OH Ligands Research Articles

A Dinculear Rhenium Complex with a Proton Responsive Ligand in the Electrochemical‐Driven CO2‐Reduction Catalysis

AbstractHerein, we present a detailed study on a dinuclear Re complex bearing an α‐diimine‐tricarbonyl motif and a proton responsive ligand in the electrochemical CO2 reduction catalysis. The complex exhibits a pyrazole‐pyridine entity as α‐diimine unit and a phenol moiety as internal proton relay, which show non‐innocent behaviour under reductive conditions. Initial two electron reduction leads to NH bond cleavage forming the deprotonated ligand LH−2. Further two electron reduction at considerable negative potential induces OH bond cleavage and ligand reduction. In the presence of CO2, the reduced species reacts with CO2 forming CO. The complex shows a moderate Faraday efficiency and the activity is similar to the mononuclear derivative [Re(bpy)(CO)3(py)]+ (py=pyridine, bpy=2,2′‐bipyridine).

Dual-Ligand Synergistic Modulated Nico-Sulfhydroxides with High Activity and Stability As Oxygen Evolution Electrocatalysts

The most knotty problem of (electro)catalysis that arises ubiquitously is the notion that the more active catalysts for oxygen evolution reaction (OER) will simultaneously suffer from low resistance toward corrosion. In developing cost-effective stable materials for the oxygen evolution reaction with high activity, precisely tuning the structure of transition-metal materials in atomic level to obtain ideal chemical properties is urgent while difficult to achieve1. In this study, we propose a “dual ligand synergistic modulation” tactics to completely solve the painful compromise between the two conflicted indicators: stability and activity. By substituting S ligand into the adjustable and stable structure of layered hydroxides, which was selected as the start noumenon, we obtain a new class of NiCo2(Sx·OH2-x)y with single phase and homogenous composition. The elaborated designed dual-ligand catalyst ideally inherits the excellent activity of the conventional transition metal sulfides and the superior stability of the conventional transition metal hydroxides and even exceeds the predecessors. Impressively, the optimized NiCo2(SOH)x performs a small overpotential of 0.32 V at 10 mA cm-2, and shows no decay after 30h accelerated ageing even at a large current density of 100 mA cm-2, both of which have entered the top of all the transition-metal hydroxides and sulfides reported to date and exceeded the commercial RuO2 and Ir/C benchmarks. Theoretical calculations further disclose that the OH ligands on the surface of NiCo2(SOH)x could attracts electrons from the antibonding orbital of M-S bonds to M-O bonds, resulting in a strengthened binding energy between metal and S and thus enhancing the stability. Meanwhile, the synergy between S ligands and OH groups appropriately tunes the electronic structure of NiCo2(SOH)x and thus renders it with optimal binding energies for OER intermediates (*OH, *O, and *OOH), which is benefit for facilitate the O2 evolution proceeding. Besides, the varied magnetism induced by the modulation of catalysts’ electronic structure significantly influences the desorption action of paramagnetic O2 from the catalyst surface. The special non-magnetic NiCo2(SOH)x suffers the lowest O2 desorption resistance and proceeds the smoothest reaction kinetics pathway among NiCo2(SxOH2-x)y catalysts, thus owning the topmost OER activity. Figure 1. (a) The ultimate unity of OER performance of NiCo2(SxOH2-x)y. (b) The reaction steps and corresponding free energy diagram of the OER process. (c) OER polarization curves of Ni, RuO2, NiCo2S4, NiCo2(OH)x, and NiCo2(SOH)x and (d) Chronoamperometric curves of Ni, NiCo2(SOH)x and NiCo2S4 at a current density of 100mA/cm2. Key words: Oxygen evolution, electrocatalysis, dual-ligand modulation Reference: Lishan Peng, Jun Wang, Yao Nie, Kun Xiong, Yao Wang, Ling Zhang, Ke Chen, Wei Ding, Li Li, and Zidong Wei*. ACS Catal. , 2017, 7, 8184-8191. Figure 1

Through-bond communication between polymer-bound phosphinic acid ligands and trivalent metal ions probed with FTIR spectroscopy

