Influence Electron Transfer Research Articles

Smart and accurate detection of nanoplastics in aquatic environments by photoelectrochemical-electrochemical dual-mode portable sensor

The harmful effects of nanoplastics (NPs) on both human health and the ecosystem have gained global attention. This study develops a photoelectrochemical-electrochemical (PEC-EC) dual-mode portable sensor based on CdS/CeO2 heterojunction for the rapid detection of polystyrene nanoplastics (PS NPs) in aquatic environments. The interaction and aggregation between protein and PS NPs, facilitated by hydrophobic properties, influence electron transfer, thereby enabling the detection of PS NPs. Integration of the sensor with a portable EC workstation controlled by a smartphone streamlines the detection process, yielding rapid and clear results, and enhancing convenience for detection. The sensor exhibits the advantages of high sensitivity, good repeatability, and exceptional portability. A wide detection linear range of 0.5–800 μg/mL accompanied by the detection limit of 0.38 ng/mL can be achieved. The relative standard deviation of the sensor for the inter-day (intra-day) precision are determined ranging from 0.4 % to 2.97 % (0.94 % to 4.65 %) in real water samples. Furthermore, the sensor features a self-checking function, establishing it as a dual-mode system that introduces a novel approach for smart detection of PS NPs, with substantial potential for assessing PS NPs pollution in aquatic environments.

The Effect of the Tetraalkylammonium Cation in the Electrochemical CO2 Reduction Reaction on Copper Electrode.

Aprotic organic solvents such as acetonitrile offer a potential solution to promote electrochemical CO2 reduction over the competing hydrogen evolution reaction. Tetraalkylammonium cations (TAA+) are widely used as supporting electrolytes in organic media due to their high solubility and conductivity. The alkyl chain length of TAA+ cations is known to influence electron transfer processes in electrochemical systems by the adsorption of TAA+, causing modifications of the double layer. In this work, we elucidate the influence of the cation chain length on the mechanism and selectivity of the CO2RR reaction under controlled dry and wet acetonitrile conditions on copper cathodes. We find that the hydrophobic hydration character of the cation, which can be tuned by the chain length, has an effect on product distribution, altering the reaction pathway. Under dry conditions, smaller cations (TEA+) preferentially promote oxalate production via dimerization of the CO2 ·- intermediate, whereas formate is favored in the presence of water via protonation reaction. Larger cations (TBA+ > TPA+ > TEA+) favor the generation of CO regardless of water content. In situ FTIR analysis showed that TBA+ cations are able to stabilize adsorbed CO more effectively than TEA+, explaining why larger cations generate a higher proportion of CO. Our findings also suggest that higher cation concentrations suppress hydrogen evolution, particularly with larger cations, highlighting the role of cation chain length size and hydrophobic hydration shell.

Performance and mechanism of azo dyes degradation and greenhouse gases reduction in single-chamber electroactive constructed wetland system

A single-chamber microbial fuel cell-microbial electrolytic cell with a novel constructed wetland system was proposed for synergistic degradation of congo red and reduction in emissions of greenhouse gases. The closed-circuit system showed higher chemical oxygen demand and congo red removal efficiencies by 98 % and 96 % on average, respectively, than traditional constructed wetland. It could also significantly reduce the emissions of CH4 and N2O (about 52 % CO2-equivalents) by increasing the electron transfer. Microbial community analysis demonstrated that the progressive enrichment of dye-degrading microorganisms (Comamonas), electroactive bacteria (Tolumonas, Trichococcus) and denitrifying microorganisms (Dechloromonas) promoted pollutant removal and electron transfer. Based on gene abundance of xenobiotics biodegradation, the congo red biodegradation pathway was described as congo red → naphthalene and alcohols → CO2 and H2O. In summary, the single-chamber closed-circuit system could significantly improve the degradation of congo red and reduce the emissions of greenhouse gases by influencing electron transfer and microbial activity.

