Correction: Core-substituted naphthalenediimides anchored on BiVO4 for visible light-driven water splitting

Correction for 'Core-substituted naphthalenediimides anchored on BiVO4 for visible light-driven water splitting' by Simelys Hernández et al., Green Chem., 2017, 19, 2448–2462

Effective storage of electrons in water by the formation of highly reduced polyoxometalate clusters

Aqueous solutions of polyoxometalates (POMs) have been shown to have potential as high-capacity energy storage materials due to their potential for multi-electron redox processes, yet the mechanism of reduction and practical limits are currently unknown. Herein, we explore the mechanism of multi-electron redox processes that allow the highly reduced POM clusters of the form {MO3}y to absorb y electrons in aqueous solution, focusing mechanistically on the Wells–Dawson structure X6[P2W18O62], which comprises 18 metal centers and can uptake up to 18 electrons reversibly (y = 18) per cluster in aqueous solution when the countercations are lithium. This unconventional redox activity is rationalized by density functional theory, molecular dynamics simulations, UV–vis, electron paramagnetic resonance spectroscopy, and small-angle X-ray scattering spectra. These data point to a new phenomenon showing that cluster protonation and aggregation allow the formation of highly electron-rich meta-stable systems in aqueous solution, which produce H2 when the solution is diluted. Finally, we show that this understanding is transferrable to other salts of [P5W30O110]15– and [P8W48O184]40– anions, which can be charged to 23 and 27 electrons per cluster, respectively

New Horizons in Computational Modeling of Polyoxometalates: Biological Activity, Energy Storage and Sustainable Catalysis

