Cheng, Yat Ho. / Thesis submitted in: October 2007. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgment --- p.iv / Contents --- p.v / Abbreviations --- p.xi / Chapter Chapter I. --- Model Studies for Catechol Dioxygenases / Chapter I.1 --- General Background / Chapter I.2 --- Intradiol-Cleaving Catechol Dioxygenases --- p.2-4 / Chapter I.3 --- Extradiol-Cleaving Catechol Dioxygenases --- p.5-8 / Chapter I.4 --- Selectivity of Intra- versus Extradiol-Cleaving Pathways --- p.8-10 / Chapter I.5 --- Early Studies on Model Complexes for Catechol Dioxygenases --- p.10-16 / Chapter I.6 --- Spin Crossover Study of Model Complexes --- p.16-18 / Chapter I.7 --- Model complexes for the Extradiol-Cleaving Dioxygenases --- p.19-23 / Chapter I.8 --- Objectives of this Work --- p.23 / Chapter I.9 --- References for Chapter I --- p.24-31 / Chapter Chapter II. --- "Synthesis and Reactivity Studies of Model Complexes of Catechol Dioxygenases Supported by the anionic Hydrotris-3,5-dimethylpyrazolylborate Ligand" / Chapter II.1 --- Introduction --- p.32-33 / Chapter II.2 --- Result and Discussion --- p.34-60 / Chapter II.2.1 --- Synthesis of Iron(III) Catecholate Complexes --- p.34-37 / Chapter II.2.2 --- Molecular Structures --- p.38-45 / Chapter II.2.3 --- Electrochemical Studies --- p.46-48 / Chapter II.2.4 --- UV-Vis Spectroscopic Studies --- p.49-55 / Chapter II.2.4.1 --- Oxygenation Studies of the Catecholate Complexes --- p.49-51 / Chapter II.2.4.2 --- Spectral Studies at low Temperature --- p.52-54 / Chapter II.2.4.3 --- Reactivity Studies with Excess Pyrazole --- p.54-55 / Chapter II.2.5 --- Identification of the degradation products --- p.56-60 / Chapter II.3 --- Summary --- p.61 / Chapter II.4 --- Experiments for Chapter II --- p.62-66 / Chapter II.4.1 --- Materials --- p.62 / Chapter II.4.2 --- Synthesis of complexes --- p.62-64 / Chapter II.4.3 --- Characterization of degradation products --- p.65-66 / Chapter II.5 --- References for Chapter II --- p.67-70 / Chapter Chapter III. --- "Synthesis and Reactivity Studies of Model Complexes of Catechol Dioxygenases Supported by the neutral Hydrotris-3,5-dimethylpyrazolylmethane Ligand" / Chapter III.1 --- Introduction --- p.71-72 / Chapter III.2 --- Results and Discussion --- p.73-96 / Chapter III.2.1 --- Synthesis --- p.73-78 / Chapter III.2.1.1 --- Synthesis of Iron(III)-Catecholate Complexes --- p.73-74 / Chapter III.2.2.2 --- Attempt to Synthesis Iron(III)-Catecholate Complexes with Pyrocatechol --- p.75-76 / Chapter III.2.2.3 --- Attempts to Remove the Chloride Ligand from the Iron(III) Catecholate Complexes --- p.76-77 / Chapter III.2.2.4 --- Synthesis of Iron(II)-Catecholate Complexes --- p.77-78 / Chapter III.2.2 --- Molecular Structures --- p.79-85 / Chapter III.2.3 --- Electrochemical Studies --- p.86-88 / Chapter III.2.4 --- UV-Vis Spectroscopic and Reactivity Studies on Oxygenation of / Chapter III.2.4.1 --- Oxygenation Studies of the Catecholate Complexes --- p.89-90 / Chapter III.2.4.2 --- Spectral changes with chloride removed from the catecholate complex --- p.91-93 / Chapter III.2.5 --- Identification of the degradation products --- p.94-96 / Chapter III.3 --- Summary --- p.96 / Chapter III.4 --- Experimental for Chapter III --- p.97-101 / Chapter III.4.1 --- Materials --- p.97 / Chapter III.4.2 --- Synthesis of complexes --- p.97-99 / Chapter III.4.3 --- Characterization of Oxygenation Products --- p.100 / Chapter III.5 --- References for Chapter III --- p.101-105 / Chapter Chapter IV. --- "Synthesis and Reactivity Studies of Manganese and Cobalt Catecholate Complexes Supported by the anionic Hydrotris-3,5-dimethyl -pyrazolylborate Ligand" / Chapter IV.1 --- Introduction --- p.106-109 / Chapter IV.2 --- Results and Discussion --- p.110-127 / Chapter IV.2.1 --- Synthesis of Manganese and Cobalt Catecholate Complexes --- p.110-111 / Chapter IV.2.2 --- Molecular Structures --- p.112-118 / Chapter IV.2.3 --- UV-Vis Spectroscopic Studies and Reactivity Studies --- p.119-124 / Chapter IV.2.3.1 --- Oxygenation studies of the Manganese(III)-Catecholate Complex --- p.119-121 / Chapter IV.2.3.1 --- Oxygenation studies of the Cobalt(II)-catecholate Comple --- p.x / Chapter IV.2.4 --- Identification of Degradation Products --- p.124-126 / Chapter IV.3 --- Summary --- p.126 / Chapter IV.4 --- Experimental for Chapter IV --- p.127-129 / Chapter IV.4.1 --- Materials --- p.127 / Chapter IV.4.2 --- Synthesis of complexes --- p.127-129 / Chapter IV.5 --- References for Chapter IV --- p.130-135 / Appendix I / Chapter A.I.1 --- General Procedure --- p.136 / Chapter A.I.2 --- Physical Characterization --- p.136-138 / Appendix II / Chapter A.II.1 --- "Selected Crystallographic Data for Compounds 1，2，4,5，7，9，14，15，16，17 and 18" --- p.142-147 / Chapter A.II.2 --- 1H and 13C NMR Spectra --- p.148-150 / Chapter A.II.3 --- Chromatogram and Mass spectra (El and Cl) from GCMS Analysis --- p.151-157 / Chapter A.II.4 --- Mass Spectra --- p.158-162

