Cationic Bis(hydrosilane)-Coinage Metal Complexes: Synthesis, Characterization, and Use as Catalysts for Outer-Sphere C=O Hydrosilylation Not Involving Metal Hydrides.

The preparation of cationic bis(hydrosilane)-coinage-metal complexes by chloride abstraction from the neutral metal chloride precursors with Na[BArF4] is described. Unlike previously reported hydrosilane-stabilized copper and silver complexes, the presented complexes are cationic and feature two bidentate ortho-(silylphenyl)phosphine ligands. These complexes were fully characterized by NMR spectroscopy and X-ray diffraction analysis, revealing that both Si-H bonds are activated by the Lewis acidic cationic metal center. The new complexes were found to be effective in catalytic carbonyl hydrosilylation, leading to the corresponding silyl ethers under mild conditions without the addition of an external base. Combined mechanistic control experiments and quantum chemical calculations support an ionic outer-sphere mechanism, in which a neutral metal alkoxide species instead of a metal hydride is the key intermediate that interacts with the silylcarboxonium ion to generate the silyl ether.

Difference in functional connectivity between end-stage renal disease patients with and without restless legs syndrome: A prospective study.

PURPOSE: The purpose of this study was to examine differences in functional connectivity between patients with end-stage renal disease (ESRD) with and without restless legs syndrome (RLS). In addition, the study aimed to identify any potential associations between RLS severity and functional connectivity. METHODS: We enrolled patients with ESRD who had been undergoing hemodialysis. Patients with and without RLS were separated into two groups. Using functional near-infrared spectroscopy (fNIRS) and a graph theory approach, we determined the functional connectivity of patients with ESRD. The data were collected during a 300-s resting state evaluation performed in the dialysis room prior to dialysis. RESULTS: Eighteen of 48 patients with ESRD were diagnosed with RLS, whereas 30 patients did not exhibit RLS symptoms. Notably, functional connectivity metrics differed significantly between patients with and without RLS. Specifically, patients with ESRD and RLS displayed higher values for mean clustering coefficient (0.474 vs. 0.352, p = 0.001), global efficiency (0.520 vs. 0.414, p = 0.001), strength (6.538 vs. 4.783, p = 0.001), and transitivity (0.714 vs. 0.521, p = 0.001), while values for diameter (5.451 vs. 7.338, p = 0.002), eccentricity (4.598 vs. 5.985, p = 0.004), and characteristic path length (2.520 vs. 3.271, p = 0.002) were lower in patients with ESRD and RLS compared to those without RLS. In addition, there were correlations between the RLS severity score and the assortative coefficient (r = 0.479, p = 0.044), the small-worldness index (r = -0.475, p = 0.046), and transitivity (r = 0.500, p = 0.034). CONCLUSIONS: We demonstrated differences in functional connectivity between patients with ESRD with and without RLS, which may shed light on the pathophysiology of RLS. Notably, a number of functional connectivity metrics demonstrated strong associations with RLS severity. Our study also confirmed the applicability of fNIRS as a tool for investigating functional connectivity in patients with RLS.

Buffer Assists Electrocatalytic Nitrite Reduction by a Cobalt Macrocycle Complex.

This work reports a combined experimental and computational study of the activation of an otherwise catalytically inactive cobalt complex, [Co(TIM)Br2]+, for aqueous nitrite reduction. The presence of phosphate buffer leads to efficient electrocatalysis, with rapid reduction to ammonium occurring close to the thermodynamic potential and with high Faradaic efficiency. At neutral pH, increasing buffer concentrations increase catalytic current while simultaneously decreasing overpotential, although high concentrations have an inhibitory effect. Controlled potential electrolysis and rotating ring-disk electrode experiments indicate that ammonium is directly produced from nitrite by [Co(TIM)Br2]+, along with hydroxylamine. Mechanistic investigations implicate a vital role for the phosphate buffer, specifically as a proton shuttle, although high buffer concentrations inhibit catalysis. These results indicate a role for buffer in the design of electrocatalysts for nitrogen oxide conversion.

Interpolation Methods for Molecular Potential Energy Surface Construction.

The concept of a potential energy surface (PES) is one of the most important concepts in modern chemistry. A PES represents the relationship between the chemical system's energy and its geometry (i.e., atom positions) and can provide useful information about the system's chemical properties and reactivity. Construction of accurate PESs with high-level theoretical methodologies, such as density functional theory, is still challenging due to a steep increase in the computational cost with the increase of the system size. Thus, over the past few decades, many different mathematical approaches have been applied to the problem of the cost-efficient PES construction. This article serves as a short overview of interpolative methods for the PES construction, including global polynomial interpolation, trigonometric interpolation, modified Shepard interpolation, interpolative moving least-squares, and the automated PES construction derived from these.

