Aqueous Electrochemical Reduction of Carbon Dioxide and Carbon Monoxide into Methanol with Cobalt Phthalocyanine

Conversion of CO₂ into valuable molecules is a field of intensive investigation with the aim of developing scalable technologies for making fuels using renewable energy sources. While electrochemical reduction into CO and formate are approaching industrial maturity, a current challenge is obtaining more reduced products like methanol. However, literature on the matter is scarce, and even more for the use of molecular catalysts. Here, we demonstrate that cobalt phthalocyanine, a well‐known catalyst for the electrochemical conversion of CO₂ to CO, can also catalyze the reaction from CO₂ or CO to methanol in aqueous electrolytes at ambient conditions of temperature and pressure. The studies identify formaldehyde as a key intermediate and an unexpected pH effect on selectivity. This paves the way for establishing a sequential process where CO₂ is first converted to CO which is subsequently used as a reactant to produce methanol. Under ideal conditions, the reaction shows a global Faradaic efficiency of 19.5 % and chemical selectivity of 7.5 %.     

Magnetic Signatures of Hydroxyl- and Water-Terminated Neutral and Tetra-Anionic Mn12-Acetate

We investigate the energetics and magnetic signatures of the parent molecular magnet Mn₁₂-Acetate [Mn₁₂O₁₂(COOR)₁₆(H₂O)₄] and a chemically decomposed version of this structure, in which the four water molecules are converted to hydroxyl groups and hydrogen molecules. We determine electron addition and water decomposition energetics for this water-containing molecule using density-functional methods and include the recent Fermi-Löwdin-Orbital self-interaction correction. We find that it only costs 0.32 eV to add four electrons to the parent molecule. Furthermore, due to the strong Coulomb attractions between hydroxyl anions and the Mn cations, the energy cost for breaking the four coordinating water molecules into four coordinating hydroxyls and two hydrogen molecules is decreased in the tetra-anionic structure relative to the neutral structure. We calculate magnetic anisotropy barriers for the neutral molecule and the dehydrogenated tetra-anion and show that large changes in the magnetic anisotropy arise the strong attraction between the hydroxyl anions and four of the crown Mn cations. We suggest that the large changes in magnetic signals associated with the [Mn₁₂O₁₂(COOR)₁₆(HOH)₄] to [Mn₁₂O₁₂(COOR)₁₆(OH⁻)₄ + 2H₂] decomposition could provide a nondestructive spectroscopic method for learning about water decomposition mechanisms in a class of realizable model catalytic systems that have been synthesized recently. © 2019 Wiley Periodicals, Inc.     

Solvent-sensitive dyes to report protein conformational changes in living cells

Covalent attachment of solvent-sensitive fluorescent dyes to proteins is a powerful tool for studying protein conformational changes, ligand binding, or posttranslational modifications. We report here new merocyanine dyes that make possible the quantitation of such protein activities in individual living cells. The quantum yield of the new dyes is sharply dependent on solvent polarity or viscosity, enabling them to report changes in their protein environment. This is combined with other stringent requirements needed in a live cell imaging dye, including appropriate photophysical properties (excitation >590 nm, high fluorescence quantum yield, high extinction coefficient), good photostability, minimal aggregation in water, and excellent water solubility. The dyes were derivatized with iodoacetamide and succinimidyl ester side chains for site-selective covalent attachment to proteins. A novel biosensor of Cdc42 activation made with one of the new dyes showed a 3-fold increase in fluorescence intensity in response to GTP-binding by Cdc42. The dyes reported here should be useful in the preparation of live cell biosensors for a diverse range of protein activities.     

Vase‐Kite Equilibrium of Resorcin[4]arene Cavitands Investigated Using Molecular Dynamics Simulations with Ball‐and‐Stick Local Elevation Umbrella Sampling

A key feature of resorcin[4]arene cavitands is their ability to switch between a closed/contracted (Vase ) and an open/expanded (Kite ) conformation. The mechanism and dynamics of this interconversion remains, however, elusive. In the present study, the Vase ‐Kite transitions of a quinoxaline‐based and of a dinitrobenzene‐based resorcin[4]arene are investigated using molecular dynamics (MD) simulations in three environments (vacuum, chloroform, and toluene) and at three temperatures (198.15, 248.15, and 298.15 K). The challenge of sampling the Vase ‐Kite transition, which occurs experimentally on the millisecond time scale, is overcome by calculating relative free energies using ball‐and stick local elevation umbrella sampling (B&S‐LEUS) to enhance the statistics on the relevant states and to promote interconversion transitions. Associated unbiased MD simulations also evidence for the first time a complete Vase ‐to‐Kite transition, as well as transitions between degenerate Kite 1 and Kite 2 forms and solvent‐exchange events. The calculated Vase ‐to‐Kite free‐energy changes ΔG are in qualitative agreement with the experimental magnitudes and trends. The level of quantitative agreement is, however, limited by the force‐field accuracy and, in particular, by the approximate treatment of intramolecular interactions at the classical level. The results are in line with a less stable Vase state for the dinitrobenzene compared to the quinoxaline compound, and a negative entropy change ΔS for the Vase ‐to‐Kite transition of the latter compound. Relative free energies calculated for intermediates also suggest that the Vase ‐Kite transition does not follow a concerted mechanism, but an asynchronous one with sequential opening of the flaps. In particular, the conformation involving two adjacent flaps open in a parallel direction (cis‐p) represents a likely intermediate, which has not been observed experimentally to date.     

