Solvent Coordination Research Articles

The synergistic effect of NiCo nanoparticles and metal organic framework: Enhancing the oxygen evolution reaction of carbon nanohorn-based catalysts

Enhancing the reactivity of nanocatalysts by the synergistic effect of MOF derivatives active nanoparticles (NP) and Metal organic framework (MOF) supported by carbon materials is a state of the art progress. Herein, a strategy for surface-mounting NP/NiCo MOF thin films on Carbon nanohorn (CNH) by controlled pyrolysis is developed. CNH is introduced to improve the conductivity and structure stability of MOF and polydopamine (PDA) is used to bond each other, resulting in CNH@PDA@MOF. Compared with CoMOF@PDA@CNH, the introduction of Ni helps to waken the bonding between the metal center (Co) and the coordination solvent and expose more unsaturated coordination centers and in turn the catalytic activity. As a result of synergistic effect on geometric and electronic structure of bimetallic center Ni and Co codes in MOF, Ni1Co4MOF@PDA@CNH shows the best catalytic activity and was further used as both the source of the framework structure and the precursor of active NP derivatives. By partial pyrolysis of MOF, the active NP/MOF/CNH can be successfully obtained at 400 ℃. The hierarchically structured NP/MOF/CNH as a synergistic electrocatalyst shows excellent activity (216 mV/cm2 at a current density of 10 mA/cm2), exceeding most previously reported bi-metallic catalysts. Obviously, the combination of NiCo NPs, partially degraded MOF and CNH makes an improvement in the increase of active species, promotion of water adsorption, and electron transfer. This universal and productive method grappling conductive active sites/porous MOF on CNH plays an important role in construction of synergistic electrocatalysts for OER.

Electrophoretic NMR of Concentrated Electrolytes for Li-Ion Batteries: Understanding the Role of Solvent Motion

In this work cation, anion, and solvent velocities are reported in concentrated Li-ion battery electrolytes using an electrophoretic NMR (eNMR) methodology. Recent computational studies suggest that in concentrated electrolytes, ion aggregation may lead to transport of Li+ in negatively-charged clusters, resulting in negative cationic transference numbers.1,2 Additionally, increasing ion–solvent coordination may lead to a significant non-zero solvent velocity. These unusual transport properties have important implications for fast-charging performance, but as of yet only limited experimental evidence exists for these phenomena.3 Pulsed-field-gradient (PFG) NMR experiments on their own give self-diffusion coefficients but do not report on the drift of charged species, or induced solvent motion; by running PFG under synchronized application of an electric field (i.e., eNMR), the sign and magnitude of electrophoretic mobilities can be determined with spectroscopic specificity. Through 7Li, 19F and 1H eNMR measurements on carbonate- and glyme-based concentrated electrolytes, we show average species velocities in good agreement with conductivity data, and also directly measure transference numbers in the solvent reference frame. eNMR may provide rapid screening of potential electrolytes at various concentrations to discern which systems (both liquid- and polymer-based) possess efficacious transport properties.(1) France-Lanord, A.; Grossman, J. C. Correlations from Ion Pairing and the Nernst-Einstein Equation. Phys. Rev. Lett. 2019, 122 (13), 136001. https://doi.org/10.1103/PhysRevLett.122.136001.(2) Molinari, N.; Mailoa, J. P.; Kozinsky, B. General Trend of a Negative Li Effective Charge in Ionic Liquid Electrolytes. The Journal of Physical Chemistry Letters 2019, 10 (10), 2313–2319. https://doi.org/10.1021/acs.jpclett.9b00798.(3) Gouverneur, M.; Schmidt, F.; Schönhoff, M. Negative Effective Li Transference Numbers in Li Salt/Ionic Liquid Mixtures: Does Li Drift in the “Wrong” Direction? Physical Chemistry Chemical Physics 2018, 20 (11), 7470–7478. https://doi.org/10.1039/C7CP08580J.

Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage

In the field of electrochemical energy storage, multielectron molecular redox couples play significant roles. These redox couples have been used both as anolytes and catholytes in redox flow batteries (RFBs). The energy stored in an RFB is proportional to the number of electrons transferred per molecule. Thus, increasing the number of electrons transferred per molecule can enhance the amount of stored energy. Previous works in this field mostly looked for molecules containing multiple 1e- redox couples. The advantage of a single 2e- redox couple over multiple 1e- redox couples is that both electrons are stored and released at the same potential. In the case of multiple 1e- redox couples, two redox potentials are usually separated by more than 0.3 V. This can cause significant shifts in battery voltage and power during charging and discharging of an RFB. Nickel (II) diethyldithiocarbamate, NiII(Et2dtc)2 undergoes 2e- oxidation at a single potential to form [NiIV(Et2dtc)3]+. In different nonaqueous solvents NiII(Et2dtc)2 can offer divergent redox behavior based on their coordination properties. This divergent redox behavior means significant changes on the electrochemistry of the complex during oxidation and reduction. Pyridine, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile (MeCN), methanol (MeOH), acetone, and dichloromethane (DCM) have been studied in this work as they have dissimilar donor numbers with different coordination abilities towards the Ni center. Both cyclic voltammetry and spectroscopic data in the above-mentioned solvents show distinct behavior which is expected as solvent coordination ability varies. Due to its highest coordination ability among the solvents used in this study, pyridine hinders the Ni (II) to Ni (IV) oxidation by coordinating strongly to the Ni (III) center to form [NiIII(Et2dtc)2(Py)2]+. On the contrary, noncoordinating DCM allows oxidation to Ni (IV) albeit through two distinguishable 1e- oxidation processes. MeCN and acetone allow Ni (II)→(IV) oxidation at a single potential. DMSO, DMF, and MeOH show intermediate redox behavior between 1e- and 2e- transfer reactions. The presence of Ni (III) in the case of highly coordinating solvents was confirmed by low temperature EPR and UV-vis absorbance spectroscopy with the use of a chemical oxidant. These studies point to the ability of solvent to aid or hinder multielectron redox strategies which use Ligand Coupled Electron Transfer where changes in coordination environment are necessary.

Controllable assembly of three [Cu2(COO)4]-based complexes using two as-synthesized aromatic tetracarboxylate linkers

Three new complexes, namely, [Cu2(H2bdcpb)2(pyridine)2] (1), [Cu3(bdcpp)2(CH3NCH3)(H2O)] (2), and [Cu2(H2bdcpp)2(H2O)2]·2H2O (3), have been synthesized through the hydro/solvothermal reaction of cupric nitrate and lab-synthesized 1,3-bis(2′,4′-dicarboxylphenyl)benzene (H4bdcpb) or 2,6-bis(2′,4′-dicarboxylphenyl)pyridine (H4bdcpp) in the presence of different solvent systems. Isostructural complexes 1 and 3 show dinuclear [Cu2(COO)4] covalent modes with different coordinate solvent molecules. In complex 2, a two-dimensional covalent layer is generated from one-dimensional loop chains interconnected by [Cu2(COO)4] paddle-wheels. Structural analyses revealed that the framework stability of complexes 1–3 originated from molecular custom-designed [Cu2(COO)4] paddle-wheel units by symmetrical 2′,4′-dicarboxyl polyaromatic ligands.

Metal-Catalyzed Hydride Transfer from Alcohols to Photoexcited Dipyridophenazine.

Dipyridophenazine (dppz) is known to react with alcohols upon photoexcitation into an n-π* transition at 378 nm to yield dihydrodipyridophenazine (dppzH2 ). This process occurs via H-atom abstraction from alcohols and subsequent disproportionation of the dppzH• radical species, to the final product. This reaction shows a primary kinetic isotope effect (KIE = 4.9) in methanol/perdeuteromethanol solvents, consistent with H-atom transfer processes. Addition of excess Zn(II) ions to the dppz solution not only accelerates the rate of photoreduction, but also lowers the KIE to 1.7, indicating a change in reaction mechanism. We postulate that the coordination of the alcoholic solvent to Zn(II) activates the alcohol α C-H bonds toward hydride transfer processes which would be consistent with the lowered KIE and faster overall reduction of the aromatic ligand. Interestingly, this appears to be an intramolecular process in which the Zn(II) is coordinated to both the dppz ligand and the reactive alcohol, as a sharp inflection in the overall rate increase is observed at a Zn:dppz ratio of 2:1. At this ratio, the dominant dppz species involves a Zn(II) bound to one dppz and several solvent molecules (methanol and water).

