Herein, a sensor platform, Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE), is pres... more Herein, a sensor platform, Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE), is presented for the detection of Cd2+ and Pb2+ using square wave anodic stripping voltammetry (SWASV). The sensor was obtained through electrografting of the GCE using 4-carboxybenzene diazonium tetrafluoroborate (4-CBD) and in situ electrodeposition of Bi3+. The stability of the grafted layer and the proposed mechanism of interaction between the metal ions and the grafted layer is supported by DFT calculations. Under the optimized conditions, Pb2+ had a linear working range of 25–500 μg L−1 with LOD of 10 μg L−1 (S/N = 3) and Cd2+ provided linear range of 50–500 μg L−1 and LOD of 25 μg L−1. The fabricated electrode presented good repeatability and reproducibility. The applicability of the electrode was tested for determination of Cd2+ and Pb2+ in tap water resulting in recoveries of 96.2–101% for Cd2+ and 98.1–104% for Pb2+Originally included in thesis in manuscript form with title: In situ Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE) as a sensor platform in square wave anodic stripping voltammetry: detection of Pb2+ and Cd2+ in tap water</p
The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s... more The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV are measured using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3:1 AE 0:3 pb À1. Integrated over the rapidity range jyj < 2, we find the product of the Çð1SÞ production cross section and branching fraction to dimuons to be ðpp ! Çð1SÞXÞ Á BðÇð1SÞ ! þ À Þ ¼ 7:37 AE 0:13 þ0:61 À0:42 AE 0:81 nb, where the first uncertainty is statistical, the second is systematic, and the third is associated with the estimation of the integrated luminosity of the data sample. This cross section is obtained assuming unpolarized Çð1SÞ production. With the assumption of fully transverse or fully longitudinal production polarization, the measured cross section changes by about 20%. We also report the measurement of the Çð1SÞ, Çð2SÞ, and Çð3SÞ differential cross sections as a function of transverse momentum and rapidity.
The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) we... more The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) were investigated using periodic density functional theory in conjunction with pseudopotential plane-wave approach. Surface hydroxyl groups covering the octahedral surface of kaolinite were found to play the role of catalysts in the transformations of FM. They induce a reduction of 31 kcal/ mol on the energy barrier for formation of its isomer aminohydroxymethylene (AHM), which is close to the reduction amount calculated for water-catalyzed reactions. This suggests that the kaolinite octahedral surface exerts a catalytic effect similar to that of the water molecule. As the tetrahedral surface does not contain catalytic surface hydroxyl groups, only water-assisted FM transformation was therefore studied on this surface whose energy barrier amounts to ∼17 kcal/mol. The combined effect of both water and kaolinite on FM rearrangements via triple hydrogen transfer reactions does not significantly lower the energy barriers, as compared to those of double hydrogen transfer reactions. The triple hydrogen transfer energy barriers amount to ∼20 and ∼36 kcal/mol, and the double ones are ∼21 and ∼40 kcal/mol for formation of formimic acid and AHM isomers, respectively. However, the energies of the systems in water-catalyzed channels lie below the available energies of the original reactants, and thus these channels are more favored than the water-free ones. With its multiple functions as both a supporting plate-form and a catalyst for FM reactions, kaolinite can thus be regarded as an important natural catalyst for prebiotic synthesis.
Advances in Natural Sciences: Nanoscience and Nanotechnology, 2012
Nd10.5Fe83.5−xGaxB6 (x=1.5, 3 and 4.5) ribbons were prepared by melt-spinning method with various... more Nd10.5Fe83.5−xGaxB6 (x=1.5, 3 and 4.5) ribbons were prepared by melt-spinning method with various wheel speeds from 5 to 40 m s−1. Strong crystallographic texture with c-axis of Nd2Fe14B crystallites along normal of the ribbon surface was observed. The texture degree can be enhanced by decreasing the quenching rate during solidification of the melt and by increasing the concentration of Ga.
The efficient formation of HCN/HNC from formamide (FM) combining the advantages of waterassistanc... more The efficient formation of HCN/HNC from formamide (FM) combining the advantages of waterassistance, self-catalyzed reactions, and the mineral surfaces was investigated. Periodic density functional theory calculations with plane-wave pseudopotential basis sets were performed to study the interaction of FM with pyrite (100) ideal and defect surfaces. Effects of sulfur vacancy defect and water on tautomerization and rearrangement barriers of FM on the (100) surface were evaluated. Calculated results show that FM adsorbs more strongly on the defect surface than on the ideal surface, with the lowest adsorption energy on the defect surface being −22 kcal/mol. The energy barriers for rearrangements of FM on these two surfaces being close to each other suggests that the adsorptions on the surfaces have small effects on the energy barriers. The energy barriers for formimic acid isomer formations are 44.5 and 46.0 kcal/mol, and those of aminohydroxymethylene formations are 72.6 and 71.9 kcal/mol on the ideal and defect surfaces, respectively. A reduction of ∼30 kcal/mol in tautomerization energy barriers is observed in waterassisted process on the defect surface. Because this reduction is close to that of the gas-phase reactions, the catalytic effect is clearly due to the presence of water molecule instead of the interaction with the surface. In this case, the pyrite surfaces with the ability to accumulate reactive species only play the role of connecting bridges between the two steps of the proposed reaction mechanism: the water-assisted rearrangement and the self-catalyzed dehydration.
