Activating a Low Overpotential CO2 Reduction Mechanism by a Strategic Ligand Modification on a Ruthenium Polypyridyl Catalyst

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru(tBu₃tpy)(bpy)(NCCH₃)]²⁺ (tBu₃tpy=4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine; bpy=2,2′‐bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO₂ to CO. The methyl group enables CO₂ binding already at the one‐electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO₂ reduction catalysts.     

Gecko-inspired composite micro-pillars with both robust adhesion and enhanced dry self-cleaning property

Enhanced dry self surfaces were fabricated which could dislodge up to 24.6% of contaminated particles with as few as 4 steps.     

Joule–Thomson Effects on the Flow of Liquid Water

We present a revised form of the energy balance for the coupled thermodynamics of liquid water flowing in porous media and give examples of situations where a commonly used formulation based on transport of enthalpy leads to erroneous results. Assuming negligible contribution from kinetic energy as well as sources and sinks such as energy from radioactive decay, total energy conservation is reduced to a balance between changes in internal energy, enthalpy, conductive heat flux, and gravitational potential energy. The Joule–Thomson coefficient is defined as the change in temperature with respect to an increase in pressure at constant enthalpy. Because liquid water has a negative Joule–Thomson coefficient at low temperatures, at a constant gravitational potential water cools as it compresses and heats as it expands. If one ignores the gravitational energy, transport of enthalpy alone leads to water heating by 2 \(^\circ \) C per kilometer as it is brought up from depth. The corrected energy balance transports methalpy, which is enthalpy plus gravitational potential energy. Although the simpler form leads to small changes in the temperature profile for typical simulations, there are several instances where this effect may prove to be important. The most important impact of the erroneous form is probably in the field of geothermal energy production, where the creation of a few degrees of heat in a simulation could lead to miscalculation of power plant efficiencies.     

Metal–Metal Single Bonds with the Magnetic Anisotropy of Quadruple Bonds: A Systematic Series of Heterobimetallic Bismuth(II)–Rhodium(II) Formamidinate Complexes

The first set of five heterobimetallic MM′(form)₄ (form=formamidinate) complexes containing a BiRh core has been successfully synthesized. The Bi?Rh bond lengths lie between 2.5196(6) and 2.572(2) Å, consistent with Bi?Rh single bonds. All complexes have rich electrochemistry, with the [BiRh]^4+/5+ redox couples spanning approximately 700 mV and showing a strong correlation to remote ligand substitution. Visible spectroscopy showed two features for complexes 1 – 5 at approximately 459 and 551 nm, unique to BiRh paddlewheel complexes that are attributed to LMCT bands into the Bi?Rh σ* orbital. The large spin–orbit coupling (SOC) of Bi creates a massive Bi?Rh magnetic anisotropy, Δχ, approximately ?4800×10^?36 m³molecule^?1, which is the largest value reported for any single bond to date.     

Identities from representation theory

We give a new Jacobi–Trudi-type formula for characters of finite-dimensional irreducible representations in type $C_n$ using characters of the fundamental representations and non-intersecting lattice paths. We give equivalent determinant formulas for the decomposition multiplicities for tensor powers of the spin representation in type $B_n$ and the exterior representation in type $C_n$. This gives a combinatorial proof of an identity of Katz and equates such a multiplicity with the dimension of an irreducible representation in type $C_n$. By taking certain specializations, we obtain identities for $q$-Catalan triangle numbers, a slight modification of the $q,t$-Catalan number of Stump, $q$-triangle versions of Motzkin and Riordan numbers, and generalizations of Touchard’s identity. We use (spin) rigid tableaux and crystal base theory to show some formulas relating Catalan, Motzkin, and Riordan triangle numbers.     

Selenium-modified TiO2 and its impact on photocatalysis

This work describes the preparation of a selenium-modified TiO(2) photocatalyst and a preliminary evaluation of its photocatalytic activity. Se-TiO(2) displayed greater visible absorption than undoped TiO(2) and was still capable of degrading quinoline at a slightly faster rate than undoped TiO(2) under UV light. Se-TiO(2) was also able to degrade organic molecules under purely visible light by a single electron transfer pathway. Irradiation with >435 nm light showed no evidence of efficient production of HO?-like species. Se-TiO(2) was also examined under hypoxic conditions, where the Se atoms were capable of trapping photogenerated electrons as evidenced by XPS.     

Incorporation of 2,3-Disubstituted-1,4-Naphthoquinones into the A1 Binding Site of Photosystem I Studied by EPR and ENDOR Spectroscopy

Transient electron paramagnetic resonance and pulsed electron-nuclear double resonance (ENDOR) spectra of the state $ P_{700}^{ \cdot + } A_{1}^{ \cdot - } $ in photosystem I containing a series of non-native naphthoquinones (NQs) are presented. Previous studies have shown that quinones bind to the A₁ site with only one of their carbonyl groups H-bonded to the protein and that the asymmetric H-bond produces an odd alternant distribution of the spin density within the quinone. It is known that the native phylloquinone binds with its methyl group meta and its phytyl tail ortho to the H-bonded carbonyl. Monosubstituted NQs with short alkyl chains have been found to bind preferentially with their alkyl side groups meta to the H-bonded carbonyl. The selectivity of the binding site toward methyl and short chain substituents is studied by incorporating disubstituted NQs that have a methyl group at the 2-position and a short chain at the 3-position of the quinone ring. The hyperfine couplings (hfcs) of the methyl group protons are sensitive to the spin density distribution on the quinone and are used to deduce the position of the methyl group relative to the H-bonded carbonyl. The measured methyl proton hfcs indicate that the disubstituted quinones bind exclusively with their methyl group in the meta position relative to the H-bonded carbonyl and no evidence for binding with the methyl group in the ortho position is found. The disubstituted quinones have also been chosen to study the effect of electron withdrawing substituents on the spin density distribution. When the short chain contains electronegative atoms such as sulfur or chlorine, the methyl proton hfcs of the quinone in the A₁ binding site are found to be significantly larger than those of 2-methyl-1,4-naphthoquinone and phylloquinone in the same environment. Solution ENDOR measurements of the quinone radical anions in isopropanol and density functional theory (DFT) calculations in vacuo show that this increase in the hfcs is mostly intrinsic to the quinones due to the electron-withdrawing ability of the short chain and is not a result of differences in the binding to the protein. The DFT calculations suggest that the main reason for the increased methyl proton hfcs is delocalization of the singly occupied molecular orbital onto the side chain, which leads to an increase of the spin density on the neighboring carbon, which carries methyl group.     

Efficient catalysis of ammonia borane dehydrogenation

In the presence of an iridium pincer complex, dehydrogenation of ammonia borane (H3NBH3) occurs rapidly at room temperature in tetrahydrofuran to generate 1.0 equivalent of H2 and [NH2BH2]5. A metal borohydride complex has been isolated as a dormant form of the catalyst which can be reactivated by reaction with H2.