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We report a photocatalytic strategy for the chemodivergent radical benzylation of 4-cyanopyridines. The chemistry uses a single photoredox catalyst to generate benzyl radicals upon N-F bond activation of 2-alkyl N-fluorobenzamides. The judicious choice of different photocatalyst quenchers allowed us to select at will between mechanistically divergent processes. The two reaction manifolds, an ipso-substitution path proceeding via radical coupling and a Minisci-type addition, enabled selective access to regioisomeric C4 or C2 benzylated pyridines, respectively. Mechanistic investigations shed light on the origin of the chemoselectivity switch.

In this study, multi-wall carbon nanotubes (MWCNTs) were electrochemically modified with nitrogen and phosphorus species and employed as platform to immobilize pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) for the fabrication of bioelectrodes for glucose detection. Depending on the upper potential limit used during the electrochemical modification of MWCNTs, the nature and amount of the nitrogen and phosphorus species incorporated in the carbon material surface can be selectively controlled. These species act as anchoring groups for the immobilization of the PQQ-GDH. The value of the upper potential limit used in the electrochemical modification influences the electron-transfer rate between the electrode and the enzyme. The performance of the bioelectrodes for glucose oxidation and detection is improved by the electrochemical modification conditions, leading to an increased sensitivity towards glucose oxidation from 39.2 to 53.6 mA gMWCNT−1 mM−1 in a linear range between 0.1 to 1.2 mM. This electrochemical modification is considered as an alternative for the preparation of highly sensitive glucose bioelectrodes.

Optimizing the kinetics of an electrode reaction is central to the design of devices whose function spans from sensing to energy conversion. Electrode kinetics depends strongly on electrode surface properties, but the search for optimal materials is often a trial-and-error process. Recent research has revealed a pronounced facet-dependent electrical conductivity for silicon, implicitly suggesting that rarely used crystallographic cuts of this technologically relevant material had been entirely overlooked for the fabrication of electrodes. By first protecting silicon from anodic decomposition through Si-C-bound organic monolayers, conductive atomic force microscopy demonstrates that conductivity decreases in the order (211) ≫ (110) > (111). However, charge-transfer rates for a model electrochemical reaction are similar on all these crystal orientations. These findings reveal the absence of a relationship between surface conductivity and kinetics of a surface-confined redox reaction and expand the range of silicon crystallographic orientations viable as electrode materials.

In this study, multi-wall carbon nanotubes (MWCNTs) were electrochemically modified with nitrogen and phosphorus species and employed as platform to immobilize pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) for the fabrication of bioelectrodes for glucose detection. Depending on the upper potential limit used during the electrochemical modification of MWCNTs, the nature and amount of the nitrogen and phosphorus species incorporated in the carbon material surface can be selectively controlled. These species act as anchoring groups for the immobilization of the PQQ-GDH. The value of the upper potential limit used in the electrochemical modification influences the electron-transfer rate between the electrode and the enzyme. The performance of the bioelectrodes for glucose oxidation and detection is improved by the electrochemical modification conditions, leading to an increased sensitivity towards glucose oxidation from 39.2 to 53.6 mA gMWCNT−1 mM−1 in a linear range between 0.1 to 1.2 mM. This electrochemical modification is considered as an alternative for the preparation of highly sensitive glucose bioelectrodes.

In Arabidopsis, two leaf-type ferredoxin-NADP(+) oxidoreductase (LFNR) isoforms function in photosynthetic electron flow in reduction of NADP(+), while two root-type FNR (RFNR) isoforms catalyse reduction of ferredoxin in non-photosynthetic plastids. As the key to understanding, the function of RFNRs might lie in their spatial and temporal distribution in different plant tissues and cell types, we examined expression of RFNR1 and RFNR2 genes using beta-glucuronidase (GUS) reporter lines and investigated accumulation of distinct RFNR isoforms using a GFP approach and Western blotting upon various stresses. We show that while RFNR1 promoter is active in leaf veins, root tips and in the stele of roots, RFNR2 promoter activity is present in leaf tips and root stele, epidermis and cortex. RFNR1 protein accumulates as a soluble protein within the plastids of root stele cells, while RFNR2 is mainly present in the outer root layers. Ozone treatment of plants enhanced accumulation of RFNR1, whereas low temperature treatment specifically affected RFNR2 accumulation in roots. We further discuss the physiological roles of RFNR1 and RFNR2 based on characterization of rfnr1 and rfnr2 knock-out plants and show that although the function of these proteins is partly redundant, the RFNR proteins are essential for plant development and survival.

Mitochondrial respiratory complex subunits assemble in supercomplexes. Studies of supercomplexes have typically relied upon antibody-based quantification, often limited to a single subunit per respiratory complex. To provide a deeper insight into mitochondrial and supercomplex plasticity, we combine native electrophoresis and mass spectrometry to determine the supercomplexome of skeletal muscle from sedentary and exercise-trained mice. We quantify 422 mitochondrial proteins within 10 supercomplex bands in which we show the debated presence of complexes II and V. Exercise-induced mitochondrial biogenesis results in non-stoichiometric changes in subunits and incorporation into supercomplexes. We uncover the dynamics of supercomplex-related assembly proteins and mtDNA-encoded subunits after exercise. Furthermore, exercise affects the complexing of Lactb, an obesity-associated mitochondrial protein, and ubiquinone biosynthesis proteins. Knockdown of ubiquinone biosynthesis proteins leads to alterations in mitochondrial respiration. Our approach can be applied to broad biological systems. In this instance, comprehensively analyzing respiratory supercomplexes illuminates previously undetectable complexity in mitochondrial plasticity.

In Arabidopsis, two leaf-type ferredoxin-NADP(+) oxidoreductase (LFNR) isoforms function in photosynthetic electron flow in reduction of NADP(+), while two root-type FNR (RFNR) isoforms catalyse reduction of ferredoxin in non-photosynthetic plastids. As the key to understanding, the function of RFNRs might lie in their spatial and temporal distribution in different plant tissues and cell types, we examined expression of RFNR1 and RFNR2 genes using beta-glucuronidase (GUS) reporter lines and investigated accumulation of distinct RFNR isoforms using a GFP approach and Western blotting upon various stresses. We show that while RFNR1 promoter is active in leaf veins, root tips and in the stele of roots, RFNR2 promoter activity is present in leaf tips and root stele, epidermis and cortex. RFNR1 protein accumulates as a soluble protein within the plastids of root stele cells, while RFNR2 is mainly present in the outer root layers. Ozone treatment of plants enhanced accumulation of RFNR1, whereas low temperature treatment specifically affected RFNR2 accumulation in roots. We further discuss the physiological roles of RFNR1 and RFNR2 based on characterization of rfnr1 and rfnr2 knock-out plants and show that although the function of these proteins is partly redundant, the RFNR proteins are essential for plant development and survival.