Unimolecular decompositions of neutral (NH 2 CHO) and protonated (NH 3 CHO +) formamide, an activ... more Unimolecular decompositions of neutral (NH 2 CHO) and protonated (NH 3 CHO +) formamide, an active precursor of biomolecules in prebiotic chemistry, are investigated in the ground (S 0) and first triplet (T 1) and singlet (S 1) excited states. Different decomposition channels including the homolytic bond dissociations, dehydration, decarbonylation, dehydrogenation, etc., are explored using coupled-cluster theory (CCSD(T)/CBS method) for both S 0 and T 1 states and RASPT2(18,15)/6-31G(d,p) computations for the S 1 state. On S 1 and T 1 energy surfaces, formamide preferentially follows C−N homolytic bond cleavages forming NH 2 + HCO radical pairs. Formation of HCN and HNC from dehydration of neutral and protonated formamide via formimic acid and aminohydroxymethylene isomers has higher energy barriers. A strong stabilization upon triplet excitation of the two latter isomers significantly facilitates the interconversions between isomers, and thus considerably reduces the energy barriers for dehydration pathways. The most probable pathways for HCN and HNC generation are found to be dehydration of formamide in the T 1 state. Dehydration pathways from the neutral S 1 and protonated T 1 forms lead to stable complexes of HCN and HNC with water but are associated with large energy barriers. Overall, in the lower-lying excited states of either neutral or protonated formamide, dehydration is not competitive with homolytic C−N bond cleavages, which finally lead to formation of CO.
The first paragraph on p. 15 of the original version should be replaced by the following paragrap... more The first paragraph on p. 15 of the original version should be replaced by the following paragraph, which deletes an incorrect reference to a figure. The uncertainties on the mistagged NTMJ background include the statistical uncertainty on the sample after loose selection, to which the mistag probability is applied; the statistical uncertainty on the mistag probability itself, ranging from <1% at 1 TeV/c 2 to ≈10% at 3 TeV/c 2 ; and the systematic uncertainty on the mistag probability application, as described in section 3.3, which is in the range of 1 to 5% depending on the tt mass. The total background uncertainty is ≈5% for the low-mass region, dominated by the systematic uncertainty, and ≈100% for the high-mass region, dominated by statistical uncertainty associated with the sample after loose selection. Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited. Open Access, Copyright CERN, for the benefit of the CMS Collaboration. Article funded by SCOAP 3 .
The supporting information includes: (1) coordinates for optimized geometries of all species, (2)... more The supporting information includes: (1) coordinates for optimized geometries of all species, (2) coordinates of geometries for all transition states, (3) Structure of two conformers of 3, (3) structure of radical:neutral molecule complexes
The usual 'quantum bouncer' is a quantum particle bouncing elastically under the influence of gra... more The usual 'quantum bouncer' is a quantum particle bouncing elastically under the influence of gravity. Here we consider a particle bouncing off an impenetrable wall, and bound to it by the harmonic potential 1 2 mω 2 x 2 instead of by the gravitational potential mgx. An analytic solution is possible, easily accessible to classes in intermediate quantum mechanics. The solution is related to Schrödinger's oscillating wavepacket (the original coherent state). Although periodic, it changes its form during the oscillation, in contrast to Schrödinger's packet. The uncertainties in the position (x) and the momentum (p) oscillate also, as does the product x p.
Free radical pathways for the synthesis of xanthine and isoguanine from formamide were studied us... more Free radical pathways for the synthesis of xanthine and isoguanine from formamide were studied using density functional theory (B3LYP/6-311G(d,p)). The proposed mechanisms are complex and appropriate for the non-aqueous scenario of prebiotic reactions. Formation of the carbonyl bond in the nucleobases proceeds through enol-keto tautomerization since the direct formation of the C@O bond is a highly endothermic step. The mechanisms show 2-amino-imidazole as a precursor for nucleobases and polyazaporphyrin. The proposed mechanisms contribute to a further understanding of the origin of biomolecules.
