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Laccases (EC 1.10.3.2) are multicopper oxidases with the capability to oxidize diverse phenolic and non-phenolic substrates. While the molecular mechanism of their activity towards phenolic substrates is well-established, their reactivity towards non-phenolic substrates, such as polycyclic aromatic hydrocarbons (PAHs), remains unclear. To elucidate the oxidation mechanism of PAHs, particularly the activation mechanism of the sp2 aromatic C–H bond, we conducted a density functional theory investigation on the oxidation of two PAHs (anthracene and benzo[a]pyrene) using an extensive model of the T1 copper catalytic site of the fungal laccase from Trametes versicolor. [ABSTRACT FROM AUTHOR]

Aims Neocosmospora species are saprobes, endophytes, and pathogens belonging to the family Nectriaceae. This study aims to investigate the taxonomy, biosynthetic potential, and application of three newly isolated Neocosmospora species from mangrove habitats in the southern part of Thailand using phylogeny, bioactivity screening, genome sequencing, and bioinformatics analysis. Methods and results Detailed descriptions, illustrations, and a multi-locus phylogenetic tree with large subunit ribosomal DNA (LSU), internal transcribed spacer (ITS), translation elongation factor 1-alpha (ef1-α), and RNA polymerase II second largest subunit (RPB2) regions showing the placement of three fungal strains, MFLUCC 17–0253, MFLUCC 17–0257, and MFLUCC 17–0259 clustered within the Neocosmospora clade with strong statistical support. Fungal crude extracts of the new species N. mangrovei MFLUCC 17–0253 exhibited strong antifungal activity to control Colletotrichum truncatum CG-0064, while N. ferruginea MFLUCC 17–0259 exhibited only moderate antifungal activity toward C. acutatum CC-0036. Thus, N. mangrovei MFLUCC 17–0253 was sequenced by Oxford nanopore technology. The bioinformatics analysis revealed that 49.17 Mb genome of this fungus harbors 41 potential biosynthetic gene clusters. Conclusion Two fungal isolates of Neocosmospora and a new species of N. mangrovei were reported in this study. These fungal strains showed activity against pathogenic fungi causing anthracnose in chili. In addition, full genome sequencing and bioinformatics analysis of N. mangrovei MFLUCC 17–0253 were obtained. [ABSTRACT FROM AUTHOR]

Sodium chloride (NaCl) represents the principal component of atmospheric particulates of marine origin. To gain a molecular-level understanding of the adsorption process of water vapor on the NaCl surface, Monte Carlo simulations performed in the Grand Canonical ensemble were carried out, considering the water adsorption at different water pressures on a NaCl(001) surface. The calculated adsorption isotherm shows four different regions, whose coverages correspond to those of the low-, transition-, high-, and pre-solution-coverage regions experimentally observed. Detailed analysis reveals how the structure of the adsorbed water molecules (islands, layer, and multi-layer) changes depending on water pressure, and how their orientation with respect to the surface varies with the distance from the surface. This detailed information further supports the picture coming from previous experimental IR absorption spectroscopy studies. [ABSTRACT FROM AUTHOR]

Nitrogen gas is a highly inert molecule and its activation under mild conditions represents a crucial goal in current research. In a recent study, the discovery of low-valence Ca(I) compounds capable of coordinating and reducing N2 was reported [B. Rösch, T. X. Gentner, J. Langer, C. Färber, J. Eyselein, L. Zhao, C. Ding, G. Frenking and S. Harder, Science, 2021, 371, 1125]. The study of low-valence alkaline earth complexes represents a new horizon in inorganic chemistry and demonstrates examples of spectacular reactivity. For example, complexes of the [BDI]2Mg2 type are selective reducing reagents in both organic and inorganic synthesis reactions. To date, however, no activity of Mg(I) complexes in the activation of the nitrogen molecule has been reported. By computational studies, in the present work, we investigated the analogies and differences of low-valence Ca(I) and Mg(I) complexes in the coordination, activation and protonation of N2. We have shown that the possibility of alkaline earth metals to employ atomic orbitals of the d type is reflected in the differences in the N2 binding energy and its coordination mode (end-on vs. side-on), as well as in the spin state of the resulting adduct (singlet vs. triplet). These divergences are finally observed in the subsequent protonation reaction, which turned out to be prohibitive in the presence of Mg. [ABSTRACT FROM AUTHOR]

