Modeling by assembly and molecular dynamics simulations of the low Cu2+ occupancy form of the mammalian prion protein octarepeat region: gaining insight into Cu2+-mediated beta-cleavage

The prion protein has garnered considerable interest because of its involvement in prion disease as well as its unresolved cellular function. The octarepeat region in the flexible N-domain is capable of binding copper through multiple coordination modes. Under conditions of low pH and low Cu²⁺ concentration, the four octarepeats (ORs) cooperatively coordinate a single copper ion. Based on the average structure of the PHGG and GWGQ portions of a copper-free OR₂ model from molecular dynamics simulations, the starting structures of the OR₄ complex could be constructed by assembling the repeating structure of PHGG and GWGQ fragments. The resulting model contains a preformed site suitable for Cu²⁺ coordination. Molecular dynamics simulations of Cu²⁺ bound to the assembled OR₄ model (Cu:OR₄) reveal a close association of specific Trp and Gly residues with the Cu²⁺ center. This low Cu²⁺-occupancy form of prion protein is redox-active and can readily initiate cleavage of the OR region, mediated by reactive oxygen species generated by Cu⁺. The OR region is known to be required for β-cleavage, as are the Trp residues within the OR region. The β-cleaved form of the prion protein accumulates in amyloid fibrils. Hence, the close approach of Trp and Gly residues to the Cu²⁺ coordination site in the low Cu²⁺-occupancy form of the OR region may signal an important interaction for the initiation of prion disease.     

Action of Heavy Metals on Hill Activity and O(2) Evolution in Anacystis nidulans

Addition of 5 micromolar Cu²⁺, Cd²⁺, and Zn²⁺ was inhibitory to 10 micromolar H₂O₂-supported Hill activity (dichlorophenolindophenol reduction) and O₂ evolution in membrane preparation from Anacystis nidulans. The reversal of Cd²⁺ and Zn²⁺ inhibition, in contrast to Cu²⁺, by exogenously added catalase (EC 1.11.1.6) suggested that the former cations were inhibitory to H₂O₂ degradation. Ascorbic acid (20 micromolar) supported 27% of the Hill activity which was insensitive to DCMU (10 micromolar) and the remaining activity, attributable to the DCMU sensitive process, was sensitive to inhibition by Cu²⁺ only. It is suggestive that the action site of Cd²⁺ and Zn²⁺ is located between the electron donation sites of H₂O₂ and ascorbic acid, while that of Cu²⁺ is located beyond it. Electron donation by reduced glutathione was insensitive to DCMU and Cu²⁺, indicating that the action site of Cu²⁺ is prior to its electron donation site. Further, the phenanthroline (10 micromolar) reversal of Cu²⁺ inhibition of Hill activity suggested a tentative action site of Cu²⁺ at the level of cytochrome.     

Relationship between NaCl- and H2O2-Induced Cytosolic Ca2+ Increases in Response to Stress in Arabidopsis

Salinity is among the environmental factors that affect plant growth and development and constrain agricultural productivity. Salinity stress triggers increases in cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) via Ca²⁺ influx across the plasma membrane. Salinity stress, as well as other stresses, induces the production of reactive oxygen species (ROS). It is well established that ROS also triggers increases in [Ca²⁺]_i. However, the relationship and interaction between salinity stress-induced [Ca²⁺]_i increases and ROS-induced [Ca²⁺]_i increases remain poorly understood. Using an aequorin-based Ca²⁺ imaging assay we have analyzed [Ca²⁺]_i changes in response to NaCl and H₂O₂ treatments in Arabidopsis thaliana. We found that NaCl and H₂O₂ together induced larger increases in [Ca²⁺]_i in Arabidopsis seedlings than either NaCl or H₂O₂ alone, suggesting an additive effect on [Ca²⁺]_i increases. Following a pre-treatment with either NaCl or H₂O₂, the subsequent elevation of [Ca²⁺]_i in response to a second treatment with either NaCl or H₂O₂ was significantly reduced. Furthermore, the NaCl pre-treatment suppressed the elevation of [Ca²⁺]_i seen with a second NaCl treatment more than that seen with a second treatment of H₂O₂. A similar response was seen when the initial treatment was with H₂O₂; subsequent addition of H₂O₂ led to less of an increase in [Ca²⁺]_i than did addition of NaCl. These results imply that NaCl-gated Ca²⁺ channels and H₂O₂-gated Ca²⁺ channels may differ, and also suggest that NaCl- and H₂O₂-evoked [Ca²⁺]_i may reduce the potency of both NaCl and H₂O₂ in triggering [Ca²⁺]_i increases, highlighting a feedback mechanism. Alternatively, NaCl and H₂O₂ may activate the same Ca²⁺ permeable channel, which is expressed in different types of cells and/or activated via different signaling pathways.     

