Pair Of Cu Ions Research Articles

Amyloid-β Tetramers and Divalent Cations at the Membrane/Water Interface: Simple Models Support a Functional Role.

Charge polarization at the membrane interface is a fundamental process in biology. Despite the lower concentration compared to the abundant monovalent ions, the relative abundance of divalent cations (Ca2+, Mg2+, Zn2+, Fe2+, Cu2+) in particular spaces, such as the neuron synapse, raised many questions on the possible effects of free multivalent ions and of the required protection of membranes by the eventual defects caused by the free forms of the cations. In this work, we first applied a recent realistic model of divalent cations to a well-investigated model of a polar lipid bilayer, di-myristoyl phosphatidyl choline (DMPC). The full atomistic model allows a fairly good description of changes in the hydration of charged and polar groups upon the association of cations to lipid atoms. The lipid-bound configurations were analyzed in detail. In parallel, amyloid-β 1-42 (Aβ42) peptides assembled into tetramers were modeled at the surface of the same bilayer. Two of the protein tetramers' models were loaded with four Cu2+ ions, the latter bound as in DMPC-free Aβ42 oligomers. The two Cu-bound models differ in the binding topology: one with each Cu ion binding each of the monomers in the tetramer; one with pairs of Cu ions linking two monomers into dimers, forming tetramers as dimers of dimers. The models here described provide hints on the possible role of Cu ions in synaptic plasticity and of Aβ42 oligomers in storing the same ions away from lipids. The release of structurally disordered peptides in the synapse can be a mechanism to recover ion homeostasis and lipid membranes from changes in the divalent cation concentration.

On the nature of pseudogap anomalies in HTSC

We proposed the model of HTSC where the interaction of electrons from oxygen band with the diatomic negative U-centers (NUC) on pairs of Cu ions in CuO2 plane is assumed to be responsible for the superconducting pairing. As follows from the model the occupation η of NUC with real electrons reduces superconducting order parameter due to decreasing of number of states available for scattering of electron pairs. The charge fluctuations between NUC and valence band will result in fluctuations of pairing interaction. In clusters, containing small number of NUC's, where the relative fluctuations of η are great enough, the superconducting gap may open at T*>Tc∞ and close at TC<TC∞, where Tc∞ is the temperature of superconducting transition for infinite cluster. The doping dependences of T* and Tc for YBa2Cu3O6+δ are calculated as two roots of the same square equation. The obtained results demonstrate the impressive agreement with experiment.

Spatial inhomogeneity and pseudogap in HTSC

It is shown that spatial inhomogeneity, pseudogap and 60 K-phase in underdoped YBa 2Cu 3O 6+ δ apparently have the same nature specified by the existence of finite clusters uniting of various numbers of negative-U centers (NUCs). These NUCs are formed in HTSC under doping on some pairs of Cu ions in CuO 2 plane at definite arrangement of the nearest localized doped charges. Electron fluctuations between NUCs and oxygen band in clusters uniting small number of NUCs result in fluctuating transitions of such clusters between superconducting and normal states owing to fluctuations of NUC occupation.

Mechanism of carrier generation and the origin of the pseudogap and 60 K phases in YBCO

In the framework of the model assuming the formation of NUC on the pairs of Cu ions in CuO$_{2}$ plane the mechanism of hole carrier generation is considered and the interpretation of pseudogap and 60 K-phases in $YBa_{2}Cu_{3}O_{6+\delta}$. is offered. The calculated dependences of hole concentration in $YBa_{2}Cu_{3}O_{6+\delta}$ on doping $\delta$ and temperature are found to be in a perfect quantitative agreement with experimental data. As follows from the model the pseudogap has superconducting nature and arises at temperature $T^{*}>T_{c\infty}>T_{c}$ in small clusters uniting a number of NUC's due to large fluctuations of NUC occupation. Here $T_{c\infty}$ and $T_{c}$ are the superconducting transition temperatures of infinite and finite clusters of NUC's, correspondingly. The calculated $T^{*}(\delta)$ and $T_{n}(\delta)$ dependences are in accordance with experiment. The area between $T^{*}(\delta)$ and $T_{n}(\delta)$ corresponds to the area of fluctuations where small clusters fluctuate between superconducting and normal states owing to fluctuations of NUC occupation. The results may serve as important arguments in favor of the proposed model of HTSC.

