In this work, a methodology for the synthesis of silica-cobalt oxide-based composites was developed by modifying the well known Stöber sol-gel method. The main novelty of the procedure was the use of colloidal suspensions of cobalt oxide or cobalt hydroxide nanoparticles (Co3O4,Co(OH)2), which were previously prepared from the precipitation of Co2+ ions in alkaline medium. The silica-cobalt composites having cobalt contents (w/w) around 8.4 to 11% were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG/DTA), temperature programmed reduction (TPR) and adsorption /desorption of nitrogen. The characteristics of the composites which were prepared by employing the colloidal suspensions were compared to those exhibited by other composites which were obtained from cobalt nitrate solution. The influence of cerium nitrate and citric acid was also evaluated. The methodology employed in the synthesis of nanoparticles and composites were reproducible and the prepared materials showed surface areas (300 to 567 cm3/g) and pore diameters (3.8 to 8.1 nm) values which were considered appropriate to use them as catalysts. The calcined composites which were prepared using colloidal suspensions of Co3O4 nanoparticles showed TPR curves with maximum picks at relatively low temperatures, in the range of 275 to 520 oC, suggesting the existence of weak silica-cobalt interactions. The average diameter of Co3O4 crystallites varied from 22 to 30 nm. However, the use of citric acid as a pore-forming agent in the sol-gel synthesis led to composites with enhanced silica-cobalt interactions as a result of the dissolution of the cobalt oxide particles and formation of cobalt silicate. The incorporation of cerium nitrate in the sol-gel mixture did not modify the textural properties of the composites but the reduction of cobalt oxide to metallic cobalt was retarded. The composite which was obtained from the cobalt hydroxide, β-Co(OH)2, colloidal suspension showed weak silica-cobalt interactions as well as intermediate ones, the average diameter of Co3O4 crystallites being 12 nm. Differently from the composites obtained from colloidal suspensions, those which were synthesized using a cobalt nitrate aqueous solution presented mainly cobalt silicate and a low quantity of Co3O4 particles of 11 and 17 nm. The TPR curves of these composites indicated very strong silica-cobalt interactions, as expected. The composites were evaluated as catalysts in the reduction reaction of NO to N2 with the oxidation of CO to CO2. The composites which were prepared from Co3O4 colloidal suspensions without the use of citric acid as pore-forming agent showed maximum conversions as high as 90% for both NO to N2 and CO to CO2, at temperatures above 600°C. On the other hand, the composite prepared using critic acid showed much lower conversions (60 %) at the same temperature.

Tetravalent metal phosphates and phosphonates form highly insoluble inorganic polymers and can act as good catalysts in some oxidative reactions. In the present work, zirconium phosphate amorphous (ZrPA), scandium exchanged zirconium phosphate amorphous (ScZrPA), sodium exchanged zirconium phosphate amorphous (NaZrPA), potassium exchanged zirconium phosphate amorphous (KZrPA), zirconium phenylphosphonate amorphous (ZrPPA) and zirconium phenylphosphonate phosphate amorphous (ZrPA/ZrPPA), were prepared and evaluated as catalysts for the oxidation of 3,7,7-trimethylbicyclo[4.1.0]hept-3-ene [(+)-3-carene)] by hydrogen peroxide, in different solvents. It was found that the oxidation reaction of (+)-3-carene yielded three major products, namely alpha-3,4-epoxycarane, carane-3 beta,4 alpha-diol and 3 beta-acetoxycaran-4 alpha-ol, depending on the catalyst and solvent conditions. No beta-3,4-epoxycarane was detected in the studied conditions. (C) 2008 Elsevier B.V. All rights reserved.

Tetravalent metal phosphates form highly insoluble inorganic polymers and act as catalysts in some oxidative reactions. In the present work, a-amorphous zirconium, tin, titanium, zirconium tungstate (acidic and basic form), crystalline vanadyl, fibrous crystalline cerium and pellicular zirconium phosphates, were prepared and evaluated as catalysts, for the hydroxylation of phenol and 2-naphthol by hydrogen peroxide, in acetic acid. Oxidation of phenol yielded hydroquinone, catechol, cis,cis-muconic and cis,trans-muconic acids, depending on the catalyst. All oxidations of 2-naphthol produced 4-(2-hydroxy-1-naphthyl)-1,2-naphthoquinone but reaction with crystalline vanadyl phosphate also resulted in the formation of 1,1'-bi(2-naphthol). (C) 2002 Elsevier Science B.V. All rights reserved.

