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Classical structural biology can only provide static snapshots of biomacromolecules. Single-molecule Forster resonance energy transfer (smFRET) paved the way for studying dynamics in macromolecular structures under biologically relevant conditions. Since its first implementation in 1996, smFRET experiments have confirmed previously hypothesized mechanisms and provided new insights into many fundamental biological processes, such as DNA maintenance and repair, transcription, translation, and membrane transport. We review 22 years of contributions of smFRET to our understanding of basic mechanisms in biochemistry, molecular biology, and structural biology. Additionally, building on current state-of-the-art implementations of smFRET, we highlight possible future directions for smFRET in applications such as biosensing, high-throughput screening, and molecular diagnostics.

Origin of mixed valence states from pi-conjugated photoresponsive systems offers self-assembled nanostructures facilitating excellent optoelectronic properties. Despite various electron-rich moieties, tethered linear pi-conjugated systems generate charged ions however limited to standard redox-active materials until now, which further extended to macrocyclic systems. Herein, we report three carbazole and triphenylamine-assisted phthalocyanine derivatives (1, 2, and 3) and discussed the nature of photobleaching/photoionization by illumination with an excitation wavelength of 350 nm. Detailed UV-visible absorption and cyclic voltammetry studies revealed that three derivatives are bleached during irradiation; however, 3 exhibits mixed valence species in CHCl3 when compared to 1 and 2. Microscopic analysis suggested that ionized 3 forms nanospheres with an average diameter of 100-400 nm upon methanol vapor diffusion approach. Thus, photoresponsive mixed valence systems facilitated well-defined nanostructures, thereby advantageous in various electronic and biological applications.

The design and synthesis of a set of supported azolium salt pre-catalysts is presented along with their utilization in the production of monoesters of glycerol and solketal by oxidative N-heterocyclic carbene (NHC)-catalysis through batch and continuous-flow approaches. After a propaedeutic study with soluble NHCs, the heterogeneous analogues (silica and polystyrene supports) were tested in a model monoesterification of glycerol using either the Kharasch oxidant or air (in the presence of electron transfer mediators) as the terminal oxidants. The best performing polystyrene-supported triazolium salt pre-catalyst afforded monoacylglycerols (MAGs) in high yields (up to 95%) and almost complete selectivity (monoester/diester >95 : 5) using air and the green solvent Me-THF. The synthesis of fully bio-based MAGs from furfural, 5-hydroxymethylfurfural (HMF), citronellal, and vanillin is also reported. Continuous-flow experiments have been finally performed by fabricating the corresponding packed-bed microreactor, which could be operated for ca. 120 hours with maintenance of conversion efficiency and selectivity.

A conducting polymer coated stainless-steel wool (SS-W) is proposed for use as a low-cost anode for microbial fuel cells (MFCs). When coated with polyaniline (PANi) and polypyrrole (PPy), the pristine SS-W, SS/PANi-W and SS/PPy-W anodes produced maximum current densities of 0.30 +/- 0.04, 0.67 +/- 0.05, 0.56 +/- 0.07 mA cm(-2), respectively, in air-cathode MFCs. Also, based on achieved power density, both SS/PANi-W and SS/PPy-W achieved 0.288 +/- 0.036 mW cm(-2) and 0.187 +/- 0.017 mW cm(-2), respectively, which were superior to 0.127 +/- 0.011 mW cm(-2) obtained with pristine SS-W. Further, in comparison with SS-P based anodes, all SS-W based anodes gave improved power densities under similar experimental conditions by at least 70%. Moreover, the charge transfer resistance of the SS-W was much lower (240 +/- 25 Omega cm(-2)) than for the SS-P (3192 +/- 239 Omega cm(-2)). The j(0(apparent)) values obtained for SS/PANi-W (0.098 +/- 0.007 Omega cm(-2)) and SS/PPy-W (0.036 +/- 0.004 mA cm(-2)) anodes were also much higher than that of the pristine SS-W (0.020 +/- 0.005 mA cm(-2)), as well as than those of all SS-P based anodes. The observed enhancement of the bioelectrocatalytic performances were well supported by physicochemical and electrochemical characterisation.

Watching single molecules in motion Structural techniques such as x-ray crystallography and electron microscopy give insight into how macromolecules function by providing snapshots of different conformational states. Function also depends on the path between those states, but to see that path involves watching single molecules move. This became possible with the advent of single-molecule Förster resonance energy transfer (smFRET), which was first implemented in 1996. Lerner et al. review how smFRET has been used to study macromolecules in action, providing mechanistic insights into processes such as DNA repair, transcription, and translation. They also describe current limitations of the approach and suggest how future developments may expand the applications of smFRET. Science , this issue p. eaan1133

Two of the major bottlenecks in achieving large-scale power generation with MFCs to date are the low power output and the usually long start-up time, both of which are mainly associated with poor bacterial kinetics and inefficient anode electrode materials. We have demonstrated in this study that the electron transfer kinetics of stainless steel (SS) can be significantly improved by modification with polyaniline (PANi) and polypyrrole (PPy). Furthermore, we have demonstrated that the kinetics of the bacterial growth can be significantly enhanced by the application of a carefully selected external resistance (R-ext), resulting in significantly shorter start-up time. The half-cell reactors used for the investigations were enriched under different conditions including without Rext (Open circuit mode), with R-ext = R-int (Ohmic region), and with very low Rext (mass transfer region). The MFC anodes enriched under R-ext = R-int gave maximum exchange current density (j(0max)) on the 4th day of operation. The calculated j(0max) for SS wool, PANi-wool, and PPy-wool anodes were 0.3 +/- 0.2 A m(-2), 10.5 +/- 0.4 A m(-2) and 5.0 +/- 0.4 A m(-2), respectively. The lowest charge transfer resistance (R-ct) of 0.23 Omega cm(-2) was obtained with SS/PANi-wool anode which exhibited the highest electron transfer kinetics and better compatibility than SS/PPy-wool. The high current drawn from the system during the biofilm establishment phase did not support electroactive biofilm formation because it prevented the growing anode-respiring bacteria (ABR) from providing sufficient electron flow to the counter electrode. (C) 2018 Elsevier Ltd. All rights reserved.