Els Polioxometal·lats (POMs) constitueixen una família d’òxids metàl·lics moleculars normalment formats per W, Mo o V en l’estat d’oxidació més elevat. Degut a les seves característiques moleculars i electròniques, els POMs han mostrat aplicabilitat en nombrosos camps. D’entre ells, aquesta tesi cobreix estudis computacionals amb l’objectiu d’entendre el paper dels POMs en aplicacions relacionades amb la bioquímica, l’emmagatzematge d’energia i la catàlisi. La discussió es pot dividir en tres parts ben diferenciades. La primera tracta la interacció dels POMs amb sistemes biològics. Específicament, hem caracteritzat la naturalesa de les interaccions POM···proteïna a nivell atomístic i els seus fonaments fisicoquímics utilitzant simulacions de dinàmica molecular. Aquest estudi també avalua com diversos paràmetres de l’estructura del POM afecten la seva afinitat pels sistemes biològics. Amés, hem estudiat dos exemples de reactivitat entre POMs i proteïnes. Aquests són la hidròlisi selectiva d’enllaços peptídics amb POMs que contenen Zr i la reducció de ponts disulfur promoguda per POMs reduïts, la qual s’ha investigat conjuntament amb col·laboradors experimentals. El segon tema està relacionat amb les propietats redox dels POMs. En particular, hem analitzat les raons per la reducció electroquímica de POMs més enllà dels seus límits prèviament coneguts observada experimentalment, que està estretament lligada al comportament col·lectiu dels POMs en solució. Finalment, en col·laboració amb diversos grups experimentals, presentem els avenços més recents en la modelització computacional de la reacció d’epoxidació d’alquens catalitzada per POMs substituïts amb Nb i Ti. Notablement, aquestes oxidacions fan servir peròxid d’hidrogen com oxidant respectuós amb el medi ambient que genera aigua com únic subproducte. En general, aquest treball representa un pas endavant en la modelització computacional de POMs i demostra encara més la capacitat dels mètodes computacionals de donar respostes precises a qüestions complexes que deriven dels últims progressos en recerca química.Los Polioxometalatos (POMs) constituyen una familia de óxidos metálicos moleculares comúnmente formados por W, Mo o V en su mayor estado de oxidación. Debido a sus características moleculares y electrónicas, los POMs han mostrado aplicabilidad en numerosos campos. Entre ellos, esta tesis cubre estudios computacionales orientados a entender el papel de los POMs en aplicaciones relacionadas con la bioquímica, el almacenaje de energía y la catálisis. La discusión se puede dividir en tres partes. La primera trata la interacción de POMs con sistemas biológicos. Específicamente, hemos caracterizado la naturaleza de las interacciones POM···proteína a nivel atomístico y sus fundamentos fisicoquímicos usando simulaciones de dinámica molecular. Este estudio también evalúa cómo diferentes parámetros estructurales del POM afectan su afinidad hacia sistemas biológicos. Además, hemos estudiado dos ejemplos de reactividad entre POMs y proteínas. Éstos son la hidrólisis selectiva de enlaces peptídicos con POMs que contienen Zr y la reducción de puentes disulfuro promovida por POMs reducidos, la cual se ha investigado conjuntamente con colaboradores experimentales. El segundo tema está relacionado con las propiedades redox de los POMs. En particular, hemos analizado las razones de la reducción electroquímica de POMs más allá de sus límites conocidos observada experimentalmente, que está estrechamente ligada al comportamiento colectivo de los POMs en solución. Finalmente, en colaboración con diferentes grupos experimentales, presentamos los adelantos más recientes en la modelización computacional de la reacción de epoxidación de alquenos catalizada por POMs sustituidos con Nb y Ti. Notablemente, estas oxidaciones usan peróxido de hidrógeno como oxidante respetuoso con el medio ambiente que genera agua como único subproducto. En general, este trabajo representa un paso adelante en la modelización computacional de POMs y demuestra todavía más la capacidad de los métodos computacionales para dar respuestas precisas a cuestiones complejas que derivan de los últimos progresos en investigación química.Polyoxometalates (POMs) constitute a family of polynuclear metal oxide clusters that are usually built up from W, Mo or V in their highest oxidation state. Owing their molecular and electronic features, POMs have shown applicability in a wide variety of fields. Among them, this thesis covers computational studies aimed to understand the role of POMs in applications related to biochemistry, energy storage or catalysis. The discussion can be divided in three well-differentiated parts. The first one deals with the interaction of POMs with biological systems. Specifically, we have characterized the nature of the POM···protein interactions at atomistic level, as well as their physicochemical foundations, using molecular dynamics simulations. This survey also evaluates how the affinity of POMs towards biological systems is influenced by several parameters of the POM structure. Furthermore, we studied two examples of reactivity between POMs and proteins. These are the selective hydrolysis of peptide bonds by Zr-containing POMs and the reduction of disulfide bridges promoted by reduced POMs, which has been investigated together with experimental collaborators. The second topic links with redox properties of POMs. In particular, we have analyzed the reasons for the experimentally observed electrochemical reduction of POMs beyond their previously known limits, which is tightly related to the collective behavior of POMs in solution. Finally, and in collaboration with several experimental groups, we report the most recent advances in the computational modeling of the alkene epoxidation reaction catalyzed by Nb- and Ti-substituted POMs. Notably, these oxidations take advantage of hydrogen peroxide as environmentally friendly terminal oxidant that generates water as sole by-product. Overall, this work represents a step forward in the computational modeling of POMs and further probes the capability of computational methods to provide accurate answers to complex questions arising from the latest progresses in chemical research

New Horizons in Computational Modeling of Polyoxometalates: Biological Activity, Energy Storage and Sustainable Catalysis