Molecular modeling techniques have become indispensable in many fields of molecular sciences in which the details related to mechanisms and reactivity need to be studied at an atomistic level. This review article provides a collection of computational modeling works on a topic of enormous interest and urgent relevance: the properties of metalloenzymes involved in the degradation and valorization of natural biopolymers and synthetic plastics on the basis of both circular biofuel production and bioremediation strategies. In particular, we will focus on lytic polysaccharide monooxygenase, laccases, and various heme peroxidases involved in the processing of polysaccharides, lignins, rubbers, and some synthetic polymers. Special attention will be dedicated to the interaction between these enzymes and their substrate studied at different levels of theory, starting from classical molecular docking and molecular dynamics techniques up to techniques based on quantum chemistry. [ABSTRACT FROM AUTHOR]

Tailoring the activity of an organometallic catalyst usually requires a targeted ligand design. Tuning the ligand bulkiness and tuning the electronic properties are popular approaches, which are somehow interdependent because substituents of different sizes within ligands can determine inter alia the occurrence of different degrees of inductive effects. Ligand basicity, in particular, turned out to be a key property for the modulation of protonation reactions occurring in vacuo at the metals in complexes bearing organophosphorus ligands; however, when the same reactions take place in a polar organic solvent, their energetics becomes dependent on the trade-off between ligand basicity and bulkiness, with the polarity of the solvent playing a key role in this regard [Bancroft et al., Inorg. Chem., 1986, 25, 3675; Rovaletti et al., J. Phys. Org. Chem., 2018, 31, e3748]. In the present contribution, we carried out molecular dynamics and density functional theory calculations on water-soluble Mo-based catalysts for proton reduction, in order to study the energetics of protonation reactions in complexes where the incipient proton binds a catalytically active ligand (i.e., an oxide or a disulphide). We considered complexes either soaked in water or in a vacuum, and featuring N-based ancillary ligands of different bulkiness (i.e. cages constituted either by pyridine or isoquinoline moieties). Our results show that the energetics of protonation events can be affected by ancillary ligand bulkiness even when the metal center does not play the role of the H+ acceptor. In vacuo, protonation at the O or S atom in the α position relative to the metal in complexes featuring the bulky isoquinoline-based ligand is more favored by around 10 kcal mol−1 when compared to the case of the pyridine-based counterparts, a difference that is almost zero when the same reactions occur in water. Such an outcome is rationalized in light of the different electrostatic properties of complexes bearing ancillary ligands of different sizes. The overall picture from theory indicates that such effects of ligand bulkiness can be relevant for the design of green chemistry catalysts that undergo protonation steps in water solutions. [ABSTRACT FROM AUTHOR]

The photogeneration of electricity and solar fuels by solar irradiation in photoelectrochemical cells is one of the sectors with the highest growth potential in the decarbonised society. However, the use of different components, in particular photosensitizers and catalysts, can present problems of charge transfer efficiency at the interface, leading to lower final efficiencies. In this work we present novel integrated photosensitizer‐catalyst dyads based on robust and, at the same time, flexible host‐guest non‐covalent interactions through the use of calix[4]arene cavities. Current photogeneration in photoelectrochemical cells showed twice greater efficiency in the integrated calixarene‐based host‐guest dyads compared to the traditional architecture based on the separate photosensitizer‐catalyst pair. Molecular dynamics studies have shown that the enhanced performance originates from an optimization of the distances between the centres of the photosensitizer, catalyst and semiconductor involved in the charge transfer processes, thus allowing a higher final efficiency of the charge photogeneration process. [ABSTRACT FROM AUTHOR]

