A new fungal morphogenic substance,pyrenolide a from Pyrenophorateres

A new ten-membered lactone, pyrenolide A, was identified as a new fungal morphogenic substance and its structure including absolute stereochemistry was elucidated.     

Kinetics of electron transfer reactions of metal complexes at impermeable redox active polymeric films on electrode surfaces and charge transport within the polymer film

At rotated Pt disk electrodes coated with thin films of the redox polymer poly-[Ru(vbpy)₃]²⁺, ruthenium and iron bipyridine complexes dissolved in acetonitrile can become oxidized by two pathways. The first is diffusion of the solute complex through the polymeric film to react at its normal potential E_sub⁰, at the Pt/polymer interface. The second is a mediated electron transfer cross-reaction between the solute complex and poly-[Ru(vbpy) ₃]²⁺ sites generated in the film at adequately positive potentials. The mediated reaction, as judged from the lack of variation of its rate k_crsΓ with the quantity of polymer mediator sites present in the multimolecular layer film, and from other evidence, is confined to the outer few (one?) monolayers of ruthenium polymer film sites. The mediated reaction becomes the dominant pathway for films with Γ_T ～2×10^?9 mol/cm² of ruthenium polymer sites, owing to the low permeability (measured independently) of the solutecomplexes into the film. The rate k_crsΓ could be measured when the solute complex oxidation potential is more positive than that of the redox film, and is too fast to measure when E_sub⁰, is more negative than the redox film E_cal?⁰, New theory is presented and evaluated to describe the rising portions of the voitammetric waves for the nine solute complexes studied. The rate of charge transport through the poly-[Ru(vbpy)₃]²⁺ film becomes controlling under certain conditions and can be thereby measured as well.     

Deposition of nickel from Ni(CO)4 on palladium and iron surfaces studied by X-ray photoelectron spectroscopy

The interaction of nickel carbonyl, Ni(CO)₄, with evaporated palladium and iron surfaces has been studied at 90 and 290 K by X-ray photoelectron spectroscopy. The carbonyl is weakly adsorbed in molecular form at 90 K on the metals giving a $\text{Ni 2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ peak at 854.6 eV, a C 1s at 287.2 eV and an O 1s at 533.8 eV. Some fraction of the carbonyl decomposes even at 90 K on iron to give deposited nickel atoms. In the interaction with palladium at 290 K, deposited nickel atoms $\text{(Ni 2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{= 852.9 eV)}$ and chemisorbed CO are observed. A satellite feature of the $\text{Ni 2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ peak varies depending on the quantity of the deposited nickel atoms; the main peak-satellite separation increases with increase in the quantity. The same variation is observed for evaporated nickel-palladium alloys. This can be ascribed to the difference in the electronic states of the nickel atoms. The difference is reflected in the reactivity of the atoms with O₂. With iron the deposited nickel atoms show an increase in binding energy of 0.4 eV in the $\text{Ni 2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ Peak and no satellite when the number of nickel atoms is small. The oxidation of the surface is also studied.     

Supramolecular Copolymerization by Sequence Reorganization of a Supramolecular Homopolymer

The homopolymeric sequence formed by the head‐to‐head association of tetrakisporphyrin 1 is completely dissociated by the competitive association of the ditopic guest G2 , resulting in the supramolecular copolymer poly‐ 1 ? G2 with an alternatingly repeating host–guest sequence. The 1:1 stoichiometry of 1 and G2 is confirmed by a Job plot using UV/Vis titration and diffusion‐ordered NMR spectroscopy (DOSY). The solution viscometry for poly‐ 1 and poly‐ 1 ? G2 suggests that the supramolecular chain of poly‐ 1 behaves like a rod, whereas the supramolecular copolymer chain of poly‐ 1 ? G2 behaves like a swelled fat chain, which is entangled in the semi‐dilute regime. Atomic force microscopy shows that the supramolecular polymer poly‐ 1 ? G2 is highly oriented through the interdigitation of the long alkyl chains.     

Spectroscopic and electrical characterization of <Emphasis Type="Italic">α</Emphasis>,<Emphasis Type="Italic">γ</Emphasis>-bisdiphenylene-<Emphasis Type="Italic">β</Emphasis>-phenylallyl radical as an organic semiconductor

The semiconductor properties of the earliest known stable radical, α,γ-bisdiphenylene-β-phenylallyl radical (Koelsch radical, 1^?) were assessed using spectroscopic and electrical techniques. This radical undergoes reversible redox processes, and it has low redox potentials. In addition, 1^? possesses long wavelength absorption bands, owing to the existence of a singly-occupied molecular orbital whose energy level lies between those of the HOMO and LUMO. A spin-coated thin-film of 1^? displays photocurrent and an electron mobility of 6.3 × 10^?7 cm² V^?1 s^?1 on a trially-fabricated organic field effect transistor.     

Patterns of spiral tip motion in cardiac tissues

In support of the spiral wave theory of reentry, simulation studies and animal models have been utilized to show various patterns of spiral wave tip motion such as meandering and drifting. However, the demonstration of these or any other patterns in cardiac tissues have been limited. Whether such patterns of spiral tip motion are commonly observed in fibrillating cardiac tissues is unknown, and whether such patterns form the basis of ventricular tachycardia or fibrillation remain debatable. Using a computerized dynamic activation display, 108 episodes of atrial and ventricular tachycardia and fibrillation in isolated and intact canine cardiac tissues, as well as in vitro swine and myopathic human cardiac tissues, were analyzed for patterns of nonstationary, spiral wave tip motion. Among them, 46 episodes were from normal animal myocardium without pharmacological perturbations, 50 samples were from normal animal myocardium, either treated with drugs or had chemical ablation of the subendocardium, and 12 samples were from diseased human hearts. Among the total episodes, 11 of them had obvious nonstationary spiral tip motion with a life span of >2 cycles and with consecutive reentrant paths distinct from each other. Four patterns were observed: (1) meandering with an inward petal flower in 2; (2) meandering with outward petals in 5; (3) irregularly concentric in 3 (core moving about a common center); and (4) drift in 1 (linear core movement). The life span of a single nonstationary spiral wave lasted no more than 7 complete cycles with a mean of 4.6+/-4.3, and a median of 4.5 cycles in our samples. Conclusion: (1) Patently evident nonstationary spiral waves with long life spans were uncommon in our sample of mostly normal cardiac tissues, thus making a single meandering spiral wave an unlikely major mechanism of fibrillation in normal ventricular myocardium. (2) A tendency toward four patterns of nonstationary spiral tip motion was observed. (c) 1998 American Institute of Physics.