Els Polioxometal·lats (POMs) constitueixen una família d’òxids metàl·lics moleculars normalment formats per W, Mo o V en l’estat d’oxidació més elevat. Degut a les seves característiques moleculars i electròniques, els POMs han mostrat aplicabilitat en nombrosos camps. D’entre ells, aquesta tesi cobreix estudis computacionals amb l’objectiu d’entendre el paper dels POMs en aplicacions relacionades amb la bioquímica, l’emmagatzematge d’energia i la catàlisi. La discussió es pot dividir en tres parts ben diferenciades. La primera tracta la interacció dels POMs amb sistemes biològics. Específicament, hem caracteritzat la naturalesa de les interaccions POM···proteïna a nivell atomístic i els seus fonaments fisicoquímics utilitzant simulacions de dinàmica molecular. Aquest estudi també avalua com diversos paràmetres de l’estructura del POM afecten la seva afinitat pels sistemes biològics. Amés, hem estudiat dos exemples de reactivitat entre POMs i proteïnes. Aquests són la hidròlisi selectiva d’enllaços peptídics amb POMs que contenen Zr i la reducció de ponts disulfur promoguda per POMs reduïts, la qual s’ha investigat conjuntament amb col·laboradors experimentals. El segon tema està relacionat amb les propietats redox dels POMs. En particular, hem analitzat les raons per la reducció electroquímica de POMs més enllà dels seus límits prèviament coneguts observada experimentalment, que està estretament lligada al comportament col·lectiu dels POMs en solució. Finalment, en col·laboració amb diversos grups experimentals, presentem els avenços més recents en la modelització computacional de la reacció d’epoxidació d’alquens catalitzada per POMs substituïts amb Nb i Ti. Notablement, aquestes oxidacions fan servir peròxid d’hidrogen com oxidant respectuós amb el medi ambient que genera aigua com únic subproducte. En general, aquest treball representa un pas endavant en la modelització computacional de POMs i demostra encara més la capacitat dels mètodes computacionals de donar respostes precises a qüestions complexes que deriven dels últims progressos en recerca química.Los Polioxometalatos (POMs) constituyen una familia de óxidos metálicos moleculares comúnmente formados por W, Mo o V en su mayor estado de oxidación. Debido a sus características moleculares y electrónicas, los POMs han mostrado aplicabilidad en numerosos campos. Entre ellos, esta tesis cubre estudios computacionales orientados a entender el papel de los POMs en aplicaciones relacionadas con la bioquímica, el almacenaje de energía y la catálisis. La discusión se puede dividir en tres partes. La primera trata la interacción de POMs con sistemas biológicos. Específicamente, hemos caracterizado la naturaleza de las interacciones POM···proteína a nivel atomístico y sus fundamentos fisicoquímicos usando simulaciones de dinámica molecular. Este estudio también evalúa cómo diferentes parámetros estructurales del POM afectan su afinidad hacia sistemas biológicos. Además, hemos estudiado dos ejemplos de reactividad entre POMs y proteínas. Éstos son la hidrólisis selectiva de enlaces peptídicos con POMs que contienen Zr y la reducción de puentes disulfuro promovida por POMs reducidos, la cual se ha investigado conjuntamente con colaboradores experimentales. El segundo tema está relacionado con las propiedades redox de los POMs. En particular, hemos analizado las razones de la reducción electroquímica de POMs más allá de sus límites conocidos observada experimentalmente, que está estrechamente ligada al comportamiento colectivo de los POMs en solución. Finalmente, en colaboración con diferentes grupos experimentales, presentamos los adelantos más recientes en la modelización computacional de la reacción de epoxidación de alquenos catalizada por POMs sustituidos con Nb y Ti. Notablemente, estas oxidaciones usan peróxido de hidrógeno como oxidante respetuoso con el medio ambiente que genera agua como único subproducto. En general, este trabajo representa un paso adelante en la modelización computacional de POMs y demuestra todavía más la capacidad de los métodos computacionales para dar respuestas precisas a cuestiones complejas que derivan de los últimos progresos en investigación química.Polyoxometalates (POMs) constitute a family of polynuclear metal oxide clusters that are usually built up from W, Mo or V in their highest oxidation state. Owing their molecular and electronic features, POMs have shown applicability in a wide variety of fields. Among them, this thesis covers computational studies aimed to understand the role of POMs in applications related to biochemistry, energy storage or catalysis. The discussion can be divided in three well-differentiated parts. The first one deals with the interaction of POMs with biological systems. Specifically, we have characterized the nature of the POM···protein interactions at atomistic level, as well as their physicochemical foundations, using molecular dynamics simulations. This survey also evaluates how the affinity of POMs towards biological systems is influenced by several parameters of the POM structure. Furthermore, we studied two examples of reactivity between POMs and proteins. These are the selective hydrolysis of peptide bonds by Zr-containing POMs and the reduction of disulfide bridges promoted by reduced POMs, which has been investigated together with experimental collaborators. The second topic links with redox properties of POMs. In particular, we have analyzed the reasons for the experimentally observed electrochemical reduction of POMs beyond their previously known limits, which is tightly related to the collective behavior of POMs in solution. Finally, and in collaboration with several experimental groups, we report the most recent advances in the computational modeling of the alkene epoxidation reaction catalyzed by Nb- and Ti-substituted POMs. Notably, these oxidations take advantage of hydrogen peroxide as environmentally friendly terminal oxidant that generates water as sole by-product. Overall, this work represents a step forward in the computational modeling of POMs and further probes the capability of computational methods to provide accurate answers to complex questions arising from the latest progresses in chemical research

