Superoxide dismutase mimetic activity of a cyclic tetrameric Schiff base N-coordinated Cu(II) complex

A pulse radiolytic study using the cyclic tetrameric Schiff base N-coordinated copper complex Cu(TAAB)²⁺ has been performed. The reaction of the Cu(TAAB)²⁺ complex with superoxide revealed pseudo first-order characteristics with the rate constant of k ₂ = (2.9 ± 0.5) × 10⁸ mol^–1 s^–1 dm³. The complex survive presence of competing serum albumin in physiological concentrations. The complex stability constant K = 1.15 × 10¹⁸ (log K = 18.06) is two orders of magnitude higher than that of Cu(II)-serum albumin (log K = 16.2). Transient changes of the stability during the oxidation/reduction process and in the presence of 600 /mol l^–1 albumin did not affect significantly either the electronic absorption of the complex or its catalytic activity.     

Cu(II) catalysed hydrolysis of thiaminepyrophosphate: structure-reactivity relationship

The kinetics of the Cu(II) catalysed hydrolysis of thiamine-pyrophosphate (TPP) has been studied in aqueous solution at 56,64 and 78° over a pH fange of 3.0 to 7.0 at a constant ionic strength of 0.10 M (KNO₃). The pH rate profiles were analysed and the overall rate constants resolved into individual specific rate constants relating to various Cu:TPP chelate species in solution. Activation parameters ΔH², ΔS^° and ΔG² for the specific rate constants of various chelate species of TPP are reported. The possible mechanism of the Cu(II) promoted hydrolysis of TPP is discussed. The structure-reactivity relationship is also discussed.     

Re-evaluating the effects of organic ligands on copper toxicity to barley root elongation in culture solution

Abstract

In the presence of weak ligands, both free ion activity and organic complexes of Cu should b considered when predicting Cu toxicity in aquatic and soil-plant systems. However, there is littl information about the quantitative contribution of Cu that is organically complexed to Cu toxicity. In thi study, a bioassay using barley root elongation in culture solution was used to investigate the effects o organic ligands with different conditional stability constants on Cu toxicity and the quantitativ contribution of the organically complexed Cu to the Cu toxicity. The results indicated that a significan decrease (p<0.05) in Cu toxicity, assessed by barley root elongation, was observed in response to th addition of organic ligands. The decrease differed, to some extent, with different organic ligands o disodium ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), oxalate and malate at low and constant free Cu²⁺ activity. Addition of EDTA or NTA resulted in strong reduction of Cu toxicity while modest reduction of Cu toxicity was observed for the addition of malate as the relatively wea ligand. Furthermore, the results of the present study revealed that the CuNTA^? and CuEDTA^2? complexes were not toxic, while the Cu–malate complexes were mildly toxic to barley root elongation More importantly, it was found that the toxicity of Cu–malate complexes were nearly 0.5-fold less than that of free Cu²⁺ ions.     

Synthesis, spectroscopic characterization and biological activity on newly synthesized copper(II) and nickel(II) complexes incorporating bidentate oxygen-nitrogen hydrazone ligands

We report the synthesis of the hydrazone ligands, 1-(phenyl-hydrazono)-propan-2-one (PHP), 1-(p-tolyl-hydrazono)-propan-2-one (THP), 1-[(4-chloro-hydrazono)]-propan-2-one (CHP), and their Ni(II) and Cu(II) metal complexes. The structure of the ligands and their complexes were investigated using elemental analysis, magnetic susceptibility, molar conductance and spectral (IR, UV, and EPR) measurements. IR spectra indicate that the free ligands exist in the hydrazo-ketone rather than azo-enol form in the solid state. Also, the hydrazo-NH exists as hydrogen bonded to the keto-oxygen either as intra or as intermolecular hydrogen bonding. In all the studied complexes, all ligands behave as a neutral bidentate ligands with coordination involving the hydrazone-nitrogen and the keto-oxygen atoms. The magnetic and spectral data indicate a square planar geometry for Cu²⁺ complexes and an octahedral geometry for Ni²⁺ complexes. The ligands and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. They were found to be more active against Gram-positive than Gram-negative bacteria. It may be concluded that the antimicrobial activity of the compounds is related to cell wall structure of bacteria.Protonation constant of (PHP) ligand and stability constants of its Cu²⁺ and Ni²⁺ complexes were determined by potentiometric titration method in aqueous solution at ionic strength of 0.1 M sodium nitrate. It has been observed that the hydrazone ligand (PHP) titrated here has one protonation constant. The divalent metal ions Cu²⁺ and Ni²⁺ form with (PHP) 1:1 and 1:2 complexes. The insolubility of (THP) and (CHP) ligands in aqueous medium does not permit the determination of their protonation constants and formation constants of the corresponding complexes in aqueous solution.     