Silver(I) derivatives with new functionalised acylpyrazolonates

Silver(I) acylpyrazolonate derivatives of formula [Ag(Q)(R₃P)]₂ and [Ag(Q)(R₃P)₂], (QH=1-phenyl-3-methyl-4-R′(CO)-pyrazol-5-one; Q^OH, R′=furane; Q^SH, R′=thiophene; R=Ph, Cy, o-tol), have been synthesised and characterised, both in the solid state and in solution. The derivatives [Ag(Q)(R₃P)]₂ contain dinuclear AgO₂NP units with the acylpyrazolonate coordinating in a bridging O,O′-Q-N fashion. The [Ag(Q)(R₃P)₂] are tetrahedral species, with the distortion from ideal geometry increasing with the bulk of the phosphine. The [Ag(Q)(R₃P)₂] derivatives are fluxional in chloroform solution when R₃P is sterically hindered (R=Cy or o-tol), dissociating partially to the [Ag(Q)(R₃P)] fragment and free R₃P. [Ag(Q^S)(Ph₃P)]₂ reacts with 1-methyl-2-mercaptoimidazole (Hmimt) affording the compound [Ag(Hmimt)(Ph₃P)(Q^S)] and [Ag(Q^O)(Ph₃P)]₂ reacts with 1-methyl-imidazole (Meim) affording the compound [Ag(Meim)(Ph₃P)(Q^O)], whereas [Ag(Q^S)(Ph₃P)]₂ reacts with 1,10-phenanthroline (phen), affording the compound [Ag(phen)(Ph₃P)](Q^S). Finally [Ag(Q^S)(Ph₃P)₂] reacts with phen producing the ionic species [Ag(phen)(Ph₃P)₂](Q^S).     

The role of Ca2+ ions in modulating changes induced in bean plants by an excess of Cu2+ ions. Chlorophyll fluorescence measurements

Ca²⁺-dependent influence of excess Cu²⁺ on the photosynthetic akpparatus monitored through chlorophyll fluorescence measurements was investigated in runner bean plants (Phaseolus coccineus L. cv. Pie kny Ja?) at three different growth stages. It was observed that the toxic effect of excess Cu²⁺ on plants depends both on their growth stages and the Ca²⁺ content in the medium. Increased Ca²⁺ content limits Cu²⁺ action on plants at their initial growth stage (I) through: stabilization of the PSII complex (increase of the ratio of variable to minimal fluorescence [F_v/F₀]), improved electron flow and reoxidative processes of the quinone primary electron acceptor of PSII (Q_A) (increase of quantum yield of PSII electron transport [φ_e] and photochemical quenching of fluorescence [q_P] values) and elimination of nonphotochemical energy dissipation (decrease of nonphotochemical fluorescence quenching from the Stern-Volmer equation [NPQ] and fraction of the absorbed light energy not used for photochemistry [LNU] values). At this growth stage excess Cu²⁺ decreases the rates of Q_A reduction as a result of decreased PSII activity at its donor side only at lower Ca²⁺ level. At the intermediate growth stage (II) the plants were less sensitive to Cu²⁺ treatment and also to changed Ca²⁺ content. A weakening of some photochemical processes by excess Cu²⁺ could be observed only at a higher Ca²⁺ dose. At the final growth stage of plants (III) Ca²⁺ ions exerted a decisively different effect on the mechanism of excess Cu²⁺ action on bean plants, visualized by decreased PSII stabilization and utilization of absorbed light energy at increased Ca²⁺ content in the medium.     