The SARS-CoV-2/Covid-19 pandemic emerged in 2019 and has been the cause of millions of deaths worldwide. The lack of established therapies and treatment guidelines, and its rapid transmission posed an enormous challenge to healthcare institutions. Nevertheless, new advanced nucleic acid therapies emerged, which placed directed target therapeutics as a powerful tool for its treatment and for future viral diseases.Ribonucleic acid (RNA) has been pointed out as the primary genetic molecule before the outcome of deoxyribonucleic acid (DNA)-based organisms. Due to the key functions of RNA, namely inhibition of gene expression, coding of proteins, and protein targeting, RNA has gathered interest as a potential therapeutic tool. Going back in time, polymers of N-(2-aminoethyl)glycine have been suggested as possible backbones for peptide nucleic acids (PNA) that may have facilitated the transmission of genetic information in the pre-RNA world. These moieties are promising therapeutics as they can bind in a sequence-specific manner to disease-causing genes, down-regulating their expression by interfering with RNA-(post)transcriptional activity. They bind to nucleic acids (both DNA and RNA) more effectively than natural nucleic acids given the lack of charged phosphate groups in their backbone that confers a state of no-electrostatic repulsion. Nevertheless, successful cell delivery of nucleic acids remains an issue, and conjugation with delivery peptides seems to be a promising approach to overcome it.Current chemical methods to ligate peptides rely on Solid-Phase Peptide Synthesis (SPPS), which involves several protection and deprotection steps and has a chain length limit of about 30-40 residues. Thus, for more complex structures, chemoenzymatic methods are used, e.g., the of use hydrolases and transpeptidases. However, those rely on previous chemical modifications adding recognition sequences to the N- and C-terminal regions, allowing attachment by the formation of an acyl-enzyme intermediate and their resolution by an incoming amine. Additionally, increasing the chain length will lead to an increase in impurities and difficulty isolating the product. Thus, we worked on developing enzymes to obtain conjugates of bioinformatically produced PNA sequences with machine learning-designed intracellular delivery peptides, by applying Molecular Dynamics (MD) simulations to study and optimize the structure of the conjugate and later Quantum Mechanics/Molecular Mechanics (QM/MM) Metadynamics to obtain the ligation profiles required for enzyme design.

It is shown how the strong interaction dynamics of a multi-quark Lagrangian affects the catalysis of dynamical symmetry breaking by a constant magnetic field in (3+1) dimensions. Attention is drawn to the local minima structure of the theory.