The binding of trivalent metal ions to immobilized ligands is analyzed to determine the principal type of interaction, the extent of ion exchange, and changes due to through-bond communication. FTIR spectroscopy is found to be a readily accessible means of determining through-bond communication and spectra provide support for a molecular level interpretation of the interaction. The affinity of the phosphinic acid ligand for Al(III), La(III), Lu(III), Fe(III), and In(III) is quantified with distribution coefficients from 0.01–6 M nitric acid solutions. High affinities are evident with In(III) > Fe(III) > Lu(III) > La(III) > Al(III). The affinities correlate with the softness parameter and thus the polarizability of the metal ion. The FTIR spectrum of the phosphinic acid has two incompletely separated bands at 1168/1126 cm−1 associated with the PO bond and two similar bands at 967/951 cm−1 due to the PO(H) bond. The bands at 1168/951 and 1126/967 cm−1 are assigned to different hydrogen bonded conformers within the metal-free polymer. Through-bond communication is evident as the extent of metal ion binding increases: the PO and PO bands at 1168 and 951 cm−1, respectively, collapse into a single band between 1040 and 1080 cm−1 representative of PO2(M) while hydrogen bonding among unexchanged P(O)OH ligands gives the bands at 1133 and 981 cm−1.

A Comparison of Experimental and Broken Symmetry Density Functional Theory (BS-DFT) Calculated Electron Paramagnetic Resonance (EPR) Parameters for Intermediates Involved in the S2 to S3 State Transition of Nature's Oxygen Evolving Complex.

A broken symmetry density functional theory (BS-DFT) magnetic analysis of the S2, S2YZ•, and S3 states of Nature's oxygen evolving complex is performed for both the native Ca and Sr substituted forms. Good agreement with experiment is observed between the tyrosyl calculated g-tensor and 1H hyperfine couplings for the native Ca form. Changes in the hydrogen bonding environment of the tyrosyl radical in S2YZ• caused by Sr substitution lead to notable changes in the calculated g-tensor of the tyrosyl radical. Comparison of calculated and experimental 55Mn hyperfine couplings for the S3 state presently favors an open cubane form of the complex with an additional OH ligand coordinating to MnD. In Ca models, this additional ligation can arise by closed-cubane form deprotonation of the Ca ligand W3 in the S2YZ• state accompanied by spontaneous movement to the vacant Mn coordination site or by addition of an external OH group. For the Sr form, no spontaneous movement of W3 to the vacant Mn coordination site is observed in contrast to the native Ca form, a difference which may lead to the reduced catalytic activity of the Sr substituted form. BS-DFT studies on peroxo models of S3 as indicated by a recent X-ray free electron laser (XFEL) crystallography study give rise to a structural model compatible with experimental data and an S = 3 ground state compatible with EPR studies.

Addition of HO‐Acids to N,N‐Bis(oxy)enamines: Mechanism, Scope and Application to the Synthesis of Pharmaceuticals

The regioselectivity of the addition of HO‐acids to the activated π bond in N,N‐bis(oxy)enamines has been found to be dramatically dependent upon the solvent. Mechanistic investigations and quantum‐chemical calculations revealed that solvent affects the reaction pathway. In basic solvents (DMF, NMP, DMSO), N,N‐bis(oxy)enamines were converted into nitrosoalkenes by a Lewis base promoted process followed by oxy‐Michael addition of the HO‐acid. In non‐polar solvents (toluene, CH2Cl2), the reaction occurs by an acid‐promoted SN′ substitution of the N‐oxy‐group via a highly reactive N‐vinyl‐N‐alkoxynitrenium species. Based on these studies, general and efficient protocols for the oximinoalkylation of various HO‐acids (carboxylic acids, phenols, hydroxamic, phosphoric and sulfonic acids) employing readily available N,N‐bis(oxy)enamines were developed. These methods proved to be applicable to the post‐modification of natural molecules bearing acidic OH groups (such as steroidal hormones, bile acids, protected amino acids and peptides) and ligands (BINOL). The resulting α‐oxyoximes were demonstrated to be useful precursors of valuable 1,2‐amino alcohol or 1,2‐hydroxylamino alcohol derivatives, including the antiarrhythmic drug Mexiletine and a potent matrix metalloproteinase inhibitor.

