by Diao, Zhenyu = 模板辅助下制备有生物形态的MoO₃化合物以及它对降解甲基紫的催化作用 / 刁振玉. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Abstracts in English and Chinese. / by Diao, Zhenyu = Mo ban fu zhu xia zhi bei you sheng wu xing tai de MoO₃ hua he wu yi ji ta dui jiang jie jia ji zi de cui hua zuo yong / Diao Zhenyu. / Abstract --- p.I / 摘要 --- p.II / Acknowledgement --- p.III / Table of contents --- p.IV / List of figures --- p.VII / List of tables --- p.X / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Biomorphic materials --- p.1 / Chapter 1.2 --- Semiconductor catalysts --- p.2 / Chapter 1.3 --- Methyl violet --- p.3 / Chapter 1.4 --- Photocatalysis --- p.4 / Chapter 1.5 --- Synthesis of biomorphic catalysts --- p.8 / Chapter 1.6 --- Objectives and thesis layout --- p.10 / References / Chapter Chapter 2 --- Methodology and Instrumentation --- p.17 / Chapter 2.1 --- Sample preparation --- p.17 / Chapter 2.1.1 --- Synthesis --- p.17 / Chapter 2.1.2 --- Paper templates and precursors --- p.18 / Chapter 2.2 --- Characterization --- p.18 / Chapter 2.2.1 --- Scanning electron microscope (SEM) --- p.18 / Chapter 2.2.2 --- X-ray powder diffractometry (XRD) --- p.20 / Chapter 2.2.3 --- Fourier transform infrared (FTIR) spectroscopy --- p.21 / Chapter 2.2.4 --- Differential thermal analysis (DTA) --- p.23 / Chapter 2.2.5 --- Thermogravimetric analysis (TGA) --- p.24 / Chapter 2.2.6 --- Ultraviolet-Visible spectroscopy (UV-Vis) --- p.24 / Chapter 2.3 --- Catalytic performance --- p.26 / References --- p.26 / Chapter Chapter 3 --- Results Introduction --- p.30 / Chapter 3.1 --- Paper template --- p.31 / Chapter 3.1.1 --- Thermal properties --- p.31 / Chapter 3.1.2 --- Composition of paper template --- p.32 / Chapter 3.1.3 --- Morphology of paper --- p.35 / Chapter 3.2 --- Chemical precursors --- p.40 / Chapter 3.3 --- Infiltrated paper templates --- p.43 / Chapter 3.4 --- Biomorphic products --- p.46 / Chapter 3.4.1. --- Influence of annealing temperature --- p.46 / Chapter 3.4.1.1 --- Phase and composition --- p.46 / Chapter 3.4.1.2. --- Surface morphology --- p.48 / Chapter 3.4.2 --- Effects of annealing durations --- p.50 / Chapter 3.4.2.1 --- Phase and composition --- p.50 / Chapter 3.4.2.2 --- Surface morphology --- p.54 / Chapter 3.5 --- Formation mechanism --- p.56 / References --- p.57 / Chapter Chapter 4 --- Catalytic performance Introduction --- p.59 / Chapter 4.1 --- Degradation of MV under visible light --- p.60 / Chapter 4-2 --- Effects of the UV irradiation on MV --- p.64 / Chapter 4-3 --- Degradation of MV dye using M0O3 under UV light --- p.65 / Chapter 4.4 --- Mechanism of photocatalysis --- p.69 / References --- p.70 / Chapter Chapter 5 --- Conclusions and future work --- p.72 / Chapter 5.1 --- Conclusions --- p.72 / Chapter 5.2 --- Future work --- p.73 / References --- p.74

