| 71. |
- Andersen, Øivind, et al.
(författare)
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The conserved Phe GH5 of importance for hemoglobin intersubunit contact is mutated in gadoid fish
- 2014
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Ingår i: BMC Evolutionary Biology. - 1471-2148. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Background Functionality of the tetrameric hemoglobin molecule seems to be determined by a few amino acids located in key positions. Oxygen binding encompasses structural changes at the interfaces between the α1β2 and α2β1 dimers, but also subunit interactions are important for the oxygen binding affinity and stability. The latter packing contacts include the conserved Arg B12 interacting with Phe GH5, which is replaced by Leu and Tyr in the α A and α D chains, respectively, of birds and reptiles. Results Searching all known hemoglobins from a variety of gnathostome species (jawed vertebrates) revealed the almost invariant Arg B12 coded by the AGG triplet positioned at an exon-intron boundary. Rare substitutions of Arg B12 in the gnathostome β globins were found in pig, tree shrew and scaled reptiles. Phe GH5 is also highly conserved in the β globins, except for the Leu replacement in the β1 globin of five marine gadoid species, gilthead seabream and the Comoran coelacanth, while Cys and Ile were found in burbot and yellow croaker, respectively. Atlantic cod β1 globin showed a Leu/Met polymorphism at position GH5 dominated by the Met variant in northwest-Atlantic populations that was rarely found in northeast-Atlantic cod. Site-specific analyses identified six consensus codons under positive selection, including 122β(GH5), indicating that the amino acid changes identified at this position may offer an adaptive advantage. In fact, computational mutation analysis showed that the replacement of Phe GH5 with Leu or Cys decreased the number of van der Waals contacts essentially in the deoxy form that probably causes a slight increase in the oxygen binding affinity. Conclusions The almost invariant Arg B12 and the AGG codon seem to be important for the packing contacts and pre-mRNA processing, respectively, but the rare mutations identified might be beneficial. The Leu122β1(GH5)Met and Met55β1(D6)Val polymorphisms in Atlantic cod hemoglobin modify the intradimer contacts B12-GH5 and H2-D6, while amino acid replacements at these positions in avian hemoglobin seem to be evolutionary adaptive in air-breathing vertebrates. The results support the theory that adaptive changes in hemoglobin functions are caused by a few substitutions at key positions.
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| 72. |
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| 73. |
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| 74. |
- Chakraborti, Sayan, et al.
(författare)
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A MISSING-LINK IN THE SUPERNOVA-GRB CONNECTION : THE CASE OF SN 2012ap
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 805:2
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly, usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However, supernovae with heavy ejecta can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for a few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. However, the ejecta from SN 2009bb was baryon loaded and in nearly free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than one-sixth of the fluence from GRB 980425. This shows for the first time that central engines in SNe Ic, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.
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| 75. |
- Chakravarty, D., et al.
(författare)
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Zirconia-Nanoparticle-Reinforced Morphology-Engineered Graphene-Based Foams
- 2015
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648. ; 27:31, s. 4534-4543
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Tidskriftsartikel (refereegranskat)abstract
- The morphology of graphene-based foams can be engineered by reinforcing them with nanocrystalline zirconia, thus improving their oil-adsorption capacity; This can be observed experimentally and explained theoretically. Low zirconia fractions yield flaky microstructures where zirconia nanoparticles arrest propagating cracks. Higher zirconia concentrations possess a mesh-like interconnected structure where the degree of coiling is dependant on the local zirconia content. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 76. |
- De La Fuente, Eduardo, et al.
(författare)
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Evidence for a gamma-ray molecular target in the enigmatic PeVatron candidate LHAASO J2108+5157
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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Tidskriftsartikel (refereegranskat)abstract
- Context . Peta-eV (PeV) astronomy emerged in 2021 with the discovery of ultra-high-energy gamma-ray sources associated with powerful natural particle accelerators known as PeVatrons. In order to determine the nature of their emission, namely whether it has a hadronic or leptonic origin, it is essential to characterise the physical parameters of the environment where it originates. Aims . We unambiguously confirm the association of molecular gas with the PeVatron candidate LHAASO J2108+5157 using unprecedented high angular-resolution (17′) 12,13CO(J = 1 → 0) observations carried out with the Nobeyama 45m radio telescope. Methods . We characterised a molecular cloud in the vicinity of the PeVatron candidate LHAASO J2108+5157 by determining its physical parameters from our 12,13CO(J = 1 → 0) line observations. We used an updated estimation of the distance to the cloud, which provided a more reliable result. The molecular emission was compared with excess gamma-ray images obtained with Fermi-LAT at energies above 2 GeV to search for spatial correlations and test a possible hadronic (π0 decay) origin for the gamma-ray emission. Results . We find that the morphology of the spatial distribution of the CO emission is strikingly similar to that of the Fermi-LAT excess gamma ray. By combining our observations with archival 21 cm HI line data, the nucleons (HI + H2) number density of the target molecular cloud is found to be 133.0 ± 45.0 cm-3, for the measured angular size of 0.55 ± 0.02 at a distance of 1.6 ± 0.1 kpc. The resulting total mass of the cloud is M(HI + H2) = 7.5±2.9×103M⊙. Under a hadronic scenario, we obtain a total energy of protons of Wp = 4.3 ± 1.5 × 1046 erg with a cutoff of 700±300 TeV, which reproduces the sub-PeV gamma-ray emission. Conclusions . We identified a molecular cloud in the vicinity of LHAASO J2107+5157 as the main target where cosmic rays from an unknown PeVatron produce the observed gamma-ray emission via π0 decay.
