Four monoferrocenyl tritylium derivatives with donor-substituted (OMe, NMe ) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one-electron reduction and a quasi-reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔE , in Mößbauer spectra agree with highly electron-deficient ferrocenes. Comparison of the experimental half-wave potentials for ferrocene oxidation, E (Fc/Fc ), with those estimated from established correlations of E (Fc/Fc ) with ΔE indicates that the E values of the anisyl-substituted congeners FcOMe and FcMeOMe are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox-induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR-silent dimers. This process is studied by temperature-dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or "offset" Jacobson-Nauta-type structures.

The family of tumor necrosis factor receptors (TNFRs) and their ligands form a regulatory signaling network that controls immune responses. Various members of this receptor family respond differently to the soluble and membrane-bound forms of their respective ligands. However, the determining factors and underlying molecular mechanisms of this diversity are not yet understood. Using an established system of chimeric TNFRs and novel ligand variants mimicking the bioactivity of membranebound TNF (mTNF), we demonstrate that the membrane-proximal extracellular stalk regions of TNFR1 and TNFR2 are crucial in controlling responsiveness to soluble TNF (sTNF). We show that the stalk region of TNFR2, in contrast to the corresponding part of TNFR1, efficiently inhibits both the receptor's enrichment/clustering in particular cell membrane regions and ligandindependent homotypic receptor preassembly, thereby preventing sTNF-induced, but not mTNF-induced, signaling. Thus, the stalk regions of the two TNFRs not only have implications for additional TNFR family members, but also provide potential targets for therapeutic intervention.

Complexes [{Ru(CO)Cl(PiPr3 )2 }2 (μ-2,5-(CH-CH)2 -(c) C4 H2 E] (E=NR; R=C6 H4 -4-NMe2 (10 a), C6 H4 -4-OMe (10 b), C6 H4 -4-Me (10 c), C6 H5 (10 d), C6 H4 -4-CO2 Et (10 e), C6 H4 -4-NO2 (10 f), C6 H3 -3,5-(CF3 )2 (10 g), CH3 (11); E=O (12), S (13)) are discussed. The solid state structures of four alkynes and two complexes are reported. (Spectro)electrochemical studies show a moderate influence of the nature of the heteroatom and the electron-donating or -withdrawing substituents R in 10 a-g on the electrochemical and spectroscopic properties. The CVs display two consecutive one-electron redox events with ΔE°'=350-495 mV. A linear relationship between ΔE°' and the σp Hammett constant for 10 a-f was found. IR, UV/Vis/NIR and EPR studies for 10(+) -13(+) confirm full charge delocalization over the {Ru}CH-CH-heterocycle-CH-CH{Ru} backbone, classifying them as Class III systems according to the Robin and Day classification. DFT-optimized structures of the neutral complexes agree well with the experimental ones and provide insight into the structural consequences of stepwise oxidations.

The nitrilase AtNIT1 from Arabidopsis thaliana was overexpressed in Escherichia coli with an N-terminal His 6 tag and puri®ed by zinc chelate anity chromatography in a single step almost to homogeneity in a 68% yield with a speci®c activity of 34.1 Uámg . The native enzyme ( 450 kDa) consists of 11±13 subunits (38 kDa). The temperature optimum was determined to be 35°C, and a pH optimum of 9 was found. Thus, recombinant AtNIT1 resembles in its properties the native enzyme and the nitrilase from Brassica napus. The stability of AtNIT1 could be signi®cantly improved by the addition of dithiothreitol and EDTA. The substrate range of AtNIT1 diers considerably from those of bacterial nitrilases.Aliphatic nitriles are the most eective substrates, showing increasing rates of hydrolysis with increasing size of the residues, as demonstrated in the series butyronitrile, octanenitrile, phenylpropionitrile. In comparison with 3-indolylacetonitrile, the rate of hydrolysis of 3-phenylpropionitrile is increased by a factor of 330, and the K m value is reduced by a factor of 23. With the exception of uoro, substituents in the a position to the nitrile function completely inhibit the hydrolysis.

We have prepared and studied extremely electron‐poor, deeply colored dicationic 1,1'‐bis(diarylmethylium)‐substituted ferrocenes [(η5‐C5H4‐CAr2)2Fe]2+ with various aryl substituents as their [B{C6H3(CF3)2‐3,5}4]– salts. Due to the strong acceptor substitution, the redox potential for the ferrocene‐based oxidation of the anisyl‐ or 2‐methylanisyl‐substituted congeners 1b2+ and 1c2+ is close to or even surpasses that of the second oxidation of parent ferrocene, i.e. the Cp2Fe+/2+ couple. The strongly Lewis‐acidic character of these complexes is manifest through strong interactions with donor solvents, which lead to a significant reduction of the intensities of the charge‐transfer bands in their electronic spectra and to solvatochromism. The reduced forms of the complexes tend to dimerize or oligomerize as revealed by EPR spectroscopy. Direduced 1b selectively reacts with molecular oxygen to form a peroxo‐bis(diarylmethyl)[4]ferrocenophane, which was also characterized by X‐ray crystallography.