Halogenation affects driving forces, reorganization energies and "rocking" motions in strained [Fe(tpy)2]2+ complexes.

Controlling the energetics of spin crossover (SCO) in Fe(II)-polypyridine complexes is critical for designing new multifunctional materials or tuning the excited-state lifetimes of iron-based photosensitizers. It is well established that the Fe-N "breathing" mode is important for intersystem crossing from the singlet to the quintet state, but this does not preclude other, less obvious, structural distortions from affecting SCO. Previous work has shown that halogenation at the 6 and 6'' positions of tpy (tpy = 2,2';6',2''-terpyridine) in [Fe(tpy)2]2+ dramatically increased the lifetime of the excited MLCT state and also had a large impact on the ground state spin-state energetics. To gain insight into the origins of these effects, we used density functional theory calculations to explore how halogenation impacts spin-state energetics and molecular structure in this system. Based on previous work we focused on the ligand "rocking" motion associated with SCO in [Fe(tpy)2]2+ by constructing one-dimensional potential energy surfaces (PESs) along the tpy rocking angle for various spin states. It was found that halogenation has a clear and predictable impact on ligand rocking and spin-state energetics. The rocking is correlated to numerous other geometrical distortions, all of which likely affect the reorganization energies for spin-state changes. We have quantified trends in reorganization energy and also driving force for various spin-state changes and used them to interpret the experimentally measured excited-state lifetimes.

Reduced-dimensional surface hopping with offline-online computations.

Molecular dynamics simulations often classically evolve the nuclear geometry on adiabatic potential energy surfaces (PESs), punctuated by random hops between energy levels in regions of strong coupling, in an algorithm known as surface hopping. However, the computational expense of integrating the geometry on a full-dimensional PES and computing the required couplings can quickly become prohibitive as the number of atoms increases. In this work, we describe a method for surface hopping that uses only important reaction coordinates, performs all expensive evaluations of the true PESs and couplings only once before simulating dynamics (offline), and then queries the stored values during the surface hopping simulation (online). Our Python codes are freely available on GitHub. Using photodissociation of azomethane as a test case, this method is able to reproduce experimental results that have thus far eluded ab initio surface hopping studies.

Electrocatalytic nitrate reduction with Co-based catalysts: comparison of DIM, TIM and cyclam ligands.

Over the past century, the global concentration of environmental nitrate has increased significantly from human activity, which has resulted in the contamination of drinking water and aquatic hypoxia around the world, so the development of effective nitrate-reducing agents is urgent. This work compares three potential macrocycle-based nitrate reduction electrocatalysts: [Co(DIM)]3+, [Co(cyclam)]3+ and [Co(TIM)]3+. Although all three complexes have similar structures, only [Co(DIM)]3+ has been experimentally determined to be an active electrocatalyst for selective nitrate reduction to produce ammonia in water. While [Co(cyclam)]3+ can reduce aqueous nitrate to ammonia and hydroxylamine at heavy metal electrodes, [Co(TIM)]3+ is inactive for the reduction of nitrate. As an initial step to understanding what structural and electronic properties are important for efficient electrocatalysts for nitrate reduction, density functional theory (DFT) was employed to investigate the electronic structure of the three Co complexes, with the reduction potentials calibrated to experimental results. Moreover, DFT was employed to explore four different reaction mechanisms for the first steps of nitrate reduction. The calculated reaction barriers reveal how a combination of electron transfer in a redox non-innocent complex, substrate binding, and intramolecular hydrogen bonding dictates the activity of Co-based catalysts toward nitrate reduction.

Efficient Approximation of Potential Energy Surfaces with Mixed-Basis Interpolation.

The potential energy surface (PES) describes the energy of a chemical system as a function of its geometry and is a fundamental concept in modern chemistry. A PES provides much useful information about the system, including the structures and energies of various stationary points, such as stable conformers (local minima) and transition states (first-order saddle points) connected by a minimum-energy path. Our group has previously produced surrogate reduced-dimensional PESs using sparse interpolation along chemically significant reaction coordinates, such as bond lengths, bond angles, and torsion angles. These surrogates used a single interpolation basis, either polynomials or trigonometric functions, in every dimension. However, relevant molecular dynamics (MD) simulations often involve some combination of both periodic and nonperiodic coordinates. Using a trigonometric basis on nonperiodic coordinates, such as bond lengths, leads to inaccuracies near the domain boundary. Conversely, polynomial interpolation on the periodic coordinates does not enforce the periodicity of the surrogate PES gradient, leading to nonconservation of total energy even in a microcanonical ensemble. In this work, we present an interpolation method that uses trigonometric interpolation on the periodic reaction coordinates and polynomial interpolation on the nonperiodic coordinates. We apply this method to MD simulations of possible isomerization pathways of azomethane between cis and trans conformers. This method is the only known interpolative method that appropriately conserves total energy in systems with both periodic and nonperiodic reaction coordinates. In addition, compared to all-polynomial interpolation, the mixed basis requires fewer electronic structure calculations to obtain a given level of accuracy, is an order of magnitude faster, and is freely available on GitHub.

