Добірка наукової літератури з теми "Galactose oxidase like complexes"

The study of many membrane enzymes in an aqueous medium is difficult due to the loss of their catalytic activity, which makes it necessary to use membrane-like systems, such as reverse micelles of surfactants in nonpolar organic solvents. However, it should be taken into account that micelles are a simplified model of natural membranes, since membranes contain many different components, a significant part of which are phospholipids. In this work, we studied the impact of the main phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), on the activity of membrane enzymes using galactonolactone oxidase from Trypanosoma cruzi (TcGAL) and L-galactono-1,4-lactone dehydrogenase from Arabidopsis thaliana (AtGALDH) as an examples. Effect of the structure (and charge) of the micelle-forming surfactant itself on the activity of both enzymes has been studied using an anionic surfactant (AOT), a neutral surfactant (Bridge-96), and a mixture of cationic and anionic surfactants (CTAB and AOT) as an examples. The pronounced effect of addition of PC and PE lipids on the activity of AtGALDH and TcGAL has been detected, which manifests as increase in catalytic activity and significant change in the activity profile. This can be explained by formation of the tetrameric form of enzymes and/or protein-lipid complexes. By varying composition and structure of the micelle-forming surfactants (AOT, CTAB, and Brijdge-96 and their combinations) it has been possible to change catalytic properties of the enzyme due to effect of the surfactant on the micelle size, lipid mobility, charge, and rigidity of the matrix itself.

π–π stacking interaction is well-known to be one of the weak interactions. Its importance in the stabilization of protein structures and functionalization has been reported for various systems. We have focused on a single copper oxidase, galactose oxidase, which has the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with the indole ring of the proximal tryptophan residue and catalyzes primary alcohol oxidation to give the corresponding aldehyde. This stacking interaction has been considered to stabilize the alkylthio-phenoxyl radical, but further details of the interaction are still unclear. In this review, we discuss the effect of the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with an indole ring.

Galactose monitoring in individuals allows the prevention of harsh health conditions related to hereditary metabolic diseases like galactosemia. Current methods of galactose detection need development to obtain cheaper, more reliable, and more specific sensors. Enzyme-containing amperometric sensors based on galactose oxidase activity are a promising approach, which can be enhanced by means of their inclusion in a redox polymer coating. This strategy simultaneously allows the immobilization of the biocatalyst to the electroactive surface and hosts the electron shuttling units. An additional deposition of capping polymers prevents external interferences like ascorbic or uric acid as well as biofouling when measuring in physiological fuels. This work studies the protection effect of poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate (MPC) and polyvinylimidazole-polysulfostyrene (P(VI-SS)) when incorporated in the biosensor design for the detection of galactose in human plasma.

La galactose oxydase (GOase), une métallo-enzyme contenant du cuivre, est l'un des biocatalyseurs les plus étudiés pour l'oxydation enzymatique des glucides. Le mécanisme couramment accepté implique la forme oxydée clé (GOaseox), dans laquelle une unité glucidique (galactose) se lie au site équatorial (libre) et subit une déprotonation, suivie d'un arrachage d'atome d'hydrogène par un radical et d'un transfert d'électron supplémentaire, conduisant ainsi à la formation du produit final, l'aldéhyde, et à la réduction de la GOase. En raison de leur potentiel pour des oxydations catalytiques hautement sélectives, des modèles moléculaires du site actif de la GOase dérivés de bases de Schiff encombrées ont été développés. Cette approche biomimétique passe par la synthèse de complexes Cu(II)-phénol servant de pré-catalyseurs, qui subissent ensuite une oxydation à un électron pour devenir la forme "active" du catalyseur. Une question cruciale demeure : quels sont les facteurs qui déterminent si l’oxydation est centrée sur le ligand, produisant des radicaux Cu(II)-phénoxyle, ou vers le métal, formant des espèces Cu(III)-phénolate ? Malgré des efforts importants, une réponse définitive à cette question reste elusive.L'objectif de cette thèse est de développer des ligands redox-actifs afin de mieux comprendre les facteurs qui influencent le site d’oxydation du complexe de cuivre correspondant. La stratégie consiste à incorporer des fonctions chimiques stabilisant l'un ou l'autre tautomère de valence (Cu(II)-radical phénoxyle et Cu(III)-phénolate) et à étudier leur impact. À cet effet, plusieurs complexes ont été synthétisés et caractérisés par spectroscopie et électrochimie. Les activités catalytiques ont également été évaluées sur divers substrats contenant des groupes hydroxyle. Enfin, des calculs de chimie quantique (DFT) ont été réalisés pour aider à élucider les mécanismes catalytiques et à mieux comprendre les caractéristiques des différents complexes
Galactose Oxidase (GOase), a copper-containing metallo-enzyme, is one of the most studied biocatalysts for the enzymatic oxidation of carbohydrates. The consensus mechanism involves the key oxidized form (GOaseox), in which an the carbohydrate substrate (galactose unit) binds to the equatorial (free) site and is subsequently deprotonated. It undergoes hydrogen atom abstraction by the radical and further electron transfer to give the final product aldehyde and the reduced form of the GOase. Due to the potential for highly selective catalytic oxidations, the development of small-molecular models of the GOase active site has been carried out. Notably, sterically hindered schiff bases, which stand as one of the most representative mimics, have garnered significant attention. This biomimetic approach has extended to encompass other strategies. Within this framework, a range of Cu(II)-phenol complexes, serving as pre-catalysts, have been synthesized, subsequently undergoing one-electron oxidation to yield the "active" catalyst form. A central question then arises: What factors determine whether the oxidation pathway proceeds toward the ligand, resulting in the formation of Cu(II)-phenoxyl radicals, or toward the metal, giving rise to the Cu(III)-phenolate species? Despite substantial efforts, a definitive answer to this question has yet to be obtained.The aim of this thesis is to develop redox-active ligands aimed at understanding the factors affecting the oxidation state of copper, able to catalyze the oxidation of an alcohol into an aldehyde. The strategy is to include chemical functions that can stabilize either valence tautomer (Cu(II)-phenoxyl radical and Cu(III)-phenolate) and study their effect. For that purpose, several complexes were synthesized and characterized by different ways to understand their properties. The catalytic activities were also tested against different families of substrates comprising hydroxyl functions. Finally, quantum chemistry (DFT) calculations have been carried to help understand the characteristics of different complexes and elucidate of the catalytic mechanisms at work

