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Training in Feed Forward Deep Neural Networks is a memory-intensive operation which is usually performed on GPUs with limited memory capacities. This may force data scientists to limit the depth of the models or the resolution of the input data if data does not fit in the GPU memory. The re-materialization technique, whose idea comes from the checkpointing strategies developed in the Automatic Differentiation literature, allows data scientists to limit the memory requirements related to the storage of intermediate data (activations), at the cost of an increase in the computational cost. This paper introduces a new strategy of re-materialization of activations that significantly reduces memory usage. It consists in selecting which activations are saved and which activations are deleted during the forward phase and then recomputing the deleted activations when they are needed during the backward phase. We propose an original computation model that combines two types of activation savings: either only storing the layer inputs or recording the complete history of operations that produced the outputs. This paper focuses on the fully heterogeneous case, where the computation time and the memory requirement of each layer is different. We prove that finding the optimal solution is NP-hard and that classical techniques from Automatic Differentiation literature do not apply. Moreover, the classical assumption of memory persistence of materialized activations, used to simplify the search of optimal solutions, does not hold anymore. Thus, we propose a weak memory persistence property and provide a dynamic program to compute the optimal sequence of computations. This algorithm is made available through the Rotor software, a PyTorch plug-in dealing with any network consisting of a sequence of layers, each of them having an arbitrarily complex structure. Through extensive experiments, we show that our implementation consistently outperforms existing re-materialization approaches for a large class of networks, image sizes, and batch sizes. [ABSTRACT FROM AUTHOR]

The growing share of renewable energies in our electricity production, together with the still lacking storage capacity, strongly reinforces the need for more flexible electricity production units. In this context, combined cycle gas turbines (CCGTs) have a role to play, both in the current and future electricity production system due to their high efficiency, high load flexibility, and low CO2 emissions compared to other conventional thermal power plants. Nevertheless, bearing in mind our current challenges concerning climate change, the CO2 emissions of these CCGTs need to be reduced drastically. The amine-based absorption carbon capture (CC) process is currently the most mature and applicable CC technology. This process is known to require a considerable amount of thermal energy, degrading plant performance. However, to back-up renewable production, CCGTs will operate most of the time under part-load conditions. The impact of these part-load operations on the CC is still relatively unknown. Within this framework, this study aims to assess the performance of the CC process applied to a typical CCGT under part-load operation using specific simulation models. The CC plant model has been successfully validated against experimental data from a pilot-scale capture facility. Then, the CC plant has been scaled-up to the CCGT scale and the process has been optimized for each operating condition. The simulation results show that the specific reboiler duty increases for part-load operation, while the specific cooling requirements decrease. Moreover, the analysis of the yearly CCGT operation highlights a relative increase in CC energy penalty of 21% for an annual CCGT load factor of 0.5, impacting significantly plant performance. The next step will involve reducing this energy penalty. [ABSTRACT FROM AUTHOR]

Summary: To limit the increase of the global average temperature in the range of 1.5°C to 2°C above pre‐industrial levels, it is mandatory to reduce anthropogenic CO2 emissions. Aggressive mitigation measures are thus needed to tackle these emissions leading to "net negative CO2 emissions." The present study focuses on direct air capture (DAC) processes among the diverse negative emissions approaches. DAC refers to man‐made technologies that selectively extract CO2 from ambient air and deliver it in a concentrated form for further use or storage. DAC technologies are currently developed at different levels of maturity and performance. They can be classified into three main approaches, the liquid sorbent approach, the solid sorbent approach, and a panel of more innovative technologies combining different approaches. They involve various unit operations and different materials and energy types (electrical and thermal). To better evaluate the status and both the environmental and economic performances, the present paper provides a literature review of the life cycle (LCA) and techno‐economic (TEA) assessments in relation to DAC process chains. It was emphasized that DAC could lead to negative emissions if paired with subsequent storage, while the production of synthetic fuels can at best be carbon neutral when using CO2 from the air. Building large DAC plants has an impact on the amount of energy required to operate them, as well as other environmental impacts with regard to land, water, and material use. Even if the carbon‐negative characteristic of DAC was confirmed, these technologies are still expensive. It was highlighted that large DAC costs ranges are currently provided in the literature, from €80/tCO2 to €1133/tCO2 for the current DAC processes, while estimations from €34 to €260/tCO2 are expected in the future. Different levers were identified to improve the environmental and economic performances of DAC processes, such as the availability of waste heat, the heat integration possibilities, and, among others, the improvement of contactors and sorbents properties. Highlights: The paper entitled "Life cycle and techno‐economic assessments of direct air capture processes: An integrated review," submitted by Dr Remi Chauvy and Dr Lionel Dubois, fills the current gap in terms of comprehensive systematic and impacts assessment research on Direct Air Capture (DAC) technologies.Indeed, to better evaluate the status and both the environmental and economic performances of DAC technologies, the present paper provides an up‐to‐date literature review of the life cycle (LCA) and techno‐economic (TEA) assessments in relation with DAC process chains.The paper goes beyond the literature review as key levers, related to technology developments, to the energy use and to the implementation characteristics, are also identified to improve the environmental and economic performances of DAC processes. [ABSTRACT FROM AUTHOR]

• CO 2 absorption into aqueous solutions of DEEA, MAPA and their mixtures. • eNRTL modeling for DEEA, MAPA and DEEA + MAPA based systems was developed. • Model developed in Aspen Plus™ by adding species in the database. • This work can be used for CO 2 absorption–regeneration process simulation. Carbone capture by absorption–regeneration technology is a well-known process. However, the development and utilization of new solvents remains crucial to lower its energy consumption. Therefore, an accurate thermodynamic modeling is essential for the process simulation and optimization. This work focuses on the thermodynamic modeling of CO 2 absorption in aqueous solutions of N , N -diethylethanolamine (DEEA), N -methyl-1,3-propanediamine (MAPA) and their mixtures using electrolyte NRTL model. A novel thermodynamic modeling of DEEA-H 2 O−CO 2 , MAPA-H 2 O−CO 2 and DEEA-MAPA-H 2 O−CO 2 systems was developed. The modeling was carried out by considering the pure vapor pressures, excess enthalpies, dielectric constants, physical solubilities of CO 2 , partial and total pressures experimental data. The predicted and correlated data such as vapor–liquid equilibrium (VLE) and heat of CO 2 absorption were compared favorably to experimental data from the literature. Liquid–liquid phase separation of a specific mixture of these two amines was also highlighted. Subsequently, the developed model could be used for further simulations at large scale considering that successful validation was performed at pilot scale. [ABSTRACT FROM AUTHOR]

Highlights • A CO 2 de-SOx and de-NOx process was simulated for full oxy-fuel cement plants. • A comprehensive chemical mechanism has been elucidated and implemented in Aspen. • Results of a parametric study were presented for a single-column configuration. • Optimizations depending on purity targets were achieved by economic evaluations. Abstract The purpose of the present work was to investigate, for a gas issued from a full oxy-fuel combustion in the cement industry, a CO 2 de-SOx and de-NOx process, called "Sour-Compression Unit" (SCU), thanks to simulations with Aspen PlusTM. An important stage necessary for the SCU modeling has been the construction of an accurate chemical mechanism. Two-column and single-column configurations have been evaluated and compared. A parametric study and a Design Of Experiments have been conducted on a single-column process to study the influence of the operating parameters on the SOx and NOx abatement ratios. As a demonstration of the effectiveness of the model, three SOx and NOx purity specifications (depending on the further applications of the CO 2) were applied to the purified gas. The feature of the investigated model lies on optimizing the way to reach the purity target in order to decrease installation costs (CAPEX) and energy requirements (OPEX). [ABSTRACT FROM AUTHOR]

