EFRC 501 - Fall 2012

This year, the Center for Bio-inspired Solar Fuel Production has instituted a special section of CHM-501 for the graduate students affiliated with the EFRC. This class will give all of the students a chance to get to know their colleagues better, and to learn about the wide variety of research going on in the Center. The class will help each of the students to see how their research fits into the big picture, and learn how their work can benefit from the efforts of others. The BisFuel Center is more than the sum of its parts, and we all need to take advantage of this opportunity. The class is designed primarily for the students who have not yet fulfilled their 501 requirement. Students who have already taken the required number of 501 classes, are also encouraged to attend the class for the benefit of student's research and the Center as a whole.

Time: 12:00 – 1:15 pm

Location: All classes will be held in ISTB5-151 

Schedule of the class:

Date Speaker Title of the talk (linked to abstract) Faculty
Aug 28   Organizational meeting Ana Moore
Sep 4 Michael Vaughn Modification of the Turnover Potential of Plastoquinol Terminal Oxidase: Can an Oxygen Reducing Enzyme Operate in Reverse? Ana Moore
Sep 11 Dalvin Mendez Synthesis and characterization of dyes for use as photosensitizers to drive water oxidation and hydrogen production Anne Jones
Sep 18 Trevor Kashey Recombinant Electron Donors and Acceptors in Heliobacterium modesticaldum Ana Moore
Sep 18 Christopher Kupitz Furthering Time Resolved Femtosecond Nanocrystallography and the Molecular Movie Ana Moore
Sep 25 Daniel Mieritz Transparent, Mesoporous Zr(1-x)Ti(x)O2 Thin Films Devens Gust
Oct 2 Dong Wang Design and characterization of peptides capable of binding divalent metals Ryan Trovitch
Oct 9 Ian Pahk Mimicry of Nonphotochemical Quenching in Photosynthesis Giovanna Ghirlanda
Oct 9 Jaro Arero The Design and synthesis of a carotenoid-phthalocyanine-fullerene triad: A model for the study of electron transfer in artificial photosynthesis Giovanna Ghirlanda
Oct 23 Chelsea Brown Water Oxidation using Functionalized Porphyrin Chromophores and an Iridium Catalyst Tom Moore
Oct 23 Marely Tejeda Synthesis of Functionalized Photosensitizer Dyes for Photoeletrochemical Solar Cell Tom Moore
Oct 30 Katie WongCarter Carotene-Phthalocyanine Dyads as a Design Model for Artificial Photosynthesis Ana Moore
Nov 6 John Tomlin Synthesis of Functionalized Organic Dyes for Photochemical Water Oxidation Hao Yan
Nov 6 Robert Schmitz Photophysics of Porphyrin Polymers Hao Yan
Nov 13 Antaeres Antoniuk-Pablant Synthesis of a High Potential Porphyrin for Use in Water Oxidation and in a Novel Electron Transfer System Petra Fromme
Nov 20 Patrick Kwan Protein Film Electrochemistry for the Investigation of Redox Enzymes Don Seo
Nov 27 Tufan K. Mukhopadhyay Development of Oxygen Evolving Complexes with Manganese and Redox-Active Ligands Kevin Redding
Nov 27 Shobeir Mazinani EPR calculations Kevin Redding
Dec 4 Palash Dutta Enhancement of Organic Dye Fluorescence using Noble Metal Nanoparticles Jim Allen
Dec 4 Reza Vatan Meidanshahi Computational and theoretical study of proton coupled electron transfer in thermodynamic and kinetic respect Jim Allen
Dec 11 Last day of classes   Ana Moore

  

ABSTRACTS of the presentations

September 4:

Michael Vaughn

Modification of the Turnover Potential of Plastoquinol Terminal Oxidase: Can an Oxygen Reducing Enzyme Operate in Reverse?

Abstract: Under various stress conditions, photosynthetic organisms temporarily require alternative electron transfer pathways to alleviate damage to the photosynthetic proteins, specifically photosystem 2. Among these conditions are nutrient limitations,high-light stress, high temperature stress, and salt stress. During these stress conditions, an alternative pathway of electrontransport is activated involving the oxidation of plastoquinol and concomitant reduction of molecular oxygen to water by plastoquinol terminal oxidase (PTOX). This oxidase is a membrane-associated helical bundle with a diiron carboxylate active site; beyond this, little is known of the structure and functional details of PTOX. As the oxygen/water half-reaction is of great technological interest, we have cloned and are optimizing expression and purification techniques to investigate the catalytic capabilities of PTOX. The central property under consideration is catalytic reversibility. We intend to use protein film voltammetry to investigate the catalytic parameters of PTOX as a heterogenous catalyst. Assuming that the reactivity of PTOX is kinetically optimized for the reductive process, we have developed a detailed homology model to serve as a rational guide for the selection of mutations. The operational potential of the active site may then be adjusted into a range suitable for the oxidation process without affecting the primary coordination sphere, thus possibly enabling this oxygen reducing enzyme to perform water oxidation at a modest overpotential.

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September 11:

Dalvin Mendez

Synthesis and characterization of dyes for use as photosensitizers to drive water oxidation and hydrogen production

Abstract: Current work attempts to mimic the natural process of photosynthesis by assembling a dual threshold photo-electrochemical cell capable of simultaneous water oxidation and hydrogen production. One strategy to increase the efficiency of this cell is to have one of the reaction centers adsorb in the blue region of the solar spectrum and the other in the red region. High-potential porphyrins are promising candidates for the blue-absorbing reaction center since they have an oxidation potential positive enough to drive water splitting. In this project, a series of bis- and tripentafluorophenyl free-base porphyrins bearing a phosphonic acid as an anchoring group have been synthesized and characterized by spectroscopy and electrochemistry.For the reduction of protons to hydrogen, phthalocyanines are interesting dyes because of their high absorptivity in the red and near-infrared regions of the solar spectrum and appropriate redox potentials. The synthesis and characterization of a series of new unsymmetrical phthalocyanines bearing phosphonic acid groups and the rationalization of their performance with the aid of density functional theory calculations will be presented.

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September 18:

Trevor Kashey

Recombinant Electron Donors and Acceptors in Heliobacterium modesticaldum

Abstract: In order to thoroughly study the biophysics of the type I reaction center from H. modesticaldum (HbRC), the endogenous components must be studied in vitro.  While the reaction center is now readily isolatable, we require the native electron donors and acceptors to reconstitute the entire system in vitro for in-depth spectroscopic studies. For example, artificial donors such as ascorbate donate to P800+ on the scale of seconds, while the membrane-bound cytochrome c553 donates in the sub-ms time scale. We have decided to pursue a recombinant expression approach to obtain these. We designed a recombinant version of cyt c553 in which the lipid attachment site is placed by a hexahistidine tag to facilitate purification. We obtain very good amounts of cyt c553 from an E. colis train that over-expresses the cytochrome maturation system. The terminal electron acceptor of the HbRC is PshB, a protein containing two Fe4S4 clusters. Interestingly, there is a PshB paralog (dubbed PshBII) that appears to have a similar function; PshBI and PshBII appear to be interchangeable. Neither of these proteins are tightly bound to the RC, which raises the question: are they subunits of the HbRC or are they part of a pool of mobile electron acceptors? This incited a search in the genome for other potential terminal electron acceptors in H. modesticaldum. The first one we have decided to test is the product of gene HM1-0860, encodes FdxB, a putative nif-specific ferredoxin involved in N2-fixation. FdxB may be the electron donor to the NifH Fe protein, which then shuttles electrons to the nitrogenase. Preliminary results indicate that FdxB can accept electrons directly from the HbRC core (lacking PshB): addition of recombinant FdxB to isolated HbRC cores suppressed charge recombination from the P800+FX- state in a dose-dependent manner, suggesting that the FXcould transfer an electron to FdxB.

Christopher Kupitz

Furthering Time Resolved Femtosecond Nanocrystallography and the Molecular Movie

Abstract: Membrane proteins have proven notoriously difficult to crystallize.   Photosystem II (PSII) is one of the most complex membrane proteins to have a structure solved to molecular resolution. Large, well-ordered crystal growth is a major bottleneck in structural determination by x-ray crystallography.  PSII microcrystals were discovered 12 years before a well-ordered crystal was grown large enough to allow the structure to be determined to high resolution. However, with the development of femtosecond serial nanocrystallography (FSX), which uses a stream of fully hydrated nanocrystals to collect diffraction “snapshots”, the need for large crystals is eliminated.