Coordination numbers in hydrated Cu(II) ions

The potential energy surface of [Cu(H₂O)_n]²⁺ clusters with n?=?12, 16, and 18 was explored by using a modified version of the simulated annealing method. Such exploration was carried out by using the PM7 semiempirical method to obtain around 100,000 isomers, which provide candidates to be optimized with PBE0-D3, M06-2X, and BHLYP exchange-correlation functionals coupled with the 6–311++G** basis set. These methods based on the Kohn-Sham approach delivered isomers with coordination numbers of 4, 5, and 6. The analysis used to obtain coordination numbers was based on geometrical parameters and the quantum theory of atoms in molecules (QTAIM) approach. Our methodology found only one isomer with fourfold coordination and its probabilities to appear in these clusters are quite small for high temperatures. The procedure used in this article predicts important populations of fivefold and sixfold coordination clusters, in fact, the fivefold coordination dominates for PBE0-D3 and BHLYP methods, although the sixfold coordination starts to be important when the number of water molecules is increased. The nature of axial and equatorial contacts is discussed in the context of the QTAIM and the noncovalent interaction index (NCI), which gives a clear classification of such orientations. Also, these methods suggest a partial covalent interaction between the Cu²⁺ and water molecules in both positions; equatorial and axial.     

A new Co(III)-hypocrellin B complex with enhanced photonuclease activity

Hypocrellin B (HB), a naturally occurring photosensitizer, has been extensively and intensively studied as a promising photodynamic therapy (PDT) agent. In this work, a new Co(III) complex [Co₂(HB)(tmp)₄]⁴⁺ (tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) was designed and synthesized with HB as bridging ligand and tmp as terminal ligand. [Co₂HB(tmp)₄]⁴⁺ exhibits improved water solubility, enhanced absorptivity in the phototherapeutic window, increased binding affinity and DNA photocleavage capability toward dsDNA with respect to HB. The photodynamic activity of [Co₂(HB)(tmp)₄]⁴⁺ stems from its ¹O₂ photosensitization ability, in sharp contrast to [Cu₂(HB)(tmp)₂]²⁺ which relies on superoxide anion radical (O₂^-) and hydroxyl radical (·OH) to photocleave DNA, though the both complexes possess similar electrochemical properties. The remarkable difference between the photodynamic mechanisms of [Co₂(HB)(tmp)₄]⁴⁺ and [Cu₂(HB)(tmp)₂]²⁺ was discussed in detail.     

A2A R mediated modulation in IP3 levels altering the [Ca2+]i through cAMP-dependent PKA signalling pathway

Stimulation of A_2A receptors (A_2A R) coupled to G_s/olf protein activates Adenylyl cyclase (AC) leading to the release of cAMP which activates the cAMP-dependent PKA phosphorylation. The possible role of A_2A R in the modulation of free cytosolic Ca²⁺ concentration ([Ca²⁺]_i) involving IP₃, cAMP and PKA was investigated in HEK 293-A_2A R. The levels of IP₃ and cAMP were observed by enzyme immunoassay detection method and [Ca²⁺]_i using Fluo-4 AM. Moreover, cAMP-dependent PKA was determined using the PKA Colorimetric Activity Kit. We observed that the cells pre-treated with A_2A R agonist NECA showed increased levels of cAMP, PKA, IP₃ and [Ca²⁺]_i levels. However, the reverse effect was observed with A_2A R antagonists (ZM241385 and caffeine). Blocking the G_αq/PLC/DAG/IP₃ pathway with neomycin, a PLC inhibitor did not affect the modulation of IP₃ and [Ca²⁺]_i levels in HEK 293-A_2A R cells. To investigate the G_αi/AC/cAMP/PKA, HEK 293-A_2A R cells pre-treated with pertussis toxin followed by forskolin in the presence of A_2A R agonist (NECA) showed no effect on cAMP levels. Further, G_αs/AC/cAMP/PKA pathway was investigated to elucidate the role of cAMP-dependent PKA in IP₃ mediated [Ca²⁺]_i modulation. In the HEK 293-A_2A R cells pre-treated with PKA inhibitor KT5720 and treated with NECA led to inhibit the IP₃ and [Ca²⁺]_i levels. The study distinctly demonstrated that A_2A R modulates IP₃ levels to release the [Ca²⁺]_i via cAMP-dependent PKA. The role of A_2A R mediated G_αs pathway inducing IP₃ mediated [Ca²⁺]_i release may open new avenues in the therapy of neurodegenerative disorder.     