The Journal of Physical Chemistry C, 119 (30), ISSN:1932-7455, ISSN:1932-7447

DNA photolyases are light-activated enzymes that repair DNA damage induced by ultraviolet (UV) radiation. UV radiation causes two of the most abundant mutagenic and cytotoxic DNA lesions: cyclobutane pyrimidine dimers and 6-4 photolesions. Photolyases selectively bind to DNA and initiate the splitting of mutagenic pyrimidine dimers via photoinduced electron transfer from a flavin adenine dinucleotide anion (FADH(-)) to the lesion triggering its repair. This review discusses the consecutive steps of the repair process, from both experimental and theoretical points of view. It covers the following issues: the process of how photolyases accommodate the lesion into their binding pockets, excitation energy transfer between two involved catalytic cofactors, photoinduced electron transfer to the lesion, the splitting of the pyrimidine dimer radical anion, and the fate of the unstable radical species created after the splitting of the thymine dimer. In particular, mechanisms of the splitting and restoration of the original bases are described in detail, and the most probable repair pathways are outlined.

A comprehensive understanding of the charge generation mechanism in organic solar cells is critical for further improvement of device performance. Currently, the origin and magnitude of the coulombic binding energy of the charge-transfer state (CTS), an intermediate state which is fundamental for the charge separation process, are still under debate. Here, we propose a new approach for determining the dissociation energy of localised CTSs for a range of devices with different alignments of molecular energy levels (tuned by chemical modifications of fullerene) and disorder (adjusted by the blend composition) using temperature-dependent pump-push photocurrent spectroscopy. We observe that the dissociation of localised CTSs from initial excitation is a temperature-dependent process, and we determined the binding energy of these CTSs by measuring a single activation energy over a wide temperature range. We propose a simple qualitative picture to explain the observation, based on the split between the bound CTSs and free charges. In all the material systems studied here, the activation energy falls within the range of 90 ± 50 meV (corresponding to ∼1 nm separation of an electron–hole pair). Surprisingly, the binding energy does not depend on the material composition or the driving energy (∼150 meV variation) for charge separation. In contrast, the number of formed bound states and their following recombination dynamics are material- and nanomorphology-sensitive. Such observations in the studied benchmark polymer:fullerene systems reveal unexpected similarities in the energetics of CTSs formed in different electronic environments. This makes our results of general importance for understanding the photophysics at the heterojunction interface and for further development of organic photovoltaics.

The role of relative concentrations of energy donors (fluorescein, D), acceptors (rhodamine, A) and silica on Forster resonance energy transfer (FRET) efficiency and dynamics in dye silica conjugates has been studied, as a part of our initial attempts to ascertain the potential of dye-silica nanoconjugates as light harvesting nanoantennae. Two types of dye-silica nanoconjugates, prepared by the co-condensation method, have been examined. The first is based on silica nanoshells (SNS-dye) while the second is based on silica nanoparticles (SNP-dye). Both these nanostructures have a diameter of approximately 25 nm. Efficient energy transfer (91% and 97%, respectively) has been observed in both, for total fluorophore concentration upto 5-6 mmol, irrespective of the D : A ratio. The lower efficiency at dye concentrations greater than these has been rationalized by the competitive self-quenching of D. A risetime of approximately 500 fs is observed in the A emission in SNS-dye, but there is no such feature in SNP-dye. The shape and size dependence of the FRET efficiency and dynamics has been rationalized as follows: the initial step of dye rich core formation in nanoparticles results in high proximity of dye molecules to each other, leading to highly efficient FRET than in nanoshells. In larger SNP-dye nanoconjugates of 65 nm in diameter, the FRET efficiency decreases to 85%, while a risetime in D emission emerges. This provides support to the proposed correlation between efficiency and packing. Hence, it is inferred that total fluorophore concentration, rather than D : A ratios, governs the FRET dynamics and efficiency in these systems.

Plasmonic hot carrier devices extract excited carriers from metal nanostructures before equilibration, and have the potential to surpass semiconductor light absorbers. However their efficiencies have so far remained well below theoretical limits, which necessitates quantitative prediction of carrier transport and energy loss in plasmonic structures to identify and overcome bottlenecks in carrier harvesting. Here, we present a theoretical and computational framework, Non-Equilibrium Scattering in Space and Energy (NESSE), to predict the spatial evolution of carrier energy distributions that combines the best features of phase-space (Boltzmann) and particle-based (Monte Carlo) methods. Within the NESSE framework, we bridge first-principles electronic structure predictions of plasmon decay and carrier collision integrals at the atomic scale, with electromagnetic field simulations at the nano- to mesoscale. Finally, we apply NESSE to predict spatially-resolved energy distributions of photo-excited carriers that impact the surface of experimentally realizable plasmonic nanostructures at length scales ranging from tens to several hundreds of nanometers, enabling first-principles design of hot carrier devices., 10 pages, 5 figures

Electrochemical reduction of an azoniahelicene affords a dimer, accompanied by a strong change in the electronic circular dichroism. The fast dimerisation event leads to a >500 mV shift of the oxidation potential, affording a large area of bistability, where the chiroptical signal only depends on the redox history.

