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[BArF 4] 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.

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.

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.

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.

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.

Correction: Ligand K-edge XAS, DFT, and TDDFT analysis of pincer linker variations in Rh(i) PNP complexes: reactivity insights from electronic structure.

Correction for 'Ligand K-edge XAS, DFT, and TDDFT analysis of pincer linker variations in Rh(i) PNP complexes: reactivity insights from electronic structure' by Jason M. Keith, Scott R. Daly, et al., Dalton Trans., 2016, 45, 9774-9785.

Desensitization Using Bortezomib and High-dose Immunoglobulin Increases Rate of Deceased Donor Kidney Transplantation.

Combination therapy of intravenous immunoglobulin (IVIG) and rituximab showed a good transplant rate in highly sensitized wait-listed patients for deceased donor kidney transplantation (DDKT), but carried the risk of antibody-mediated rejection. The authors investigated the impact of a new combination therapy of bortezomib, IVIG, and rituximab on transplantation rate.This study was a prospective, open-labeled clinical trial. The desensitization regimen consisted of 2 doses of IVIG (2  g/kg), a single dose of rituximab (375  mg/m), and 4 doses of bortezomib (1.3  mg/m). The transplant rate was analyzed. Anti-Human leukocyte antigen (HLA) DRB antibodies were determined by a Luminex solid-phase bead assay at baseline and after 2, 3, and 6 months in the desensitized patients.There were 19 highly sensitized patients who received desensitization and 17 patients in the control group. Baseline values of class I and II panel reactive antibody (%, peak mean fluorescence intensity) were 83  ±â€Š 16.0 (14952  ±  5820) and 63  ±  36.0 (10321  ±  7421), respectively. Deceased donor kidney transplantation was successfully performed in 8 patients (42.1%) in the desensitization group versus 4 (23.5%) in the control group. Multivariate time-varying covariate Cox regression analysis showed that desensitization increased the probability of DDKT (hazard ratio, 46.895; 95% confidence interval, 3.468-634.132; P = 0.004). Desensitization decreased mean fluorescence intensity values of class I panel reactive antibody by 15.5% (20.8%) at 2 months. In addition, a liberal mismatch strategy in post hoc analysis increased the benefit of desensitization in donor-specific antibody reduction. Desensitization was well tolerated, and acute rejection occurred only in the control group.In conclusion, a desensitization protocol using bortezomib, high-dose IVIG, and rituximab increased the DDKT rate in highly sensitized, wait-listed patients.

Association between Smoking and the Progression of Computed Tomography Findings in Chronic Pancreatitis.

BACKGROUND/AIMS: Smoking and alcohol intake are two wellknown risk factors for chronic pancreatitis. However, there are few studies examining the association between smoking and changes in computed tomography (CT) findings in chronic pancreatitis. The authors evaluated associations between smoking, drinking and the progression of calcification on CT in chronic pancreatitis. METHODS: In this retrospective study, 59 patients with chronic pancreatitis who had undergone initial and follow-up CT between January 2002 and September 2010 were included. Progression of calcification among CT findings was compared according to the amount of alcohol intake and smoking. RESULTS: The median duration of followup was 51.6 months (range, 17.1 to 112.7 months). At initial CT findings, there was pancreatic calcification in 35 patients (59.3%). In the follow-up CT, progression of calcification was observed in 37 patients (62.7%). Progression of calcification was more common in smokers according to the multivariate analysis (odds ratio [OR], 9.987; p=0.006). The amount of smoking was a significant predictor for progression of calcification in the multivariate analysis (OR, 6.051 in less than 1 pack per day smokers; OR, 36.562 in more than 1 pack per day smokers; p=0.008). CONCLUSIONS: Continued smoking accelerates pancreatic calcification, and the amount of smoking is associated with the progression of calcification in chronic pancreatitis.

Kidney donor risk index is a good prognostic tool for graft outcomes in deceased donor kidney transplantation with short, cold ischemic time.

BACKGROUND: We performed a retrospective cohort study to determine the prognostic value of standard criteria donor/expanded criteria donor (SCD/ECD) designation, with regard to one-yr GFR and graft survival rate, in a region with short, cold ischemic time (CIT), and how this designation compares with the kidney donor risk index (KDRI) and zero-time kidney biopsies. METHODS: We reviewed 362 cases of deceased donor kidney transplantation (DDKT). Donor kidneys were classified as SCD or ECD. They were also assessed by the KDRI. Zero-time kidney biopsy was performed in 196 patients, and histologic score was assessed. RESULTS: Median follow-up duration was 46 months. Forty-two cases (11.6%) used ECD kidneys. The mean CIT was only 4.9 ± 2.7 h. Graft survival rates were not significantly different between ECD and SCD groups. The KDRI showed the best correlation with one-yr estimations of glomerular filtration rate (eGFR) (R(2) = 0.230, p < 0.001), and higher KDRI was associated with a higher risk of graft failure (hazard ratio 2.63, 95% confidence interval 1.01-6.87). However, higher histologic score was not associated with a higher risk of graft failure. CONCLUSION: KDRI has greater predictive value for short-term outcomes in DDKT with short CIT than the SCD/ECD designation or pathology.

Impact of combined acute rejection on BK virus-associated nephropathy in kidney transplantation.

BK virus-associated nephropathy (BKVAN) is one of the major causes of allograft dysfunction in kidney transplant (KT) patients. We compared BKVAN combined with acute rejection (BKVAN/AR) with BKVAN alone in KT patients. We retrospectively analyzed biopsy-proven BKVAN in KT patients from 2000 to 2011 at Seoul National University Hospital. Among 414 biopsies from 951 patients, biopsy-proven BKVAN was found in 14 patients. Nine patients had BKVAN alone, while 5 patients had both BKVAN and acute cellular rejection. BKVAN in the BKVAN alone group was detected later than in BKVAN/AR group (21.77 vs 6.39 months after transplantation, P=0.03). Serum creatinine at diagnosis was similar (2.09 vs 2.00 mg/dL). Histological grade was more advanced in the BKVAN/AR group (P=0.034). Serum load of BKV, dose of immunosuppressants, and tacrolimus level showed a higher tendency in the BKVAN alone group; however it was not statistically significant. After anti-rejection therapy, immunosuppression was reduced in the BKVAN/AR group. Renal functional deterioration over 1 yr after BKVAN diagnosis was similar between the two groups (P=0.665). These findings suggest that the prognosis of BKVAN/AR after anti-rejection therapy followed by anti-BKV therapy might be similar to that of BKVAN alone after anti-BKV therapy.

Outcomes of combination therapy for chronic antibody-mediated rejection in renal transplantation.

AIM: Chronic antibody-mediated rejection (CAMR) in renal transplant patients has poor allograft outcomes. However, treatment strategy has not been established yet. