Photophysical properties of hexanuclear copper(I) and silver(I) clusters

Sabin, Frank; Ryu, Chong Kul; Ford, Peter C.; Vogler, Arnd

doi:10.1021/ic00036a040

Cited by 154 publications

(105 citation statements)

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“…This 335-nm CD band (and the associated 340-nm absorption band) observed as more than 12 Cu(1) are added to Zn-metallothionein, is thought to originate from an intra-Cu(1) transition. A similar transition has been proposed for the near-ultraviolet absorption in the hexanuclear clusters M1s(mtc)6 [MI = Cu', Ag'; mtc = di-n-propylmonothiocarbamate] [44]. This transition may be symmetry forbidden for Cu(1) trigonally bound to three thiolate ligands, thus yielding a small absorbance with up to, 12 Cu' added.…”

Section: Formation Of Cu( [)-Thiolate Clusters From Zn-metallothioneinsupporting

confidence: 60%

Copper Binding to Rabbit Liver Metallothionein

Presta

Green

Żelazowski

et al. 1995

European Journal of Biochemistry

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Circular dichroism and ultraviolet absorption spectral data have been used to probe the binding mechanism for formation and the structure of the copper(1)-thiolate binding clusters in rabbit liver metallothiionein during addition of Cu' to aqueous solutions of Zn,-metallothionein 2 and Cd,Zn,-metallothionein 2. Mammalian metallothionein binds metals in two binding sites, namely the a and P domains. Spectral data which probe the distribution of Cu(1) between the two binding domains clearly show that both the site of binding (a or p), and the structures of the specific metal-thiolate clusters formed, are dependent on temperature and on the nature of the starting protein (either Zn,-metallothionein or Cd,Zn,-metallothionein). CD spectra acquired during the addition of Cu' to Zn,-metallothionein show that Cu' replace the bound Zn(I1) in a domain-distributed manner with complete removal of the Zn(I1) after addition of 12 Cu'. Spectral and metal analyses prove that a series of Cu(1)-metallothionein species are formed by a non-cooperative metal-binding mechanism with a continuum of Cu(1) :metallothionein stoichionietries. Observation of a series of spectral saturation points signal the formation of distinct optically active Cu(1)-thiolate structures for the Cu,Zn,-metallothionein, Cu,,-metallothionein, and the Cu,,-metallothiionein species. These data very clearly show that for Cu(1) binding to Zn,-metallothionein, there are sleveral key Cu(1):metallothionein stoichiometric ratios, and not just the single value of 12. The CD spectra up to the Cu,,-metallothionein species are defined by bands located at 255(+) nm and 280(--) nm. Interpretation of the changes in the CD and ultraviolet absorption spectral data recorded between 3°C and 52°C as Cu' is added to Zn-metallothionein show that copper-thiolate cluster formation is strongly temperature dependent. These changes in spectral properties are interpreted in terms of kinetic versus thermodynamic control of the metal-binding pathways as Cu' binds to the protein. At low temperatures (3 "C and 10OC) the spectral data indicate a kinetically controlled mechanism whereby an activation barrier inhibits formation of ordered copper-thiolate structures until formation of Cu,,-metallothionein. At higher temperatures (>3OoC) the activation barrier is overcome, allowing formation of new Cu(1)-thiolate clusters with unique spectral properties, especially at the Cu,Zn,-metallothionein point. The CD spectra also show that a Cu,,-metallothionein species with a well-defined, three-dimensional structure forms at all temperatures, characterized by a band near 335 nm, indicating the presence of digonal Cu(1). Complicated CD spectral changes are observed when Cu' is added to Cd,Zn,-metallothionein. The spectral data are interpreted in terms of domain-distributed binding followed by rearrangement to form the domain-specific product. In the Cu,Cd,-metallothionein species, the Cu' are ultimately bound specifically to the p domain of the protein. This complex is characterised by the CD spectrum o...