The genomes of many filamentous fungi, such as Aspergillus spp., include diverse biosynthetic gene clusters of unknown function. We previously showed that low copper levels upregulate a gene cluster that includes crmA, encoding a putative isocyanide synthase. Here we show, using untargeted comparative metabolomics, that CrmA generates a valine-derived isocyanide that contributes to two distinct biosynthetic pathways under copper-limiting conditions. Reaction of the isocyanide with an ergot alkaloid precursor results in carbon-carbon bond formation analogous to Strecker amino-acid synthesis, producing a group of alkaloids we term fumivalines. In addition, valine isocyanide contributes to biosynthesis of a family of acylated sugar alcohols, the fumicicolins, which are related to brassicicolin A, a known isocyanide from Alternaria brassicicola. CrmA homologs are found in a wide range of pathogenic and non-pathogenic fungi, some of which produce fumicicolin and fumivaline. Extracts from A. fumigatus wild type (but not crmA-deleted strains), grown under copper starvation, inhibit growth of diverse bacteria and fungi, and synthetic valine isocyanide shows antibacterial activity. CrmA thus contributes to two biosynthetic pathways downstream of trace-metal sensing. The genomes of filamentous fungi, such as Aspergillus, include many biosynthetic gene clusters of unknown function. Here, the authors show that copper starvation induces expression of an enzyme that generates a valine-derived isocyanide participating in two different pathways, for biosynthesis of acylated sugar alcohols and modified ergot alkaloids. [ABSTRACT FROM AUTHOR]

The photon upconversion based on triplet–triplet annihilation (TTA) is a mechanism that converts the absorbed low-energy electromagnetic radiation into higher energy photons also at extremely low excitation intensities, but its use in actual technologies is still hindered by the limited availability of efficient annihilator moieties. We present here the results obtained by the synthesis and application of two new fluorinated chromophores based on phenazine and acridine structures, respectively. Both compounds show upconverted emission demonstrating their ability as TTA annihilator. More interesting, the acridine-based chromophore shows an excellent TTA yield that overcomes the one of some of best model systems. By correlating the experimental data and the quantum mechanical modeling of the investigated compound, we propose an alternative efficient pathway for the generation of the upconverted emissive states involving the peculiar high-energy triplet levels of the dye, thus suggesting a new development strategy for TTA annihilators based on the fine tuning of their high-energy excited states properties. [ABSTRACT FROM AUTHOR]

Many fungi develop both asexual and sexual spores that serve as propagules for dissemination and/or recombination of genetic traits. Asexual spores are often heavily pigmented and this pigmentation provides protection from UV light. However, little is known about any purpose pigmentation that may serve for sexual spores. The model Ascomycete Aspergillus nidulans produces both green pigmented asexual spores (conidia) and red pigmented sexual spores (ascospores). Here we find that the previously characterized red pigment, asperthecin, is the A. nidulans ascospore pigment. The asperthecin biosynthetic gene cluster is composed of three genes: aptA, aptB, and aptC, where deletion of either aptA (encoding a polyketide synthase) or aptB (encoding a thioesterase) yields small, mishappen hyaline ascospores; while deletion of aptC (encoding a monooxygenase) yields morphologically normal but purple ascospores. ∆aptA and ∆aptB but not ∆aptC or wild type ascospores are extremely sensitive to UV light. We find that two historical ascospore color mutants, clA6 and clB1, possess mutations in aptA and aptB sequences, respectively. [ABSTRACT FROM AUTHOR]

Fungi produce a wealth of pharmacologically bioactive secondary metabolites (SMs) from biosynthetic gene clusters (BGCs). It is common practice for drug discovery efforts to treat species' secondary metabolomes as being well represented by a single or a small number of representative genomes. However, this approach misses the possibility that intraspecific population dynamics, such as adaptation to environmental conditions or local microbiomes, may harbor novel BGCs that contribute to the overall niche breadth of species. Using 94 isolates of Aspergillus flavus, a cosmopolitan model fungus, sampled from seven states in the United States, we dereplicate 7,821 BGCs into 92 unique BGCs. We find that more than 25% of pangenomic BGCs show population-specific patterns of presence/absence or protein divergence. Population-specific BGCs make up most of the accessory-genome BGCs, suggesting that different ecological forces that maintain accessory genomes may be partially mediated by population-specific differences in secondary metabolism. We use ultra-high-performance high-resolution mass spectrometry to confirm that these genetic differences in BGCs also result in chemotypic differences in SM production in different populations, which could mediate ecological interactions and be acted on by selection. Thus, our results suggest a paradigm shift that previously unrealized population-level reservoirs of SM diversity may be of significant evolutionary, ecological, and pharmacological importance. Last, we find that several population-specific BGCs from A. flavus are present in Aspergillus parasiticus and Aspergillus minisclerotigenes and discuss how the microevolutionary patterns we uncover inform macroevolutionary inferences and help to align fungal secondary metabolism with existing evolutionary theory. [ABSTRACT FROM AUTHOR]