A problem commonly faced in Computer Science research is the lack of real usage data that can be used for the validation of algorithms. This situation is particularly true and crucial in Cloud Computing. The privacy of data managed by commercial Cloud infrastructures, together with their massive scale, makes them very uncommon to be available to the research community. Due to their scale, when designing resource allocation algorithms for Cloud infrastructures, many assumptions must be made in order to make the problem tractable. This paper provides deep analysis of a cluster data trace recently released by Google and focuses on a number of questions which have not been addressed in previous studies. In particular, we describe the characteristics of job resource usage in terms of dynamics (how it varies with time), of correlation between jobs (identify daily and/or weekly patterns), and correlation inside jobs between the different resources (dependence of memory usage on CPU usage). From this analysis, we propose a way to formalize the allocation problem on such platforms, which encompasses most job features from the trace with a small set of parameters. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of assigning a set of clients with demands to a set of servers with capacities and degree constraints. The goal is to find an allocation such that the number of clients assigned to a server is smaller than the server's degree and their overall demand is smaller than the server's capacity, while maximizing the overall throughput. This problem has several natural applications in the context of independent tasks scheduling or virtual machines allocation. We consider both the offline (when clients are known beforehand) and the online (when clients can join and leave the system at any time) versions of the problem. We first show that the degree constraint on the maximal number of clients that a server can handle is realistic in many contexts. Then, our main contribution is to prove that even if it makes the allocation problem more difficult (NP-Complete), a very small additive resource augmentation on the servers degree is enough to find in polynomial time a solution that achieves at least the optimal throughput. After a set of theoretical results on the complexity of the offline and online versions of the problem, we propose several other greedy heuristics to solve the online problem and we compare the performance (in terms of throughput) and the cost (in terms of disconnections and reconnections) of all proposed algorithms through a set of extensive simulation results. [ABSTRACT FROM AUTHOR]

Wild-type bacteriophage T4 lysozyme contains a hydrophobic cavity with binding properties that have been extensively studied by X-ray crystallography and NMR. In the present study, the monitoring of ¹H chemical shift variations under xenon pressure enables the determination of the noble gas binding constant (K = 60.2 M1-). Although the interaction site is highly localized, dipolar cross-relaxation effects between laser-polarized xenon and nearby protons (SPINOE) are rather poor. This is explained by the high value of the xenon-proton dipolar correlation time (0.8 ns), much longer than the previously reported values for xenon in medium-size proteins. This indicates that xenon is highly localized within the protein cavity, as confirmed by the large chemical shift difference between free and bound xenon. The exploitation of the xenon line width variation vs xenon pressure and protein concentration allows the extraction of the exchange correlation time between free and bound xenon. Comparison to the exchange experienced by protein protons indicates that the exchange between the open and closed conformations of T4 lysozyme is not required for xenon binding. [ABSTRACT FROM AUTHOR]

The hydrophobic cavity of Lipid Transfer Protein 1 from Nicotiana tabacum is investigated in detail by NMR using xenon as a spy. The analysis of the 129Xe chemical shifts and self-relaxation times gives evidence of protein-xenon interaction. Thermodynamics of the binding is characterized through the study of aliphatic ¹H and 13C chemical shift variation as a function of xenon pressure. The binding constant is evaluated to 75.5 ± 1.0 M-1 at 293 K. The location of xenon inside the cavity is deduced from SPINOE experiments. The noble gas appears to occupy four sites, and xenon self-relaxation experiments indicate that it quickly jumps between different sites. The chemical shifts of amide protons and nitrogens also depend on the xenon concentration, either specifically or nonspecifically for atoms at the external surface of the protein. Yet, contrary to aliphatic atoms, they do not correspond to short-range interactions as confirmed by magnetization transfer experiments between laser-polarized xenon and protons in H2O. These 15N chemical shift variations, used in combination with 15N transverse self-retaxation rates to determine the lower limit of the binding rate, consequently reveal subtle changes in the structure of the protein upon binding. [ABSTRACT FROM AUTHOR]

Molecular hydrophobic cavities can be mapped thanks to the detection of magnetization transfer from laser polarized xenon to nearby protons. This so called SPINOE approach is described. The study of the spin dynamics during this experiment and its consequences on the practical implementation are detailed. We show that thanks to the knowledge of the physical properties of the system, it becomes possible to choose the best experimental conditions in order to be able to assign magnetization transfer through two dimensional NMR methods. As an illustration, the first 2D SPIROE-TOCSY experiment is reported. To cite this article: L. Dubois et al., C. R. Physique 5 (2004). [Copyright &y& Elsevier]

The dimanganese(ll,ll) complexes 1a [Mn[sub 2](L)(OAc)[sub 2](CH[sub 3]OH)](CIO[sub 4]) and lb [Mn2(L)(OBz)[sub 2](H[sub 2]O)](CIO[sub 4]), where HL is the unsymmetrical phenol ligand 2-(bis-(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomet hyl)4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The disproportionation reaction was monitored by electrospray ionization mass spectrometry (ESI-MS) and EPR and UV-visible spectroscopies. Extensive EPR studies have shown that a species (2) exhibiting a 16-line spectrum at g ∼ 2 persists during catalysis. ESI-MS experiments conducted similarly during catalysis associate 2a with a peak at 729 (791 for 2b) corresponding to the formula [Mn[sup III]Mn[sup IV]V(L)(O)[sub 2](OAc)][sup +] ([Mn[sup III]Mn[sup IV](L)(O)[sub 2](OBz)][sup +] for 2b). At the end of the reaction, it is partly replaced by a species (3) possessing a broad unfeatured signal at g ∼ 2. ESI-MS associates 3a with a peak at 713 (775 for 3b) corresponding to the formula [Mn[sup II]Mn[sup III](L)(O)(OAc)][sup +] ([Mn[sup II]Mn[sup III](L)(O)(OBz)][sup +] for 3b). In the presence of H[sub 2, sup 18]O, these two peaks move to 733 and to 715 indicating the presence of two and one oxo ligands, respectively. When H[sub 2, sup 18]O[sub 2] is used, 2a and 3a are labeled showing that the oxo ligands come from H[sub 2]O[sub 2]. Interestingly, when an equimolar mixture of H[sub 2]O[sub 2] and H[sub 2, sup 18]O[sub 2] is used, only unlabeled and doubly labeled 2a/b are formed, showing that its two oxo ligands come from the same H[sub 2]O[sub 2] molecule. All these experiments lead to attribute the formula [Mn[sup III]Mn[sup IV](L)-(O)[sub 2](OAc)][sup +] to 2a and to 3a the formula [Mn[sup II]Mn[sup III](L)(O)(OAc)][sup +]. Freeze-quench/EPR experiments revealed that 2a appears at 500 ms and that another species with a 6-line spectrum is formed transiently at ca. 100 ms. 2a was prepared by reaction of la with reft-butyl hydroperoxide as shown by EPR and UV-visible spectroscopies and ESI-MS experiments, its structure was studied by X-ray absorption experiments which revealed the presence of two or three O atoms at 1.87 Å and three or two N/O atoms at 2.14 Å. In addition one N atom was found at a longer distance (2.3 Å) and one Mn at 2.63 Å. 2a can be one-electron oxidized at E[sub ½] = 0.91 V[sub NHE] (ΔE[sub ½] = 0.08 V) leading to its Mn[sup IV]Mn[sup IV] analogue. The formation of 2a from la was monitored by UV-visible and X-ray absorption spectroscopies. Both concur to show that an intermediate Mn[sup II]Mn[sup III] species, resembling 4a [Mn[sub 2](L)(OAc)[sub 2](H[sub 2]O)](ClO[sub 4])[sub 2], the one-electron-oxidized form of 1a, is formed initially and transforms into 2a. The structures of the active intermediates 2 and 3 are discussed in light of their: spectroscopic properties, and potential mechanisms are considered and discussed in the context of the biological reaction. [ABSTRACT FROM AUTHOR]