Electron Spin Resonance inSr0.60Ca0.40CuO2

ESR measurements have been made on a powder sample of Sr 0.60 Ca 0.40 CuO 2 (the SrCuO 2 structure) at room and liquid nitrogen temperatures. Its ESR spectrum consists of seven hyperfine lines associated with a pair of identical Cu ions. The hyperfine term in the spin Hamiltonian takes the form A S ·( I 1 + I 2 ), where A is a hyperfine constant; S the total electronic spin of a pair of Cu ions; and I 1 , I 2 the nuclear spins of Cu ions. The spectroscopic splitting factor g =2.18, and | A |=72×10 -4 cm -1 . The spectrum indicates that a fine structure contributes to broadening hyperfine lines. At liquid nitrogen temperature, microwave absorption was detected over the complete range of a magnetic field sweep, being accompanied with the ESR absorption due to Cu ion pairs.

Crystal structure and magnetic susceptibility of copper (II) chloride tetramethylsulfoxide [CuCl2(TMSO)] and copper (II) chloride monodimethylsulfoxide [CuCl2(DMSO)]: Ferromagnetic spin-½ Heisenberg linear chains

The crystal structures of the title compounds [${\mathrm{C}}_{4}$${\mathrm{H}}_{8}$SO (TMSO), ${\mathrm{C}}_{2}$${\mathrm{H}}_{6}$SO (DMSO)] have been determined. The TMSO salt is orthorhombic [space group $\mathrm{Pbca}$, $a=13.844(10)$, $b=6.418(12)$, and $c=17.480(16)$ \AA{}] while the DMSO salt is monoclinic [space group $\frac{P{2}_{1}}{c}$, $a=7.774(1)$, $b=13.557(3)$, $c=6.475(1)$ \AA{}, and $\ensuremath{\beta}=103.83(1)\ifmmode^\circ\else\textdegree\fi{}$]. Each contain linear chains of Cu ions with three bridging ligands (2 C1, 1 O) between each pair of Cu ions. The bridging Cu-$L$-Cu angles are \ensuremath{\sim} 87\ifmmode^\circ\else\textdegree\fi{} for the symmetrical bridges and \ensuremath{\sim} 80\ifmmode^\circ\else\textdegree\fi{} for the asymmetrical bridges. In each salt, the copper coordination geometry is severely distorted from octahedral with four short Cu-ligand bonds (three chlorine and one oxygen) and two long Cu-ligand bonds (one chlorine and one oxygen). Adjacent chains are well isolated from each other by the sulfoxide groups in one direction, but short sulfur-sulfur contacts occur between adjacent chains in the other direction. The susceptibility of the salts has been measured between 2.0 and 300 K on a PAR vibrating-sample magnetometer and on a Faraday balance. The high-temperature data show positive deviation from Curie behavior, indicative of ferromagnetic coupling. However, considerable magnetic interactions between chains exist and the $\ensuremath{\chi}T$ vs $T$ plots show maxima at low temperature. The data have been analyzed with several one-dimensional models. The best fit is obtained with an Heisenberg linear chain with ferromagnetic interaction ($\frac{J}{k}=39\ifmmode^\circ\else\textdegree\fi{}$K, TMSO; $\frac{J}{k}=45\ifmmode^\circ\else\textdegree\fi{}$K, DMSO) with a mean-field correction for the antiferromagnetic interchain interactions ($\frac{Z{J}^{\ensuremath{'}}}{k}=\ensuremath{-}1.6\ifmmode^\circ\else\textdegree\fi{}$K, TMSO; $\frac{Z{J}^{\ensuremath{'}}}{k}=\ensuremath{-}4.0\ifmmode^\circ\else\textdegree\fi{}$K, DMSO). Thus, the relevant ratio defining the ideality of the system, $\frac{J}{{J}^{\ensuremath{'}}}$, is \ensuremath{\sim} 50 for the TMSO salt and \ensuremath{\sim} 25 for the DMSO salt.

Magnetic susceptibility of CuCl2⋅TMSO, a ferromagnetic spin 1/2 linear chain

The crystal structure of the title compound (TMSO≡C4H8SO) consists of linear chains of Cu ions with three bridging ligands (2 Cl, 1 O) between each pair of Cu ions. The susceptibility of the salt has been measured between 2.0 and 120 K on a PAR vibrating sample magnetometer and from 80 to 300 on a Faraday balance. The high temperature data shows positive deviation from Curie behavior, with a Curie-Weiss constant of 18.7 K. However, considerable interactions between chains exist and the χT vs T plot shows a maximum at T=7.5 K. The data has been analyzed with several one-dimensional models. At present, the best fit is obtained with an Heisenberg linear chain (J=24.6 cm−1) with a mean field correction for interchain interactions (ZJ′=−1.3 cm−1).

ESR study of exchange coupled pairs in copper diethyldithiocarbamate

ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)2, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g ‖=2.1025,g +=2.031,A=75.1×10−4 cm−1,B=14.8×10−4,D=276.0×10−4 cm−1 andE=46.7×10−4 cm−1. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm−1. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)2—direct exchange and superexchange through the bridging sulphurs—are discussed.