The MoCu CO dehydrogenase enzyme not only transforms CO into CO2 but it can also oxidise H2. Even if its hydrogenase activity has been known for decades, a debate is ongoing on the most plausible mode for the binding of H2 to the enzyme active site and the hydrogen oxidation mechanism. In the present work, we provide a new perspective on the MoCu-CODH hydrogenase activity by improving the in silico description of the enzyme. Energy refinement—by means of the BigQM approach—was performed on the intermediates involved in the dihydrogen oxidation catalysis reported in our previously published work (Rovaletti, et al. "Theoretical Insights into the Aerobic Hydrogenase Activity of Molybdenum–Copper CO Dehydrogenase." Inorganics 7 (2019) 135). A suboptimal description of the H2–HN(backbone) interaction was observed when the van der Waals parameters described in previous literature for H2 were employed. Therefore, a new set of van der Waals parameters is developed here in order to better describe the hydrogen–backbone interaction. They give rise to improved binding modes of H2 in the active site of MoCu CO dehydrogenase. Implications of the resulting outcomes for a better understanding of hydrogen oxidation catalysis mechanisms are proposed and discussed. [ABSTRACT FROM AUTHOR]

This perspective aims at illustrating a computational viewpoint on some specific issues concerning structure–activity relationships related to [FeFe]-hydrogenase ([FeFe]-H2ase) biomimicry. Most of the research outlined herein has been addressed by means of density functional theory (DFT) based tools, in some cases in conjunction with experimental techniques. The number of computational, experimental and mixed approach studies on the "hydrogenase models" topic is extraordinarily high. Accordingly, several comprehensive reviews have been published over the last twenty years. Moreover, the number of iron compounds of increasing nuclearity that have been considered as "biomimetic models" of [FeFe]-H2ase has grown exponentially over time. Additionally, the issues regarding some mismatches existing between the natural system and related synthetic analogues, are quite variegated. As a consequence of the countless examples that could be considered as related to "hydrogenase mimicry", the intent of the present contribution is to provide an account of a limited number of recent study cases, in which DFT has been employed to elucidate redox properties, reactivity issues of selected examples of diiron biomimicry. Herein the treated topics have been explicitly chosen to show how DFT has allowed us to rationalize and complement experimental observations, with a special focus on electrocatalysis aspects. Finally, the specific purpose of this perspective is to show how mutually intertwined are the various issues concerning a fascinating branch of biomimetic research. [ABSTRACT FROM AUTHOR]

Filamentous fungi differentiate along complex developmental programs directed by abiotic and biotic signals. Currently, intrinsic signals that govern fungal development remain largely unknown. Here we show that an endogenously produced and secreted fungal oxylipin, 5,8-diHODE, induces fungal cellular differentiation, including lateral branching in pathogenic Aspergillus fumigatus and Aspergillus flavus, and appressorium formation in the rice blast pathogen Magnaporthe grisea. The Aspergillus branching response is specific to a subset of oxylipins and is signaled through G-protein coupled receptors. RNA-Seq profiling shows differential expression of many transcription factors in response to 5,8-diHODE. Screening of null mutants of 33 of those transcription factors identifies three transcriptional regulators that appear to mediate the Aspergillus branching response; one of the mutants is locked in a hypo-branching phenotype, while the other two mutants display a hyper-branching phenotype. Our work reveals an endogenous signal that triggers crucial developmental processes in filamentous fungi, and opens new avenues for research on the morphogenesis of filamentous fungi. Fungi produce oxygenated fatty acids, or oxylipins, of unclear function. Here, Niu et al. show that an Aspergillus oxylipin induces various developmental processes in several fungi, including lateral branching in human pathogenic Aspergillus species, and appressorium formation in the plant pathogen Magnaporthe grisea. [ABSTRACT FROM AUTHOR]

