Matching Items (19)

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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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Date Created
  • 2014-05

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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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Date Created
  • 2018-05

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Dopamine Adsorption on TiO2 Anatase Surfaces

Description

The dopamine-TiO2 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

The dopamine-TiO2 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)P2 [bdt = benzene-1,2-dithiolate; P2 = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal iron (Fed)

Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P2 [bdt = benzene-1,2-dithiolate; P2 = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal iron (Fed) 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, HBF4·OEt2, triggers quantitative CO uptake by 1 to form a dicarbonyl analogue [1(H)-CO]+ that can be reversibly converted back to 1 by deprotonation using NEt3. 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)+ susceptible to external CO binding.

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Date Created
  • 2014-09-01

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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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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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Design and synthesis of artificial photosynthetic molecules to mimic aspects of natural photosynthetic mechanisms

Description

Natural photosynthesis features a complex biophysical/chemical process that requires sunlight to produce energy rich products. It is one of the most important processes responsible for the appearance and sustainability of

Natural photosynthesis features a complex biophysical/chemical process that requires sunlight to produce energy rich products. It is one of the most important processes responsible for the appearance and sustainability of life on earth. The first part of the thesis focuses on understanding the mechanisms involved in regulation of light harvesting, which is necessary to balance the absorption and utilization of light energy and in that way reduce the effect caused by photooxidative damage. In photosynthesis, carotenoids are responsible not only for collection of light, but also play a major role in protecting the photosynthetic system. To investigate the role of carotenoids in the quenching of the excited state of cyclic tetrapyrroles, two sets of dyads were studied. Both sets of dyads contain zinc phthalocyanine (Pc) covalently attached to carotenoids of varying conjugation lengths. In the first set of dyads, carotenoids were attached to the phthalocyanine via amide linkage. This set of dyads serves as a good model for understanding the molecular "gear-shift" mechanism, where the addition of one double bond can turn the carotenoid from a nonquencher to a very strong quencher of the excited state of a tetrapyrrole. In the second set of dyads, carotenoids were attached to phthalocyanine via a phenyl amino group. Two independent studies were performed on these dyads: femtosecond transient absorption and steady state fluorescence induced by two-photon excitation. In the transient absorption study it was observed that there is an instantaneous population of the carotenoid S1 state after Pc excitation, while two-photon excitation of the optically forbidden carotenoid S1 state shows 1Pc population. Both observations provide a strong indication of the existence of a shared excitonic state between carotenoid and Pc. Similar results were observed in LHC II complexes in plants, supporting the role of such interactions in photosynthetic down regulation. In the second chapter we describe the synthesis of porphyrin dyes functionalized with carboxylate and phosphonate anchoring groups to be used in the construction of photoelectrochemical cells containing a porphyrin-IrO2·nH2O complex immobilized on a TiO2 electrode. The research presented here is a step in the development of high potential porphyrin-metal oxide complexes to be used in the photooxidation of water. The last chapter focuses on developing synthetic strategies for the construction of an artificial antenna system consisting of porphyrin-silver nanoparticle conjugates, linked by DNA of varied length to study the distance dependence of the interaction between nanoparticles and the porphyrin chromophore. Preliminary studies indicate that at the distance of about 7-10 nm between porphyrin and silver nanoparticle is where the porphyrin absorption leading to fluorescence shows maximum enhancement. These new hybrid constructs will be helpful for designing efficient light harvesting systems.

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Created

Date Created
  • 2011

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Bioinspired Electrocatalytic Hydrogen Production: Synthetic and Biological Approaches

Description

Development of efficient and renewable electrocatalytic systems is foundational to creation of effective means to produce solar fuels. Many redox enzymes are functional electrocatalysts when immobilized on an electrode, but

Development of efficient and renewable electrocatalytic systems is foundational to creation of effective means to produce solar fuels. Many redox enzymes are functional electrocatalysts when immobilized on an electrode, but long-term stability of isolated proteins limits use in applications. Thus there is interest in developing bio-inspired functional catalysts or electrocatalytic systems based on living organisms. This dissertation describes efforts to create both synthetic and biological electrochemical systems for electrocatalytic hydrogen production.

The first part of this dissertation describes the preparation of three different types of proton reduction catalysts. First, four bioinspired diiron complexes of the form (μ-SRS)Fe(CO)3[Fe(CO)(N-N)] for SRS = 1,2-benzenedithiolate (bdt) and 1,3-propanedithiolate (pdt) and N-N = 2,2’-bipyridine (bpy) and 2,2’-bypyrimidine (bpym), are described. Electrocatatlytic experiments show that although the byprimidinal complexes are not catalysts, the bipyridyl complexes produce hydrogen from acetic acid under reducing conditions. Second, three new mononuclear FeII carbonyl complexes of the form [Fe(CO)(bdt)(PPh2)2] in which P2 = bis-phosphine: 4,5-Bis(diphenylphosphino)- 9,9-dimethylxanthene (Xantphos), 1,2-Bis(diphenylphosphino)benzene (dppb), or cis- 1,2-Bis(diphenylphosphino)ethylene (dppv) are described. All are functional bio-inspired models of the distal Fe site of [FeFe]-hydrogenases. Of these, the Xanthphos complex is the most stable to redox reactions and active as an electrocatalyst. Third, a molybdenum catalyst based on the redox non-innocent PDI ligand framework is also shown to produce hydrogen in the presence of acid.

The second part of this dissertation describes creating functional interfaces between chemical and biological models at electrode surfaces to create electroactive systems. First, covalent tethering of the redox probe ferrocene to thiol-functionalized reduced graphene oxide is demonstrated. I demonstrate that this attachment is via the thiol functional groups. Second, I demonstrate the ability to use electricity in combination with light to drive production of hydrogen by the anaerobic, phototrophic microorganism Heliobacterium modesticaldum.

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Date Created
  • 2017

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Application and study of water oxidation catalysts and molecular dyes for solar-fuel production

Description

Developing a system capable of using solar energy to drive the conversion of an abundant and available precursor to fuel would profoundly impact humanity's energy use and thereby the condition

Developing a system capable of using solar energy to drive the conversion of an abundant and available precursor to fuel would profoundly impact humanity's energy use and thereby the condition of the global ecosystem. Such is the goal of artificial photosynthesis: to convert water to hydrogen using solar radiation as the sole energy input and ideally do so with the use of low cost, abundant materials. Constructing photoelectrochemical cells incorporating photoanodes structurally reminiscent of those used in dye sensitized photovoltaic solar cells presents one approach to establishing an artificial photosynthetic system. The work presented herein describes the production, integration, and study of water oxidation catalysts, molecular dyes, and metal oxide based photoelectrodes carried out in the pursuit of developing solar water splitting systems.

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Date Created
  • 2013