyme activity (ii) intermittency in single enzymes, (iii) liquids crystal dynamics (iv) modulation of electron transfer kinetics during photosynthesis, and (v) anomalous polymer translocation dynamics. All of these problems can be defined in terms of quantity that changes randomly in time because of environmental fluctuations with broad distributions of relaxation times. In this thesis I show that a generalization of a model that describes simple Brownian Motion can be used to understand many of the dynamical aspects of these problems.