Mitochondrial respiratory complex subunits assemble in supercomplexes. Studies of supercomplexes have typically relied upon antibody-based quantification, often limited to a single subunit per respiratory complex. To provide a deeper insight into mitochondrial and supercomplex plasticity, we combine native electrophoresis and mass spectrometry to determine the supercomplexome of skeletal muscle from sedentary and exercise-trained mice. We quantify 422 mitochondrial proteins within 10 supercomplex bands in which we show the debated presence of complexes II and V. Exercise-induced mitochondrial biogenesis results in non-stoichiometric changes in subunits and incorporation into supercomplexes. We uncover the dynamics of supercomplex-related assembly proteins and mtDNA-encoded subunits after exercise. Furthermore, exercise affects the complexing of Lactb, an obesity-associated mitochondrial protein, and ubiquinone biosynthesis proteins. Knockdown of ubiquinone biosynthesis proteins leads to alterations in mitochondrial respiration. Our approach can be applied to broad biological systems. In this instance, comprehensively analyzing respiratory supercomplexes illuminates previously undetectable complexity in mitochondrial plasticity.

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 mechanisms for the oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives (Cp∗ = η5-C5Me5) by nitrous oxide via selective oxygen atom transfer reactions have been systematically studied by means of density functional theory (DFT) calculations. On the basis of the calculations, we investigated the original mechanism proposed by Hillhouse and co-workers for the activation of N2O. The calculations showed that the complex with an initial O-coordination of N2O to the coordinatively unsaturated Hf center is not a local minimum. Then we proposed a new reaction mechanism to investigate how N2O is activated and why N2O selectively oxidize phenyl and hydride ligands of. Frontier molecular orbital theory analysis indicates that N2O is activated by nucleophilic attack by the phenyl or hydride ligand. Present calculations provide new insights into the activation of N2O involving the direct oxygen atom transfer from nitrous oxide to metal-ligand bonds instead of the generally observed oxygen abstraction reaction to generate metal-oxo species., QC 20160202. QC 20160205

[EN] The model reaction of photoinduced donor-acceptor interaction in linked systems (dyads) has been used to study the comparative reactivity of a well-known anti-inflammatory drug, (S)-naproxen (NPX) and its (R)-isomer. (R)- or (S)-NPX in these dyads is linked to (S)-N-methylpyrrolidine (Pyr) using a linear or cyclic amino acid bridge (AA or CyAA), to give (R)-/(S)-NPX-AA-(S)-Pyr flexible and (R)-/(S)-NPX-CyAA-(S)-Pyr rigid dyads. The donor-acceptor interaction is reminiscent of the binding (partial charge transfer, CT) and electron transfer (ET) processes involved in the extensively studied inhibition of the cyclooxygenase enzymes (COXs) by the NPX enantiomers. Besides that, both optical isomers undergo oxidative metabolism by enzymes from the P450 family, which also includes ET. The scheme proposed for the excitation quenching of the (R)- and (S)-NPX excited state in these dyads is based on the joint analysis of the chemically induced dynamic nuclear polarization (CIDNP) and fluorescence data. The H-1 CIDNP effects in this system appear in the back electron transfer in the biradical-zwitterion (BZ), which is formed via dyad photoirradiation. The rate constants of individual steps in the proposed scheme and the fluorescence quantum yields of the local excited (LE) states and exciplexes show stereoselectivity. It depends on the bridge's length, structure and solvent polarity. The CIDNP effects (experimental and calculated) also demonstrate stereodifferentiation. The exciplex quantum yields and the rates of formation are larger for the dyads containing (R)-NPX, which let us suggest a higher contribution from the CT processes with the (R)-optical isomer.

[EN] The model reaction of photoinduced donor-acceptor interaction in linked systems (dyads) has been used to study the comparative reactivity of a well-known anti-inflammatory drug, (S)-naproxen (NPX) and its (R)-isomer. (R)- or (S)-NPX in these dyads is linked to (S)-N-methylpyrrolidine (Pyr) using a linear or cyclic amino acid bridge (AA or CyAA), to give (R)-/(S)-NPX-AA-(S)-Pyr flexible and (R)-/(S)-NPX-CyAA-(S)-Pyr rigid dyads. The donor-acceptor interaction is reminiscent of the binding (partial charge transfer, CT) and electron transfer (ET) processes involved in the extensively studied inhibition of the cyclooxygenase enzymes (COXs) by the NPX enantiomers. Besides that, both optical isomers undergo oxidative metabolism by enzymes from the P450 family, which also includes ET. The scheme proposed for the excitation quenching of the (R)- and (S)-NPX excited state in these dyads is based on the joint analysis of the chemically induced dynamic nuclear polarization (CIDNP) and fluorescence data. The H-1 CIDNP effects in this system appear in the back electron transfer in the biradical-zwitterion (BZ), which is formed via dyad photoirradiation. The rate constants of individual steps in the proposed scheme and the fluorescence quantum yields of the local excited (LE) states and exciplexes show stereoselectivity. It depends on the bridge's length, structure and solvent polarity. The CIDNP effects (experimental and calculated) also demonstrate stereodifferentiation. The exciplex quantum yields and the rates of formation are larger for the dyads containing (R)-NPX, which let us suggest a higher contribution from the CT processes with the (R)-optical isomer.

The cytochrome (cyt) bc(1) complex is an integral component of the respiratory electron transfer chain sustaining the energy needs of organisms ranging from humans to bacteria. Due to its ubiquitous role in the energy metabolism, both the oxidation and reduction of the enzyme's substrate co-enzyme Q has been studied vigorously. Here, this vast amount of data is reassessed after probing the substrate reduction steps at the Q(i)-site of the cyt bc(1) complex of Rhodobacter capsulatus using atomistic molecular dynamics simulations. The simulations suggest that the Lys251 side chain could rotate into the Q(i)-site to facilitate binding of half-protonated semiquinone - a reaction intermediate that is potentially formed during substrate reduction. At this bent pose, the Lys251 forms a salt bridge with the Asp252, thus making direct proton transfer possible. In the neutral state, the lysine side chain stays close to the conserved binding location of cardiolipin (CL). This back-and-forth motion between the CL and Asp252 indicates that Lys251 functions as a proton shuttle controlled by pH-dependent negative feedback. The CL/K/D switching, which represents a refinement to the previously described CL/K pathway, fine-tunes the proton transfer process. Lastly, the simulation data was used to formulate a mechanism for reducing the substrate at the Q(i)-site.