International audience; Solvent effects in beta-phosphorylated nitroxides show that nitrogen and phosphorus hyperfine coupling constants a(N) and a(p), increase and decrease with increasing polarity, polarizity, and Hydrogen Bond Donor effects of solvents, respectively. In a series of articles, it was shown that the driving interaction controlling the change in a(p) is the maximization of the N+center dot O-center dot center dot center dot center dot center dot center dot P+-O- dipole - dipole interaction. In this work, we show that the steric strain in Spiro beta-phosphotylated nitroxides affords the opposite trend for a(p) that is, a(p) increases with increasing solvent properties features. (C) 2017 Elsevier Ltd. All rights reserved.

There is considerable interest in improving plant productivity by altering the dynamic responses of photosynthesis in tune with natural conditions. This is exemplified by the ‘energy-dependent' form of non-photochemical quenching ( q E ), the formation and decay of which can be considerably slower than natural light fluctuations, limiting photochemical yield. In addition, we recently reported that rapidly fluctuating light can produce field recombination-induced photodamage (FRIP), where large spikes in electric field across the thylakoid membrane (Δ ψ ) induce photosystem II recombination reactions that produce damaging singlet oxygen ( 1 O 2 ). Both q E and FRIP are directly linked to the thylakoid proton motive force ( pmf ), and in particular, the slow kinetics of partitioning pmf into its ΔpH and Δ ψ components. Using a series of computational simulations, we explored the possibility of ‘hacking' pmf partitioning as a target for improving photosynthesis. Under a range of illumination conditions, increasing the rate of counter-ion fluxes across the thylakoid membrane should lead to more rapid dissipation of Δ ψ and formation of ΔpH. This would result in increased rates for the formation and decay of q E while resulting in a more rapid decline in the amplitudes of Δ ψ -spikes and decreasing 1 O 2 production. These results suggest that ion fluxes may be a viable target for plant breeding or engineering. However, these changes also induce transient, but substantial mismatches in the ATP : NADPH output ratio as well as in the osmotic balance between the lumen and stroma, either of which may explain why evolution has not already accelerated thylakoid ion fluxes. Overall, though the model is simplified, it recapitulates many of the responses seen in vivo , while spotlighting critical aspects of the complex interactions between pmf components and photosynthetic processes. By making the programme available, we hope to enable the community of photosynthesis researchers to further explore and test specific hypotheses. This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.

We demonstrate that efficient and nearly field-independent charge separation of electron hole pairs in organic planar heterojunction solar cells can be described by an incoherent hopping mechanism. Using kinetic Monte Carlo simulations that include the effect of on-chain delocalization as well as entropic contributions, we simulate the dissociation of the charge-transfer state in polymer fullerene bilayer solar cells. The model further explains experimental results of almost field independent charge separation in bilayers of molecular systems with fullerenes and provides important guidelines at the molecular level for maximizing the efficiencies of organic solar cells. Thus, utilizing coherent phenomena is not necessarily required for highly efficient charge separation in organic solar cells. This project has received funding from the Universidad Carlos III de Madrid, the European Union’s Seventh Framework Programme for research, technological development, and demonstration under Grant Agreement No. 600371, el Ministerio de Economı́a, Industria y Competitividad (COFUND2014-51509), el Ministerio de Educación, cultura y Deporte (CEI-15-17), and Banco Santander. We also acknowledge additional funding from the German Research Foundation DFG (GRK1640) and the Bavarian University Centre for Latin America (BAYLAT).

Ultrafast spectroscopy offers temporal resolution for probing processes in the femto- and picosecond regimes. This has allowed for investigation of energy and charge transfer in numerous photoactive compounds and complexes. However, analysis of the resultant data can be complicated, particularly in more complex biological systems, such as photosystems. Historically, the dual approach of global analysis and target modelling has been used to elucidate kinetic descriptions of the system, and the identity of transient species respectively. With regards to the former, the technique of lifetime density analysis (LDA) offers an appealing alternative. While global analysis approximates the data to the sum of a small number of exponential decays, typically on the order of 2-4, LDA uses a semi-continuous distribution of 100 lifetimes. This allows for the elucidation of lifetime distributions, which may be expected from investigation of complex systems with many chromophores, as opposed to averages. Furthermore, the inherent assumption of linear combinations of decays in global analysis means the technique is unable to describe dynamic motion, a process which is resolvable with LDA. The technique was introduced to the field of photosynthesis over a decade ago by the Holzwarth group. The analysis has been demonstrated to be an important tool to evaluate complex dynamics such as photosynthetic energy transfer, and complements traditional global and target analysis techniques. Although theory has been well described, no open source code has so far been available to perform lifetime density analysis. Therefore, we introduce a python (2.7) based package, PyLDM, to address this need. We furthermore provide a direct comparison of the capabilities of LDA with those of the more familiar global analysis, as well as providing a number of statistical techniques for dealing with the regularization of noisy data.

Light-induced chemical reactions on bulk metal surfaces have been explored for more than 50 years. Light absorption at the metal surface plays a key role in inducing photochemical transformations of adsorbed molecules. Our current ability to control both the absorption cross-sections and the energy of absorbed light by metal plasmonic nanoparticles opens new pathways for the manipulation of photochemical reactions. Physical phenomena associated with the localized surface plasmon resonances, such as energetic surface states and intensified electric fields, force us to revisit our traditional understanding of photochemical reactions at metal surfaces. Long standing goals in the field – such as bond selectivity and increased efficiency of photocatalytic processes – might now be achievable, assisted by plasmonic nanoparticles. This Progress Report intends to examine some of the elementary concepts and mechanisms behind these processes in the context of the most recent advancements in the fields of plasmonic-assisted chemistry, charge transfer at the nanoscale, and surface photochemistry.