            PSII changed our biosphere by splitting water and evolving oxygen 2.5 billion years ago.  We are attempting to develop a method of time-resolved FSX to unravel the mechanism of water splitting by determining the conformational changes that take place during the oxygen evolving process.  PSII microcrystals are grown using a free interface diffusion method.  In this method, the precipitant is dropped slowly through the protein layer, allowing an interface to form an area of both high protein and precipitant.  The formed crystals will sediment through the precipitant layer into an area of low to no protein concentration, effectively stopping crystal growth.

            The work in this project has increased the resolution of the crystals used.  The resolution currently stands at ~4Å, and while this resolution does not approach the 1.9Å structure published by Shen et. al, it is a definite improvement over the previous 8Å data.  Preliminary data analysis suggests that in the excitation to the S­3 state, a slight conformational change in the oxygen-evolving complex is visible. (unpublished).

 

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September 25:

Daniel Mieritz

Transparent, Mesoporous Zr(1-x)Ti(x)O2 Thin Films

Abstract:  A sol-gel method for mesoporous Zr-doped TiO2 (ZTO), developed with an emphasis of thin coatings production, employs in situ formed polymeric sacrificial gel template.  In this one-pot synthetic method, both inorganic and polymer precursors are first dissolved in an ethanol/water solvent.  By controlling the synthetic parameters, interpenetrating gel networks of hydrous ZTO and resorcinol-formaldehyde polymer were formed in the solution, where the continuity of the inorganic gel component was ensured.  Subsequent drying and calcination of the inorganic/polymer hybrid gels afforded monolithic mesoporous ZTO products.  For thin film synthesis, a precursor solution was mixed with epichlorihydrin and doctor-bladed onto an FTO substrate.  By adjusting the Zr-content between 0-30 at%, transparent and robust films were produced with pore volumes ranging from 0.1 to 0.26 cm3/g, specific surface areas from 45 to 136 m2/g and pore widths averaging ~6 nm.  Strategies such as pyrolysis before calcination, using different solvents, and using different monomers have shown potential for controlling the pore characteristics.  Additionally, dense ZTO films have been produced, without the use of resorcinol-formaldehyde polymer, to form a blocking-layer onto which a mesoporous coating can be deposited.

 

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October 2:

Dong Wang

Design and Characterization of Peptides Capable of Binding Divalent Metals

Abstract:  To investigate the binding of divalent metals to peptides, a total of 4 peptides were designed and synthesized with carboxylates and histidine ligands based upon a Cu2+-binding peptide (Rockcliffe et al. (2006) Inorg. Chem. 54, 472-474). Circular dichroism spectroscopy showed a preferential binding of Cu2+ and Ni2+ compared to Zn2+ and Mn2+. Cu2+ binding showed a pronounced pH dependence with a pKa around 6.5 indicating that histidine serves as one of the ligands. For a peptide with the carboxylates and histidines replaced with asparagine, a single metal binds by coordination of the amidated C terminus region. Electron paramagnetic resonance spectroscopy indicated the interaction strength was dependent upon the specific Cu2+ ligands. Cyclic voltammetry measurement of Cu2+/peptide complex yielded a mid-point potential of 321 mV vs standard hydrogen electrode. The application of these results for the design of metal binding peptides is discussed, including producing effective catalysts for water oxidation.

 

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October 9:

Ian Pahk

Mimicry of Nonphotochemical Quenching in Photosynthesis

Abstract:  Light harvesting antenna are a subject of great interest as they can provide much needed regulatory and photoprotective features to developing solar fuel technologies.  This research is focused on mimicking a protective mechanism known as non-photochemical quenching (NPQ).  Strong sunlight provides energy in excess of what photosynthetic systems can process.  NPQ dissipates superfluous excitation energy to prevent the deleterious stagnation of high energy photosynthetic intermediates.  Previous efforts to mimic this process have yielded a multi-porphyrin antenna bearing a rhodamine dye that efficiently quenches excitation energy when titrated with acid.  Incorporation of this dye into a porphyrin-fullerene antenna-reaction center model should allow for pH-regulation of the quantum yield of photoinduced charge separation, a form of energy conversion.  The synthesis of such a model is currently underway.  Fine tuning of the final steps of this synthesis is still required in order to obtain a product of sufficient purity for photophysical characterization.