Synthesis,characterization and bioactivities of a new covalent copper(II) compound derived from {P2Mo5O23}6− and thiosemicarbazones

In this article, a new compound H₂[{Cu(HL)(H₂O)}₂(P₂Mo₅O₂₃)]·5H₂O (1) (HL = 2-acetylpyrazine thiosemicarbazone) has been synthesized and structurally characterized by single-crystal X-ray diffraction of and other detection techniques. Interestingly, the structure of 1 is different from many reported copper-based complexes, in which the [P₂Mo₅O₂₃]⁶⁻, two Cu²⁺ ions and two HL were directly connected by covalent bands. Biological studies demonstrated that 1 indicated moderate antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and a better cytotoxicity against human hepatic cancer line (SMMC-7721) than Mitoxantrone (Mito), the current clinical anticancer drug. Besides, the antibacterial mechanisms of 1 have been studied by the membrane integrity disruption, the destructive reactive oxygen species generation (ROS), the glutathione (GSH) depletion and the depressed enzymatic activity of respiratory chain dehydrogenases (RCD). These results revealed that the combination of HL, Cu²⁺, [P₂Mo₅O₂₃]⁶⁻ shows a higher antibacterial and cytotoxic activity.     

Inactivation of mushroom tyrosinase by hydrogen peroxide

Hydrogen peroxide (H₂O₂) inactivates mushroom tyrosinase in a biphasic manner, with the rate being faster in the first phase than in the second one. The inactivation of the enzyme is dependent on H₂O₂ concentration (in the range of 0.05–5.0 mM), but independent of the pH (in the range of 4.5–8.0). The rate of inactivation of mushroom tyrosinase by H₂O₂ is faster under anaerobic conditions (nitrogen) than under aerobic ones (air). Substrate analogues such as L-mimosine, L-phenylalanine, p-fluorophenylalanine and sodium benzoate protect the enzyme against inactivation by H₂O₂. Copper chelators such as tropolone and sodium azide also protect the enzyme. Under identical conditions, apotyrosinase is not inactivated by H₂O₂, unlike holotyrosinase. The inactivation of mushroom tyrosinase is not accelerated by an OH^?dot generating system (Fe²⁺-EDTA-H₂O₂) nor is it protected by OH^dot scavengers such as mannitol, urate, sodium formate and histidine. Exhaustive dialysis or incubation with catalase does not restore the activity of H₂O₂-inactivated enzyme. The data suggest that Cu²⁺ at the active site of mushroom tyrosinase is essential for the inactivation by H₂O₂. The inactivation does not occur via the OH^dot radical in the bulk phase but probably via an enzyme-bound OH^dot.     