Reactions of the unsymmetrical phenol ligand 2-(bis(2-pyridyimethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminometh yl)-4-methylphenol with Mn(OAc)[sub 2]·4H[sub 2]O or Mn(H[sub 2]O)[sub 6](ClO[sub 4])[sub 2] in the presence of NaOBz affords the dimanganese(II) complexes 1(CH[sub 3]OH), [Mn[sub 2](L)(OAc)[sub 2](CH[sub 3]OH)](ClO[sub 4]), and 2(H[sub 2]O), [Mn[sub 2](L)(OBz)[sub 2](H[sub 2]O)](ClO[sub 4]), respectively. On the other hand, reaction of the ligand with hydrated manganese(III) acetate furnishes the mixedvalent derivative 3(H[sub 2]O), [Mn[sub 2](L)(OAc)[sub 2](H[sub 2]O)](ClO[sub 4])[sub 2]. The three complexes have been characterized by X-ray crystallography. 1(CH[sub 3]OH) crystallizes in the monoclinic system, space group P2[sub 1]/c, with a = 10.9215(6) Å, b = 20.2318(12) Å, c = 19.1354(12) Å, α = 90°, β = 97.5310(10)°, γ = 90°, V = 4191.7 A³, and Z = 4. 2(H[sub 2]O) crystallizes in the monoclinic system, space group P2[sub 1]/n, with a = 10.9215(6) Å, b = 20.2318(12) Å, c = 19.1354(12) Å, α = 90°, β = 97.5310(10)°, γ = 90°, V = 4191.7 ų, and Z = 4.3(H[sub 2]O) crystallizes in the monoclinic system, space group P2[sub 1]/c, with a = 11.144(6) Å, b = 18.737(10) Å, c = 23.949(13) Å, α = 90°, β = 95.910(10)°, γ = 90°, V-4974(5) ų, and Z = 4. Magnetic measurements revealed that the three compounds exhibit very similar magnetic exchange interactions -J = 4.3(3) cm[sup -1]. They were used to establish tentative magnetostructural correlations which show that for the dimanganese(II) complexes -J decreases when the Mn-O[sub phenoxo] distance increases as expected from orbital overlap considerations. For the dimanganese(II,III) complexes, crystallographic results show that the Mn[sup II]-O[sub phenoxo] and Mn[sup III]-O[sub phenoxo] bond lengths are inversely correlated. An... [ABSTRACT FROM AUTHOR]

Examines the properties of the dinuclear manganese complex. Outcome on the reaction of manganese compounds with ethylamines compounds; X-ray crystallography of the binuclear manganese compounds; Electrochemical behavior of the manganese complex.

• Power-to-gas has a strong potential in the transition to a renewable network. • Advanced CO 2 capture process allows to reduce the energy consumption. • Heat integration improves the competitiveness of the global Power-to-Gas chain. • Attractiveness of Power-to-gas is economically sensitive to electricity cost. The Power-to-Gas strategy has become a mainstream topic for decarbonization and development of renewables and flexibility in energy systems. One of the key arguments for decarbonizing the gas network is to take advantage of existing network infrastructure, gradually transitioning to lower fossil carbon sources of methane from Power-to-Gas. This work proposes the techno-economic investigation of an integrated system considering an advanced CO 2 capture process, in terms of solvent and process configuration, to treat about 10% of a cement plant's flue gas and convert the captured CO 2 into synthetic natural gas using renewable hydrogen generated from a large-scale wind powered electrolyzer. An optimized heat recovery system is proposed, drastically decreasing the external hot utility demand of the CO 2 capture unit. In addition, it leads to the production of complementary electricity (about 1.06 MW), reducing thus also the electrical demand of the integrated process. The synthetic natural gas produced has a composition (CH 4 92.9 mol.%, CO 2 3.7 mol.%, and H 2 3.4 mol.%) and a Wobbe index (46.72 MJ/m3), corresponding to specification for gas grid injection at 50 bar in Germany. With an overall system efficiency of 72.6%, the process produces 0.40 ton synthetic natural gas per ton of captured CO 2. The cost of the synthetic natural gas produced is higher when compared to the present natural gas market price, but cost reductions and possible commercial use of coproducts like oxygen, represent a likely alternative. Costs are mainly driven by high capital investments (the electrolyzer), and the price of renewable electricity, which is expected to decrease in the coming years. [ABSTRACT FROM AUTHOR]

The carbon capture, utilisation and storage (CCUS) process chain is subject to increasing interest, and its overwhelming implementation on the industrial scale appears to be one of the main ways to reduce CO 2 emissions. In this context, the optimisation of a CO 2 purification process for oxy-combustion cement plant flue gases is proposed. This optimisation is based on a multidimensional study on the energy, exergy, economy, and environmental impacts of the process. The results of the optimisations carried out show that it is more favourable to increase the CO 2 recovery above 90%, from an energy, exergy and economic point of view. The analysis of the evolution of the capture cost as a function of the CO 2 recovery shows that for a given carbon tax, there is a minimum for the total cost which includes the sum of the carbon tax contributions for the uncaptured CO 2 and the capture cost. As the unit uses only electrical energy, the cost and the electricity generation will directly impact the capture cost as well as the overall balance in terms of CO 2 avoided. As the electricity price increases from 50 to 250 €/MWh, the CO 2 capture cost increases by almost 250%. An analysis of the parameter uncertainties allows to observe their impacts on the results, and to define a standard deviation from the optimised points and show the robustness of these. Considering the technical parametric uncertainties, the standard deviation on the electrical consumption (3.65 kWh/t CO2), CO 2 recovery (0.09%) and exergy efficiency (0.92%) is limited. • Study of hybrid CO 2 capture system combining cryogenic and membrane technologies. • 4E analyses considering recovery, energy consumption, exergy yield and capture cost. • Maximum exergy efficiency for the cases where the CO 2 recovery is above 90%. • High sensitivity of the electricity price on the CO 2 capture cost. • Uncertainty quantification of modelling assumptions and impact on 4E analyses. [ABSTRACT FROM AUTHOR]