For eukaryotes like fungi to regulate biological responses to environmental stimuli, various signalling cascades are utilized, like the highly conserved mitogen‐activated protein kinase (MAPK) pathways. In the model fungus Aspergillus nidulans, a MAPK pathway known as the pheromone module regulates development and the production of secondary metabolites (SMs). This pathway consists five proteins, the three kinases SteC, MkkB and MpkB, the adaptor SteD and the scaffold HamE. In this study, homologs of these five pheromone module proteins have been identified in the plant and human pathogenic fungus Aspergillus flavus. We have shown that a tetrameric complex consisting of the three kinases and the SteD adaptor is assembled in this species. It was observed that this complex assembles in the cytoplasm and that MpkB translocates into the nucleus. Deletion of steC, mkkB, mpkB or steD results in abolishment of both asexual sporulation and sclerotia production. This complex is required for the positive regulation of aflatoxin production and negative regulation of various SMs, including leporin B and cyclopiazonic acid (CPA), likely via MpkB interactions in the nucleus. These data highlight the conservation of the pheromone module in Aspergillus species, signifying the importance of this pathway in regulating fungal development and secondary metabolism. [ABSTRACT FROM AUTHOR]

A bisphosphide-bridged diiron hexacarbonyl complex 3 with NEt2 groups on the phosphide bridge was synthesized to examine a new proton relay system from the NEt2 group to the bridging hydride between the two iron centers. As a precursor of the bridging moiety, peri-Et2NP–PNEt2-bridged naphthylene 5 was synthesized by the reaction of 1,8-dilithionaphthylene with two equivalents of Cl2PNEt2 followed by reductive P–P bond formation by magnesium. The reaction of the diphosphine ligand 5 with Fe2(CO)9 gave the diiron hexacarbonyl complex 3, in which the P–P bond of the ligand was cleaved to form the bisphosphide-bridge. The molecular structure of 3 indicated that the trigonal plane of the NEt2 group was forced to face the Fe–Fe bond to avoid steric congestion with the naphthylene group linking the two phosphide groups. The NEt2 group could be protonated by p-toluenesulfonic acid. Density functional theory (DFT) calculations confirmed that the proton of the N(H)Et2 group adopted a position close to the bridging hydride. The DFT results for the ferrocene analogue 1, in which the 1,8-naphthylene group of 3 was replaced with the 1,1′-ferrocenylene group, also revealed that the most stable orientation of the protonated NHEt2 group was that in the protonated 3. As a result, electrochemical proton reduction reactions using complexes 1 and 3 proceeded with similar catalytic efficiencies. Unfortunately, the catalytic efficiencies (CEs) of these complexes were much lower than those of the complexes with a proton relay system of the terminal hydrogen, indicating that the reactive properties of the bridging hydride in the present proton relay system cannot exceed those of the terminal hydride. [ABSTRACT FROM AUTHOR]

The chemical groups present at the surface of graphite have been thought for a long time to be mainly responsible for its catalytic activity in the oxygen reduction reaction. Recently, it was proposed that the surface defects of graphite also significantly contribute to promote this reaction. Although the behaviour of surface defects has been reported, only few comments have been dedicated to their involvement in the mechanism and the possible intermediate species in the oxygen reduction reaction. Herein, we aim to present a more detailed explanation of the catalytic activity of graphite particles based on the structure of their defects and their size. Structural, spectroscopic and magnetic investigation (X-ray diffraction, Raman and electron spin resonance) and electrochemical measurements were performed to describe the nature of the defects and their aptitude to transfer electrons. Computational description supplied precise details of the energy of the different defects and their ability to promote the reduction, also suggesting the structure of the intermediate adduct in the oxygen reduction. The results indicated that molecular oxygen preferentially interacts with graphite defects, which involve the π-electron system and accumulation of the spin density on the edges of the grains, in particular, on the zig-zag edges present on ball-milled graphite. This promotes the reactivity of this nanomaterial. Furthermore, the activation increases by decreasing the particle size. [ABSTRACT FROM AUTHOR]