Direct measurement of the self-exchange rate of stellacyanin by a novel e.p.r. method.

A method for reconstituting the blue copper protein stellacyanin with the stable copper isotopes 63Cu and 65Cu is reported. Small differences in the e.p.r. spectra of the two isotopic forms of stellacyanin have been used to monitor the electron self-exchange reaction of stellacyanin by rapid-freeze e.p.r. methods. The self-exchange rate constant (k11) for stellacyanin has been determined as 1.2 X 10(5) M-1 X S-1 at 20 degrees C. This value is in close agreement with values obtained from less-direct methods.     

Metal-directed synthesis of a chiral acyclic pentaamine and pendant-arm macrocyclic hexaamine derived from an amino acid

l-3-Phenylpropane-1,2-diamine (dapp) was prepared by a three-step synthesis based on l-phenylalanine and characterized, including determination of stability constants with M²⁺ ions (Ni, Cu, Zn, Cd). The reaction of L-3-phenylpropane-1,2-diamine as the [Cu(dapp)₂]²⁺ complex ion with formaldehyde and nitroethane in basic solution yields the acyclic (5-methyl-5-nitro-1,9-diphenyl-3,7-diazanonane-1,9-diamine)copper(II) complex ion, [Cu(1)]²⁺, as the major product. In addition, small amounts of the macrocyclic complex ion (2,10-diphenyl-6,13-dimethyl-6,13-dinitro-1,4,8,11-tetraazacyclotetradecane)copper(II), [Cu(2)]²⁺, form. Reduction of the [Cu(1)]²⁺ ion with zinc in aqueous acid yields the acyclic polyamine 5-methyl-1,9-diphenyl-3,7-diazanonane-1,5,9-triamine (3), an analogue of the previously reported pentaamine 5-methyl-3,7-diazanonane-1,5,9-triamine. Using the bis(l-3-phenylpropane-1,2-diamine)palladium(II) as precursor and an excess of other reagents, the macrocyclization reaction to produce [Pd(2)]²⁺ proved more successful. Reduction and recomplexation to copper(II) allowed isolation of the 2,9-dibenzyl-6,13-diammonio-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane)copper(II) ion, [Cu(4H₂²⁺)]⁴⁺. The acyclic complex [Cu(1)]²⁺ promotes the hydrolytic cleavage of plasmid DNA modestly; a mechanism to support this observation is presented.     

Inhibition of nitrogen fixation in alfalfa by arsenate, heavy metals, fluoride, and simulated Acid rain

The acute effects of aqueous solutions of As, Cd, Cu, Pb, F, and Zn ions at concentrations from 0.01 to 100 micrograms per milliliter and solutions adjusted to pH 2 to 6 with nitric or sulfuric acid were studied with respect to acetylene reduction, net photosynthesis, respiration rate, and chlorophyll content in Vernal alfalfa (Medicago sativa L. cv. Vernal). The effects of the various treatments on acetylene reduction varied from no demonstrable effect by any concentration of F⁻ and 42% inhibition by 100 micrograms Pb²⁺ per milliliter, to 100% inhibition by 10 micrograms Cd²⁺ per milliliter and 100 micrograms per milliliter As, Cu²⁺, and Zn²⁺ ions. Zn²⁺ showed statistically significant inhibition of activity at 0.1 micrograms per milliliter. Acid treatments were not inhibitory above pH 2, at which pH nitric acid inhibited acetylene reduction activity more than did sulfuric acid. The inhibition of acetylene reduction by these ions was Zn²⁺ > Cd²⁺ > Cu²⁺ > AsO₃⁻ > Pb²⁺ > F⁻. The sensitivity of acetylene reduction to the ions was roughly equal to the sensitivity of photosynthesis, respiration, and chlorophyll content when Pb²⁺ was applied, but was 1,000 times more sensitive to Zn²⁺. The relationship of the data to field conditions and industrial pollution is discussed.     