Small push pull molecules attract much attention as prospective donor materials for organic solar cells (OSCs). By chemical engineering, it is possible to combine a number of attractive properties such as broad absorption, efficient charge separation, and vacuum and solution processabilities in a single molecule. Here we report the synthesis and early time photophysics of such a molecule, TPA-2T-DCV-Me, based on the triphenylamine (TPA) donor core and dicyanovinyl (DCV) acceptor end group connected by a thiophene bridge. Using time-resolved photoinduced absorption and photoluminescence, we demonstrate that in blends with [70]PCBM the molecule works both as an electron donor and hole acceptor, thereby allowing for two independent channels of charge generation. The charge-generation process is followed by the recombination of interfacial charge transfer states that takes place on the subnanosecond time scale as revealed by time-resolved photoluminescence and nongeminate recombination as follows from the OSC performance. Our findings demonstrate the potential of TPA-DCV-based molecules as donor materials for both solution-processed and vacuum-deposited OSCs.

The reduction of an aryl iodide is generally believed to involve a clean-cut two-electron: reduction to produce an aryl anion and iodide. This is in contradiction to what is observed if a highly efficient grafting agent, such as an aryldiazonium salt, is employed. The difference in behavior is explained by the much more extreme potentials required for reducing an aryl iodide; which facilitates the further reduction of the aryl radical formed as an intermediate. However, in this study we disclose that electrografting of aryl iodides is indeed possible upon extended voltammetric cycling. This implies that even if the number of aryl radicals left unreduced at the electrode surface is exceedingly small, a functionalization of the surface may still be promoted. In fact,, the grafting efficiency is found to increase during the grafting process, which may be explained by the inhibiting effect the growing film exerts on the competing reduction of the aryl radical. The, slow buildup of the organic film results in a well-ordered structure as shown by the well-defined electrochemical response frond a grafted film containing ferrocenylmethyl groups. Hence, the reduction of aryl Iodides allows a precisely controlled, albeit slow, growth of thin organic films.

Access to fresh water and energy is ranked as one of the most severe challenges to humankind. The restricted availability of fossil fuels and clean water does not match the increasing energy demands and growing population needs, which, desirably, should be satisfied in the most sustainable, clean and inexpensive way. Here, we report clean and sustainable conversion of solar energy into electricity by photo-and bio-electrocatalytic recycling of the H2O/O-2 redox couple in a hybrid bio-photovoltaic (BPV) membraneless cell comprising a sunlight-illuminated water-oxidizing semiconductor anode (either Zn-doped hematite or TiO2) and an oxygen-reducing enzymatic biocathode, in such environmental media as seawater. Upon simulated solar light illumination (AM 1.5G, 100 mW cm(-2)), the maximum power density (P-max) generated by the cell was 236 and 21.4 mu W cm(-2) in 1 M Tris-HCl and seawater, both at pH 8, respectively. In seawater its ionic content inhibited mostly the activity of the photoanode, but not that of the biocathode. The obtained Pmax values were orders of magnitude higher than those of a photo-electrochemical cell with a Pt mesh cathode (0.32 mu W cm(-2) in seawater). The demonstrated thermodynamically feasible coupling of cost-effective photoactive materials such as TiO2 or hematite semiconductors and enzymatic counterparts in seawater media opens a prospective clean and sustainable way of transformation of the most abundant, clean and renewable source of energy - solar light - and the Earth's most massive water resource - seawater - into electricity, which can also be used for fresh water production.

This work addresses the development of a compact paper-based enzymatic microfluidic glucose/O2 fuel cell that can operate using a very limited sample volume (≈35 µl) and explores the energy generated by glucose at concentrations typically found in blood samples at physiological conditions (pH 7.4). Carbon paper electrodes combined with a paper sample absorption substrate all contained within a plastic microfluidic casing are used to construct the paper-based fuel cell. The anode catalysts consist of glucose dehydrogenase and [Os(4,4′-dimethoxy-2,2′-bipyridine)2(poly-vinylimidazole)10Cl]+ as mediator, while the cathode catalysts were bilirubin oxidase and [Os(2,2′-bipyridine)2(poly-vinylimidazole)10Cl]+ as mediator. The fuel cell delivered a linear power output response to glucose over the range of 2.5–30 mM, with power densities ranging from 20 to 90 µW cm−2. The quantification of the available electrical power as well as the energy density extracted from small synthetic samples allows planning potential uses of this energy to power different sensors and analysis devices in a wide variety of in-vitro applications., Peter Ó Conghaile is thanked for synthesis of the redox polymers. Neus Sabaté acknowledges funding from the European H2020 Framework Programme (Grant Agreement 648518 - SUPERCELL - ERC 2014 CoG). Juan Pablo Esquivel would like to thank the support from Marie Curie International Outgoing Fellowship (APPOCS) within the 7th European Community Framework Programme. F. Javier del Campo acknowledges funding from the Spanish Ministry of Economy through the DADDi2 project (TEC2013-48506-C3). Dónal Leech acknowledges support from Grant number 607793 under the Bioenergy FP7-PEOPLE-2013-ITN Programme.

A series of diketopyrrolopyrrole (DPP) dyes with a terminal phosphonic acid group for attachment to metal oxide surfaces were synthesised and the effect of side chain modification on their properties investigated. The organic photosensitisers feature strong visible light absorption (λ = 400 to 575 nm) and electrochemical and fluorescence studies revealed that the excited state of all dyes provides sufficient driving force for electron injection into the TiO2 conduction band. The performance of the DPP chromophores attached to TiO2 nanoparticles for photocatalytic H2 evolution with co-immobilised molecular Co and Ni catalysts was subsequently studied, resulting in solar fuel generation with a dye-sensitised semiconductor nanoparticle system suspended in water without precious metal components. The performance of the DPP dyes in photocatalysis did not only depend on electronic parameters, but also on properties of the side chain such as polarity, steric hinderance and hydrophobicity as well as the specific experimental conditions and the nature of the sacrificial electron donor. In an aqueous pH 4.5 ascorbic acid solution with a phosphonated DuBois-type Ni catalyst, a DPP-based turnover number (TONDPP) of up to 205 was obtained during UV-free simulated solar light irradiation (100 mW cm−2, AM 1.5G, λ > 420 nm) after 1 day. DPP-sensitised TiO2 nanoparticles were also successfully used in combination with a hydrogenase or platinum instead of the synthetic H2 evolution catalysts and the platinum-based system achieved a TONDPP of up to 2660, which significantly outperforms an analogous system using a phosphonated Ru tris(bipyridine) dye (TONRu = 431). Finally, transient absorption spectroscopy was performed to study interfacial recombination and dye regeneration kinetics revealing that the different performances of the DPP dyes are most likely dictated by the different regeneration efficiencies of the oxidised chromophores.

