Electrochemical impedance spectroscopy is used to identify a slow electron transport process in hydrogen evolution catalysed by amorphous molybdenum sulphides on glassy carbon. A new chemical synthesis leads to an amorphous molybdenum sulfide catalyst with a higher electronic conductivity.
A series of new pyrido[3,4-b] pyrazine-based organic sensitizers (PP-I and APP-I-IV) containing different donors and p-spacers have been synthesized and employed in dye-sensitized solar cells (DSSCs). The absorption spectra properties of dyes are analysed by density functional theory (DFT). The calculated results in combination with the experiments suggest that the absorption characteristics and excited state features will mainly be dominated by charge transfer transitions from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) and to higher LUMO orbitals. Furthermore, attaching the octyloxy groups significantly extends the p-conjugation of the donor in APPIV, which raises the HOMO energy and facilitates its oxidation. As a consequence, APP-IV exhibits the lowest HOMO-LUMO energy gap among all dyes, which, in turn, corresponds well with the red shift of the absorption spectra. Transient photovoltage and photocurrent decay experiments as well as electrochemical impedance spectroscopy indicate that the electron lifetime and charge recombination resistance are increased due to the introduction of octyloxy chains on the donor unit, resulting in the high photovoltage based on APP-IV. It was found that APP-IV based DSSCs with liquid electrolyte display the highest power conversion efficiency (PCE) of 7.12%. Importantly, a PCE of 6.20% has been achieved for APP-IV based DSSCs with ionic-liquid electrolytes and retained 97% of the initial value after continuous light soaking for 1000 h at 60 degrees C. This renders these pyrido[3,4-b] pyrazine-based sensitizers quite promising candidates for highly efficient and stable DSSCs.
The ability to electronically interface living cells with electron accepting scaffolds is crucial for the development of next-generation biophotovoltaic technologies. Although recent studies have focused on engineering synthetic interfaces that can maximize electronic communication between the cell and scaffold, the efficiency of such devices is limited by the low conductivity of the cell membrane. This review provides a materials science perspective on applying a complementary, synthetic biology approach to engineering membrane-electrode interfaces. It focuses on the technical challenges behind the introduction of foreign extracellular electron transfer pathways in bacterial host cells and the past and future efforts to engineer photosynthetic organisms with artificial electron-export capabilities for biophotovoltaic applications. The article highlights advances in engineering protein-based, electron-exporting conduits in a model host organism, E. coli, before reviewing state-of-the-art biophotovoltaic technologies that use both unmodified and bioengineered photosynthetic bacteria with improved electron transport capabilities. A thermodynamic analysis is used to propose an energetically feasible pathway for extracellular electron transport in engineered cyanobacteria and identify metabolic bottlenecks amenable to protein engineering techniques. Based on this analysis, an engineered photosynthetic organism expressing a foreign, protein-based electron conduit yields a maximum theoretical solar conversion efficiency of 6-10% without accounting for additional bioengineering optimizations for light-harvesting.
The remarkable characteristics of electrogenerated chemiluminescence (ECL) as a readout method are successfully exploited in numerous microbead-based immunoassays. However there is still a lack of understanding of the extremely high sensitivity of such ECL bioassays. Here the mechanisms of the reaction of the Ru(bpy)(3)(2+) luminophore with two efficient co-reactants (TPrA or DBAE) were investigated by mapping the ECL reactivity at the level of single Ru(bpy)(3)(2+)-functionalized beads. Micrometric non-conductive beads were decorated with the ruthenium label via a sandwich immunoassay or via a peptide bond. Mapping the ECL reactivity on one bead demonstrates the generation of the excited state at a micrometric distance from the electrode by reaction of surface-confined Ru(bpy)(3)(2+) with diffusing TPrA radicals. The signature of the TPAc center dot+ lifetime is obtained from the ECL profile. Unlike the reaction with Ru(bpy)(3)(2+) in solution, DBAE generates very low ECL intensity in the bead-based format suggesting more unstable radical intermediates. The 3D imaging approach provides insights into the ECL mechanistic route operating in bioassays and on the optical effects that focus the ECL emission.
