Three-Dimensional Morphology of a Coronal Prominence Cavity

We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft-X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally-extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step towards quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI) observations from the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explains the observed variation in cavity visibility for the east vs. west limb

Reactivity of Metal-Free and Metal-Associated Amyloid-?? with Glycosylated Polyphenols and Their Esterified Derivatives

Both amyloid-?? (A??) and transition metal ions are shown to be involved in the pathogenesis of Alzheimer???s disease (AD), though the importance of their interactions remains unclear. Multifunctional molecules, which can target metal-free and metal-bound A?? and modulate their reactivity (e.g., A?? aggregation), have been developed as chemical tools to investigate their function in AD pathology; however, these compounds generally lack specificity or have undesirable chemical and biological properties, reducing their functionality. We have evaluated whether multiple polyphenolic glycosides and their esterified derivatives can serve as specific, multifunctional probes to better understand AD. The ability of these compounds to interact with metal ions and metal-free/-associated A??, and further control both metal-free and metal-induced A?? aggregation was investigated through gel electrophoresis with Western blotting, transmission electron microscopy, UV-Vis spectroscopy, fluorescence spectroscopy, and NMR spectroscopy. We also examined the cytotoxicity of the compounds and their ability to mitigate the toxicity induced by both metal-free and metal-bound A??. Of the polyphenols investigated, the natural product (Verbascoside) and its esterified derivative (VPP) regulate the aggregation and cytotoxicity of metal-free and/or metal-associated A?? to different extents. Our studies indicate Verbascoside represents a promising structure for further multifunctional tool development against both metal-free A?? and metal-A??.open0

Photophysical properties of the new phosphorescent platinum(II) and palladium(II) complexes of benzoporphyrins and chlorins

Several phosphorescent platinum(II) and palladium(II) complexes of tetrapyrrole dyes are prepared in an attempt to improve the compatibility with red laser diodes. The nature of meso-substituents in benzoporphyrin macrocycle is found to affect mainly the position of the Soret band and has little influence on the Q-bands. In rigid polymeric matrices these dyes possess more favourable photochemical properties than corresponding meso-tetraphenyltetrabenzoporphyrins. Platinum(II) chlorins show good compatibility with 635 nm laser diode and 632.8 line of He-Ne laser, and have moderate brightness with emission yields ∼2%. Photophysical properties and photostability of these dyes is assessed and compared with the known NIR-emitting oxygen indicators. © 2009 Elsevier B.V. All rights reserved

Insights into antiamyloidogenic properties of the green tea extract (-)-epigallocatechin-3-gallate toward metal-associated amyloid-beta species

Despite the significance of Alzheimer's disease, the link between metal-associated amyloid-?? (metal-A??) and disease etiology remains unclear. To elucidate this relationship, chemical tools capable of specifically targeting and modulating metal-A?? species are necessary, along with a fundamental understanding of their mechanism at the molecular level. Herein, we investigated and compared the interactions and reactivities of the green tea extract, (-)-epigallocatechin-3-gallate [(2R,3R)-5,7-dihydroxy-2- (3,4,5-trihydroxyphenyl)-3,4-dihydro-2H-1-benzopyran-3-yl 3,4,5- trihydroxybenzoate; EGCG], with metal [Cu(II) and Zn(II)]-A?? and metal-free A?? species. We found that EGCG interacted with metal-A?? species and formed small, unstructured A?? aggregates more noticeably than in metal-free conditions in vitro. In addition, upon incubation with EGCG, the toxicity presented by metalfree A?? and metal-A?? was mitigated in living cells. To understand this reactivity at the molecular level, structural insights were obtained by ion mobility-mass spectrometry (IM-MS), 2D NMR spectroscopy, and computational methods. These studies indicated that (i) EGCG was bound to A?? monomers and dimers, generating more compact peptide conformations than those from EGCGuntreated A?? species; and (ii) ternary EGCG-metal-A?? complexes were produced. Thus, we demonstrate the distinct antiamyloidogenic reactivity of EGCG toward metal-A?? species with a structurebased mechanism.close282

Interaction and reactivity of synthetic aminoisoflavones with metal-free and metalassociated amyloid-beta

Metal ion homeostasis in conjunction with amyloid-b (Ab) aggregation in the brain has been implicated in Alzheimer’s disease (AD) pathogenesis. To uncover the interplay between metal ions and Ab peptides, synthetic, multifunctional small molecules have been employed to modulate Ab aggregation in vitro. Naturally occurring flavonoids have emerged as a valuable class of compounds for this purpose due to their ability to modulate both metal-free and metal-induced Ab aggregation. Although flavonoids have shown anti-amyloidogenic effects, the structural moieties of flavonoids responsible for such reactivity have not been fully identified. In order to understand the structure–interaction–reactivity relationship within the flavonoid family for metal-free and metal-associated Ab, we designed, synthesized, and characterized a set of isoflavone derivatives, aminoisoflavones (1–4), that displayed reactivity (i.e., modulation of Ab aggregation) in vitro. NMR studies revealed a potential binding site for aminoisoflavones between the N-terminal loop and central helix of prefibrillar Ab, which is different from the non-specific binding observed for other flavonoids. The absence or presence of the catechol group differentiated the binding affinities and enthalpy/entropy balance between aminoisoflavones and Ab. Furthermore, having a catechol group influenced the binding mode with fibrillar Ab. Inclusion of additional substituents moderately tuned the impact of aminoisoflavones on Ab aggregation. Overall, through these studies, we obtained valuable insights into the requirements for parity among metal chelation, intermolecular interactions, and substituent variation for Ab interaction