Effect of Cu Toxicity on Growth of Cowpea (Vigna unguiculata)

Accurate determination of the rhizotoxicity of Cu in dilute nutrient solutions is hindered by the difficulty of maintaining constant, pre-determined concentrations of Cu (micromolar) in solution. The critical Cu²⁺ activity associated with a reduction in the growth of solution-grown cowpea (Vigna unguiculata (L.) Walp. cv. Caloona) was determined in a system in which Cu was maintained constant through the use of a cation exchange resin. The growth of roots and shoots was found to be reduced at solution Cu²⁺ activities ≥1.7 μM (corresponding to 90% maximum growth). Although root growth was most likely reduced due to a direct Cu²⁺ toxicity, it is considered that the shoot growth reduction is attributable to a decrease in tissue concentrations of K, Ca, Mg, and Fe and the formation of interveinal chlorosis. At high Cu²⁺ activities, roots were brown in color, short and thick, had bent root tips with cracking of the epidermis and outer cortex, and had local swellings behind the roots tips due to a reduction in cell elongation. Root hair growth was reduced at concentrations lower than that which caused a significant reduction in overall root fresh weight.     

The Effects of Fulvic Acid on Copper Bioavailability to Porcine Oviductal Epithelial Cells

This study assessed the effect of dissolved organic matter on the copper (Cu) bioavailability to mammalian cells, porcine oviductal epithelial cells (POEC), in order to imply its effect onto humans. Cu toxicity was investigated in the presence of with and without fulvic acid (FA). Dissociation and exchange rate constants were calculated by using competing ligand Chelex-100, and optical parameters were employed to help explain the complexation of their aromatic and aliphatic structures. Their morphological change was observed using transmission electron microscope (TEM), and Cu species were calculated using MINTEQA2 program. The results showed that the dissociation rate constant of Cu²⁺–FA was equal to 9.08?×?10^?4?s^?1, which was slower than the exchange rate at 1.95?×?10^?3?s^?1. Although Cu–FA was significantly absorbed into the cells higher than Cu²⁺, it showed less damage than tested with Cu²⁺. TEM and optical studies showed many aggregations around nucleus suggesting the amphipathic character of FA helped binging to the nuclear surfaces of both Cu–FA and FA treatments. Even though the MINTEQA2 calculations showed that there was free Cu²⁺ in the mixed solutions around 39.2%, it could not bind with the cell surface. This suggested that the effect of FA was strong and had a lot of influence on the living surface of POEC, modifying the effect of Cu toxicity.     

Thioctic Acid and Dihydrolipoic Acid are Novel Antioxidants Which Interact With Reactive Oxygen Species

Thioctic acid (TA) and its reduced form dihydrolipoic acid (DHLA) have recently gained somc recognition as useful biological antioxidants. In particular, the ability of DHLA to inhibit lipid peroxidation has been reported. In the present study, the effects of TA and DHLA on reactive oxygen species (ROS) generated in the aqueous phase have been investigated. Xanthine plus xanthine oxidase-generated superoxide radicals (O₂), detected by electron spin resonance spectroscopy (ESR) using DMPO as a spin trap. were eliminated by DHLA but not by TA. The sulhydryl content of DHLA, measured using Ellman's reagent decreased subsequent to the incubation with xanthine plus xanthine oxidase confirming the interaction between DHLA and O₂^-. An increase of hydrogen peroxide concentration accompanied the reaction between DHLA and O₂x, suggesting the reduction of O₂^- by DHLA. Competition of O₂^- with epinephrine allowed us to estimate a second order kinetic constant of the reaction between O₂^- and DHLA, which was found to be a 3.3 × 10⁵ M^-1 s^-1. On the other hand, the DMPO signal of hydroxyl radicals (HO ·) generated by Fenton's reagent were eliminated by both TA and DHLA. Inhibition of the Fenton reaction by TA was confirmed by a chemiluminescence measurement using luminol as a probe for HO ·. There was no electron transfer from Fe²⁺ to TA or from DHLA to Fe^{3 +} detected by measuring the Fe²⁺ -phenanthroline complex. DHLA did not potentiate the DMPO signal of HO · indicating no prooxidant activity of DHLA. These results suggest that both TA and DHLA possess antioxidant properties. In particular. DHLA is very effective as shown by its dual capability by eliminating both O₂^-; and HO ·.     

