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Highly efficient, durable, and economically viable electrocatalysts for oxygen reduction reaction (ORR) is central for energy conversion and storage devices such as fuel cells and metal–air batteri...

We report on an additive-free Mn(I)-catalyzed dehydrogenative silylation of terminal alkenes. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn–alkyl bond to yield an acyl intermediate which undergoes rapid Si–H bond cleavage of the silane HSiR3 forming the active 16e– Mn(I) silyl catalyst [Mn(dippe)(CO)2(SiR3)] together with liberated butanal. A broad variety of aromatic and aliphatic alkenes was efficiently and selectively converted into E-vinylsilanes and allylsilanes, respectively, at room temperature. Mechanistic insights are provided based on experimental data and DFT calculations revealing that two parallel reaction pathways are operative: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as sacrificial hydrogen acceptor.

Tallennetaan lopullinen OA-artikkeli, kun julkaistu | openaire: EC/H2020/824070/EU//CONNECT Electrode fouling is a major factor that compro-mises the performance of biosensors inin vivousage. It can beroughly classified into (i) electrochemical fouling, caused by theanalyte and its reaction products, and (ii) biofouling, caused byproteins and other species in the measurement environment. Here,we examined the effect of electrochemical fouling [in phosphatebuffer saline (PBS)], biofouling [in cell-culture media (F12-K)with and without proteins], and their combination on the redoxreactions occurring on carbon-based electrodes possessing distinctmorphologies and surface chemistry. The effect of biofouling onthe electrochemistry of an outer sphere redox probe, [Ru-(NH3)6]3+, was negligible. On the other hand, fouling had amarked effect on the electrochemistry of an inner sphere redox probe, dopamine (DA). We observed that the surface geometryplayed a major role in the extent of fouling. The effect of biofouling on DA electrochemistry was the worst on planar pyrolyticcarbon, whereas the multiwalled carbonnanotube/tetrahedral amorphous carbon (MWCNT/ta-C), possessing spaghetti-likemorphology, and carbon nanofiber (CNF/ta-C) electrodes were much less seriously affected. The blockage of the adsorption sitesfor DA by proteins and other components of biological media and electrochemical fouling components (byproducts of DAoxidation) caused rapid surface poisoning. PBS washing for 10 consecutive cycles at 50 mV/s did not improve the electrodeperformance, except for CNF/ta-C, which performed better after PBS washing. Overall, this study emphasizes the combined effect ofbiological and electrochemical fouling to be critical for the evaluation of the functionality of a sensor. Thus, electrodes possessingcomposite nanostructures showed less surface fouling in comparison to those possessing planar geometry.

Nickel superoxide dismutase (NiSOD) is an enzyme that protects cells against O2·-. While the structure of its active site is known, the mechanism of the catalytic cycle is still not elucidated. Its active site displays a square planar NiII center with two thiolates, the terminal amine and an amidate. We report here a bioinspired NiII complex built on an ATCUN-like binding motif modulated with one cysteine, which demonstrates catalytic SOD activity in water (kcat = 8.4(2) × 105 M-1 s-1 at pH = 8.1). Its reactivity with O2·- was also studied in acetonitrile allowing trapping two different short-lived species that were characterized by electron paramagnetic resonance or spectroelectrochemistry and a combination of density functional theory (DFT) and time-dependent DFT calculations. Based on these observations, we propose that O2·- interacts first with the complex outer sphere through a H-bond with the peptide scaffold in a [NiIIO2·-] species. This first species could then evolve into a NiIII hydroperoxo inner sphere species through a reaction driven by protonation that is thermodynamically highly favored according to DFT calculations.

Heterogeneous photocatalysis is less common but can provide unique avenues for inducing novel chemical transformations and can also be utilized for energy transductions, i.e., the energy in the photons can be captured in chemical bonds. Here, we developed a novel heterogeneous photocatalytic system that employs a lead-halide perovskite nanocrystal (NC) to capture photons and direct photogenerated holes to a surface bound transition metal Cu-site, resulting in a N-N heterocyclization reaction. The reaction starts from surface coordinated diamine substrates and requires two subsequent photo-oxidation events per reaction cycle. We establish a photocatalytic pathway that incorporates sequential inner sphere electron transfer events, photons absorbed by the NC generate holes that are sequentially funneled to the Cu-surface site to perform the reaction. The photocatalyst is readily prepared via a controlled cation-exchange reaction and provides new opportunities in photodriven heterogeneous catalysis.

Hydroxide ion is a common electrolyte when electrode reactions take place in alkaline media. In the case of oxygen reduction reaction on Pt(111), we demonstrate by ab initio molecular dynamics calculations that the desorption of hydroxyl (OH*) from the electrode surface to form a solvated OH- is a cross-sphere process, with the OH* reactant in the inner sphere and the OH- product directly generated in the aqueous outer sphere. Such a mechanism is distinct from the typical inner sphere and outer sphere reactions. It is dictated by the strong hydrogen bonding interactions between a hydroxide ion and water molecules and is facilitated by proton transfer through solvation layers. It should play a significant role whenever OH* desorption, or its reverse, OH- adsorption, is involved in an electrochemical reaction.

Palladium-catalyzed asymmetric allylic alkylation (AAA) of vinyl benzoxazinanones has become an important strategy for the synthesis of chiral nitrogen-containing heterocycle compounds. However, the asymmetric synthesis of linear-selective products has rarely been reported. The simultaneous control of regio-, E/Z- and enantioselectivities constitutes a major challenge and inhibits the advancement of this chemistry. Herein, we present a palladium-catalyzed AAA of vinyl benzoxazinanones with α-thiocyanato ketones, affording various chiral thiocyanates characterized with high linear-, E- and stereoselectivities. The reaction has a broad substrate scope and the chiral thiocyanates can be transformed to useful heterocycles. Experimental and computational studies suggest an inner-sphere mechanism for AAA process, which results from the acidic and coordination effect of the nucleophilic substrates with palladium catalyst.

The mainstream applications of visible‐light photoredox catalysis predominately involve outer‐sphere single‐electron transfer (SET) or energy transfer (EnT) processes of precious metal RuII or IrIII complexes or of organic dyes with low photostability. Earth‐abundant metal‐based MnLn‐type (M=metal, Ln=polydentate ligands) complexes are rapidly evolving as alternative photocatalysts as they offer not only economic and ecological advantages but also access to the complementary inner‐sphere mechanistic modes, thereby transcending their inherent limitations of ultrashort excited‐state lifetimes for use as effective photocatalysts. The generic process, termed visible‐light‐induced homolysis (VLIH), entails the formation of suitable light‐absorbing ligated metal–substrate complexes (MnLn‐Z; Z=substrate) that can undergo homolytic cleavage to generate Mn−1Ln and Z. for further transformations., The use of earth‐abundant metal complexes in photoredox catalysis offers a complementary mode of activation for organic substrates through visible‐light‐induced homolysis (VLIH) of metal–substrate bonds. This Minireview describes different electronic transitions that occur in photoexcited metal–substrate complexes as well as recent advancements and future prospects in this area.

The effect of a closed boundary on the hydrodynamic drag of a nonconcentric semipermeable sphere in an incompressible viscous fluid is investigated. Darcy’s law holds in the permeable region and Stokes flow used inside the spherical cavity. Suitable boundary conditions are used on the surface of a semipermeable sphere and spherical cavity. Two spherical coordinate systems are used to solve the problem. By superposition principle, a general solution is constructed from the solutions based on the semipermeable sphere and spherical cavity. Numerical results for the hydrodynamic drag force exerted on the particle is obtained with good convergence for various values of the relative distance between the centers of the inner sphere and spherical cavity, permeability parameter and the separation parameter. The numerical values of the hydrodynamic drag force generalize the results obtained for an eccentric solid sphere.