Origin of the Boosting Effect of Polyoxometalates in Photocatalysis: The Case of CO 2 Reduction by a Rh-Containing Metal–Organic Framework

International audienceThe immobilization of polyoxometalates (POMs) near catalytic centers of metal–organic frameworks (MOFs) has been reported as an advantageous strategy to boost their photocatalytic activity toward strategic reactions such as CO2 reduction (CO2RR) or hydrogen evolution (HER), although the reasons for such enhancement are still poorly understood. Unveiling the role of POM guests in the reaction mechanisms is therefore a key step toward the development of the next generation of multicomponent catalytic materials with optimal photocatalytic performances. Here, we elucidate the remarkable role of encapsulated [PW12O40]3– (PW12) polyoxometalates in boosting the photocatalytic activity of the Rh-functionalized UiO-67 MOF toward CO2RR and HER by combining theoretical density functional theory and microkinetic modeling approaches with experimental photophysical and spectroscopic techniques. First, we characterized in detail the reaction mechanism for CO2RR and HER catalyzed by the PW12-containing Rh-functionalized MOF, using [Ru(bpy)3]2+ as the photosensitizer (PS) and triethanolamine (TEOA) as the sacrificial electron donor in acetonitrile. Our results reveal that the encapsulated POMs act as efficient electron reservoirs, which quench [Ru(bpy)3]+─the photogenerated reduced form of the PS─and transfer the electrons to the Rh catalytic sites of the MOF. Notably, this is shown to favor the regeneration of the oxidized PS over its unproductive degradation, boosting the turnover numbers of the photocatalytic system. Such a mechanism can explain not only the higher formate and H2 product yields in the POM-containing catalyst but also the experimentally observed higher impact on the HER pathway than that on the CO2RR one, as the source of protons is generated in the reductive quenching of the photoexcited PS by TEOA. Finally, our computational exploration was extended to a whole variety of POMs, which allowed establishing relationships between their redox potentials and the activity of the related POM-containing catalytic materials. The optimal activity is reached when both the ability of the POM to accept electrons and that of its reduced form to reduce the Rh catalyst are simultaneously maximized, leading to a volcano plot whereby POMs with a moderate redox potential display the highest impact on photocatalytic performances

Electrocatalytic Conversion of CO2 to Formate at Low Overpotential by Electrolyte Engineering in Model Molecular Catalysis

International audienceWe report electrolyte engineering strategy for CO 2 reduction into formate with a model molecular catalyst, i.e. [Rh(bpy)(Cp*)Cl]Cl, by modifying the solvent (organic or aqueous), the proton source (H 2 O or acetic acid) and the electrode/solution interface with imidazolium- and pyrrolidinium-based ionic liquids (ILs). Our experimental and theoretical DFT investigations suggest that π + -π interactions between the imidazolium-based IL cation and the reduced bipyridine ligand of the catalyst improve the efficiency of the CO 2 reduction reaction (CO 2 RR) by lowering the overpotential, while granting partial suppression of hydrogen evolution reaction (HER). This allows tuning the selectivity towards formate, reaching for this catalyst an unprecedented faradaic efficiency (FE HCOO -) ≥ 90 % and energy efficiency = 66 % in acetonitrile solution. For the first time, relevant CO 2 conversion to formic acid/formate is reached at low overpotential (0.28 V) using a homogenous catalyst in acidic aqueous solution (pH = 3.8). These results open up a new strategy based on electrolyte engineering for enhancing carbon balance in CO 2 RR

Molecular Characteristics of a Mixed-Valence Polyoxovanadate {V IV/V 18 O 42 } in Solution and at the Liquid-Surface Interface