Conventional ligand design in transition metal catalysis capitalizes on the ability of phosphorous, nitrogen, carbon, oxygen, and sulfur-based donors to modify the steric and electronic properties of a reactive metal center. Heterobimetallic transition metal complexes that contain a dative metal-metal bond provide a unique approach to ligand design where the reactivity of the metal center can be modified by metal-metal electronic communication. Our laboratory is interested in using the unique properties of heterobimetallic complexes to address significant limitations in current transition metal catalysis. My PhD work has focused on the ability of early/late transition metal heterobimetallic complexes to facilitate catalysis by speeding up reductive processes that occur at the late transition metal center. My initial studies were aimed at understanding the importance of the metal-metal interaction to catalysis in allylic amination reactions catalyzed by Pd–Ti heterobimetallic complexes and the potential of these catalysts to enable reactivity with challenging nitrogen nucleophiles. We also explored the substrate scope of the allylic amination with a variety of hindered amines and allylic chloride substrates under mild conditions. Aminations of this type have previously been shown to require harsh reaction conditions and tend to give low yields. A variety of sterically hindered secondary amine nucleophiles were able to readily undergo allylic substitution. Many of these aminations were complete within ten minutes. A series of allylic electrophiles were also shown to undergo the reaction. We have also looked at the ability of hindered amines to undergo intramolecular cyclizations to produce pyrrolidine and piperidine products. My continuing efforts in the laboratory are focused on developing chiral titanium-phosphinoamide ligands for enantioselective heterobimetallic catalysis. We have synthesized a series of chiral diamine-based phosphinoamide-titanium ligands in order to investigate enantioselective intramolecular aminations. Importantly, each of these new Ti-ligands enables room temperature catalysis in intramolecular aminations with hindered amines, suggesting contributions by the Ti center. Similar reactivity has not been achieved with monometallic chiral Pd catalysts in our lab. Importantly, many of these ligands enable modest enantioselectivity in the allylic aminations.

No description available.

High-valent metal-oxo complexes are vital as active oxidants in enzymatic and synthetic catalytic oxidations. Inspired by the ubiquitous cytochrome P450 enzyme, researchers have explored the power of metalloporphyrins to mimic one of Nature’s premier catalytic entities. In this work, four manganese(III)porphyrin systems, including three electronwithdrawing ligands and one electron-donating ligand, were investigated with regard to their ability to form high-valent manganese(IV)-oxo porphyrin systems. The porphyrin ligands studied were 5,10,15,20-tetra(2,6-difluorophenyl)porphyrin [H2(2,6-F2TPP)], 5,10,15,20-tetra(4-trifluoromethylphenyl)porphyrin [H2(4-CF3TPP)], 5,10,15,20-tetra(4- fluorophenyl)porphyrin [H2(4-FTPP)], and 5,10,15,20-tetra(2,6- dimethoxyphenyl)porphyrin [H2(TDMPP)]. All were synthesized purified and characterized spectroscopically. Using the mild oxidant iodobenzene diacetate, manganese(IV)-oxo porphyrins [MnIV(Por)O] were successfully generated in all systems as confirmed through spectroscopic methods. Meanwhile, a new photochemical approach was explored for its efficacy in producing the MnIV-oxo complexes by visible light irradiation of manganese(III) precursors containing the photolabile chlorate as the axial ligand. More importantly, the MnIV-oxo complexes obtained by chemical generation were tested for their abilities as oxygen atom transfer agents (OATs) with aryl alkenes, alkenes and thioanisoles in CH3CN. The apparent second-order rate constants for sulfoxidation ranged between (2.29 ± 0.08) and (12.9 ± 2.0) M-1s-1 x 10-2 which were, on average, a magnitude larger than the rates for epoxidation of the aryl alkenes. Most notably in reactions with substrate, the order of reactivity of [MnIV(Por)O] was [(4-F)TPP] > [(4- CF3)TPP] > [(2,6-F2)TPP], which is inverted from the expected result based on the electron-demands of the porphyrin ligands. The apparent rate constants for reaction with cyclohexene was found to be 1 to 2 orders of magnitude larger than those with sulfide substrates. The kinetic results are consistent with a reaction model involving disproportionation of MnIV(Por)O to give MnIII(Por) and MnV(Por)O species, the latter of the two being the active oxidant. Alternatively, the results from the sulfoxidations are consistent in part with a direct oxygen atom transfer by [MnIV(Por)O]