Overcoming Electron Transfer Efficiency Bottlenecks for Hydrogen Production in Highly Crystalline Carbon Nitride‐Based Materials

AbstractThe hydrogen evolution reaction (HER) is a complex reaction involving many interdependent physicochemical steps. Highly ordered carbon nitride‐based materials, such as Na‐PHI and K‐PHI, display some of the highest activities for H2 evolution among the carbon nitride‐based materials, due to their electronic properties, but also the presence of cyanimide terminations, which favors the charge transfer for the Pt cocatalyst nanoparticles (NPs). For such highly optimized semiconductor structures, the necessity to control and improve other steps of the photocatalytic process becomes essential, in particular the poor electron transfer from the Pt NPs to the protons in solution over the Helmholtz or Stern layer. Taking highly ordered Na‐PHI as a test material, the influence of water‐dissolved alkali cations on the HER is systematically studied and it is experimentally verified that the electron transfer from the Pt NPs to the protons in solution limits the efficiency of heterogeneous carbon nitride‐based catalysts. This paper explains how hydrated alkali cations influence electron transfer and are able to boost the H2 evolution rate of the same Na‐PHI from 2401 up to 5330 µmol h−1 g−1 with an apparent quantum yield of 13% at 420 nm.

Electron Transfer Dissociation Parameter Optimization Using Design of Experiments Increases Sequence Coverage of Monoclonal Antibodies.

Middle-down analysis of monoclonal antibodies (mAbs) by tandem mass spectrometry (MS2) can provide detailed insight into their primary structure with minimal sample preparation. The middle-down approach uses an enzyme to cleave mAbs into Fc/2, LC, and Fd subunits that are then analyzed by reversed phase liquid chromatography tandem mass spectrometry (RPLC-MS2). As maximum sequence coverage is desired to obtain meaningful structural information at the subunit level, a host of dissociation methods have been developed, and sometimes combined, to bolster fragmentation and increase the number of identified fragments. Here, we present a design of experiments (DOE) approach to optimize MS2 parameters, in particular those that may influence electron transfer dissociation (ETD) efficiency to increase the sequence coverage of antibody subunits. Applying this approach to the NIST monoclonal antibody standard (NISTmAb) using three RPLC-MS2 runs resulted in high sequence coverages of 67%, 67%, and 52% for Fc/2, LC, and Fd subunits, respectively. In addition, we apply this DOE strategy to model the parameters required to maximize the number of fragments produced in "low", "medium", and "high" mass ranges, which ultimately resulted in even higher sequence coverages of NISTmAb subunits (75%, 78%, and 64% for Fc/2, LC, and Fd subunits, respectively). The DOE approach provides high sequence coverage percentages utilizing only one fragmentation method, ETD, and could be extended to other state-of-the-art techniques that combine multiple fragmentation mechanisms to increase coverage.

Research on the electrocatalytic reduction of CO2 by microorganisms with a nano-titanium carburizing electrode

The reduction of CO2 to organics using microbial electrosynthesis (MES) is currently a popular research direction in the environmental field. In this study, we evaluated the effect of the electrode material on the production of organics from CO2 in microbial electrosynthesis with a mixed-culture biocathode. The electrode material is an important factor influencing electron transfer, since it directly affects the efficiency of CO2 reduction. In this study, we compared the performance of a graphite electrode and a metal-based carbon hybrid material electrode for the electro-reduction of CO2. The cathode potential was set to −0.8 V (vs Ag/AgCl). When the cathode material was changed from a graphite electrode to a nano-titanium carburizing electrode, the current density of MES increased from 1.66 ± 0.2 A·m−2 to 2.75 ± 0.2 A·m−2, acetate accumulation increased from 127 mg/L to 234 mg/L, butyrate accumulation increased from 46 mg/L to 86.5 mg/L, and the total electron recovery of MES increased to nearly 70%. The results show that improving electrode performance can effectively improve the efficiency of MES for reducing CO2. Metal-based carbon hybrid materials have good biological affinity and stability and also have good electrochemical performance.