Catalytic H2 oxidation has been dissected by means of DFT into the key steps common to the Fe2 unit of both the [FeFe]‐hydrogenase cofactor and selected biomimics. The aim was to elucidate the molecular details underlying the very different performances of the two systems. We found that the better enzyme performance is based on a single iron atom that is maintained electron‐poor, favoring H2 binding, although embedded within a highly electron‐rich cofactor, ensuring a facile oxidation of the Fe2–H2 adduct. This is due to 1) CN− coordinating to both iron atoms, due to their amphipathic Lewis acid/base properties, and 2) the 4Fe4S subunit further withdrawing electrons from the Fe2 core. Preserving a moderate electron deficiency at a single iron also helps the cofactor preserve hydride affinity, which favors H2 cleavage. Such valuable characteristics allow the biocatalyst to turnover close to equilibrium conditions. All previous biomimicry has shown, in contrast, the impossibility to properly balance the two apparently contrasting aforementioned requisites, although evident progress has been made by the H2‐ase community. Disclosure of the differences identified could inspire the design of novel biomimics, for instance, reconsidering the use of CN− in the catalyst architecture. Indeed, in the presence of bases normally employed in oxidative catalysis, undesired stable protonation at coordinated CN−, which affects the opposite process (proton reduction), could be overcome. Nature versus biomimicry: Dissecting H2 oxidation by the [FeFe]‐H2ase core in comparison with a series of Fe2S2 models has revealed that CN− ligands and the 4Fe4S subunit are the key to the higher catalytic performance of the enzyme compared with the synthetic compounds. Indeed, cyanides and cubane provide a single electron‐poor iron (which assists H2 binding) embedded within an electron‐rich environment, which in turn ensures a facile subsequent oxidation. [ABSTRACT FROM AUTHOR]

In this paper, we propose a framework based on Hierarchical Reinforcement Learning for dialogue management in a Conversational Recommender System scenario. The framework splits the dialogue into more manageable tasks whose achievement corresponds to goals of the dialogue with the user. The framework consists of a meta-controller, which receives the user utterance and understands which goal should pursue, and a controller, which exploits a goal-specific representation to generate an answer composed by a sequence of tokens. The modules are trained using a two-stage strategy based on a preliminary Supervised Learning stage and a successive Reinforcement Learning stage. [ABSTRACT FROM AUTHOR]

The extraordinary capability of [NiFe]-hydrogenases to catalyse the reversible interconversion of protons and electrons into dihydrogen (H2) has stimulated numerous experimental and theoretical studies addressing the direct utilization of these enzymes in H2 production processes. Unfortunately, the introduction of these natural H2-catalysts in biotechnological applications is limited by their inhibition under oxidising (aerobic and anaerobic) conditions. With the aim of contributing to overcome this limitation, we studied the oxidative inactivation mechanism of [NiFe]-hydrogenases by performing Density Functional Theory (DFT) calculations on a very large model of their active site in which all the amino acids forming the first and second coordination spheres of the NiFe cluster have been explicitly included. We identified an O2 molecule and two H2O molecules as sources of the two oxygen atoms that are inserted at the active site of the inactive forms of the enzyme (Ni-A and Ni-B) under aerobic and anaerobic conditions, respectively. Furthermore, our results support the experimental evidence that the Ni-A-to-Ni-B ratio strongly depends on the number of reducing equivalents available for the process and on the oxidizing conditions under which the reaction takes place. [ABSTRACT FROM AUTHOR]

The present paper reports a study on the energetics of protonation of a hydrogenase biomimetic complex, [Fe2(μ-adt)(CO)4(PMe3)2] (adt = N-benzylazadithiolate), and of its homologue featuring triphenylphosphine ligands in place of trimethylphosphines. Formation of a terminal hydride on one of the Fe centres was considered first, given the key relevance of terminal hydride species in the enzymatic mechanism. Theoretical calculations highlight that, in a vacuum, terminal protonation of the selected Fe ion in the PPh3-bearing organometallic complex is highly favoured when compared to the analogous reaction involving the PMe3-containing species, but the trend is inverted in the case of models optimized in a continuum polarizable. An unexpected parallel is thus established between relative basicities of PPh3 and PMe3 in vacuum or in solution phase [C. A. Tolman, J. Am. Chem. Soc. 1970, 92, 2953; G. M. Bancroft, Inorg. Chem. 1986, 25, 3675], and the energetics of terminal hydride formation upon protonation of [FeFe]-hydrogenase biomimetic complexes bearing such organophosphorous ligands. Bridging hydride formation was also considered in the present study: calculations showed that protonation of the PMe3-bearing organometallic complex is again strongly favoured in vacuo, as compared to the case of the PPh3-containing model. However, protonation energies become significantly smaller when solvent effects are taken into account. Such differences between protonation reactions modelled in vacuo and in the polarizable continuum are rationalized in light of the different electrostatic properties of the diiron complexes here considered. Implications for the design and modelling of biomimetic catalysts are briefly discussed in light of recent literature. [ABSTRACT FROM AUTHOR]

