Study Of Electron Transfer Processes Research Articles

Clicked BODIPY-Fullerene-Peptide Assemblies: Studies of Electron Transfer Processes in Self-Assembled Monolayers on Gold Surfaces.

Two BODIPY-C60 -peptide assemblies were synthesized by CuAAC reactions of BODIPY-C60 dyads and a helical peptide functionalized with a terminal alkyne group and an azide group, respectively. The helical peptide within these assemblies was functionalized at its other end by a disulfide group, allowing formation of self-assembled monolayers (SAMs) on gold surfaces. Characterizations of these SAMs, as well as those of reference molecules (BODIPY-C60 -alkyl, C60 -peptide and BODIPY-peptide), were carried out by PM-IRRAS and cyclic voltammetry. BODIPY-C60 -peptide SAMs are more densely packed than BODIPY-C60 -alkyl and BODIPY-peptide based SAMs. These findings were attributed to the rigid peptide helical conformation along with peptide-peptide and C60 -C60 interactions within the monolayers. However, less dense monolayers were obtained with the target assemblies compared to the C60 -peptide, as the BODIPY entity likely disrupts organization within the monolayers. Finally, electron transfer kinetics measurements by ultra-fast electrochemistry experiments demonstrated that the helical peptide is a better electron mediator in comparison to alkyl chains. This property was exploited along with those of the BODIPY-C60 dyads in a photo-current generation experiment by converting the resulting excited and/or charge separated states from photo-illumination of the dyad into electrical energy.

Kinetic study of electron transfer process in methyl orange decolorization by shewanella in MFCs with covalent organic frameworks modified anode

As a new electrode material for electrochemical systems, covalent organic framework (COF) materials have been gradually applied to bioelectrochemical systems. In our previous study, the COFBTA-DPPD-rGO composite was synthesized via Schiff-base coupling between benzene-1,3,5-tricarbaldehyde (BTA) and 3,8-diamino-6-phenylphenanthridine (DPPD) on reduced graphene oxide (rGO) at room temperature. Here, COFBTA-DPPD-rGO modified MFC anode was used to assist microorganisms to decolorize methyl orange (MO), and the properties of MFCs were studied. The results showed that compared to the unmodified electrode MFC (28 mA m−2, 4.20 mW m−2) the current density and maximum power density of the anode MFC modified by COFBTA-DPPD-rGO (134.5 mA m−2, 21.78 mW m−2) were increased by 380.3% and 423.6%, respectively. The transferred electron number n and charge transfer coefficient α of the modified COFBTA-DPPD-rGO anode (4 and 0.43) compared to the unmodified electrode (2.4 and 0.38) were increased by 67% and 13%, respectively. The decolorization ratio of MO could reach 90.3% at 10 h. Compared with the unmodified electrode MFC (53.0%), the decolorization ratio and kinetic constant of decolorization process were enhanced by 26% and 372%, respectively. Therefore, COFBTA-DPPD-rGO could be a new choice for applying to the MFCs.

Control Over Protein Multimerization Induced by Water-Soluble Porphyrins

Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. However, combined small- and wide-angle X-ray scattering experiments revealed the formation of multimers with a wide range of complex sizes. Binding interactions were explored using wild-type and 12 mutants of PpcA, a 3-heme c-type cytochrome from Geobacter sulfurreducens, with several anionic water-soluble derivatives of tetraphenylporphyrin.

Characterization and Control Over Protein Multimerization Induced by Porphyrins

Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. However, combined small- and wide-angle X-ray scattering experiments revealed the formation of multimers with a wide range of complex sizes. Binding interactions were explored using wild-type and 12 mutants of PpcA, a 3-heme c-type cytochrome from Geobacter sulfurreducens,with several anionic water-soluble derivatives of tetraphenylporphyrin. Thermodynamic interaction parameters and complex binding stoichiometries were established with isothermal calorimetry.The binding sites of porphyrin were mapped out using HSQC with varying levels of porphyrin concentration to protein. All-atom molecular dynamics simulations revealed quick complex formation with binding sites well matching the areas identified in our experimental work. The obtained results demonstrate that multimerization of solution-state proteins by large water-soluble ligands can be tuned to control shape and size of the formed complexes. Molecular level mapping of the binding sites allows us to build a theory explaining the size of the formed complexes and provides opportunities for targeted design of multi-subunit protein complexes as well as targeted disruption of self-assembled complexes.