Jaro Arero

The Design and Synthesis of a Carotenoid-Pthalocyanine-Fullerene Triad: a Model for the Study of Electron Transfer and Artificial Photosynthesis

 

Abstract: Natural photosynthesis utilizes a well organized chain of molecules to carry out the photoinduced electron transfer process used to convert sunlight to useful form of energy. The molecule that plays the central roles of light harvesting, energy transfer and electron transfer is chlorophyll. Carotenoids working alongside chlorophyll serve additional energy transfer, electron and photoprotection roles. In artificial photosynthesis a carotenoid- phthalocyanine- fullerene molecular triad model is a synthetically simpler system for the study of photoinduced electron transfer. The strong absorption of phthalocyanines in the red region and the strong absorption of carotenoids in the visible region of the spectrum will allow a wider absorbance range and maximize the solar energy capture for application in solar cell. In this presentation, the design and synthesis of carotenoid-phthalocyanine-fullerene triad model   and their potential application as organic photovoltaics will be discussed.

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October 23:

Chelsea Brown

Water Oxidation using Functionalized Porphyrin Chromophores and Iridium Catalyst

Abstract: The burning of fossil fuels has been the major cause of the rise of CO2 levels in the atmosphere. The search for an alternative fuel source has become a worldwide project. Current research focuses on artificial photosynthesis because it is a natural way of using sunlight to convert water, an abundant resource, into oxygen and hydrogen gas. Hydrogen is a storable fuel, which, when burned, produces water. Hydrogen fuel is a zero emission fuel and is entirely renewable. The design of a cell for artificial photosynthesis requires two components, working simultaneously, to oxidize water and to produce hydrogen gas. This project focuses on the water oxidation component of the photoelectrochemical cell. The photoanode requires a high potential, blue-absorbing porphyrin attached to tin oxide and subsequently attached to the water oxidation catalyst. The high-potential porphyrin light absorber is attached to the tin oxide electrode by a dicarboxylic anchoring group and bears a free azide. The azide is used to attach the iridium oxide particles capped with an alkyne directly to the porphyrin via click-chemistry. The synthesis of the high-potential porphyrin for this construct will be discussed.

 

Marely Tejeda

Synthesis of Functionalized Photosensitezer Dyes for Photochemical Solar Cell

Abstract: In response to the emergent need for alternative energy sources, artificial photosynthesis has become an important research area. Photoelectrochemical solar cells can produce hydrogen from the hydrolysis of water that can be storage and used as fuel.  One side of the solar cell, where the water splitting occurs, needs high potential blue absorbing dyes to drive the oxidation of water by a catalyst. Porphyrins have suitable oxidation potential for carrying out this redox reaction, therefore are good candidates. However they need to have a good anchoring group to be attached to the SnO2 such as phosphonic or carboxylic acid. The proton reduction component of the cell needs low potential red absorbing dyes, phthalocyanine compounds meet these characteristics. The phthalocyanine molecules need an anchoring group to be attached to the TiO2 nanoparticles and improve their performance in the cell. Some molecular design and modifications need to be done to the dyes in order to make them fulfill these requisites like the length and position of the substituents on the macrocycles. In this project the synthesis of modified porphyrins and phthalocyanines and their performance in solar cells are presented.

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October 30:

Katie WongCarter

Carotene-Phthalocyanine Dyads as a Design Model for Artificial Photosynthesis

Abstract: Carotenes have two roles in the photosynthetic process: they act as an antenna to collect and transfer the energy to chlorophylls down a thermodynamic gradient, and they also act as a singlet oxygen scavenger preventing photoxidative damage. Both of these processes are useful for the proposed tandem solar cell proposed by the BISfuel center at ASU. FTIR (Alexandre, 2007) and Resonance Raman (Gall, 2011) studies of natural photosynthetic systems have demonstrated that the carotene and chlorophyll chromophores delocalize the carotene triplet state and minimize oxygenic stress; however the carotenes and chlorophylls that share the triplet signal vary in distance and orientation making it difficult to correlate the degree of coupling needed for this phenomenon. This project aims to study three different carotene-phthalocyanine dyads and their degree of triplet delocalization using ultra-fast fluorescence, FTIR, and Resonance Raman spectroscopy. Two previously studied dyads containing amine (Kolz, 2011) and amide (Berera, 2006) linkages demonstrated large electronic coupling and photoprotective ability, and in our current study they shared the carotene triplet state as expected. A new dyad containing an ether linkage will help determine the interdependence of triplet delocalization and electronic connectivity between the two pigments. Using modern time-dependent spectroscopy and organic chemistry we can further understand the photoprotective role carotenes have in photosynthetic organisms using artificial systems and then apply them to solar energy harvesting devices.