A sustentabilidade tem sido alvo de preocupação e interesse crescente na nossa sociedade. O desenvolvimento sustentável, introduzido em 1987, é definido como a capacidade de satisfazer as necessidades do presente, sem comprometer a capacidade das gerações futuras de satisfazer as suas próprias necessidades. A química tem um papel fundamental na inovação sustentável. Nesse sentido surgiu a química verde, a invenção, desenvolvimento e aplicação de produtos químicos e processos, para reduzir ou eliminar o uso e a formação de substâncias perigosas. A procura da inovação sustentável levou os químicos orgânicos a considerarem métodos versáteis e eficazes para promover reações químicas e desenvolver novos produtos. A irradiação micro-ondas, a ativação mecânica e a irradiação ultrassom, entre outras vantagens, permitem uma diminuição do tempo de reação, do solvente e reações mais seletivas. Isto, aliado ao desenvolvimento de processos catalíticos mais eficazes, constitui a base para o desenvolvimento sustentável de processos e produtos químicos.O objetivo principal deste estudo é desenvolver processos sustentáveis de preparação de catalisadores derivados de N-heterocíclos (porfirinas, C-escorpionatos e carbenos N-heterocíclicos), com o intuito de, numa estratégia bottom-up, tornar as reações catalíticas em que se utilizam mais sustentáveis. O estudo e desenvolvimento de novos procedimentos para a síntese de macrociclos tetrapirrólicos constitui a primeira parte do trabalho descrito nesta dissertação. O processo desenvolvido para a síntese de porfirinas em dois passos sob ação mecânica, permitiu a redução dos tempos de reação para apenas uma hora e a substituição de oxidantes e solventes nocivos por opções ambientalmente mais adequadas. A síntese de di-hidroporfirinas, por hidrogenação de porfirinas utilizando como agente redutor diimida, gerada in situ a partir de hidrato de hidrazina sob ação mecânica, permitiu obter estes compostos com elevado rendimento e sustentabilidade, evidenciado pelos valores das métricas de química verde calculados para este processo. As metaloporfirinas destacam-se pela sua aplicação como catalisadores em diversos tipos de reações químicas. Neste contexto, foram desenvolvidas duas metodologias sintéticas para obtenção de metaloporfirinas. A metodologia para a síntese de metaloporfirinas hidrofóbicas permite a preparação destes compostos a partir apenas da porfirina e do sal metálico correspondente com elevado rendimento. O método para a síntese de metaloporfirinas com caráter hidrofílico, permite obter estes compostos utilizando quantidades estequiométricas das correspondentes porfirinas e do sal metálico em 1 mL de água sob irradiação ultrassom. Ambos os processos apresentam um considerável aumento da sustentabilidade, quantificada através do cálculo da economia atómica, Fator E e EcoScale, quando comparados com métodos previamente descritos.Na segunda parte desta dissertação apresenta-se a síntese de uma nova família de C-escorpionatos, o desenvolvimento da metodologia de preparação do pró-ligando, do catalisador e a sua aplicação na reação de ciclo-adição azida-alcino catalisada por cobre sob ação mecânica. Os C-escorpionatos com um grupo oxima no carbono metínico foram obtidos por reação de nitroso-alcenos, gerados in situ a partir de α-halogenooximas com pirazoles sob ação mecânica, na ausência de solvente. Estes foram complexados com quantidades estequiométricas de sal metálico sob ação mecânica sem solvente. Os C-escorpionatos de cobre(II) assim obtidos foram utilizados como catalisadores na reação de ciclo-adição azida-alcino. Esta reação, ícone da click chemistry, foi realizada sob ação mecânica, sem solvente, tendo-se obtido melhores rendimentos na síntese de triazoles com o C-escorpionato derivado do [(1-hidroximino)metil]tris(1H-pirazol-1-il)metano. O processo global, desde a síntese do pró-ligando até à reação de ciclo-adição é realizado na ausência de solvente e, sempre que possível, sem excesso de reagentes, formando-se produtos secundários com baixo peso molecular, tal como o brometo de sódio, características que vão ao encontro dos ideais da química verde, o que se evidencia nos valores das métricas de sustentabilidade obtidos.Na última parte é apresentada a síntese de diversos carbenos N-heterocíclicos simétricos e assimétricos e os estudos exploratórios da síntese de complexos de manganês. Foi desenvolvida a síntese de carbenos N-heterocíclicos sem solvente com parâmetros de sustentabilidade otimizados. A síntese de carbenos N-heterocíclicos assimétricos, muito menos explorados como pró-ligandos, foi conseguida utilizando os correspondentes imidazoles N-substituídos numa estratégia sem solvente sob irradiação de ultrassons. Apesar dos moderados rendimentos obtidos, a metodologia aumenta a disponibilidade destes ligandos para a preparação de novos catalisadores.