The combined molecular dynamics (MD) simulations and quantum mechanical/molecular mechanics (QM/MM) calculations have been performed to address the longstanding issue of the “dioxygen activation” b...

The formal hydroamination/hydroamidation utilizing metal hydride is an appealing synthetic tool for the construction of valuable nitrogen-containing compounds from unsaturated hydrocarbons. While significant advances have been made for the functionalizations of alkenes in this realm, the direct hydroamidation of alkynes remains rather limited due to the high feasibility of the key metal-alkenyl intermediate to choose other reaction pathways. Herein, we report a NiH-catalyzed strategy for the hydroamidation of alkynes with dioxazolones, which allows convenient access to synthetically useful secondary enamides in (E)-anti-Markovnikov or Markovnikov selectivity. The reaction is viable for both terminal and internal alkynes and is also tolerant with a range of subtle functional groups. With H2O found as an essential component for high catalyst turnovers, the involvement of inner-sphere nitrenoid transfer is proposed that outcompetes an undesired semireduction process, thus representing the first example to show the competence of Ni catalysis for metal-nitrenoid formation from dioxazolones.

An inner-sphere disproportionation mechanism of the Co(I) precursor CoCl(PPh3 )3 is described through a Density Functional Theory study. The essential role of oleylamine in this process is unravelled. A detailed analysis of the electronic structure of Cobalt dimers of the general formula Co2 Cl2 Ln (L=NH3 and PH3 ) demonstrates that electron transfer is triggered by asymetric coordination of amine and phosphine to stabilize a mixed-valence Co(II)-Co(0) dimer. This is consistent with the HSAB statement that both amine and phosphine ligands are required to stabilize the reaction products, respectively Co(II) and Co(0) centers. We propose a quasi-athermic multi-step disproportionation mechanism with low activation barriers where the electron transfer goes through simple ligand exchanges between Co.

Novel mixed-ligands complexes of cytosine (M-cytH-isaH, where isaH denotes isatin) and cytosine capped silver nanoparticles (cytH-AgNPs) are synthesized. The complexes are characterized by different spectroscopic techniques and thermal analyses. Cytosine exhibits different binding modes with the metal ions through the ring nitrogen N(3) and/or C=O forming square planar or octahedral geometries. The ESR spectra of the Cu(II) complexes point to the existence of spin exchange interaction between the metal centers. For all complexes, the thermal decomposition of the inner sphere starts at T ~ 200 °C indicating their high thermal stability. Structure of cytH-AgNPs is investigated by proper microscopic techniques; SEM, TEM, EDX and XRD. The crystal pattern of AgNPs is FCC symmetry with spherical shape and an average nanoparticle size of 5.72–16.31 nm. Biological screening of the synthesized compounds shows that Cu(II) complex, [Cu2(cyt)(isa)2Cl], displays the highest antibacterial activity with inhibition zone diameter of 21 mm/mg sample similar to that of ampicillin. Furthermore, only AgNPs exhibits significant antifungal activity against A. flavus where its smaller size is assumed to play an important role in blocking cell communication mechanisms. Density functional theory, DFT, and molecular docking studies are performed to evaluate the quantum chemical parameters and to shed light on the sites of interaction with the selected protein 1bqb of S. aureus. The scoring energy of [Cu2(cyt)(isa)2Cl] is in good agreement with the superior inhibition activity measured experimentally for this complex.

The positive impact of having access to well-defined starting materials for applied actinide technologies – and for technologies based on other elements – cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac3+ and Cm3+ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H2O)6(1)(O2CMe)3(1) compound was the major species in solution for the large Ac3+. In contrast, smaller Cm3+ preferred forming an anion. There were approximately four bound O2CMe1− ligands and one to two inner sphere H2O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH4)2M(O2CMe)5 (M = Eu3+, Am3+ and Cm3+) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements)., Actinide complexation from aqueous acetic acid/acetate buffered solutions is described. The number of water ligands was directly correlated with the acetate concentration and characterized by X-ray absorption and optical spectroscopy.

The bisoxine hexadentate chelating ligand, H3glyox was investigated for its affinity for Mn2+, Cu2+ and Lu3+ ions; all three metal ions are relevant with applications in nuclear medicine and medicinal inorganic chemistry. The aqueous coordination chemistry and thermodynamic stability of all three metal complexes were thoroughly investigated by detailed DFT structure calculations and stability constant determination, by employing UV in-batch spectrophotometric titrations, giving pM values (pM = −log[Mn+]free when [Mn+] = 1 μM, [L] = 10 μM at pH 7.4 and 25 °C) – pCu (25.2) > pLu (18.1) > pMn (12.0). DFT calculated structures revealed different geometries and coordination preferences of the three metal ions; notable was an inner sphere water molecule in the Mn2+ complex. H3glyox labels [52gMn]Mn2+, [64Cu]Cu2+ and [177Lu]Lu3+ at ambient conditions with apparent molar activities of 40 MBq μmol−1, 500 MBq μmol−1 and 25 GBq μmol−1, respectively. Collectively, these initial investigations provide insight into the effects of metal ion size and charge on the chelation with the hexadentate H3glyox and indicate that further investigations of the Mn2+–H3glyox complex in 52g/55Mn-based bimodal imaging might be worthwhile.

The reduction of molecular oxygen (O2) and hydrogen peroxide (H2O2) by [RuII(edta)(pz)]2− (edta4− = ethylenediaminetetraacetate; pz = pyrazine) has been studied spectrophotometrically and kinetically in aqueous solution. Exposure of the aqua-analogue [RuII(edta)(H2O)]2− to O2 and H2O2 resulted in the formation of [RuIII(edta)(H2O)]− species, with subsequent formation of the corresponding RuVO complex. A working mechanism for the O2 and H2O2 reduction reactions mediated by the RuII(edta) complexes is proposed. The role of the coordinated water molecule (by its absence or presence in the primary coordination sphere) in controlling the mechanistic pathways, outer-sphere or inner-sphere, is discussed.

In the extraction of lanthanides by the sulfur donor ligand, Cyanex 301 (HC301, bis(2,4,4-trimethylpentyl)dithiophosphinic acid), a transition in the coordination mode of extracted complexes has been observed between Eu and Gd. The light lanthanides La–Eu tend to be extracted as inner sphere complexes with HC301 directly coordinating the metal whereas the second half of the series Gd–Lu have a tendency to be extracted as outer sphere complexes. Without extended actinide studies, spanning the transplutonium actinides, it was unclear if a similar change in the extraction mechanism occurs in the actinide series. To assess this, solvent extraction studies were completed examining the slope dependence of the actinides and lathanides in the presence of varied nitrate and acid concentrations. Significant variation in the slope dependences was not observed for either the actinides or the lanthanides as pCH+ varied, however, the nitrate dependence and neodymium spectroscopy data suggest that the formation of outer sphere complexes is suppressed by higher nitrate concentrations. This suppression of outer sphere complexes enhanced the extraction of lanthanides, but not the actinides and suggests that the actinides form inner sphere complexes. Therefore, the HC301 separations chemistry observed thus far suggest differences in the chemistry of the actinides and lanthanides continues to persist deep into the actinide series.