Structure, acidity, and metal complexing properties of oxythioarsenites in hydrothermal solutions

In the pursuit of understanding the aqueous chemistry of oxythioarsenites (i.e., H3AsO2S and H3AsOS2) on a microscopic scale, first principles molecular dynamics (FPMD) simulations were performed to investigate the hydration structures, acidity constants, and metal-complexing properties of these species in aqueous solutions at temperatures up to 573K. The simulations showed that the oxythioarsenite species are stable and have trigonal pyramidal structures in both low- and high-temperature fluids. Their solvated structures were characterized in detail and it was found that the S or H atoms of the SH ligands form very weak H-bonds with the solvating water molecules and the OH ligands form H-bonds with water as both donors and acceptors. Furthermore, the dangling S or O sites act as strong acceptors to form H-bonds. Their acidity constants were calculated by using the FPMD-based vertical energy gap method. Together with our previous work (Liu et al., 2015, Chemical Geology, 411, 192–199), we found that in the arsenite-thioarsenite series (i.e., H3AsO3−xSx for x varying from 0 to 3), the pKa values of the oxythioarsenite species (H3AsO2S and H3AsOS2) were always located between those of the end members, H3AsO3 and H3AsS3, and decreased with the increasing temperature up to 573K. Based on the calculated acidity constants, the speciation versus pH distributions were obtained at temperatures ranging from ambient temperature to 573K. It was found that both H2AsO2S− and H2AsOS2− are the predominant species at near neutral pH for H3AsO2S and H3AsOS2 species, respectively. In addition, the structures and the dissociation free energy of the oxythioarsenite-metal complexes at 573K indicated that these As-S moieties are effective ligands for complexing with ore-forming metals in geological fluids.

Binding energies of hydrated cobalt hydroxide ion complexes: A guided ion beam and theoretical investigation.

The sequential bond energies of CoOH+(H2O)x complexes, where x = 1-4, are measured by threshold collision-induced dissociation using a guided ion beam tandem mass spectrometer. The primary dissociation pathway for all reactants consists of loss of a single water molecule. This is followed by the sequential loss of additional water molecules at higher collision energies for the x = 2-4 complexes, whereas the x = 1 reactant loses the OH ligand competitively with the H2O ligand. The kinetic energy dependent cross sections for dissociation of CoOH+(H2O)x complexes are modeled to obtain 0 and 298 K binding energies. Our experimental results agree well with theoretically determined bond dissociation energies (BDEs) at the B3LYP, B3LYP-GD3BJ, B3P86, and MP2(full) levels of theory with a 6-311+G(2d,2p) basis set using geometries and vibrational frequencies determined at the B3LYP/6-311+G(d,p) level. Thermochemical information for the loss of OH from CoOH+(H2O)x where x = 0-4 is also derived by combining the present experimental HO-Co+(H2O) and water loss BDEs from CoOH+(H2O)x with those for Co+(H2O)y from the literature. These BDEs are also compared to theory with mixed results.

Two-dimensional silicon suboxides nanostructures with Si nanodomains confined in amorphous SiO2 derived from siloxene as high performance anode for Li-ion batteries

SiOx owing to high reversible capacity and moderate volume expansion has been attracting a lot of attention as state-of-the-art anodes for the next generation of Li-ion batteries. However, poor cycling performance and poor rate capability, respectively associated with detrimental volume expansion and insulative amorphous SiO2, are still challenging issues which need to be addressed for the actual employment as anodes for Li-ion batteries. In this regard, here we design, synthesize, characterize and test carbon coated sheet-like SiO1.1 nanocomposites formed by Si-nanodomains confined inside amorphous SiO2 (nano-Si/a-SiO2). As a proof-of-concept, we achieve sheet-like SiOx nanocomposites via in-situ transformation of delaminated siloxene. In particular, self-prepared siloxene with oxygen-inserted Si6 rings terminated with H and OH ligands is prepared by delamination of CaSi2 in dilute HCl. Importantly, the resulting carbon coated nano-Si/a-SiO2 material shows enhanced reaction kinetics and structural stability leading to 946 mAh g−1 capacity at 0.15Ag−1. Intriguingly, 38.0% (~360 mAh g−1) of the maximum capacity is maintained even at 7.5Ag−1, corresponding to a remarkable less than 3min charge/discharge time. Finally, the electrode shows merely 24% of volume expansion and minor cracks with capacity retention of 92% after 300 cycles at 7.5Ag−1.

