On the stability of 2 \sqrt{2} x 2 \sqrt{2} oxygen ordered superstructures in YBa2Cu3O6+x

We have compared the ground-state energy of several observed or proposed " 2 \sqrt{2} x 2 \sqrt{2} oxygen (O) ordered superstructures " (from now on HS), with those of "chain superstructures" (CS) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa2Cu3O6+x. The model Hamiltonian contains i) the Madelung energy, ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and iii) covalency effects based on known results for $t-J$ models in one and two dimensions. The optimum distribution of charge is determined minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure, and long-range Coulomb interactions, are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation.Comment: 24 text pages, Latex, one fig. included as ps file, to be publisheb in Phys. Rev.

Are Small GTPases Signal Hubs in Sugar-Mediated Induction of Fructan Biosynthesis?

External sugar initiates biosynthesis of the reserve carbohydrate fructan, but the molecular processes mediating this response remain obscure. Previously it was shown that a phosphatase and a general kinase inhibitor hamper fructan accumulation. We use various phosphorylation inhibitors both in barley and in Arabidopsis and show that the expression of fructan biosynthetic genes is dependent on PP2A and different kinases such as Tyr-kinases and PI3-kinases. To further characterize the phosphorylation events involved, comprehensive analysis of kinase activities in the cell was performed using a PepChip, an array of >1000 kinase consensus substrate peptide substrates spotted on a chip. Comparison of kinase activities in sugar-stimulated and mock(sorbitol)-treated Arabidopsis demonstrates the altered phosphorylation of many consensus substrates and documents the differences in plant kinase activity upon sucrose feeding. The different phosphorylation profiles obtained are consistent with sugar-mediated alterations in Tyr phosphorylation, cell cycling, and phosphoinositide signaling, and indicate cytoskeletal rearrangements. The results lead us to infer a central role for small GTPases in sugar signaling

CMS physics technical design report : Addendum on high density QCD with heavy ions

Peer reviewe

An electrochemical investigation on the reduction path of the arene complexes [CpM(arene)] 2+ and [(η-9-SMe 2-7,8-C 2B 9H 10)M(arene)] 2+ (M=Rh, Ir)

The reduction behavior of the isoelectronic complexes [CpM III(η 6-C 6R 6)] 2+ (M=Rh, Ir; R=H, Me) and [(η-9-SMe 2-7,8-C 2B 9H 10)M III(η 6-C 6R 6)] 2+ (M=Rh, Ir; C 6R 6∈= ∈C 6H 6, C 6H 5OMe, C 6H 3Me 3) has been studied by cyclic voltammetry and controlled potential coulometry in acetonitrile and propylene carbonate at 253 and 298 K, respectively. The extent of chemical reversibility of the pertinent sequences Rh(III)/Rh(II)/Rh(I) and Ir(III)/Ir(I) is highly dependent on both the nature of the solvent and the intrinsic electronic properties of the arene substituents. The arene η 6 coordination makes the derivatives in their lower oxidation states notably short lived, even if, in some cases, the use of propylene carbonate improves their stability or causes the increase in their lifetimes before changing the arene coordination from η 6 to η 4. Cations [(η-9-SMe 2-7,8-C 2B 9H 10)M(η 6- C 6R 6)] 2+ were obtained by the bromide abstraction from [(η-9-SMe 2-7,8-C 2B 9H 10)MBr 2] 2 with Ag + in the presence of benzene and its derivatives. The structure of [(η-9-SMe 2-7,8-C 2B 9H 10)Ir(η 6- C 6H 5OMe)](BF 4) 2 was determined by X-ray diffraction. © 2007 Springer-Verlag

(Tetramethylcyclobutadiene)cobalt complexes with phosphacarborane ligands

Reactions of the 11-vertex phosphadicarbollide anions [10-R-7,8,9-PC 2B 8H 9] - (R = H (1a) and Cl (1b)) and [9-Cl-7,8,11-PC 2B 8H 9] - (7) with [Cb*Co(MeCN) 3]PF 6 or [Cb*Co(C 6H 6)]PF 6 (Cb* = C 4Me 4) give the expected cobaltaphosphadicarbollides 1-Cb*-5-R-1,2, 3,4-CoPC 2B 8H 9 (R = H (2a) and Cl (2b)) and 1-Cb*-4-Cl-1,2,3,6-CoPC 2B 8H 9 (5b), respectively. 2a rearranges to a mixture of 1-Cb*-1,2,4,5-CoPC 2B 8H 10 (4a) and 1-Cb*-1,2,3,6-CoPC 2B 8H 10 (5a) at 110°C and further to 1-Cb*-1,2,3,5-CoPC 2B 8H 10 (6a) at 160°C. Heating of the Cl-substituted derivative 2b at 65°C results in 1-Cb*-5-Cl-1,2,4,8-CoPC 2B 8H 9 (3b). Both 2b and 5b rearrange at 100°C, giving 1-Cb*-5-Cl-1,2,3,10-CoPC 2B 8H 9 (8b) as a main product. The observed rearrangement sequence of Cb*CoPC 2B 8H 10 isomers correlates well with the relative stabilities of their nonmethylated analogues estimated by DFT calculations. Reaction of the diphosphacarbollide anion [7,8,10-P 2CB 8H 9] - (11) with Cb*Co(CO) 2I at 160°C affords the nonrearranged complex 1-Cb°-1,2,3,5-CoP 2CB 8H 9 (12). The structures of 2a, 3b, and 4a were determined by X-ray diffraction. The electrochemical study revealed that phosphadicarbollide ligands are stronger acceptors compared with tricarbollide [C 3B 8H 11] - and charge-compensated dicarbollide [9-L-7,8-C 2B 9H 10] -. © 2006 American Chemical Society