Herein, a sensor platform, Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE), is pres... more Herein, a sensor platform, Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE), is presented for the detection of Cd2+ and Pb2+ using square wave anodic stripping voltammetry (SWASV). The sensor was obtained through electrografting of the GCE using 4-carboxybenzene diazonium tetrafluoroborate (4-CBD) and in situ electrodeposition of Bi3+. The stability of the grafted layer and the proposed mechanism of interaction between the metal ions and the grafted layer is supported by DFT calculations. Under the optimized conditions, Pb2+ had a linear working range of 25–500 μg L−1 with LOD of 10 μg L−1 (S/N = 3) and Cd2+ provided linear range of 50–500 μg L−1 and LOD of 25 μg L−1. The fabricated electrode presented good repeatability and reproducibility. The applicability of the electrode was tested for determination of Cd2+ and Pb2+ in tap water resulting in recoveries of 96.2–101% for Cd2+ and 98.1–104% for Pb2+Originally included in thesis in manuscript form with title: In situ Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE) as a sensor platform in square wave anodic stripping voltammetry: detection of Pb2+ and Cd2+ in tap water</p
The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s... more The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV are measured using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3:1 AE 0:3 pb À1. Integrated over the rapidity range jyj < 2, we find the product of the Çð1SÞ production cross section and branching fraction to dimuons to be ðpp ! Çð1SÞXÞ Á BðÇð1SÞ ! þ À Þ ¼ 7:37 AE 0:13 þ0:61 À0:42 AE 0:81 nb, where the first uncertainty is statistical, the second is systematic, and the third is associated with the estimation of the integrated luminosity of the data sample. This cross section is obtained assuming unpolarized Çð1SÞ production. With the assumption of fully transverse or fully longitudinal production polarization, the measured cross section changes by about 20%. We also report the measurement of the Çð1SÞ, Çð2SÞ, and Çð3SÞ differential cross sections as a function of transverse momentum and rapidity.
The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) we... more The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) were investigated using periodic density functional theory in conjunction with pseudopotential plane-wave approach. Surface hydroxyl groups covering the octahedral surface of kaolinite were found to play the role of catalysts in the transformations of FM. They induce a reduction of 31 kcal/ mol on the energy barrier for formation of its isomer aminohydroxymethylene (AHM), which is close to the reduction amount calculated for water-catalyzed reactions. This suggests that the kaolinite octahedral surface exerts a catalytic effect similar to that of the water molecule. As the tetrahedral surface does not contain catalytic surface hydroxyl groups, only water-assisted FM transformation was therefore studied on this surface whose energy barrier amounts to ∼17 kcal/mol. The combined effect of both water and kaolinite on FM rearrangements via triple hydrogen transfer reactions does not significantly lower the energy barriers, as compared to those of double hydrogen transfer reactions. The triple hydrogen transfer energy barriers amount to ∼20 and ∼36 kcal/mol, and the double ones are ∼21 and ∼40 kcal/mol for formation of formimic acid and AHM isomers, respectively. However, the energies of the systems in water-catalyzed channels lie below the available energies of the original reactants, and thus these channels are more favored than the water-free ones. With its multiple functions as both a supporting plate-form and a catalyst for FM reactions, kaolinite can thus be regarded as an important natural catalyst for prebiotic synthesis.
Advances in Natural Sciences: Nanoscience and Nanotechnology, 2012
Nd10.5Fe83.5−xGaxB6 (x=1.5, 3 and 4.5) ribbons were prepared by melt-spinning method with various... more Nd10.5Fe83.5−xGaxB6 (x=1.5, 3 and 4.5) ribbons were prepared by melt-spinning method with various wheel speeds from 5 to 40 m s−1. Strong crystallographic texture with c-axis of Nd2Fe14B crystallites along normal of the ribbon surface was observed. The texture degree can be enhanced by decreasing the quenching rate during solidification of the melt and by increasing the concentration of Ga.
The efficient formation of HCN/HNC from formamide (FM) combining the advantages of waterassistanc... more The efficient formation of HCN/HNC from formamide (FM) combining the advantages of waterassistance, self-catalyzed reactions, and the mineral surfaces was investigated. Periodic density functional theory calculations with plane-wave pseudopotential basis sets were performed to study the interaction of FM with pyrite (100) ideal and defect surfaces. Effects of sulfur vacancy defect and water on tautomerization and rearrangement barriers of FM on the (100) surface were evaluated. Calculated results show that FM adsorbs more strongly on the defect surface than on the ideal surface, with the lowest adsorption energy on the defect surface being −22 kcal/mol. The energy barriers for rearrangements of FM on these two surfaces being close to each other suggests that the adsorptions on the surfaces have small effects on the energy barriers. The energy barriers for formimic acid isomer formations are 44.5 and 46.0 kcal/mol, and those of aminohydroxymethylene formations are 72.6 and 71.9 kcal/mol on the ideal and defect surfaces, respectively. A reduction of ∼30 kcal/mol in tautomerization energy barriers is observed in waterassisted process on the defect surface. Because this reduction is close to that of the gas-phase reactions, the catalytic effect is clearly due to the presence of water molecule instead of the interaction with the surface. In this case, the pyrite surfaces with the ability to accumulate reactive species only play the role of connecting bridges between the two steps of the proposed reaction mechanism: the water-assisted rearrangement and the self-catalyzed dehydration.
