| 1. |
- Feuerbacher, M., et al.
(författare)
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The Samson phase, β-Mg2Al3, Revisited
- 2007
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Ingår i: Zeitschrift für Kristallographie. - 0044-2968. ; 222:6, s. 259-288
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Tidskriftsartikel (refereegranskat)
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| 2. |
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| 3. |
- Foley, S., et al.
(författare)
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Global Characteristics Of Gamma-Ray Bursts Observed With Integral
- 2009
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Ingår i: Baltic Astronomy. - 1392-0049. ; 18:3-4, s. 279-283
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Tidskriftsartikel (refereegranskat)abstract
- The gamma-ray instruments on board INTEGRAL have detected and localized 62 gamma-ray bursts (GRBs) to date. The peak flux distribution of these bursts shows that INTEGRAL detects proportionally more weak GRBs than Swift because of its higher sensitivity in a smaller field of view. Spectral lags, i.e., the time delay in the arrival of low-energy gamma rays with respect to high-energy gamma rays, are measured for 31 of the GRBs. Two groups are identified in the spectral lag distribution of INTEGRAL GRBs, one with short lags < 0.75 s (between 25-50 keV and 50-300 keV) and one with long lags > 0.75 s. Most of the long-lag GRBs are inferred to have low redshifts because of their long spectral lags. They are mainly observed in the direction of the supergalactic plane and hence reflect the local large-scale structure of the Universe. This low-luminosity population appears to be distinct from typical cosmological GRBs.
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| 4. |
- Neira-Carrillo, Andronico, et al.
(författare)
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Synthesis and characterization of sulfonated polymethylsiloxane polymer as template for crystal growth of CaCO3
- 2009
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Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 287:4, s. 385-393
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to synthesize a sulfonated polymethylsiloxane (S-PMS) by hydrosilylation and sulfonation reactions and to investigate their effect on the growth of CaCO3 crystals using a gas diffusion method as a function of concentration, pH, and time. The result of IR and NMR shows good agreement with all proposed structures. Scanning electron microscopy images of CaCO3 showed small well-defined calcite-forming short piles (ca 5 mu m) and elongated calcite (ca 20 mu m) crystals. The morphology of the resultant CaCO3 crystals reflects the electrostatic interaction of sulfonate moieties and Ca2+ modulated by S-PMS adsorbed onto the CaCO3 surface. X-ray diffraction confirmed the crystalline calcite polymorph. Energy dispersive spectroscopy of CaCO3 crystals determined the presence of Si atoms from S-PMS. The use of PMS chemistry as an organic additive for the production of CaCO3 particles is a viable approach for studying the biomineralization and could be useful for the design of novel materials with desirable shape and properties.
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| 5. |
- Nieira-Carrillo, Andronico, et al.
(författare)
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Calcium carbonate growth modification by constituents releases from porous cellulose filter membranes
- 2008
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Ingår i: Journal of the Chilean Chemical Society (Print). - 0717-9324 .- 0717-9707. ; 53:2, s. 1469-1473
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Tidskriftsartikel (refereegranskat)abstract
- Filtration of a suspension of calcium carbonate (CaCO3) or other inorganic solutions are often part of the methodology for recovering crystals during biomimetic mineralization experiments performed by various procedures. However, the use of cellulose filter membranes (FM) may cause a problem in in vitro crystallization experiments, because constituents released from the filters into the filtrates can alter the morphology of CaCO3 crystals. Therefore, it is possible to misinterpret data obtained when the effect of specific additives tested in the investigation of biomineralization mechanisms. Herein, we present essential information to avoid such misinterpretations of data obtained from mineralization experiments. CaCO3, was precipitated at room temperature by the gas diffusion method in the presence of FM as support and particularly as filtrates of calcium chloride (CaCl2) obtained from various commercial FM. The occurrence or absence of morphological modifications of the calcite and vaterite crystals obtained with different FM correlates well with the different elemental compositions of the solutions where crystals are grown because of the constituents released from the filters into the filtrate. X-ray photoelectron spectroscopy (XPS) data indicate significant differences in the filter elemental composition. We assume that the observed chronological changes in CaCO3 crystal modification could be due to incorporation into the calcite lattice of constituents released from the FM, most likely monomers, oligomers, or short-chain polymers.
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| 6. |
- Tellez, Luis A., et al.
(författare)
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Thermal unfolding of triosephosphate isomerase from Entamoeba histolytica : dimer dissociation leads to extensive unfolding
- 2008
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 47:44, s. 11665-11673
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Tidskriftsartikel (refereegranskat)abstract
- In mesophiles, triosephosphate isomerase (TIM) is an obligated homodimer. We have previously shown that monomeric folding intermediates are common in the chemical unfolding of TIM, where dissociation provides 75% of the overall conformational stability of the dimer. However, analysis of the crystallographic structure shows that, during unfolding, intermonomeric contacts contribute to only 5% of the overall increase in accessible surface area. In this work several methodologies were used to characterize the thermal dissociation and unfolding of the TIM from Entamoeba histolytica (EhTIM) and a monomeric variant obtained by chemical derivatization (mEhTIM). During EhTIM unfolding, sequential transitions corresponding to dimer dissociation into a compact monomeric intermediate followed by unfolding and further aggregation of the intermediate occurred. In the case of mEhTIM, a single transition, analogous to the second transition of EhTIM, was observed. Calorimetric, spectroscopic, hydrodynamic, and functional evidence shows that dimer dissociation is not restricted to localized interface reorganization. Dissociation represents 55% (DeltaH(Diss) = 146.8 kcal mol(-1)) of the total enthalpy change (DeltaH(Tot) = 266 kcal mol(-1)), indicating that this process is linked to substantial unfolding. We propose that, rather than a rigid body process, subunit assembly is best represented by a fly-casting mechanism. In TIM, catalysis is restricted to the dimer; therefore, the interface can be viewed as the final nucleation motif that directs assembly, folding, and function.
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| 7. |
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