A one-dimensional Mn(II)-based metal organic oxide: structure and properties

A one-dimensional metal organic oxide of Mn(II), with formula [Mn3(OH)2(Hpdc)2]n (H3pdc = 3,5-pyrazoledicarboxylic acid), was prepared via the hydrothermal method and its structure solved by single-crystal X-ray diffraction. The compound exhibits a three-dimensional framework structure, comprising three crystallographically unique Mn atoms bridged by OH ligands (O9 and O10) and O atoms from the Hpdc ligands, forming one-dimensional metal–organic oxide chains. Two kinds of magnetic exchange are observed: a strong antiferromagnetic intra-chain interaction, arising from the short distance between Mn(II) centers, and a ferromagnetic inter-chain interaction, due to the larger distances between the chains. The compound shows good photocatalytic activity for the decomposition of methylene blue in aqueous medium under simulated sunlight.

P and Si functionalized MXenes for metal-ion battery applications

MXenes are a family of two-dimensional materials, composed of early transition metal carbides, nitrides, and carbonitrides, with great potential in energy storage systems, in particular in electrodes for Li, Na, K-ion batteries. However, so far the capacities are not competitive. In this context, we investigate P and Si functionalized MXenes for metal-ion battery applications, using first-principles calculations, since P and Si provide reaction products with high ion content. Replacement of the F and OH ligands of Ti2C and V2C with P and Si is demonstrated to be feasible (energy barriers of less than 0.128 eV) and the ion diffusion barriers turn out to be less than 0.32 eV. Importantly, the Li, Na, and K capacities are predicted to be 1767 mAh g−1, 711 mAh g−1, and 711 mAh g−1, respectively, thus being much higher than in the case of F and OH functionalization.

Binuclear zinc(II) complexes of N(4)-substituted bis(thiosemicarbazone) ligands incorporating hydroxyl group and their non-hydroxyl analogues

We have reported the synthesis and physical and chemical studies of the new zinc complexes of N(4)-substituted bis(thiosemicarbazones). The complexes characterized by spectroscopic methods. The crystal structures of the compounds [Zn2L2(CH3COO)]·EtOH and [Zn2L4(CH3COO)]·MeOH is determined. Bis(thiosemicarbazones) involving a pendant OH group having SNONS donor sequences can hold two metal ions in close proximity. The coordination sphere has been formed by the imine nitrogen and sulfur atom, and the remaining positions, in a square-based pyramid, has been occupied by three oxygen atoms derived of pendant OH, ether group and acetate ligand. Acetate ligand and alkoxide oxygen are bridged between two metal centers. Whereas, their non-hydroxyl analogues are dimer. In dimer complexes, two ligands are tetradentate coordinated via N2S2 donor atoms. The presence of bulky groups on the nitrogens of thiosemicarbazide enforce an s-trans conformation for the H2L1 and H2L3 ligands in [ZnL1]2·MeOH and [ZnL3]2·MeOH. Fluorescence studies suggest that the [ZnL1]2·MeOH complex can be utilized as a fluorescent imaging agent.

Isomerism of Trimeric Aluminum Complexes in Aqueous Environments: Exploration via DFT-Based Metadynamics Simulation.

The chemistry of aluminum or oxo-aluminum in water is still relatively unknown, although it is the basis for many chemical and industrial processes, including flocculation in water treatment plants. Trimeric species have a predominant role in the formation of the Keggin cations, which are the basic building blocks of aluminum-based chemicals. Despite this, details of the structural evolution of these small solvated clusters and how this is related to the processes leading to the formation of larger aggregates are still an open issue. To address these questions, here, we have applied the metadynamics (MTD) simulation technique [ Barducci , A. ; Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2010 , 1 , 826 - 843 ] with density functional theory-based molecular dynamics to disclose the dynamics and structural conversions of trimeric aluminum complexes in an aqueous environment. The existence of a variety of competing metastable conformations, for example, book-like, cyclic boat, and linear shape conformations, is revealed in the MTD simulation. Furthermore, equilibrium simulations of the various intermediate states encountered along the MTD trajectory are used to assess their (meta)stability, determine the rearrangement of the OH ligands, and discuss the role of the solvating water.