A detailed reaction mechanism of acetylene cyclotrimerization catalyzed by V(i PrNPMe2 )3 Fe-PMe3 (denote as CAT), a heterobimetallic complex featuring V-Fe triple bond, was computationally investigated using density functional theory. The calculated results show that the first acetylene firstly attaches to the V atom of CAT to get a four-membered ring structure through [2 + 2] cycloaddition reaction. For the second acetylene addition, there are two cyclotrimerization mechanisms, outer sphere mechanism and inner mechanism. The inner sphere reaction pathway is the main reaction pathway. By replacing the V with Nb and Ta, Fe with Ru and Os, a series of new catalysts are screened computationally. The calculated results show that, all of the nine heterobimetallic complexes show high activity at mild condition. The energy barrier of the rate determining step is related to the natural population analysis (NPA) charge of M' and the Wiberg bond index (WBI) of M-M' bond. The more negative NPA charge of M' and the smaller WBI of M-M' bond, the lower energy barrier is.

Sulfur-bridged bimetallic 2M-2S type structures are essential cofactors that participate in biological long-range electron transport and metabolism. Metal-sulfur bond covalency is a decisive property for inner sphere (through-bond) type electron transfer that dominates in buried or hydrophobic protein environments. This work reports on a combined experimental and computational study of the effect of ligand charge on the electronic structure of a 2Ni-2S model site that adopts the biologically relevant S = 1/2 redox state. Starting out from an isostructural dinickel(1.5+)-dithiophenolate platform with sulfur-bridged tetrahedral Ni sites, η2:η2-μ-coordination of the S = 1/2 [2Ni-2S]+ core to either a neutral π-system or strongly σ-donating cyclohexadienido renders its electronic structure substantially different. Density functional theory analysis corroborates pulse and continuous wave electron paramagnetic resonance data that associate co-ligand charge with the significant change in the mechanism and size of electron-31P nuclear spin hyperfine coupling to a phosphine reporter ligand at each nickel center. An increasing level of charge donation attenuates direct and through-bridge electronic coupling of the metal sites, resulting in a stronger electronic coupling of the 2Ni-2S core to its terminal phosphine donors. Drawing a connection to biological 2M-2S sites, our 2Ni-2S system indicates that a fine balance of intracore and core-protein electronic coupling is key to biological function for which the degree of charge donation by peripheral donors appears to be a significant parameter.

2-Oxopropanoic acid reacts in ethanol with N-(prop-2-en-1-yl)hydrazinecarbothioamide in a 1 : 1 mole ratio to form thiosemicarbazone H2L. Coordination compounds Cu(HL)X [X = Cl–, Br–, NO3–], Cu(H2O)(L), Ni(HL)2, Co(HL)2X [X = Cl–, Br–], and Fe(HL)2X [X = NO3–, Br–] are formed in the reactions of H2L with copper(II), nickel(II), cobalt(II), and iron(III) salts. The reactions of Cu(H2O)(L) with imidazole (Im) and 3,4-dimethylpyridine (3,4-Lut) result in mixed-ligand complexes Cu(A)(L) [A = Im, 3,4-Lut]. The structures of two copper complexes were determined by single crystal X-ray diffraction analysis. The synthesized complexes exhibit selective antimicrobial and antifungal activity in the concentration range of 15.62–1000 μg/mL. The introduction of amines into the inner sphere of copper complexes leads to an increase in the antimicrobial activity.

Mesoporous zerovalent iron-magnetite nanocomposites (ZVI-MNCs) were developed to circumvent the limitations of magnetite, such as its susceptibility to phase transition in air-water interfaces. High-resolution transmission electron microscopy images revealed the presence of Fe0 and Fe3O4 in the as-prepared adsorbent. High-resolution X-ray photoelectron spectroscopy (HR-XPS) Fe 2p deconvoluted spectra showed that electron transfer between Fe0 and Fe3O4 controlled the magnetite transformation. The isotherm equilibrium data for As(III) and As(V) are described by the Sips model, which suggests single- and multilayer formation onto a heterogeneous surface with different binding sites, whereas adsorption is controlled by a pseudo-second-order kinetic model, which indicates chemisorption. The maximum sorption capacities (qm) for As(III) and As(V) are 632.6 and 1000 μmol g-1, respectively, which are larger than the qm of similar adsorbents. The greater qm for As(V) is attributed to a higher multilayer formation and a stronger bonding force compared with As(III). The arsenic uptake capacity showed that the as-prepared adsorbent was effective over a wide pH range, and an optimal uptake capacity was recorded between pH 5.0 and 9.0 for As(III) and 3.0 and 7.0 for As(V). The adsorbent exhibited a remarkable regeneration performance for As(III) and As(V) uptake. Several microscopic analytical tools, including Fourier transform infrared spectroscopy, HR-XPS, and X-ray absorption near-edge structure together with zeta potential, confirmed that the binding mode of As(III) and As(V) on ZVI-MNCs was predominantly inner-sphere coordination. Partial redox transformation occurred for As(III) and As(V) on nearly 10 nm of the adsorbent, which indicates that a surface redox mechanism contributed partially to arsenic uptake on the near surface of the ZVI-MNCs. Extended X-ray absorption fine structure spectral analysis proposed that a corner-sharing monodentate mononuclear (1V) complex occurred for As(III) with a small portion of a corner-sharing bidentate binuclear (2C) complex, whereas As(V) formed a corner-sharing bidentate binuclear (2C) complex with octahedral Fe bonding.

Conspectus SmI2 was introduced to organic chemistry as a single electron transfer agent in 1977. After ca. 15 years of latency, the scientific community has realized the high potential of this reagent, and its chemistry has started blooming. This versatile reagent has mediated a myriad of new bond formations, cyclizations, and other reactions. Its popularity stems largely from the fact that three different intermediates, radical anions, radicals, and anions, depending on the ligand or additive used, could be obtained. Each of these intermediates could in principle lead to a different product. While these options vastly enrich the repertoire of SmI2, they necessitate a thorough mechanistic understanding, especially concerning how appropriate ligands direct the SmI2 to the desired intermediate. Our first paper on this subject dealt with the reduction of an activated double bond. The results were puzzling, especially the H/D isotope effect, which depended on the order of the reagents addition. This seminal paper was fundamental to an understanding of how the SmI2 works and enabled us to later explain various phenomena. For example, it was found that in a given reaction, when MeOH is used as a proton source, a spiro compound is obtained, while a bicyclic product is obtained when t-BuOH is used. Our contribution culminated in formulating guidelines for the rational use of proton donors in SmI2 reactions. The need to understand the complexity of the effect of additives on various processes is nicely demonstrated in photoinduced reactions. For example, hexamethylphosphoramide (HMPA) enhances the reduction of anthracene while hampering the reaction of benzyl chloride. The mechanistic understanding gained enabled us also to broaden the scope of photostimulated reactions from substrates reacting by a dissociative electron transfer mechanism to normal reductions, which are difficult to accomplish at the ground state. Harnessing the classical knowledge of proton transfer mechanisms to our SmI2 research enabled us to decipher an old conundrum: why does the combination of water and amine have such an enhancing effect on the reactivity of SmI2, which is not typical of these two when used separately. In our studies on the affinity of ligands to SmI2, we discovered that, in contradistinction to the accepted dogma, SmI2 is much more azaphilic than it is oxophilic. On the basis of the size difference between Sm3+ and Sm2+, we developed a simple diagnostic tool for the nature of the steps following the electron transfer. The reduction of imines showed that substrate affinity to SmI2 plays also a crucial role. In these reactions, new features such as autocatalysis and catalysis by quantum dots were discovered. Several studies of the ligand effect lead to a clear formulation of when an inner sphere or outer sphere electron transfer should be expected. In addition, several reactions where proton-coupled electron transfer (PCET) is the dominant mechanism were identified. Finally, the surprisingly old tool of NMR “shift reagents” was rediscovered and used to directly derive essential information on the binding constants of ligands and substrates to SmI2.

