| 1. |
- Abelev, Betty, et al.
(författare)
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Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at root s=7 TeV
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at root s = 7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L-int = 5.6 nb(-1). The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p(t) > 1,3 GeV/c and rapidity vertical bar y vertical bar < 0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the psi(2S) and chi(c) resonances, is sigma(prompt J/psi) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 8.3 +/- 0.8(stat.) +/- 1.1 (syst.)(-1.4)(+1.5) (syst. pol.) mu b. The cross section for the production of b-hadrons decaying to J/psi with p(t) > 1.3 GeV/c and vertical bar y vertical bar < 0.9 is a sigma(J/psi <- hB) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 1.46 +/- 0.38 (stat.)(-0.32)(+0.26) (syst.) mu b. The results are compared to QCD model predictions. The shape of the p(t) and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b (b) over bar pair total cross section and d sigma/dy at mid-rapidity.
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| 2. |
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| 3. |
- Fernandes, P. A., et al.
(författare)
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Thermodynamic pathway for the formation of SnSe and SnSe2 polycrystalline thin films by selenization of metal precursors
- 2013
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 15:47, s. 10278-10286
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Tidskriftsartikel (refereegranskat)abstract
- In this work, tin selenide thin films (SnSex) were grown on soda lime glass substrates by selenization of dc magnetron sputtered Sn metallic precursors. Selenization was performed at maximum temperatures in the range 300 degrees C to 570 degrees C. The thickness and the composition of the films were analysed using step profilometry and energy dispersive spectroscopy, respectively. The films were structurally and optically investigated by X-ray diffraction, Raman spectroscopy and optical transmittance and reflectance measurements. X-Ray diffraction patterns suggest that for temperatures between 300 degrees C and 470 degrees C, the films are composed of the hexagonal-SnSe2 phase. By increasing the temperature, the films selenized at maximum temperatures of 530 degrees C and 570 degrees C show orthorhombic-SnSe as the dominant phase with a preferential crystal orientation along the (400) crystallographic plane. Raman scattering analysis allowed the assignment of peaks at 119 cm(-1) and 185 cm(-1) to the hexagonal-SnSe2 phase and those at 108 cm(-1), 130 cm(-1) and 150 cm(-1) to the orthorhombic-SnSe phase. All samples presented traces of condensed amorphous Se with a characteristic Raman peak located at 255 cm(-1). From optical measurements, the estimated band gap energies for hexagonal-SnSe2 were close to 0.9 eV and 1.7 eV for indirect forbidden and direct transitions, respectively. The samples with the dominant orthorhombic-SnSe phase presented estimated band gap energies of 0.95 eV and 1.15 eV for indirect allowed and direct allowed transitions, respectively.
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| 4. |
- Sousa, M. G., et al.
(författare)
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Cu2ZnSnS4 absorber layers obtained through sulphurization of metallic precursors : Graphite box versus sulphur flux
- 2013
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 535, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- In this work we employed a hybrid method, combining RF-magnetron sputtering with evaporation, for the deposition of tailor made metallic precursors, with varying number of Zn/Sn/Cu (ZTC) periods and compared two approaches to sulphurization. Two series of samples with 1x, 2x and 4x ZTC periods have been prepared. One series of precursors was sulphurized in a tubular furnace directly exposed to a sulphur vapour and N-2 + 5% H-2 flux at a pressure of 5.0 x 10(+4) Pa. A second series of identical precursors was sulphurized in the same furnace but inside a graphite box where sulphur pellets have been evaporated again in the presence of N-2 + 5% H-2 and at the same pressure as for the sulphur flux experiments. The morphological and chemical analyses revealed a small grain structure but good average composition for all three films sulphurized in the graphite box. As for the three films sulphurized in sulphur flux grain growth was seen with the increase of the number of ZTC periods whilst, in terms of composition, they were slightly Zn poor. The films' crystal structure showed that Cu2ZnSnS4 is the dominant phase. However, in the case of the sulphur flux films SnS2 was also detected. Photoluminescence spectroscopy studies showed an asymmetric broad band emission which occurs in the range of 1-1.5 eV. Clearly the radiative recombination efficiency is higher in the series of samples sulphurized in sulphur flux. We have found that sulphurization in sulphur flux leads to better film morphology than when the process is carried out in a graphite box in similar thermodynamic conditions. Solar cells have been prepared and characterized showing a correlation between improved film morphology and cell performance. The best cells achieved an efficiency of 2.4%.
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| 5. |
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| 6. |
- Dourado, Daniel F A R, et al.
(författare)
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Glutathione Transferase A1-1 : Catalytic Importance of Arginine 15
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:4, s. 1690-1697
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Tidskriftsartikel (refereegranskat)abstract
- Glutathione transferases (GSTs) are fundamental enzymes of the cell detoxification system. They catalyze the nucleophilic attack Of glutathione (GSH) on electrophilic substrates to produce less toxic compounds. The resulting Substrate can then be recognized by ATP-dependent transmembrane PUMPS and consequently expelled from the cell. Despite all the existing studies on GSTs, many aspects of the catalytic events are still poorly understood. Recently, using as a model the GSTAI-1 enzyme, we proposed it GSH activation mechanism. Resorting to the density functional theory (DFT), we demonstrated that a water molecule could assist a proton transfer between (lie GSH thiol and (x-carboxylic groups. after all initial conformational rearrangement of GSH, as evidenced by potential of mean force calculations. In this work to elucidate the catalytic role of Arg 15, a strictly conserved active site residue in class alpha GSTs. we analyzed the activation energy barrier and Structural details associated with the GSTAI-1 Mutants R15A, R15R epsilon, eta-c (an Arg residue with the epsilon-eta-nitrogens Substituted by carbons), and R 15Rneutral (a neutral Arg residue due to the a addition of a hydride in the zeta-carbon. A similar mechanism to the one used in Our GSH activation proposal was implemented.