The evolution in the design of modern parallel platforms leads to revisit the scheduling jobs on distributed heterogeneous resources. The goal of this survey is to present the main existing algorithms, to classify them based on their underlying principles, and to propose unified implementations to enable their fair comparison, in terms of running time and quality of schedules, on a large set of common benchmarks that we made available for the community. Beyond this comparison, our goal is also to understand the main difficulties that heterogeneity conveys and the shared principles that guide the design of efficient algorithms. [ABSTRACT FROM AUTHOR]

Tris-copper centers are present at the active site of multicopper oxidases (MCO) which couple the four-electron reduction of molecular oxygen to water with the oxidation of substrates. Modelling these sites with small molecular complexes has thus attracted the interest of many groups in the (bio)inorganic community over the past three decades and still appears a challenge. These enzymes and their model complexes presently enjoy a renewed interest as potential non-precious metal catalyst for the Oxygen Reduction Reaction. Moreover recent work has revealed that tris-copper centers can catalyze methane oxidation. Therefore the elaboration of tris-copper system constitutes an important and timely issue. The aim of the present review is to analyze the various attempts at preparing tris-copper complexes in terms of strategy of ligand design. Of course the challenge to be met is to force three independent binding sites to converge and react in concert. Three main approaches have been developed to anchor these binding sites based on the use of (i) a node either (a) a single atom node (tren-based systems and related), or (b) an hexa -atom node (mesityl-based systems and derivatives), (ii) macrocyclic systems, and (iii) combination of mono- and dinuclear sites. The structures of the different systems will be described and analyzed accordingly. Then the various reactivities exhibited by these systems will be presented so as to evaluate how the ligand design influences the reactivity and to discern promising future directions. [ABSTRACT FROM AUTHOR]

Using Si as anode materials for Li-ion batteries remain challenging due to its morphological evolution and SEI modification upon cycling. The present work aims at developing a composite consisting of carbon-coated Si nanoparticles (Si@C NPs) intimately embedded in a three-dimensional (3D) graphene hydrogel (GHG) architecture to stabilize Si inside LiB electrodes. Instead of simply mixing both components, the novelty of the synthesis procedure lies in the in situ hydrothermal process, which was shown to successfully yield graphene oxide reduction, 3D graphene assembly production, and homogeneous distribution of Si@C NPs in the GHG matrix. Electrochemical characterizations in half-cells, on electrodes not containing additional conductive additive, revealed the importance of the protective C shell to achieve high specific capacity (up to 2200 mAh.g−1), along with good stability (200 cycles with an average Ceff > 99%). These performances are far superior to that of electrodes made with non-C-coated Si NPs or prepared by mixing both components. These observations highlight the synergetic effects of C shell on Si NPs, and of the single-step in situ preparation that enables the yield of a Si@C-GHG hybrid composite with physicochemical, structural, and morphological properties promoting sample conductivity and Li-ion diffusion pathways. [ABSTRACT FROM AUTHOR]

We consider the classical problem of broadcasting a large message at an optimal rate in a large scale distributed network under the multi-port communication model. In this context, we are interested in both building an overlay network and providing an explicit algorithm for scheduling the communications. From an optimization point of view, we aim both at maximizing the throughput (i.e., the rate at which nodes receive the message) and minimizing the degree of the participating nodes, i.e., the number of TCP connections they must handle simultaneously. The main novelties of our approach are the introduction of this degree constraint and the classification of the set of participating nodes into two parts: open nodes that stay in the open-Internet and “guarded” nodes that lie behind firewalls or NATs. Two guarded nodes cannot communicate directly, but rather need to use an open node as a gateway for transmitting a message. In the case without guarded nodes, we prove that it is possible to reach the optimal throughput, at the price of a quasi-optimal (up to a small additive increase) degree of the participating nodes. In presence of guarded nodes, our main contributions are a closed form formula for the optimal cyclic throughput and the proof that the optimal solution may require arbitrarily large degrees. In the acyclic case, we propose an algorithm that reaches the optimal throughput with low degree. Then, we prove a worst case ratio between the optimal acyclic and cyclic throughput and show through simulations that this ratio is on average very close to 1, what makes acyclic solutions efficient both in terms of throughput maximization and degree minimization. [ABSTRACT FROM AUTHOR]

• Study of hybrid CO 2 capture system combining VPSA and CPU technologies. • Optimization of integrated capture CO 2 process and purification unit. • High CO 2 recovery (90–99 %) and high CO 2 purity (>99.99 %) • Complete analyses considering recovery, energy consumption, and capture cost. • Impact of the electricity source on the total CO 2 recovery. The imperative challenge posed by climate change requires urgent actions to counteract the harmful effects of greenhouse gas emissions, particularly CO 2 , which contributes to approximately 80 % of emissions responsible for global warming. A hybrid system combining Vacuum Pressure Swing Adsorption (VPSA) unit with a Cryogenic Carbon Purification Unit (CPU) is evaluated to enhance recovery and purity of CO 2 captured from flue gas containing CO 2 concentration ranging from 5 % to 20 %. VPSA preconcentrates the CO 2 and CPU completes the separation and purifies the CO 2. The study uses surrogate models for multi-objective optimization, considering energy consumption, cost, and CO 2 recovery, providing a time-efficient approach for investigating computationally demanding processes. Results from the study indicate that the hybrid system achieves over 90 % recovery for flue gas concentration range considered, while ensuring the production of high-purity CO 2 (>99.99 %) suitable for transportation. A trade-off analysis reveals the balance between recovery, electricity consumption, and economic viability. A sensitivity analysis identifies parameters influencing recovery and energy consumption, providing guidance for future optimization efforts. The techno-economic analysis highlights the impact of electricity prices and carbon taxes on total costs, identifying an optimum towards higher recovery values under rising carbon taxes. Furthermore, the research underscores concentration-dependent economic feasibility, emphasizing the attractiveness of concentrations above 10 % compared with other technologies, which require higher concentrations. For an electricity price of 75 €.MWh−1, the total cost of the CO 2 capture hydride system considering CO 2 emissions with carbon tax of 100 €.t CO2 −1 for concentrations ranging from 10 % to 20 % is from 123 to 80 €.t CO2 −1, respectively. The analysis of the electricity source shows the importance of a low-carbon emission energy mix for optimal carbon emission reduction. [ABSTRACT FROM AUTHOR]

Abstract: The presence of highly concentrated dissolved laser-polarized xenon (∼1mol/L, polarization up to 0.2) induces numerous effects on proton and xenon NMR spectra. We show that the proton signal enhancements due to 129Xe–1H cross-relaxation (SPINOE) and overall shifts of the proton resonances due to the average dipolar shift created by the intense xenon magnetization are correlated. Protons behave as very useful sensors of the xenon magnetization. Indeed the xenon resonances exhibit many features such as superimposition of narrow lines on the main resonance due to clustering effects, or such as a polarization-dependent line broadening that is tentatively assigned to the effects of temperature fluctuations that decorrelate some distant dipolar field effects from local interactions, transforming xenon spins from “like” to “unlike” spins. These spectral features make difficult the determination of the average dipolar field by means of the xenon resonance but have interesting consequences on the heteronuclear polarization transfer experiment in Hartmann–Hahn conditions (SPIDER). [Copyright &y& Elsevier]