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Section: Formation Of Cu( [)-Thiolate Clusters From Zn-metallothioneinsupporting

confidence: 60%

Copper Binding to Rabbit Liver Metallothionein

Presta

Green

Żelazowski

et al. 1995

European Journal of Biochemistry

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“…The luminescence properties of inorganic tetra-and hexanuclear Cu(I) clusters and similar clusters in Cu(I)-MTs have been reported (26,43,44,46). Although the Cu(I) 6 clusters exhibit only a single low energy band at ϳ700 nm, high and low energy bands at ϳ430 and 620 nm are observed in the luminescence spectra of Cu(I) 4 clusters.…”

Section: Characterization Of Cu(i)znmt-3 Species By Cu(i)mentioning

confidence: 57%

“…However in polynuclear Cu(I) complexes, including the Cu(I) 8 MT-1 complex, which exhibit relatively short Cu...Cu distances (Ͻ2.8 Å) an intramolecular d 10 -d 10 interaction of adjacent Cu(I) ions leads to a number of excited states with a largely metal character. These weak low energy bands have been assigned to formally spin forbidden 3d 3 4s metal cluster-centered (CC) transitions (42)(43)(44)(45). Thus, the occurrence of similar transitions in Cu(I) 4 Zn 4 MT-3 suggest the presence of a Cu(I) 4 -thiolate cluster.…”

Section: Formation and Stability Of Cuznmt-3 In Air-mentioning

confidence: 99%

Redox Silencing of Copper in Metal-linked Neurodegenerative Disorders

Meloni

Faller

Vašák

2007

Journal of Biological Chemistry

120

159

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Dysregulation of copper and zinc homeostasis in the brain plays a critical role in Alzheimer disease (AD). Copper binding to amyloid-␤ peptide (A␤) is linked with the neurotoxicity of A␤and free radical damage. Metallothionein-3 (MT-3) is a small cysteine-and metal-rich protein expressed in the brain and found down-regulated in AD. This protein occurs intra-and extracellularly, and it plays an important role in the metabolism of zinc and copper. In cell cultures Zn 7 MT-3, by an unknown mechanism, protects neurons from the toxicity of A␤. We have, therefore, used a range of complementary spectroscopic and biochemical methods to characterize the interaction of Zn 7 MT-3 with free Cu 2؉ ions. We show that Zn 7 MT-3 scavenges free Cu Essential transition metals like copper and zinc play a critical role in neurobiology. The homeostasis of both metals is tightly regulated and essential for brain physiology (1). In vitro evidence suggests that in physiological conditions micromolar concentrations of zinc and copper are actively released from neurons during neurotransmission processes into pre-and postsynaptic clefts. However, at present it is not known whether the released copper is present in a chemically exchangeable form (2). Dysregulated metal metabolism (zinc and copper) occurs in neurodegenerative disorders such as Alzheimer (3, 4), Parkinson (5), and prion (6) diseases. In these diseases increased extracellular copper concentrations and free-radical production have been found. There is now direct evidence that copper is bound to amyloid-␤ peptide (A␤) 2 in senile plaque of Alzheimer disease (AD) (7). Copper is also linked with the neurotoxicity of A␤ and free radical damage (8).Because of its redox-active nature (Cu ϩ /Cu 2ϩ ), its reactivity with molecular oxygen (O 2 ) generates the reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radicals (9, 10). The redox cycling of copper requires its reduction by biological components, including ascorbate, which actively accumulates in the brain at concentrations between 0.5 and 10 mM (11). Hence, copper chelation and its redox-silencing may represent critical events in preventing the progression of neurodegenerative diseases. In recent years a metal chelation therapy has emerged as a promising tool to attenuate abnormal metal-protein interactions that lead to increased free-radical toxicity (10).The natural metal chelator metallothionein-3 (MT-3), also known as the growth inhibitory factor, is a small non-inducible cysteine-and metal-rich protein mainly expressed in the brain. In the brain its expression was found in zinc-enriched neurons. Like other mammalian metallothioneins (MTs), MT-3 binds with a high affinity essential monovalent and divalent d 10 metal ions Cu(I) and Zn(II). Recently, the interaction of Zn 7 MT-3 with the small-GTPase Rab3a, which is strictly linked to the exo-endocytotic cycle of synaptic vesicles, has been demonstrated. It has been suggested that Zn 7 MT-3 actively participates in synaptic cycle of zinc vesicles...

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“…There is a continuing interest in the structure of Cu I -Sclusters with sulfide bridges because of their photo-physical properties [1], possible use as models for enzyme-active sites [2], and in relation to the froth flotation of copper containing ores [3]. Copper(I) dialkyldithiophosphate (Cu I R 2 dtp, R = alkyl) complexes are tetra- [4], hexa- [5] or octa-nuclear [5][6][7] and contain only ligands of the bridging type.…”

Section: Introductionmentioning

confidence: 99%