The effect of resonances in 8Be on α-α bremsstrahlung

The effect of the quadrupole transition between the ⁸Be 4⁺(11.4 MeV) and 2⁺(2.9 MeV) states is included in low energy α-α bremsstrahlung (E_1ab < 30 MeV). In the equal-angle Harvard geometry this dominates for θ < 30°, and so enables an estimate to be made of B(E2, 4⁺ → 2⁺, ⁸Be). The problem of non-coplanarity is also discussed.     

Decoherence of flux qubits due to 1/f flux noise

We have investigated decoherence in Josephson-junction flux qubits. Based on the measurements of decoherence at various bias conditions, we discriminate contributions of different noise sources. We present a Gaussian decay function extracted from the echo signal as evidence of dephasing due to 1/f flux noise whose spectral density is evaluated to be about (10(-6)Phi0)2/Hz at 1 Hz. We also demonstrate that, at an optimal bias condition where the noise sources are well decoupled, the coherence observed in the echo measurement is limited mainly by energy relaxation of the qubit.     

Crystal structure and spectroscopy of the high-spin compound: Tris-(2,2′-bipyridine-1,1′-dioxide)Iron(III) tris(perchlorate) bis(acetonitrile), [Fe(bpdo)3](ClO4)3(CH3CN)2

The first high-spin iron(III) compound with the ligand 2,2-bipyridine-1,1-dioxide (abbreviated as bpdo) is reported. The compound [Fe(bpdo)₃](ClO₄)₃(CH₃CN)₂ crystallizes in the space group P , with a = 11.767(3), b = 13.166(4), c = 15.951(4) Å, = 104.62(3), = 101.66(3), = 112.14(3)°, and Z = 2. The Fe(III) atom is octahedrally surrounded by six oxygen atoms of three bpdo ligands. In the far-infrared region the Fe—O vibration is observed at 411 cm^–1. The magnetic susceptibility reveals a of 6.04 ± 0.04 BM in the 10–280 K region, typical of high-spin Fe(III).     

Replacing the cholesterol hydroxyl group with the ketone group facilitates sterol flip-flop and promotes membrane fluidity

The 3alpha-hydroxyl group is a characteristic structural element of all membrane sterol molecules, while the 3-ketone group is more typically found in steroid hormones. In this work, we investigate the effect of substituting the hydroxyl group in cholesterol with the ketone group to produce ketosterone. Extensive atomistic molecular dynamics simulations of saturated lipid membranes with either cholesterol or ketosterone show that, like cholesterol, ketosterone increases membrane order and induces condensation. However, the effect of ketosterone on membrane properties is considerably weaker than that of cholesterol. This is largely due to the unstable positioning of ketosterone at the membrane-water interface, which gives rise to a small but significant number of flip-flop transitions, where ketosterone is exchanged between membrane leaflets. This is remarkable, as flip-flop motions of sterol molecules have not been previously reported in analogous lipid bilayer simulations. In the same context, ketosterone is found to be more tilted with respect to the membrane normal than cholesterol. The atomic level mechanism responsible for the increase of the steroid tilt and the promotion of flip-flops is the decrease in polar interactions at the membrane-water interface. Interactions between lipids or water and the ketone group are found to be weaker than in the case of the hydroxyl group, which allows ketosterone to penetrate through the hydrocarbon region of a membrane.     