Reactions of the B-phenylborole complex [CpRh(eta5-C4H4BPh)] with metalloelectrophiles [(ring)M]2+

Thirty-valence-electron dicationic triple-decker complexes with a bridging borole ligand [CpRh(μ-η5:η5-C4H4BPh)M(ring)]2+ [M(ring) = CoCp* (3), IrCp* (6), Ru(η-C6H3Me3-1,3,5) (8a), Ru(η-C6Me6) (8b)] were obtained by stacking reactions of [CpRh(η5-C4H4BPh)] (2) with the corresponding half-sandwich fragments [M(ring)]2+. Minor formation of arene-type complexes [CpRh(μ-η5:η6-C4H4BPh)M(ring)]2+ was observed for M(ring) = IrCp* and Ru(arene). On the contrary, the arene-type complex [CpRh(μ-η5:η6-C4H4BPh)RhCp*]2+ (5) was isolated as the sole product from the reaction of 2 with the fragment [RhCp*]2+; an intermediate formation of the triple-decker complex [CpRh(μ-η5:η5-C4H4BPh)RhCp*]2+ (4) in this reaction was detected by 1H NMR spectroscopy. Heating 6 in nitromethane gives the symmetrical triple-decker complex [Cp*Ir(μ-η5:η5-C4H4BPh)IrCp*]2+ (10). The cations were isolated as salts with the BF4– anion. The structures of 2, 5(BF4)2, 6(BF4)2 and 8a(BF4)2 were determined by X-ray diffraction. The electrochemical properties of the complexes were also investigated

Synthesis of μ-Diborolyl Triple-decker complexes by electrophilic stacking. Similar bonding properties of anions [CpCo(1,3-C 3B 2H 5)]- and Cp- toward transition metals

Triple-decker complexes with a bridging diborolyl ligand CpCo(μ-1,3-C 3B 2Me 5)M(ring) (M(ring) = RuCp, 4; RuCp*, 5; Co(C 4Me 4), 6) were synthesized by electrophilic stacking of the sandwich anion [CpCo(1,3-C 3B 2Me 5)]- with the [(ring)M(MeCN) 3]+ cations. Structures of 4-6 were confirmed by X-ray diffraction. The electrochemical and spectroelectrochemical behavior of the complexes prepared was studied. DFT calculations of the redox potentials were also performed. Similar bonding properties of anions [CpCo(1,3-C 3B 2R 5)]- and [C 5R 5]- (R = H, Me) toward [M(ring)]+ cations were established both experimentally (synthesis, electrochemistry, and X-ray diffraction) and theoretically (energy decomposition and Mulliken population analysis). © 2009 American Chemical Society

Ferracarborane benzene complexes [(--9-L-7,8-C2B 9H10)Fe(-C6H6)]+ (L = SMe2, NMe3): Synthesis, reactivity, electrochemistry, mössbauer effect studies, and bonding

The benzene complexes [(eta-9-L-7,8-C2B9R5H8)Fe(eta-C6H6)](+) (3a: L = SMe2, R = H; 3b: L = SMe2, R = Me; 3c: L = NMe3, R = H) were prepared by photochemical reaction of [(eta(5)-C6H7)Fe(eta-C6H6)]+ with carborane anions [9-L-7,8-C2B9R2H8](-) (1a-c) followed by treatment of' the (eta-9-L-7,8-C2B9R2H8)Fe(eta(5)-C6H7) (2a c) ferracarboranes formed with HCl. Visible light irradiation of 3a with (BuNC)-Bu-t or P(OMe)(3) in acetonitrile results in replacement of the benzene ligand, giving the tris(ligand) derivatives (eta-9-SMe2-7,8-C2B9H10)Fe(ligand)3]+ (4, 5). The unsymmetrical carborane complex (eta-9-SMe2-7,8-C2B9H10) (eta-Fe(eta-9-NMe3-7,8-C2B9H10) (6) was obtained by photochemical reaction of 3a with 1c. The structures of 2a, 3aBPh(4), and 6 were determined by X-ray diffraction. Temperature-dependent Mossbauer spectroscopy has been used to elucidate the hyperfine parameters and metal atom vibrational amplitudes in a number of these complexes. The redox activity of the farracarboranes 2a,c. and 3a,c has been investigated! by electrochemical techniques and compared with that of the related cyclopentadienyl complexes. Electrochemistry gives evidence that the conversion of 2a c to 3a c can also be triggered by a two-electron oxidation followed by deprotonation. DFT calculations of the redox potentials and the respective geometrical changes were performed. Data on electrostatic potentials at iron nuclei suggest that anions la,c are stronger donors than Cp- in cationic complexes, but weaker donors in the neutral derivatives