Intramolecular Hydrogen Bonding Facilitates Electrocatalytic Reduction of Nitrite in Aqueous Solutions.

This work reports a combined experimental and computational mechanistic investigation into the electrocatalytic reduction of nitrite to ammonia by a cobalt macrocycle in an aqueous solution. In the presence of a nitrite substrate, the Co(III) precatalyst, [Co(DIM)(NO2)2]+ (DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene), is formed in situ. Cyclic voltammetry and density functional theory (DFT) calculations show that this complex is reduced by two electrons, the first of which is coupled with nitrite ligand loss, to provide the active catalyst. Experimental observations suggest that the key N-O bond cleavage step is facilitated by intramolecular proton transfer from an amine group of the macrocycle to a nitro ligand, as supported by modeling several potential reaction pathways with DFT. These results provide insights into how the combination of a redox active ligand and first-row transition metal can facilitate the multiproton/electron process of nitrite reduction.

A flexible, redox-active macrocycle enables the electrocatalytic reduction of nitrate to ammonia by a cobalt complex.

The cobalt macrocycle complex [Co(DIM)Br2]+ (DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene) is an electrocatalyst for the selective reduction of nitrate to ammonia in aqueous solution. The catalyst operates over a wide pH range and with very high faradaic efficiency, albeit with large overpotential. Experimental investigations, supported by electronic structure calculations, reveal that catalysis commences when nitrate binds to the two-electron reduced species CoII(DIM-), where cobalt and the macrocycle are each reduced by a single electron. Several mechanisms for the initial reduction of nitrate to nitrite were explored computationally and found to be feasible at room temperature. The reduced DIM ligand plays an important role in these mechanisms by directly transferring a single electron to the bound nitrate substrate, activating it for further reactions. These studies further reveal that the DIM macrocycle is critical to nitrate reduction, specifically its combination of redox non-innocence, hydrogen-bonding functionality and flexibility in coordination mode.

Dual fistulas of ascending aorta and coronary artery to pulmonary artery.

Coronary artery fistula to pulmonary artery is common. However, to the best of our knowledge, a case of coronary artery fistula to pulmonary artery associated with aortopulmonary fistula remains unreported. We herein report a 64-year-old female with a left anterior descending coronary artery and ascending aorta to pulmonary artery fistulas, and conduct a brief review of the literature.

Arthrobacter subterraneus sp. nov., isolated from deep subsurface water of the South Coast of Korea.

Strain CH7T, a pale yellow-pigmented bacterium and new isolate from deep subsurface water of the South Coast of Korea, was subjected to a polyphasic taxonomic study. CH7T grew between 5 and 37 degrees C, pH 5.3-10.5, and tolerated up to 13% NaCl. A phylogenetic analysis based on 16S rRNA gene sequences showed that strain CH7T was associated with the genus Arthrobacter and phylogenetically closely related to the type strains Arthrobacter tumbae (99.4%) and Arthrobacter parietis (99.1%). However, DNA-DNA hybridization experiments revealed 2.1% and 12% between strain CH7T and Arthrobacter tumbae and Arthrobacter parietis, respectively. Thus, the phenotypic and phylogenetic differences suggested that CH7T should be placed in the genus Arthrobacter as a novel species, for which the name Arthrobacter subterraneus sp. nov. is proposed. In addition, the type strain for the new species is CH7T (=KCTC 9997T=DSM 17585T).

Vibrio litoralis sp. nov., isolated from a Yellow Sea tidal flat in Korea.

Two Gram-negative, facultatively anaerobic bacterial strains, MANO22D(T) and MANO22P, were isolated from a tidal flat area of Dae-Chun, Chung-Nam, Korea. The isolates were rod-shaped and were motile by means of one or more polar flagella. They grew at 1-12 % NaCl, 4-45 degrees C and pH 4.1-8.8 and were oxidase-positive, arginine dihydrolase-negative and sensitive to the vibriostatic agent O/129. The isolates required Na(+) for growth, produced acid, but no gas, from D-glucose under anaerobic conditions and utilized a wide range of compounds as sole carbon and energy sources. A phylogenetic analysis based on 16S rRNA gene sequences revealed that the strains belong to the Gammaproteobacteria and are specifically related to Vibrio species. They were most closely related to Vibrio rumoiensis FERM P-14531(T), with which they were found to share 98.65 % 16S rRNA gene sequence similarity. In the phylogenetic tree, the two novel strains comprised a relatively long subline of descent, sharing a branching point with the outlying species V. rumoiensis, and were found to occupy a phylogenetically distant position on the main Vibrio branch. The levels of DNA-DNA hybridization with respect to V. rumoiensis FERM P-14531(T), which is their most closely related phylogenetically related Vibrio species, were 7.4 % (MANO22D(T)) and 3.9 % (MANO22P). Thus, the two novel isolates appear to represent a novel species within the genus Vibrio, for which the name Vibrio litoralis sp. nov. is proposed. The type strain is MANO22D(T) (=KCTC 12520(T)=DSM 17657(T)).