Exploration of N-oxo pyridine 2-carboxamide ligands towards coordination chemistry, solvent extraction, and DFT investigation for the development of novel solvent for lanthanide and actinide separation

In this study the coordination chemistry of three ligands, C5H4NOCONRR′ (where, R, R′ = iC3H7 (L1); R, R′ = iC4H9 (L2); and R = H, R′ = tC4H9 (L3) composed of N-oxide and carboxamide groups have been explored with uranyl nitrate and some selected lanthanide (La, Sm, and Eu) nitrates. All the synthesized ligands as well as their complexes (1–12) of type UO2(NO3)2L (where, L = L1, L2, and L3 for 1, 2, and 3 respectively) and Ln(NO3)3(H2O)L2 (where, Ln = La, L = L1 for 4, L = L2 for 5, and L = L3 for 6; Ln = Sm, L = L1 for 7, L = L2 for 8, and L = L3 for 9; Ln = Eu, L = L1 for 10, L = L2 for 11, and L = L3 for 12) have been characterized by elemental analysis, spectroscopic analyses such as FTIR, 1H NMR, and electrospray ionization mass spectrometry (ESI-MS). Solid-state structural analysis of L1, 3, and 10 is carried out by X-ray crystallographic technique. The CO and NO groups of L1 are placed almost mutually perpendicular to each other in the crystal structure of L1. The X-ray data show that in [UO2(NO3)2{C5H4NOCONH(tC4H9)}] (3), the ligand acts as a bidentate chelating ligand and is bonded through both the N-oxo and amide oxygen atoms, whereas, in [Eu(NO3)3(H2O){C5H4NOCON(iC3H7)2}2] (10), the ligands show monodentate behavior and are bonded only through N-oxo oxygen atoms. Quantum mechanical calculation at DFT level corroborates the possibility of various bonding modes of these ligands towards uranium and europium nitrate with the preference of bonding as observed in the synthesized complexes. Solvent extraction studies using N,N-dioctyl N-oxo pyridine 2-carboxamide ligand (L4) in n-dodecane with UO22+, Pu4+, Am3+ and Eu3+ indicate the trend Pu4+ ˃ UO22+ > Am3+ > Eu3+ at acidity range from 0.01 M to 6 M HNO3. The ligands show good radiation stability at gamma dose up to 500 kGy and chemical stability at 3 M HNO3 for up to 200 h without much affecting the metal ion extraction. Theoretical calculations show the possibility of presence of different metal species in the organic phase, other than the products obtained from dichloromethane during the solvent extraction of UO22+ and Eu3+ in water/dodecane biphasic media. Energy decomposition analysis supports the higher extraction coefficient of UO22+ than Eu3+ with an evidence of higher orbital interaction of the ligands with UO22+.

DFT Study on the Electrocatalytic Reduction of CO2 to CO by a Molecular Chromium Complex.

A variety of molecular transition metal-based electrocatalysts for the reduction of carbon dioxide (CO2) have been developed to explore the viability of utilization strategies for addressing its rising atmospheric concentrations and the corresponding effects of global warming. Concomitantly, this approach could also meet steadily increasing global energy demands for value-added carbon-based chemical feedstocks as nonrenewable petrochemical resources are consumed. Reports on the molecular electrocatalytic reduction of CO2 mediated by chromium (Cr) complexes are scarce relative to other earth-abundant transition metals. Recently, our group reported a Cr complex that can efficiently catalyze the reduction of CO2 to carbon monoxide (CO) at low overpotentials. Here, we present new mechanistic insight through a computational (density functional theory) study, exploring the origin of kinetic selectivity, relative energetic positioning of the intermediates, speciation with respect to solvent coordination and spin state, as well as the role of the redox-active bipyridine moiety. Importantly, these studies suggest that under certain reducing conditions, the formation of bicarbonate could become a competitive reaction pathway, informing new areas of interest for future experimental studies.

Solvent coordination engineering for high-quality hybrid organic-inorganic perovskite films

Identifying the structure of iodoplumbate complexes in various solutions is essential for linking the coordination environment of the perovskite precursor to its final properties. In this study, we investigate the structure of methylammonium lead iodide (MAPbI3) perovskite precursor solutions as a function of the volume ratio of N,N-dimethylformamide and dimethyl sulfoxide (DMSO) using X-ray absorption fine structure spectroscopy. It was demonstrated that DMSO modifies the precursor structure at the atomic level. X-ray diffraction, scanning electron microscopy, and UV–Vis spectroscopy analyses showed that the coordination environment of iodoplumbate complexes in precursor solutions is strongly correlated with the morphology of perovskite films. The appropriate amount of DMSO in the precursor solution modifies the Pb-O and Pb-I coordination of iodoplumbate complexes, which could change the growth process of high-crystallization perovskite films. This study sheds light on the formation mechanism of perovskite films from precursor solutions, which will lead to the development of high-quality films and ultimately high-efficiency devices.

