Electronic and geometric structure-function correlations of the coupled binuclear copper active site

Abstract

-Chemical-spectroscopic studies of the coupled bimuclear copper active site are presented which interpret the unique spectral features associated with oxyhemocyamim. These features are them used to generate a 'spectroscopically effective' model for this active site. First the met apo [Cu(II) -I and half met [Cu(II)Cu(I)J derivatives are spectroscopically compared; they demonstrate that exogenous ligands bridge the two coppers in the mixed valent form providing a pathway for electron delocalization. Detailed spectral studies are presented which probe the ground state wavefunction. Next, the dimer and met [Cu(II)Cu(II)] denyatives are compared to demonstrate that there is also am endogenous bridge between the two coppers. It provides a superexchamge pathway for the antiferromagnetic coupling and is responsible for the EPR-mondetectable mature of the coupled binuclear cupnic site. Finally, the unique optical features of oxyhemocyanin are interpreted as charge transfer transitions from a p-l,2 peroxide bridge.These chemical-spectroscopic studies are then extended oven the metalloproteins which contain a coupled bimuclear copper active site and are involved in a variety of biological functions. Spectral studies of hemocyanin derivatives from the arthropod and mollusc phyla indicate that there is a structural distortion present at the arthropod site. This distortion interferes with exogenous ligand binding and correlates with the lack of catalase activity. A "spectral probe" derivative which contains a small fraction of EPR-detectable half met sites in the hemocyamin biopolymer is reported. This derivative is used to probe changes at the active site induced by shifts from relaxed to tensed protein quaternary structure. Parallel chemical-spectroscopic studies on tyrosinase are presented which indicate that its active site is extremely similar to that of the hemocyanins but highly accessible for coordination of organic substrates. An active site structural mechanism for the monooxygenation reaction is then proposed. Finally, these studies are extended to the coupled binuclear copper active site in the multicopper oxidase, laccase. Deoxy [Cu(I)Cu(I)J, met [Cu(II)Cu(II)] and half met [Cu(II)Cu(I)] derivatives of the type-2-depleted enzyme form are studied; these allow correlation to the hemocyanins and tyrosinase. While the site is found to be similar with respect to the presence of an endogenous protein bridge and N and 0 ligation of the coppers, significant differences are observed which indicate that exogenous ligands do not bridge the two coppers. This appears to correlate to irreversible binding of the peroxide intermediate produced in the four-electron reduction of dioxygen to water.

Electron paramagnetic resonance study of water distribution in starch granules

“…This deficit might be caused, e.g., by clustering of some Cu 2þ ions adsorbed on the granule surface, which were not detectable by EPR due to an antiferromagnetic coupling. 26 Higher overall intensity of the potato starch spectrum could result from two reasons: easier and more efficient interaction and/or retention of Cu 2þ aqua complexes with potato than with wheat starch. Such effects, noticed by us previously, 20 might be connected not only with the B-type crystalline structure but also with the phosphate groups present in this starch.…”

“…Disappearing of the isotropic broad signal (attributed to the strongly interacting Cu 2þ species) with lowering temperature, could be explained by the increase of the copper coupling of the antiferromagnetic type. 26 Removing of water molecules during dehydration at 393 K resulting in disappearance of isotropic signals with g av equal to 2.164 and 2.189 for potato and wheat starch, respectively, confirmed our earlier attribution of these signals to freely rotating [Cu(H 2 O) 6 ] 2þ complexes coordinating water retained by the amorphous regions of the starch granules, i.e., the amorphous growth rings as well as the amorphous lamellae of the semicrystalline growth rings.…”

H2S Emissions from a Submerged Pilot‐Scale Fixed Bed Biofilm Reactor

“…In the case of starch enriched with copper ions, similar discrepancy was observed. It was observed mainly in monostarch phosphates and could be due to the presence of clustered Cu(II) or Fe(III) ions, not visible in the EPR spectra because of strong antiferromagnetic coupling 33 or the presence of not oxidized Fe(II). Amounts of Fe(III) and Cu(II) species giving EPR signals were the highest in monostarch phosphates and were only slightly dependent on the kind of starch (Table 1).…”

Synthesis, characterization and antimicrobial activity of macrocylic phenoxo-bridged di- and tetra-nuclear complexes from N,N-bis[2,6-diiminomethyl-4-methyl-1-hydroxyphenyl]succinoyl/sebacoyldicarboxamides

“…These types of complexes have contributed to a better knowledge of oxygen transport and activation by metalloenzymes such as haemocyanin (Cu 2 ) [1] and cytochrome-C-oxidase (CuFe) [1] as well as of some industrial catalytic processes [2]. A number of magnetically interacting dinuclear copper(II) complexes have been shown to be catalytically active in the oxidation of two electron reducing substrates like ascorbic acid, 3,5-di-t-butylcatechol (3,5-DTBC) [3] and one-electron reducing substrate N,N,N¢,N¢-tetra-methyl-p-phenylenediamine (TMPD) by oxygen [4].…”