Arsenic is found in the environment in several oxidation states as well as in a variety of organoarsenic compounds. This situation puts additional demands on the analysis in that it is desirable to measure the amount of each species, not just all of the arsenic. The reason for this is that the different species have greatly different toxicities; of the major inorganic forms, As(III) is much more toxic than As(V). The goal of this research was to develop a convenient method for the analysis of mixtures of As(III) and As(V) at trace levels. Electroanalytical methods are inherently sensitive to oxidation states of elements and therefore are a natural choice for this problem. In fact, a method was developed some years ago for As(III) that used differential pulse polarography: the detection limit is 0.3 parts per billion (ppb). However, As(V) was not detected since in its usual form as an oxyanion it is electrochemically inactive. There are coordinate compounds formed with catechol, AsL(,n)(n = 1-3), that can be reduced at a mercury electrode, but the active species, AsL, is only a small fraction of the major species, AsL(,3), so the detection limit is only 500 ppb. Many details of the electrochemistry of this unusual compound were examined in this work. In order to improve detection limits, a method involving cathodic stripping was developed. It involves codeposition of copper with arsenic on a mercury electrode to effectively concentrate the analyte. Then the elemental arsenic is converted to arsine, AsH(,3), during a cathodic potential scan. The resulting current peak is proportional to As(III) in the absence of catechol and to the sum of As(III) and As(V) in the presence of catechol. It was observed that the current peak was considerably larger than expected and additional experiments revealed that there was evolution of hydrogen during the formation of arsine. This is rather unusual in electrochemical reactions and so some of the details of this catalyzed coreaction were examined. The result is a fortunate enhancement of detection limit so that As(v) at 40 ppb can be measured.