Cryptophanes bearing OCH2COOH groups in place of the methoxy groups represent a new class of xenon-carrier molecules soluble in water at biological pH. By using ¹H and 129Xe NMR (thermally- and laser-polarized dissolved gas), the structural and dynamical behaviors of these host molecules as well as their interaction with xenon are studied. They are shown to exist in aqueous solution under different conformations in very slow exchange. A saddle form present for one of these conformations could explain the ¹H NMR spectra. Whereas the cryptophanes in such a conformation are unable to complex xenon, unprecedented high binding constants are found for cryptophanes in the other canonical crown-crown conformation. These host molecules could therefore be valuable candidates for biosensing using 129Xe MRI. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cellulosic biomass-based glucose is selectively oxidized in a co-generation direct fuel cell. • Real-time evidence of glucose oxidation in fuel cell by C1-position to gluconate (90% selectivity). • Glucuronate production (10% selectivity) via the glucose oxidation at the C6-position. • Products distribution in direct alkaline glucose fuel cell is the same as in half-cell setup. Cellulosic biomass, which is basically a polymer of glucose, is the most abundant organic polymer on earth and there is significant interest in the development of advanced materials for its valorization through the waste-to-energy and water-to-chemical scenarios. Hence, a precise investigation of the monomer (glucose) electrooxidation in electrochemical reactors is a key starting point to tackle the whole cellulose and ultimately the entire biomass. To this end, we report herein new insights about the operation of a cogeneration direct alkaline glucose fuel cell (which includes an anion exchange membrane) that simultaneously produces electricity and mainly gluconate as the reaction product. The AuPt nanocatalysts of 3–5 nm particle size finely dispersed onto reduced graphene oxide (rGO) at a 20 wt% metal loading are obtained from an organic surfactant-free method, so-called the bromide anion exchange (BAE). Specifically, the electroanalytical investigation carried out with high-performance liquid ionic chromatography (HPLIC) and liquid chromatography coupled to mass spectrometry (LC-MS) demonstrate no carbon–carbon bond cleavage occurs, which represents an advance towards a CO 2 -free biomass valorization process. The comparison of the results commonly obtained in a three-electrode half-cell with those in an anion exchange membrane fuel cell shows that the trends in selectivity are the same. The fuel cell operation produces gluconate via a two-electron transfer process at 90% selectivity and 65% Faradaic efficiency. In addition to gluconate, glucuronate is also observed; both compounds are high value-added chemicals. This work contributes towards the engineering of novel electrocatalytic interfaces for the valorization of the surplus biomass into energy and chemicals. [ABSTRACT FROM AUTHOR]

As the world moves toward electromobility and a concomitant decarbonization of its electrical supply, modern society is also entering a so-called fourth industrial revolution marked by a boom of electronic devices and digital technologies. Consequently, battery demand has exploded along with the need for ores and metals to fabricate them. Starting from such a critical analysis and integrating robust structural data, this review aims at pointing out there is room to promote organic-based electrochemical energy storage. Combined with recycling solutions, redox-active organic species could decrease the pressure on inorganic compounds and offer valid options in terms of environmental footprint and possible disruptive chemistries to meet the energy storage needs of both today and tomorrow. We review state-of-the-art developments in organic batteries, current challenges, and prospects, and we discuss the fundamental principles that govern the reversible chemistry of organic structures. We provide a comprehensive overview of all reported cell configurations that involve electroactive organic compounds working either in the solid state or in solution for aqueous or nonaqueous electrolytes. These configurations include alkali (Li/Na/K) and multivalent (Mg, Zn)-based electrolytes for conventional "sealed" batteries and redox-flow systems. We also highlight the most promising systems based on such various chemistries relying on appropriate metrics such as operation voltage, specific capacity, specific energy, or cycle life to assess the performances of electrodes. [ABSTRACT FROM AUTHOR]

In 1968 Wolfson et al. published the concept for producing energy inside the body using catalytic electrodes exposed to the body fluid as an electrolyte and utilising naturally occurring fuels such as glucose. Since then, the technology has advanced to enhance the levels of power using enzymes immobilised within three-dimensional bioelectrodes that are nanostructured. Current research in the field of enzymatic fuel cells is directed toward applying electrochemical and nanostructural expertise to increase the energy density, to increase the power density, to increase the operational stability, and to increase the voltage output. Nonetheless, biocompatibility remains the major challenge for increasing the life-time for implanted enzymatic biofuel cells. Here, we discuss the current issues for biocompatibility and suggest directions to enhance the design of biofuel cells so as to increase the life-time of implantation whilst maintaining sufficient performance to provide power for implanted medical devices. [ABSTRACT FROM AUTHOR]

Abstract Chemically tuned pillared graphene structures show ability to limit restacking of graphene sheets for electrochemical energy storage in SCs. A comprehensive electrochemical characterization using various ion sizes allowed identification of ion-sieving in the cross-linked galleries of reduced pillared graphene materials (RPs). The access to the cross-linked galleries, which provide additional ion sorption sites, offered slightly increased capacitances in RPs compared to completely restacked sheets in reduced graphene oxide (RGO). We performed electrochemical impedance analyses on RPs and RGO to understand the ion transport inside the cross-linked graphene galleries. RGO adsorbs ions in the inter-particle micro/meso pores and the ion access to such sites from the bulk electrolyte occurs with relative ease. RPs sieve ions into their inter-layer gallery pores based on effective ion sizes and the ion transport process is resistive compared to RGO. A control study using 3D pillared graphene hydrogel with improved macro porosity assigns this resistive behavior and the moderate capacitances to limited ion access to the active sites due to excess number of pillars. The obtained results on the ion transport dynamics between graphene layers provide perspectives towards further optimization of these graphene materials for SCs. Graphical abstract Ion transport inside the inter-layer galleries of pillared graphene materials is impeded by the pillars. Image 1 [ABSTRACT FROM AUTHOR]

The problem of partitioning dense matrices into sets of sub-matrices has received increased attention recently and is crucial when considering dense linear algebra and kernels with similar communication patterns on heterogeneous platforms. The problem of load balancing and minimizing communication is traditionally reducible to an optimization problem that involves partitioning a square into rectangles. This problem has been proven to be NP-Complete for an arbitrary number of partitions. In this paper, we present recent approaches that relax the restriction that all partitions be rectangles. The first approach uses an original mathematical technique to find the exact optimal partitioning. Due to the complexity of the technique, it has been developed for a small number of partitions only. However, even at a small scale, the optimal partitions found by this approach are often non-rectangular and sometimes non-intuitive. The second approach is the study of approximate partitioning methods utilizing recursive partitioning algorithms. In particular we use the work on optimal partitioning to improve pre-existing algorithms. In this paper we discuss the different perspectives this approach opens and present two algorithms, SNRPP which is a $\sqrt{\frac{3}{2}}$ approximation, and NRPP which is a $\frac{2}{\sqrt{3}}$ approximation. While sub-optimal, the NRRP approach works for an arbitrary number of partitions. We use the first exact approach to analyse how close to the known optimal solutions the NRRP algorithm is for small numbers of partitions. [ABSTRACT FROM AUTHOR]