The dative Pd→B interaction in a series of RDPBR’ Pd0 and PdII complexes (RDPBR’=(o‐PR2C6H4)2BR’, diphosphinoborane) was analyzed using XRD, 11B NMR spectroscopy and NBO/NLMO calculations. The borane acceptor discriminates between the oxidation state PdII and Pd0, stabilizing the latter. Reaction of lithium amides with [(RDPBR’)PdII(4‐NO2C6H4)I] chemoselectively yields the C−N coupling product. DFT modelling indicates no significant impact of PdII→B coordination on the inner‐sphere reductive elimination rate., Ligand effects: The borane acceptor in diphosphinoborane ligands discriminates between the oxidation state PdII and Pd0, stabilizing the latter. The impact of the Pd→B interaction on inner‐sphere C−N bond reductive elimination of N,N‐dimethyl‐4‐nitroaniline was investigated (see scheme).

The inner-sphere adsorption of AsO43-, PO43-, and SO42- on the hydroxylated α-Al2O3(001) surface was modeled with the goal of adapting a density functional theory (DFT) and thermodynamics framework for calculating the adsorption energetics. While DFT is a reliable method for predicting various properties of solids, including crystalline materials comprised of hundreds (or even thousands) of atoms, adding aqueous energetics in heterogeneous systems poses steep challenges for modeling. This is in part due to the fact that environmentally relevant variations in the chemical surroundings cannot be captured atomistically without increasing the system size beyond tractable limits. The DFT + thermodynamics approach to this conundrum is to combine the DFT total energies with tabulated solution-phase data and Nernst-based corrective terms to incorporate experimentally tunable parameters such as concentration. Central to this approach is the design of thermodynamic cycles that partition the overall reaction (here, inner-sphere adsorption proceeding via ligand exchange) into elementary steps that can either be fully calculated or for which tabulated data are available. The ultimate goal is to develop a modeling framework that takes into account subtleties of the substrate (such as adsorption-induced surface relaxation) and energies associated with the aqueous environment such that adsorption at mineral-water interfaces can be reliably predicted, allowing for comparisons in the denticity and protonation state of the adsorbing species. Based on the relative amount of experimental information available for AsO43-, PO43-, and SO42- adsorbates and the well-characterized hydroxylated α-Al2O3(001) surface, these systems are chosen to form a basis for assessing the model predictions. We discuss how the DFT + thermodynamics results are in line with the experimental information about the oxyanion sorption behavior. Additionally, a vibrational analysis was conducted for the charge-neutral oxyanion complexes and is compared to the available experimental findings to discern the inner-sphere adsorption phonon modes. The DFT + thermodynamics framework used here is readily extendable to other chemical processes at solid-liquid interfaces, and we discuss future directions for modeling surface processes at mineral-water and environmental interfaces.

Ti atoms incorporated into the framework of zeolite *BEA (Ti-BEA) or grafted onto SBA-15 (Ti-SBA-15) catalyze alkene epoxidation with hydrogen peroxide (H2O2), t-butyl hydrogen peroxide (TBHP), or ...

The study reports the optimized incorporation of pyridinic nitrogen in nitrogen-doped carbon nanotubes (CNTs) to realize effective Fe-Nx centers throughout the framework. The study unveils nitrogen as a valuable asset to promote the homogeneous dispersion of Fe moieties throughout the CNT framework, which is a necessary component to institute uniform Fe-Nx centers. In addition, pyridinic nitrogen causes disruption in strongly delocalized π-electrons, which impart electron-withdrawing nature in the carbon matrix, resulting in an anodic shift in oxygen reduction reaction (ORR) onset potential (Eonset). The direct interaction of Fe-Nx with O2, as evidenced by poisoning and computational studies, ensures the preferential inner sphere electron transfer mechanism. Despite the alkaline medium, the outer sphere electron transfer mechanism was muted, with suppressed HO2- generation, preferential 4e- reduction pathways, and excellent cyclic stability. The study indicates the dependency of ORR half-wave potential on the electron transfer mechanism. The poisoning study unveils the direct involvement of Fe-Nx electroactive centers in facilitating ORR in alkaline medium. It further indicates a noticable increase (up to ∼25%) in peroxide generation-an unwanted ORR intermediate-and concomitant reduction in average electron transfer no. per oxygen molecule.

Dimeric [CrL]2 , where L is the conjugate base of bis-pyrazolyl pyridine, is evaluated for its ability to undergo inner sphere and outer sphere redox chemistry. It reacts with Cp2 Fe+ to give [Cr4 (HL)4 (μ4 -O)]2+ , still containing divalent Cr. Reduction (KC8 ) of [CrL]2 by two electrons gives [K2 (THF)3 Cr3 L3 (μ3 -O)], and by four electrons gives [K4 (THF)10 Cr2 L2 (μ-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. [K4 (THF)10 Cr2 L2 (μ-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L3- and CrII , illustrating that this pincer is proton-responsive, redox active, and a versatile donor to associated K+ ions here. The K+ electrophiles interact with electron-rich oxo, but do not significantly (>5 kcal mol-1 ) alter spin state energies. Inner sphere oxidation of [CrL]2 with a quinone gives [Cr2 L2 (semiquinone)2 ], while pre-reduced [CrL]22- reacts with quinone to give [K3 (THF)3 Cr2 L2 (catecholate)2 (μ-OH)], a product of capture of two undercoordinated LCr(catecholate)1- by hydroxide.

Calculations of high-spin isomers of MO4V20 $${\text{O}}_{{46}}^{{n-}}$$ anions (S = 9) with MO4 tetraoxo anions located in the inner and outer spheres of the mixed-valence V20O46 cage have been performed by the density functional theory method. It has been shown that for all systems the endohedral isomers are considerably more favorable than the exohedral isomers. For the complexes with transition metal atoms M (M = Ti, V, Cr), the centered ortho isomer MO4@V20 $${\text{O}}_{{46}}^{{n-}}$$ is clearly more preferable. For the complexes with main-group metal atoms (M = Si, Ge, P, As, S, Se), the meta isomer MO3@V20 $${\text{O}}_{{47}}^{{n-}}$$ has been localized in addition to ortho-MO4@V20 $${\text{O}}_{{46}}^{{n-}}$$ . The meta isomer has a pyramidal МО3 anion and the fourth oxygen atom bound to a trivalent vanadium atom of the cage through an inner О=VIII bond. For complexes with $${\text{SO}}_{4}^{{2-}}$$ and $${\text{SeO}}_{4}^{{2-}}$$ dianions, both ortho and meta structures do not correspond to stationary points of the potential energy surface: upon optimization, they convert without a barrier to the MO2@V20 $${\text{O}}_{{48}}^{{2-}}$$ isomer with two М−О−VIII bridges and two inner О=VIII bonds. The character of geometric distortions, normal mode shifts, and electron and spin density redistribution between the inserted MO4 guest and the cage as compared with isolated $${\text{MO}}_{4}^{{n-}}$$ and V20O46 systems has been considered. The results are compared with previous calculations of MO4@V20 $${\text{O}}_{{50}}^{{n-}}$$ complexes with the same anions into the valence-saturated V20O50 cluster. The stability and structure of the “nested” V4O6@V20O50 (S = 9) cluster with the more complex tetrahedral guest V4O6 inside the V20O50 cage are predicted.