Phosphorus and Iron Doped-Porous Carbon As an Efficient Electrocatalyst for Oxygen Reduction Reaction in Alkaline Medium

The U.S. Energy Information Administration has projected a 27% growth in energy consumption by the year 2050.1 The continuous increase in the energy demands worldwide and the environmental concerns reaching critical levels, has required researchers to make the development of clean and sustainable energy conversion devices their paramount challenge. Fuel cells and metal-air batteries with high efficiency and low cost are the prime candidates. Platinum loaded carbon substrate is the catalyst of choice in fuel cells for anodic oxidation of H2 and cathodic reduction of O2 but large-scale commercial production is restricted by its prohibitive cost, limited supply, and weak durability.2 Platinum’s vulnerability to potential drift over time and easy loss of activity through methanol poisoning, questions its competitive catalytic activity. Electrocatalyst that are easily synthesized, have low cost and are earth-abundant is still highly desired. Heteroatom doped carbon electrocatalysts are highly considered candidates and are well researched because of their high abundance and low cost, with transition metal and nitrogen doped carbon material showing competitive result towards the oxygen reduction reaction (ORR).3 , 4 Among those heteroatoms phosphorus doped carbon is an emerging catalyst with high potential. The attraction towards phosphorus arises from the fact that it has a larger atomic radius- hence larger covalent radius- and higher electron-donating ability than nitrogen, making it a promising dopant with an ability to modify the electron transport properties. The Introduction of phosphorus, an atom with lower electronegativity, changes the charge density distribution and electronic properties of a high surface area carbon structure. Phosphorus doping increases the affinity towards an acceptor molecule such as oxygen5, hence a better interaction with the oxygen intermediate and enhances their electrocatalytic activities towards ORR. Such heteroatoms are typically covalently bonded within a carbon framework ensuring long-term stability. The advantages of a heteroatom doped porous carbon are twofold, stabilization of the non-precious metal in the alkaline medium and generation of active sites for facilitating the oxygen reduction reaction. Electrocatalytic activity of phosphorus doped and iron treated phosphorus doped carbon has only been covered by few groups and needs more improvements.6,7 The purpose of the study of electron transfer processes is to understand the reactivity of a relatively new, doped porous carbon complexes incorporating phosphorus as a heteroatom bonded to a metal center. According to DFT calculations, O2 and other ORR intermediates can be stably adsorbed on to Fe sites8, making phosphorus and iron doped carbon a prime candidate for ORR. Using a single precursor as a source of phosphorus, we propose a simple one-step chemical activation, with anhydrous ZnCl2 and anhydrous FeCl2 as the agents of carbonization, yielding P and Fe-doped porous carbon (PFeC). The electrocatalytic activity towards ORR was studied using a rotating ring-disk electrode (RRDE) technique and rotating disk electrode (RDE) connected to the CHI 600 potentiostat. The electrochemical activity of PFeC was compared with the commercially available 20 wt% Pt/C. PFeC showed high activity towards ORR, with comparable onset potential and a small negative shift in half-wave potential. PFeC electrocatalyst selectively catalyzes oxygen to water via a direct four-electron pathway. PFeC showed to be inert toward alcohol oxidation and had superior long-term stability. References (1) U.S. EIA. Annual Energy Outlook 2018 with Projections to 2050. Annu. Energy Outlook 2018 with Proj. to 2050 2018, 44 (8), 1–64. (2) Steele, B. C.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414 (November), 345–352. (3) Lin, L.; Zhu, Q.; Xu, A. W. Noble-Metal-Free Fe-N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions. J. Am. Chem. Soc. 2014, 136 (31), 11027–11033. (4) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-Doped Carbon Nanotube Arrays with High Electroctalytic Activity for Oxygen Reduction. Science (80-. ). 2009, 323 (FEBRUARY), 760–764. (5) Cruz-Silva, E.; Lopez-Urias, F.; Munoz-Sandoval, E.; Sumpter, B. G.; Terrones, H.; Charlier, J. C.; Meunier, V.; Terrones, M. Phosphorus and Phosphorus-Nitrogen Doped Carbon Nanotubes for Ultrasensitive and Selective Molecular Detection. Nanoscale 2011, 3 (3), 1008–1013. (6) Razmjooei, F.; Singh, K. P.; Bae, E. J.; Yu, J.-S. A New Class of Electroactive Fe- and P-Functionalized Graphene for Oxygen Reduction. J. Mater. Chem. A 2015, 3 (20), 11031–11039. (7) Singh, K. P.; Bae, E. J.; Yu, J. S. Fe-P: A New Class of Electroactive Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2015, 137 (9), 3165–3168. (8) Lee, D. H.; Lee, W. J.; Lee, W. J.; Kim, S. O.; Kim, Y. H. Theory, Synthesis, and Oxygen Reduction Catalysis of Fe-Porphyrin-like Carbon Nanotube. Phys. Rev. Lett. 2011, 106 (17), 8–11.

