Galactic and Extragalactic Samples of Supernova Remnants: How They Are Identified and What They Tell Us

Supernova remnants (SNRs) arise from the interaction between the ejecta of a supernova (SN) explosion and the surrounding circumstellar and interstellar medium. Some SNRs, mostly nearby SNRs, can be studied in great detail. However, to understand SNRs as a whole, large samples of SNRs must be assembled and studied. Here, we describe the radio, optical, and X-ray techniques which have been used to identify and characterize almost 300 Galactic SNRs and more than 1200 extragalactic SNRs. We then discuss which types of SNRs are being found and which are not. We examine the degree to which the luminosity functions, surface-brightness distributions and multi-wavelength comparisons of the samples can be interpreted to determine the class properties of SNRs and describe efforts to establish the type of SN explosion associated with a SNR. We conclude that in order to better understand the class properties of SNRs, it is more important to study (and obtain additional data on) the SNRs in galaxies with extant samples at multiple wavelength bands than it is to obtain samples of SNRs in other galaxiesComment: Final 2016 draft of a chapter in "Handbook of Supernovae" edited by Athem W. Alsabti and Paul Murdin. Final version available at https://doi.org/10.1007/978-3-319-20794-0_90-

Age-dependent response of murine female bone marrow cells to hyperbaric oxygen

Consequences of age on the effects of hyperbaric oxygen (HBO) on bone marrow (BM) derived stem cells and progenitors (SCPs) are largely unknown. We treated 2- and 18-month old C57BL/6 female mice by HBO. Hematopoietic stem cells and progenitors, enumerated as colony-forming units in culture, were doubled only in peripheral leukocytes and BM cells of young mice receiving HBO. In old mice colony-forming unit fibroblast numbers, a measure of mesenchymal stromal cells (MSCs) from BM, were high but unaffected by HBO. To further explore this finding, in BM-MSCs we quantified the transcripts of adipocyte early-differentiation genes peroxisome proliferator-activated receptor-γ, CCAAT/enhancer binding protein-β and fatty-acid binding protein 4; these transcripts were not affected by age or HBO. However, osteoblast gene transcripts runt-related transcription factor 2, osterix (OSX) and alkaline phosphatase (AP) were twofold to 20-fold more abundant in MSCs from old control mice relative to those of young control mice. HBO affected expression of osteoblast markers only in old MSCs (OSX gene expression was reduced by twofold and AP expression was increased threefold). Our data demonstrate the impact of aging on the response of BM SCPs to HBO and indicate the potentially different age-related benefit of HBO in wound healing and tissue remodeling

Mechanism of subunit interaction at ketosynthase-dehydratase junctions in trans-AT polyketide synthases

Modular polyketide synthases (PKSs) produce numerous structurally complex natural products with diverse applications in medicine and agriculture. They typically consist of several multienzyme subunits that utilize structurally-defined docking domains (DDs) at their N- and C-termini to ensure correct assembly into functional multi-protein complexes. Here we report a fundamentally different mechanism for subunit assembly in trans-AT modular PKSs at the junction between ketosynthase (KS) and dehydratase (DH) domains. This involves direct interaction of a largely unstructured docking domain (DD) at the C-terminus of the KS with the surface of the downstream DH. Acyl transfer assays and mechanism-based cross-linking established that the DD is required for the KS to communicate with the acyl carrier protein appended to the DH. Two distinct regions for binding of the DD to the DH were identified using NMR spectroscopy, carbene foot-printing and mutagenesis, providing a foundation for future elucidation of the molecular basis for interaction specificity

Hypericum sp.: essential oil composition and biological activities

Phytochemical composition of Hypericum genus has been investigated for many years. In the recent past, studies on the essential oils (EO) of this genus have been progressing and many of them have reported interesting biological activities. Variations in the EO composition of Hypericum species influenced by seasonal variation, geographic distribution, phenological cycle and type of the organ in which EO are produced and/or accumulated have also been reported. Although many reviews attributed to the characterization as well as biological activities of H. perforatum crude extracts have been published, no review has been published on the EO composition and biological activities of Hypericum species until recently (Crockett in Nat Prod Commun 5(9):1493–1506, 2010; Bertoli et al. in Global Sci Books 5:29–47, 2011). In this article, we summarize and update information regarding the composition and biological activities of Hypericum species EO. Based on experimental work carried out in our laboratory we also mention possible biotechnology approaches envisaging EO improvement of some species of the genus.Fundação para a Ciência e a Tecnologia (FCT) - project PTDC/AGR AAM/70418/2006, SFRH/BD/ 13283/2003

Conformational analysis of octa- and tetrabromo tetraphenylporphyrins and their Ni(II) and Tb(III) complexes