A copper complex bearing a TEMPO moiety as catalyst for the aerobic oxidation of primary alcohols

A new bifunctional, triazine-based ligand has been designed with the aim to generate a copper(II) complex holding a TEMPO (2,2,6,6-tetramethylpiperidinyloxy) moiety. The coordination compound obtained from the ligand 4-(2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)ethoxy)-6-(4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-N,N-diphenyl-1,3,5-triazin-2-amine (pypzt-1) and copper(II) bromide (i.e. complex 8) is capable of catalysing the selective, aerobic oxidation of benzyl alcohol to 84% of benzaldehyde in 24 h. This "galactose oxidase activity" of the copper/TEMPO complex is observed as well for the conversion of the non-activated alkyl alcohol octan-1-ol to octanal with a yield of 29% after the same reaction time. The single-crystal X-ray structure of 8 shows that its crystal lattice contains [Cu(I)Br(2)](-) anions which appear to be stabilised by means of both anion-pi and hydrogen bonding interactions. In addition, the solid state structure of 8 exhibits (lone-pair)-pi interactions between the nitrogen atom of an acetonitrile molecule and a triazine ring. The magnetic properties of 8 have been investigated by EPR and magnetic susceptibility measurements.     

Membrane potential and electrostatics of phospholipid bilayers with asymmetric transmembrane distribution of anionic lipids

It is well-established that native plasma membranes are characterized by an asymmetric distribution of charged (anionic) lipids across the membrane. To clarify how the asymmetry can affect membrane electrostatics, we have performed extensive atomic-scale molecular dynamics simulations of asymmetric lipid membranes composed of zwitterionic (phosphatidylcholine (PC) or phosphatidylethanolamine (PE)) and anionic (phosphatidylserine (PS)) leaflets. It turns out that the asymmetry in transmembrane distribution of anionic lipids gives rise to a nonzero potential difference between the two sides of the membrane. This potential arises from the difference in surface charges of the two leaflets. The magnitude of the intrinsic membrane potential was found to be 238 mV and 198 mV for PS/PC and PS/PE membranes, respectively. Remarkably, this potential is of the same sign as the membrane potential in cells. Our findings, being in reasonable agreement with available experimental data, lend support to the idea that the transmembrane lipid asymmetry typical of most living cells contributes to the membrane potential.     

A New Sulfur‐containing Schiff‐Base Ligand and Binding to Copper(II) and Cobalt(II)

A new Schiff‐base ligand having a potentially coordinating thioether group (2‐quinoline‐N‐(2′‐methylthiophenyl)methyleneimine, qmtpm ) has been prepared. The synthesis, structure, UV‐Vis and EPR studies of one copper(II) and two cobalt(II) complexes from this ligand is reported. The X‐ray structures of the Cu^II and Co^II chlorido complexes 1 and 2 reveal the metal atoms in highly distorted square‐pyramidal environments constituted of one tridentate ligand and two anions. On the other hand, the thiocyanato Co^II compound 3 exhibits a distorted trigonal‐bipyramidal structure. These structural variations are apparently due to the different counter‐ions which leads to distinct lattice interactions. The spectroscopic data obtained by EPR and UV‐Vis investigations are in agreement with the solid‐state structures of the coordination compounds.     

Mononuclear manganese(III) complexes as building blocks for the design of trinuclear manganese clusters: study of the ligand influence on the magnetic properties of the [Mn3(mu3-O)](7+) core

The synthesis, crystal structure, and magnetic properties of three new manganese(III) clusters are reported, [Mn 3(mu 3-O)(phpzH) 3(MeOH) 3(OAc)] (1), [Mn 3(mu 3-O)(phpzMe) 3(MeOH) 3(OAc)].1.5MeOH (2), and [Mn 3(mu 3-O)(phpzH) 3(MeOH) 4(N 3)].MeOH (3) (H 2phpzH = 3(5)-(2-hydroxyphenyl)-pyrazole and H 2phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole). Complexes 1- 3 consist of a triangle of manganese(III) ions with an oxido-center bridge and three ligands, phpzR (2-) (R = H, Me) that form a plane with the metal ions. All the complexes contain the same core with the general formula [Mn 3(mu 3-O)(phpzR) 3] (+). Methanol molecules and additional bridging ligands, that is, acetate (complexes 1 and 2) and azide (complex 3), are at the terminal positions. Temperature dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between manganese(III) ions in 1 and 3, while both antiferromagnetic and ferromagnetic intramolecular interactions are operative in 2.