Antifungal cyclopentenediones from Piper coruscans

Coruscanones A and B, two new antifungal cyclopentenedione derivatives, have been isolated from Piper coruscans and their structures elucidated by spectroscopic and chemical methods. Coruscanone A exhibits significant antifungal activity against Candida albicans and its azole-resistant strains and may serve as a template for a new class of antifungal agents.     

Metal-metal bonding in tetracyanometalates (M=PtII, PdII, NiII) of monovalent thallium. Crystallographic and spectroscopic characterization of the new compounds Tl2Ni(CN)4 and Tl2Pd(CN)4

The new crystalline compounds Tl2Ni(CN)4 and Tl2Pd(CN)4 were synthesized by several procedures. The structures of the compounds were determined by single-crystal X-ray diffraction. The compounds are isostructural with the previously reported platinum analogue, Tl2Pt(CN)4. A new synthetic route to the latter compound is also suggested. In contrast to the usual infinite columnar stacking of [M(CN)4]2- ions with short intrachain M-M separations, characteristic of salts of tetracyanometalates of NiII, PdII, and PtII, the structure of the thallium compounds is noncolumnar with the two TlI ions occupying axial vertices of a distorted pseudo-octahedron of the transition metal, [MTl2C4]. The Tl-M distances in the compounds are 3.0560(6), 3.1733(7), and 3.140(1) A for NiII, PdII, and PtII, respectively. The short Tl-Ni distance in Tl2Ni(CN)4 is the first example of metal-metal bonding between these two metals. The strength of the metal-metal bonds in this series of compounds was assessed by means of vibrational spectroscopy. Rigorous calculations, performed on the molecules in D4h point group symmetry, provide force constants for the Tl-M stretching vibration constants of 146.2, 139.6, and 156.2 N/m for the NiII, PdII, and PtII compounds, respectively, showing the strongest metal-metal bonding in the case of the Tl-Pt compound. Amsterdam density-functional calculations for isolated Tl2M(CN)4 molecules give Tl-M geometry-optimized distances of 2.67, 2.80, and 2.84 A for M = NiII, PdII, and PtII, respectively. These distances are all substantially shorter than the experimental values, most likely because of intermolecular Tl-N interactions in the solid compounds. Time-dependent density-functional theory calculations reveal a low-energy, allowed transition in all three compounds that involves excitation from an a1g orbital of mixed Tl 6pz-M ndz2 character to an a2u orbital of dominant Tl 6pz character.     

Slope and Line of Best Fit: A Transfer of Knowledge Case Study

This paper brings together research on slope from mathematics education and research on line of best fit from statistics education by considering what knowledge of slope students transfer to a novel task involving determining the placement of an informal line of best fit. This study focuses on two students who transitioned from placing inaccurate to accurate lines of best fit during a task‐based interview. The analysis focuses on describing shifts in slope reasoning that accompanied the change to accurately placed lines, and investigates factors that may have influenced the shift in reasoning. The results have implications for the teaching of both slope and the line of best fit.     

Anomalous electrochemical behaviour of palladium in base

Noble metal hydrous oxides are known to be recalcitrant systems, i.e. they either undergo reduction at high overpotential or fail to undergo this reaction, due to the intervention of high-energy, virtually isolated atom or nanocluster states of the element as primary reduction products. Hydrogen absorption by activated palladium in base results in enhanced levels of surface activation and eventually to the spontaneous generation of recalcitrant hydrous oxide species which deactivate the electrode surface. Hydrous oxide behaviour at palladium in base is significantly more complicated than in acid; the deposits in question are less readily formed in base, and the main component of a multilayer oxide film grown in acid (HO2) seems to alter to a more readily reducible form (HO1) on transferring the electrode to base. However, evidence was obtained serendipitously in the present work for the formation of a recalcitrant oxide deposit on palladium in base; the involvement of metastable metal and hydrous oxide states provides the basis of energy storage and anomalous heat emission behaviour which is a controversial topic in the case of this electrode system.     

Electrocatalysis at polycrystalline silver in base: an example of the complexity of surface active state behaviour

Four low-level redox responses, attributed to the involvement of four different types of active surface state (or site) transitions, were observed within the double layer region in the case of polycrystalline silver electrodes in base; there is now independent evidence for such premonolayer behaviour in data reported by other authors. The potentials for each of these transitions were correlated with the onset/termination potentials of different electrocatalytic processes, usually for oxidations or reductions but in some cases for both types. The data obtained are in good agreement with the IHOAM model of electrocatalysis which was outlined earlier for the other Group 11 metals, gold and copper. Electronic Publication     

The letter “s” (and the sQGP)

Data from the Relativistic Heavy Ion Collider over the last five years have led many to conclude that the medium created is not the expected quark–gluon plasma (QGP), but rather a strongly coupled or strongly interacting quark–gluon plasma (sQGP). We explore the meaning of this possible paradigm shift and the experimental and theoretical arguments that are associated with it. In this proceedings we detail only a small subset of the relevant issues as discussed at the Hot Quarks 2006 Workshop. PACS 25.75.-q; 25.75.Nq