Copper(II) N,N,O-Chelating Complexes as Potential Anticancer Agents.

Three novel dinuclear Cu(II) complexes based on a N,N,O-chelating salphen-like ligand scaffold and bearing varying aromatic substituents (−H, −Cl, and −Br) have been synthesized and characterized. The experimental and computational data obtained suggest that all three complexes exist in the dimeric form in the solid state and adopt the same conformation. The mass spectrometry and electron paramagnetic resonance results indicate that the dimeric structure coexists with the monomeric form in solution upon solvent (dimethyl sulfoxide and water) coordination. The three synthesized Cu(II) complexes exhibit high potentiality as ROS generators, with the Cu(II)/Cu(I) redox potential inside the biological redox window, and thus being able to biologically undergo Cu(II)/Cu(I) redox cycling. The formation of ROS is one of the most promising reported cell death mechanisms for metal complexes to offer an inherent selectivity to cancer cells. In vitro cytotoxic studies in two different cancer cell lines (HeLa and MCF7) and in a normal fibroblast cell line show promising selective cytotoxicity for cancer cells (IC50 about 25 μM in HeLa cells, which is in the range of cisplatin and improved with respect to carboplatin), hence placing this N,N,O-chelating salphen-like metallic core as a promising scaffold to be explored in the design of future tailor-made Cu(II) cytotoxic compounds.

A new approach to study combination mixture organic solvent ethylene carbonate with lithium-ion for alkali-ion battery: A density functional theory

Using first-principles calculations, we predicted different structures of lithium (Li) atoms with solid electrolytes (e.g., ethylene carbonate (EC)) and their coordination number (n = 3) for the first time. Additionally, we explored the unique properties of the EC absorption of the Li atom using both the equilibrium EC solvent and complex cluster of Li+. Vibrational spectral analysis confirmed that only one type of Li coordinates with EC molecules. The coordination number of EC molecules increases with decreasing minimization or optimization energy and the charge of Li ions. Due to electron affinity and ion charges, only the optimized energy investigation supports the coordination of the EC solvent, which can be calculated by Li+Bn n = 1–3, where B is the organic solvent (ethylene).

Recent Progress in Trivalent Actinide and Lanthanide Solvent Extraction and Coordination Chemistry with Triazinylpyridine N Donor Ligands

ABSTRACT A follow up to an earlier review on the coordination and extraction of trivalent actinide and lanthanide ions with triazinylpyridine N-donor ligands is presented. It reviews the recent development in the fields of ligand modifications and improvements, considering both hydrophobic compounds (to be used as extracting agents) and hydrophilic compounds (to be used as stripping agents), with a focus on fundamental studies.

Singlet Fission in a Flexible Bichromophore with Structural and Dynamic Control.

Singlet fission (SF), i.e., the splitting of a high-energy exciton into two lower-energy triplet excitons, has the potential to increase the efficiency for harvesting spectrally broad light. The path from the photopopulated singlet state to free triplets is complicated by competing processes that decrease the overall SF efficiency. A detailed understanding of the whole cascade and the nature of the photoexcited singlet state is still a major challenge. Here, we introduce a pentacene dimer with a flexible crown ether spacer enabling a control of the interchromophore coupling upon solvent-induced self-aggregation as well as cation binding. The systematic change of solvent polarity and viscosity and excitation wavelength, as well as the available conformational phase space, allows us to draw a coherent picture of the whole SF cascade from the femtosecond to microsecond time scales. High coupling leads to ultrafast SF (<2 ps), independent of the solvent polarity, and to highly coupled correlated triplet pairs. The absence of a polarity effect indicates that the solvent coordinate does not play a significant role and that SF is driven by intramolecular modes. Low coupling results in much slower SF (∼500 ps), which depends on viscosity, and leads to weakly coupled correlated triplet pairs. These two triplet pairs could be spectrally distinguished and their contribution to the overall SF efficiency, i.e., to the population of free triplets, could be determined. Our results reveal how the overall SF efficiency can be increased by conformational restrictions and control of the structural fluctuation dynamics.