Molecular mechanics (MM) calculations were used to analyze the puckering of metalloporphyrins as a function of metal ion size and the position of substituents on the porphyrin periphery, on a three series of octa- and tetrabromo tetraphenylporphyrins: without metal, and with Ni(II), and Tb(III) as representative small and large metal ions, respectively. Molecular energy optimization calculations were carried out using the Consistent Force Field (CFF) program, with the parameters developed previously and new parameters for bromine atom. Normal-coordinate structural decomposition (NSD) analysis was performed on the equilibrium structures obtained by MM calculations. The conformers are also stereochemically characterized, compared with available X-ray structures and with the conformers obtained in our previous MM study using chloro instead of bromo P-pyrrole substituents. (C) 2004 Elsevier Inc. All rights reserved

Conformational analysis of octa- and tetrahalogenated tetraphenylporphyrins and their metal derivatives

A new maximally diagonal force field for molecular modelling of metalloporphyrins is developed and optimized on the crystal structures of nickel(II) porphine, nickel(II) mono-tert-butylporphyrin and nickel(II) di-tert-butylporphyrin. It is then used to investigate non-planar distortions of octa- and tetrachloro tetraphenylporphyrins (TPP) and their Ni(II) and Tb(III) complexes. Molecular mechanics (MM) calculations reproduced very well the structure of Tb(III) octachloro-TPP (so far the only example of a crystallographically characterized chloro TPP metal derivative). Normal-coordinate structural decomposition (NSD) analysis was performed on the equilibrium structures obtained by MM calculations. As expected, sad distortion dominates in octachloro structures irrespective of the presence or the size of the central metal atom; dom distortion dominates in tetrachloro structures with large Th(III) central atom, while sad, ruf, wav and pro distortions are present in various amounts in other tetrachloro structures (TPP free base and Ni(II) complex) depending on the pattern of peripheral chloro substitution on the pyrrole rings. Other observed regularities are: reduction of the conformational flexibility of the porphyrin core upon metallation, and increase of the dihedral angle between the phenyl groups and the mean LSQ plane of the porphyrin core, as well as the overall increase in structural regularity upon the increase of the size of the central metal atom. (C) 2001 Elsevier Science B.V. All rights reserved

Conformational analysis of EDTA-type chromium(III) complexes with beta-propionato metal chelate rings

Conformational analysis of the three geometrical isomers of (aqua)(ethylenediamine-tripropionato)cliromium(III) has been performed with the Consistent Force Field (CFF) program. Four stable conformations were identified for trans(H2O,O) and trans(H2O,N-H), and five stable conformations for trans(H2O,N') geometrical isomer. Their structure and relative strain were analyzed and compared with the available experimental data. The conformer representing the global minimum (population 58% at 298 K) was found to match closely the X-ray structure of the trans(H2O,N-H) isomer. The factors which determine the individual chelate ring conformations, and conformational transmission through the entire ligand system was elucidated, and a possible extension of this analysis to other EDTA-type complexes is indicated. (C) 2002 Elsevier Science B.V. All rights reserved

Structural characterization of the trans-equatorial isomer of (aqua)(ethylenediamine-N,N,N '-tripropionato)chromium(III) trihydrate, [Cr(edtrp)(H2O)]center dot 3H(2)O

The structure of trans-equatorial [Cr(edtrp)(H2O)]. 3H(2)O (edtrp(3-) is the anion of ethylenediamine-N,N,N'-tripropionic acid) was determined by single crystal X-ray diffraction. The chromium(III) ion is surrounded octahedrally by the two nitrogen and three oxygen atoms of the quinquedentate edtrp(3-), forming a five-membered diamine ring and the three six-membered beta-propionato chelate rings. The remaining coordination position is occupied by the H2O ligand. The crystal structure conformation is compared to the result of recent molecular mechanics analysis. The ring strain of R and G chelate rings was found to be in agreement with the previously proposed mechanisms for the C-N bond cleavage and recombination

Structural characterization and conformational analysis of (aqua)(ethylenediamine-N,N,N '-triacetato)chromium(III) monohydrate complex. Crystal structure of the cis-equatorial isomer of [Cr(ed3a)(H2O)]center dot H2O

The structure of the cis-equatorial isomer of [Cr(ed3a)(H2O)] .H2O (ed3a = ethylenediamine-N, N, N'-triacetate ion) was determined by X-ray diffraction method. The complex crystallizes in the monoclinic space group P2(1)/n, a = 7.004(l) Angstrom, b = 15.958(2) Angstrom, c = 11.046(l) Angstrom, beta = 97.16(l)degrees , and Z = 4. Conformational analysis of the three possible geometrical isomers, trans(H2O,N'), trans(H2O,N-H), and trans(H2O,O) of [Cr(ed3a)(H2O)] moiety, performed using the consistent force field (CFF) program with the recently developed parameters for EDTA-type complexes, yielded structural details and energies of the minimized form for each of the isomers. Calculated energies showed that the cis-eq isomer is the most stable one, with the geometry in a very good agreement with the crystallographic structure. Comparison of the molecular mechanics calculations with those for the analogous [Cr(ed3p)(H2O)] - H2O (ed3p = ethylenediamine-N, N, N'-tripropionate ion) revealed some general patterns for the conformational preference of EDTA-type complexes. (C) 2003 Elsevier B.V. All rights reserved