N-Acenoacenes

The syntheses of new, fourfold alkynylated tetraazaacenoacenes (tetraazaanthracenoanthracene, tetraazatetracenotetracene and tetraazapentacenopentacene) are reported. This novel heteroacenoacene motif exhibits surprisingly strong electronic coupling between its constituting diazaacene units.     

Low-pressure pyrolysis of tBu2SO: synthesis and IR spectroscopic detection of HSOH

Sulfenic acid (HSOH, 1 ) has been synthesized in the gas‐phase by low‐pressure high‐temperature (1150 °C) pyrolysis of di‐tert‐butyl sulfoxide (tBu₂SO, 2 ) and characterized by means of matrix isolation and gas‐phase IR spectroscopy. High‐level coupled‐cluster (CC) calculations (CCSD(T)/cc‐pVTZ and CCSD(T)/cc‐pVQZ) support the first identification of the gas‐phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix‐isolated 1 have been assigned, and its rotational‐resolved gas‐phase IR spectrum provides additional information on the O–H and S–H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gas‐phase FT‐IR spectroscopy reveal that, up to 500 °C, 2 decomposes selectively into tert‐butylsulfenic acid, (tBuSOH, 3 ), and 2‐methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3 a ) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas‐phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6‐311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3 , monitored by matrix IR spectroscopy, yields short‐lived 1 along with 2‐methylpropene, but also H₂O, and most probably sulfur atoms. In addition, HSSOH ( 6 ), H₂, and S₂O are found among the final pyrolysis products observed at 1150 °C in the gas phase owing to competing intra‐ and intermolecular decomposition routes of 3 . The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6‐311G* and second‐order Møller–Plesset (MP2/6‐311G* and RI‐MP2/QZVPP) levels of theory.     

Cycling behaviour of Li/Li4Ti5O12 cells studied by electrochemical impedance spectroscopy

We studied the behaviour of Li/Li(4)Ti(5)O(12) cells by electrochemical impedance spectroscopy to gain insight into the changes at the electrode/electrolyte interfaces during extensive cycling. A simple equivalent-circuit model is able to describe the impedance of the complete battery as a function of both state-of-charge and state-of-degradation. The formation of the solid-electrolyte interface and dendrite growth at the Li metal electrode have a strong influence on the impedance measurements although the battery performance is not significantly affected.     

Sorption of U(VI) onto granite surfaces: A kinetic approach

Surface sorption experiments of U(VI) onto the surfaces of a Korean granite rock are carried out in order to investigate the kinetics and reversibility of U(VI) sorption as a function of pH and surface types such as fresh intact surfaces and natural fracture surfaces. It was shown that the effect of pH is significant in the sorption of U(VI) onto both types of the granite surfaces. However the sorption rates do not greatly depend upon the pH regardless of the surface types. A two-step first order kinetic behavior dominates onto both the intact surfaces and natural fracture surfaces of granite and that the linearization approach of the kinetic model agrees well with experimental sorption data. The desorption results showed that the sorption process of U(VI) was a little irreversible for the two types of granite surfaces regardless of pH and surface types. This kinetic approach could give a better understanding of U(VI) sorption onto granite surfaces depending on pH and surface types. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ox-LDL suppresses PMA-induced MMP-9 expression and activity through CD36-mediated activation of PPAR-g

During chronic inflammatory response, mono- cytes/macrophages produce 92-kDa matrix metalloproteinase-9 (MMP-9), which may contribute to their extravasation, migration and tissue remodeling. Activation of peroxisome proliferator- activated factor receptor-g (PPAR-g) has been shown to inhibit MMP-9 activity. To evaluate whether ox-LDL, a PPAR-g activator, inhibits PMA-induced MMP-9 expression and activity, and if so, whether CD36 and PPAR-g are involved in this process, we investigated the effect of ox-LDL on MMP-9 expression and activity in PMA-activated human monocytic cell line U937. PMA-induced MMP-9 expression and activity were suppressed by the treatment with ox-LDL (50 mg/ml) or PPAR-g activators such as troglitazone (5 mM), ciglitazone (5 mM), and 15d- PGJ2 (1 mM) for 24 h. This ox-LDL or PPAR-g activator-mediated inhibition of MMP-9 activity was diminished by the pre-treatment of cells with a blocking antibody to CD36, or PGF2a (0.3 mM), which is a PPAR-g inhibitor, as well as overexpression of a dominant-negative form of CD36. Taken together, these results suggest that ox-LDL suppresses PMA-induced MMP-9 expression and activity through CD36-mediated activation of PPAR-g.