Phosphorus and Iron Doped-Porous Carbon As an Efficient Electrocatalyst for Oxygen Reduction Reaction in Alkaline Medium

The U.S. Energy Information Administration has projected a 27% growth in energy consumption by the year 2050.1 The continuous increase in the energy demands worldwide and the environmental concerns reaching critical levels, has required researchers to make the development of clean and sustainable energy conversion devices their paramount challenge. Fuel cells and metal-air batteries with high efficiency and low cost are the prime candidates. Platinum loaded carbon substrate is the catalyst of choice in fuel cells for anodic oxidation of H2 and cathodic reduction of O2 but large-scale commercial production is restricted by its prohibitive cost, limited supply, and weak durability.2 Platinum’s vulnerability to potential drift over time and easy loss of activity over methanol poisoning, questions its competitive catalytic activity in comparison to Pt or Pt-alloy based catalyst and are easily synthesized, have low cost and are earth-abundant is still highly desired. Heteroatom doped carbon electrocatalysts are highly considered and well researched because of their high abundance and low cost, with transition metal and nitrogen doped carbon material showing competitive result towards the oxygen reduction reaction (ORR).3 , 4 Among those heteroatoms phosphorus doped carbon is an emerging catalyst with high potential. The attraction towards phosphorus arises from the fact that it has a larger atomic radius- hence larger covalent radius- and higher electron-donating ability than nitrogen, making it a promising dopant with an ability to modify the electron transport properties. The Introduction of phosphorus, an atom with lower electronegativity, changes the charge distribution and electronic properties of high surface area carbon structure. Phosphorus doping increases the affinity towards an acceptor molecule such as Oxygen5, hence a better interaction with the oxygen intermediate and enhances their electrocatalytic activities towards ORR. Such heteroatoms are typically covalently bonded within a carbon framework ensuring long-term stability. The advantages of a heteroatom doped porous carbon are twofold, stabilization of the non-precious metal in the alkaline medium and generation of active sites for facilitating the oxygen reduction reaction. Electrocatalytic activity of phosphorus doped and Iron treated phosphorus doped carbon has only been covered by few groups and needs more improvements.6,7 The purpose of the study of electron transfer processes is to understand the reactivity of a relatively new, doped porous carbon complexes incorporating the Phosphorus as a heteroatom bonded to a metal center. According to DFT calculations, O2 and other ORR intermediates can be stably adsorbed on to Fe sites8, making phosphorus and iron doped carbon a prime candidate for ORR. Using a single precursor as a source of phosphorus, we propose a simple one-step chemical activation, with anhydrous ZnCl2 and anhydrous FeCl2 as the agents of carbonization, yielding P and Fe-doped porous carbon (PFeC). The electrocatalytic activity towards ORR was studied using a rotating ring-disk electrode (RRDE) technique and rotating disk electrode connected to the CHI 600 potentiostat. The electrochemical activity of PFeC was compared with the commercially available 20 wt% Pt/C. PFeC showed high activity towards ORR, with comparable onset potential and a small negative shift in half-wave potential. PFeC selectively catalyzes oxygen to water via a direct four-electron pathway. PFeC showed to be inert toward alcohol oxidation and had superior long-term stability. References (1) U.S. EIA. Annual Energy Outlook 2018 with Projections to 2050. Annu. Energy Outlook 2018 with Proj. to 2050 2018, 44 (8), 1–64. (2) Steele, B. C.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414 (November), 345–352. (3) Lin, L.; Zhu, Q.; Xu, A. W. Noble-Metal-Free Fe-N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions. J. Am. Chem. Soc. 2014, 136 (31), 11027–11033. (4) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-Doped Carbon Nanotube Arrays with High Electroctalytic Activity for Oxygen Reduction. Science (80-. ). 2009, 323 (FEBRUARY), 760–764. (5) Cruz-Silva, E.; Lopez-Urias, F.; Munoz-Sandoval, E.; Sumpter, B. G.; Terrones, H.; Charlier, J. C.; Meunier, V.; Terrones, M. Phosphorus and Phosphorus-Nitrogen Doped Carbon Nanotubes for Ultrasensitive and Selective Molecular Detection. Nanoscale 2011, 3 (3), 1008–1013. (6) Razmjooei, F.; Singh, K. P.; Bae, E. J.; Yu, J.-S. A New Class of Electroactive Fe- and P-Functionalized Graphene for Oxygen Reduction. J. Mater. Chem. A 2015, 3 (20), 11031–11039. (7) Singh, K. P.; Bae, E. J.; Yu, J. S. Fe-P: A New Class of Electroactive Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2015, 137 (9), 3165–3168. (8) Lee, D. H.; Lee, W. J.; Lee, W. J.; Kim, S. O.; Kim, Y. H. Theory, Synthesis, and Oxygen Reduction Catalysis of Fe-Porphyrin-like Carbon Nanotube. Phys. Rev. Lett. 2011, 106 (17), 8–11.