A new example of a tetranuclear iron(III) cluster containing the [Fe4O2] core: preparation, X-ray crystal structure, magnetochemistry and Mössbauer study of [Fe4O2(O2CMe)6(N3)2(phen)2]

Two synthetic procedures have been employed that allow access to the new tetranuclear cluster [Fe₄O₂(O₂CMe)₆(N₃)₂(phen)₂] (1), where phen is 1,10-phenanthroline. Complex 1 · 3MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe₄O₂]⁸⁺ core that can be considered as a hybrid of the bent (butterfly) and planar dispositions of four metal ions seen previously in such compounds with transition metals. Complex 1 has been characterized by variable-temperature magnetic susceptibility studies, and by IR and variable-temperature ⁵⁷Fe Mössbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S=0) with antiferromagnetic body-body and body-wingtip interactions between the iron(III) ions of the butterfly core (J_bb=−11 cm⁻¹, J_wb=−70 cm⁻¹). Magnetochemical and Mössbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types.     

Three new multidimensional organic-inorganic hybrids based on polyoxometalates and copper coordination polymers with 4,4′-bipyridine ligands

Three new organic-inorganic hybrid materials with 4,4′-bipy ligands and copper cations as linkers, [Cu^II(H₂O)(4,4′-bipy)₂][Cu^II(H₂O)(4,4′-bpy)₂]₂H[Cu^IIP₈Mo₁₂O₆₂H₁₂] · 5H₂O (1), [Cu^I(4,4′-bipy)][Cu^II(4,4′-bipy)]₂ (BW₁₂O₄₀) · (4,4′-bipy) · 2H₂O (2) and [Cu^I (4,4′-bipy)]₃ (PMo₁₂O₄₀) · (pip) · 2H₂O (3) (pip = piperazine; 4,4′-bipy = 4,4′-bipyridine), have been hydrothermally synthesized. The single X-ray structural analysis reveals that the structure of 1 is constructed from [Cu(H₂O)(4,4′-bipy)₂] complexes into a novel, three-dimensional supermolecular network with 1-D channels in which Cu[P₄Mo₆]₂ dimer clusters reside. To the best of our knowledge, compound 1 is the first complex in which the [P₄Mo₆] clusters have been used as a non-coordinating anionic template for the construction of a novel, three-dimensional supermolecular network. Compound 2 is constructed from the six-supported [BW₁₂O₄₀]⁵⁻ polyoxoanions and [Cu^I(4,4′-bipy)] and [Cu^II(4,4′-bipy)] groups into a novel, 3-D network. Compound 3 exhibits unusual 3-D supramolecular frameworks, which are constructed from tetrasupporting [PMo₁₂O₄₀]³⁻ clusters and [Cu^I (4,4′-bipy)_n] coordination polymer chains. The electrochemical properties of 2 and 3 have been investigated in detail.     

Synthesis and characterization of new unsaturated macrobicyclic and bis(macrocyclic) copper(II) complexes containing N-CH2-N linkages

New copper(II) complexes [CuL²]²⁺ (L²=7,7,9-trimethyl-1,3,6,10,13-pentaazabicyclo[11,2,1^1.13]hexadec-9-ene) and [Cu₂(L³)(H₂O)₂]⁴⁺ have been prepared by the reaction of [CuL¹]²⁺ (L¹=5,5,7-trimethyl-1,4,8,11,14-pentaazatetradce-7-ene) and formaldehyde. The mononuclear complex [CuL²]²⁺ has a square-planar coordination geometry with a 5-6-5-6 chelate ring sequence and is relatively stable even in low pH at room temperature. The dinuclear complex [Cu₂(L³)(H₂O)₂]⁴⁺ consists of two unsaturated 15-membered pentaaza macrocyclic units (7,7,9-trimethyl-1,3,6,10,13-pentaazacyclopentadec-9-ene) that are linked together by a methylene group in a tilted face-to-face arrangement [Cu?Cu distance: 7.413(2) Å ]. Each macrocyclic unit of [Cu₂(L³)(H₂O)₂]⁴⁺ contains one four-membered chelate ring and has a severely distorted octahedral coordination polyhedron. The dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile but is decomposed to [CuL¹]²⁺ and [CuL²]²⁺ in pure water.     