Direct Air Capture (DAC) technologies are gaining interest in the concept of carbon utilization and Power-to-Gas (PtG), as the economic valorization of the CO 2 into methane provides a viable pathway to allow DAC systems to mature. However, research on DAC mainly focuses on isolated systems, and the system performance depends on parameters that are highly uncertain. To study the integration of DAC in PtG, we developed a DAC-PtG model, performed an Energy, Exergy, Economic and Environmental (4E) analysis and implemented uncertainty quantification to consider the uncertain environment. The results illustrate that the DAC-PtG system is autothermal when introducing a two-stage mechanical vapor recompression unit at the DAC outlet. The exergy efficiency ranges between 51.3% and 52.6% within 3 standard deviations, for which the uncertainty is driven by the ambient conditions and the uncertain heat of desorption. The methane issued from DAC-PtG has a lower carbon footprint than fossil methane when the carbon footprint of the electricity supply is below or equal to 0.12 kg˙CO˙2-eq /kWh. The Levelized Cost of Synthetic Natural Gas (LCSNG) ranges between 130 €/ MWh and 744 €/ MWh, following an uncertain electricity price and uncertain expenses related to DAC and electrolysis. Therefore, bulk manufacturing, further maturing of these technologies and more demonstration projects are required to reduce the uncertainty of the LCSNG. Future works will consider intermittent renewable energy sources to supply power. • Integrated direct air capture and CO 2 methanation are investigated. • Exergy efficiency ranges between 51.3% and 52.6% within three standard deviations. • The levelized cost of synthetic natural gas ranges between 130 €/MWh and 744 €/MWh. • Electricity emission intensity below 0.12 kg CO2-eq /kWh results in carbon reduction. • To reduce uncertainty, bulk manufacturing and more pilot projects are needed. [ABSTRACT FROM AUTHOR]

Supercapacitors offer high power densities but require further improvements in energy densities for widespread commercial applications. In addition to the conventional strategy of using large surface area materials to enhance energy storage, recently, matching electrolyte ion sizes to material pore sizes has been shown to be particularly effective. However, synthesis and characterization of materials with precise pore sizes remain challenging. Herein, we propose to evaluate the layered structures in graphene derivatives as being analogous to pores and study the possibility of ion sieving. A class of pillared graphene based materials with suitable interlayer separation were synthesized, readily characterized by X-ray diffraction, and tested in various electrolytes. Electrochemical results show that the interlayer galleries could indeed sieve electrolyte ions based on size constrictions: ions with naked sizes that are smaller than the interlayer separation access the galleries, whereas the larger ions are restricted. These first observations of ion sieving in pillared graphene-based materials enable efficient charge storage through optimization of the d-spacing/ion size couple. [ABSTRACT FROM AUTHOR]

Graphene hydrogels with high electrical conductivity were prepared by a one-step process using hydrazine hydrate as gel assembly agent (GH-HD). Conventional two-step process of gel formation and further reduction to prepare highly conducting gels was replaced by a single step involving equivalent amount of hydrazine. Optimized graphene oxide concentration was established to facilitate such monolith formation. Extensive characterization and control studies enabled understanding of the material properties and gel formation mechanism. The synthesized gel shows a high electrical conductivity of 1141 S/m. The supercapacitor based on GH-HD delivers a high specific capacitance of 190 F/g at a current density of 0.5 A/g and 123 F/g at very high current density of 100 A/g. Furthermore, excellent power capability and cyclic stability were also observed. 3D macroporous morphology of GH-HD makes it ideal for high rate supercapacitor applications. [ABSTRACT FROM AUTHOR]

Triarylamines oxidized to radical cations can be used as stable spins sources for the design of high-spin compounds. Here, we present the synthesis of the polyarylamine-containing hexaazacyclophanes linked via meta-terphenyl bridges. Spins, created after oxidation of the polymer, can be coupled magnetically in cyclophane moieties via meta-phenyl and along the polymer chain via meta-terphenyl units. The formation of a quintet spin state was evidenced by pulsed-EPR nutation spectroscopy. Two exchange coupling constants via both couplers were determined experimentally and corresponded to J/k = 89 K in the cyclophane moiety and j/k = 17 K via meta-terphenyl. Most importantly, in this polymer, four spins can be ferromagnetically ordered via both couplers, which leads to the high spin state. [ABSTRACT FROM AUTHOR]

The interfacing of polyoxometalates and graphene can be considered to be an innovative way to generate hybrid structures that take advantage of the properties of both components. Polyoxometalates are redox-sensitive and photosensitive compounds with high temperature stability (up to 400 °C for some), showing tunable properties depending on the metal incorporated inside the complex. Graphene has a unique electronic band structure combined with good material properties for electrical and optical applications. The spontaneous, rather than electrochemical, functionalization of epitaxial graphene on SiC with Keggin phosphomolybdate derivative TBA3[PMo11O39{Sn(C6H4)CC(C6H4)N2}] (named KMoSn[N2+]) bearing a phenyl diazonium unit is investigated. Graphene decoration is evidenced by means of AFM, Raman, XPS, and cyclic voltammetry, indicating a successful immobilization of the polyoxomolybdate. The covalent bonding of the polyoxometalate to the graphene substrate can be deduced from the appearance of a D band in the Raman spectra and from the loss of mobility in the electrical conduction. High-resolution XPS spectra reveal an electron transfer from the graphene to the Mo complex. The comparison of charge-carrier density measurements before and after grafting supports the p-type doping effect, which is further evidenced by work function UPS measurements. [ABSTRACT FROM AUTHOR]

Silicon nanoparticles (NPs) serve a wide range of optical, electronic, and biological applications. Chemical grafting of various molecules to Si NPs can help to passivate their reactive surfaces, 'fine-tune' their properties, or even give them further interesting features. In this work, 1H, 13C, and 29Si solid-state NMR spectroscopy has been combined with density functional theory calculations to study the surface chemistry of hydride-terminated and alkyl-functionalized Si NPs. This combination of techniques yields assignments for the observed chemical shifts, including the contributions resulting from different surface planes, and highlights the presence of physisorbed water. Resonances from near-surface 13C nuclei were shown to be substantially broadened due to surface disorder and it is demonstrated that in an ambient environment hydride-terminated Si NPs undergo fast back-bond oxidation, whereas long-chain alkyl-functionalized Si NPs undergo slow oxidation. Furthermore, the combination of NMR spectroscopy and DFT calculations showed that the employed hydrosilylation reaction involves anti-Markovnikov addition of the 1-alkene to the surface of the Si NPs. [ABSTRACT FROM AUTHOR]

The preparation and characterization of a series of complexes of the Yb and Eu cations in the oxidation state II and III with the tetradentate N,O-donor tripodal ligands (tris(2-pyridylmethyl)amine (TPA), BPA− (HBPA=bis(2-pyridylmethyl)(2-hydroxybenzyl)amine), BPPA− (HBPPA=bis(2-pyridylmethyl)(3.5-di- tert-butyl-2-hydroxybenzyl)amine), and MPA2− (H2MPA=(2-pyridylmethyl)bis(3.5-di- tert-butyl-2-hydroxybenzyl)amine) is reported. The X-ray crystal structures of the heteroleptic Ln2+ complexes [Ln(TPA)I2] (Ln=Eu, Yb) and [Yb(BPA)I(CH3CN)]2, of the Ln2+ homoleptic [Ln(TPA)2]I2 (Ln=Sm, Eu, Yb) and [Eu(BPA)2] complexes, and of the Ln3+ [Eu(BPPA)2]OTf and [Yb(MPA)2K(dme)2] (dme=dimethoxyethane) complexes have been determined. Cyclic voltammetry studies carried out on the bis-ligand complexes of Eu3+ and Yb3+ show that the metal center reduction occurs at significantly lower potentials for the BPA− ligand as compared with the TPA ligand. This suggests that the more electron-rich character of the BPA− ligand results in a higher reducing character of the lanthanide complexes of BPA− compared with those of TPA. The important differences in the stability and reactivity of the investigated complexes are probably due to the observed difference in redox potential. Preliminary reactivity studies show that whereas the bis-TPA complexes of Eu2+ and Yb2+ do not show any reactivity with heteroallenes, the [Eu(BPA)2] complex reduces CS2 to afford the first example of a lanthanide trithiocarbonate complex. [ABSTRACT FROM AUTHOR]