A mononuclear hexa-coordinated iron carbonyl complex [Fe(mu-bdt)(CO)(2)(PTA)(2)](1) (bdt = 1,2-benzenedithiolate; PTA = 1,3,5-triaza-7-phosphaadamantane) with two bulky phosphine ligands in the trans position was synthesized and characterized by X-ray structural analysis coulometry data, FTIR, electrochemistry and electronic structure calculations. The complex undergoes a facilitated two-electron reduction 1/1(2-) and shows an inverted one-electron reduction for 1/1(-) at higher potentials. Electrochemical investigations of 1 are compared to the closely related [Fe(bdt)(CO)(2)(PMe3)(2)] compound. A mechanistic suggestion for the hydrogen evolution reaction upon proton reduction from acid media is derived. The stability of 1 in both weak and strong acids is monitored by cyclic voltammetry.

CONSPECTUS: Biomacromolecules, such as nucleic acids, proteins, and virus particles, are persistent molecular entities with dimensions that exceed' the range of their intermolecular forces hence undergoing degradation by thermally induced bond scission upon heating. Consequently, for this type of molecule, the absence of a liquid phase can be regarded as a general phenomenon. However, certain advantageous properties usually associated with the liquid state of matter, such as processability, flowability, or molecular mobility, are highly sought-after features for biomacromolecules in a solvent-free environment. Here, we provide an overview over the design principles and synthetic pathways to obtain solvent-free liquids of biomacromolecular architectures approaching the topic from our own perspective of research. We will highlight the milestones in synthesis, including a recently developed general surfactant complexation method applicable to a large variety of biomacromolecules as well as other synthetic principles granting access to electrostatically complexed proteins and DNA. These synthetic pathways retain the function and structure of the biomacromolecules even under extreme, nonphysiological conditions at high temperatures in water-free melts challenging the existing paradigm on the role of hydration in structural biology. Under these conditions, the resulting complexes reveal their true potential for previously unthinkable applications. Moreover, these protocols open a pathway toward the assembly of anisotropic architectures, enabling the formation of solvent free biomacromolecular thermotropic liquid crystals. These ordered biomaterials exhibit vastly different mechanical properties when compared to the individual building blocks. Beyond the preparative aspects, we will shine light on the unique potential applications and technologies resulting from solvent-free biomacromolecular fluids: From charge transport in dehydrated liquids to DNA electrochromism to biocatalysis in the absence of a protein hydration shell. Moreover, solvent-free biological liquids containing viruses can be used as novel storage and process media serving as a formulation technology for the delivery of highly concentrated bioactive compounds. We are confident that this new class of hybrid biomaterials will fuel further studies and applications of biomacromolecules beyond water and other solvents and in a much broader context than just the traditional physiological conditions.

New hybrid nanomaterials, with improved photocatalytic performance in pollutants removal, were obtained through the modification of titanate nanotubes (TNT) with a cobalt porphyrin, the cyanocobalamin, also knowing as vitamin B12 (812). The nanocrystalline TNT were produced by hydrothermal treatment and after treated with cobalamin to produce B12-TNT materials. The characterization of the new hybrid material was performed by XRD, FTIR, TEM-EDS, DRS, XPS and ICP. The results show that the immobilization of the cobalt containing specie is dependent on the point of zero charge of the TNT and no modifications on the structure and morphology were observed. No significant changes in the optical band gap were observed after B12 incorporation, but an increasing in the visible light absorption, which arises from charge transfer and d-d transitions of the cobalt, was visualized. The samples photocatalytic performance was studied for the hydroxyl radical production and the highest catalytic ability was achieved by the B12-HTNT sample. The catalytic ability of these new hybrid nanomaterials for two model pollutants photodegradation, phenol and rhodamine B (RhB) was investigated. For both pollutants, the best results were achieved using B12-HTNT with a removal of 94% of a 10 ppm RhB and 87% of a 20 ppm phenol solution in 90 min of irradiation (150 mL, 0.2 g catalyst/L). (C) 2016 Elsevier Masson SAS. All rights reserved. Fundacao para a Ciencia e a Tecnologia [PTDC/CTM-NAN/113021/2009, DID/MULTI/ 00612/2013, IF/01210/2014] info:eu-repo/semantics/publishedVersion

The azaBODIPYs containing one and two formyl functional groups on the 1,7-aryl groups present at the azaBODIPY core were synthesized over sequence of steps and characterized by mass, NMR, absorption, and electro-chemical techniques. The monoformylated and diformylated azaBODIPYs are very useful synthons to prepare a wide variety of new fluorescent compounds. The mono- and diformylated azaBODIPYs were treated with pyrrole under mild acidic conditions followed by column chromatographic purification to afford azaBODIPYs appended with one and two dipyrromethanyl groups. The dipyrramethanyl groups of azaBODIPYs were oxidized with DDQand complexed with BF3-Et2O to obtain covalently linked azaBODIPY-BODIPY dyads and azaBODIPY-(BODIPY)(2) triads. The dyads and triads were characterized in detail by HR-MS, 1D and 2D NMR, absorption, fluorescence, and electrochemical techniques and the structure of one of the triads was deduced by X-ray crystallography. The crystal structure of azaBODIPY-(BODIPY)2 triad revealed that the two BODIPY units were in perpendicular orientation with azaBODIPY unit. The absorption and electrochemical studies indicated a weak interaction among the BODIPY and azaBODIPY moieties and the moieties retain their independent characteristic features in dyads and triads. The preliminary fluorescence studies supported an efficient energy transfer from BODIPY unit(s) to azaBODIPY unit in dyads and triads.