A highly active supramolecular system for visible light-driven water oxidation was developed with cyclodextrin-modified ruthenium complex as the photosensitizer, phenyl-modified ruthenium complexes as the catalysts, and sodium persulfate as the sacrificial electron acceptor. The catalysts were found to form 1:1 host-guest adducts with the photosensitizer. Stopped-flow measurement revealed the host-guest interaction is essential to facilitate the electron transfer from catalyst to sensitizer. As a result, a remarkable quantum efficiency of 84% was determined under visible light irradiation in neutral aqueous phosphate buffer. This value is nearly 1 order of magnitude higher than that of noninteraction system, indicating that the noncovalent incorporation of sensitizer and catalyst is an appealing approach for efficient conversion of solar energy into fuels., QC 20150508

BACKGROUND: The utilization of different kinds of ion exchange membrane is a common practice in bioelectrochemical systems such as two-chambered microbial fuel cells (MFCs). However, little is known about the effect of membrane materials on the anodic microbial community diversity.; RESULTS: The effect of two cationic and one anionic exchange membranes (Nafion N-117, Ultrex CMI-7000, and Ultrex AMI-7000) on the microbial community dynamics of Eubacteria and Archaea has been assessed in two-chambered MFCs. The experimental results indicated that the eubacterial community in the anodic chamber was not affected by the membrane materials, being predominantly populations of Bacteroidetes (Porphyromonadaceae) and -proteobacteria (Alcaligenaceae and Comamonadaceae). On the other hand, the archaeal counterpart appears to be highly dependent on the type of membrane used, as was evidenced by the selective enrichment of Methanosarcina sp. in the MFC equipped with the membrane Nafion N-117 which was the MFC that showed the highest current production.; CONCLUSIONS: The results obtained in the present study suggest that membrane materials affect archaeal diversity whereas both anodofilic eubacteria and methanogenic archaea populations could play an important role in the overall MFC process performance., Peer Reviewed, Postprint (author’s final draft)

Supporting Information 1 H NMR spectra of compounds 1c and 2a, 1 H and 13C spectra of probes 2b−d. UV−vis and emission titration profiles. Cartesian coordinates of the optimized geometries. This material is available free of charge via the Internet at http:// pubs.acs.org., [EN] Four imidazoanthraquinone derivatives (2a−d) were synthesized and characterized and their coordination behavior against selected anions and cations tested. Acetonitrile solutions of probes showed charge-transfer absorptions in the 407−465 nm range. The four probes emitted in the 533− 571 nm interval. The recognition ability of 2a−d was evaluated in the presence of F−, Cl−, Br−, I−, OCN−, BzO−, ClO4 −, AcO−, HSO4 −, H2PO4 −, and CN−. Only F−, AcO−, and H2PO4 − induced a new red-shifted absorption band that was attributed to a deprotonation process involving the amine moiety of the imidazole ring. Moreover, upon increasing quantities of F−, AcO−, and H2PO4 −, moderate quenching was induced in the emission of 2a−d together with the appearance of a new red-shifted band. The UV−visible and emission behavior of the four probes in the presence of Cu2+, Co2+, Mg2+, Fe3+, Ba2+, Fe2+, Ni2+, Ca2+, Zn2+, Pb2+, Cd2+, Cr3+, Al3+, K+ , and Li+ was also assessed. Only addition of Fe3+, Cr3+, and Al3+ caused a new blue-shifted band in 2a−d that was ascribed to a preferential coordination with the acceptor part of the probes. Moreover, an important quenching of the emission was observed which was ascribed to the interaction between these trivalent cations and 2a−d.

Supporting Information 1 H NMR spectra of compounds 1c and 2a, 1 H and 13C spectra of probes 2b−d. UV−vis and emission titration profiles. Cartesian coordinates of the optimized geometries. This material is available free of charge via the Internet at http:// pubs.acs.org., [EN] Four imidazoanthraquinone derivatives (2a−d) were synthesized and characterized and their coordination behavior against selected anions and cations tested. Acetonitrile solutions of probes showed charge-transfer absorptions in the 407−465 nm range. The four probes emitted in the 533− 571 nm interval. The recognition ability of 2a−d was evaluated in the presence of F−, Cl−, Br−, I−, OCN−, BzO−, ClO4 −, AcO−, HSO4 −, H2PO4 −, and CN−. Only F−, AcO−, and H2PO4 − induced a new red-shifted absorption band that was attributed to a deprotonation process involving the amine moiety of the imidazole ring. Moreover, upon increasing quantities of F−, AcO−, and H2PO4 −, moderate quenching was induced in the emission of 2a−d together with the appearance of a new red-shifted band. The UV−visible and emission behavior of the four probes in the presence of Cu2+, Co2+, Mg2+, Fe3+, Ba2+, Fe2+, Ni2+, Ca2+, Zn2+, Pb2+, Cd2+, Cr3+, Al3+, K+ , and Li+ was also assessed. Only addition of Fe3+, Cr3+, and Al3+ caused a new blue-shifted band in 2a−d that was ascribed to a preferential coordination with the acceptor part of the probes. Moreover, an important quenching of the emission was observed which was ascribed to the interaction between these trivalent cations and 2a−d.

Enhancing the charge transfer process in nanocrystal sensitized solar cells is vital for the improvement of their performance. In this work we show a means of increasing photo-induced ultrafast charge transfer in successive ionic layer adsorption and reaction (SILAR) CdS-TiO2 nanocrystal heterojunctions using pulsed laser sintering of TiO2 nanocrystals. The enhanced charge transfer was attributed to both morphological and phase transformations. At sufficiently high laser fluences, volumetrically larger porous networks of the metal oxide were obtained, thus increasing the density of electron accepting states. Laser sintering also resulted in varying degrees of anatase to rutile phase transformation of the TiO2, producing thermodynamically more favorable conditions for charge transfer by increasing the change in free energy between the CdS donor and TiO2 acceptor states. Finally, we report aspects of apparent hot electron transfer as a result of the SILAR process which allows CdS to be directly adsorbed to the TiO2 surface.

