Efficient C-H Bond Activations O_2 Cleavage by a Dianionic Cobalt(II) Complex

A dianionic, square planar cobalt(II) complex reacts with O_2 in the presence of acetonitrile to give a cyanomethylcobalt(III) complex formed by C-H bond cleavage. Interestingly, PhIO and -tolylazide react similarly to give the same cyanomethylcobalt(III) complex. Competition studies with various hydrocarbon substrates indicate that the rate of C-H bond cleavage greatly depends on the pK_a of the C-H bond, rather than on the C-H bond dissociation energy. Kinetic isotope experiments reveal a moderate KIE value of ca. 3.5 using either O_2 or PhIO. The possible involvement of a cobalt(IV) oxo species in this chemistry is discussed

Analysis of resonance Raman data on the blue copper site in pseudoazurin: excited state π and σ charge transfer distortions and their relation to ground state reorganization energy

The short Cu^(2+)-S(Met) bond in pseudoazurin (PAz) results in the presence of two relatively intense S_p(π) and S_p(σ) charge transfer (CT) transitions. This has enabled resonance Raman (rR) data to be obtained for each excited state. The rR data show very different intensity distribution patterns for the vibrations in the 300-500 cm^(-1) region. Time-dependent density functional theory (TDDFT) calculations have been used to determine that the change in intensity distribution between the S_p(π) and S_p(σ) excited states reflects the differential enhancement of S(Cys) backbone modes with Cu-S(Cys)-C_β out-of-plane (oop) and in-plane (ip) bend character in their respective potential energy distributions (PEDs). The rR excited state distortions have been related to ground state reorganization energies (λ s) and predict that, in addition to M-L stretches, the Cu-S(Cys)-C_β oop bend needs to be considered. DFT calculations predict a large distortion in the Cu-S(Cys)-C_β oop bending coordinate upon reduction of a blue copper (BC) site; however, this distortion is not present in the X-ray crystal structures of reduced BC sites. The lack of Cu-S(Cys)-C_β oop distortion upon reduction corresponds to a previously unconsidered constraint on the thiolate ligand orientation in the reduced state of BC proteins and can be considered as a contribution to the entatic/rack nature of BC sites

Activation of N2O reduction by the fully reduced micro4-sulfide bridged tetranuclear Cu Z cluster in nitrous oxide reductase

J. Am. Chem. Soc., 2003, 125 (51), pp 15708–15709 DOI: 10.1021/ja038344nThe tetranuclear CuZ cluster catalyzes the two-electron reduction of N2O to N2 and H2O in the enzyme nitrous oxide reductase. This study shows that the fully reduced 4CuI form of the cluster correlates with the catalytic activity of the enzyme. This is the first demonstration that the S = 1/2 form of CuZ can be further reduced. Complementary DFT calculations support the experimental findings and demonstrate that N2O binding in a bent mu-1,3-bridging mode to the 4CuI form is most efficient due to strong back-bonding from two reduced copper atoms. This back-donation activates N2O for electrophilic attack by a proton

Cu-ZSM-5: A biomimetic inorganic model for methane oxidation

The present work highlights recent advances in elucidating the methane oxidation mechanism of inorganic Cu-ZSM-5 biomimic and in identifying the reactive intermediates that are involved. Such molecular understanding is important in view of upgrading abundantly available methane, but also to comprehend the working mechanism of genuine Cu-containing oxidation enzymes

Spectroscopic and Theoretical Study of CuI Binding to His111 in the Human Prion Protein Fragment 106-115

The ability of the cellular prion protein (PrPC) to bind copper in vivo points to a physiological role for PrPC in copper transport. Six copper binding sites have been identified in the nonstructured N-terminal region of human PrPC. Among these sites, the His111 site is unique in that it contains a MKHM motif that would confer interesting CuI and CuII binding properties. We have evaluated CuI coordination to the PrP(106-115) fragment of the human PrP protein, using NMR and X-ray absorption spectroscopies and electronic structure calculations. We find that Met109 and Met112 play an important role in anchoring this metal ion. CuI coordination to His111 is pH-dependent: at pH >8, 2N1O1S species are formed with one Met ligand; in the range of pH 5-8, both methionine (Met) residues bind to CuI, forming a 1N1O2S species, where N is from His111 and O is from a backbone carbonyl or a water molecule; at pH <5, only the two Met residues remain coordinated. Thus, even upon drastic changes in the chemical environment, such as those occurring during endocytosis of PrPC (decreased pH and a reducing potential), the two Met residues in the MKHM motif enable PrPC to maintain the bound CuI ions, consistent with a copper transport function for this protein. We also find that the physiologically relevant CuI-1N1O2S species activates dioxygen via an inner-sphere mechanism, likely involving the formation of a copper(II) superoxide complex. In this process, the Met residues are partially oxidized to sulfoxide; this ability to scavenge superoxide may play a role in the proposed antioxidant properties of PrPC. This study provides further insight into the CuI coordination properties of His111 in human PrPC and the molecular mechanism of oxygen activation by this site.Fil: Arcos López, Trinidad. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Qayyum, Munzarin. University of Stanford; Estados UnidosFil: Rivillas Acevedo, Lina. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Miotto, Marco César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina. Max Planck Laboratory for Structural Biology; ArgentinaFil: Grande Aztatzi, Rafael. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Fernandez, Claudio Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina. Max Planck Laboratory for Structural Biology; ArgentinaFil: Hedman, Britt. University of Stanford; Estados UnidosFil: Hodgson, Keith O.. University of Stanford; Estados UnidosFil: Vela, Alberto. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Solomon, Edward I.. University of Stanford; Estados UnidosFil: Quintanar, Liliana. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; Méxic