Conformational analysis of the riboflavin-responsive ETF:QO-p.Pro456Leu variant associated with mild multiple acyl-CoA dehydrogenase deficiency

Multiple-CoA dehydrogenase deficiency (MADD) is an inborn disorder of fatty acid and amino acid metabolism caused by mutations in the genes encoding for human electron transfer flavoprotein (ETF) and its partner electron transfer flavoprotein:ubiquinone oxidoreductase (ETF:QO). Albeit a rare disease, extensive newborn screening programs contributed to a wider coverage of MADD genotypes. However, the impact of non-lethal mutations on ETF:QO function remains scarcely understood from a structural perspective. To this end, we here revisit the relatively common MADD mutation ETF:QO-p.Pro456Leu, in order to clarify how it affects enzyme structure and folding. Given the limitation in recombinant expression of human ETF:QO, we resort to its bacterial homologue from Rhodobacter sphaeroides (Rs), in which the corresponding mutation (p.Pro389Leu) was inserted. The in vitro biochemical and biophysical investigations of the Rs ETF:QO-p.Pro389Leu variant showed that, while the mutation does not significantly affect the protein α/β fold, it introduces some plasticity on the tertiary structure and within flavin interactions. Indeed, in the p.Pro389Leu variant, FAD exhibits a higher thermolability during thermal denaturation and a faster rate of release in temperature-induced dissociation experiments, in comparison to the wild type. Therefore, although this clinical mutation occurs in the ubiquinone domain, its effect likely propagates to the nearby FAD binding domain, probably influencing electron transfer and redox potentials. Overall, our results provide a molecular rational for the decreased enzyme activity observed in patients and suggest that compromised FAD interactions in ETF:QO might account for the known riboflavin responsiveness of this mutation.

Human muscle pathology is associated with altered phosphoprotein profile of mitochondrial proteins in the skeletal muscle

Analysis of human muscle diseases highlights the role of mitochondrial dysfunction in the skeletal muscle. Our previous work revealed that diverse upstream events correlated with altered mitochondrial proteome in human muscle biopsies. However, several proteins showed relatively unchanged expression suggesting that post-translational modifications, mainly protein phosphorylation could influence their activity and regulate mitochondrial processes. We conducted mitochondrial phosphoprotein profiling, by proteomics approach, of healthy human skeletal muscle (n = 10) and three muscle diseases (n = 10 each): Dysferlinopathy, Polymyositis and Distal Myopathy with Rimmed Vacuoles. Healthy human muscle mitochondrial proteins displayed 253 phosphorylation sites (phosphosites), which contributed to metabolic and redox processes and mitochondrial organization etc. Electron transport chain complexes accounted for 84 phosphosites. Muscle pathologies displayed 33 hyperphosphorylated and 14 hypophorphorylated sites with only 5 common proteins, indicating varied phosphorylation profile across muscle pathologies. Molecular modelling revealed altered local structure in the phosphorylated sites of Voltage-Dependent Anion Channel 1 and complex V subunit ATP5B1. Molecular dynamics simulations in complex I subunits NDUFV1, NDUFS1 and NDUFV2 revealed that phosphorylation induced structural alterations thereby influencing electron transfer and potentially altering enzyme activity. We propose that altered phosphorylation at specific sites could regulate mitochondrial protein function in the skeletal muscle during physiological and pathological processes.