A biomassa é a fonte de carbono mais abundante do planeta e a partir dela podemser obtidos compostos orgânicos de elevado valor em síntese química. O furano e seusderivados, nomeadamente o 2-metilfurano, são exemplos de blocos de construção quepermitem sintetizar compostos com aplicabilidade em farmácia, química dos materiais eem fotoquímica. Devido à problemática ambiental dos nossos dias, e pelo facto de abiomassa ser uma fonte de matéria-prima renovável, é cada vez mais importantedesenvolver sínteses e metodologias que permitam obter, de forma sustentável,compostos derivados do furano de elevada diversidade estrutural.O propósito deste trabalho foi utilizar o 2-metilfurano como reagente de partidade uma reação multicomponente promovida por ação mecânica – mecanoquímica. Areação ocorre entre uma dicetona (pentan-2,4-diona), um alcino (2-octinal) e o derivadode furano que, num único passo, permite obter um composto híbrido de furano e dieno.Estudou-se o efeito que diferentes catalisadores de zinco, nomeadamente sais de zinco(ZnX2, X= Cl, Br, I) e complexos C-escorpionatos correspondentes, apresentavam noresultado da reação. Após 2 horas no moinho de bolas vibracional, observou-se que ocatalisador tinha uma forte influência não só no rendimento (32-59%), mas também nasdiferentes relações de isómeros que se obtinham. Os escorpionatos deram origem arendimentos mais baixos relativamente aos sais do mesmo metal e observou-se que estetipo de catalisadores se degradava aquando da reação. Utilizando o acetato de zinco e oescorpionato análogo, obteve-se apenas o produto da condensação de Knoevenagel entreo 2-octinal e a dicetona.Para além da avaliação da sustentabilidade da nova metodologia através dasmétricas da Química Verde, realizou-se um estudo preliminar da influência dosparâmetros inerentes ao ball milling no rendimento da reação. Concluiu-se que, de entrea massa, volume, número, área de superfície, entre outros, a massa total e o número dasbolas colocadas dentro do jarro, são as variáveis com maior importância e que apresentampotencial para a otimização das condições de reação.

Particle-resolved direct numerical simulation (PR-DNS) is known to provide an accurate detailed insight into the local flow phenomena in static particle arrays. Most PR-DNS studies in literature do not account for reactions taking place inside the porous particles. In this study, PR-DNS is performed for catalytic reactions inside the particles using the multifluid approach where all heat and mass transfer phenomena are directly resolved both inside and outside the particles. These simulation results are then used to verify existing 1D model closures from literature over a number of different reaction parameters including different reaction orders, multiple reactions and reactants, interacting reactions, and reactions involving gas volume generation/consumption inside the particle. Results clearly showed that several modifications to existing 1D model closures are required to reproduce PR-DNS results. The resulting enhanced 1D model was then used to accurately simulate steam methane reforming, which includes all of the aforementioned reaction complexities. The effect of multiple reactants was found to be the most influential in this case.

Multicomponent reactions (MCRs) are a valuable tool in diversity-oriented synthesis. Its application to privileged structures is gaining relevance in the fields of organic and medicinal chemistry. Isatin, due to its unique reactivity, can undergo different MCRs, affording multiple interesting scaffolds, namely oxindole-derivatives (including spirooxindoles, bis-oxindoles and 3,3-disubstituted oxindoles) and even, under certain conditions, ring-opening reactions occur that leads to other heterocyclic compounds. Over the past few years, new methodologies have been described for the application of this important and easily available starting material in MCRs. In this review, we explore these novelties, displaying them according to the structure of the final products obtained.

Swinholides are 42-carbon ring polyketides with a 2-fold axis of symmetry. They are potent cytotoxins that disrupt the actin cytoskeleton. Swinholides were discovered from the marine sponge Theonella sp. and were long suspected to be produced by symbiotic bacteria. Misakinolide, a structural variant of swinholide, was recently demonstrated to be the product of a symbiotic heterotrophic proteobacterium. Here, we report the production of swinholide A by an axenic strain of the terrestrial cyanobacterium Nostoc sp. strain UHCC 0450. We located the 85-kb trans-AT polyketide synthase (PKS) swinholide biosynthesis gene cluster from a draft genome of Nostoc sp. UHCC 0450. The swinholide and misakinolide biosynthesis gene clusters share an almost identical order of catalytic domains, with 85% nucleotide sequence identity, and they group together in phylogenetic analysis. Our results resolve speculation around the true producer of swinholides and demonstrate that bacteria belonging to two distantly related phyla both produce structural variants of the same natural product. In addition, we described a biosynthesis cluster from Anabaena sp. strain UHCC 0451 for the synthesis of the cytotoxic and antifungal scytophycin. All of these biosynthesis gene clusters were closely related to each other and created a group of cytotoxic macrolide compounds produced by trans-AT PKSs of cyanobacteria and proteobacteria. © 2018 American Society for Microbiology.