The ability to obtain carbon and energy is a major requirement to exist in any environment. For several ascomycete fungi, (post-)genomic analyses have shown that species that occupy a large variety of habitats possess a diverse enzymatic machinery, while species with a specific habitat have a more focused enzyme repertoire that is well-adapted to the prevailing substrate. White-rot basidiomycete fungi also live in a specific habitat, as they are found exclusively in wood. In this study, we evaluated how well the enzymatic machinery of the white-rot fungus Dichomitus squalens is tailored to degrade its natural wood substrate. The transcriptome and exoproteome of D. squalens were analyzed after cultivation on two natural substrates, aspen and spruce wood, and two non-woody substrates, wheat bran and cotton seed hulls. D. squalens produced ligninolytic enzymes mainly at the early time point of the wood cultures, indicating the need to degrade lignin to get access to wood polysaccharides. Surprisingly, the response of the fungus to the non-woody polysaccharides was nearly as good a match to the substrate composition as observed for the wood polysaccharides. This indicates that D. squalens has preserved its ability to efficiently degrade plant biomass types not present in its natural habitat.

Multi-nuclear cobalt cores have been proposed as molecular analogues of the natural oxygen evolving complex, enabling water oxidation for artificial photosynthesis schemes and the production of solar fuels. In particular, cobalt containing polyoxometalates (Co-POMs) display a record activity as water oxidation catalysts (WOCs) in terms of the turnover number, turnover frequency, and quantum yield, when combined in a light activated oxygen evolving cycle with Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) as the photosensitizer. The unique behavior of high-nuclearity cobalt clusters is addressed herein by employing Co-POMs with Co >= 9 as molecular WOCs. The temporal dissection of the catalytic events is framed herein to investigate the initial photo-induced electron transfer (ET) occurring in the micro-to-millisecond time domain, and followed by the oxygen evolution kinetics taking place within a minute-to-hours regime. In particular, flash photolysis shows ET from the Co-POM to photogenerated Ru(bpy)(3)(3+) with well-behaved diffusional kinetics (bimolecular rate constants in the range k(ET) = 2.1-5.0 x 10(9) M-1 s(-1)) and counting up to 32 ET events in a 60 ms timeframe. The evolution of the Co-POMs is then traced under oxygenic conditions, where infrared and X-ray absorption spectroscopy (XAS) indicate that POM based structures are competent catalysts under the photo-assisted turnover regime.

The widespread application of quantum dots greatly profits from their broad absorption band. However, the variable nature of excitations within these bands is expected to result in undesired excitation energy dependence of steady state emission properties. We demonstrate the different role played by hot and cold carrier trapping in determining fluorescence quantum yields. Our analysis relates the energetic parameters with the available knowledge on the dynamics of charge trapping. It turns out that detrapping processes play a pivotal role in determining steady state emission properties. We studied excitation dependent photoluminescence quantum yields (PLQY) in different CdSe/CdxZn1-xS (x = 0, 0.5, and 1) quantum dots to identify best performing heterostructures in terms of shell thickness and composition. Our rationalization of the observed behavior is focused on the modulation of trapping and detrapping rates. The combination of experimental results and PLQY kinetics modeling reveals the need to consider hot-carrier trapping, supporting recent dynamics observations. This work provides a deeper insight into the trapping process in quantum dots, relating its energetics and dynamics.

The reaction of 2,2'-bipyridine-3,3'-diol (H2L) and cis-Os-II(bpy)(2)Cl-2 (bpy = 2,2'-bipyridine) results in isomeric forms of [Os-II(bpy)(2)(HL-)]ClO4, [1]ClO4 and [2]ClO4, because of the varying binding modes of partially deprotonated HL-. The identities of isomeric [1]ClO4 and [2]ClO4 have been authenticated by their single crystal X-ray structures. The ambidentate HL- in [2]ClO4 develops the usual N,N bonded five-membered chelate with a strong O-H center dot center dot center dot O hydrogen bonded situation (O-H center dot center dot center dot O angle: 160.78 degrees) at its back face. The isomer [1]ClO4 however represents the monoanionic O-,N coordinating mode of HL-, leading to a six-membered chelate with the moderately strong O-H center dot center dot center dot N hydrogen bonding interaction (O-H center dot center dot center dot N angle: 148.87 degrees) at its backbone. The isomeric [1]ClO4 and [2]ClO4 also exhibit distinctive spectral, electrochemical, electronic structural, and hydrogen bonding features. The pK(a) values for [1]ClO4 and [2]ClO4 have been estimated to be 0.73 and 50 degrees) in paramagnetic [Os-III(bpy)(2)(L'(2-))]ClO4 ([4]ClO4). The electronic structural aspects of the complexes reveal the noninnocent potential of the coordinated HL-, L2-, and L'(2-). The K-c value of 49 for 3(3+) reveals a class I mixed-valent (OsOsIII)-Os-II state.

The rates of hole transfer between guanine and adenine in single strand DNA have been evaluated by using Fermi’s golden rule and Kubo’s generating function approach for the Franck–Condon weighted density of states. The whole sets of the normal modes and vibrational frequencies of the two nucleobases, obtained at DFT/B3LYP level of calculation, have been considered in computations. The results show that in single strand the pyramidalization/planarization mode of the amino groups of both nucleobases plays the major role. At room temperature, the Franck–Condon density of states extends over a wide range of hole site energy difference, 0–1 eV, giving some hints about the design of oligonucleotides of potential technological interest.