Control of Protein Self-Assembly with Water-Soluble Porphyrins

Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. Here, we explored interaction of wild-type and 12 mutants of PpcA, a 3-heme c-type cytochrome (cyt) from Geobacter sulfurreducenswith several anionic water-soluble derivatives of tetraphenylporphyrin. Combined small- and wide-angle X-ray scattering experiments revealed formation of multimers with a wide range of complex sizes. Thermodynamic interaction parameters and complex binding stoichiometries were established with isothermal calorimetry. All-atom molecular dynamics simulations revealed quick complex formation with binding sites well matching the areas identified in our experimental work. The obtained results demonstrate that multimerization of solution-state proteins by large water-soluble ligands can be tuned to control shape and size of the formed complexes. Molecular level mapping of the binding sites allows us to build a theory explaining the size of the formed complexes and provides opportunities for targeted design and assembly of multi-subunit protein complexes.

Study of electron transfer process in aqueous methanol system by using tryptophan based short peptide – Amino acid pairs

The present study demonstrated the nature of synergistic solvation behaviour in water – methanol binary solvent mixture(s) and its role on photo-induced electron transfer (PET) process during the interactions of different tryptophan based peptide conjugates with selected non-aromatic amino acids and also with standard coumarins – amines pairs. The highest degree of solvation was obtained in water rich region near Xwater = 0.85 with ETN(30) value 1.05, which was observed more compared to both pure water (1.00) and methanol (0.76). An analytical solvent exchange model was used to estimate the extent of synergistic solvation and found ∼2 times stronger than the preferential solvation efficiency. Such unconventional associative solvation behaviour was confirmed by fluorescence study of the solvatochromic probe which suggested that the weak nature of intermolecular interaction is responsible for such behaviour. The selected pairs of different amino acids as donors, and established pre-synthesized new tryptophan based peptide conjugates as acceptors were used to check the PET event in the polar environment(s) to know the reorganization energy of the binary solvent mixture. An inverted region was observed and estimated the value of reorganization energy (λ) in Xwater = 0.85. The values of λ in water, methanol and Xwater = 0.85 solution were further used to determine its dependency on solvent parameters. Interestingly, our observations revealed that the solvent viscosity depicted linear dependence with reorganization energy (λ) where the value of λ increases with increasing solvent viscosity. Therefore, the photo-physical event i.e. PET, in present solvent system, is significantly dependent on the physical properties of polar solvents.

Porphyrin-Induced Multimerization of Solution-State Proteins

Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. Here, we explored interaction of four solution-state proteins (horse heart cytochrome c, hen egg-white lysozyme, 3-heme c-type cytochrome (cyt) PpcA from Geobacter sulfurreducens, 2-heme cyt c4 from Pseudomonas stutzeri) with several cationic and anionic water-soluble derivatives of tetraphenylporphyrin. Combined small- and wide-angle X-ray scattering experiments revealed formation of multimers with a wide range of complex sizes. Thermodynamic interaction parameters and complex binding stoichiometries were established with isothermal calorimetry. Locations of porphyrin binding sites were determined with heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY) NMRs for PpcA,.while covalent labeling shielding experiments followed by LC-MS analysis of tryptic digests were used to map ligand binding sites on cyt c, cyt c4 and lysozyme surfaces. All-atom molecular dynamics simulations revealed quick complex formation with binding sites well matching the areas identified in our experimental work. The obtained results demonstrate that multimerization of solution-state proteins by large water-soluble ligands appears to be a wide-spread phenomenon controlled by a delicate interplay of electrostatic and hydrophobic forces. Molecular level mapping of the binding sites allows us to build a theory explaining the size of the formed complexes and provides opportunities for targeted design and assembly of multi-subunit protein complexes.