In the present Letter several carbolactones (oxidative products) are obtained under aprotic cathodic conditions in the preparative scaled electrolysis of 1,2-quinones in a divided electrochemical cell and in the presence of oxygen. When 9,10-phenanthrenequinone is reduced 6H-dibenzo[b,d]pyran-6-one and [1,1′-biphenyl]-2,2′-dicarboxylic acid are obtained as major products. In the reduction of 1,2-naphthoquinone, 2-benzopyran-1(1H)-one, and 2-(2-carboxyethenyl)-benzoic acid were formed as main products. The proposed mechanism to explain the formation of these and other products, that involves an electron-transfer reaction to the oxygen in air, is now discussed.

peer-reviewed, The electrochemical properties of cytochrome c (cyt c) immobilized on multilayer nanozeolite-modified electrodes have been examined in aqueous and nonaqueous solutions. Layers of Linde type-L zeolites were assembled on indium tin oxide (ITO) glass electrodes followed by the adsorption of cyt c, primarily via electrostatic interactions, onto modified ITO electrodes. The heme protein displayed a quasi-reversible response in aqueous solution with a redox potential of +324 mV (vs NHE), and the surface coverage (Gamma*) increased linearly for the first four layers and then gave a nearly constant value of 200 pmol cm(-2). On immersion of the modified electrodes in 95% (v/v) nonaqueous solutions, the redox potential decreased significantly, a decrease that originated from changes in both the enthalpy and entropy of reduction. On reimmersion of the modified electrode in buffer, the faradic response immediately returned to its original value. These results demonstrate that nanozeolites are potential stable supports for redox proteins and enzymes., ACCEPTED, peer-reviewed

peer-reviewed, The range of salts used as supporting electrolytes in electrochemical studies of redox proteins and enzymes varies widely, with the choice of an electrolyte relying on the assumption that the electrolyte used does not affect the electrochemical properties of the proteins and enzymes under investigation. Examination of the electrochemical properties of the redox protein cytochrome c (cyt c) at a 4,4'-bipyridyl modified gold electrode demonstrates that both the redox potential (E-o') and the faradaic current are influenced by the nature of the electrolyte used, in a manner explained primarily by Hofmeister effects. The faradaic peak currents display an atypical trend on switching from kosmotropic to chaotropic anions, with a maximum current observed in the presence of Cl-. For a series of cations, the peak current increased in the sequence: Li+ (0.34 mu A) Br- (0.35 mu A) > ClO4- (0.35 mu A) > SCN- (0.31 mu A) > F- (0.30 mu A). E-o' decreased by a total of 24 mV across the series F- > Cl- > Br- > ClO4- > SCN- whereas no specific ion effect on E-o' was observed for cations. Factorisation of E-o' into its enthalpic and entropic components showed that while no specific trends were observed, large changes in Delta H-o' and Delta S-o' occurred with individual ions. The effect of anions on the faradaic peak current can be qualitatively explained by considering Collins' empirical rule of 'matching water affinities'. The effect of cations cannot be explained by this rule. However, both anion and cation effects can be understood by taking into account the cooperative action of electrostatic and ion dispersion forces. The results demonstrate that the choice of a supporting electrolyte in electrochemical investigations of redox proteins is important and emphasize that care needs to be taken in the determination and comparison of E-o', Delta H-o' and Delta S-o' in different solutions., ACCEPTED, peer-reviewed

In the present Letter several carbolactones (oxidative products) are obtained under aprotic cathodic conditions in the preparative scaled electrolysis of 1,2-quinones in a divided electrochemical cell and in the presence of oxygen. When 9,10-phenanthrenequinone is reduced 6H-dibenzo[b,d]pyran-6-one and [1,1′-biphenyl]-2,2′-dicarboxylic acid are obtained as major products. In the reduction of 1,2-naphthoquinone, 2-benzopyran-1(1H)-one, and 2-(2-carboxyethenyl)-benzoic acid were formed as main products. The proposed mechanism to explain the formation of these and other products, that involves an electron-transfer reaction to the oxygen in air, is now discussed.

Enhancing the charge transfer process in nanocrystal sensitized solar cells is vital for the improvement of their performance. In this work we show a means of increasing photo-induced ultrafast charge transfer in successive ionic layer adsorption and reaction (SILAR) CdS-TiO2 nanocrystal heterojunctions using pulsed laser sintering of TiO2 nanocrystals. The enhanced charge transfer was attributed to both morphological and phase transformations. At sufficiently high laser fluences, volumetrically larger porous networks of the metal oxide were obtained, thus increasing the density of electron accepting states. Laser sintering also resulted in varying degrees of anatase to rutile phase transformation of the TiO2, producing thermodynamically more favorable conditions for charge transfer by increasing the change in free energy between the CdS donor and TiO2 acceptor states. Finally, we report aspects of apparent hot electron transfer as a result of the SILAR process which allows CdS to be directly adsorbed to the TiO2 surface.

A molecular water oxidation catalyst (2) has been synthesized and immobilized together with a molecular photosensitizer (1) on nanostructured TiO2 particles on FTO conducting glass, forming a photoactive anode (TiO2(1+2)). By using the TiO2(1+2) as working electrode in a three-electrode photoelectrochemical cell (PEC), visible light driven water splitting has been successfully demonstrated in a phosphate buffer solution (pH 6.8), with oxygen and hydrogen bubbles evolved respectively from the working electrode and counter electrode. By applying 0.2 V external bias vs NHE, a high photocurrent density of more than 1.7 rnA.cm(-2) has been achieved. This value is higher than any PEC devices with molecular components reported in literature., QC 20130507

The photochemical processes occurring in diastereomeric dyads (S, S)-1 and (S, R)-1, prepared by conjugation of (S)-2-(2-hydroxy-1,1'-biphenyl-4-yl) propanoic acid ((S)-BPOH) with (S)- and (R)-Trp, have been investigated. In acetonitrile, the fluorescence spectra of (S, S)-1 and (S, R)-1 were coincident in shape and position with that of (S)-BPOH, although they revealed a markedly stereoselective quenching. Since singlet energy transfer from BPOH to Trp is forbidden (5 kcal mol(-1) uphill), the quenching was attributed to thermodynamically favoured (according to Rehm-Weller) electron transfer or exciplex formation. Upon addition of 20% water, the fluorescence quantum yield of (S)-BPOH decreased, while only minor changes were observed for the dyads. This can be explained by an enhancement of the excited state acidity of (S)-BPOH, associated with bridging of the carboxy and hydroxy groups by water, in agreement with the presence of water molecules in the X-ray structure of (S)-BPOH. When the carboxy group was not available for coordination with water, as in the methyl ester (S)-BPOHMe or in the dyads, this effect was prevented; accordingly, the fluorescence quantum yields did not depend on the presence or absence of water. The fluorescence lifetimes in dry acetonitrile were 1.67, 0.95 and 0.46 ns for (S)-BPOH, (S, S)-1 and (S, R)-1, respectively, indicating that the observed quenching is indeed dynamic. In line with the steady-state and time-resolved observations, molecular modelling pointed to a more favourable geometric arrangement of the two interacting chromophores in (S, R)-1. Interestingly, this dyad exhibited a folded conformation in the solid state.