Synthesis, characterization and structural analysis of isostructural dinuclear molybdenum and tungsten oxo-bis-μ-sulfido-benzenedithiolene complexes

Reactions of the molybdenum and tungsten precursors [MO₂S₂]²⁻ with equimolar amounts of benzenedithiol in acetonitrile give the title compounds [M₂O₂(μ-S)₂(bdt)₂]²⁻ with M = Mo, W and bdt = benzene-dithiolate. In case a tungsten to ligand ratio of 1:2 is used the dimer forms as well but only as a minor species whereas the monomer [WO(bdt)₂]²⁻ is the main product. In both dimeric compounds the syn-isomers are formed referring to the position of the apical oxo ligands with respect to the M₂S₂ plane. For the molybdenum compound this contrasts with a published crystal structure of the anti-isomer. Both complexes give highly symmetric isomorphous crystals but still show subtle differences in their bond lengths and angles around the central metal. The X-ray crystal structures of both are analyzed in detail and compared with each other and with the isomeric molybdenum compound. Differences and similarities between tungsten and both isomers of molybdenum complexes are shown to be more influenced by the conformation than by the central metal and a reason for the formation of syn- and anti-isomers based on the respective synthetic procedures is proposed.     

Dinuclear triply bridged copper(II)-carboxylato compounds with different bischelating ligands: Synthesis, crystal structure, spectroscopic and magnetic properties

Three new triply bridged dinuclear copper(II) compounds containing carboxylato bridges, [Cu₂(μ-CH₃COO-κ-O¹,O²)₂(μ-CH₃COO-κ-O¹)(dpyam)₂](BF₄) (1), [Cu₂(μ-CH₂CH₃COO-κ-O¹,O²)(μ-OH)(μ-OH₂)(bpy)₂](ClO₄)₂ (2) and [Cu₂(μ-CH₃COO-κ-O¹,O²)(μ-OH)(μ-OH₂)(phen)₂](ClO₄)₂ (3) (in which dpyam = di-2-pyridylamine, bpy = 2,2-bipyridine, phen = phenanthroline), have been synthesized in order to investigate the magnetic super-exchange pathway between coupled copper(II) centres. All three compounds display a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₃ chromophore. Compound 1 has three acetato bridges, two of which connect each square pyramid at two equatorial sites in a triatomic bridging mode and the third acetato bridge acts at the apical site in the monoatomic bridging mode. The structures of compounds 2 and 3 are mutually similar. In each dinuclear unit, both copper(II) ions are linked at two equatorial positions through a hydroxo bridge and a triatomic carboxylato bridge and at the axial position through a water molecule.The magnetic susceptibility measurements, measured from 5 to 300 K, revealed an antiferromagnetic interaction between the Cu(II) ions in compound 1 and a ferromagnetic interaction for compounds 2 and 3 with singlet-triplet energy gaps (J) of −56, 149 and 120 cm⁻¹, for compounds 1, 2 and 3, respectively.     

Synthesis, crystal structure and magnetic properties of quasi-linear tetranuclear copper(II) Schiff base complexes formed by covalent linkage of asymmetrically dibridged dicopper(II) units

Alkoxo-phenoxo bridged tetranuclear copper(II) complexes [Cu₄L₂(O₂CC₆H₄-p-OH)₂] (1) and [Cu₄L₂(O₂CC₆H₄-o-OH)₂] (2) containing pentadentate Schiff base ligand N,N^′-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H₃L) are prepared and structurally characterized. Crystal structures of the complexes show the covalent linkage between two {Cu₂L(O₂CR)}(R = C₆H₄-p-OH, C₆H₄-o-OH) units through the phenoxo atoms of the Schiff base ligand showing axial/equatorial bonding modes. The Cu(1)-O(2)-Cu(2) alkoxo bridge angle is 131° in 1 and 2. The pendant ortho- and para- OH groups of the three-atom bridging carboxylate ligands show no apparent bonding interactions with the metal or other group(s). The complexes show a d-d band near 635 nm in CH₂Cl₂. Variable temperature magnetic susceptibility measurements in the temperature range 300-18 K show antiferromagnetically coupled spin system. A theoretical fit of the magnetic data using exchange parameters J₁ and J₂ for the intradimer and interdimer units of the quasi-linear tetrameric core gave values as: J₁=−132,J₂=−72 cm⁻¹ for 1 and J₁=−167,J₂=−67 cm⁻¹ for 2.     