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| 7. |
- Dourado, Daniel F. A. R., et al.
(författare)
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Isomerization of Delta(5)-Androstene-3,17-dione into Delta(4)-Androstene-3, 17-dione Catalyzed by Human Glutathione Transferase A3-3 : A Computational Study Identifies a Dual Role for Glutathione
- 2014
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:31, s. 5790-5800
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Tidskriftsartikel (refereegranskat)abstract
- Glutathione transferases (GSTs) are important enzymes in the metabolism of electrophilic xenobiotic and endobiotic toxic compounds. In addition, human GST A3-3 also catalyzes the double bond isomerization of Delta 5-androstene-3,17-dione (Delta(5)-AD) and Delta(5)-pregnene-3,20-dione (Delta(5)-PD), which are the immediate precursors of testosterone and progesterone. In fact, GST A3-3 is the most efficient human enzyme known to exist in the catalysis of these reactions. In this work, we have used density functional theory (DFT) calculations to propose a refined mechanism for the isomerization of Delta(5)-AD catalyzed by GST A3-3. In this mechanism the glutathione (GSH) thiol and Tyr9 catalyze the proton transfer from the Delta(5)-AD C4 atom to the Delta(5)-AD C6 atom, with a rate limiting activation energy of 15.8 kcal.mol(-1). GSH has a dual function, because it is also responsible for stabilizing the negative charge that is formed in the 03 atom of the enolate intermediate. The catalytic role of Tyr9 depends on significant conformational rearrangements of its side chain. Neither of these contributions to catalysis has been observed before. Residues Phe10, Leul11, Ala 208, and Ala 216 complete the list of the important catalytic residues. The mechanism detailed here is based on the GST A3-3:GSH:Delta(4)-AD crystal structure and is consistent with all available experimental data.
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| 8. |
- Dourado, Daniel F. A. R., et al.
(författare)
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Mechanism of Glutathione Transferase P1-1-Catalyzed Activation of the Prodrug Canfosfamide (TLK286, TELCYTA)
- 2013
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 52:45, s. 8069-8078
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Tidskriftsartikel (refereegranskat)abstract
- Canfosfamide (TLK286, TELCYTA) is a prodrug that upon activation by glutathione transferase P1-1 (GST P1-1) yields an anticancer alkylating agent and a glutathione derivative. The rationale underlying the use of TLK286 in chemotherapy is that tumor cells overexpressing GST P1-1 will be locally exposed to the released alkylating agent with limited collateral toxicity to the surrounding normal tissues. TLK286 has demonstrated clinical effects in phase II and III clinical trials for the treatment of malignancies, such as ovarian cancer, nonsmall cell lung cancer, and breast cancer, as a single agent and in combination with other chemotherapeutic agents. In spite of these promising results, the detailed mechanism of GST P1-1 activation of the prodrug has not been elucidated. Here, we propose a mechanism for the TLK286 activation by GST P1-1 on the basis of density functional theory (DFT) and on potential of mean force (PMF) calculations. A catalytic water molecule is instrumental to the activation by forming a network of intermolecular interactions between the active-site Tyr7 hydroxyl and the sulfone and COO- groups of TLK286. The results obtained are consistent with the available experimental kinetic data and provide an atomistic understanding of the TLK286 activation mechanism.
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| 9. |
- Salomé, Pedro M. P., et al.
(författare)
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Secondary crystalline phases identification in CuZnSnSe thin films : contributions from Raman scattering and photoluminescence
- 2014
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 49:21, s. 7425-7436
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present the Raman peak positions of the quaternary pure selenide compound CuZnSnSe (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, CuSnSe, ZnSe, SnSe, SnSe, MoSe and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials' model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.
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| 10. |
- Zhang, Wei, et al.
(författare)
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Multidimensional epistasis and fitness landscapes in enzyme evolution
- 2012
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 445, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- The conventional analysis of enzyme evolution is to regard one single salient feature as a measure of fitness, expressed in a milieu exposing the possible selective advantage at a given time and location. Given that a single protein may serve more than one function, fitness should be assessed in several dimensions. In the present study we have explored individual mutational steps leading to a triple-point-mutated human GST (glutathione transferase) A2-2 displaying enhanced activity with azathioprine. A total of eight alternative substrates were used to monitor the diverse evolutionary trajectories. The epistatic effects of the imitations on catalytic activity were variable in sign and magnitude and depended on the substrate used, showing that epistasis is a multidimensional quality. Evidently, the multidimensional fitness landscape can lead to alternative trajectories resulting in enzymes optimized for features other than the selectable markers relevant at the origin of the evolutionary process. In this manner the evolutionary response is robust and can adapt to changing environmental conditions.
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