Unwanted photoinduced responses are well-known adverse effects of most promazine drugs, including levomepromazine (LPZ, Levoprome((R)) or Nozinan((R))). This drug is indicated in psychiatry primarily for the treatment of schizophrenia and other schizoaffective disorders. Levomepromazine's particular sedative properties make it especially fit for use in psychiatric intensive care. Nevertheless, it is photolabile under UV-A and UV-B light in aerobic conditions resulting in the formation of its sulfoxide. The LPZ photochemistry in acetonitrile (MeCN) is completely different from that in methanol (MeOH) and phosphate buffer solutions (PBS, pH = 7.4). The major photoproduct in PBS and MeOH under aerobic conditions is levomepromazine sulfoxide (LPZSO), although the amount is considerably higher in the aqueous environment. The corresponding main photoproduct in MeCN could not be characterized. The destruction quantum yields of LPZ in PBS, MeOH and MeCN are 0.13, 0.02 and <10(-3), respectively. It is further demonstrated that LPZSO does not form by the reaction of singlet oxygen with ground-state LPZ. This oxidation product is actually produced by the reaction of the cation radical of LPZ (LPZ.(+)) with molecular oxygen. This cation radical in turn, is produced by an electron transfer process between the (3)LPZ* and ground-state molecular oxygen.

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.

The photochemical processes occurring in diastereomeric dyads (S, S)-1 and (S, R)-1, prepared by conjugation of (S)-2-(2-hydroxy-1,1'-biphenyl-4-yl) propanoic acid ((S)-BPOH) with (S)- and (R)-Trp, have been investigated. In acetonitrile, the fluorescence spectra of (S, S)-1 and (S, R)-1 were coincident in shape and position with that of (S)-BPOH, although they revealed a markedly stereoselective quenching. Since singlet energy transfer from BPOH to Trp is forbidden (5 kcal mol(-1) uphill), the quenching was attributed to thermodynamically favoured (according to Rehm-Weller) electron transfer or exciplex formation. Upon addition of 20% water, the fluorescence quantum yield of (S)-BPOH decreased, while only minor changes were observed for the dyads. This can be explained by an enhancement of the excited state acidity of (S)-BPOH, associated with bridging of the carboxy and hydroxy groups by water, in agreement with the presence of water molecules in the X-ray structure of (S)-BPOH. When the carboxy group was not available for coordination with water, as in the methyl ester (S)-BPOHMe or in the dyads, this effect was prevented; accordingly, the fluorescence quantum yields did not depend on the presence or absence of water. The fluorescence lifetimes in dry acetonitrile were 1.67, 0.95 and 0.46 ns for (S)-BPOH, (S, S)-1 and (S, R)-1, respectively, indicating that the observed quenching is indeed dynamic. In line with the steady-state and time-resolved observations, molecular modelling pointed to a more favourable geometric arrangement of the two interacting chromophores in (S, R)-1. Interestingly, this dyad exhibited a folded conformation in the solid state.

Excited-state interactions between (S)- or (R) fluorescence (S)- or (R)-FBP) and thymidine (dThd) covalently linked in dyads 1 or 2 have been investigated. In both dyads, the only emitting species is (FBP)-F-1*, but with a lower fluorescence quantum yield (phi(F)) and a shorter fluorescene lifetime (tau(F)) than when free in solution. These an results indicate that dynamic quenching occurs either by electron transfer or via exciplex formation, with FBP as the charge-donating species. In acetonitrile, both mechanisms are favored, while in dioxane exciplex formation is predominating. Isomer 1 displays lower values of OF and rF than its analogue 2, indicating that the relative spatial arrangement of the chromophores plays a significant role. The triplet quantum yields (0-F) of 1 and 2 are significantly higher than the expectations based solely on 'FBP* dThd intersystem crossing quantum yields (Oisc), with OT (1) > OT (2). This can be explained in terms of intramolecular charge recombination at the radical ion pairs and/or the exciplexes, which would be again dependent on geometrical factors. The triplet lifetimes (IT) of 3FBP* dThd and free 3FBP* are similar, indicating the lack of excited-state interactions at this stage. The FBP dThd dyads could, in principle, constitute appropriate model systems for the elucidation of the excited-state interactions in noncovalent DNA ligand complexes.

Excited-state interactions between (S)- or (R) fluorescence (S)- or (R)-FBP) and thymidine (dThd) covalently linked in dyads 1 or 2 have been investigated. In both dyads, the only emitting species is (FBP)-F-1*, but with a lower fluorescence quantum yield (phi(F)) and a shorter fluorescene lifetime (tau(F)) than when free in solution. These an results indicate that dynamic quenching occurs either by electron transfer or via exciplex formation, with FBP as the charge-donating species. In acetonitrile, both mechanisms are favored, while in dioxane exciplex formation is predominating. Isomer 1 displays lower values of OF and rF than its analogue 2, indicating that the relative spatial arrangement of the chromophores plays a significant role. The triplet quantum yields (0-F) of 1 and 2 are significantly higher than the expectations based solely on 'FBP* dThd intersystem crossing quantum yields (Oisc), with OT (1) > OT (2). This can be explained in terms of intramolecular charge recombination at the radical ion pairs and/or the exciplexes, which would be again dependent on geometrical factors. The triplet lifetimes (IT) of 3FBP* dThd and free 3FBP* are similar, indicating the lack of excited-state interactions at this stage. The FBP dThd dyads could, in principle, constitute appropriate model systems for the elucidation of the excited-state interactions in noncovalent DNA ligand complexes.

As the dimensions of a conductor approach the nanoscale, quantum effects begin to dominate, and it becomes possible to control the conductance through direct manipulation of the electron wavefunction. Such control has been demonstrated in various mesoscopic devices at cryogenic temperatures(1-4), but it has proved to be difficult to exert control over the wavefunction at higher temperatures. Molecules have typical energy level spacings (similar to eV) that are much larger than the thermal energy at 300 K (similar to 25 meV), and are therefore natural candidates for such experiments. Previously, phenomena such as giant magnetoresistance(5), Kondo effects(6) and conductance switching(7-11) have been observed in single molecules, and theorists have predicted that it should also be possible to observe quantum interference in molecular conductors(12-18), but until now all the evidence for such behaviour has been indirect. Here, we report the observation of destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. We studied five different rigid p-conjugated molecular wires, all of which form self-assembled monolayers on a gold surface, and find that the degree of interference can be controlled by simple chemical modifications of the molecular wire.