The structural evolution of SF-soot (derived from the rapid pyrolysis of ShenFu bituminous coal) and a carbon black (Printex) was performed for air oxidation at 1273 and 1473 K. The morphology and nanostructure transformations were examined at conversion fractions ~0.2, 0.4, 0.6, and 0.8. Three modes of behavior were evident. The behavior of SF-soot followed an internal oxidation model (IOM) at 1273 K. The oxygen was able to fully permeate into the particle core, producing a sphere with variable removal of the interior structure with conversion. However, at the higher temperature, the SF-soot formed a concentric spherical structure with gradual consumption of the inner sphere due to restricted oxygen penetration. The fragmentation of hollow interior particles, on which the available literature is not extensive, was observed from HRTEM and SEM micrographs for the first time. During the oxidation of SF-soot, micropores were mainly generated during the 0–0.2 conversion, while the mesopore surface rapidly increased during the 0.6–0.8 conversion. The X-ray diffraction (XRD) patterns and Raman spectra both show that the oxidation of SF-soot is mainly a disordering process. The graphitic microcrystals were mainly consumed along the longitudinal orientation during the 0–0.2 conversion but were mainly consumed along the horizontal during the 0.4–0.8 conversion. The true densities of SF-soot and carbon black initially increase and then decrease monotonically during oxidation.

Because of its significant toxicological effects on the environment and human health, arsenic (As) is a major global issue. In this study, an Fe-based metal-organic framework (MOF) (Materials of Institut Lavoisier: MIL-100 (Fe)) which was impregnated with reduced graphene oxide (rGO) by using a simple hydrothermal method and coated with birnessite-type manganese oxide (δ-MnO2) using the one-pot reaction process (MIL-100(Fe)/rGO/δ-MnO2 nanocomposites) was synthesized and applied successfully in As removal. The removal efficiency was rapid, the equilibrium was achieved in 40 min and 120 min for As(III) and As(V), respectively, at a level of 5 mg/L. The maximum adsorption capacities of As(III) and As(V) at pH 2 were 192.67 mg/g and 162.07 mg/g, respectively. The adsorbent revealed high stability in pH range 2–9 and saturated adsorbent can be fully regenerated at least five runs. The adsorption process can be described by the pseudo-second-order kinetic model and Langmuir monolayer adsorption. The adsorption mechanisms consisted of electrostatic interaction, oxidation and inner sphere surface complexation.

The paper deals with the scattering of an electromagnetic plane wave by a system of core/shell microspheres and a single nanoparticle placed outside the spheres. Backscattering intensity perturbation caused by the nanoparticle was studied, and it was found that the position of the inner sphere can be used as a new effective tool to both detect a particle and to determine its size. The system of core/shell microspheres provides a longer particle detection distance compared with a single sphere system. It is shown that the maximum value of the perturbation of backscattering is reached at the interspherical distance corresponding to the maximal energy of the electromagnetic wave concentrated in the vicinity of the nanojet.

The mutable structures of metal-organic frameworks (MOFs) allow their use as novel supports for transition metal catalysts. Herein we prepare an iridium bis(ethylene) catalyst bound to the neutral N-donors of a MOF structure and show that the compound is a stable gas phase ethylene hydrogenation catalyst. The data illustrate the need to carefully consider the inner sphere (support) and outer sphere (anion) chemistry.

The present study aims at understanding the sorption mechanism of Eu(iii) by γ-alumina in the presence of picolinic acid (PA), a decontaminating agent used in the nuclear industry, through batch sorption studies, spectroscopy and surface complexation modeling. PA is weakly sorbed by γ-alumina, with the sorption increasing with pH up to 4.5 and decreasing with further increase in pH. Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) measurements indicate that PA forms an inner sphere surface complex on γ-alumina. The presence of PA does not affect Eu(iii) sorption by γ-alumina at low [Eu(iii)], while it drastically reduces Eu(iii) sorption at high [Eu(iii)]. Similar Eu(iii) sorption profiles with different addition sequences of Eu(iii) and PA suggest identical Eu(iii) surface species for Eu(iii) sorption on γ-alumina in the presence of PA which has been validated by time resolved fluorescence spectroscopy (TRFS). TRFS measurements of Eu(iii) sorbed on γ-alumina in the absence (binary systems) and presence of PA (ternary systems) exhibited two components 1 & 2. The lifetime value of component 1 in ternary systems is enhanced compared to that in binary systems signifying the formation of new surface species containing Eu(iii), PA and the γ-alumina surface whereas the similarity of component 2 in both the binary and ternary systems reveals an almost identical coordination environment of Eu(iii) in the two types of system. Using the spectroscopic information obtained from TRFS, Eu(iii) sorption, at high [Eu(iii)], in ternary systems has been successfully modeled by considering Eu(iii) bridged PA surface species at both low and high affinity sites of γ-alumina. At low [Eu(iii)] both PA and Eu(iii) bridged ternary surface complexes only at high affinity sites of γ-alumina could describe the Eu(iii) sorption adequately.

We investigated the adsorption performance of five Fe-based MOFs (Fe-BTC, MIL-100(Fe), MIL-101(Fe), MIL-53(Fe) and MIL-88C(Fe)) for removal of antimonite (Sb(III)) and antimonate (Sb(V)) from water. Among these MOFs, MIL-101(Fe) exhibited the best adsorption capacities for both Sb(III) and Sb(V) (151.8 and 472.8 mg/g, respectively) which were higher than those of most adsorbents previously reported. The effect of steric hindrance was evident during Sb removal using the Fe-based MOFs, and the proper diameter of the smallest cage windows/channels should be considered an important parameter during the evaluation and selection of MOFs. Additionally, the adsorption capacities of MIL-101(Fe) for Sb(V) decreased with increasing initial pH values (from 3.0 to 8.0), while the opposite trend was observed for Sb(III). Chloride, nitrate and sulfate ions had a negligible influence on Sb(V) adsorption, while NO3− and SO42− improved Sb(III) adsorption. This result implies that inner sphere complexes might form during both Sb(III) and Sb(V) adsorption.

In this study, efficient sulfamethoxazole (SMX) degradation was demonstrated in a novel neutral Fered-Fenton like/oxalate (electro-Fe2+/PDS/Ox, Fered-FL/Ox) system adopting pre-anodized Ti@TiO2 cathode. Optimization of operational parameters was conducted and the whole reaction mechanism based on the critical solid-liquid interfacial reactions was explored. An efficient neutral heterogeneous-homogenous iron cycle would exist in the Fered-FL/Ox system, depending on the formation of specific C O Ti bonds through the inner sphere surface complex (ISSC) of Fe(C2O4)33−. It would induce ultrafast electron transfer from the cathode to the FeIII core, effectively accelerating the neutral Fenton-like reactions and complete mineralization of SMX with relative low dosage of ferrous catalyst and applied voltage. The result of this study is expected to supply a good alternative in treating complex neutral industrial wastewaters

A new heteroleptic octahedral [NiL(H2O)3](NO3)2·1/2H2O complex with the tridentate pincer type ligand L; 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine, was synthesized and characterized using self assembly and single crystal X-ray diffraction, respectively. The Ni(II) ion is coordinated with one organic ligand unit (L) as NNN-chelate and three water molecules in the inner sphere while the outer sphere contains two nitrate anions and half crystal water molecule. The nitrate ions and the crystal water molecule connected the complex cation units via O–H⋯O hydrogen bonding interactions. Also, the nitrate ions are effectively interacting with the coordinated organic ligand via anion-π stacking interactions. The percentages of the O⋯H contacts range from 34.5 to 37.7% using Hirshfeld analysis. As a result of the interaction between the Ni(II) and ligand groups, its charge and spin densities were reduced to 0.86 and 1.68 e, respectively instead of 2.00 e. The nature and strength of the Ni–O and Ni–N coordination interactions were discussed using atoms in molecules theory. The Ni–N(triazine) and the equatorial Ni–O bonds showed the highest interaction energies among the Ni–N and Ni–O bonds, respectively. Antimicrobial studies on selected Ni(II) pincer complexes of L indicated high selectivity against the Gram positive bacteria with very close actions to the positive control Gentamycin. The organic ligand showed no antimicrobial action at the applicable concentration.