Modeling PGM-Free Active Site Structures: Activity and Durability

Two of the largest hurdles facing platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte fuel cell (PEFC) cathodes are the need for improved activity and increased durability. Quantum chemical modeling (in particular, density functional theory, DFT, coupled with thermochemical models) can be utilized to better understand both activity and durability of these materials at the atomic scale. In this work, we apply quantum chemical modeling approaches to study the activity of N-coordinated Mn, Fe, Co, and Ni containing zig-zag edge sites. Both Metal-N4 as well as Metal2-N5edge structures are considered. Spontaneous *OH ligand modification in which the *OH intermediate is persistently bound to metal centers above a relatively low potential is found to be applicable to both structures but only for certain metal species. Experimentally determined trends in activity as a function of metal species fit well with theoretical predictions based on the spontaneous *OH ligand modification hypothesis. In addition, strain-modification of structures and resultant shifts in activity are explored. It is found that, due to anisotropic changes in binding energies with strain, this approach can lead to minor improvements of the computationally obtained ORR activity descriptor. With regards to the durability hurdle of PGM-free electrocatalysts, a structurally sensitive and computationally accessible descriptor is explored. First-principles molecular dynamics derived knock-on displacement threshold energy may serve as a high-throughput, corrosion-mechanism-agnostic descriptor of active site structure durability that does take into account the kinetics of local bond breaking. Further comparisons between computational predictions and experimental findings are required to ascertain the applicability of this simplified durability descriptor for non-PGM active site structures. Current progress and future directions will be discussed.

Binary Fe-Free Transition Metal Catalysts for the Oxygen Reduction Reaction

Platinum group metal (PGM)-free catalysts with high volumetric activity and low hydrogen peroxide yields are needed as replacements for expensive and scarce platinum-based catalysts for the oxygen reduction reaction (ORR). State-of-the-art PGM-free ORR catalysts are currently synthesized from a variety of carbon-nitrogen-iron (C-N-Fe) precursors. While these C-N-Fe catalysts have shown promising ORR activity and selectivity, a concern exists on the possibility of harmful Fenton (Fe2+/H2O2) and Fenton-like (Fe3+/H2O2) side reactions generating hydroxyl radicals risking the durability of polymer electrolyte fuel cells due to membrane degradation. Therefore, in an effort to mitigate that risk, development of Fe-free catalysts with similar ORR activity to the C-N-Fe system but with alternative transition metal precursors are being pursued. Our previous results have shown improved ORR activity from (CM+PANI)-Co-C catalysts with a half-wave potential of 0.77 V nearing that of Fe-based catalysts [1]. While this improvement is significant, further development is necessary to enhance both activity and selectivity of Fe-free catalysts. In this work, we will exploit the synergism between theoretical and experimental approaches to develop binary Fe-free transition metal ORR catalysts. Earlier results from quantum-chemical models linking atomic scale structure to ORR activity based on density functional theory (DFT) suggest increased ORR activity for mixed-metal-species active site structures in the Fe-Co system [2]. The same effect was observed from the Mn-Co system. A Sabatier principle relationship between ORR activity and single-transition-metal active sites was observed in both theoretical and experimental studies. A similar experimental-theoretical relationship will be developed from our findings of binary Fe-free transition metal sites. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. [1] Martinez, U., Holby, E.F., Dumont, J.H., Chung, H.T., Zelenay, P. “Non-PGM ORR Catalysts Based on Transition Metals Alternative to Iron.” ECS Meeting s, 2016. [2] Holby, E.F., Taylor, C.D. “Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands,” Scientific Reports, 2015, 5, 9286.

Octanuclear Heterobimetallic {Ni4Ln4} Assemblies Possessing Ln4 Square Grid [2 × 2] Motifs: Synthesis, Structure, and Magnetism.