The reactivity of [Fe-2(CO)(4)(kappa(2)-LL)(mu-pdt)](+) complexes (pdt = S(CH2)(3)S, propanedithiolate) with different substrates L' (L' = CO, MeCN, P(OMe)(3)) was investigated electrochemically in order to assess the influence of the chelating ligand kappa(2)-LL (LL = I-Me-CH2-I-Me (1(+)), dppe (2(+)); I-Me = 1-methylimidazol-2-ylidene). This latter ligand is effectively shown to affect the reactivity of the cations in different ways: when L' = CO, the adduct [Fe-2(CO)(4)(mu-CO)(kappa(2)-dppe)(mu-pdt)](+) (2-CO+) was clearly observed by cyclic voltammetry, whereas [Fe-2(CO)(4)(mu-CO)(kappa(2)-I-Me-CH2-I-Me)(mu-pdt)](+) (1-CO+) was not detected, although DFT calculations show that the energies of the products and the activation barriers to their formation are similar. When L' = MeCN, the adducts X-MeCN+ with X = 1, 2 are both observed, but the formation is easier when LL = dppe. Finally, the reaction of [Fe-2(CO)(4)(kappa(2)-I-Me-CH2-I-Me)(mu-pdt)](+) (1(+)) with P(OMe)(3) produces the disubstituted dication [Fe-2(CO)(2){P(OMe)3}(2)(kappa(2)-I-Me-CH2-I-Me)(mu-CO)(mu-pdt)](2+) (4(2+)) via a disproportionation reaction, while previous studies demonstrated that monocationic derivatives were obtained when LL = dppe. Complex 4[PF6](2) was fully characterized, and its X-ray crystal structure confirms the presence of a carbonyl ligand in a bridging position, which did not exist in the related P(OMe)(3)-substituted kappa(2)-dppe cations.

[EN] The influence of ring size on the photobehaviour of condensed 1,4-naphthoquinone systems, such as pyrano-and furano-derivatives (1 and 2, respectively) has been investigated. The absorption spectra for both families of naphthoquinones reveal clear differences; in the case of 2 they extend to longer wavelengths. A solvatochromic red shift in polar solvents is consistent with the pi,pi* character of the S-0 -> S-1 electronic transition in all cases. Theoretical (B3LYP) analysis of the HOMO and LUMO Kohn-Sham molecular orbitals of the S-0 state indicates that they are pi and pi* in nature, consistent with the experimental observation. A systematic study on the efficiency of singlet oxygen generation by these 1,4-naphthoquinones is presented, and values larger than 0.7 were found in every case. In accordance with these results, laser flash photolysis of deoxygenated acetonitrile solutions led to the formation of detectable triplet transient species with absorptions at 390 and 450 nm (1) and at 370 nm (2), with phi(ISC) close to 1. Additionally, the calculated energies for the T-1 states relative to the S-0 states at UB3LYP/6-311++G** are ca. 47 kcal mol(-1) for 1 and 43 kcal mol(-1) for 2. A comparison of the geometrical parameters for the S-0 and T-1 states reveals a marked difference with respect to the arrangement of the exocyclic phenyl ring whilst a comparison of electronic parameters revealed the change from a quinone structure to a di-dehydroquinone diradical structure.

[EN] The influence of ring size on the photobehaviour of condensed 1,4-naphthoquinone systems, such as pyrano-and furano-derivatives (1 and 2, respectively) has been investigated. The absorption spectra for both families of naphthoquinones reveal clear differences; in the case of 2 they extend to longer wavelengths. A solvatochromic red shift in polar solvents is consistent with the pi,pi* character of the S-0 -> S-1 electronic transition in all cases. Theoretical (B3LYP) analysis of the HOMO and LUMO Kohn-Sham molecular orbitals of the S-0 state indicates that they are pi and pi* in nature, consistent with the experimental observation. A systematic study on the efficiency of singlet oxygen generation by these 1,4-naphthoquinones is presented, and values larger than 0.7 were found in every case. In accordance with these results, laser flash photolysis of deoxygenated acetonitrile solutions led to the formation of detectable triplet transient species with absorptions at 390 and 450 nm (1) and at 370 nm (2), with phi(ISC) close to 1. Additionally, the calculated energies for the T-1 states relative to the S-0 states at UB3LYP/6-311++G** are ca. 47 kcal mol(-1) for 1 and 43 kcal mol(-1) for 2. A comparison of the geometrical parameters for the S-0 and T-1 states reveals a marked difference with respect to the arrangement of the exocyclic phenyl ring whilst a comparison of electronic parameters revealed the change from a quinone structure to a di-dehydroquinone diradical structure.

Triplet-mediated pyrimidine (Pyr) dimerisation is a key process in photochemical damage to DNA. It may occur in the presence of a photosensitiser, provided that a number of requirements are fulfilled, such as favourable intersystem crossing quantum yield and high triplet energy. The attention has been mainly focused on cyclobutane pyrimidine dimers, as they are by far the most relevant Pyr photoproducts obtained by sensitisation. The present perspective deals with the involved chemistry, not only in DNA but also in its simple building blocks. It also includes the photophysical characterisation of the Pyr triplet excited states, as well as a brief discussion of the theoretical aspects.

Cytochrome P450 monooxygenases are valuable biocatalysts due to their ability to hydroxylate unactivated carbon atoms using molecular oxygen. We have cloned the gene for a new cytochrome P450 monooxygenase, named CYP154H1, from the moderately thermophilic soil bacterium Thermobifida fusca. The enzyme was overexpressed in Escherichia coli at up to 14% of total soluble protein and purified to homogeneity in three steps. CYP154H1 activity was reconstituted using putidaredoxin reductase and putidaredoxin from Pseudomonas putida DSM 50198 as surrogate electron transfer partners. In biocatalytic reactions with different aliphatic and aromatic substrates of varying size, the enzyme converted small aromatic and arylaliphatic compounds like ethylbenzene, styrene, and indole. Furthermore, CYP154H1 also accepted different arylaliphatic sulfides as substrates chemoselectively forming the corresponding sulfoxides and sulfones. The enzyme is moderately thermostable with an apparent melting temperature of 67A degrees C and exhibited still 90% of initial activity after incubation at 50A degrees C.