The electrocatalytic reduction of CO2 is an appealing method for converting renewable energy sources into value-added chemical feedstocks. We report a co-electrocatalytic system for the reduction of CO2 to CO comprised of a molecular Cr complex and dibenzothiophene-5,5-dioxide (DBTD) as a redox mediator, which achieves high activity (TOF=1.51-2.84×105 s-1 ) and quantitative selectivity. Under aprotic or protic conditions, DBTD produces a co-electrocatalytic response with 1 by coordinating trans to the site of CO2 binding and mediating electron transfer from the electrode with quantitative efficiency for CO. This assembly is reliant on through-space electronic conjugation between the π frameworks of DBTD and the bpy fragment of the catalyst ligand, with contributions from dispersive interactions and weak sulfone coordination.

Reported are the syntheses and characterization of six new heterometallic UO22+/Pb2+ compounds. These materials feature rare instances of M-oxo interactions, which influence the bonding properties of the uranyl cation. The spectroscopic effects of these interactions were measured using luminescence and Raman spectroscopy. Computational density functional theory-based natural bonding orbital and quantum theory of atoms in molecules methods indicate interactions arise predominantly through charge transfer between cationic units via the electron-donating uranyl O spx lone pair orbitals and electron-accepting Pb2+ p orbitals. The interaction strength varies as a function of Pb-oxo interaction distance and angle with energy values ranging from 0.47 kcal/mol in the longer contacts to 21.94 kcal/mol in the shorter contacts. Uranyl units with stronger interactions at the oxo display an asymmetric bond weakening and a loss of covalent character in the U═O bonds interacting closely with the Pb2+ ion. Luminescence quenching is observed in cases in which strong Pb-oxo interactions are present and is accompanied by red-shifting of the uranyl symmetric Raman stretch. Changes to inner sphere uranyl bonding manifest as a weakening of the U═O bond as a result of interaction with the Pb2+ ion. Comprehensive evaluation of the effects of metal ions on uranyl spectra supports modeling efforts probing uranyl bonding and may inform applications such as forensic signatures.

Metal-free arylation of thiols with diaryliodonium salts has been developed. The application of a strong organic base ena-bles the C–S bond formation under mild and experimentally simple conditions. The method allows for the synthesis of aryl sulfides containing a broad range of aryl groups from an array of thiols, including aryl, heteroaryl, and alkyl ones. The mechanism of the reaction was studied by DFT calculations, demonstrating that is follows the inner sphere pathway involv-ing the incipient formation of Ar2I(SR) intermediate, followed by the reductive elimination.

Στην παρούσα διδακτορική διατριβή ασχοληθήκαμε με την εξακρίβωση του μηχανισμού εναπόθεσης του καταλυτικά δραστικού στοιχείου βαναδίου στην επιφάνεια της τιτάνιας, που λαμβάνει χώρα στο στάδιο της ισορροπίας της μεθόδου “Εναπόθεση Ισορροπίας-Διήθηση”, καθώς και της τοπικής δομής των σχηματιζόμενων επιφανειακών ειδών, τόσο στο στάδιο της ισορροπίας όσο και κατά την περαιτέρω αύξηση της θερμοκρασίας.Για να πετύχουμε τα παραπάνω, ακολουθήσαμε τα εξής τέσσερα βήματα:1ο βήμα: προσδιορίσαμε τα φυσικοχημικά χαρακτηριστικά του οξειδίου μας (προσδιορισμός ισοηλεκτρικού σημείου με πειράματα μικροηλεκτροφόρησης και προσδιορισμός σημείου μηδενικού φορτίου με πειράματα ποτενσιομετρικών τιτλοδοτήσεων) και μελετήσαμε τη διαφασική περιοχή που αναπτύσσεται μεταξύ του οξειδίου και του ηλεκτρολυτικού διαλύματος.2ο βήμα: προσδιορίσαμε τις φυσικοχημικές παραμέτρους της διεπιφανειακής περιοχής τιτάνιας/ηλεκτρολυτικού διαλύματος (εγγενείς σταθερές πρωτονίωσης των δύο ειδών επιφανειακών οξυγόνων της τιτάνιας, χωρητικότητες C1 και C2 της εσωτερικής και εξωτερικής στοιβάδας Stern αντίστοιχα, σταθερές σχηματισμού των ιοντικών ζευγών και κατανομή του φορτίου zi των αντισταθμιστικών ιόντων του ηλεκτρολύτη που σχηματίζουν τα ιοντικά ζεύγη). Αυτό το πετύχαμε με την περιγραφή ποτενσιομετρικών καμπυλών τιτλοδότησης αιωρημάτων τιτάνιας, με τη βοήθεια κατάλληλου υπολογιστικού προγράμματος επίλυσης χημικών ισορροπιών. Για το σκοπό αυτό υιοθετήσαμε το συνδυασμό ενός μοντέλου για την περιγραφή της διεπιφάνειας, τη σύγχρονη εκδοχή του μοντέλου των τριών επιπέδων (Three Plane Model, TPM), με δύο μοντέλα για την περιγραφή φόρτισης της επιφάνειας, το μοντέλο Music και το μοντέλο Α. Το μοντέλο Music δέχεται την ύπαρξη δύο ειδών επιφανειακών οξυγόνων, τα ακραία (TiOΗ) και τα γεφυρωμένα (Ti2O) με φορτία -0.33 και -0.67 αντίστοιχα και επιφανειακή πυκνότητα ίση με 6θέσεις/nm2. Τα παραπάνω φορτία προσδιορίζονται με την αρχή του σθένους δεσμού κατά Pauling. Το μοντέλο Α δέχεται την ύπαρξη δύο ειδών επιφανειακών οξυγόνων, τα ακραία (TiO) και τα γεφυρωμένα (Ti2O) με φορτία -0.35 και -0.57 αντίστοιχα και επιφανειακή πυκνότητα ίση με 5.6θέσεις/nm2. Το φορτίο των επιφανειακών οξυγόνων υπολογίστηκε με χρήση της θεωρίας του συναρτησιακού της ηλεκτρονικής πυκνότητας (Density Functional Theory, DFT) με το συναρτησιακό των Perdew-Burke-Ernzerhof το οποίο περιλαμβάνει και διορθώσεις βαθμίδας.3ο βήμα: εκτέλεση μιας πειραματικής μεθοδολογίας η οποία περιλαμβάνει ηλεκτροχημικές τεχνικές (ποτενσιομετρικές τιτλοδοτήσεις και πειράματα μικροηλεκτροφόρησης αιωρημάτων τιτάνιας παρουσία και απουσία βαναδικών ειδών), πειράματα προσρόφησης (για συγκεντρώσεις V(V) 2*10-2Μ – 3*10-3Μ και pH 4.0 – 9.0) και φασματοσκοπικές τεχνικές. Τα δείγματα HKVXOYZ-/TiO2 που ελήφθησαν από τα παραπάνω πειράματα προσρόφησης, χαρακτηρίστηκαν με φασματοσκοπία Laser-Raman. Σκοπός των πειραματικών μεθοδολογιών είναι ο προσδιορισμός του τρόπου της διεπιφανειακής εναπόθεσης των βαναδικών ειδών, καθώς επίσης και η απόκτηση μιας πρώτης εικόνας για την τοπική δομή των σχηματιζόμενων επιφανειακών ειδών.4ο βήμα: εφαρμογή κατάλληλων υπολογιστικών μεθοδολογιών σκοπός των οποίων είναι η περιγραφή των παραπάνω πειραματικών αποτελεσμάτων. Για το σκοπό αυτό χρησιμοποιήθηκε το υπολογιστικό πρόγραμμα επίλυσης χημικών ισορροπιών (Visual Minteq), στο οποίο ενσωματώθηκαν όλες οι φυσικοχημικές παράμετροι της διεπιφανειακής περιοχής που προσδιορίστηκαν παραπάνω. Η πολύ καλή περιγραφή των πειραματικών δεδομένων μας οδήγησε στην εξακρίβωση της τοπικής δομής των επιφανειακών ειδών, αλλά και στον προσδιορισμό των εγγενών σταθερών σχηματισμού τους.Οι πειραματικές μεθοδολογίες έδειξαν ότι υπάρχει μεγάλη χημική συγγένεια μεταξύ των βαναδικών ειδών και των επιφανειακών ομάδων της τιτάνιας. Παρατηρείται σημαντική έκταση της προσρόφησης των αρνητικών βαναδικών ειδών ακόμα και σε πολύ υψηλές τιμές pH, όπου η επιφάνεια έχει ομόσημο με αυτά φορτίο. Έτσι η διεπιφανειακή εναπόθεση των βαναδικών ειδών δεν είναι ηλεκτροστατικής φύσεως αλλά λαμβάνει χώρα μέσω χημικών δυνάμεων.Οι υπολογιστικές μεθοδολογίες έδειξαν ότι τα βαναδικά είδη μπορούν να προσροφώνται στην επιφάνεια της τιτάνιας σχηματίζοντας μόνο- και δι-υποκατεστημένα μονομερή σύμπλοκα εσωτερικής σφαίρας και δι-υποκατεστημένα τετραμερή σύμπλοκα εσωτερικής σφαίρας. Η παρουσία των υπόλοιπων πολυμερών ειδών βαναδίου δεν είχε καμία συνεισφορά στην προσρόφηση. Επιπλέον, βρέθηκε ότι είναι πολύ πιθανό να υπάρχει αλληλεπίδραση μέσω δεσμών υδρογόνου στην ελεύθερη πλευρά των προσροφημένων τετραμερών συμπλόκων εσωτερικής σφαίρας. Τα παραπάνω ευρήματα των υπολογιστικών μεθοδολογιών επιβεβαιώθηκαν πλήρως από τη φασματοσκοπία Laser-Raman.