Solvent effects on intramolecular hydrophobic ligandligand interactions in binary and ternary complexes

The stability constants of mixed ligand complexes of the type M(Phen)(ACA)⁺, where M = Cu²⁺ or Zn²⁺, Phen = 1,10-phenanthroline and ACA^? = propionate, valerate and 2-cyclohexylacetate, were determined by potentiometric pH titration in 50% (v/v) dioxanewater and were compared with the stabilities of the corresponding ternary complexes formed with formate and acetate. The ternary complexes containing the alkanecar?ylates (ACA^?) are significantly more stable, due to intramolecular hydrophobic interactions between the alkyl residue of the ACAt¯ligands and the 1,10-phenanthroline molecule. For Zn(Phen)(valerate)⁺ this intramolecular ligand-ligand interaction was confirmed by¹H NMR shift measurements. The formation degree of the intramolecular adducts in the ternary Cu²⁺ and Zn²⁺ complexes was calculated and the position of the intramolecular equilibrium between the opened and closed isomer was determined: the closed isomer occurs between about 10 to 35 percent. Comparisons with related data show that the extent of this interaction is about the same in water and in 50% aqueous dioxane; this contrasts with the experience made with simple unbridged adducts, which are destabilized by the addition of dioxane (or other organic solvents). Furthermore, evaluation of the available stability data for the Cu²⁺/leucinate (Leu^?) system shows that addition of some dioxane to an aqueous solution (in which of the closed isomer exists to about 20%) favors the intramolecular interaction between the two isopropyl residues in Cu(Leu)₂ considerably: in 40 to 50% aqueous dioxane the formation degree of the closed isomer reaches about 80%. Higher concentrations of the organic solvent destabilize the hydrophobic interaction. The overall stability of Cu(Leu)⁺ and Cu(Leu)₂, as well of Cu(alaninate)⁺ and Cu(alaninate)₂, is governed by the polarity of the solvent while the extent of the intramolecular ligand-ligand interaction is influenced by the hydrophobic properties of the solvent molecules. Based on the stability data it is shown that intramolecular ligandligand interactions are quite a common feature for many binary and ternary amino acid complexes: e.g., M(norvalinate)₂, M(phenyl-alaninate)₂, M(tyrosinate)₂ [M = Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺] or Cu(tyrptophanate)₂ and M(phenylalaninate)(norvalinate) or M(phenylalaninate)(tyrosinate) [M = Co²⁺, Ni²⁺, Cu²⁺]. In addition, evidence is presented that direct M²⁺-aromatic interactions are of no significance in these amino acid complexes in solution. The relevance of the present results with regard to biological systems is indicated.     

Copper bioreduction and nanoparticle synthesis by an enrichment culture from a former copper mine

Microorganisms can facilitate the reduction of Cu²⁺, altering its speciation and mobility in environmental systems and producing Cu-based nanoparticles with useful catalytic properties. However, only a few model organisms have been studied in relation to Cu²⁺ bioreduction and little work has been carried out on microbes from Cu-contaminated environments. This study aimed to enrich for Cu-resistant microbes from a Cu-contaminated soil and explore their potential to facilitate Cu²⁺ reduction and biomineralisation from solution. We show that an enrichment grown in a Cu-amended medium, dominated by species closely related to Geothrix fermentans, Azospira restricta and Cellulomonas oligotrophica, can reduce Cu²⁺ with subsequent precipitation of Cu nanoparticles. Characterisation of the nanoparticles with (scanning) transmission electron microscopy, energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy supports the presence of both metallic Cu(0) and S-rich Cu(I) nanoparticles. This study provides new insights into the diversity of microorganisms capable of facilitating copper reduction and highlights the potential for the formation of distinct nanoparticle phases resulting from bioreduction or biomineralisation reactions. The implications of these findings for the biogeochemical cycling of copper and the potential biotechnological synthesis of commercially useful copper nanoparticles are discussed.     

Association of antitumor antibiotic Mithramycin with Mn2+ and the potential cellular targets of Mithramycin after association with Mn2+

Mithramycin (MTR), an aureolic acid group of antitumor antibiotic is used for the treatment of several types of tumors. We have reported here the association of MTR with an essential micronutrient, manganese (Mn²⁺). Spectroscopic methods have been used to characterize and understand the kinetics and mechanism of complex formation between them. MTR forms a single type of complex with Mn²⁺ in the mole ratio of 2:1 [MTR: Mn²⁺] via a two step kinetic process. Circular dichroism (CD) spectroscopic study indicates that the complex [(MTR)₂ Mn²⁺] has a right-handed twist conformation similar in structure with the complexes reported for Mg²⁺ and Zn²⁺. This conformation allows binding via minor groove of DNA with (G, C) base preference during the interaction with double-stranded B-DNA. Using absorbance, fluorescence, and CD spectroscopy we have shown that [(MTR)₂ Mn²⁺] complex binds to double-stranded DNA with an apparent dissociation constant of 32?μM and binding site size of 0.2 (drug/nucleotide). It binds to chicken liver chromatin with apparent dissociation constant value 298?μM. Presence of histone proteins in chromatin inhibits the accessibility of the complex for chromosomal DNA. We have also shown that MTR binds to Mn²⁺ containing metalloenzyme manganese superoxide dismutase from Escherichia coli.     