This thesis describes the synthesis of diphenolate and dithiophenolate complexes of ZnII, NiII and CuII that derive inspiration from the natures of the active sites of the nickel-containing superoxide dismutase (NiSOD) and the copper-containing galactose oxidase (GO). Chapter One introduces the roles of transition metals in biology. The structures of the active sites of NiSOD and GO are described, together with a discussion of the proposed mechanisms of their action. A brief review of the coordination chemistry relevant to the chemistry of the actives sites of NiSOD and GO is presented and the aims of the research described in this thesis are set out. Chapter Two describes the syntheses and structural characterisations of a series of pentacoordinate ZnII, NiII and CuII diphenolate complexes MRLoNMe (M= Zn, Ni, Cu; R = Cl, Br, Nap, Ph, PhMe, PhOMe, tBu/Br, tBu/Ph, tBu/PhMe, tBu/PhOMe; page xiii) that differ in the natures of the substituents at the 3- and 5-positions of the phenolate rings within the ligand backbone. X-ray crystallographic studies on the ZnII, NiII and CuII complexes, and room temperature and frozen solution EPR spectroscopic experiments on the CuII complexes provide insight into the influence of the 3- and 5- substitution on the coordination geometries. The changes in substitution at the 3 position of the phenolate rings in MRLoNMe (M= Zn, Ni, Cu; R = tBu/Ph, tBu/PhMe, tBu/PhOMe) have significantly less influence on the geometry about the metal centre when compared to complexes that have substitutions that vary at the 3 and 5 positions in MRLoNMe (M= Zn, Ni, Cu; R = Ph, PhMe, PhOMe). DFT calculations provide a qualitative description of the electronic structures of these complexes, suggesting an increase in the metal character within the HOMOs for the NiII complexes relative to those of their ZnII and CuII counterparts. Chapter Three describes the electrochemical characterisations of the complexes synthesised in Chapter Two [MRLoNMe (M= Zn, Ni, Cu; R = Cl, Br, Nap, Ph, PhMe, PhOMe, tBu/Br, tBu/Ph, tBu/PhMe, tBu/PhOMe)]. Cyclic voltammetry demonstrates that MRLoNMe (M= Zn, Cu; R = Cl, Br, Nap, tBu/Br) possess oxidation processes that are not reversible. MRLoNMe (M= Ni; R = Cl, Br, Nap, tBu/Br) possess a reversible oxidation process assigned to the NiIII/NiII redox couple. MRLoNMe (M= Zn, Ni, Cu; R = Ph, PhMe, PhOMe, tBu/Ph, tBu/PhMe, tBu/PhOMe) display multiple oxidation processes, some of which demonstrate electrochemical reversibility, particularly when M = Ni or Cu. UV/Vis and EPR spectroscopic studies on the oxidised species [MRLoNMe]+ (M= Zn, Ni, Cu; R = Ph, PhMe, PhOMe, tBu/Ph, tBu/PhMe, tBu/PhOMe), supported by DFT calculations, suggest that the first oxidation process is significantly more metal based when M = Ni than for M = Cu or Zn and for the generation of [NiRLoNMe]+ is associated with the formation of formal NiIII species. The UV/vis and EPR spectroscopic results also suggest that [NiPhOMeLoNMe]+ exhibits temperature-dependent NiIII-phenolate  NiII-phenoxyl redox tautomerism. The variation of the aromatic substituents systematically decreases the redox potential in the order R = Ph > PhMe > PhOMe, consistent with the relative electron donor properties of each group. Chapter Four examines complexes that incorporate an aromatic, N-donor group pendant to the ligand background. These complexes serve as analogues of the active site of NiSOD. The dithiophenolate and diphenolate complexes NitBuLSPy, NitBuLSPyOMe, NitBuLOPy, NitBuLOPyOMe, and NitBuLOPh are prepared and characterised to examine the effect of different N-donor groups as potential axial donors to the metal centre on the redox properties of each complex. Advanced pulsed ESSEM and HYSCORE EPR spectroscopic studies probe the weak superhyperfine couplings involving the 14N imine donors in [NitBuLSPy]+, and benchmark the spin densities associated with these donors calculated by DFT. These spectroscopically validated DFT calculations show how the distribution of spin density varies between complexes incorporating an N-donor pendant to the ligand backbone and those that do not. Thus, those incorporating an additional N-donor possess spin density that is considerably more localised at the formal NiIII centre than those that do not. Chapter Five discusses the key conclusions of the research described in this thesis and compares and contrasts the chemistry exhibited by ZnII, NiII and CuII diphenolate and dithiophenolate complexes. The structural and electrochemical differences observed upon the introduction of alternative diphenolate substituents in MRLoNMe (M= Zn, Ni, Cu; R = Cl, Br, Nap, Ph, PhMe, PhOMe, tBu/Br, tBu/Ph, tBu/PhMe, tBu/PhOMe) are summarised, together with the importance of the geometric structure of NitBuLSPy in controlling the redox chemistry of this centre. Finally, implications for the chemistry of the active sites of GO and NiSOD are discussed.