Electrocatalytic methanol oxidation over Cu, Ni and bimetallic Cu-Ni nanoparticles supported on graphitic carbon nitride

Ni, Cu and Cu–Ni nanostructures have been fabricated and homogeneously embedded on ultrathin two-dimensional (2D) carbon nitride (g-C3N4), and the surface morphology and composition of the resulting hybrid nanostructures were studied by XRD, TEM, HRTEM-elemental mapping, Raman spectroscopy and XPS. The new hierarchical hetero-structures dropcasted on GC anodes have been visualised by SEM and their catalytic performance have been examined in methanol electrooxidation reaction (MOR) under alkaline conditions. Nanosized Ni particles dispersed finely over g-C3N4 are very active electrocatalysts with MOR onset at potential 0.35 V and charge transfer resistance 0.12 kΩ. The stability of modyfied GC electrodes, examined under chronoamperometric conditions showed that for electrode loading with 4% (wt. %) of NiO the stable current density ca. 36 A g−1 (12 A cm2) was obtained during whole experiment (up to 160 min). For all catalyst studied the curent density obtained during MOR reaction was enhanced when electrode was iluminated by UV light λ∼400 nm, and the highest value were obtained for 4% Ni/CN catalyst ca. 127 A g−1 (22 A cm2). The Cu incorporation in the hybrid material evoke loss of activity mostly due to Cu+ irreversible reduction/oxidation to Cu° and Cu2+, CuO segregation and influencing electron transfer process which results in the increasing in the redox potential. These results represent an important step towards light-enhanced electro-reactive systems and sensors in which heterojunction formation can facilitate electron-hole separation and enable more efficient energy transfer.

Switchable electrode functionalized with an azobenzene-containing copolymer thin film using the Langmuir–Schaefer technique for a “smart” uric acid/air fuel cell

A new photoswitchable electrode triggered by a brief light signal was fabricated by depositing an azobenzene-containing copolymer on an indium tin oxide substrate decorated with gold nanoparticles. The polymer formed a compact, complete thin film on the electrode surface using the Langmuir–Schaefer technique and offered reversible and stable switching performance. The conductivity and hydrophilicity of the electrode changed under UV/visible light due to the photoisomerization of the azobenzene moieties in the polymer film, influencing electron transfer and mass transport at the electrode. The electrochemical characterization demonstrated that the electrode exhibited reversibly switchable electrochemical behavior. In its active state, the as-prepared electrode possessed efficient electrocatalytic capability towards uric acid oxidation with a maximum anodic current density of 0.97mA·cm−2. The uric acid/air fuel cell assembled from the photo-triggered anode and a Pt/C-modified cathode operated with an open circuit voltage of 0.12V and a maximum power density of 41.33μW·cm−2. The cell exhibited reversible switching performance (four cycles) and high stability: after one month the power output was 94.2% of the original maximum value.

Peptides as Bio-inspired Molecular Electronic Materials.

Understanding the electronic properties of single peptides is not only of fundamental importance to biology, but it is also pivotal to the realization of bio-inspired molecular electronic materials. Natural proteins have evolved to promote electron transfer in many crucial biological processes. However, their complex conformational nature inhibits a thorough investigation, so in order to study electron transfer in proteins, simple peptide models containing redox active moieties present as ideal candidates. Here we highlight the importance of secondary structure characteristic to proteins/peptides, and its relevance to electron transfer. The proposed mechanisms responsible for such transfer are discussed, as are details of the electrochemical techniques used to investigate their electronic properties. Several factors that have been shown to influence electron transfer in peptides are also considered. Finally, a comprehensive experimental and theoretical study demonstrates that the electron transfer kinetics of peptides can be successfully fine tuned through manipulation of chemical composition and backbone rigidity. The methods used to characterize the conformation of all peptides synthesized throughout the study are outlined, along with the various approaches used to further constrain the peptides into their geometric conformations. The aforementioned sheds light on the potential of peptides to one day play an important role in the fledgling field of molecular electronics.

Regulation of electron transfer processes affects phototrophic mat structure and activity.