Sulfitobacter litoralis sp. nov., a marine bacterium isolated from the East Sea, Korea.

A Gram-negative, aerobic, halophilic bacterium, designated strain Iso 3(T), was isolated from the East Sea in Korea. Strain Iso 3(T) was motile by means of polar flagella, occasionally formed rosette-like aggregates and contained 18 : 1omega7c as the dominant cellular fatty acid. Strain Iso 3(T) grew at NaCl concentrations of 1-10 % and temperatures of 4-30 degrees C. The optimal growth temperature was 20 degrees C. Analysis of the 16S rRNA gene sequence revealed that this strain is affiliated with a subcluster of the Alphaproteobacteria. However, strain Iso 3(T) generated metabolic energy by sulfide oxidation. The 16S rRNA gene sequence similarity between strain Iso 3(T) and the type strain of the most closely related species, Sulfitobacter pontiacus, was 97.7 %. DNA-DNA relatedness between strain Iso 3(T) and Sulfitobacter pontiacus DSM 10014(T) was 24.1 %. On the basis of phenotypic properties and phylogenetic distinctiveness, strain Iso 3(T) is classified within a novel Sulfitobacter species, for which the name Sulfitobacter litoralis sp. nov. is proposed, with the type strain Iso 3(T) (=KCTC 12521(T)=DSM 17584(T)).

Pseudoalteromonas marina sp. nov., a marine bacterium isolated from tidal flats of the Yellow Sea, and reclassification of Pseudoalteromonas sagamiensis as Algicola sagamiensis comb. nov.

Two Gram-negative, motile and strictly aerobic marine bacteria were isolated from a tidal flat sediment sample obtained from Dae-Chun, Chung-Nam, Korea. They were preliminarily identified as Pseudoalteromonas-like bacteria, based on 16S rRNA gene sequence analysis showing nearly identical sequences (>99.7 % sequence similarity) and the highest similarity (98.4 %) to the species Pseudoalteromonas undina. Some phenotypic features of the newly isolated strains were similar to those of members of the genus Pseudoalteromonas, but several physiological and chemo-taxonomical properties readily distinguished the new isolates from previously described species. DNA-DNA hybridization with type strains of phylogenetically closely related species demonstrated that the isolates represent a novel Pseudoalteromonas species, for which the name Pseudoalteromonas marina sp. nov. is proposed, with the type strain mano4(T) (=KCTC 12242(T)=DSM 17587(T)). In addition, on the basis of this study and polyphasic data obtained from previous work, it is proposed that the species Pseudoalteromonas sagamiensis should be reclassified as Algicola sagamiensis comb. nov. and that strain B-10-31(T) (=DSM 14643(T)=JCM 11461(T)) be designated the type strain.

Marinobacterium halophilum sp. nov., a marine bacterium isolated from the Yellow Sea.

A moderately halophilic, aerobic, Gram-negative bacterium was isolated from a tidal flat area of Dae-Chun, Chung-Nam, Korea. The strain, designated mano11(T), comprised rod-shaped cells that were motile by means of polar flagella. It grew with 3-12 % NaCl and at 4-37 degrees C and pH 5.3-9.3. The predominant menaquinone present in this strain was Q-8 [corrected] and diaminopimelic acid was not found in the cell-wall peptidoglycan. A phylogenetic analysis based on 16S rRNA gene sequences showed that strain mano11(T) belongs to the genus Marinobacterium. Strain mano11(T) exhibited 92.8-98.3 % 16S rRNA gene sequence similarity when compared with the type strains of three other species of the genus Marinobacterium. DNA-DNA hybridization between strain mano11(T) and Marinobacterium georgiense DSM 11526(T), its closest relative in terms of 16S rRNA gene sequence similarity, was 13 %. On the basis of the phenotypic, genetic and phylogenetic data, strain mano11(T) represents a novel species of the genus Marinobacterium, for which the name Marinobacterium halophilum sp. nov. is proposed. The type strain is mano11(T) (=KCTC 12240(T)=DSM 17586(T)).