The adduct between Tris[3-(trifluoromethylhydroxymethilene)-d-camphorate]europium(III) and 4,4'-Bis( N, N-dimethylamino)benzophenone (EABP) presents an absorption band in the visible region that the neat reagents do not display, making this system interesting as an antenna system devoted to an efficient absorption in the visible region. The UV-Vis spectroscopic properties of the reagents and the adduct have been determined by a combined experimental and theoretical investigation. The equilibrium constant of the adduct formation has been determined. The theoretical investigation, carried out in the framework of density functional theory and its time-dependent extension by using the PBE1PBE and B3-LYP hybrid functionals, allowed to nicely reproduce the features of the experimental spectra of the neat reagents and of the mixture and to propose an interpretation at the molecular level of the observed appearance of the absorption band for the adduct in the visible region: It originates from the redshift of the S → S transition observed in EABP-essentially deriving from the π → π* excitation-due to the energy stabilization of the LUMO of EABP consequent to the electrostatic interaction between the Eu ion and EABP in the adduct. [ABSTRACT FROM AUTHOR]

The Mo/Cu-dependent CO dehydrogenase from Oligotropha carboxidovorans is an enzyme that is able to catalyze CO oxidation to CO2; moreover, it can also oxidize H2, thus eliciting a characteristic EPR signal. Interestingly, the Ag-substituted enzyme form proved unable to catalyze H2 oxidation. In the present contribution, we characterized the reactivity of the enzyme with H2 by quantumchemical calculations. It was found that dihydrogen binding to the wild-type enzyme requires significant structural rearrangements of the active site Theoretical EPR spectra for plausible H2-bound models of the partially reduced, paramagnetic active site are also presented and compared with the experimental counterpart. Finally, density functional theory modeling shows that Ag substitution impairs H2 binding at the active site. [ABSTRACT FROM AUTHOR]

[NiFe]-hydrogenases catalyse the relevant H → 2H + 2e reaction. Aerobic oxidation or anaerobic oxidation of this enzyme yields two inactive states called Ni-A and Ni-B. These states differ for the reactivation kinetics which are slower for Ni-A than Ni-B. While there is a general consensus on the structure of Ni-B, the nature of Ni-A is still controversial. Indeed, several crystallographic structures assigned to the Ni-A state have been proposed, which, however, differ for the nature of the bridging ligand and for the presence of modified cysteine residues. The spectroscopic characterization of Ni-A has been of little help due to small differences of calculated spectroscopic parameters, which does not allow to discriminate among the various forms proposed for Ni-A. Here, we report a DFT investigation on the nature of the Ni-A state, based on systematic explorations of conformational and configurational space relying on accurate energy calculations, and on comparisons of theoretical geometries with the X-ray structures currently available. The results presented in this work show that, among all plausible isomers featuring various protonation patterns and oxygenic ligands, the one corresponding to the crystallographic structure recently reported by Volbeda et al. (J Biol Inorg Chem 20:11-22, 19)-featuring a bridging hydroxide ligand and the sulphur atom of Cys64 oxidized to bridging sulfenate-is the most stable. However, isomers with cysteine residues oxidized to terminal sulfenate are very close in energy, and modifications in the network of H-bond with neighbouring residues may alter the stability order of such species. [ABSTRACT FROM AUTHOR]