In humans and most eukaryotes, thymidylate synthase (TSase) serves as a key enzyme that catalyzes the reductive methylation of deoxyuridine monophosphate (dUMP) to synthesize deoxythymidine monophosphate (dTMP), a key component of DNA. The N5, N10- methylene-5,6,7,8-tetrahydrofolate (MTHF) serves as both the methylene donor and the hydride donor while generating dihydrofolate (H2folate) as the byproduct. However, in 2002, Myllykallio reported the discovery of flavin-dependent thymidylate synthase (FDTS) that also functions to maintain the dTMP pool, although the mechanism is different. Since then, considerable progress was made in characterizing this enzyme. It was found that structurally FDTS is substantially different from TSase both with respect to structure and with respect to the mechanistic pathway of catalysis. In the FDTS-catalyzed methylation of dUMP, MTHF serves only as the methylene donor, generating tetrahydrofolate (H4folate), unlike TSase, and FDTS utilizes NADPH as a reductant. Activity of the enzyme depends on the presence of the noncovalently bound prosthetic group, flavin adenine dinucleotide (FAD). Interestingly, the enzyme FDTS is present in several human pathogens that cause diseases including syphilis, tuberculosis, anthrax poisoning, typhus, botulism, peptic ulcers and more, but is absent in humans; thus, it poses an attractive target for antibiotics. In the modern world, antibiotic resistance is a menace; consequently, new targets for new antibiotics are being sought. Hence, elucidating the chemical mechanism of FDTS is of paramount interest, as we and others believe this could allow for rational design of drugs that selectively target these pathogens with minimal human toxicity. Although several chemical mechanisms for FDTS catalysis have been put forward, complete understanding has still not been achieved. One of the primary concerns was the role of FAD in catalysis, and we found – as described in Chapter II and III – that FAD is a methylene carrier rather than just a hydride donor, as previously postulated. Secondly, all mechanisms proposed so far predict the presence of a noncovalently bound putative exocyclic methylene intermediate (an isomer of dTMP) occurring in the catalytic pathway of FDTS. However, direct evidence to prove its existence was lacking. Recently, we have been able to synthesize this intermediate, as described in Chapter IV. As shown in Chapter V and VI, we used steady-state kinetics, isotopic substitution and NMR studies to test this intermediate with FDTS. We believe our findings will greatly improve the understanding of this enzyme and will impact drug design by government agencies, pharmaceutical companies, and academic laboratories.

The relationship between enzyme dynamics and enzymatic catalysis has become a central topic in modern enzymology, and studies in this area promise to enrich our current understanding of catalysis in biological systems. Escherichia coli dihydrofolate reductase (EcDHFR) has been a frequent subject of study in the context of protein dynamics, due to its small size, biological ubiquity, and the fact that its structural, kinetic and mechanistic characteristics are well established. Intrinsic kinetic isotope effects (KIEs) have proven to be highly sensitive probes of the role of dynamics in EcDHFR catalyzed reaction, as they circumvent the kinetic complexity of the enzyme-catalyzed reactions, and extract information directly pertaining to the chemical step. Previously, studies of their temperature-dependence were used to probe the effect of mutations at residues distant from the active site upon the hydride-transfer reaction catalyzed by EcDHFR. The results of these experiments supported the presence of a network of residues that were dynamically linked to the hydride-transfer step, and were in excellent agreement with computational studies predicting the presence of such a network. This thesis aims to extend upon these results to study the nature and extent of the dynamic network in EcDHFR, both by using an established experimental methods and by developing new biophysical probes of protein dynamics in this system. The major experimental methodology utilized in the following chapters is the determination and analysis of KIEs in a variety of EcDHFR mutants. To facilitate these measurements, new synthetic routes to a range of isotopically labeled nicotinamide cofactors have been developed. Some of the labeled materials have been used to establish a sensitive, triple-isotope technique to competitively measure deuterium isotope effects in enzyme-catalyzed reactions in EcDHFR. Synthesized materials were usd to measure the temperature dependence of intrinsic KIEs in selected dynamically altered mutants of EcDHFR, viz. W133F and F125M DHFR. Crystal structures have been obtained for both these mutants as well as for the previously studied G121V isozyme, and the combination of kinetic and structural information discussed in the context of catalytically important dynamic fluctuations in EcDHFR. Pressure-dependence of deuterium KIEs is also developed as a tool to probe the role of dynamics and tunneling in the EcDHFR reaction, with the ultimate aim of establishing high-pressure KIE measurements as a complementary method to variable temperature measurements. Finally, molecular recognition force spectroscopy (MRFS) measurements of an EcDHFR self-assembled monolayer (SAM) on gold are described. The surprisingly active enzymatic SAM has been shown to be a promising platform for future MRFS experiments to measure the forces involved in EcDHFR dynamics. All together, these studies advanced our ability to study the role of enzyme dynamics and quantum tunneling in enhancing their chemistry.

