Doping-Induced Electron Transfer at Organic/Oxide Interfaces: Direct Evidence from Infrared Spectroscopy
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Charge transfer at organic/inorganic interfaces critically influences the properties of molecular adlayers. Although for metals such charge transfers are well documented by experimental and theoretical results, in the case of semiconductors, clear and direct evidence for a transfer of electrons or holes from oxides with their typically high ionization energy is missing. Here, we present data from infrared reflection-absorption spectroscopy demonstrating that despite a high ionization energy, electrons are transferred from ZnO into a prototype strong molecular electron acceptor, hexafluoro-tetracyano-naphthoquinodimethane (F6-TCNNQ). Because there are no previous studies of this type, the interpretation of the pronounced vibrational red shifts observed in the experiment was aided by a thorough theoretical analysis using density functional theory. The calculations reveal that two mechanisms govern the pronounced vibrational band shifts of the adsorbed molecules: electron transfer into unoccupied molecular levels of the organic acceptor and also the bonding between the surface Zn atoms and the peripheral cyano groups. These combined experimental data and the theoretical analysis provide the so-far missing evidence of interfacial electron transfer from high ionization energy inorganic semiconductors to molecular acceptors and indicates that n-doping of ZnO plays a crucial role.Keywords:
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Abstract Electron transfer from bacteria to external electron acceptors is a biologically important phenomenon that is increasingly being harnessed as useful technology such as in the Micredox® assay and in microbial fuel cells (MFCs). Optimisation of these systems is limited by incomplete knowledge of the underlying genetics of electron transfer. The Keio collection of single gene knock-out Escherichia coli strains is being tested to find genes involved in electron transfer from bacteria to external electron acceptors. Initially, 21 E. coli strains from the Keio collection were selected and tested for altered electro-activity using the Micredox® assay. The Micredox® assay provides a rapid measurement of electron transfer from cells to a soluble electron acceptor (potassium hexacyanoferrate(III)) and was previously developed as a general test for BOD and toxicant measurement. Of the 21 Keio strains, 10 were found to have significantly reduced electron transfer and two were found to have significantly increased electron transfer. The mutant with the lowest electron transfer rate (nuoA) and the highest electron transfer rate (arcA) were then tested for electron transfer in microbial fuel cells (MFCs). The arcA mutant had slightly higher electron transfer rates than the wild type in mediator-less MFC while the nuoA mutant strain had very similar electro-activity to the wild type. However, in a mediated MFC, the mutants were consistently different from the wild type. These results demonstrate that single gene deletion strains of E. coli can have significantly altered electron transfer capabilities, both in the Micredox® assay and in MFCs. Importantly, the Micredox® assay was found to be a rapid and easily scaled-up method to discover genes that are important in electron transfer. Keywords: Micredox®microbial fuel cells E. coli electron transferBOD sensor Acknowledgements This work was supported by funding from the New Zealand Foundation for Research, Science and Technology, Contract LVLX0703. The Keio collection strains used in this work were kindly supplied by National BioResource Project (NIG, Japan): E. coli.
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Abstract Ausgehend von dem Dimethylester (I) wird das Paracyclophan (IV) (Fdd2; Z=16) synthetisiert.
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The spectroscopic and electrical properties of poly (p-dimethylaminostyrene) complexes with a variety of electron acceptors have been measured. Weak electron acceptors yield charge-transfer complexes, whereas strong electron acceptors are partially converted into radical anions. As may be concluded from measurements of the Seebeck coefficient, charge transport is caused by electrons. The electrical conductivity of the complexes is critically dependent on acceptor concentration and is attributed to hopping processes between radical anions and neutral acceptor molecules.
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Herein we report theoretical and experimental studies that revealed two different reactivity of various 1,4-quinones with electronically different diazo acetates (electron acceptor–electron donor, acceptor and acceptor–acceptor) under blue LED.
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Bis(phenylsulfone) as a strong electron acceptor of thermally activated delayed fluorescent emitters
Bis(phenylsulfone) was developed as a strong electron acceptor of thermally activated delayed fluorescent emitters. The connection of two electron withdrawing phenylsulfone moieties through meta-position of phenyl produced the bis(phenylsulfone) acceptor and the strong electron acceptor strength of bis(phenylsulfone) enabled preparation of sky-blue and green thermally activated delayed fluorescent emitters in combination with weak carbazole donors. The bis(phenylsulfone) acceptor and carbazole donor combined organic materials performed as thermally activated delayed fluorescent emitters with a high quantum efficiency of 18.3%.
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To maximise microbial electroactivity in bioelectrochemical systems, soluble electron acceptors are typically omitted as they compete with the electrode. While practical, this approach provides engineered conditions that do not reflect the natural environment of electroactive microorganisms, which may contain both soluble and insoluble electron acceptors. This study investigates the behaviour of weak electricigens, a relatively understudied category of microorganisms whose members switch between non-electroactive and electroactive states. Enrichments were performed in microbial fuel cells containing both an electrode and the soluble alternative fumarate to probe extracellular electron transfer of weak electricigens. Using fluorescence spectroscopy, chromatography and voltammetry, the electron shuttle riboflavin was not found in these conditions but was found in controls in which only the electrode was available to reduce. Despite this dichotomy in ability to perform riboflavin-based mediated electron transfer, communities of weak electricigens were similarly electroactive in each condition (19.36 ± 0.9 mW m −2 vs 20.25 ± 2.0 mW m −2 ). 16S rRNA gene sequencing revealed similar communities enriched in each condition, but with differing abundance. Understanding extracellular electron transfer in natural environments is of both fundamental and applied interest, as it can inform the design of real-world bioelectrochemical systems whose influents are likely to contain competing electron acceptors.
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Abstract Quenching of fluorescence due to electron transfer is observed in monolayer assemblies when electron donor and electron acceptor, both immobile, are either in the same monolayer or in adjacent monolayers. When the donor and acceptor monolayers are separated by two fatty acid interlayers no fluorescence quenching is detected. Two types of light induced electron transfer have been observed. The donor is excited and the electron is transferred from the S 1 state of the donor into the lowest unoccupied orbital of the acceptor. The donor fluorescence is quenched. The acceptor is excited and the electron is transferred from the S 0 state of the donor into the highest occupied orbital of the acceptor. The acceptor fluorescence is quenched. In both processes the initial situation is recovered by back transfer of an electron from the reduced acceptor to the highest occupied orbital of the donor. These electron transfer processes have been studied by varying the concentration of the acceptor. The fluorescence quenching depends on the average distance R̃ between acceptor molecules and values of R̃ 1/2 (average distance in the acceptor layer at which the fluorescence intensity is half of the intensity without electron transfer) have been determined. The value of R̃ 1/2 depends on the energetic position of both the electron donating level and the electron accepting level as calculated from electrochemical and spectroscopic data.
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A negatively charged region on the surface of photosystem II (PSII) near Q(A) has been identified as a docking site for cationic exogenous electron acceptors. Oxygen evolution activity, which is inhibited in the presence of the herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), is recovered by adding Co(III) complexes. Thus, a new electron-transfer pathway is created with Co(III) as the new terminal electron acceptor from Q(A)(-). This binding site is saturated at ∼2.5 mM [Co(III)], which is consistent with the existence of low-affinity interactions with a solvent-exposed surface. This is the first example of a higher plant PSII in which the electron-transfer pathway has been redirected from the normal membrane-associated quinone electron acceptors to water-soluble electron acceptors. The proposed Co(III) binding site may enable efficient collection of electrons generated from photochemical water oxidation by PSII immobilized on an electrode surface.
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