The interesting structural, electronic, and optical properties of DNA provide fascinating opportunities for developing nanoscale smart materials by integrating DNA with opto-electronic components. In this article we demonstrate the electrostatic binding of an amine-terminated dithienylethene (DET) molecular switch to double-stranded synthetic polynucleotides. The DET switch can undergo photochemical ring-closure and opening reactions. Circular dichroism (CD) and UV-vis spectroscopy show that both the open, 1o, and the closed, 1c, forms of the switch bind to DNA. Upon addition of DNA to a solution of 1o or 1c, the UV-vis spectrum displays a hypochromic effect, indicative of an interaction between the switch and the DNA. The chirality of the DNA double helix is transmitted to the switching unit which displays a well-defined CD signal upon supramolecular complexation to the DNA. Additionally, the CD signal of the DNA attenuates, demonstrating that both components of the complex mutually influence each other's structure; the DNA induces chirality in the switch, and the switch modifies the structure of the DNA. Modulation of the chiroptical properties of the complex is achieved by photochemically switching the DET between its ring open and closed isomers. A pH dependence study of the binding shows that when the pH is increased the switches lose their binding ability, indicating that electrostatic interactions between protonated amines and the negatively charged phosphate backbone are the dominant driving force for binding to the DNA. A comparison of poly(deoxyguanylic-deoxycytidylic) acid [poly(dGdC)(2)] polynucleotides with poly(deoxyadenylic-deoxythymidylic) acid [poly(dAdT)(2)] shows distinct differences in the CD spectra of the complexes.

A series of new tetrathiafulvalene (TTF) derivatives bearing dimethoxycarbonyl and phenyl or phthalimidyl groups fused to the TTF core (6 and 15-18) has been synthesized as potential soluble semiconductor materials for organic field-effect transistors (OFETs). The electron-withdrawing substituents lower the energy of the HOMO and LUMO levels and increase the solubility and stability of the semiconducting material. Crystal structures of all new TTF derivatives are also described, and theoretical DFT calculations were carried out to study the potential of the crystals to be used in OFET. In the experimental study, the best performing device exhibited a hole mobility up to 7.5 × 10-3 cm2 V-1 s-1). © 2010 American Chemical Society.

A stable 1 : 1 : 1 inclusion complex of Ru(bpy)(3)-phenol (1), MV2+ and cucurbit[8]uril (CB[8]) is formed in aqueous solution. In the presence of triethanolamine (TEOA), a light-induced formation of unusual partner radical trimer 1-(MV+center dot)(2)-CB[8] has been observed for the first time., QC 20100525

We present an electron spin resonance (ESR) study at excitation frequencies of 9.4 and 222.4 GHz of powders and single crystals of a Prussian blue analog (PBA), RbMn[Fe(CN)(6)]center dot H2O in which Fe and Mn undergoes a charge-transfer transition between 175 and 300 K. The ESR of PBA powders, also reported by Pregelj et al. [J. Magn. Magn. Mater. 316, e680 (2007)], is assigned to cubic magnetic clusters of Mn2+ ions surrounding Fe (CN)(6) vacancies. The clusters are well isolated from the bulk and are superparamagnetic below 50 K. In single crystals, various defects with lower symmetry are also observed. Spin-lattice relaxation broadens the bulk ESR beyond observability. This strong spin relaxation is unexpected above the charge-transfer transition and is attributed to a mixing of the Mn3+-Fe2+ state into the prevalent Mn2+-Fe3+ state.

Dynamic control over the formation of H- or J-type aggregates of chromophores is of fundamental importance for developing responsive organic optoelectronic materials. In this study, the first example of photoswitching between a nonstacked and an intramolecularly H-stacked arrangement of perylenebisimides (PBI) is demonstrated. The system is composed of a central switching unit (overcrowded alkene) tethered to two PBI chromophores. cis-trans isomerization of the switching unit, induced by alternate irradiation at 312 and 365 nm, can drive two PBI chromophores reversibly between an intramolecularly "aggregated" and "nonaggregated" state. Distinct changes in UV-vis absorption and fluorescence spectra are observed following photoisomerization. This approach allows for efficient control of intramolecular H-stack formation with no significant intermolecular interactions spanning over at least 4 orders of magnitude of concentration (from 10(-8) to 10(-4) M) and a range of solvents and temperatures.

Anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) is assumed to be a syntrophic process, in which methanotrophic archaea produce an interspecies electron carrier (IEC), which is subsequently utilized by sulfate-reducing bacteria. In this paper, six methanogenic substrates are tested as candidate-IECs by assessing their effect on AOM and SR by an anaerobic methanotrophic enrichment. The presence of acetate, formate or hydrogen enhanced SR, but did not inhibit AOM, nor did these substrates trigger methanogenesis. Carbon monoxide also enhanced SR but slightly inhibited AOM. Methanol did not enhance SR nor did it inhibit AOM, and methanethiol inhibited both SR and AOM completely. Subsequently, it was calculated at which candidate-IEC concentrations no more Gibbs free energy can be conserved from their production from methane at the applied conditions. These concentrations were at least 1,000 times lower can the final candidate-IEC concentration in the bulk liquid. Therefore, the tested candidate-IECs could not have been produced from methane during the incubations. Hence, acetate, formate, methanol, carbon monoxide, and hydrogen can be excluded as sole IEC in AOM coupled to SR. Methanethiol did inhibit AOM and can therefore not be excluded as IEC by this study

Desulfovibrio vulgaris is a metabolically flexible micro-organism. It can use sulfate as an electron acceptor to catabolize a variety of substrates, or in the absence of sulfate can utilize organic acids and alcohols by forming a syntrophic association with a hydrogen-scavenging partner to relieve inhibition by hydrogen. These alternative metabolic types increase the chance of survival for D. vulgaris in environments where one of the potential external electron acceptors becomes depleted. In this work, whole-genome D. vulgaris microarrays were used to determine relative transcript levels as D. vulgaris shifted its metabolism from syntrophic in a lactate-oxidizing dual-culture with Methanosarcina barkeri to a sulfidogenic metabolism. Syntrophic dual-cultures were grown in two independent chemostats and perturbation was introduced after six volume changes with the addition of sulfate. The results showed that 132 genes were differentially expressed in D. vulgaris 2 h after addition of sulfate. Functional analyses suggested that genes involved in cell envelope and energy metabolism were the most regulated when comparing syntrophic and sulfidogenic metabolism. Upregulation was observed for genes encoding ATPase and the membrane-integrated energy-conserving hydrogenase (Ech) when cells shifted to a sulfidogenic metabolism. A five-gene cluster encoding several lipoproteins and membrane-bound proteins was downregulated when cells were shifted to a sulfidogenic metabolism. Interestingly, this gene cluster has orthologues found only in another syntrophic bacterium, Syntrophobacter fumaroxidans, and four recently sequenced Desulfovibrio strains. This study also identified several novel c-type cytochrome-encoding genes, which may be involved in the sulfidogenic metabolism