International audience; In this work, we show that a dithienylethene (DTE) modified dipicolinic amide ligand can be a versatile tool to modulate Eu(III) and Yb(III) luminescence using light as an external stimulus. The nature of the modulation depends on the lanthanide emitter: with the europium ion, the DTE ligand quenches the red luminescence upon ring closure, whereas with the ytterbium ion, ring closure can be used to turn on the luminescence in the NIR range.

Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2 nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2 on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results.

International audience; An expedient synthesis of the first examples of iron-carbonyl complex-coumarin conjugates is reported. 7-Amino/7-hydroxycoumarin derivatives have been readily derivatized through an easily implemented single-step reaction involving the tricarbonyl(eta(5)-cyclohexadienyl)iron(1+) cation [(C6H7)Fe(CO)(3)](+). The scope and limitations of this N-/O-alkylation reaction were also investigated. The fluorescence properties of these novel metal-carbonyl complexes have been studied and support their further use as valuable building blocks in the design of bimodal contrast agents for combined vibrational and fluorescence imaging. (C) 2016 Elsevier Ltd. All rights reserved

Morphology of organic photovoltaic bulk heterojunctions (BHJs) – a nanoscale texture of the donor and acceptor phases – is one of the key factors influencing efficiency of organic solar cells. Detailed knowledge of the morphology is hampered by the fact that it is notoriously difficult to investigate by microscopic methods. Here we all-optically track the exciton harvesting dynamics in the fullerene acceptor phase from which subdivision of the fullerene domain sizes into the mixed phase (2–15 nm) and large (>50 nm) domains is readily obtained via the Monte-Carlo simulations. These results were independently confirmed by a combination of X-ray scattering, electron and atomic-force microscopies, and time-resolved photoluminescence spectroscopy. In the large domains, the excitons are lost due to the high energy disorder while in the ordered materials the excitons are harvested with high efficiency even from the domains as large as 100 nm due to the absence of low-energy traps. Therefore, optimizing of blend nanomorphology together with increasing the material order are deemed as winning strategies in the exciton harvesting optimization.

Three porphyrin-cobaloxime dyads, suitable for application in photoinduced hydrogen generation with sacrificial donors, are characterized by ultrafast spectroscopy in order to clarify the primary photochemical events.

A metal organic framework (MOF) based on the [Cu(4)I(4)DABCO(2)] cluster (DABCO = 1,4-diazabicyclo[2.2.2]octane), MOF 1, shows bright emission with a maximum at 556 nm and an emission quantum yield of 0.53 in the solid state. When the large cavities of the MOF are loaded during the synthesis with different amounts of ferrocene {FeCp2, [((5)-C5H5)(2)Fe-II]}, the luminescence of MOF 1 decreases with the increase in the ferrocene content, reaching an almost complete quenching for 3.5 wt.-% of cage loading, corresponding to the complete filling of the MOF cavities. When an electric potential is applied to the FeCp2@MOF 1 deposited onto an ITO glass, the (FeCp2)-Cp-II is oxidised to (FeCp2+)-Cp-III, and the MOF 1 emission is partially switched on again, indicating that a photoinduced electron-transfer reaction is contributing to the quenching process.

The electrochemical and spectroelectrochemical properties of a bis-pyrid-4-yl functionalised vinylenedithio-TFF derivative, 1, in solution are reported. The compound was immobilised on a Pt electrode and the resulting layers formed were investigated using electrochemical techniques. Two oxidation processes were observed for 1, typical of TTF derivatives. A solvent dependence study revealed that the stabilisation of the radical cation intermediate, 1(center dot+), towards further oxidation is achieved in solvents with a low Gutmann donor number such as dichloromethane. Analysis of 1(2+) in solution under aerobic and anaerobic conditions reveal that its stability is compromised in the presence of oxygen and therefore the stability of monolayers of 1 is greatly enhanced under anaerobic conditions. Time dependent OFT calculations of the compound in several oxidation states are discussed to obtain information on the location of the various redox processes. (C) 2013 Elsevier Ltd. All rights reserved.

International audience; The present paper focuses on a simplified method to study the orientation and the anisotropy of two different alkanethiols self-assembled monolayers on gold surfaces. The alkanethiols of interest vary only by their terminal functionalities (COOH and COOCH3), thus allowing one to highlight the influence of these ending chemical groups on the final orientation of the adsorbed molecules. 11-Mercaptoundecanoic acid [HS-(CH2)10-COOH] and the methyl-11-mercaptoundecanoate [HS-(CH2)10-COOCH3] were grafted under adequate conditions to obtain a high grafting density on gold substrates. These latter, before and after the alkanethiol adsorption, were analyzed mainly by the polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) technique to access orientation angles, and by atomic force microscopy (AFM) to check the homogeneity of the grafted layer. By applying an original PM-IRRAS simplified method, the results showed an orientation closer to the normal of the surface plane in the case of the acid thiol compared with the ester one, which is probably because of the lateral hydrogen bonds established between the adjacent COOH functions. This method offers a direct and simple way to quantify the orientation angles in the alkanethiol nanofilms.