Magic-angle spinning dynamic nuclear polarization (MAS-DNP) has been proven to be a powerful technique to enhance the sensitivity of solid-state NMR (SSNMR) in a wide range of systems. Here, we show that DNP can be used to polarize lipids using a lipid-anchored polarizing agent. More specifically, we introduce a C16-functionalized biradical, which allows localization of the polarizing agents in the lipid bilayer and DNP experiments to be performed in the absence of excess cryo-protectant molecules (glycerol, dimethyl sulfoxide, etc.). This constitutes another original example of the matrix-free DNP approach that we recently introduced. [ABSTRACT FROM AUTHOR]

In order to reduce the environmental impact of human activities especially transportation and portable electronics, a more sustainable way is required to produce and store electrical energy. Actually lithium battery is one of the most promising solutions for energy storage. Unfortunately this technology is based on the use of transition metal-based active materials for electrodes which are rare, expensive, extracted by mining, can be toxic and hard to recycle. Organic materials are an interesting alternative to replace inorganic counterparts due to their high electrochemical performances and the possibility to produce them from renewable resources. A quinone derivative is synthetized and investigated as novel active material for rechargeable lithium ion batteries which shows higher performances. [ABSTRACT FROM AUTHOR]

Thisreport describes the study of a dimer d2+and a linear trimer t3+of amminium radical cations coupled by 3,4′-biphenylspin coupling units. The synthesis of the parent diamine and triamineand their optical and electrochemical properties obtained by UV–visibleand cyclic voltammetry are presented. The chemical doping of the parentdiamine dand triamine twas performed quantitativelyto obtain samples containing the corresponding dimer d2+and trimer t3+in almost pure high-spin states as evidenced by pulsed EPRnutation spectroscopy. The Jcoupling constants ofthe corresponding S= 1 and S=3/2 spin states were measured (J/k= 135 K) and compared quantitatively to DFT calculations. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) is used as a conductive additive for nanosilicon-based lithium battery anodes with the high active-mass loading typically required for industrial applications. In contrast to conventional Si electrodes that use acetylene black (AcB) as an additive, the rGO system shows pronounced improvement of electrochemical performance, irrespective of the cycling conditions. With capacity limitation, the rGO system results in improved coulombic efficiency (99.9%) and longer cycle life than conventional electrodes. Upon cycling without capacity limitation, much higher discharge capacity is maintained (2000 mAh g−1 after 100 cycles for 2.5 mg of Si cm−2). Used in conjunction with the bridging carboxymethyl cellulose binder, the crumpled and resilient rGO allows highly reversible functioning of the electrode in which the Si particles repeatedly inflate and deflate upon alloying and dealloying with lithium. [ABSTRACT FROM AUTHOR]

Polyarylamine containing meta–para–para-aniline units in the main chain and meta–para-aniline units in the pendant chains was synthesized. The polymercan be oxidized to radical cations in chemical or electrochemicalways. The presence of meta-phenylenes in the polymerchemical structure allows for the ferromagnetic coupling of electronicspins, which leads to the formation of high spin states. Detailedpulsed-EPR study indicates that the S= 2 spin statewas reached for the best oxidation level. Quantitative magnetizationmeasurements reveal that the doped polymer contains mainly S= 2 spin states and a fraction of S=3/2 spin states. The efficiency of the oxidation was determined tobe 74%. To the best of our knowledge, this polymer is the first exampleof a linear doped polyarylamine combining such high spin states withhigh doping efficiency. [ABSTRACT FROM AUTHOR]

The heterodinuclear complexes [FeIII,MnII,(L-Bn)(μ-OAc)2](ClO4)2 (1) and [FeIIMnII(L-Bn)(μ<-OAc)2](ClO4) (2) with the unsymmetrical dinucleating ligand HL-Bn {[2-bis[(2-pyridylmethyl)aminomethyl]]-6-[benzyl-2-(pyridylmethyl)-aminomethyl]-4-methylphenol} were synthesized and character-ized as biologically relevant models of the new Fe/Mn class of nonheme enzymes. Crystallographic studies have been completed on compound 1 and reveal an FeIIIMnIIμ-phenoxobis(μ-carbox- ylato) core. A single location of the FeIII ion in 1 and of the FeII ion in 2 was demonstrated by Mossbauer and ¹H NMR spectroscopies, respectively. An investigation of the temperature dependence of the magnetic susceptibility of 1 revealed a moderate antiferromagnetic interaction (J = 20 cm-1) between the high-spin FeIII and MnII ions in 1, which was confirmed by Mossbauer and electron paramagnetic resonance (EPR) studies. The electrochemical properties of complex 1 are described. A quasireversible electron transfer at --40 mV versus Ag/AgCl corresponding to the FeIIIMnII/FeIIMnII couple appears in the cyclic voltammogram. Thorough investigations of the Mossbauer and EPR signatures of complex 2 were performed. The analysis allowed evidencing of a weak antiferromagnetic interaction (J = 5.72 cm-1) within the FeuMn" pair consistent with that deduced from magnetic susceptibility measurements (j = 6.8 cm-1). Owing to the similar value of the Fe11 zero-field splitting (DFe = 3.55 cm-1), the usual treatment within the strong exchange limit was precluded and a full analysis of the electronic structure of the ground state of complex 2 was developed. This situation is reminiscent of that found in many diiron and iron--manganese enzyme active sites. [ABSTRACT FROM AUTHOR]

Abstract: Keggin-type dodecatungstosilicates polyoxometallates (POMs) ([SiW12O40]4−) were immobilized in a straightforward manner by electrostatic interactions on ammonium layers covalently grafted on silicon. This method does not require any POM modification synthetical steps. The presence of [SiW12O40]4− on the surface is demonstrated by X-ray Photoelectron Spectroscopy from a specific modification of the tungsten 4f7/2 signal. Moreover the surface coverage of [SiW12O40]4− has been improved by 35% upon changing the nature of the anchoring ammonium groups from protonated to methylated amino groups. The organic–inorganic composite films have also been characterized by cyclic voltammetry showing that POMs have a specific behavior on silicon surfaces. In addition the use of a polyallylamine capping layer proved to stabilize efficiently the POM electrochemical response. [Copyright &y& Elsevier]