Activating Metal Sites for Biological Electron Transfer

This review focuses on the unique spectroscopic features of the blue copper active sites. These reflect a novel electronic structure that activates the site for rapid long-range electron transfer in its biological function. The role of the protein in determining the geometric and electronic structure of this site is defined, as is its contribution to function. This has been referred to as the entatic/rack-induced state. These concepts are then extended to cytochrome , which is also determined to be in an entatic state

Efficient C-H Bond Activations O_2 Cleavage by a Dianionic Cobalt(II) Complex

A dianionic, square planar cobalt(II) complex reacts with O_2 in the presence of acetonitrile to give a cyanomethylcobalt(III) complex formed by C-H bond cleavage. Interestingly, PhIO and -tolylazide react similarly to give the same cyanomethylcobalt(III) complex. Competition studies with various hydrocarbon substrates indicate that the rate of C-H bond cleavage greatly depends on the pK_a of the C-H bond, rather than on the C-H bond dissociation energy. Kinetic isotope experiments reveal a moderate KIE value of ca. 3.5 using either O_2 or PhIO. The possible involvement of a cobalt(IV) oxo species in this chemistry is discussed

Spectroscopic Definition of the CuZ° Intermediate in Turnover of Nitrous Oxide Reductase and Molecular Insight into the Catalytic Mechanism

Fundacao para a Ciencia e Tecnologia - PTDC/QUI-BIQ/116481/2010, PTDC/BBB-BQB/0129/2014, SFRH/BD/87898/2012 ; Unidade de Ciencias Biomoleculares Aplicadas-UCIBIO - FCT/MEC - UID/Multi/04378/2013 ; ERDF - POCI-01-0145-FEDER-007728Spectroscopic methods and density functional theory (DFT) calculations are used to determine the geometric and electronic structure of CuZ°, an intermediate form of the Cu4S active site of nitrous oxide reductase (N2OR) that is observed in single turnover of fully reduced N2OR with N2O. Electron paramagnetic resonance (EPR), absorption, and magnetic circular dichroism (MCD) spectroscopies show that CuZ° is a 1-hole (i.e., 3CuICuII) state with spin density delocalized evenly over CuI and CuIV. Resonance Raman spectroscopy shows two Cu-S vibrations at 425 and 413 cm-1, the latter with a -3 cm-1 O18 solvent isotope shift. DFT calculations correlated to these spectral features show that CuZ° has a terminal hydroxide ligand coordinated to CuIV, stabilized by a hydrogen bond to a nearby lysine residue. CuZ° can be reduced via electron transfer from CuA using a physiologically relevant reductant. We obtain a lower limit on the rate of this intramolecular electron transfer (IET) that is >104 faster than the unobserved IET in the resting state, showing that CuZ° is the catalytically relevant oxidized form of N2OR. Terminal hydroxide coordination to CuIV in the CuZ° intermediate yields insight into the nature of N2O binding and reduction, specifying a molecular mechanism in which N2O coordinates in a μ-1,3 fashion to the fully reduced state, with hydrogen bonding from Lys397, and two electrons are transferred from the fully reduced μ4S2- bridged tetranuclear copper cluster to N2O via a single Cu atom to accomplish N-O bond cleavage.authorsversionpublishe

Oxygen precursor to the reactive intermediate in methanol synthesis by Cu-ZSM-5

The reactive oxidizing species in the selective oxidation of methane to methanol in oxygen activated Cu-ZSM-5 was recently defined to be a bent mono(μ-oxo)dicopper(II) species, [Cu_2O]^(2+). In this communication we report the formation of an O_2-precursor of this reactive site with an associated absorption band at 29,000 cm^(-1). Laser excitation into this absorption feature yields a resonance Raman (rR) spectrum characterized by ^(18)O_2 isotope sensitive and insensitive vibrations, νO-O and νCu-Cu, at 736 (Δ^(18)O_2 = 41 cm^(-1)) and 269 cm^(-1), respectively. These define the precursor to be a μ-(η^2:η^2) peroxo dicopper(II) species, [Cu_2(O_2)]^(2+). rR experiments in combination with UV-vis absorption data show that this [Cu_2(O_2)]^(2+) species transforms directly into the [Cu_2O]^(2+) reactive site. Spectator Cu^+ sites in the zeolite ion-exchange sites provide the two electrons required to break the peroxo bond in the precursor. O_2-TPD experiments with ^(18)O_2 show the incorporation of the second ^(18)O atom into the zeolite lattice in the transformation of [Cu_2(O_2)]^(2+) into [Cu_2O]^(2+). This study defines the mechanism of oxo-active site formation in Cu-ZSM-5