Physical properties of superhard and ultrahard fullerites created from solid C60 by high-pressure-high-temperature treatment

60 in the pressure range and the temperature range were studied. These properties are the specific gravity, specific heat in the range , sound velocities, elastic moduli, electrical properties, resistance to uniaxial stress and stability against oxidation. These properties are different from those of diamond and other carbon forms. The hardness of ultrahard fullerites exceed the hardness of diamond. The structures of the samples are described on the basis of X-ray data. Received: 27 September 1996/Accepted: 19 December 1996     

499 bis—The surface compartment model—voltage clamp

Solutions of the SCM equations under voltage clamp show that a transient inward sodium flux can occur at certain settings of the parameters. If there is a nonspecific increase in cation permeability upon depolarization, the positive sodium flux arises because the ion concentration changes in the electrical double layer compensate for the decrease in the electrical driving force, while parallell changes in the potassium ion concentrations lead to a decreased (but still outward) potassium flux. The sodium flux is quite sensitive to the magnitudes of the ionic permeabilities and mobilities, as well as the ion binding equilibrium and release rate constants. The values of the parameters determined here suggest magnitudes for the properties of the membrane components associated with the permeability change.     

A His-Pro-Aib peptide that exhibits an Asx-Pro-turn-like structure

[formula: see text] Small peptides 1 and 2, which differ only in that 1 possesses a BOC-Phe residue at the N-terminus, where 2 bears a BOC-(tau-benzyl)His, were found to exhibit very different structures. In both the solid state (X-ray) and in solution (NMR and IR), peptide 1 exists as a beta-turn, whereas peptide 2 exists in a conformation that resembles the Asx-Pro motif.     

First direct observation of two protons in the decay of 45Fe with a time-projection chamber

The decay of the ground-state two-proton emitter 45Fe was studied with a time-projection chamber and the emission of two protons was unambiguously identified. The total decay energy and the half-life measured in this work agree with the results from previous experiments. The present result constitutes the first direct observation of the individual protons in the two-proton decay of a long-lived ground-state emitter. In parallel, we identified for the first time directly two-proton emission from 43Cr, a known beta-delayed two-proton emitter. The technique developed in the present work opens the way to a detailed study of the mechanism of ground state as well as beta-delayed two-proton radioactivity.     

Temperature gradients in fast collisionless magnetic reconnection

Temperature gradients are shown to deform and shift the magnetic islands that grow during fast collisionless reconnection when electron inertia decouples the plasma motion from the magnetic field. A kinetic electron model describes the collisionless processes during the reconnection of field lines originating in regions with different temperatures. Using a novel model of the reconnecting instability as a surface mode, the kinetic effects are treated analytically in the linear and nonlinear stages of the instability of a current-carrying low-beta plasma slab in a strong magnetic guide field.     

"Competitive quenching": a mechanism by which perihydroxylated perylenequinone photosensitizers can prevent adverse phototoxic damage caused by verteporfin during photodynamic therapy

Incorporation of photodynamic therapy into clinical practice for induction of vascular photo-occlusion highlights the need to prevent adverse phototoxicity to sensitive juxtaposed tissues, particularly in the retina. We developed a system termed "competitive quenching" to prevent adverse phototoxic damage. It involves differential compartmentalization of a photoactivator to the intravascular compartment for photoexcitation and delivery of phototoxicity to targeted vessels. A different photodynamic agent is partitioned to the extravascular retinal space to quench reactive oxygen species generated by photosensitization, thereby protecting the adjacent retinal tissues from adverse phototoxicity. The absorption spectra of quenchers must span wavelengths that are shorter and excluded from the spectral range of photoexcitation light to prevent photoactivation of the quencher. Perihydroxylated perylenequinones were found to be suitable to function as "competitive quenchers" with the prototype hypericin identified as a potent quencher. Here we examined the mechanisms operative in competitive quenching and suggest that hypericin forms a complex with verteporfin, thereby quenching singlet oxygen formation. Furthermore, we show that hypericin, with six phenolic hydroxyls, protects retinal and endothelial hybridoma cells from phototoxicity more effectively than the dimethyl tetrahydroxy helianthrone structural analog with only four such phenolic hydroxyls. The findings suggest that hydroxyl numbers contribute to the efficacy of competitive quenching.