On the covalency of silver-fluorine bonds in compounds of Silver(I), Silver(II) and Silver(III)

Unconventional covalence: For the higher silver fluorides the silver-fluorine chemical bonding is significantly covalent, in contrast to the conventional "ionic" picture most frequently used in the chemistry of inorganic fluorides. For KAgF4, an Ag(III) fluoride, the Ag(4d) states (see picture) are more within the "ligand band" (60%) than within the "metal band" (40%) reflecting significant covalency of the Ag-F bond, and an electronic band with significant hole production within the anionic F(2p) states

39K NMR and EPR study of multiferroic K3Fe5F15

39K NMR spectra and relaxation times of polycrystalline K3Fe5F15 have been used as a microscopic detector of the local magnetic fields at the magnetic transition at TN = 123 K. The NMR lineshape widens abruptly upon crossing TN due to the onset of internal magnetic fields, while we find no significant lineshift. The paraelectric to ferroelectric transition at Tc = 490 K and the magnetic transition at TN have also been studied using X-band EPR (electron paramagnetic resonance). An increase and subsequent decrease in the EPR susceptibilities is observed on approaching TN from above. There is also a significant increase in the linewidth. At the same time the g-factor first decreases and then increases with decreasing temperature. The local magnetic field is different at different K sites and is much smaller than the magnetic field around the Fe sites. This seems to be consistent with the behaviour of a weak ferrimagnet. The ferrimagnetism does not seem to be due to spin canting as the lattice is disordered, but may arise from thermal blocking of superparamagnetic percolation clusters. The ferroelectric transition at Tc shows no electronic anomaly, demonstrating that we are dealing with a classical phonon anomaly as found in conventional oxides rather than an electronic transition

Reaction of silver(I) and (II) fluorides with C-60: thermodynamic control over fluorination level

Silver(I) fluoride is shown to be a weak fluorinating agent (FA) for C-60 and gives mainly C60F18. Fluorination with silver(II) fluoride yields C60F44, a new compound, as the predominant product (> 80% in the crude). Fluorination degree of fullerenes in reaction with binary metal fluorides is found to be mainly thermodynamically controlled. The correlation between the level of C-60 fluorination and oxidising fluorinating strength of the metal fluorides used for fluorofullerene preparations is discussed, permitting development of a self-consistent quantitative scale for inorganic FAs

Neuronal overexpression of insulin receptor substrate 2 leads to increased fat mass, insulin resistance, and glucose intolerance during aging

The insulin receptor substrates (IRS) are adapter proteins mediating insulin's and IGF1's intracellular effects. Recent data suggest that IRS2 in the central nervous system (CNS) is involved in regulating fuel metabolism as well as memory formation. The present study aims to specifically define the role of chronically increased IRS2-mediated signal transduction in the CNS. We generated transgenic mice overexpressing IRS2 specifically in neurons (nIRS2 (tg)) and analyzed these in respect to energy metabolism, learning, and memory. Western blot (WB) analysis of nIRS2 (tg) brain lysates revealed increased IRS2 downstream signaling. Histopathological investigation of nIRS2 (tg) mice proved unaltered brain development and structure. Interestingly, nIRS2 (tg) mice showed decreased voluntary locomotoric activity during dark phase accompanied with decreased energy expenditure (EE) leading to increased fat mass. Accordingly, nIRS2 (tg) mice develop insulin resistance and glucose intolerance during aging. Exploratory behavior, motor function as well as food and water intake were unchanged in nIRS2 (tg) mice. Surprisingly, increased IRS2-mediated signals did not change spatial working memory in the T-maze task. Since FoxO1 is a key mediator of IRS2-transmitted signals, we additionally generated mice expressing a dominant negative mutant of FoxO1 (FoxO1DN) specifically in neurons. This mutant mimics the effect of increased IRS2 signaling on FoxO-mediated transcription. Interestingly, the phenotype observed in nIRS2 (tg) mice was not present in FoxO1DN mice. Therefore, increased neuronal IRS2 signaling causes decreased locomotoric activity in the presence of unaltered exploratory behavior and motor coordination that might lead to increased fat mass, insulin resistance, and glucose intolerance during aging independent of FoxO1-mediated transcription