Unimolecular decompositions of neutral (NH 2 CHO) and protonated (NH 3 CHO +) formamide, an activ... more Unimolecular decompositions of neutral (NH 2 CHO) and protonated (NH 3 CHO +) formamide, an active precursor of biomolecules in prebiotic chemistry, are investigated in the ground (S 0) and first triplet (T 1) and singlet (S 1) excited states. Different decomposition channels including the homolytic bond dissociations, dehydration, decarbonylation, dehydrogenation, etc., are explored using coupled-cluster theory (CCSD(T)/CBS method) for both S 0 and T 1 states and RASPT2(18,15)/6-31G(d,p) computations for the S 1 state. On S 1 and T 1 energy surfaces, formamide preferentially follows C−N homolytic bond cleavages forming NH 2 + HCO radical pairs. Formation of HCN and HNC from dehydration of neutral and protonated formamide via formimic acid and aminohydroxymethylene isomers has higher energy barriers. A strong stabilization upon triplet excitation of the two latter isomers significantly facilitates the interconversions between isomers, and thus considerably reduces the energy barriers for dehydration pathways. The most probable pathways for HCN and HNC generation are found to be dehydration of formamide in the T 1 state. Dehydration pathways from the neutral S 1 and protonated T 1 forms lead to stable complexes of HCN and HNC with water but are associated with large energy barriers. Overall, in the lower-lying excited states of either neutral or protonated formamide, dehydration is not competitive with homolytic C−N bond cleavages, which finally lead to formation of CO.
The first paragraph on p. 15 of the original version should be replaced by the following paragrap... more The first paragraph on p. 15 of the original version should be replaced by the following paragraph, which deletes an incorrect reference to a figure. The uncertainties on the mistagged NTMJ background include the statistical uncertainty on the sample after loose selection, to which the mistag probability is applied; the statistical uncertainty on the mistag probability itself, ranging from <1% at 1 TeV/c 2 to ≈10% at 3 TeV/c 2 ; and the systematic uncertainty on the mistag probability application, as described in section 3.3, which is in the range of 1 to 5% depending on the tt mass. The total background uncertainty is ≈5% for the low-mass region, dominated by the systematic uncertainty, and ≈100% for the high-mass region, dominated by statistical uncertainty associated with the sample after loose selection. Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited. Open Access, Copyright CERN, for the benefit of the CMS Collaboration. Article funded by SCOAP 3 .
The supporting information includes: (1) coordinates for optimized geometries of all species, (2)... more The supporting information includes: (1) coordinates for optimized geometries of all species, (2) coordinates of geometries for all transition states, (3) Structure of two conformers of 3, (3) structure of radical:neutral molecule complexes
The usual 'quantum bouncer' is a quantum particle bouncing elastically under the influence of gra... more The usual 'quantum bouncer' is a quantum particle bouncing elastically under the influence of gravity. Here we consider a particle bouncing off an impenetrable wall, and bound to it by the harmonic potential 1 2 mω 2 x 2 instead of by the gravitational potential mgx. An analytic solution is possible, easily accessible to classes in intermediate quantum mechanics. The solution is related to Schrödinger's oscillating wavepacket (the original coherent state). Although periodic, it changes its form during the oscillation, in contrast to Schrödinger's packet. The uncertainties in the position (x) and the momentum (p) oscillate also, as does the product x p.
Free radical pathways for the synthesis of xanthine and isoguanine from formamide were studied us... more Free radical pathways for the synthesis of xanthine and isoguanine from formamide were studied using density functional theory (B3LYP/6-311G(d,p)). The proposed mechanisms are complex and appropriate for the non-aqueous scenario of prebiotic reactions. Formation of the carbonyl bond in the nucleobases proceeds through enol-keto tautomerization since the direct formation of the C@O bond is a highly endothermic step. The mechanisms show 2-amino-imidazole as a precursor for nucleobases and polyazaporphyrin. The proposed mechanisms contribute to a further understanding of the origin of biomolecules.
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