Comparing intermediate range order for alkyl- vs. ether-substituted cations in ionic liquids

X-ray scattering data from four pairs of ionic liquids (ILs) are compared. The alkyl-substituted cations show a first sharp diffraction peak between 3 and 4 nm(-1) that is not observed for ILs having cations with ether- or hydroxy-substitutions. These observations indicate a significant difference in the intermediate range order for these liquids.     

Convergent synthesis and discovery of a natural product-inspired paralog-selective Hsp90 inhibitor

A convergent synthesis of benzoquinone ansamycin analogs is described that proceeds by a sequence of metallacycle-mediated alkyne-alkyne coupling, followed by site- and stereoselective dihydroxylation and global carbamate formation. These studies have led to (1) validation of alkyne-alkyne coupling to produce geldanamycin analogs that lack the problematic quinone, (2) the discovery that C6-C7 bis-carbamate functionality is compatible with Hsp90 inhibition, and (3) the identification of 1 as a nonquinone geldanamycin-inspired paralog-selective Hsp90 inhibitor.     

Assembly of [Mn(II)2Mn(III)2] S = 9 clusters via azido bridges: a new single-chain magnet

In the present work, we report a new manganese single-chain magnet built from tetranuclear Mn(II)(2)Mn(III)(2) mixed-valence units linked by end-on azido and oximato bridges. All of the intra- and intercluster interactions involve end-on azido bridges, resulting in one ferromagnetic chain of ferromagnetic clusters with local ground state S = 9.     

Communication: X-ray scattering from ionic liquids with pyrrolidinium cations

We report the structure functions obtained from x-ray scattering experiments on a series of four homologous ionic liquids. The ionic liquids are 1-alkyl-1-methylpyrrolidinium cations paired with the bis(trifluoromethylsulfonyl)amide anion, with alkyl chain lengths of n = 4, 6, 8, and 10. The structure functions display two intense diffraction peaks for values of the scattering vector q in the range from 0.6 to 1.5 ?(-1) for all samples. Both diffraction peaks shift to lower values of q for increasing temperature. First sharp diffraction peaks are observed in the structure functions for q < 0.5 ?(-1) for liquids with n = 6, 8, and 10.     

Synthesis and structure of a dinuclear gold(II) complex with terminal fluoride ligands

The potential for reductive elimination of fluorine from dinuclear gold(II) for catalysis has prompted our efforts to synthesize a dinuclear gold(II) fluoride complex. This has been achieved with bis(2,6-dimethylphenyl)formamidinate bridging ligands. In order to obtain this product, it was necessary first to synthesize the corresponding dinuclear gold(II) nitrate, which reacts readily with KF in a metathesis reaction. The nitrate complex and fluoride complexes have been structurally characterized. The Au-Au distance in the dinuclear fluoride, 2.595 ?, is longer than the distance found in the analogous chloride complex, 2.567 ?. This result is consistent with the presence of a fluoride "π electron effect" on the filled Au 5d orbitals. The Raman spectrum shows an Au-Au stretch at 206 cm(-1), which agrees with Woodruff's rules and the density functional theory computational model used for modeling the complex.     

Examining epistemic beliefs across conceptual and procedural knowledge in statistics

The purpose of this paper was to examine whether students’ epistemic beliefs differed as a function of variations in procedural versus conceptual knowledge in statistics. Students completed Hofer’s (Contem Edu Psychol 25:378–405, 2000) Discipline-Focused Epistemological Beliefs Questionnaire five times over the course of a semester. Differences were explored between students’ initial beliefs about statistics knowledge and their specific beliefs about conceptual knowledge and procedural knowledge in statistics. Results revealed differences across these contexts; students’ beliefs differed between procedural versus conceptual knowledge. Moreover, students’ initial beliefs about statistics knowledge were more similar to their beliefs about conceptual knowledge rather than procedural knowledge. Finally, regression analyses revealed that students’ beliefs about the justification of knowledge, attainability of truth and source of knowledge were significant predictors of examination performance, depending on the examination. These results have important theoretical, methodological and pedagogical implications.     

Detection of pulse trains in the electrically stimulated cochlea: effects of cochlear health

Perception of electrical stimuli varies widely across users of cochlear implants and across stimulation sites in individual users. It is commonly assumed that the ability of subjects to detect and discriminate electrical signals is dependent, in part, on conditions in the implanted cochlea, but evidence supporting that hypothesis is sparse. The objective of this study was to define specific relationships between the survival of tissues near the implanted electrodes and the functional responses to electrical stimulation of those electrodes. Psychophysical and neurophysiological procedures were used to assess stimulus detection as a function of pulse rate under the various degrees of cochlear pathology. Cochlear morphology, assessed post-mortem, ranged from near-normal numbers of hair cells, peripheral processes and spiral ganglion cells, to complete absence of hair cells and peripheral processes and small numbers of surviving spiral ganglion cells. The psychophysical and neurophysiological studies indicated that slopes and levels of the threshold versus pulse rate functions reflected multipulse integration throughout the 200 ms pulse train with an additional contribution of interactions between adjacent pulses at high pulse rates. The amount of multipulse integration was correlated with the health of the implanted cochlea with implications for perception of more complex prosthetic stimuli.     

In Vitro Reconstitution Reveals a Central Role for the N-Oxygenase PvfB in (Dihydro)pyrazine-N-oxide and Valdiazen Biosynthesis

The Pseudomonas virulence factor (pvf) operon is essential for the biosynthesis of two very different natural product scaffolds: the (dihydro)pyrazine-N-oxides and the diazeniumdiolate, valdiazen. PvfB is a member of the non-heme diiron N-oxygenase enzyme family that commonly convert anilines to their nitroaromatic counterparts. In contrast, we show that PvfB catalyzes N-oxygenation of the α-amine of valine, first to the hydroxylamine and then the nitroso, while linked to the carrier protein of PvfC. PvfB modification of PvfC-tethered valine was observed directly by protein NMR spectroscopy, establishing the intermediacy of the hydroxylamine. This work reveals a central role for PvfB in the biosynthesis of (dihydro)pyrazine-N-oxides and valdiazen.