Solvation dynamics in electronically polarizable solvents: Theoretical treatment using solvent-polarizable three-dimensional reference interaction-site model theory combined with time-dependent density functional theory.

The theory of solvation structure in an electronically polarizable solvent recently proposed by us, referred to as the "solvent-polarizable three-dimensional reference interaction-site model theory," is extended to dynamics in this study through the combination with time-dependent density functional theory. Test calculations are performed on model charge-transfer systems in water, and the effects of electronic polarizability on solvation dynamics are examined. The electronic polarizability slightly retards the solvation dynamics. This is ascribed to the decrease in the curvature of the nonequilibrium free energy profile along the solvation coordinate. The solvent relaxation is bimodal, and the faster and the slower modes are assigned to the reorientational and the translational modes, respectively, as was already reported by the surrogate theory combined with the site-site Smoluchowski-Vlasov equation. The relaxation path along the solvation coordinate is a little higher than the minimum free energy path because the translational mode is fixed in the time scale of the reorientational relaxation.

Solvent manipulation of the pre-reduction metal-ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles.

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. In this study, we show that the nucleation and growth rates are correlated with the thermodynamics of metal-ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal-ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles.

Experimental observation of the unique solvation process along multiple solvation coordinates of photodissociated products.

Chemical reaction dynamics in solution are closely related to solvation dynamics, and understanding solvent responses remains a crucial issue in chemistry and chemical biology. In this study, we experimentally and computationally investigated the solvation dynamics along different solvation coordinates of the same molecule: the electronically excited state and ground state of the p-aminophenylthiyl radical generated by the photodissociation of bis(p-aminophenyl)disulfide. Time profiles of the peak shifts from the transient absorption and emission spectra after photodissociation were extracted to discuss the solvent reorganization process in various ionic liquids (ILs) with different viscosities. The absorption peak position of the radical followed common solvation dynamics, shifting to a lower energy with time due to reorganization of the surrounding solvent molecules in response to the charge redistribution and molecular volume change caused by photodissociation. On the other hand, the emission band of the radical did not show a meaningful spectral shift with time. It was also found that the solvation time in the ground state was not strongly dependent on the solvent viscosity. These experimental results deviate from the conventional dynamic Stokes shift theory. To discuss the experimental results, non-equilibrium molecular dynamics simulations were conducted. The spectral shift obtained by MD simulations indicated the existence of a large solvation energy change and solvation dynamics around the radical after the photodissociation. On the other hand, the electronic excitation of the radical brought about a relatively smaller solvation energy change, especially at the long delay time after the photodissociation. These differences might be one of the reasons for the unique experimentally observed solvation dynamics.

Fluorene-containing β-diketonato ligands and their Rhodium(I) complexes

In this study, the fluorene-group was added to metal complexes, via the easily synthesized β-diketonato ligand. This enables the incorporation of a fluorescent tag into a variety of metal complexes. Three fluorene-containing β-diketones (1–3) were synthesized, characterized and pKa-values determined. The synthesized ligands were complexed with rhodium(I) (4–6). The electrochemistry of compounds 1–6 were studied. The fluorene-group exhibits no electrochemical activity in the solvent window studied. The β-diketonato ligands showed an electrochemically reversible reduction of the ligand backbone at around −2000 mV vs ferrocene as an internal standard. The rhodium(I) complexes exhibited the same ligand reduction at around −2200 mV, with increased chemical reversibility, while the metal center was oxidized at ~300 mV, followed by solvent coordination forming a rhodium(III) species with reduction of this newly formed species at ~1300 mV. The absorbance and fluorescence of all synthesized complexes (1–6) were studied and fluorescence quantum yields were determined and found to be between 0.001 and 0.0001 as measured against anthracene as standard.