Polyethercarbonate polyols from carbon dioxide (CO2) are starting to be synthesized on industrial scale. These polyols can be further processed into polyurethanes enabling CO2 to be utilized in large amounts. Utilization of CO2 as alternative carbon feedstock for polyols is motivated from the potential to reduce greenhouse gas (GHG) emissions and fossil resource depletion. This article presents a life cycle assessment for production of CO2-based polyethercarbonate polyols in a real industrial pilot plant. The considered cradle-to-gate system boundaries include polyol production and all upstream processes such as provision of energy and feedstocks. In particular, provision of CO2 from a lignite power plant equipped with a pilot plant for CO2 capture is considered. Production of polyols with 20 wt% CO2 in the polymer chains causes GHG emissions of 2.65-2.86 kg CO2-eq kg(-1) and thus, does not act as GHG sink. However, compared to production of conventional polyether polyols, production of polyols with 20 wt% CO2 allows for GHG reductions of 11-19%. Relating GHG emission reductions to the amount of CO2 incorporated, up to three kg CO2-eq emissions can be avoided per kg CO2 utilized. The use of fossil resources can be reduced by 13-16%. The impacts reductions increase with further increasing the CO2 content in the polyols. All other investigated environmental impacts such as eutrophication, ionizing radiation, ozone depletion, particulate matter formation, photochemical oxidant formation, and terrestrial acidification are also lowered. Therefore, synthesis of polyethercarbonate polyols from CO2 is clearly favorable compared to conventional polyether polyols from an environmental point of view.
Photoredox catalysis has been developed to achieve oxidative C-H chlorination of aromatic compounds using NaCl as the chlorine source and Na2S2O8 as the oxidant. The reactions occur at room temperature and exhibit exclusive selectivity for C(sp(2))-H bonds over C(sp(3))-H bonds. The method has been used for the chlorination of a diverse set of substrates, including the expedited synthesis of key intermediates to bioactive compounds and a drug.
Single molecule studies using nanopores have gained attention due to the ability to sense single molecules in aqueous solution without the need to label them. In this study, short DNA molecules and proteins were detected with glass nanopores, whose sensitivity was enhanced by electron reshaping which decreased the nanopore diameter and created geometries with a reduced sensing length. Further, proteins having molecular weights (MW) ranging from 12 kDa to 480 kDa were detected, which showed that their corresponding current peak amplitude changes according to their MW. In the case of the 12 kDa ComEA protein, its DNA-binding properties to an 800 bp long DNA molecule was investigated. Moreover, the influence of the pH on the charge of the protein was demonstrated by showing a change in the translocation direction. This work emphasizes the wide spectrum of detectable molecules using nanopores from glass nanocapillaries, which stand out because of their inexpensive, lithography-free, and rapid manufacturing process.
In this feature article, we review and examine evidence that the primary photoexcited species in conjugated polymers is considerably delocalized. Localization occurs via a series of complex relaxation mechanisms on the <200 femtosecond time scale. We show that short-lived delocalization in the neutral excited state and charge separated state of bulk heterojunction blends might play an essential role in ensuring efficient formation of free charge carriers for photovoltaic applications. Finally, the additional parameter of intramolecular charge transfer character in the excited state of more recently developed donor-acceptor copolymers is discussed. Both delocalization and partial charge transfer reduce the binding of the electron and hole in photoexcited organic semiconductors and can help to overcome the bottleneck to macroscopic current generation in polymer solar cells.
Light-induced charge formation is essential for the generation of photocurrent in organic solar cells. In order to gain a better understanding of this complex process, we have investigated the femtosecond dynamics of charge separation upon selective excitation of either the fullerene or the polymer in different bulk heterojunction blends with well-characterized microstructure. Blends of the pBTTT and PBDTTPD polymers with PCBM gave us access to three different scenarios: either a single intermixed phase, an intermixed phase with additional pure PCBM clusters, or a three-phase microstructure of pure polymer aggregates, pure fullerene clusters and intermixed regions. We found that ultrafast charge separation (by electron or hole transfer) occurs predominantly in intermixed regions, while charges are generated more slowly from excitons in pure domains that require diffusion to a charge generation site. The pure domains are helpful to prevent geminate charge recombination, but they must be sufficiently small not to become exciton traps. By varying the polymer packing, backbone planarity and chain length, we have shown that exciton diffusion out of small polymer aggregates in the highly efficient PBDTTPD: PCBM blend occurs within the same chain and is helped by delocalization.
The CTX-M family of beta lactamases mediate broad-spectrum antibiotic resistance and are present in the majority of drug-resistant Gram-negative bacterial infections worldwide. Allosteric mutations that increase catalytic rates of these drug resistance enzymes have been identified in clinical isolates but are challenging to predict prospectively. We have used molecular dynamics simulations to predict allosteric mutants increasing CTX-M9 drug resistance, experimentally testing top mutants using multiple antibiotics. Purified enzymes show an increase in catalytic rate and efficiency, while mutant crystal structures show no detectable changes from wild-type CTX-M9. We hypothesize that increased drug resistance results from changes in the conformational ensemble of an acyl intermediate in hydrolysis. Machine-learning analyses on the three top mutants identify changes to the binding-pocket conformational ensemble by which these allosteric mutations transmit their effect. These findings show how molecular simulation can predict how allosteric mutations alter active-site conformational equilibria to increase catalytic rates and thus resistance against common clinically used antibiotics.