by Chan Sau Han.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2001.
Includes bibliographical references.
Abstracts in English and Chinese.
ABSTRACT --- p.i
摘要 --- p.ii
ACKNOWLEDGMENT --- p.iii
CONTENTS --- p.iv
ABBREVIATIONS --- p.vi
Chapter CHAPTER 1 --- General Introduction
Chapter 1-A. --- Role of Copper in Biology --- p.1
Chapter 1-B. --- A Brief Review on Radical Copper Proteins --- p.4
Chapter 1-C. --- Objectives of This Work --- p.12
Chapter 1-D. --- References --- p.13
Chapter CHAPTER 2 --- Copper(II) and Zinc(II) Complexes containing N3O Tetradentate Ligands
Chapter 2-A. --- Introduction Results and Discussion --- p.14
Chapter 2-B. --- Preparation of Tetradentate Ligands and Complexes --- p.27
Chapter 2-C. --- Characterization --- p.36
Chapter 2-D. --- Generation of Metal Phenoxyl Radical Species --- p.51
Chapter 2-E. --- Summary --- p.57
Chapter 2-F. --- References --- p.59
Chapter CHAPTER 3 --- Copper(I) Complexes with N30 Tetradentate Ligands
Chapter 3-A. --- Introduction Results and Discussion --- p.62
Chapter 3-B. --- Preparation of Copper(I) Complexes with N30 Tetradentate Ligands --- p.75
Chapter 3-C. --- Characterization --- p.79
Chapter 3-D. --- Reactivities of 86，87 and 88 toward Dioxygen --- p.88
Chapter 3-E. --- Summary --- p.93
Chapter 3-F. --- References --- p.94
Chapter CHAPTER 4 --- Experimental Sections
Chapter 4-A. --- General Preparations and Physical Measurements --- p.97
Chapter 4-B. --- Compounds Described in Chapter2 --- p.99
Chapter 4-C. --- Compounds Described in Chapter3 --- p.113
Chapter 4-D. --- Oxo-Transfer to Triphenylphosphine as Described in Chapter3 --- p.117
Chapter 4-E. --- References --- p.119
Chapter APPENDIX A --- 1H and13 C̐ưث1H ̐ưحNMR Spectra
Chapter A-1. --- Compounds Described in Chapter2 --- p.120
Chapter A-2. --- Compounds Described in Chapter3 --- p.127
Chapter APPENDIX B --- Crystallographic Data
Chapter B-1. --- X-ray Crystal Structure Data for Complexes in Chapter2 --- p.131
Chapter B-2. --- X-ray Crystal Structure Data for Complexes in Chapter3 --- p.133
Chapter APPENDIX C --- GC-MS Spectra
Chapter C-1. --- GC-MS Spectra for Standard Samples --- p.134
Chapter C-2. --- GC-MS Spectra for the Reactions with Triphenylphosphine Described in Chapter3 --- p.136