Octanuclear heterobimetallic complexes, [Ln4Ni4(H3L)4(μ3-OH)4(μ2-OH)4]4Cl·xH2O·yCHCl3 (Dy(3+), x = 30.6, y = 2 (1); Tb(3+), x = 28, y = 0 (2) ; Gd(3+), x = 25.3, y = 0 (3); Ho(3+), x = 30.6, y = 3 (4)) (H5L = N1,N3-bis(6-formyl-2-(hydroxymethyl)-4-methylphenol)diethylenetriamine) are reported. These are assembled by the cumulative coordination action of four doubly deprotonated compartmental ligands, [H3L](2-), along with eight exogenous -OH ligands. Within the core of these complexes, four Ln(3+)'s are distributed to the four corners of a perfect square grid while four Ni(2+)'s are projected away from the plane of the Ln4 unit. Each of the four Ni(2+)'s possesses distorted octahedral geometry while all of the Ln(3+)'s are crystallographically equivalent and are present in an elongated square antiprism geometry. The magnetic properties of compound 3 are dominated by an easy-plane single-ion anisotropy of the Ni(2+) ions [DNi = 6.7(7) K] and dipolar interactions between Gd(3+) centers. Detailed ac magnetometry reveals the presence of distinct temperature-dependent out-of-phase signals for compounds 1 and 2, indicative of slow magnetic relaxation. Magnetochemical analysis of complex 1 implies the 3d and the 4f metal ions are engaged in ferromagnetic interactions with SMM behavior, while dc magnetometry of compound 2 is suggestive of an antiferromagnetic Ni-Tb spin-exchange with slow magnetic relaxation due to a field-induced level crossing. Compound 4 exhibits an easy-plane single-ion anisotropy for the Ho(3+) ions and weak interactions between spin centers.

Role of [FeOx(OH)y] surface sites on the adsorption of β-lactamic antibiotics on Al2O3 supported Fe oxide

In this work, [FeOx(OH)y]/Al2O3 composites with different Fe oxyhydroxy contents, i.e. 10, 20 and 50wt% treated at 150, 200, 300 and 450°C were investigated as adsorbents of β-lactamic antibiotics, i.e. cephalexin, ceftriaxone and especially amoxicillin, from aqueous solutions. The obtained results showed that the nature of the surface Fe3+ species play a fundamental role on the adsorption process. The most efficient adsorption was obtained for the sample 150Fe50A (50% [FeOx(OH)y] supported in Al2O3 treated at 150°C) whereas the thermal treatment at higher temperatures caused a strong decrease on the adsorption capacity. Mössbauer, XRD, FTIR, Raman, TG-MS, SEM, CHN and BET of the composite 150Fe50A suggested an approximate composition of FeO0.65(OH)1.7 whereas at 450°C strong dehydroxylation process takes place to form FeO1.4(OH)0.21. These results combined with competitive adsorption using amoxicillin mixed with phosphate or H2O2 suggest that the antibiotic molecules adsorb by complexation on surface sites likely based on FeOx(OH)y by the replacement of the labile OH ligands.

Kagóme Cobalt(II)-Organic Layers as Robust Scaffolds for Highly Efficient Photocatalytic Oxygen Evolution.

Two Kagóme cobalt(II)-organic layers of [Co3 (μ3 -OH)2 (bdc)2 ]n (1) and [Co3 (μ3 -OH)2 (chdc)2 ]n (2) (bdc=o-benzenedicarboxylate and chdc=1,2-cyclohexanedicarboxylate) that bear bridging OH(-) ligands were explored as water oxidation catalysts (WOCs) for photocatalytic O2 production. The activities of 1 and 2 towards H2 O oxidation were assessed by monitoring the in situ O2 concentration versus time in the reaction medium by utilizing a Clark-type oxygen electrode under photochemical conditions. The oxygen evolution rate (RO2 ) was 24.3 μmol s(-1) g(-1) for 1 and 48.8 μmol s(-1) g(-1) for 2 at pH 8.0. Photocatalytic reaction studies show that 1 and 2 exhibit enhanced activities toward the oxidation of water compared to commercial nanosized Co3 O4 . In scaled-up photoreactions, the pH value of the reaction medium decreased from 8.0 to around 7.0 after 20 min and the O2 production ceased. Based on the amounts of the sacrificial oxidant (K2 S2 O8 ) used, the yield of O2 produced is 49.6 % for 2 and 29.8 % for 1. However, the catalyst can be recycled without a significant loss of catalytic activity. Spectroscopic studies suggest that the structure and composition of recycled 1 and 2 are maintained. In isotope-labeling H2 (18) O (97 % enriched) experiments, the distribution of (16) O(16) O/(16) O(18) O/(18) O(18) O detected was 0:7.55:92.45, which is comparable to the theoretical values of 0.09:5.82:94.09. This work not only provides new catalysts that resemble ligand-protected cobalt oxide materials but also establishes the significance of the existence of OH(-) (or H2 O) binding sites at the metal center in WOCs.