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November 6:

John Tomlin

Synthesis of Functionalized Organic Dyes for Photochemical Water Oxidation

Abstract: As the demand for energy increases the need to discover new methods to acquire it also does. Many methods have been proposed, however one of the cleanest and most abundant sources of energy is the sun1. The Goal of this research is to design and synthesize a porphyrin based dye that is able to be attached to both an iridium oxide nanoparticle catalyst, and a titanium dioxide electrode2,3. The dye then uses light to shuttle electrons from the catalyst to the electrode in order to facilitate the oxidation of water as part of EFRC Subtask 4. The excess electrons can then be used to reduce protons to produce hydrogen gas. In addition some work on introducing beta substitutions to high potential porphyrins will be presented4,5.

  1. Gust, D; Moore, T. A.; Moore, A. L. Solar Fuels via Artificial Photosynthesis. Acc. Chem. Res. 2009, 42, 12, 1890-1898
  2. Loewe, et al., Porphyrins Bearing Mono or Tripodal Benzylphosphonic Acid Tethers for Attachment to Oxide Surfaces. J. Org. Chem. 2004, 69, 1453-1460
  3. Lindsey S., Synthetic Routes to meso-Substituted Porphyrins, Acc. Chem. Rev. 2009, 43, 300-311
  4. Posakony, J. J.; Pratt, R. C.; Rettig, S. J.; James, B. R.; Skov, K. A. Porphyrins incorporating heterocyclic N-Oxides: (oxidopyridyl)porphyrins, porphyrin-N-oxides, and a tirapazamine-porphyrin conjugate. Can. J. Chem. 1999, 77, 182-198
  5. Campbell, W. M.; Jolley, K. W.; Wagner, P.; Wagner, K.; Walsh, P. J.; Gordon, K. C.; Schmidt-Mende, L.; Nazeeruddin, M. K.; Wang, Q.; Gratzel, M.; Officer, D. L. J. Phys. Chem. C 2007, 111, 11760-11762.

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Robert Schmitz

Photophysics of porphyrin polymers

Abstract: Recently, organic polymers have been made with efficiencies as high as 11%. Most high efficiency organic polymers contain small molecule chromophore units, but few large molecule polymers have been studied for their light-harvesting properties. In this project a soluble porphyrin polymer has been created via palladium-catalyzed coupling. This new polymer improves upon old designs, utilizing hexyl chains, which add to its solubility in organic solvents, making its ease of use and characterization far more facile. The absorption and emission spectra show a dependence on solvent polarity, indicating that there is an excited state with charge transfer character. Transient emission data from multiple samples along with smaller models have been used to construct a Jablonski diagram of the relaxation pathways within the polymer.

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November 13:

Antaeres Antoniuk-Pablant

Synthesis of a High Potential Porphyrin for Use in Water Oxidation and in a Novel Electron Transfer System

Abstract: It is becoming increasingly important to find a clean, renewable, and cheap source of energy. As the sun is a viable source of renewable energy, methods of converting sunlight into useful energy are being sought after. One method of achieving this is by mimicking photosynthesis. Artificial photosynthetic systems are being designed to harvest solar energy and convert it to redox potentials to both oxidize water and drive hydrogen production. Some research has been done on light driven water oxidation systems that consist of dye sensitizers coupled to water oxidation catalysts.1 Due to the properties of porphyrins, it has been proposed that the use of porphyrins as dyes in light driven water oxidation systems may aid in developing viable systems 2,3, therefore dyes with the necessary redox potentials are being investigated. In order to efficiently design artificial photosynthetic systems it is important to understand the one of the basic steps in photosynthetic systems, the generation of a long lived charge separated state. A specialized porphyrin with cyano substituents at the β-pyrrole positions (CyP), was a candidate to be used for both these tasks.4 Through the development of a new synthetic method, which allowed new data to be gathered, a CyP was found to have the necessary potentials and properties to theoretically be used as sensitizer in light driven water oxidation. It was also determined that a CyP could be used as an important component in a novel organic compound that may be used to study long lived charge separated states. The synthetic method for the synthesis of a CyP with the necessary functional groups to anchor to both a semiconductor and a water oxidation catalyst for light driven water oxidation is currently being developed. A novel organic compound, a triad, that will theoretically utilize C60 as a electron transfer bridge and ultimately as an electron donor to a CyP, which is thermodynamically poised to accept an electron from C60-., is also currently being developed and synthesized. Utilizing the electron transfer properties of C60 in this way may allow for a better understanding of C60 in electron transfer systems and may provide a unique way of generating long lived charge separated states.