Stable complexes of pentavalent uranyl [UO2(salan-tBu2)(py)K)n(3), [UO2(salan-tBu2)(py)K(18C6)] (4), and [UO2(salophen-tBu2)(thf)]K(thf)2)n (8) have been synthesized from the reaction of the complex ([UO2py5][Kl2py2])n (1) with the bulky amine-phenolate ligand potassium salt K2(salan-tBu2) or the Schiff base ligand potassium salt K2(salophen-tBu2) in pyridine. They were characterized by NMR, Rl, elemental analysis, single crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, low-temperature EPR, and variable-temperature magnetic susceptibility. X-ray diffraction shows that 3 and 8 are polymeric and 4 is monomeric. Crystals of the monomeric complex [UVIO2(salan-tBu2)(py)][Cp*2Co], 6, were also isolated from the reduction of [UIVO2(salan-tBu2)(py)], 5, with Cp*2Co. Addition of crown ether to 1 afforded the highly soluble pyridine stable species [UO2py5]l.py (2). The measured redox potentials E1/2 (UVI/UV) are significantly different for 2 (-0.91 and -0.46 V) in comparison with 3, 4, 5, 7 and 9 (in the range -1.65 to -1.82 V). Temperature-dependent magnetic susceptibility data are reported for 4 and 7 and give μeff of 2.20 and 2.23 μB at 300 K respectively, which is compared with a μeff of 2.6(1) μB (300 K) for 2. Complexes 1 and 2 are EPR silent (4 K) while a rhombic EPR signal (gx = 1.98; gy = 1.25; gz = 0.74 (at 4 K) was measured for 4. The magnetic and the EPR data can be qualitatively analyzed with a simple crystal field model where the f electron has a nonbonding character. However, the temperature dependence of the magnetic susceptibility data suggests that one or more excited states are relatively low-lying. DFT studies show unambiguously the presence of a significant covalent contribution to the metal-ligand interaction in these complexes leading to a significant lowering of the πu. The presence of a back-bonding interaction is likely to play. a role in the observed solution stability of the [UO2(salan-tBu2)(py)K] and [UO2(salophen-tBu2)(py)K) complexes with respect to disproportionation and hydrolysis. [ABSTRACT FROM AUTHOR]

Nickel(II) β-azido-meso-tetraphenylporphyrin was successfully anchored on silicon using a bifunctional linker that bears two terminal alkyne functions by the sequence (i) hydrosilylation of a C=C triple bond of the linker by surface Si-H groups and (ii) 1,3-Huisgen cycloaddition between the alkyne-terminated silicon surface and the azidoporphyrin derivative. [ABSTRACT FROM AUTHOR]

Nickel(ii) β-azido-meso-tetraphenylporphyrin was successfully anchored on silicon using a bifunctional linker that bears two terminal alkyne functions by the sequence (i) hydrosilylation of a CC triple bond of the linker by surface Si–H groups and (ii) 1,3-Huisgen cycloaddition between the alkyne-terminated silicon surface and the azidoporphyrin derivative. [ABSTRACT FROM AUTHOR]

Abstract: We describe a method to improve the yield and the kinetics of the difficult syntheses of α,β-unsaturated porphyrins, which enabled us to obtain a new chiral porphyrin derived from (S)-(−)-perillaldehyde in a 6% yield. Variable temperature NMR experiments on the free base, the zinc(II) and the nickel(II) complexes showed that two distinct and consecutive dynamic processes linked with the meso substituents rotation occurred. These processes can be analyzed as an evolution of the conformer composition upon temperature change. Higher values are found for the free energies of rotation of the substituent (measured by variable temperature 1H NMR) compared to those of other equivalent porphyrins like meso-tetraphenyl porphyrin or meso-tetracyclohexyl porphyrin. [Copyright &y& Elsevier]

Reaction of the unsymmetrical phenol ligand 2-((bis(2-pyridylmethyl)amino)methyl)-6-(((2-pyridylmethyl)benzylamino)methyl)-4-methylphenol (HL-Bn) or its 2,6-dichlorobenzyl analogue (HL-BnCI2) with Fe(H2O)6(ClO4)2 in the presence of disodium m-phenylenedipropionate (Na2(mpdp)) followed by exposure to atmosphere affords the diiron(II,III) complexes [Fe2(L-Bn)(mpdp)(H2O)](ClO4)2 and [Fe2(L-BnCI2)(mpdp)(CH3OH)](CIO4)2, respectively. The latter complex has been characterized by X-ray crystallography. It crystallizes in the monoclinic system, space group P21/n, with a -13.3095(14) Å, b = 20.1073(19) Å, c = 19.4997(19) Å, α = 90°, β = 94.471(2)°, γ = 90°, V= 5202.6(9) ų, and Z = 4. The structure of the compound is very similar to that of [Fe2(L-Bn)(mpdp)(H2O)](BPh4)2 determined earlier, except for the replacement of a water by a methanol on the ferrous site. Magnetic measurements of [Fe2(LBn)(mpdp)(H2O)](BPh4)2 reveal that the two high-spin Fe ions are moderately antiferromagnetically coupled (J = -3.2(2) cm-1). Upon dissolution in acetonitrile the terminal ligand on the ferrous site is replaced by a solvent molecule. The acetonitrile-water exchange has been investigated by various spectroscopic techniques (UV-visible, NMR, Mössbauer) and electrochemistry. The substitution of acetonitrile by water is clearly evidenced by Mössbauer spectroscopy by a reduction of the quadrupole splitting value from 3.14 to 2.41 mm/s. In addition, it causes a 210 mV downshift of the oxidation potential of the ferrous site and a similar reduction of the stability domain of the mixed-valence state. Exhaustive electrolysis of a solution of [Fe2(L-Bn)(mpdp)(H2O)]2+ shows that the aqua diferric species is not stable and undergoes a chemical reaction which can be partly reversed by reduction to the mixedvalent state. This and other electrochemical observations suggest that upon oxidation of the diiron center to the diferric state the aqua ligand is deprotonated to a hydroxo. This hypothesis is supported by Mössbauer spectroscopy. Indeed, this species possesses a large quadrupole splitting value (ΔEQ ≥ 1.0 mm·s-1) similar to that of analogous complexes with a terminal phenolate ligand. This study illustrates the drastic effects of aqua ligand exchange and deprotonation on the electronic structure and redox potentials of diiron centers. [ABSTRACT FROM AUTHOR]

The coupling of electron and proton transfers is currently under intense scrutiny. This Communication reports a new kind of proton-coupled electron transfer within a homodinuclear first-row transition-metal complex. The triply-bridged complex [FeIII(μ-OPh)(μ2-mpdp)FeII(NH2Bn)] (1; mpdp2- = m-phenylenedipropionate) bearing a terminal aminobenzyl ligand can be reversibly deprotonated to the anilinate complex 2 whose core [FeII(μ-OPh)(μ2-mpdp)FeIII(NHBn)] features an inversion of the iron valences. This observation is supported by a combination of UV-visible, 1H NMR, and Mössbauer spectroscopic studies. [ABSTRACT FROM AUTHOR]

A new series of complexes of Eu2+ and Yb2+ with tripodal aminophenolate ligands are reported by M. Mazzanti and colleagues in their Full Paper on page 15188 ff. Cyclic voltammetry studies show that these ligands can be effectively used to tune the redox properties and reactivity of lanthanide ions possessing weak reducing power. The increased reducing power of Eu2+ in a homoleptic aminophenolate complex allows the reduction of CS2 and affords the first example of a lanthanide trithiocarbonate complex. [ABSTRACT FROM AUTHOR]