Probing Electrode Heterogeneity Using Fourier-Transformed Alternating Current Voltammetry: Application to a Dual-Electrode Configuration.

Quantitative studies of electron transfer processes at electrode/electrolyte interfaces, originally developed for homogeneous liquid mercury or metallic electrodes, are difficult to adapt to the spatially heterogeneous nanostructured electrode materials that are now commonly used in modern electrochemistry. In this study, the impact of surface heterogeneity on Fourier-transformed alternating current voltammetry (FTACV) has been investigated theoretically under the simplest possible conditions where no overlap of diffusion layers occurs and where numerical simulations based on a 1D diffusion model are sufficient to describe the mass transport problem. Experimental data that meet these requirements can be obtained with the aqueous [Ru(NH3)6]3+/2+ redox process at a dual-electrode system comprised of electrically coupled but well-separated glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Simulated and experimental FTACV data obtained with this electrode configuration, and where distinctly different heterogeneous charge transfer rate constants (k0 values) apply at the individual GC and BDD electrode surfaces, are in excellent agreement. Principally, because of the far greater dependence of the AC current magnitude on k0, it is straightforward with the FTACV method to resolve electrochemical heterogeneities that are ∼1-2 orders of magnitude apart, as applies in the [Ru(NH3)6]3+/2+ dual-electrode configuration experiments, without prior knowledge of the individual kinetic parameters (k01 and k02) or the electrode size ratio (θ1:θ2). In direct current voltammetry, a difference in k0 of >3 orders of magnitude is required to make this distinction.

Porphyrin Induced Multimerization of Solution-State Proteins

Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. Here, we explored interaction of four solution-state proteins (horse heart cytochrome c, hen egg-white lysozyme, 3-heme c-type cytochrome PpcA from Geobacter sulfurreducens, 2-heme cyt c4 from Pseudomonas stutzeri) with several cationic and anionic water-soluble derivatives of tetraphenylporphyrin. Combined small- and wide-angle X-ray scattering experiments revealed formation of multimers with a wide range of complex sizes. Thermodynamic interaction parameters and complex binding stoichiometries were established with isothermal calorimetry. Locations of porphyrin binding sites were determined with heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY) NMRs for PpcA and cytochrome c, while covalent labeling shielding experiments followed by LC-MS analysis of tryptic digests were used to map ligand binding sites on cyt c4 and lysozyme surfaces. The obtained results demonstrate that multimerization of solution-state proteins by large water-soluble ligands appears to be a wide-spread phenomenon controlled by a delicate interplay of electrostatic and hydrophobic forces. Molecular level mapping of the binding sites allows us to build a theory explaining the size of the formed complexes and provides opportunities for targeted design and assembly of multi-subunit protein complexes.

Multimerization of Solution-State Proteins by Water Soluble Porphyrins

Abstract: Interactions between charged porphyrins and complimentary or similarly charged proteins provide important models systems for studies of electron transfer processes, artificial photosynthesis, and control of protein-protein interactions. Typically, the experimental results are analyzed and discussed assuming that the proteins exist in a monodisperse state. Here, we explored interaction of four solution-state proteins (horse heart cytochrome c, hen egg-white lysozyme, 3-heme c-type cytochrome PpcA from Geobacter sulfurreducens, 2-heme cyt c4 from Pseudomonas stutzeri) with several cationic and anionic water-soluble derivatives of tetraphenylporphyrin. Combined small- and wide-angle X-ray scattering experiments revealed quick formation of mutlimers with a wide range of complex sizes. Thermodynamic interaction parameters and complex binding stoichiometries were established with isothermal calorimetry. Locations of porphyrin binding sites were determined with heteronuclear NMR and chemical modification shielding experiments. The obtained results demonstrate that multimerization of solution-state proteins by large water-soluble ligands appears to be a wide-spread phenomenon controlled by a delicate interplay of electrostatic and hydrophobic forces. Molecular level mapping of the binding sites allows us to build a theory explaining the size of the formed complexes and provides opportunities for targeted design and assembly of multi-subunit protein complexes.