Phototrophic microbial mats are among the most diverse ecosystems in nature. These systems undergo daily cycles in redox potential caused by variations in light energy input and metabolic interactions among the microbial species. In this work, solid electrodes with controlled potentials were placed under mats to study the electron transfer processes between the electrode and the microbial mat. The phototrophic microbial mat was harvested from Hot Lake, a hypersaline, epsomitic lake located near Oroville (Washington, USA). We operated two reactors: graphite electrodes were polarized at potentials of -700 mVAg/AgCl [cathodic (CAT) mat system] and +300 mVAg/AgCl [anodic (AN) mat system] and the electron transfer rates between the electrode and mat were monitored. We observed a diel cycle of electron transfer rates for both AN and CAT mat systems. Interestingly, the CAT mats generated the highest reducing current at the same time points that the AN mats showed the highest oxidizing current. To characterize the physicochemical factors influencing electron transfer processes, we measured depth profiles of dissolved oxygen (DO) and sulfide in the mats using microelectrodes. We further demonstrated that the mat-to-electrode and electrode-to-mat electron transfer rates were light- and temperature-dependent. Using nuclear magnetic resonance (NMR) imaging, we determined that the electrode potential regulated the diffusivity and porosity of the microbial mats. Both porosity and diffusivity were higher in the CAT mats than in the AN mats. We also used NMR spectroscopy for high-resolution quantitative metabolite analysis and found that the CAT mats had significantly higher concentrations of osmoprotectants such as betaine and trehalose. Subsequently, we performed amplicon sequencing across the V4 region of the 16S rRNA gene of incubated mats to understand the impact of electrode potential on microbial community structure. These data suggested that variation in the electrochemical conditions under which mats were generated significantly impacted the relative abundances of mat members and mat metabolism.

ChemInform Abstract: Electron Transfer in Peptides

AbstractReview: 76 refs.

Electron transfer in peptides.

In this review, we discuss the factors that influence electron transfer in peptides. We summarize experimental results from solution and surface studies and highlight the ongoing debate on the mechanistic aspects of this fundamental reaction. Here, we provide a balanced approach that remains unbiased and does not favor one mechanistic view over another. Support for a putative hopping mechanism in which an electron transfers in a stepwise manner is contrasted with experimental results that support electron tunneling or even some form of ballistic transfer or a pathway transfer for an electron between donor and acceptor sites. In some cases, experimental evidence suggests that a change in the electron transfer mechanism occurs as a result of donor-acceptor separation. However, this common understanding of the switch between tunneling and hopping as a function of chain length is not sufficient for explaining electron transfer in peptides. Apart from chain length, several other factors such as the extent of the secondary structure, backbone conformation, dipole orientation, the presence of special amino acids, hydrogen bonding, and the dynamic properties of a peptide also influence the rate and mode of electron transfer in peptides. Electron transfer plays a key role in physical, chemical and biological systems, so its control is a fundamental task in bioelectrochemical systems, the design of peptide based sensors and molecular junctions. Therefore, this topic is at the heart of a number of biological and technological processes and thus remains of vital interest.

Localized electron transfer rates and microelectrode-based enrichment of microbial communities within a phototrophic microbial mat

Phototrophic microbial mats frequently exhibit sharp, light-dependent redox gradients that regulate microbial respiration on specific electron acceptors as a function of depth. In this work, a benthic phototrophic microbial mat from Hot Lake, a hypersaline, epsomitic lake located near Oroville in north-central Washington, was used to develop a microscale electrochemical method to study local electron transfer processes within the mat. To characterize the physicochemical variables influencing electron transfer, we initially quantified redox potential, pH, and dissolved oxygen gradients by depth in the mat under photic and aphotic conditions. We further demonstrated that power output of a mat fuel cell was light-dependent. To study local electron transfer processes, we deployed a microscale electrode (microelectrode) with tip size ~20 μm. To enrich a subset of microorganisms capable of interacting with the microelectrode, we anodically polarized the microelectrode at depth in the mat. Subsequently, to characterize the microelectrode-associated community and compare it to the neighboring mat community, we performed amplicon sequencing of the V1–V3 region of the 16S gene. Differences in Bray-Curtis beta diversity, illustrated by large changes in relative abundance at the phylum level, suggested successful enrichment of specific mat community members on the microelectrode surface. The microelectrode-associated community exhibited substantially reduced alpha diversity and elevated relative abundances of Prosthecochloris, Loktanella, Catellibacterium, other unclassified members of Rhodobacteraceae, Thiomicrospira, and Limnobacter, compared with the community at an equivalent depth in the mat. Our results suggest that local electron transfer to an anodically polarized microelectrode selected for a specific microbial population, with substantially more abundance and diversity of sulfur-oxidizing phylotypes compared with the neighboring mat community.