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| 77. |
- DeFrancisco, Justin R., et al.
(författare)
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Torsional Bias as a Strategy To Tune Single-triplet Gaps in Organic Diradicals
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:23, s. 12148-12157
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Tidskriftsartikel (refereegranskat)abstract
- Quinoidal compounds with proaromatic structures possess differing degrees of diradical character, where the open-shell diradical resonance form has restored aromaticity throughout the compound. Methods to tune the diradical character of these compounds have traditionally focused on altering the length and the molecular composition of the pi-conjugated backbones. However, other molecular design strategies to tune the singlet-triplet gap of pi-conjugated quinoidal molecules have not been extensively explored. We previously reported a strikingly small energy gap between the quinoidal and diradical states of a quinoidal small molecule containing methano[10]annulene (TMTQ) that was dictated in large part by the unusual aromaticity of the central annulene ring. Here, we report on two alkylated derivatives of TMTQthat present substantially different torsional biases to the planarity of the TMTQ pi-system. Using a combination of electronic and vibrational spectroscopies, magnetic measurements, and quantum chemical calculations, we demonstrate here how a steric effect rather than pi-electron compositional molecular engineering can dramatically narrow the singlet-triplet gap of a quinoidal compound to as small as -0.52 kcal/mol, determined experimentally. This study offers important insight for the continued development of open-shell diradical molecules that need not rely exclusively on the design of synthesis of new and complex conjugated systems.
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| 78. |
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| 79. |
- Gangopadhyay, Shubhashis, et al.
(författare)
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Cash or In-kind Transfers? Evidence from a Randomised Controlled Trial in Delhi, India
- 2015
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Ingår i: Journal of Development Studies. - : Informa UK Limited. - 0022-0388 .- 1743-9140. ; 51:6, s. 660-673
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Tidskriftsartikel (refereegranskat)abstract
- This article examines a randomised intervention in Delhi, India, that provided unconditional cash transfers to a group of households as a replacement for the food security offered by a below-poverty-level card. The experimental approach can differentiate beneficial effects due to either unconditional cash transfers or newly opened bank accounts. The unconditional cash transfer does not induce a decline in food security; rather, it provides opportunities for households to shift to other nutritious options in non-cereal product categories.
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| 80. |
- Ghosh, Swagatha, 1987, et al.
(författare)
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Modulation of biliverdin dynamics and spectral properties by Sandercyanin
- 2022
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 12:31, s. 20296-20304
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Tidskriftsartikel (refereegranskat)abstract
- Biliverdin IX-alpha (BV), a tetrapyrrole, is found ubiquitously in most living organisms. It functions as a metabolite, pigment, and signaling compound. While BV is known to bind to diverse protein families such as heme-metabolizing enzymes and phytochromes, not many BV-bound lipocalins (ubiquitous, small lipid-binding proteins) have been studied. The molecular basis of binding and conformational selectivity of BV in lipocalins remains unexplained. Sandercyanin (SFP)-BV complex is a blue lipocalin protein present in the mucus of the Canadian walleye (Stizostedion vitreum). In this study, we present the structures and binding modes of BV to SFP. Using a combination of designed site-directed mutations, X-ray crystallography, UV/VIS, and resonance Raman spectroscopy, we have identified multiple conformations of BV that are stabilized in the binding pocket of SFP. In complex with the protein, these conformers generate varied spectroscopic signatures both in their absorption and fluorescence spectra. We show that despite no covalent anchor, structural heterogeneity of the chromophore is primarily driven by the D-ring pyrrole of BV. Our work shows how conformational promiscuity of BV is correlated to the rearrangement of amino acids in the protein matrix leading to modulation of spectral properties.
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