Unspecific peroxygenase (EC 1.11.2.1) represents a group of secreted hemethiolate proteins that are capable of catalyzing the selective mono-oxygenation of diverse organic compounds using only H2O2 as a cosubstrate. In this study, the peroxygenase from Agrocybe aegerita (AaeUPO) was found to catalyze the hydroxylation of various linear (e.g n-hexane), branched (e.g. 2,3-dimethylbutane) and cyclic alkanes (e.g. cyclohexane). The size of n-alkane substrates converted by AaeUPO ranged from gaseous propane (C3) to n-hexadecane (C16). They were mono-hydroxylated mainly at the C2 and C3 position, rather than at the terminal carbon, and the corresponding ketones were formed as a result of overoxidation. In addition, a number of alkenes were epoxidized by AaeUPO, including linear terminal (e.g. 1-heptene), branched (2-methyl-2-butene) and cyclic alkenes (e.g. cyclopentene), as well as linear and cyclic dienes (buta-1,3-diene, cyclohexa-1,4-diene). Furthermore, the conversion of terminal alkynes (e.g. 1- octyne) gave the corresponding 1-alkyn-3-ol in low yield. Some of the reactions proceeded with complete regioselectivity and - in the case of linear alkanes, terminal linear alkenes and alkynes - with moderate to high stereoselectivity. The conversion of n-octane gave (R)-3-octanol with 99% enantiomeric excess (ee) and the preponderance of the (S)-enantiomer reached up to 72% ee of the epoxide product for the conversion of 1-heptene. Catalytic efficiencies (kcat/ Km) determined for the hydroxylation and respectively epoxidation of the model compounds cyclohexane and 2-methyl-2-butene were 2.0 × 103 M-1 s-1 and 2.5 × 105 M−1 s−1. The results obtained in the deuterium isotope effect experiment with semideuterated n-hexane and the radical clock experiment with norcarane clearly demonstrated that the hydroxylation of alkanes proceeds via hydrogen abstraction, the formation of a substrate radical and a subsequent oxygen rebound mechanism. Moreover, stopped-flow experiments and substrate kinetics proved the involvement of a porphyrin radical cation species (compound I; AaeUPO-I) as reactive intermediate in the catalytic cycle of AaeUPO, similar to other hemethiolate enzymes (e.g. cytochrome P450 monooxygenases, P450s). / Die Gruppe der Unspezifischen Peroxygenasen (EC 1.11.2.1) umfasst extrazelluläre Häm-Thiolat-Enzyme, die mittels H2O2 als Cosubstrat die selektive Monooxygenierung unterschiedlicher organischer Verbindungen katalysieren. In der vorliegenden Arbeit konnte gezeigt werden, dass die von Agrocybe aegerita sekretierte Peroxygenase (AaeUPO) verschiedene lineare (z. B. n-Hexan), verzweigte (z. B. 2,3-Dimethylbutan) und zyklische Alkane (z. B. Cyclohexan) hydroxyliert. Die Größe der von der AaeUPO umgesetzten Substrate reichte vom gasförmigen Propan (C3) bis hin zu n-Hexadekan (C16). Die Alkane wurden bevorzugt am zweiten und dritten Kohlenstoffatom (C2 und C3) hydroxyliert; eine Hydroxylierung am terminalen Kohlenstoff konnte nur vereinzelt und in geringem Umfang beobachtet werden. Die Überoxidationen der primär gebildeten, sekundären Alkohole führte außerdem zur Entstehung der entsprechenden Ketonderivate. Darüber hinaus wurde eine Vielzahl linearer terminaler (z. B. 1-Hepten), verzweigter (z. B. 2-Methyl-2-Buten) und zyklischer Alkene (z. B. Cyclopenten) sowie linearer und zyklischer Diene (1,3-Butadien, 1,4-Cyclohexadien) durch die AaeUPO epoxidiert. Die Umsetzung terminaler Alkine (z. B. 1-Octin) führte zur Entstehung der jeweiligen 1-Alkin-3-ole. Manche dieser Reaktionen verliefen ausgeprägt regioselektiv und, im Falle der linearen Alkane sowie der linearen terminalen Alkene und Alkine, mit mittlerer bis hoher Stereoselektivität. So ergab beispielsweise die Umsetzung von n-Octan einen Enantiomerenüberschuss größer 99% für (R)-3-Octanol; die Epoxidierung von 1-Hepten lieferte einen Enatiomeerenüberschuss (ee) von bis zu 72% für das (S)-Enantiomer. Die katalytischen Effizienzen, die für die Hydroxylierung bzw. Epoxidierung der Modellverbindungen Cyclohexan und 2-Methyl-2-Buten ermittelt wurden, betragen 2.0 × 103 M-1 s-1 und 2.5 × 105 M−1 s−1. Der ausgeprägte Deuterium-Isotopen-Effekt, der im Zuge der Umsetzung von semideuteriertem n-Hexan beobachtet wurde sowie die Ergebnisse des Radical-Clock-Experiments mit Norcarane als Substrat bestätigten, dass die Hydroxylierung von Alkanen über Wasserstoffabstraktion, die Bildung eines Substratradikals und anschließende direkte Sauerstoffrückbindung verläuft. Die Stopped-Flow-Experimente belegen zudem das Auftreten eines Porphyrin-Kationradikal-Intermediates (Compound I; AaeUPO-I) im katalytischen Zyklus der AaeUPO (vergleichbar mit dem reaktiven Intermediat der P450-Monooxygenasen).