Investigation on the micro-mechanisms of Al3+ interfering the reactivities of aspartic acid and its biological processes with Mg2+

Density functional theory (DFT) has been applied to study the micro-mechanisms of Al³⁺ interfering the reactivities of aspartic acid (H₂asp) and its biological processes with Mg²⁺. All the 46 stable conformers of Hasp^- and 3 of asp²⁻ have been determined at the B3LYP/6-311++G** level, showing that the 7 most stable conformers of Hasp⁻ all present a very strong and linear O–H···O H-bond between carboxyl and carboxylic acid groups with the bond energy high up to 162 kJ mol⁻¹. The reaction thermodynamics and micro-mechanism between Al³⁺ and Hasp⁻ (or asp²⁻) in aqueous phase have been investigated by the combined application of supramolecular model and polarizable continuum IEFPCM solvent model, firstly revealing Al³⁺ interfering in the biological processes of aspartic acid. The substitution thermodynamics and mechanisms of Mg²⁺ by Al³⁺ in the biological processes between the species of aspartic acid and Mg²⁺ in aqueous phase were probed, revealing the facile displacement of Mg²⁺ by Al³⁺. These results may provide a reasonable mechanism of Al³⁺ biological toxicity at the microscopic level.     

NMR and density study of Co site binding by polyelectrolytes

The changes of density and chemical shifts of the water proton upon addition of CoCl₂ to aqueous solutions of tetramethylammonium salts of seven polyelectrolytes (polyphosphate, maleic acid-methylvinylether alternated copolymer, polyacrylic acid, carboxymethylcellulose of substitution degree 0.98, 1.3, 2.1, 2.65) have been measured. Assuming a negligible contribution of pseudo-contact interaction to the water proton chemical shift and a constant hyperfine constant upon displacement of water molecules by other ligands, has permitted the calculation of (i) the number of water molecules released by Co²⁺ ions upon binding and the approximate fraction of Co²⁺ ions bound with loss of water, and (ii) the total volume change upon binding and the individual contributions of counterions and polyelectrolyte charged sites to this volume change. Our results are generally in agreement with those obtained using other methods.     

A comparison of the inhibitory potency of reversibly acting inhibitors of anion transport on chloride and sulfate movements across the human red cell membrane

The effects of a variety of chemically diverse, reversibly acting inhibitors have been measured on both Cl^? and SO₄^2? equilibrium exchange across the human red cell membrane. The measurements were carried out under the same conditions (pH 6.3, 8°C) and in the same medium for both the Cl^? and SO₂⁴ tracer fluxes. Under these conditions the rate constant for Cl^?-Cl^? exchange is about 20 000 times larger than that for SO₄^2?-SO₄^2? exchange. Despite this large difference in the rates of transport of the two anions, eight different reversibly acting inhibitors have virtually the same effect on the Cl^? and SO₄^2? transport. The proteolytic enzyme papain also has the same inhibitory effect on both the Cl^? and SO₄^2? self-exchange. In addition, the slowly penetrating disulfonate 2-(4′-aminophenyl)-6-methylbenzenethiazol-3′,7-disulfonic acid (APMB) is 5-fold more effective from the outer than from the inner membrane surface in inhibiting both Cl^? and SO₄^2? self-exchange. We interpret these results as evidence that the rapidly penetrating monovalent anion Cl^? and the slowly penetrating divalent anion SO₄^2? are transported by the same system.     

Oxidation of (hydroxyethyl)ferrocene by [2-pyridylmethylbis(2-ethylthioethyl)/amine]copper(II)