References:

  1. Youngblood, W. et al. J. Am. Chem. Soc. 2009, 131, 926
  2. Gust, D.; Moore, T.; Moore, A. Accounts of Chemical Research 2009, 42, 12
  3. Imahori, H.; Umeyama, T.; Ito, S. Accounts of Chemical Research 2009, 42, 11
  4. Giraudeau, A.; Callot. H.; Gross, M. Inorg. Chem. 1979, 18, 201

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November 20:

Patrick Kwan

Protein film electrochemistry for the investigation of redox enzymes

Abstract: Protein film electrochemistry is an excellent tool for studying the redox properties of various enzymes via direct adsorption onto the electrode surface.  Direct electron transfer between redox proteins and electrodes has been demonstrated for a variety of proteins and (semi)conductor materials.  In this presentation, a thin film of mesoporous antimony-doped tin oxide (ATO) is used for direct electrochemical investigation of the redox proteins cytochrome c (cytC) and diaphorase from Bacillus stearothermophilus (BDI).  Because of the optical transparency of the ATO material, electrochemical experiments can be performed with simultaneous optical absorbance experiments.  In this work, cytC adsorbed on an ATO electrode has been reduced electrochemically via a potentiostat while simultaneously monitoring the corresponding change in the absorbance spectra of the Soret band and Q-bands of cytC.  BDI enzyme was also adsorbed on ATO electrodes, and catalytic NADH oxidation was observed, demonstrating that enzymes adsorbed in ATO pores can retain native catalytic activity.  Additionally, protein film electrochemistry on graphite was used to investigate the redox properties of the soluble hydrogenase I from Pyrococcus furiosus (PfSHI).  PfSHI is an oxygen-tolerant soluble hydrogenase composed of 4 subunits.  Using protein film electrochemistry, proton reduction by PfSHI was demonstrated in the presence of 1% O2, thus illustrating the enzyme’s oxygen tolerance.  Further experiments demonstrate that PfSHI is able to partially reactivate at oxidizing potentials, indicating that PfSHI forms two inactive states:  one which can be reactivated at higher potentials, and one which requires negative potentials to reactivate.  Furthermore, because Pyrococcus furiosus is a thermophile, high-temperature experiments were carried out to investigate the temperature dependence of this oxidative partial reactivation.

References

  1. P. Kwan, D. Schmitt, A. M. Volosin, C. L. McIntosh, D. K. Seo and A. K. Jones, Chemical Communications, 2011, 47, 12367-12369.
  2. C. Leger and P. Bertrand, Chemical Reviews, 2008, 108, 2379-2438.
  3. C. Leger, S. J. Elliott, K. R. Hoke, L. J. C. Jeuken, A. K. Jones and F. A. Armstrong, Biochemistry, 2003, 42, 8653-8662.
  4. M. Collinson and E. F. Bowden, Analytical Chemistry, 1992, 64, 1470-1476.
  5. M. Collinson, E. F. Bowden and M. J. Tarlov, Langmuir, 1992, 8, 1247-1250.
  6. E. Margoliash and N. Frohwirt, Biochemical Journal, 1959, 71, 570-578.
  7. J. C. Fontecilla-Camps, A. Volbeda, C. Cavazza and Y. Nicolet, Chemical Reviews, 2007, 107, 4273-4303.
  8. A. K. Jones, E. Sillery, S. P. J. Albracht and F. A. Armstrong, Chemical Communications, 2002, 866-867.
  9. M. Hambourger, M. Gervaldo, D. Svedruzic, P. W. King, D. Gust, M. Ghirardi, A. L. Moore and T. A. Moore, Journal of the American Chemical Society, 2008, 130, 2015-2022.
  10. C. L. McIntosh, F. Germer, R. d. Schulz, J. Appel and A. K. Jones, Journal of the American Chemical Society, 133, 11308-11319.
  11. R. Sapra, M. F. Verhagen and M. W. Adams, Journal of bacteriology, 2000, 182, 3423-3428.
  12. R. C. Hopkins, J. Sun, F. E. Jenney, Jr., S. K. Chandrayan, P. M. McTernan and M. W. W. Adams, Plos One, 6, e26569.

