In this article, we examined different synthetic approaches with varying adding starting materials for the thiol containg schiff-base complex [ZnL1]2(L1=o-C6H4(SH)(CH=NC6H4SH-o)). We found that the key step for successful synthesis of [ZnL1]2 is the formation of zinc aldehyde intermediate. We also break the [ZnL2]2 dimer by adding chelating agent, TMEDA, to obtain the Zn(L1)(TMEDA) monomer. It¡¦s single crystal X-ray structure confirmed, the structure of the target ligand L1. We also synthesized [NiL1]2 by transmetalation of [ZnL1]2 - an easier synthetic approach. We further reduced the imine part on L1 of [ZnL1]2 and Zn(L1)(TMEDA) to get [ZnL2]2(L2=o-C6H4(SH)(CH2NHC6H4SH-o)) and Zn(L2)(TMEDA) respectively for future reactivity studies.

In this study, we took four diamines of different carbon chain lengthes to synthesize several thiosalen derived zinc(II) complexes, i.e. N, N¡¦-Bis- (2-thio-benzylidene)- 1,3-propylenediaminato-zinc(II)(1),N,N¡¦-Bis(2-thio-benzylidene)-2,2-dimethyl- 1,3-propylenediaminato-zinc(II)(2),N,N¡¦-Bis-(2-thio-benzylidene)-1,2-ethylene- diaminato-zinc(II)(3),andN,N¡¦-Bis(2-thio-benzylidene)-1-methyl-1,2-ethylene- diaminato-zinc(II)(4). The crystal structure of 1 was shown to be trimeric. We then used NaBH4 to reduced complexes1, 2, and 4 to get complexes 5, 6, and 7 respectively for reactivity and structure studies. To expand our current study, we also synthesized nickel analogue (8) of complex 1 by transmetallation.

No description available.

Thesis advisor: James P. Morken / This dissertation presents the development of catalytic enantioselective synthesis and selective functionalization of geminal or vicinal borylsilanes and bis(boronates). In the first chapter, a modular approach to the catalytic synthesis of enantioenriched anti-1,2-borylsilanes will be described, which is enabled by the stereospecific 1,2-metallate shift that occurs during Pd-catalyzed conjunctive cross-coupling reaction. In the second chapter, the Cu-catalyzed site-selective cross-coupling of vicinal bis(boronates) to an array of electrophiles is developed to provide a new method to construct complex boron-containing products from terminal alkenes. A dramatic rate acceleration in transmetalation to copper is enabled by the neighboring activating boronate group in the substrate. Mechanistic experiments suggest that the formation of a chelated cyclic ate complex may play a role in facilitating the transmetalation. As a follow-up project, the site-selective cross-coupling of vicinal diborylsilanes is also investigated. A Pt-catalyzed enantioselective hydrosilylation of (Z)-1,2-diborylethylene provides access to a vicinal 1,2-diboryl-1-silylalkane that can be used in catalytic cross-coupling reactions. Depending on the catalyst employed and the electrophile class, the coupling reaction can occur at either the α or β carbon relative to the silane center. In the last chapter, a practical method is developed to prepare a TiO2 supported gold nanoparticle catalyst that facilitates the cis-diboration of terminal alkynes. The resulting products can undergo a practical Cu-catalyzed site-selective cross-coupling with proton or other non-aryl/alkenyl electrophiles to yield α-substituted alkenyl boronates with excellent yield and site-selectivity. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