Combined Computational and Experimental Investigation on the Nature of Hydrated Iodoplumbate Complexes: Insights into the Dual Role of Water in Perovskite Precursor Solutions

Water is generally considered an enemy of metal halide perovskites, being responsible for their rapid degradation and, consequently, undermining the long-term stability of perovskite-based solar cells. However, beneficial effects of liquid water have been surprisingly observed, and synthetic routes including water treatments have shown to improve the quality of perovskite films. This suggests that the interactions of water with perovskites and their precursors are far from being completely understood, as water appears to play a puzzling dual role in perovskite precursor solutions. In this context, studying the basic interactions between perovskite precursors in the aqueous environment can provide a deeper comprehension of this conundrum. In this context, it is fundamental to understand how water impacts the chemistry of iodoplumbate perovskite precursor species, PbIx2–x. Here, we investigate the chemistry of these complexes using a combined experimental and theoretical strategy to unveil their peculiar structural and optical properties and eventually to assign the species present in the solution. Our study indicates that iodide-rich iodoplumbates, which are generally key to the formation of lead halide perovskites, are not easily formed in aqueous solutions because of the competition between iodide and solvent molecules in coordinating Pb2+ ions, explaining the difficulty of depositing lead iodide perovskites from aqueous solutions. We postulate that the beneficial effect of water when used as an additive is then motivated by its behavior being similar to high coordinative polar aprotic solvents usually employed as additives in one-step perovskite depositions.

Solvation Structure and Electrochemical Properties of a New Weakly Coordinating Aluminate Salt as a Nonaqueous Electrolyte for Zinc Batteries

In continuation of our interest in developing multivalent electrolytes for energy storage, we report a new zinc salt with a weakly coordinating anion, tetrakis(perfluoro-tert-butoxy) aluminate (TPFA), as a stable electrolyte for nonaqueous systems. We examined the electrochemical and structural properties of this nonaqueous electrolyte in various solvents. ZnTPFA2 supports highly reversible Zn deposition and stripping behavior in acetonitrile and ethereal solvents, with up to 91% Coulombic efficiency. A variety of analytical techniques were used to identify the local coordination structure around Zn2+ in both the crystal phase and the solution phase, providing clear evidence of solvent coordination around the cation.

The Importance of Competitive Solvent and Anion Coordination for Multivalent Battery Electrolytes

Multivalent battery concepts based on magnesium or calcium metal anodes have the potential to provide higher energy density than traditional lithium ion batteries. However, current multivalent electrolytes possess less than optimal compatibility with these reactive metals and with desirable high voltage cathode materials. Understanding the origin of these issues requires an understanding of multivalent cation coordination environments in both the bulk and at the relevant interfaces. In this presentation, elucidation of the relative coordination strengths of “state-of-the-art” multivalent battery salts and solvents will be described. Moreover, the impact of these competitive coordination tendencies on metal deposition efficiency will be discussed along with the efficacy of tuning such interactions to improve magnesium and calcium electrolyte performance.This work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Mobile loop dynamics in adenosyltransferase control binding and reactivity of coenzyme B12

Cobalamin is a complex organometallic cofactor that is processed and targeted via a network of chaperones to its dependent enzymes. AdoCbl (5'-deoxyadenosylcobalamin) is synthesized from cob(II)alamin in a reductive adenosylation reaction catalyzed by adenosyltransferase (ATR), which also serves as an escort, delivering AdoCbl to methylmalonyl-CoA mutase (MCM). The mechanism by which ATR signals that its cofactor cargo is ready (AdoCbl) or not [cob(II)alamin] for transfer to MCM, is not known. In this study, we have obtained crystallographic snapshots that reveal ligand-induced ordering of the N terminus of Mycobacterium tuberculosis ATR, which organizes a dynamic cobalamin binding site and exerts exquisite control over coordination geometry, reactivity, and solvent accessibility. Cob(II)alamin binds with its dimethylbenzimidazole tail splayed into a side pocket and its corrin ring buried. The cosubstrate, ATP, enforces a four-coordinate cob(II)alamin geometry, facilitating the unfavorable reduction to cob(I)alamin. The binding mode for AdoCbl is notably different from that of cob(II)alamin, with the dimethylbenzimidazole tail tucked under the corrin ring, displacing the N terminus of ATR, which is disordered. In this solvent-exposed conformation, AdoCbl undergoes facile transfer to MCM. The importance of the tail in cofactor handover from ATR to MCM is revealed by the failure of 5'-deoxyadenosylcobinamide, lacking the tail, to transfer. In the absence of MCM, ATR induces a sacrificial cobalt-carbon bond homolysis reaction in an unusual reversal of the heterolytic chemistry that was deployed to make the same bond. The data support an important role for the dimethylbenzimidazole tail in moving the cobalamin cofactor between active sites.