La gran eficiència, selectivitat i les condicions suaus exhibides per les reaccions que tenen lloc al centre actiu de les metal·looxigenases són la font d'inspiració per la present dissertació. Amb l'objectiu de dissenyar catalitzadors d'oxidació eficients hem fet ús de dues estratègies: la primera consisteix en el disseny de complexos amb baix pes molecular inspirats en aspectes estructurals de la primera esfera de coordinació del centre metàl·lic d'enzims de ferro i de manganès. Aquests complexos s'han estudiat com a catalitzadors en l'oxidació selectiva d'alcans i d'alquens fent servir oxidants "verds" com ara l'H2O2. La segona estratègia està basada en l'ús de la química supramolecular per tal de desenvolupar estructures moleculars auto-acoblades amb la forma i les propietats químiques desitjades. Concretament, la construcció de nanocontenidors amb un catalitzador d'oxidació incrustat a la seva estructura ens permetria dur a terme reaccions més selectives, tal com passa en les reaccions catalitzades per enzims. / The high efficiency, selectivity and mild conditions exhibited by the reactions that take place in the active site of metallooxygenases are the source of inspiration of the present dissertation. With the aim of designing efficient oxidation catalysts, we make use of two different strategies: the first one is the design of low molecular weight complexes inspired by structural aspects of the first coordination sphere of the metal active site of non-heme iron and manganese enzymes. These complexes are studied as catalysts for the selective oxidation of alkanes and alkenes using green oxidants such as H2O2. The second strategy is based on the use of supramolecular chemistry to develop self-assembled molecular structures with desired shape and chemical properties. Particularly, the construction of cavity-containing 3D nanovessels with an oxidation catalyst embedded in their structures would allow us to perform more selective reactions, analogously to the reactions catalyzed by enzymes.

The major goals of this work were to: develop a new methodology for the preparation of site-isolated catalytic sites on a silica surface, prepare the first truly single-site supported metallocene/CGC polymerization catalyst, and develop structure-reactivity relationships for these new systems. To synthesize these novel catalysts, the approach taken was to develop a protocol which allows for the synthesis of an aminosilica material with isolated, uniform amine sites. This patterned aminosilica was then used as a scaffold to support a constrained geometry catalyst. These functionalizations occurred at essentially a quantitative level, in stark contrast to previous literature reports. The patterned catalysts were evaluated in the polymerization of ethylene and compared to densely loaded literature materials. Overall, it was found the patterned materials were 5-10 times more active than traditional immobilized CGC catalysts. The patterned catalysts were also found to be effective catalysts for the copolymerization of norbornenes (including functionalized norbornenes) and ethylene, the first reported use of a tethered CGC for the production of ethylene-norbornene copolymers. The control materials were inactive in these polymerizations, providing further evidence that the patterning protocol allows for the synthesis of unique highly active, isolated catalytic sites. Various structural components of the immobilized CGC developed in this work were tested for their impact on catalyst synthesis and reactivity in ethylene polymerizations. The results showed the patterned materials in general behaved according to the trends seen in homogeneous CGC polymerizations. These results, while congruent with similar homogeneous CGC studies, are in direct conflict with previous work on supported CGCs reported in the literature. This discrepancy is likely the result of the difference between the isolated, possibly single-site patterned catalysts developed in the course of this work and the multi-sited catalysts prepared by traditional supporting protocols. This also further illustrates the difficulty in developing structure-reactivity relationships when ill-defined solid catalysts are used.

Polyimide membranes containing nickel dithiolenes were investigated for the separation of propylene and propane. Permeation and sorption experiments were conducted as well thermal property analyses. Results indicate that the dithiolene has an antiplasticizing effect on the polymers studied. Upon addition of the dithiolene there is a subsequent reduction in the permeability coefficient and the permeability selectivity remains relatively unchanged. There is some evidence of increases in solubility selectivity, but a larger decrease in diffusivity selectivity results in a decrease in the permeability selectivity. Investigation of the thermal and mechanical properties of dithiolene-containing films indicates a reduction in fractional free volume as well as the glass transition temperature when compared to the pure polymer. There is also an increase in the modulus of the films upon addition of the dithiolene. The implications of these results and their correlation with antiplasticization are discussed.