Characterization of Mutations in Barley fch2 Encoding Chlorophyllide a Oxygenase

The barley (Hordeum vulgare L.) mutants fch2 and clo-f2 comprise an allelic group of 14 Chl b-deficient lines. The genetic map position of fch2 corresponds to the physical map position of the gene encoding chlorophyllide a oxygenase. This enzyme converts chlorophyllide a to chlorophyllide b and it is essential for Chl b biosynthesis. The fch2 and clo-f2 barley lines were shown to be mutated in the gene for chlorophyllide a oxygenase. A five-base insertion was found in fch2 and base deletions in clo-f2.101, clo-f2.105, clo-f2.2800 and clo-f2.3613. In clo-f2.105 and clo-f2.108, nonsense base exchanges were discovered. All of these mutations led to a premature stop of translation and none of the mutants formed Chl b. The mutant clo-f2.2807 was transcript deficient and formed no Chl b. Missense mutations in clo-f2.102 (leading to the amino acid exchange D495N) and clo-f2.103 (G280D) resulted in a total lack of Chl b, whereas in the missense mutants clo-f2.107 (P419L), clo-f2.109 (A94T), clo-f2.122 (C320Y), clo-f2.123 (A94T), clo-f2.133 (A376V) and clo-f2.181 (L373F) intermediate contents of Chl b were determined. The missense mutations affect conserved residues, and their effect on chlorophyllide a oxygenase is discussed. The mutations in clo-f2.102, clo-f2.103, clo-f2.133 and clo-f2.181 may influence electron transfer as illustrated in the active site of a structural model protein. The changes in clo-f2.107, clo-f2.109, clo-f2.122 and clo-f2.123 may lead to Chlb deficiency by interfering with the regulation of chlorophyllide a oxygenase. The correlation of mutations and phenotypes strongly supports that the barley locus fch2 encodes chlorophyllide a oxygenase.

Electrochemical and spectroelectrochemical properties of nitroxyl radical species in PTMA, an organic radical polymer. Influence of the microstructure

In this work, an electrochemical and ESR-spectrochemical study of the oxidation properties for nitroxide radicals contained in the structure of poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidin- N-oxyl) (PTMA) in acetonitrile solution was performed. Results revealed that this polymer contains two types of nitroxide radical species, the first associated to a multielectronic and reversible electron transfer process. Remaining radical species are irreversibly oxidized at more positive potential values. Proportions obtained for the respective amount of each oxidized species, 78% and 22% respectively, are similar to the values expected due to the difference in syndiotactic:heterotactic triads in the polymer and reported values for the experimental charge/discharge efficiencies of batteries constructed with this material. These effects also influence electron transfer kinetics during the oxidation of each type of radical species in the polymer. These findings suggest that the detailed understanding of the oxidation processes of different microstructures in radical polymers is useful to analyze performance based in these materials.