 

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November 27:

Tufan Mukhopadhyay

Development of Oxygen Evolving Complexes with Manganese and Redox-Active Ligands

Abstract: The major problem to the world right now is the utilization of energy resources. Fossil fuels are also getting scarce. Replacing this by any renewable energy resource has been a global objective to the scientific community. To utilize the natural resources is interesting. For example, solar energy is converted into chemical energy in the leaves and in this process water is oxidized to give dioxygen and four protons. These four protons form pH gadient, which is used for synthesis of ATP. The water oxidation is caused by the oxygen evolving complex (OEC) at PSII. OEC is a redox catalytic site that consists of a cluster of four manganese ions and one calcium ion with bridged oxo functionalities. There are evidences where chemists designed Mn complexes with redox active ligands which can catalyze the water oxidation process under suitable conditions. Complexes are also designed which can be attached to an electrode with the help of a conjugated system to make artificial photosynthetic cell. This presentation will mainly focus on development of complexes with manganese and redox non-innocent ligands. Based on the literature, it has been found that mononuclear and dinuclear manganese complexes are proved to be the best as WOC. Redox non-innocent ligands can accept charge from electron rich metal and therefore the metal will be oxidized. Design of ligands, preparation of the complexes with manganese, their characterizations, the reactivity and the applicability of the complexes will be discussed.

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November 27:

Shobeir Mazinani

EPR calculations

Abstract: TBA

 

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December 4:

Reza Vatan Meidanshahi

Computational and theoretical study of proton coupled electron transfer in thermodynamic and kinetic respect

 

Abstract: Proton-Coupled Electron Transfer (PCET) is a highly important pathway of charge transport in radical enzymes, biological energy conversion systems, and in catalytic water splitting. It is believed that PCET contributes to high efficiency of energy conversion in biological systems. Therefore, a detailed understanding of PCET is a useful asset in the quest for designing novel systems for efficient energy conversion, photocatalysis, etc.

The common approach for theoretical-computational investigation of the rate of charge transport in chemical processes is the classical Marcus theory. But, Marcus Theory has a couple of limitations for dealing with PCET reactions. These include: i) quantum effects cannot be taken into account in the equation; ii) it is hard to theoretically expand this model to include both kinds of charge (proton and electron) transfer.

Given the fact that the computation of intermolecular transfer rates can be described by the same formalism employed for description of electron transport in the presence of external bias, we believe that calculation of electron conductance in several model systems can be used as a means for estimating intermolecular charge transfer rates. The advantage of this approach is that quantum effects are intrinsically taken into account in the calculation of the electron conductance.

We highlight a couple of results obtained for the Quinone-Imidazole dyad, which is a prototype of the tyrosine-histidine system present in PSII, using this approach. Apart from enabling the incorporation of quantum mechanical effects in the calculation of electron and proton transfer rates, it also provides another means of experimental determination of electron transfer rates.

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December 4:

Palash Dutta

Enhancement of Organic Dye Fluoresence Using Noble Metal Nanoparticles

Abstract:

One of the leading topics in photonics is the enhancement of fluorescence of fluorophores due to its application in single molecule detection. Here we demonstrated the fluorescence enhancement of organic dye molecules using gold nanoparticles (AuNP). Because of the presence of high electric field between closely spaced AuNPs, which is necessary for fluorescence enhancement, the dimeric AuNP-dye arrangement shows enhancement whereas the monomeric AuNP-dye arrangement shows fluorescence quenching. The fluorescence not only depends on monomer or dimer of the electric field but also on the distance between NP and dye molecule

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Center for Bio-Inspired Solar Fuel Production 
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