Study of Electron Transfer Process Between Fullerenes and Membrane Cells of E-coli in Presence of Dihydrostreptomycin in NaCl and Sucrose Medias

Study of Electron Transfer Process Between Fullerenes and Membrane Cells of E-coli in Presence of Dihydrostreptomycin in NaCl and Sucrose Medias

Theoretical study of electron transfer process between fullerenes and neurotransmitters; acetylcholine, dopamine, serotonin and epinephrine in nanostructures [neurotransmitters].C n complexes.

Neurotransmitters are the compounds which allow the transmission of signals from one neuron to the next across synapses. They are the brain chemicals that communicate information throughout brain and body. Fullerenes are a family of carbonallotropes, molecules composed entirely of carbon, that take the forms of spheres, ellipsoids, and cylinders. Various empty carbon fullerenes (Cn) with different carbon atoms have been obtained and investigated. Topological indices have been successfully used to construct effective and useful mathematical methods to establish clear relationships between structural data and the physical properties of these materials. In this study, the number of carbon atoms in the fullerenes was used as an index to establish a relationship between the structures of neurotransmitters (NTs) acetylcholine (AC) 1, dopamine (DP) 2, serotonin (SE) 3, and epinephrine (EP) 4 as the well-known redox systems and fullerenes C n (n = 60, 70, 76, 82, and 86) which create [NT].Cn; A-1 to A-5 up to D-1 to D-5. The relationship between the number of carbon atoms and the free energy of electron transfer (ΔG et(n); n = 1-4) is assessed using the Rehm-Weller equation for A-1 to A-5 up to D-1 to D-5 supramolecular [NT].Cn complexes. The calculations are presented for the four reduction potentials ( (Red.) E 1 to (Red.) E 4 ) of fullerenes C n . The results were used to calculate the four free energy values of electron transfer (ΔG et(1) to ΔG et(4)) of the supramolecular complexes A-1 to A-8 up to D-1 to D-8 for fullerenes C60 to C120. The first to fourth free activation energy values of electron transfer and the maximum wavelength of the electron transfers, ΔG (#) et(n) and λ et (n = 1-4), respectively, were also calculated in this study for A-1 to A-8 up to D-1 to D-8 in accordance with the Marcus theory.

Study of electron transfer process between fullerenes and membrane cells of Escherichia coli in the presence of dinitrophenol and dicyclohexylcarbodiimide

Microorganisms are the basis of all known biological activities. The electrical potential difference (ΔΨ) across the membrane of Escherichia coli was utilized for theoretical study of electron transfer (ET) process between fullerenes and the membrane cells of E. coli bacteria. The strains of E. coli which were selected in this study are: FRAG-5, TK-1207 and TK-1208. Dinitrophenol (2,4-DNP) and dicyclohexylcarbodiimide (DCC) are the compounds in the reported experimental conditions which were selected in this study. Various empty fullerenes (Cn) with different carbon atoms have been obtained and investigated before. Topological indices have been successfully used to construct effective and useful mathematical methods to establish clear relationships between structural data and the physical properties of these materials. The relationship between the number of carbon atoms of the fullerenes and the free energies of electron transfer (ΔGet) were assessed using the Rehm–Weller equation for ET-process between fullerenes and the membrane cells of E. coli with strains FRAG-5, TK-1207 and TK-1208 and TK-1235 in the presence of DNP and DCC. The calculations are presented on the basis of the oxidation potential (Ox.E1) of fullerenes Cn. In this study, the results were used to calculate the free-energies of electron transfer (ΔGet) of the ET-process for the fullerenes. The first free activation energies of electron transfer (ΔGet#) and the maximum wave length of the electron transfers (λet), were also calculated for the selected conditions in accordance with the Marcus theory.