Previously, we reported a visible light-activated Cu(I) photocatalyst capable of facilitating C-O bond formation of glycosyl bromides and aliphatic alcohols with a high degree of diastereoselectivity. This catalyst functions equally well in the presence of radical traps, suggesting an entirely inner sphere mechanism atypical for heteroleptic Cu photocatalysis. Further, experimental estimates put the chromophore reducing power at -1.30 V vs Ag/AgCl. This is much more positive than the ∼-2.0 V vs Ag/AgCl onset observed for irreversible reduction of glycosyl bromides in our experiments. Theoretical investigations were undertaken to explain the function of the catalyst. Outer sphere electron transfer from a chromophore to substrate was discounted based on thermodynamics and electron transfer barriers determined by Marcus theory and non-equilibrium solvation calculations. Unactivated and activated chromophores were found to disproportionate to Cu(0) and Cu(II) species. The resulting Cu(0) species undergoes oxidative addition with a glycosyl bromide generating a Cu(II) species. Addition of a nucleophilic alcohol and oxidation of the Cu(II) species to Cu(III) result in rapid reductive elimination forming products and resetting the catalytic cycle.

Fourier Transform Infra-Red (FTIR) spectroscopy provides structural information of prime importance to understand ions coordination to adsorbents. This consequently aids in the design of improved ion exchange materials and help in deriving the optimum adsorption conditions. In the present work, the adsorption mechanism of both U(VI)/Th(IV) and Ra(II)/Ba(II) radionuclides couples onto polystyrene-nano manganese dioxide (PS-NMO) composite is reported in relation to the effect of working solution pH. The separation of each radionuclide couple; i.e. U(VI)/Th(IV) and Ra(II)/Ba(II); could be effectively achieved at pH=3 and pH=1 respectively. The pH values not only determine the species of the respected elements that are mainly present in aqueous solution before applying the adsorbent, but it also alters the structure of the composite adsorbent. FTIR spectroscopy showed that Th(IV) formed inner sphere complexes and occupied the A site in the dioxide layer, while U(VI) formed outer sphere complexes on the surface of the composite. Spectra subtraction showed that some aromatic bands and vinyl C-H bands were split or shifted to lower wavenumbers with the loading of Ba(II). This was attributed to changes in the composite stereochemistry to accommodate Ba(II). The working solution pH could be the key in the separation process of both U(VI)/Th(IV) and Ra(II)/Ba(II) from their mixture, and FTIR spectroscopy stands as a useful technique to explain the difference between metal ions responses to adsorbants.

Magnesium plays a critical role in the structure, dynamics, and function of RNA. The precise microscopic effect of chelated magnesium on RNA structure is yet to be explored. Magnesium is known to act through its diffuse cloud around RNA, through the outer sphere (water-mediated), inner sphere, and often chelated ion-mediated interactions. A mechanism is proposed for the role of experimentally discovered site-specific chelated magnesium ions on the conformational dynamics of SAM-I riboswitch aptamers in bacteria. This mechanism is observed with atomistic simulations performed in a physiological mixed salt environment at a high temperature. The simulations were validated with phosphorothioate interference mapping experiments that help to identify crucial inner-sphere Mg2+ sites prescribing an appropriate initial distribution of inner- and outer-sphere magnesium ions to maintain a physiological ion concentration of monovalent and divalent salts. A concerted role of two chelated magnesium ions is newly discovered since the presence of both supports the formation of the pseudoknot. This constitutes a logical AND gate. The absence of any of these magnesium ions instigates the dissociation of long-range pseudoknot interaction exposing the inner core of the RNA. A base triple is the epicenter of the magnesium chelation effect. It allosterically controls RNA pseudoknot by bolstering the direct effect of magnesium chelation in protecting the functional fold of RNA to control ON and OFF transcription switching.