A kinetic study of the oxidation of (hydroxyethyl)ferrocene (HEF) by [2-pyridylmethylbis(2-ethyl-thioethyl)ainine]copper(II) (Cu(pmas)²⁺) is reported, with the objective of documenting the influence of the two thioether sulfur ligands on the electron transfer rate. Both reactants exhibit a first-order dependence at pH 6, I = 0.1 M(NaNO₃); k(25°C) = 1.3 × 10⁴M⁻¹sec⁻¹, ΔH3 = 10.1 kcal/mole, ΔS3 = −6 eu. The apparent Cu(pmas)^2+/+ self-exchange electron transfer rate constant calculated from this reaction on the basis of relative Marcus theory (4.7 × 10¹M⁻¹ sec⁻¹) agrees well with previous findings on ferrocytochrome c, Fe(CN)₆⁴⁻, and Ru(NH₃)₅py²⁺ oxidations. Spectrophotometric titrations of Cu(pmas)²⁺ and Cu(tmpa)²⁺ (tmpa = tris(2-pyridylmethyl)amine) with azide ion showed that both Cu(pmas)N₃)⁺ (K_f1 = 3.1 × 10³M⁻¹) and Cu(pmas)(N₃)₂ (K_f2 = 3.5 × 10¹M⁻¹) but Cu(tmpa)(N₃)⁺ (K_f = 6.6 × 10²M⁻¹) are formed up to 0.15 M N₃⁻ (25°C, pH 6, I = 0.2 M), suggesting that a thioether sulfur atom is displaced in the uptake of a second N₃⁻ ion by Cu(pmas)(N₃)⁺. The effect of thioether sulfur displacement by azide ion on the HEF-Cu(pmas)²⁺ reaction rate may be understood entirely through the tendency of N₃⁻ to shift the position of the redox equilibrium towards the reactant side, without invoking any special role for the sulfur ligand in promoting electron transfer reactivity.     

Analysis of the kinetics of electron transfer reactions of hemoglobin and myoglobin with inorganic complexes.

The kinetics of methemoglobin reduction by Fe(EDTA)^2? have been studied and found to follow a second order rate law with k = 29.0 $\text{M}$^?1 s^?1 [25°C, μ = 0.2 $\text{M}$, pH 7.0 (phosphate)], $\text{ΔH}{}^3\text{= 5.5 ± 0.7 kcal/mol}$, and $\text{ΔS}{}^2\text{= ?33 ± 2 e.u.}$. The electrostatics-corrected self-exchange rate constant (k₁₁^corr) for hemoglobin based on the Fe(EDTA)^2? cross-reaction is 2.79×10^?3$\text{M}$^?1 s^?1. This rate constant is compared with others reported for a water-soluble iron porphyrin and calculated from published data for the reactions of myoglobin and hemoglobin with Fe(EDTA)^2? and Fe(CDTA)^2?/?. The k₁₁^corr values for these systems range over ten orders of magnitude with heme ? myoglobin > hemoglobin.     

Overexpression of amyloid precursor protein increases copper content in HEK293 cells

Amyloid precursor protein (APP) is a transmembrane glycoprotein widely expressed in mammalian tissues and plays a central role in Alzheimer’s disease. However, its physiological function remains elusive. Cu²⁺ binding and reduction activities have been described in the extracellular APP135-156 region, which might be relevant for cellular copper uptake and homeostasis. Here, we assessed Cu²⁺ reduction and ⁶⁴Cu uptake in two human HEK293 cell lines overexpressing APP. Our results indicate that Cu²⁺ reduction increased and cells accumulated larger levels of copper, maintaining cell viability at supra-physiological levels of Cu²⁺ ions. Moreover, wild-type cells exposed to both Cu²⁺ ions and APP135-155 synthetic peptides increased copper reduction and uptake. Complementation of function studies in human APP751 transformed Fre1 defective Saccharomyces cerevisiae cells rescued low Cu²⁺ reductase activity and increased ⁶⁴Cu uptake. We conclude that Cu²⁺ reduction activity of APP facilitates copper uptake and may represent an early step in cellular copper homeostasis.     

Multinuclear nuclear magnetic resonance and density functional theoretical studies on the structure of bisperoxovanadium complexes with bidentate donors

Solid state and solution ⁵¹V and ¹³C NMR studies on four fundamental bisperoxovanadium complexes containing bidendate donor ligands were reported, together with DFT calculations of structural and NMR parameters. The ⁵¹V solid-state NMR characterization of the four complexes with [VO(O₂)₂L]ⁿ⁻ anion {abbr. bpVL, where L = oxalic acid dianion (ox), pyridine-2-carboxylic acid (pic), bipyridine (bipy), and 1,10-phenanthroline (phen)} show that the ligands have a significant effect on the electric-field gradient tensor, with the quadrupolar coupling constant ranging from 4.0 to 5.8 MHz. The experimental and theoretical results suggest that the vanadium center of bpVpic, bpVphen and bpVbipy in solid state and aqueous solution are all seven-coordinated except that bpVox is six-coordinated in aqueous solution. The steric space hindrance of the organic ligands and the bonding between vanadium with the coordination influences the activity of bpVL complexes.