DFT calculations were used to investigate the cycloaddition reaction of CO2 to styrene oxide for the formation of styrene carbonate. The uncatalyzed process alongside the reactions assisted by tetrabutylammonium bromide (TBAB), the novel nonsymmetrical single-center aluminum(III) salen-acac hybrid complex (salenac) (Al1cat) and the binary Al1cat/TBAB system were all investigated and for all of them the optimized structures, rate-determining steps, and lowest energy barrier reaction pathways were intercepted for both gas-phase and solvent environments. For the catalyzed systems, the reaction mechanism consists of three key elementary steps: 1) epoxy ring opening; 2) CO2 electrophilic attack and 3) intramolecular cyclization. In the presence of Al1cat, the central metal of the catalyst coordinates with an oxygen atom of the epoxide, activating it towards a nucleophilic attack by the halide. An oxyanion species is formed that affords the corresponding cyclic carbonate after reaction with CO2. Our results provide important hints on the cycloaddition of CO2 and epoxides promoted by nonsymmetrical aluminum complex containing a single metal center, and can satisfactorily explain the previous experimental observations allowing the development of more efficient catalysts for organic carbonate production. [ABSTRACT FROM AUTHOR]

Multi-view video streaming is an emerging video paradigm that enables new interactive services, such as 3D video, free viewpoint television, and immersive teleconferencing. Because of the high bandwidth cost they come with, multi-view streaming applications can greatly benefit from the use of network coding, in particular in transmission scenarios such as wireless network, where the channels have limited capacity and are affected by losses. In this paper, we address the topic of cooperative streaming of multi-view video content, wherein users who recently acquired the content can contribute parts of it to their neighbors by providing linear combinations of the video packets. We propose a novel method for selection and network encoding of the transmitted frames based on the users' preferences for the different views and the rate-distortion properties of the stream. Using network coding enables the users to retrieve the content in a faster and more reliable manner and without the need for coordination among the senders. Our experimental results prove that our preference-based approach provides a high-quality decoding even when the uplink capacity of each node is only a small fraction of the rate of the stream. [ABSTRACT FROM AUTHOR]

Ad hoc quantum chemical modeling of the acetyl-CoA synthase local structure and folding allowed us to identify an unprecedented coordination mode of histidine sidechain to protein-embedded metal ions. [ABSTRACT FROM AUTHOR]

Blind Source Separation (BSS) deals with the recovery of source signals from a set of observed mixtures, when little or no knowledge of the mixing process is available. BSS can find an application in the context of network coding, where relaying linear combinations of packets maximizes the throughput and increases the loss immunity. By relieving the nodes from the need to send the combination coefficients, the overhead cost is largely reduced. However, the scaling ambiguity of the technique and the quasi-uniformity of compressed media sources makes it unfit, at its present state, for multimedia transmission. In order to open new practical applications for BSS in the context of multimedia transmission, we have recently proposed to use a non-linear encoding to increase the discriminating power of the classical entropy-based separation methods. Here, we propose to append to each source a non-linear message digest, which offers an overhead smaller than a per-symbol encoding and that can be more easily tuned. Our results prove that our algorithm is able to provide high decoding rates for different media types such as image, audio, and video, when the transmitted messages are less than 1.5 kilobytes, which is typically the case in a realistic transmission scenario. [ABSTRACT FROM PUBLISHER]

Upon irradiation with ultraviolet wavelengths, Fe2(S2C3H6)(CO)6, a simple model of the [FeFe]-hydrogenase active site, undergoes CO dissociation to form the unsaturated Fe2(S2C3H6)(CO)5 species and successively a solvent adduct at the vacant coordination site. In the present work, the CO-photolysis of Fe2(S2C3H6)(CO)6 was investigated by density functional theory (DFT) and time-dependent DFT (TDDFT). Trans Fe2(S2C3H6)(CO)5 form and the corresponding trans heptane or acetonitrile solvent adducts are the lowest energy ground state forms. CO dissociation barriers computed for the lowest triplet state are roughly halved with respect to those for the ground state suggesting that some low-lying excited potential energy surface (PES) could be loosely bound with respect to FeC bond cleavage. The TDDFT excited state PESs and geometry optimizations for the excited states likely involved in the CO-photolysis suggest that the FeS bond elongation and the partial isomerization toward the rotated form could take place simultaneously, favoring the trans CO photodissociation. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]