Graduation date: 1993

No / Scytalidium catalase is a homotetramer including heme d in each subunit. Its primary function is the dismutation of H2O2 to water and oxygen, but it is also able to oxidase various small organic compounds including catechol and phenol. The crystal structure of Scytalidium catalase reveals the presence of three linked channels providing access to the exterior like other catalases reported so far. The function of these channels has been extensively studied, revealing the possible routes for substrate flow and product release. In this report, we have focussed on the semi-conserved residue Val228, located near to the vinyl groups of the heme at the opening of the lateral channel. Its replacement with Ala, Ser, Gly, Cys, Phe and Ile were tested. We observed a significant decrease in catalytic efficiency in all mutants with the exception of a remarkable increase in oxidase activity when Val228 was mutated to either Ala, Gly or Ser. The reduced catalytic efficiencies are characterized in terms of the restriction of hydrogen peroxide as electron acceptor in the active centre resulting from the opening of lateral channel inlet by introducing the smaller side chain residues. On the other hand, the increased oxidase activity is explained by allowing the suitable electron donor to approach more closely to the heme. The crystal structures of V228C and V228I were determined at 1.41 and 1.47 Å resolution, respectively. The lateral channels of the V228C and V228I presented a broadly identical chain of arranged waters to that observed for wild-type enzyme.

A study of the anodic polarography of catechol in 0.100 F sodium perchlorate is presented. A new wave is observed in alkaline solutions which is different from the simple oxidation wave of catechol to ortho-quinone observed by previous workers. The importance of buffer materials is discussed and a possible explanation of the new wave is suggested. A study of the polarography behavior of Fe(II) and Fe(III) in the presence of catechol is reported. In the case of reduction of Fe(III) in the presence of catechol, two steps occur at about -1.5 and -1.8 volts (vs. SCE) at pH higher than 11.6 corresponding to one electron reduction of Fe(III) to Fe(II) and successive two electron reduction of Fe(II) to Fe(s). At lower pH these two steps are too close together to be resolved. An oxidation wave and a reduction wave are recorded for the electrolysis of Fe(II) in the presence of catechol: the oxidation wave is observed between pH 7 and 12.3. The curve showing dependence of the limiting current on pH is similar to the distribution curve of Fe(cat). It is therefore suggested that only Fe(cat) is oxidized and observed here. The reduction wave of Fe(II) in the presence of catechol is irreversible and shifted from -1.5 to -1.8 volts upon complex formation. A calculation of formation constants, 81 and 82, was achieved according to an equation which relates the shifts of halfwave potential to the formation constants.

Thesis (M.Sc.)--University of Adelaide, Dept. of Physiology, 1977.

Thesis (MSc.(Physiology)--Faculty of Health Sciences)-University of Pretoria, 2004. / Also available on the Internet via the World Wide Web.

The enzyme polyphenolase, which catalyses the oxidation of phenols to catechols and subsequently dehydrogenates these to o-quinones, is widely distributed in nature. The multicopy plasmid vector pIJ702 contains a mel gene from Streptomyces antibioticus, that codes for the production of a polyphenol oxidase. The plasmid was isolated from Streptomyces lividans 66pIJ702 and subjected to a variety of mutagenic treatments in order to establish a structurefunction relationship for the polyphenolase enzymes. An attempt was made to engineer the polyphenolase enzyme by localized random mutagenesis in vitro of the mel gene on pIJ702, in order to alter properties like productivity, activity and substrate specificity. It was hoped to alter the amino acid sequence of the active site of the enzyme in order to facilitate catalysis in an organic environment. The plasmid was subsequently transformed into a plasmid-free Streptomyces strain, and enzyme production was carried out in batch culture systems, in order to determine the effect of the height treatment, and to isolate and propagate functional polyphenolase mutants for organic synthesis.

No description available.

The chemical properties of guanidinium tris(catecholato)siliconate, (H2N)2C=NH2J2(Si(C6H402)j]-XH20 (0 This same compound was, upon addition of' (H2N)2C=NH.HC1, isolated from 0.2, M aqueous catechol solutions buffered at pH 10 and containing the silicate minerals albite, andradite, muscovite, pyrophyllite, talc, and wollastonite, and also from unbuffered catechol solutions containing wollastonite and andradite. It is concluded from this work that the formation of an anionic catechol-silicon complex, Si(C6H402)32~ is largely responsible for the dissolution of the minerals mentioned above. From this conclusion, it is proposed that naturally occurring members of the class of organic compounds to which catechol belongs, the aromatic vic-diols, may play a role in chemical weathering, in the development of certain soil profiles, and in the entry and accumulation of silica in plants.