Asymmetric synthesis with biocatalyst has become an increasingly interesting and cost effective manufacturing process in fine chemicals, pharmaceuticals, and agrochemical intermediates. Enoate reductases from the Old Yellow Enzyme family offer high substrate efficiency, region, stereo-, and enantioselectivity in the catalyzed biotransformations. Asymmetric reduction of activated C=C bond is one of the most widely applied synthetic tools for the potential to generate up to two stereogenic centers in one step reaction. The thesis contributed to the development and characterization of the Old Yellow Enzyme family members including NRSal from Salmonella typhimurium, YersER from Yersinia bercoviei, KYE1 from Kluyveromyces lactis, and XenA from Pseudomonas putida. We explored the possible new chemistry, gathered further understanding of enzymes functionality and biochemistry, evaluated parameters such as enzyme stability, productivity, and selectivity, and improved enzyme specificity through computational guided protein engineering method. In overall, the increasing knowledge about this Old Yellow Enzyme family together with recent advances in biotechnology renders the enoate reductases a tool of choice for industrial applications.

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Regiomeric mixture of HMe2Si(CH2)3(i-Bu)6Si7O9(OH)3 (6), containing a Si-H group in one of the ligands of the silsesquioxane, was tethered onto a vinyl terminated hyperbranched poly(siloxysilane) polymer via a hydrosilation reaction to generate extremely active catalysts, P1-8 and c-P1-8. The synthesis of 6, in good yield, was accomplished via hydrosilation of CH2=CHCH2(i-Bu)7Si8O12 (1) to generate ClMe2Si(CH2)3(i-Bu)7Si8O12 (3) followed by the reduction of 3 with LiAlH4 to afford HMe2Si(CH2)3(i-Bu)7Si8O12 (4) where the base-catalyzed excision of one framework silicon was employed to generate a regiomeric mixture of 6. [Ti(NMe2){Et3Si(CH2)3(i-Bu)6Si7O12}] (7), [Ti(NMe2){HMe2Si(CH2)3(i-Bu)6Si7O12}] (8), [Ti(NMe2){(i-C4H9)7Si7O12}] (9) and [Ti(NMe2){(c-C6H11)7Si7O12}] (10) were synthesized via protonolysis of Ti(NMe2)4 with one equivalent of the trisilanol precursor in order to determine if the presence of isomers would be intrinsically different as compared to the uniformly substituted catalysts. Isomers 8 and 9, demonstrated lower activity as compared to the uniformly substituted catalysts 9 and 10, however the isomers still exhibited extremely high catalytic activity for the epoxidation of 1-octene using tert-butyl hydroperoxide (TBHP) relative to titanium catalysts used in industry. Additionally, 9, 10, P1-8 and c-P1-8 were very selective catalysts for the epoxidation of various olefins such as terminal (1-octene), cyclic (cyclohexene or 1-methylcyclohexene), and more demanding olefins (limonene or α-pinene) employing TBHP as the oxidant. Furthermore, P1-8 and c-P1-8 were recyclable with minimal loss of titanium however the catalysts could also be repaired if a loss in activity was observed. Preliminary epoxidation reactions employing P1-8 and c-P1-8 along with hydrogen peroxide (H2O2) as the oxidant were also explored using different solvents. P1-8 degraded quickly due to the hydrolysis of the titanium from the large amount of water present in the reaction mixture however c-P1-8 showed activity for the epoxidation of cyclohexene. Finally, regiomeric mixture of Ti(NMe2)(HS(CH2)3)(i-C4H9)6Si7O12) (13), was tethered onto gold nanoparticles for the conversion of propene to propylene oxide using molecular hydrogen and oxygen. While the catalysts showed low activity under our reaction conditions, numerous improvements can be investigated in order to improve upon the catalysts.

published_or_final_version / abstract / toc / Chemistry / Doctoral / Doctor of Philosophy

Alkenes are remarkably versatile motifs as they can be further functionalized by a vast array of addition, reduction, and oxidation reactions. Thus their efficient synthesis is highly desired. Over the past 35 years, the Suzuki-Miyaura cross-coupling reaction has emerged as a powerful synthetic tool for the formation of carbon-carbon bonds. Herein is described the development of a one-pot two-step protocol for the synthesis of (E)-alkenes comprising palladium-catalyzed Suzuki-Miyaura cross-coupling of aryl or heteroaryl halides, including chlorides, with alkenyl pinacolboronates, prepared in situ via solvent-free zirconium-catalyzed hydroboration of terminal alkynes. Avoiding isolation of intermediates saves time and reduces waste. The regio- and stereochemistry of the alkene is set by initial hydrozirconation of the alkyne. Addition of water to the second step deactivates the zirconocene catalyst, which is otherwise deleterious to cross-coupling. Thus this sequence exploits the water tolerance of the Suzuki-Miyaura reaction.