In this article, three truexene-based dyes with 2-cyanoacrylic acid as acceptor and starburst triarylamine as donor (S5, S6, and S7) were conveniently synthesized and used for dye-sensitized solar cells (DSSCs). A compact sensitizer layer is molecular interfacially engineered on the TiO2 surface via cone-shaped sensitizers. As a result, the approach of the electrolyte to the TiO2 surface is blocked significantly by the compact sensitizer layer formed and the charge recombination in the DSSCs is proved to be retarded effectively. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is near 90%. In addition, S7-sensitized solar cells yield an open-circuit voltage of 752 mV and it fill factor of 0.70, which are even higher than those of N719 under the same conditions., QC 20110415

The dye-sensitized solar cell (DSC) is a promising efficient low-cost molecular photovoltaic device. One of the key components in DSCs is the dye, as it is responsible for the capture of sunlight. State-of-the-art DSC devices, based on ruthenium dyes, show record efficiencies of 10-12 %. During the last decade, metal-free organic dyes have been extensively explored as sensitizers for DSC application. The use of organic dyes is particularly attractive as it enables easy structural modifications, due to fairly short synthetic routes and reduced material cost. Novel dye should in addition to the light-harvesting properties also be compatible with the DSC components. In this thesis, a series of new organic dyes are investigated, both when integrated in the DSC device and as individual components. The evaluation methods consisted of different electrochemical and photoelectrochemical techniques. Whereas the light-harvesting properties of the dyes were fairly easily improved, the behavior of the dye integrated in the DSC showed less predictable photovoltaic results. The dye series studied in Papers II and IV revealed that their dye energetics limited vital electron-transfer processes, the dye regeneration (Paper II) and injection quantum yield (Paper IV). Further, in Papers III-VI, it was observed that different dye structures seemed to alter the interfacial electron recombination with the electrolyte. In addition to the dye structure sterics, some organic dyes appear to enhance the interfacial recombination, possibly due to specific dye-redox acceptor interaction (Paper V). The impact of dye sterical modifications versus the use of coadsorbent was explored in Paper VI. The dye layer properties in the presence and absence of various coadsorbents were further investigated in Paper VII. The core of this thesis is the identification of the processes and properties limiting the performance of the DSC device, aiming at an overall understanding of the compatibility between the D, QC 20100730

The dye-sensitized solar cell (DSC) is a promising efficient low-cost molecular photovoltaic device. One of the key components in DSCs is the dye, as it is responsible for the capture of sunlight. State-of-the-art DSC devices, based on ruthenium dyes, show record efficiencies of 10-12 %. During the last decade, metal-free organic dyes have been extensively explored as sensitizers for DSC application. The use of organic dyes is particularly attractive as it enables easy structural modifications, due to fairly short synthetic routes and reduced material cost. Novel dye should in addition to the light-harvesting properties also be compatible with the DSC components. In this thesis, a series of new organic dyes are investigated, both when integrated in the DSC device and as individual components. The evaluation methods consisted of different electrochemical and photoelectrochemical techniques. Whereas the light-harvesting properties of the dyes were fairly easily improved, the behavior of the dye integrated in the DSC showed less predictable photovoltaic results. The dye series studied in Papers II and IV revealed that their dye energetics limited vital electron-transfer processes, the dye regeneration (Paper II) and injection quantum yield (Paper IV). Further, in Papers III-VI, it was observed that different dye structures seemed to alter the interfacial electron recombination with the electrolyte. In addition to the dye structure sterics, some organic dyes appear to enhance the interfacial recombination, possibly due to specific dye-redox acceptor interaction (Paper V). The impact of dye sterical modifications versus the use of coadsorbent was explored in Paper VI. The dye layer properties in the presence and absence of various coadsorbents were further investigated in Paper VII. The core of this thesis is the identification of the processes and properties limiting the performance of the DSC device, aiming at an overall understanding of the compatibility between the D, QC 20100730

The active center of Chlamydia trachomatis (Ct) ribonucleotide reductase (RNR) has been studied using B3LYP hybrid density functional theory. Class Ic Ct RNR lacks the radical-bearing tyrosine that is crucial for activity in conventional class I (subclass a and b) RNR. Instead of the Fe(III)Fe(III)Tyr(rad) active state in conventional class I, Ct RNR has Mn(IV)Fe(III) at the metal center of subunit H. Based on calculated (H+, e(-))-binding energies for Ct R2, iron-substituted Ct R2, and R2 from Escherichia coli (Ec), an explanation is proposed for why the enzyme needs this novel metal center. Mn(IV) is shown to be an equally strong oxidant as the tyrosyl radical in Ec R2. Fe(IV), however, is a much too strong oxidant and would therefore not be possible in the active cofactor. The structure of the catalytic center of the active state, such as protonation state and position of Mn, is discussed. Ct R2 has a different ligand structure than conventional class I R2 with a fourth Glu (like MMO) instead of three Glu and one Asp. Calculations indicate that, in the presence of Tyr, Glu at this position is less flexible than Asp, whereas with Phe both Glu and Asp are equally flexible. This may be a reason why conventional class I RNR has an Asp, while Ct R2, lacking the tyrosine, has a Glu., authorCount :2

The dye-sensitized solar cell (DSC) is a promising efficient low-cost molecular photovoltaic device. One of the key components in DSCs is the dye, as it is responsible for the capture of sunlight. State-of-the-art DSC devices, based on ruthenium dyes, show record efficiencies of 10-12 %. During the last decade, metal-free organic dyes have been extensively explored as sensitizers for DSC application. The use of organic dyes is particularly attractive as it enables easy structural modifications, due to fairly short synthetic routes and reduced material cost. Novel dye should in addition to the light-harvesting properties also be compatible with the DSC components. In this thesis, a series of new organic dyes are investigated, both when integrated in the DSC device and as individual components. The evaluation methods consisted of different electrochemical and photoelectrochemical techniques. Whereas the light-harvesting properties of the dyes were fairly easily improved, the behavior of the dye integrated in the DSC showed less predictable photovoltaic results. The dye series studied in Papers II and IV revealed that their dye energetics limited vital electron-transfer processes, the dye regeneration (Paper II) and injection quantum yield (Paper IV). Further, in Papers III-VI, it was observed that different dye structures seemed to alter the interfacial electron recombination with the electrolyte. In addition to the dye structure sterics, some organic dyes appear to enhance the interfacial recombination, possibly due to specific dye-redox acceptor interaction (Paper V). The impact of dye sterical modifications versus the use of coadsorbent was explored in Paper VI. The dye layer properties in the presence and absence of various coadsorbents were further investigated in Paper VII. The core of this thesis is the identification of the processes and properties limiting the performance of the DSC device, aiming at an overall understanding of the compatibility between the D, QC 20100730