This dissertation mainly contains two parts: one is C-X (C, O, S) bond formation through gold(I) catalysis, one is new applications via gold(I/III) redox catalysis. In first part, gold(I) catalysts would be introduced and their general applications, then the TA-Au species will be emphasized including the design, synthesis, characters and their application in catalysis. The applications are well developed during the past decade in our group, but here only involves three examples regarding C-C, C-O and C-S bond formations. From these effective applications, the unique stability and reactivity of TA-Au will be studied and explained, which is the reason and value of TA-Au discovery. In second part, gold(I/III) redox catalysis will be presented through two application examples: cross-coupling of terminal alkynes, multiple bond di-functionalization. The most challenging part for coupling reactions is the competition between homo-coupling and cross-coupling products, while in our project, we have successfully developed a new method to selectively obtain cross-coupling as major product to homo-coupling product (ratio 12:1). Later on, we found a new method to achieve gold (I/III) redox cycle by using mild oxidant diazonium salt instead of PIDA or Selectfluor strong oxidant. The new mild and efficient method have largely extended the application of gold(I/III) redox catalysis into organic synthesis. In sum, the new gold catalysts and catalysis methods reported here are important to the development of gold catalysis field, which are critical and useful to help people understand the reason of applying noble gold species as catalysts, and the advantages that other metals do not have.

Medium-sized organic ring synthesis poses a seemingly insurmountable challenge, and because of this it is a field under immense investigation. Heterocyclic containing medium-sized rings are common structural motifs in nature, which has caused researchers to investigate their potential biological activity and properties as materials. This research focused on the grand challenge of medium-sized heterocyclic ring synthesis, providing the synthesis community with new tools to generate these highly evasive products, while elucidating energetic and geometric properties of one of Nature's least understood organic ring systems. Cobalt(II)-Amidoporphyrins, [Co(D2-Por)], are an emerging class of metalloradical catalysts (MRC) which can facilitate a wide range of atom and group transfer reactions. A strategy was employed using [Co(D2-Por)] to carry out an intramolecular C-H amination reaction using sulfamoyl azides as the radical nitrene source to aminate the highly reactive aldehydic C-H bond. This newfound reaction allowed for the generation of previously unobtainable medium-sized heterocycles, which surprisingly provided a racemic mixture of chiral medium-sized rings. A wide array of chiral amidoporphyrins including meso-heteroatom containing porphyrins were synthesized as well during the course of research to probe their potential as new chiral ligands for the emerging field of cobalt(II)-amidoporphyrin catalyzed MRC system. A practical synthetic scheme was discovered employing the highly selective Zn(II)-bromoporphyrin synthon to generate a new library of chiral amidoporphyrin ligands for the MRC system through well-established cross-coupling methodologies.

The oxidation of 4-t-butyltoluene in glacial acetic acid by hydrogen peroxid in a process catalysed by cobalt(II) acetate tetrahydrate and sodium bromide has been studied with the aim of increasing the selectivity towards 4-t-butylbenzaldehyde.

In order to clarify the role that water plays in the photocatalytic process, changes in the IR and Raman spectra of P25 TiO₂ thin films were observed upon exposure to liquid water. Further investigation of these spectral changes via dehydration of thin films under nitrogen and oxygen of different humidities led to the observation of spectroscopic features that have been assigned to localised surface phonon modes. When the effect of UV irradiation on these features was investigated, a broad IR absorption due to transitions of electrons in shallow traps was detected under dry nitrogen but not under dry oxygen. Further investigation of the photocatalytic properties of P25 TiO₂ showed a complete removal of a stearic acid film. The final products have been tentatively assigned to a mixture of short chain carbonyl species and adsorbed carbonates as well as carbon dioxide and water. The IR spectrum of the fuel cell membrane material Nafion is complex and literature data varies in some of the assignments. The compound perfluoro(2-ethoxyethane)sulfonic acid was used as a model compound for the Nafion side chain resulting in a clearer assignment of the Nafion IR spectrum. In light of these new assignments changes induced in the region 1100-1300 cm⁻� by variation in humidity and ion exchange have been shown to be mainly the result of changes in the sulfonate asymmetric stretching modes. By flowing a series of solutions containing tetramethylammonium ions and perchlorate ions the surface charge characteristics of a Pt black film were determined in the pH range 2-12. There proved to be a weak positive charge below pH 4 and a weak negative charge above pH 9. Between these points there appeared to be no overall charge on the surface. When perfluoro(2-ethoxyethane)sulfonic acid was adsorbed to a Pt black film changes in its IR spectrum indicated a strong binding via interactions between the sulfonate groups and the Pt surface. The nature of the adsorption of Nafion was less clear cut and, whilst adsorption is strong, it seems possible that hydrophobic interactions between the Nafion backbone and the surface are involved.