Mg2+- and ATP-dependent inhibition of transient receptor potential melastatin 7 by oxidative stress

Transient receptor potential melastatin 7 (TRPM7) is a Ca²⁺- and Mg²⁺-permeable nonselective cation channel that contains a unique carboxyl-terminal serine/threonine protein kinase domain. It has been reported that reactive oxygen species associated with hypoxia or ischemia activate TRPM7 current and then induce Ca²⁺ overload resulting in neuronal cell death in the brain. In this study, we aimed to investigate the molecular mechanisms of TRPM7 regulation by hydrogen peroxide (H₂O₂) using murine TRPM7 expressed in HEK293 cells. Using the whole-cell patch-clamp technique, it was revealed that the TRPM7 current was inhibited, not activated, by the application of H₂O₂ to the extracellular solution. This inhibition was not reversed after washout or treatment with dithiothreitol, suggesting irreversible oxidation of TRPM7 or its regulatory factors by H₂O₂ under whole-cell recording. Application of an electrophile, N-methylmaleimide (NMM), which covalently modifies cysteine residues in proteins, also inhibited TRPM7 current irreversibly. The effects of H₂O₂ and NMM were dependent on free [Mg²⁺]_i; the inhibition was stronger when cells were perfused with higher free [Mg²⁺]_i solutions via pipette. In addition, TRPM7 current was not inhibited by H₂O₂ when millimolar ATP was included in the intracellular solution, even in the presence of substantial free [Mg²⁺]_i, which is sufficient for TRPM7 inhibition by H₂O₂ in the absence of ATP. Moreover, a kinase-deficient mutant of TRPM7 (K1645R) was similarly inhibited by H₂O₂ just like the wild-type TRPM7 in a [Mg²⁺]_i- and [ATP]_i-dependent manner, indicating no involvement of the kinase activity of TRPM7. Thus, these data suggest that oxidative stress inhibits TRPM7 current under pathological conditions that accompany intracellular ATP depletion and free [Mg²⁺]_i elevation.     

Two novel hybrid compounds based on [MW12O40] (M = B, Al) heteropolyanions and copper coordination polymer with bpp ligands

Under hydrothermal condition, two novel organic-inorganic hybrid compounds, [Cu(bpp)][Cu_2.5(bpp)₃(Hbpp)]H_0.5[BW₁₂O₄₀]·1.5H₂O (1) and [Cu(en)₂(H₂O)]{[Cu(bpp)]₃[AlW₁₂O₄₀]}·H₂O (2) (bpp = 1,3-bis(4-pyridyl)propane; en = ethylenediamine), have been synthesized based on B/Al atom-centered Keggin-type polyoxometalates combined with Cu ions and bpp ligands. The two compounds are characterized through single-crystal X-ray diffraction analysis, elemental analyse, IR, UV and TG. For compound 1, as the nodes, the [BW₁₂O₄₀]⁵⁻ polyanions link to the [Cu_2.5(bpp)₃(Hbpp)]^3.5+ oligomers, leading to the formation of 1D helical chains which further attach to the macrocycles [Cu₂(bpp)₂]²⁺ via the Cu-O weak interaction to construct the 2D “wave-like” layers. For compound 2, the {[Cu(bpp)]₄[AlW₁₂O₄₀]₂} unit is obtained by the interaction between two Keggin-type [AlW₁₂O₄₀]⁵⁻ polyanions and one tetranuclear macrocycle composed by four [Cu(bpp)]⁺ complex cations. Furthermore, the units are sandwiched by two 1D “wave-like” polymeric chains resulting in a new 1D structure. In addition, the electrochemical properties and electrocatalytic activities of these two compounds have been studied in this paper.