A cor vermelha brilhante característica do presunto Parma é resultante, principalmente, do pigmento Zinco-protoporfirina IX (ZnPP). A ZnPP é formada a partir da mioglobina por uma reação de transmetalação, catalisada pela enzima ferroquelatase (FECH), em que o íon de Fe(II) coordenado ao grupo heme é substituído pelo íon Zn(II). O presunto Parma apresenta uma maior estabilidade oxidativa em relação aos demais produtos cárneos curados além de não conter nitrito e nitrato, portanto, são considerados mais saudáveis. A utilização da FECH no processamento de carnes curadas pode permitir a produção de produtos cárneos curados mais saudáveis e em menor tempo. No presente trabalho a proteína ferroquelatase de Bacillus subtilis (BsFECH) foi expressa em células de E. coli BL21(DE3), purificada por cromatografia de afinidade ao níquel e exclusão por tamanho e caracterizada por dicroísmo circular, emissão de fluorescência do triptofano e cromatografia de exclusão por tamanho analítico. Em termos de estabilidade foi encontrado que altas concentrações de sal aumentam a estabilidade da proteína frente aos agentes denaturantes ureia e temperatura. A BsFECH produzida é capaz de ligar-se ao substrato modelo de porfirina (TPPS), conforme verificado por espectroscopia de UV-Vis, com uma Ka = 3,8x105 M-1 e é capaz de se associar à metamioglobina, conforme verificado por reação de cross-linking com dissuccinimidil suberato e avaliado por SDS-PAGE. A BsFECH aumenta significativamente a taxa de inserção de íons de zinco na TPPS e mostra uma cinética de saturação com uma constante de ligação aparente de Zn(II) ao complexo [BsFECH-TPPS] de 1,3x104 M e uma constante de primeira ordem de 6,6x10-1 h-1 para a dissociação do complexo ternário. A reação de troca ferro/zinco na mioglobina catalisada pela BsFECH é facilitada pela proteólise limitada da mioglobina com pepsina que abre um caminho para a reação de troca metálica com base na interação proteína-proteína entre o fragmento globina da mioglobina e a BsFECH. / The bright red color, characteristic of the Parma ham, results mainly of the pigment Zinc-Protoporphyrin IX (ZnPP). The ZnPP is formed from myoglobin by the reaction, catalyzed by ferrochelatase enzyme (FECH), in which Fe(II) ions coordinated to the heme group is replaced by Zn(II) ions. Parma ham shows greater oxidative stability when compared to others cured meat products besides do not contain nitrite and nitrate and, therefore, is considered healthier. The use of FECH in the processing of cured meats may allow the production of healthier cured meat products in a shorter period of time. In this work, the ferrochelatase protein from Bacillus subtilis was expressed in E. coli BL21(DE3) cells, purified by nickel affinity chromatography and size exclusion, and characterized by circular dichroism, fluorescence emission of tryptophan and analytical size exclusion chromatography. In terms of stability, it was found that the high salt content enhances the protein stability against the denaturation agents urea and temperature. The BsFECH produced is able to bind to the porphyrin model substrate (TPPS), as verified by UV-Vis spectroscopy, with Ka = 3.8x105 M-1 and is capable to associate to metamyoglobin as verified by cross-linking reaction with dissuccinimidil suberato, as observed by SDS-PAGE. The BsFECH increases, significantly, the zinc ions insertion rate in TPPS and shows a saturation kinetics behavior with an apparent biding constant of Zn(II) to the [BsFECH-TPPS] complex of 1.3x104 M and a first order rate constant for the dissociation of ternary complex of 6.6x10-1 h-1. The Fe/Zn exchange reaction in the myoglobin as catalyzed by BsFECH is facilitated by myoglobin-limited proteolysis with pepsin that opens a reaction channel for the metallic exchange based on protein-protein interaction between the globin moiety of myoglobin and BsFECH.

No description available.