The understanding of the molecular state of vanadium-oxo clusters (polyoxovanadates, POVs) in solution and on surface is a key to their target application in catalysis as well as molecular electronics and spintronics. We here report the results of a combined experimental and computational study of the behavior of nucleophilic polyoxoanions [VIV10VV8O42(I)]5– charged balanced by Et4N+ in water, in a one-phase organic solution of N,N-dimethylformamid (DMF) or acetonitrile (MeCN), in a mixed solution of MeCN–water, and at the hybrid liquid–surface interface. The molecular characteristics of the compound (NEt4)5[V18O42(I)] (1) in the given environments were studied by microspectroscopic, electrochemical, scattering, and molecular mechanics methods. Contrary to the situation in pure water, where we observe great agglomeration with a number of intercalated H2O molecules between POVs that are surrounded by the Et4N+ ions, no or only minor agglomeration of redox-active POVs in an unprecedented cation-mediated fashion was detected in pure DMF and MeCN, respectively. An inclusion of 1% water in the MeCN solution does not have an effect significant enough to reinforce agglomeration; however, this leads to the POV···POV interface characterized by the presence of the Et4N+ ions and a small number of H2O molecules. Water amounts of ≥5% trigger the formation of higher oligomers. The deposition of compound 1 from MeCN onto an Au(111) surface affords nearly round-shaped particles (∼10 nm). The use of DMF instead of MeCN results in bigger, irregularly shaped particles (∼30 nm). This change of solvent gives rise to more extensive intermolecular interactions between polyoxoanions and their countercations as well as weaker binding of ion-pairing induced agglomerates to the metallic substrate. Lower concentration of adsorbed molecules leads to a submonolayer coverage and an accompanied change of the POV’s redox state, whereas their higher concentration results in a multilayer coverage that offers the pristine mixed-valence structure of the polyoxoanion. Our study provides first important insights into the reactivity peculiarities of this redox-responsive material class on a solid support

Heterogenized Molecular Rhodium Phosphine Catalyst within Metal-Organic Framework for Ethylene Hydroformylation

Molecularly-defined organometallic rhodium phosphine complexes were efficiently heterogenized within a MOF structure without affecting neither their molecular nature nor their catalytic behavior. Phosphine-functionalized MOF-808 served as solid ligand in a series of eight rhodium phosphine catalysts. These MOF-heterogenized molecular catalysts showed activity up to 2100 h-1 for ethylene hydroformylation towards pro-pionaldehyde as sole carbon-containing product. Combined experimental and computational methods applied to this unique MOF-based molecular system allowed unravelling structure and evolution of the Rh active species within the MOF under catalytic conditions, in line with molecular mechanisms at play during the hydroformylation reaction. The MOF-808 designed as a porous crystalline macroligand for well-defined molecular catalysts allows benefiting from molecular-scale understanding of interactions and mechanisms as well as from stabilization through site-isolation and recycling ability

Light-Driven Hydrogen Evolution Reaction Catalyzed by a Molybdenum-Copper Artificial Hydrogenase

International audienceOrange Protein (Orp) is a small bacterial metalloprotein of unknown function that harbors a unique molybdenum/copper (Mo/Cu) heterometallic cluster, [S2MoS2CuS2MoS2]3−. In this paper, the performance of Orp as a catalyst for the photocatalytic reduction of protons into H2 has been investigated under visible light irradiation. We report the complete biochemical and spectroscopic characterization of holo-Orp containing the [S2MoS2CuS2MoS2]3− cluster, with docking and molecular dynamics simulations suggesting a positively charged Arg, Lys-containing pocket as the binding site. Holo-Orp exhibits an excellent photocatalytic activity, in the presence of ascorbate as the sacrificial electron donor and [Ru(bpy)3]Cl2 as the photosensitizer, for hydrogen evolution with a maximum turnover number of 890 after 4 hours irradiation. DFT calculations were used to propose a consistent reaction mechanism in which the terminal sulfur atoms are playing a key role in promoting H2 formation. A series of dinuclear [S2MS2M’S2MS2](4n)− clusters, with M = MoVI, WVI and M’(n+) = CuI, FeI, NiI, CoI , ZnII, CdII were assembled in Orp, leading to different M/M’-Orp versions which are shown to display catalytic activity, with the Mo/Fe-Orp catalyst giving a remarkable TON of 1150 after 2.5 hours reaction and an initial turnover frequency (TOF°) of 800 h-1 establishing a record among previously reported artificial hydrogenases