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University/Publisher Johns Hopkins University
Abstract Enzymes where the active site contains one or more copper ions catalyze a wide range of organic substrate transformations in Nature. The structures and function of such active sites have been finely tuned by evolution to reach the point where dioxygen binding, activation, and utilization for oxidative chemistry has become finely modulated. As is overviewed in Chapter 1, it is useful to categorize the enzymes supported by two copper centers in their active sites as 'uncoupled' (i.e. in peptidylglycine -hydroxylating monooxygenase (PHM) and in dopamine -monooxygenase (DM)) or 'coupled' (i.e. in tyrosinase (Tyr) and in catechol oxidase (Co)) on the basis of the spatial proximity of the two metals in the three-dimensional matrix of the protein. This proximity has profound effects on the chemistry displayed by these two classes of enzymes. Importantly, dioxygen binding to the copper centers is the first step of the catalytic cycle in all of these systems. However, both mononuclear 1:1 and dinuclear 2:1 copper/O2 adducts forming in the enzymes have been shown to be unstable and their detection and their study has been difficult. As it is also discussed in Chapter 1, low temperature spectroscopic techniques together with synthetic model chemistry have come into play and greatly improved our understanding of the mechanistic details involved in such kinds of reactivity. In this work, laser flash-photolysis techniques in combination with copper-synthetic model chemistry have been employed to help the elucidation of fundamental physical and chemical properties of copper/O2 coordination and dynamics. One of the methods that has been successfully employed to study labile copper/dioxygen adducts is laser flash-photolysis of synthetic (L)copper(I)-CO compounds (L =ligand) in the presence of O2 in organic solvents. In Chapter 2, a flash-photolysis study of tridentate N-donor ligand-copper(I)-CO complexes is presented using such techniques. The implications of tricoordination vs. tetracoordination of copper ion on the dynamics of CO and O2 binding to the metal are discussed for these metal complexes. Tricoordinate environments are more similar in their coordination sphere with those present in the enzymes, as compared to their tetracoordinated synthetic counterparts. In Chapter 3, a new method to study copper/dioxygen binding for mononuclear copper complexes is presented. The previously employed carbon monoxide utilization to start from stable (L)copper(I)-CO complexes is bypassed, in this work, by affording direct O2 photo-release from relatively stable mononuclear copper(II)-superoxide complexes. Interestingly, a different quantum yield for O2 release was found depending on the excitation wavelength used and in collaborative efforts, this effect has been investigated by means of Time-Dependent Density Functional Theory (TD-DFT) studies. This work was further extended and presented in Chapter 4, where the same technique was employed for dinuclear 2:1 Cu/O2 synthetic adducts with a peroxo fragment bound in a side-on mode to the…
Subjects/Keywords Oxygen activation, coupled copper enzymes, uncoupled copper enzymes, mononuclear and dinuclear copper?O2 adducts, copper synthetic model chemistry, laser flash-photolysis, physical properties, transient absorption spectroscopy, carbon monoxide, dioxygen, tricoordinate, tetracoordinate, flash-and-trap method, copper(II)-superoxide, dicopper(II) peroxo, quantum yield, excitation wavelength, TD-DFT, end-on, side-on, irradiation, visible light, one-photon two-electron, oxidation, hydrogen atom abstraction, reversible, thermodynamics, kinetics, kinetic relaxation model, pseudo-first-order, second-order, rate constant, binding dynamics, tyrosinase, hemocyanin, catechol oxidase, PHM, DBM, irradiation, laser.
Contributors Karlin, Kenneth D (advisor)
Country of Publication us
Format application/pdf
Record ID oai:jscholarship.library.jhu.edu:1774.2/37054
Repository jhu
Date Retrieved
Date Indexed 2016-10-05
Issued Date 2014-01-26 00:00:00

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…from Lucas HR, Karlin KD Met. Ions Life Sci. 2009, 6, 295. 6 Figure 2. Schematic of two synthetic copper(II) 1-superoxide complexes for comparison to the analogous precatalytic O2-species crystallized for PHMcc. Figure modified from Lucas…

…hydrogen atom abstraction from the substrate. On the other hand, Amzel and coworkers reported the crystal structure of a 6 precatalytic PHMcc analogue that has a superoxide fragment bound in an end-on fashion to the copper(II) present in the…

…catalytic site (Figure 2)35 favoring the hypothesis of a copper(II)-superoxide intermediate as active species in the catalytic cycle of PHM, instead.18,21 Theoretical studies (DFT) performed by Chen and Solomon also support this…

…occur on the basis of an unexpected reactivity of the CuH site with carbon monoxide in PHMcc. Stabilization of copper(II)-superoxide species has proven to be challenging both in synthetic and in natural systems. A huge effort made by synthetic…

…x28;II)-superoxide species with a second equivalent of copper(I). Figure 2 shows two cases where stabilization of such copper(II)superoxide species was achieved;37-39 in Chapter 3 it will be mentioned an even more recent case…

…where an intramolecular hydrogen bond contributes to the stabilization of the superoxo complex [(PV-TMPA)CuII(O2)]+.40 7 Figure 2. Schematic of two synthetic copper(II) 1-superoxide complexes for comparison to…

…x28;N5)CuI2(CH3CN)2](BArF)2. 143 Table 1. Comparison of reduction potentials for some copper complexes. G is the estimated free Gibbs energy variation for the dissociation reaction of O2 from the relative copper(II

…constituted by a copper(II) core with a distorted tetrahedral geometry and it coordinates two 5 histidines (His242 and His244, both bound through their -nitrogens), a methionine (Met314), and a water molecule. This domain is…