A cor vermelha brilhante característica do presunto Parma é resultante, principalmente, do pigmento Zinco-protoporfirina IX (ZnPP). A ZnPP é formada a partir da mioglobina por uma reação de transmetalação, catalisada pela enzima ferroquelatase (FECH), em que o íon de Fe(II) coordenado ao grupo heme é substituído pelo íon Zn(II). O presunto Parma apresenta uma maior estabilidade oxidativa em relação aos demais produtos cárneos curados além de não conter nitrito e nitrato, portanto, são considerados mais saudáveis. A utilização da FECH no processamento de carnes curadas pode permitir a produção de produtos cárneos curados mais saudáveis e em menor tempo. No presente trabalho a proteína ferroquelatase de Bacillus subtilis (BsFECH) foi expressa em células de E. coli BL21(DE3), purificada por cromatografia de afinidade ao níquel e exclusão por tamanho e caracterizada por dicroísmo circular, emissão de fluorescência do triptofano e cromatografia de exclusão por tamanho analítico. Em termos de estabilidade foi encontrado que altas concentrações de sal aumentam a estabilidade da proteína frente aos agentes denaturantes ureia e temperatura. A BsFECH produzida é capaz de ligar-se ao substrato modelo de porfirina (TPPS), conforme verificado por espectroscopia de UV-Vis, com uma Ka = 3,8x105 M-1 e é capaz de se associar à metamioglobina, conforme verificado por reação de cross-linking com dissuccinimidil suberato e avaliado por SDS-PAGE. A BsFECH aumenta significativamente a taxa de inserção de íons de zinco na TPPS e mostra uma cinética de saturação com uma constante de ligação aparente de Zn(II) ao complexo [BsFECH-TPPS] de 1,3x104 M e uma constante de primeira ordem de 6,6x10-1 h-1 para a dissociação do complexo ternário. A reação de troca ferro/zinco na mioglobina catalisada pela BsFECH é facilitada pela proteólise limitada da mioglobina com pepsina que abre um caminho para a reação de troca metálica com base na interação proteína-proteína entre o fragmento globina da mioglobina e a BsFECH. / The bright red color, characteristic of the Parma ham, results mainly of the pigment Zinc-Protoporphyrin IX (ZnPP). The ZnPP is formed from myoglobin by the reaction, catalyzed by ferrochelatase enzyme (FECH), in which Fe(II) ions coordinated to the heme group is replaced by Zn(II) ions. Parma ham shows greater oxidative stability when compared to others cured meat products besides do not contain nitrite and nitrate and, therefore, is considered healthier. The use of FECH in the processing of cured meats may allow the production of healthier cured meat products in a shorter period of time. In this work, the ferrochelatase protein from Bacillus subtilis was expressed in E. coli BL21(DE3) cells, purified by nickel affinity chromatography and size exclusion, and characterized by circular dichroism, fluorescence emission of tryptophan and analytical size exclusion chromatography. In terms of stability, it was found that the high salt content enhances the protein stability against the denaturation agents urea and temperature. The BsFECH produced is able to bind to the porphyrin model substrate (TPPS), as verified by UV-Vis spectroscopy, with Ka = 3.8x105 M-1 and is capable to associate to metamyoglobin as verified by cross-linking reaction with dissuccinimidil suberato, as observed by SDS-PAGE. The BsFECH increases, significantly, the zinc ions insertion rate in TPPS and shows a saturation kinetics behavior with an apparent biding constant of Zn(II) to the [BsFECH-TPPS] complex of 1.3x104 M and a first order rate constant for the dissociation of ternary complex of 6.6x10-1 h-1. The Fe/Zn exchange reaction in the myoglobin as catalyzed by BsFECH is facilitated by myoglobin-limited proteolysis with pepsin that opens a reaction channel for the metallic exchange based on protein-protein interaction between the globin moiety of myoglobin and BsFECH.

Olefin metathesis is a powerful tool for the making and breaking of carbon-carbon double bonds. Among well-defined homogenous catalysts for olefin metathesis, ruthenium-based alkylidenes stand out for their robustness and relative ease-of-use. Synthesis of the most active Ru-based metathesis catalysts remains challenging, however, and there is continued interest in new and improved routes to alkylidene installation as metathesis begins to see wide uptake in industry. The first part of this thesis focuses on developing new routes to known catalysts. Magnesium carbenoids are investigated as a potential alkylidene source, and in the process a novel route to benzylmagnesium carbenoids is developed. Initially promising results showing ca. 40% conversion to first generation metathesis catalysts failed to lead to a viable high-yield route to Ru-alkylidenes. A high yield route to RuCl2(H2IMes)(py)4 (previously reported in low yields as a decomposition product of the third-generation Grubbs’ metathesis catalyst) is developed and this complex is investigated as a precursor to indenylidene-based catalysts. Although RuCl2(H2IMes)(py)4 is shown to be substitutionally labile, indenylidene installation could not be achieved. Finally, zinc aryloxides are investigated as an alternative to thallium and silver reagents for the installation of aryloxide ligands. Initial results indicate that zinc aryloxides are kinetically, though not thermodynamically, competent for the installation of the challenging aryloxide C6F5O- on the second-generation Hoveyda catalyst. The second part of this thesis concerns progress towards the development of a new low-valent catalyst platform. Initial experiments involving treating the second-generation Hoveyda catalyst with various reducing agents fail to produce low-valent alkylidenes, leading instead to decomposition of alkylidene. Drawing inspiration from early transition metal systems, the remainder of the second part focuses on alpha-hydride elimination from a RuII alkyl as a means of accessing low-valent alkylidenes. To this end, a novel benzylruthenium complex as well as bis-benzyl and mono-aryloxide derivatives are developed. While attempts to induce benzyl-to-benzyl hydride abstraction or intramolecular deprotonation of the benzyl ligand failed to produce alkylidenes, ligand-induced benzyl-to-aryloxide hydride abstraction appears to be successful, leading to the observation of a broad 1H NMR signal in the region characteristic for low-valent Ru-alkylidenes.