CO2 Capture in Aluminum‐Based Metal‐organic Frameworks: A Theoretical Study

AbstractBased on density functional theory calculations with van der Waals corrected functional, we study the in‐ teractions between CO2 and two novel Aluminum‐Based metal‐organic frameworks (MOFs) with two kinds of organic linkers: 2, 5‐thiophenedicarboxylic acid (TDC), 2, 5‐furandicarboxylic acid (FDC), named Al‐TDC and Al‐FDC. Our calculations show that CO2 can interact with Al‐TDC and Al‐FDC MOFs via three kinds of interactions: (1) weak hydrogen bond interactions by an OCO2 with the elec‐ tron‐deficient H atom of the linker (thiophene ring and furan ring) or of the OH ligand; (2) Lewis‐base in‐ teraction by an OCO2 with the linker (thiophene ring and furan ring); (3) lone pair interaction between OCO2 and S atom of thioph‐ene ring or O atom of furan ring. We show that a judicious modification of the organic linker increases the binding energy from −30.31∼−33.86 kcal/mol (FDC) to −33.98∼−38.92 kcal/mol (TDC). The results may provide useful information for the design of future CO2‐philes MOFs.

Selective Chlorination of Substrates by the Halogenase SyrB2 Is Controlled by the Protein According to a Combined Quantum Mechanics/Molecular Mechanics and Molecular Dynamics Study

The enzyme SyrB2 employs an FeIV–oxo species to achieve selective C–H halogenation of l-threonine. Herein, we use combined quantum mechanical/molecular mechanical (QM/MM) calculations and molecular dynamics (MD) simulations to decipher the mechanism of selective halogenation by SyrB2. Our QM/MM calculations show the presence of three Cl–FeIV–oxo isomers which interconvert, and only the one having its oxo ligand pointing toward the target C–H bond is active during the hydrogen atom abstraction (H-abstraction) process. The fate of the formed Cl–FeIII–OH/R• intermediate is determined by a hydrogen-bonding interaction between the Arg254 residue and the OH ligand of Cl–FeIII–OH. The hydrogen bond not only prevents the OH group from participating in the followup rebound step to form a hydroxylated product but also facilitates the isomerization of the Cl–FeIII–OH/R• intermediate so that the Cl is directed toward the alkyl radical. The role of Arg254 in regulating the selectivity of chlorination is further discus...

Nanoscaled Zinc Pyrazolate Metal-Organic Frameworks as Drug-Delivery Systems.

This work describes synthesis at the nanoscale of the isoreticular metal-organic framework (MOF) series ZnBDP_X, based on the assembly of Zn(II) metal ions and the functionalized organic spacers 1,4-bis(1H-pyrazol-4-yl)-2-X-benzene (H2BDP_X; X = H, NO2, NH2, OH). The colloidal stability of these systems was evaluated under different relevant intravenous and oral-simulated physiological conditions, showing that ZnBDP_OH nanoparticles exhibit good structural and colloidal stability probably because of the formation of a protein corona on their surface that prevents their aggregation. Furthermore, two antitumor drugs (mitroxantrone and [Ru(p-cymene)Cl2(pta)] (RAPTA-C) where pta = 1,3,5-triaza-7-phospaadamantane) were encapsulated within the pores of the ZnBDP_X series in order to investigate the effect of the framework functionalization on the incorporation/delivery of bioactive molecules. Thus, the loading capacity of both drugs within the ZnBDP_X series seems to directly depend on the surface area of the solids. Moreover, ligand functionalization significantly affects both the delivery kinetics and the total amount of released drug. In particular, ZnBDP_OH and ZnBDP_NH2 matrixes show a slower rate of delivery and higher percentage of release than ZnBDP_NO2 and ZnBDP_H systems. Additionally, RAPTA-C delivery from ZnBDP_OH is accompanied by a concomitant and progressive matrix degradation due to the higher polarity of the BPD_OH ligand, highlighting the impact of functionalization of the MOF cavities over the kinetics of delivery.