Given their environmental abundances, it has been long hypothesized that geochemical interactions between reactive forms of manganese and nitrogen may play important roles in the cycling of these elements. Indeed, recent studies have begun shedding light on the possible role of soluble, ligand-bound Mn(III) in promoting abiotic transformations under environmentally relevant conditions. Here, using the kinetic data of Karolewski et al. (Geochim Cosmochim Acta 293:365–378, 2021), we provide the chemical mechanism for the abiotic oxidation of nitrite (NO2−) by Mn(III)-pyrophosphate, MnIIIPP, to form nitrate (NO3−). Nitrous acid (HNO2), not NO2−, is the reductant in the reaction, based on thermodynamic and kinetic considerations. As soluble Mn(III) complexes react in a one-electron transfer reaction, two one-electron transfer steps must occur. In step one, HNO2 is first oxidized to nitrogen dioxide, ·NO2, a free radical via a hydrogen atom transfer (HAT) reaction. We show that this inner sphere reaction process is the rate-limiting step in the reaction sequence. In step two, ·NO2 reacts with a second MnIIIPP complex to form the nitronium ion (NO2+), which is isoelectronic with CO2. Unlike the poor electron-accepting capability of CO2, NO2+ is an excellent electron acceptor for both OH− and H2O, so NO2+ reacts quickly with water to form the end-product NO3− (step 3 in the reaction sequence). Thus, water provides the O atom in this nitrification reaction in accordance with the O-isotope data. This work provides mechanistic perspective on a potentially important interaction between Mn and nitrogen species, thereby offering a framework in which to interpret kinetic and isotopic data and to further investigate the relevance of this reaction under environmental conditions.

We present a computational approach to simulate linear sweep and cyclic voltammetry experiments that does not require a discretized grid in space to quantify diffusion. By using a Green’s function solution coupled to a standard implicit ordinary differential equation solver, we are able to simulate current and redox species concentrations using only a small grid in time. As a result, where benchmarking is possible, we find that the current method is faster than (and quantitatively identical to) established techniques. The present algorithm should help open the door for studying adsorption effects in inner sphere electrochemistry.

Alkoxylation and hydroxylation reactions of 1,5-cyclooctadiene (cod) in an iridium complex with alcohols and water promoted by the reduction of oxygen to hydrogen peroxide are described. The exo configuration of the OH/OR groups in the products agrees with nucleophilic attack at the external face of the olefin as the key step. The reactions also require the presence of a coordinating protic acid (such as picolinic acid (Hpic)) and involve the participation of a cationic diolefin iridium(III) complex, [Ir(cod)(pic)], which has been isolated. Independently, this cation is also involved in easy alkoxy group exchange reactions, which are very unusual for organic ethers. DFT studies on the mechanism of olefin alkoxylation mediated by oxygen show a low-energy proton-coupled electron-transfer step connecting a superoxide–iridium(II) complex with hydroperoxide–iridium(III) intermediates, rather than peroxide complexes. Accordingly, a more complex reaction, with up to four different products, occurred upon reacting the diolefin–peroxide iridium(III) complex with Hpic. Moreover, such hydroperoxide intermediates are the origin of the regio- and stereoselectivity of the hydroxylation/alkoxylation reactions. If this protocol is applied to the diolefin–rhodium(I) complex [Rh(pic)(cod)], free alkyl ethers ORC8H11 (R=Me, Et) resulted, and the reaction is enantioselective if a chiral amino acid, such as l-proline, is used instead of Hpic., Generous financial support from MINECO/FEDER (CTQ2017‐83421‐P, C.T., and CTQ2017‐87889‐P, A.L.) and the Gobierno de Aragón/FEDER (GA/FEDER, Inorganic Molecular Architecture Group E08_17R, C.T.) is gratefully acknowledged. M.P.d.R. and P.A. thank MINECO/FEDER for a JdC contract and a FPI fellowship, respectively.

An inner sphere electron transfer process via a cyanide bridge is proposed for the reactions of Cu(III,II) peptide complexes with Fe(CN)63−,4−, Mo(CN)83−,4− and W(CN)83−,4−. Cu(III) peptide complexes were generated electrolytically from the Cu(II) precursors. The direction of spontaneous reactions is such that Fe(CN)64− and W(CN)84− reduce Cu(III) peptide complexes and Mo(CN)83− oxidizes Cu(II) peptide complexes at pH ca. 10. However, since all reactions are equilibrium processes, by the very fast continuous decomposition of the reduced Cu(II) product in a slightly acidic reaction medium (pH 5), the Mo(CN)84− reduction of Cu(III) peptide complexes could be driven to completion and studied kinetically. Kinetically determined equilibrium constants and electrochemically calculated equilibrium constants are mutually consistent. The experimentally observed inner sphere rate constants, kis, for these reactions are significantly larger than the corresponding outer sphere rate constant, kos, for the outer sphere electron transfer processes calculated with the Marcus theory, with or without work terms. It is concluded that if the kinetic advantage kis/kos is substantially larger than 1, it provides evidence for an inner sphere reaction pathway. The magnitude of the kinetic advantage of the present redox reactions varies from 1 to 63 and is dependent on the metal-to-metal distance in the cyanide-bridged intermediates.

The activation of dioxygen at typically isolated two-electron reduced centers can lead to the formation of electrophilic superoxo or peroxo species, providing an essential route to form reactive O2-derived species in biological, organometallic, and heterogeneous catalysts. Alternatively, O2 activation can proceed via outer sphere routes, circumventing the formation of bound peroxo (OO*) species during oxidation catalysis by forming H2O2(g), which can react with another reduced center to form H2O. The electronic and binding properties of metal oxides that determine the relative rates of these activation routes are assessed here by systematic theoretical treatments using density functional theory (DFT). These methods are combined with conceptual frameworks based on thermochemical cycles and crossing potential models to assess the most appropriate descriptors for the activation barriers for each route using Keggin polyoxometalates as illustrative examples. In doing so, we show that inner sphere routes, which form OO* species via O2 activation on the O-vacancies (*) formed in the reduction part of redox cycles, are mediated by early transition states that only weakly sense the oxide binding properties. Outer sphere routes form H2O2(g) via O2 activation on OH pairs (H/OH*) formed by dissociation of H2O on O-vacancies; their rates and activation barriers reflect the rates of the first H-atom transfer from H/OH* to O2. The activation barriers for this H-transfer step depend on the binding energy of more weakly-bound H-atom in H/OH* pairs (HAE2) and on the OOH-surface interaction energy at its product state ( E int 0 ). The E int 0 values are similar among oxides unless a large charge-balancing cation is present and interacts with OOH; consequently, HAE2 acts as an appropriate descriptor of the outer sphere dynamics. HAE2 also determines the thermodynamics of H2O dissociation on O-vacancies, which influence the inner and outer sphere rates by setting the relative coverage of * and H/OH*. These results, in turn, show that HAE2 is a complete descriptor of the reactivity and selectivity of oxides for O2 activation; the O-atoms in more reducible oxides (more negative HAE2) exhibit a greater preference for the inner sphere routes and for the formation of electrophilic OO* intermediates that mediate epoxidation and O-insertion reactions during catalytic redox cycles. Large charge-balancing cations locally modify E int 0 values that determine the outer sphere rates and thus can be used to alter the preference of O-atoms to either inner or outer sphere routes.

Quantum chemical modeling of Fe(III), Fe(II), and Fe(I) aqua-, aqua-hydroxo-, and aquadihydroxocomplexes is presented. The mechanism of a consecutive transfer of two electrons is studied as these forms are electrochemically reduced from an aqueous solution. The reorganization energy of the solvent and the inner sphere of studied reagents is calculated, standard redox potentials are estimated. Based on Marcus theory, the activation energy of two steps of Fe(III) reduction is estimated and the second electron transfer is shown to be rate controlling, while the energy barrier is increased due to the products of Fe(III) hydrolysis. The model predictions are in qualitative agreement with previously reported experimental data.