International audience; Electrochemical and photophysical analysis of new donoracceptor systems 2 and 3, in which a benzothiadiazole (BTD) unit is covalently linked to a tetrathiafulvalene (TTF) core, have verified that the lowest excited state can be ascribed to an intramolecular-charge-transfer (ICT) (TTF)(benzothiadiazole) transition. Owing to better overlap of the HOMO and LUMO in the fused scaffold of compound 3, the intensity of the 1ICT band is substantially higher compared to that in compound 2. The corresponding CT fluorescence is also observed in both cases. The radical cation TTF+. is easily observed through chemical and electrochemical oxidation by performing steady-state absorption experiments. Interestingly, compound 2 is photo-oxidized under aerobic conditions.

l-galactono-1,4-lactone dehydrogenase (GALDH) catalyzes the terminal step of vitamin C biosynthesis in plant mitochondria. Here we investigated the communication between Arabidopsis thaliana GALDH and its natural electron acceptor cytochrome c (Cc). Using laser-generated radicals we observed the formation and stabilization of the GALDH semiquinone anionic species (GALDHSQ ). GALDHSQ oxidation by Cc exhibited a nonlinear dependence on Cc concentration consistent with a kinetic mechanism involving protein-partner association to form a transient bimolecular complex prior to the electron transfer step. Oxidation of GALDHSQ by Cc was significantly impaired at high ionic strength, revealing the existence of attractive charge-charge interactions between the two reactants. Isothermal titration calorimetry showed that GALDH weakly interacts with both oxidized and reduced Cc. Chemical shift perturbations for (1) H and (15) N nuclei of Cc, arising from the interactions with unlabeled GALDH, were used to map the interacting surface of Cc. For Arabidopsis Cc and yeast Cc, similar residues are involved in the interaction with GALDH. These residues are confined to a single surface surrounding the heme edge. The range of chemical shift perturbations for the physiological Arabidopsis Cc-GALDH complex is larger than that of the non-physiological yeast Cc-GALDH complex, indicating that the former complex is more specific. In summary, the results point to a relatively low affinity GALDH-Cc interaction, similar for all partner redox states, involving protein-protein dynamic motions. Evidence is also provided that Cc utilizes a conserved surface surrounding the heme edge for the interaction with GALDH and other redox partners.

Cyclotriphosphazene and cyclotetraphosphazene appended with six and eight covalently linked porphyrin-ferrocene conjugates respectively were synthesized by treating N3P3Cl6 and N4P4Cl8 with appropriate equivalents of ferrocene linked porphyrin containing meso-hydroxyphenyl group in THF in the presence of Cs2CO3 followed by column chromatographic purification. NMR and absorption studies indicated a weak interaction between adjacent porphyrin-ferrocene conjugates. Electrochemical studies supported electrochemical equivalence of ferrocenyl and porphyrinyl moieties in these multiporphyrin-ferrocene conjugate assemblies. The fluorescence studies showed significant quenching of porphyrin fluorescence due to photo-induced electron transfer from ferrocene to singlet state of porphyrin unit in these assemblies. (C) 2012 Elsevier B. V. All rights reserved.

Water oxidation in photosynthesis takes place in photosystem II (PSII). This photosystem is built around a reaction center (RC) where sunlight-induced charge separation occurs. This RC consists of various polypeptides that bind only a few chromophores or pigments, next to several other cofactors. It can handle far more photons than the ones absorbed by its own pigments and therefore, additional excitations are provided by the surrounding light-harvesting complexes or antennae. The RC is located in the PSII core that also contains the inner light-harvesting complexes CP43 and CP47, harboring 13 and 16 chlorophyll pigments, respectively. The core is surrounded by outer light-harvesting complexes (Lhcs), together forming the so-called supercomplexes, at least in plants. These PSII supercomplexes are complemented by some extra Lhcs, but their exact location in the thylakoid membrane is unknown. The whole system consists of many subunits and appears to be modular, i.e., both its composition and organization depend on environmental conditions, especially on the quality and intensity of the light. In this review, we will provide a short overview of the relation between the structure and organization of pigment-protein complexes in PSII, ranging from individual complexes to entire membranes and experimental and theoretical results on excitation energy transfer and charge separation. It will become clear that time-resolved fluorescence data can provide invaluable information about the organization and functioning of thylakoid membranes. At the end, an overview will be given of unanswered questions that should be addressed in the near future. © 2013 The Author(s).

International audience; The molecule {Cp*(dppe)Fe(C C-)}(3)(1,3,5-C6H3) (Fe3) was adsorbed on a single-crystal gold surface and studied using ultrahigh-vacuum scanning tunneling microscopy (STM). Both the singly oxidized Fe3(+) and doubly oxidized Fe3(2+) are mixed-valence ions, and localization of the charge at specific metal centers was observed as the appearance of pronounced asymmetry in STM images. Switching the tip sample bias voltage demonstrates that this asymmetry is electronic in nature. The nature of intramolecular structure and the degree of asymmetry produced in STM images varies according to the state of the scanning tip. Constrained density functional theory was used to simulate STM images for the neutral molecule and for both mixed-valence species, and simulated images agreed closely with observed results. In particular, changing the number of molecular electronic states contributing to contrast in the STM image produced a good match to the variation in structures measured experimentally.

International audience; A two-step reaction sequence for accessing meso-(dialkoxyphosphoryl) porphyrins from readily available trans-A(2)-type porphyrins was developed. This approach involves bromination and subsequent palladium-catalyzed phosphonylation. Optimal conditions for both steps were identified after exploration of various reaction parameters such as solvent, temperature and catalyst. A series of dialkoxyphosphoryl-substituted A2B-porphyrins Zn3(a-g) bearing electron-donating, electron-withdrawing or sterically bulky substituents at the meso-aryl groups were prepared in overall yields close to 40 %. These compounds, being air-stable and soluble in most organic solvents, are valuable synthetic intermediates because they can be readily transformed into functionalized trans-A(2)BC-type porphyrins through regioselective functionalization at the unsubstituted meso position of the macrocycle. Therefore, this approach offers considerable promise for application to the synthesis of trans-A(2)BC-type porphyrins, including water-soluble derivatives, push-pull chromophores and bis(porphyrin)s.