Study of electron transfer process of TCNQ under external electric field

A series of electron transfer process of 7,7,8,8-tetracyanoquinodimethane (TCNQ) under external electric field was observed according to the ultraviolet-visible and Fourier transformed Raman spectra of TCNQ obtained with the self-made biservice electrochemistrical thin film cell for ultra-violet/Raman spectrometer in the present work. The concrete process refers to TCNQ turned into TCNQ-, then into TCNQ2- as well as the process of TCNQ2- being oxidated into dicyano-p-toluoyl cyanide (DCTC-) in the presence of oxygen under external electric field. The behaviors of some characteristic peaks, such as the one around 400 nm of TCNQ, around 700 to 900 nm of TCNQ- and around 330 and 488 nm of TCNQ2- at different circumstances were found according to the aforementioned spectra. Meanwhile, the interpretation of these peaks was presented in this study. This paper is valuable in pharmacokinetics, biomembrane and chemical sensor, etc. Key words: Electron transfer, TCNQ, spectra, electric field.

异质二聚体反应中心的电荷转移过程

异质二聚体反应中心的电荷转移过程

Femtosecond to millisecond studies of electron transfer processes in a donor–(π-spacer)–acceptor series of organic dyes for solar cells interacting with titania nanoparticles and ordered nanotube array films

Time-resolved emission and absorption spectroscopy are used to study the photoinduced dynamics of forward and back electron transfer processes taking place between a recently synthesized series of donor-(π-spacer)-acceptor organic dyes and semiconductor films. Results are obtained for vertically oriented titania nanotube arrays (inner diameters 36 nm and 70 nm), standard titania nanoparticles (25 nm diameter) and, as a reference, alumina nanoparticle (13 nm diameter) films. The studied dyes contain a triphenylamine group as an electron donor, cyanoacrylic acid part as an electron acceptor, and differ by the substituents in a spacer group that causes a shift of its absorption spectra. Despite a red-shift of the dye absorption band resulting in an improved response to the solar spectrum, smaller electron injection rates and smaller extinction coefficients result in reduced dye sensitized solar cell (DSSC) conversion efficiencies. For the most efficient dye, TPC1, electron injection from the hot locally excited state to titania on a time scale of about 100 fs is suggested, while from the relaxed charge transfer state it proceeds in a non-exponential way with time constants from 1 ps to 50 ps. Our results imply that the latter process involves the trap states below the conduction band edge (or the sub-bandgap tail of the acceptor states), localized close to the dye radical cation, and is accompanied by fast electron recombination to the parent dye's ground state. This process should limit the efficiency of DSSCs made using these types of organic dyes. The residual, slower recombination can be described by a stretched exponential decay with a characteristic time of 0.5 μs and a dispersion parameter of 0.33. Both the electron injection and back electron transfer dynamics are similar in titania nanoparticles and nanotubes. Variations between the two film types are only found in the time resolved emission transients, which are explained in terms of the difference in local electric fields affecting the position of the emission bands.

Ab initio quantum mechanical/molecular mechanical simulation of electron transfer process: fractional electron approach.

Electron transfer (ET) reactions are one of the most important processes in chemistry and biology. Because of the quantum nature of the processes and the complicated roles of the solvent, theoretical study of ET processes is challenging. To simulate ET processes at the electronic level, we have developed an efficient density functional theory (DFT) quantum mechanical (QM)/molecular mechanical (MM) approach that uses the fractional number of electrons as the order parameter to calculate the redox free energy of ET reactions in solution. We applied this method to study the ET reactions of the aqueous metal complexes Fe(H(2)O)(6)(2+/3+) and Ru(H(2)O)(6)(2+/3+). The calculated oxidation potentials, 5.82 eV for Fe(II/III) and 5.14 eV for Ru(II/III), agree well with the experimental data, 5.50 and 4.96 eV, for iron and ruthenium, respectively. Furthermore, we have constructed the diabatic free energy surfaces from histogram analysis based on the molecular dynamics trajectories. The resulting reorganization energy and the diabatic activation energy also show good agreement with experimental data. Our calculations show that using the fractional number of electrons (FNE) as the order parameter in the thermodynamic integration process leads to efficient sampling and validate the ab initio QM/MM approach in the calculation of redox free energies.

Laser flash photolysis study of electron transfer processes of adsorbed anthracene on titania–silica surfaces

Abstract We have studied the photophysics of anthracene adsorbed to photocatalytic silica–titania mixed oxide systems prepared by two different methods: a sol–gel synthesis and an impregnation route. The observed photophysics depend upon the method of synthesis, with the sol–gel prepared samples resulting in enhanced radical cation formation via static excited singlet state quenching. This mechanism, whilst operative, does not give rise to long-lived charge separation in the case of the impregnated samples. These results are discussed in terms of differing sample morphologies.