Rapid kinetics investigations of peracid oxidation of ferric cytochrome P450cam: Nature and possible function of compound ES

Previously, we reported spectroscopic properties of cytochrome P450cam compound I, (ferryl iron plus a porphyrin π-cation radical (Fe IV = O/Por + )), as well as compound ES (Fe IV = O/Tyr ) in reactions of substrate-free ferric enzyme with m-chloroperbenzoic acid [T. Spolitak, J.H. Dawson, D.P. Ballou, J. Biol. Chem. 280 (2005) 20300-9]. Compound ES arises by intramolecular electron transfer from nearby tyrosines to the porphyrin π-cation radical of Compound I, and has been characterized by rapid-freeze-quench-Mössbauer/EPR spectroscopy; the tyrosyl radical was assigned to Tyr96 for wild type or to Tyr75 for the Tyr96Phe variant [V. Schünemann, F. Lendzian, C. Jung, J. Contzen, A.L. Barra, S.G. Sligar, A.X. Trautwein, J. Biol. Chem. 279 (2004) 10919–10930]. Here we report rapid-scanning stopped-flow studies of the reactions of peracids with substrate-free ferric Y75F, Y96F, and Y96F/Y75F P450cam variants, showing how these active site changes influence electron transfer from nearby tyrosines and affect formation of intermediates. Curiously, rates of generation of Compounds I and ES for both single mutants were not very different from wild type. Contrasting with the earlier EPR results, the Y96F/Y75F variant was also shown to form an ES-like species, but more slowly. When substrate is not present, or is improperly bound, compound I rapidly converts to compound ES, which can be reduced to form H 2O and ferric P450, thus avoiding the modification of nearby protein groups or release of reactive oxygen species.

Triarylamine on Nanocrystalline TiO2 Studied in Its Reduced and Oxidized State by Photoelectron Spectroscopy

The electronic and molecular structures of an electrochemically reduced and oxidized triarylamine layer (((3-ethyl(p-N,N-dimethylamino)phenyl)amino)propyl-1-phosphonic acid) adsorbed on a nanocrystalline TiO2 film have been investigated. Photoelectron spectroscopy (PES) measurements on electrochemically prepared surfaces and density functional theory (DFT) calculations for the free triarylamine molecule were performed. The major electronic difference between the reduced and oxidized state of the triarylamine molecules appears on the nitrogen atom. In the PES measurement a shift of the N 1s signal of 1.5 eV toward higher binding energies was measured between triarylamine in its reduced and oxidized states. The molecular structure of the surface layer was found to depend on the electrolyte used in the electrochemical preparation. The oxidized triarylamine molecule is positively charged and must therefore be accompanied by a negative counterion. The identity of the counterion was found to influence electron transfer between adjacent molecules, as explained by geometrical differences of the surface layer. During the measurements the PES N 1s signal was affected by the continuous X-ray illumination. Interestingly, a reversible photoreduction of the oxidized triarylamine was observed. The effect is accounted for by X-ray induced electron hole-pair generation in the TiO2 and subsequent electron transfer from the TiO2 conduction band to the singly occupied molecular orbital of the adsorbed molecule.

Functional LH1 antenna complexes influence electron transfer in bacterial photosynthetic reaction centers

The effect of the light harvesting 1 (LH1) antenna complex on the driving force for light-driven electron transfer in the Rhodobacter sphaeroides reaction center has been examined. Equilibrium redox titrations show that the presence of the LH1 antenna complex influences the free energy change for the primary electron transfer reaction through an effect on the reduction potential of the primary donor. A lowering of the redox potential of the primary donor due to the presence of the core antenna is consistently observed in a series of reaction center mutants in which the reduction potential of the primary donor was varied over a 130 mV range. Estimates of the magnitude of the change in driving force for charge separation from time-resolved delayed fluorescence measurements in the mutant reaction centers suggest that the mutations exert their effect on the driving force largely through an influence on the redox properties of the primary donor. The results demonstrate that the energetics of light-driven electron transfer in reaction centers are sensitive to the environment of the complex, and provide indirect evidence that the kinetics of electron transfer are modulated by the presence of the LH1 antenna complexes that surround the reaction center in the natural membrane.