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Gadolinium (Gd) is the basis of contrast media most used in magnetic resonance imaging (MRI). Because it is a very toxic metal ion, all Gd-based contrast media present chelating agents in their composition. Gd-based formulations are commercially available in concentrations of 1 and 0.5 mol L-1, which are almost exclusively excreted by the kidneys without producing toxic effects. In 2006, however, two European groups independently suggested a link between the administration of gadolinium chelates and the occurrence of nephrogenic systemic fibrosis (NSF) in patients with renal insufficiency. NSF is a serious disease, which origin is attributed to transmetalation reactions between Gd and endogenous metals. In this work, we used the techniques atomic absorption spectrometry, mass spectrometry with inductively coupled plasma and liquid chromatography with mass detector to investigate metals present as impurities and / or contaminants in five Gd-based contrast formulations and their possible transmetalation reactions. The results showed that several metals are present in the formulations, the rare earth elements (Sc, Y, La, Ce, Pr, Nd, Eu, Tb, Dy, Ho, Er and Tm) and others such as Al, As and Pb, notoriously toxic to humans. To evaluate transmetallation reactions the Gd-DTPA complex (gadopentetate dimeglumine) was used as template model. It was found that practically all elements present as contaminants in the formulation are able to replace Gd in the complex. Even endogenous metals such as Cu and Fe, which do not present any toxicological potential, may cause , due to transmetallation reations, free Gd3 + to be formed. / O gadolínio (Gd) é a base do meio de contraste mais utilizado em ressonância magnética (RM). Por se tratar de um íon metálico muito tóxico, todos os meios de contraste com Gd possuem agentes quelantes em sua composição. As formulações de Gd estão comercialmente disponíveis em concentrações de 0,5 e 1 mol L-1, sendo estas, quase exclusivamente, excretadas por via renal, sem produzir efeitos tóxicos. Porém, em 2006, dois grupos europeus independentes sugeriram uma relação entre a administração de complexos gadolínicos e a ocorrência de fibrose sistêmica nefrogênica (FSN) em pacientes com insuficiência renal. A FSN é uma doença grave, atribuída a reações de transmetalação do Gd de seus complexos por metais endógenos. Neste trabalho, utilizaram-se técnicas de espectrometria de absorção atômica, espectrometria de massa com plasma indutivamente acoplado e cromatografia líquida com detector de massa para investigar metais presentes como impurezas e/ou contaminantes em cinco formulações de contrastes a base de Gd e suas reações de transmetalação. Os resultados encontrados mostraram que outros metais, além do Gd, estão presentes nas formulações, os elementos terras-raras (Sc, Y, La, Ce, Pr, Nd, Eu, Tb, Dy, Ho, Er e Tm) e elementos como Al, As e Pb, sabidamente tóxicos para o ser humano. Para verificar a transmetalação, o complexo Gd-DTPA (Gadopentetato dimeglumina) foi utilizado como modelo e verificou-se que, praticamente, todos os elementos presentes como contaminantes nas formulações substituíram o Gd no complexo, ou seja, mesmo a presença de metais endógenos como Cu e Fe, que não apresentariam potencial toxicológico podem, através da transmetalação, levar à presença de Gd3+ livre.