Matching Items (19)

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Computational Characterization of a Ni Catalyst

Description

Industrial interest in electrocatalytic production of hydrogen has stimulated considerable research in understanding hydrogenases, the biological catalysts for proton reduction, and related synthetic mimics. Structurally closely related complexes are often

Industrial interest in electrocatalytic production of hydrogen has stimulated considerable research in understanding hydrogenases, the biological catalysts for proton reduction, and related synthetic mimics. Structurally closely related complexes are often synthesized to define structure-function relationships and optimize catalysis. However, this process can also lead to drastic and unpredictable changes in the catalytic behavior. In this paper, we use density functional theory calculations to identify changes in the electronic structure of [Ni(bdt)(dppf)] (bdt = 1,2-benzenedithiolate, dppf = 1,1ʹ-bis(diphenylphosphino)ferrocene) relative to [Ni(tdt)(dppf)] (tdt = toluene-3,4-dithiol) as a means to explain the substantially reduced electrocatalytic activity of the tdt complex. An increased likelihood of protonation at the sulfur sites of the tdt complex relative to the Ni is revealed. This decreased propensity of metal protonation may lead to less efficient metal-hydride production and subsequently catalysis.

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Created

Date Created
  • 2018-05

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Controlling Surface Defects and Photophysics in TiO2 Nanoparticles

Description

Titanium dioxide (TiO2) is widely used for photocatalysis and solar cell applications, and the electronic structure of bulk TiO2 is well understood. However, the surface structure of nanoparticulate TiO2, which

Titanium dioxide (TiO2) is widely used for photocatalysis and solar cell applications, and the electronic structure of bulk TiO2 is well understood. However, the surface structure of nanoparticulate TiO2, which has a key role in properties such as solubility and catalytic activity, still remains controversial. Detailed understanding of surface defect structures may help explain reactivity and overall materials performance in a wide range of applications. In this work we address the solubility problem and surface defects control on TiO2 nanoparticles. We report the synthesis and characterization of ∼4 nm TiO2 anatase spherical nanoparticles that are soluble and stable in a wide range of organic solvents and water. By controlling the temperature during the synthesis, we are able to tailor the density of defect states on the surface of the TiO2 nanoparticles without affecting parameters such as size, shape, core crystallinity, and solubility. The morphology of both kinds of nanoparticles was determined by TEM. EPR experiments were used to characterize the surface defects, and transient absorption measurements demonstrate the influence of the TiO2 defect states on photoinduced electron transfer dynamics.

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Created

Date Created
  • 2014-11-13

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Simple and accurate correlation of experimental redox potentials and DFT-calculated HOMO/LUMO energies of polycyclic aromatic hydrocarbons

Description

The ability to accurately predict the oxidation and reduction potentials of molecules is very useful in various fields and applications. Quantum mechanical calculations can be used to access this information,

The ability to accurately predict the oxidation and reduction potentials of molecules is very useful in various fields and applications. Quantum mechanical calculations can be used to access this information, yet sometimes the usefulness of these calculations can be limited because of the computational requirements for large systems. Methodologies that yield strong linear correlations between calculations and experimental data have been reported, however the balance between accuracy and computational cost is always a major issue. In this work, linear correlations (with an R-2 value of up to 0.9990) between DFT-calculated HOMO/LUMO energies and 70 redox potentials from a series of 51 polycyclic aromatic hydrocarbons (obtained from the literature) are presented. The results are compared to previously reported linear correlations that were obtained with a more expensive computational methodology based on a Born-Haber thermodynamic cycle. It is shown in this article that similar or better correlations can be obtained with a simple and cheaper calculation.

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Date Created
  • 2013-10-28

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Characterization of a Polyclonal Antibody Specific for Synechococcus WH8102 Plastoquinol Terminal Oxidase.

Description

Photosynthesis is a critical process that fixes the carbon utilized in cellular respiration. In higher plants, the immutans gene codes for a protein that is both involved in carotenoid biosynthesis

Photosynthesis is a critical process that fixes the carbon utilized in cellular respiration. In higher plants, the immutans gene codes for a protein that is both involved in carotenoid biosynthesis and plastoquinol oxidation (Carol et al 1999, Josse et al 2003). This plastoquinol terminal oxidase (PTOX) is of great interest in understanding electron flow in the plastoquinol pool. In order to characterize this PTOX, polyclonal antibodies were developed. Expression of Synechococcus WH8102 PTOX in E. coli provided a useful means to harvest the protein required for antibody production. Once developed, the antibody was tested for limit of concentration, effectiveness in whole cell lysate, and overall specificity. The antibody raised against PTOX was able to detect as low as 10 pg of PTOX in SDS-PAGE, and could detect PTOX extracted from lysed Synechococcus WH8102. The production of this antibody could determine the localization of the PTOX in Synechococcus.

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Created

Date Created
  • 2014-05

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Dopamine Adsorption on TiO2 Anatase Surfaces

Description

The dopamine-TiO[subscript 2] system shows a specific spectroscopic response, surface enhanced Raman scattering (SERS), whose mechanism is not fully understood. In this study, the goal is to reveal the key

The dopamine-TiO[subscript 2] system shows a specific spectroscopic response, surface enhanced Raman scattering (SERS), whose mechanism is not fully understood. In this study, the goal is to reveal the key role of the molecule–nanoparticle interface in the electronic structure by means of ab initio modeling. The dopamine adsorption energy on anatase surfaces is computed and related to changes in the electronic structure. Two features are observed: the appearance of a state in the material band gap, and charge transfer between molecule and surface upon electronic excitation. The analysis of the energetics of the systems would point to a selective adsorption of dopamine on the (001) and (100) terminations, with much less affinity for the (101) plane.

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Date Created
  • 2014-09-04

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Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

Description

Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P[subscript 2] [bdt = benzene-1,2-dithiolate; P[subscript 2] = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal

Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P[subscript 2] [bdt = benzene-1,2-dithiolate; P[subscript 2] = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal iron (Fe[subscript d]) of the active site of [FeFe]-hydrogenase. X-ray crystal structures of the complexes reveal that, despite similar ν(CO) stretching band frequencies, the two complexes have different coordination geometries. In X-ray crystal structures, the iron center of 1 is in a distorted trigonal bipyramidal arrangement, and that of 2 is in a distorted square pyramidal geometry. Electrochemical investigation shows that both complexes catalyze electrochemical proton reduction from acetic acid at mild overpotential, 0.17 and 0.38 V for 1 and 2, respectively. Although coordinatively unsaturated, the complexes display only weak, reversible binding affinity toward CO (1 bar). However, ligand centered protonation by the strong acid, HBF[subscript 4]·OEt[subscript 2], triggers quantitative CO uptake by 1 to form a dicarbonyl analogue [1(H)-CO][superscript +] that can be reversibly converted back to 1 by deprotonation using NEt[subscript 3]. Both crystallographically determined distances within the bdt ligand and density functional theory calculations suggest that the iron centers in both 1 and 2 are partially reduced at the expense of partial oxidation of the bdt ligand. Ligand protonation interrupts this extensive electronic delocalization between the Fe and bdt making 1(H)[superscript +] susceptible to external CO binding.

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Created

Date Created
  • 2014-09-01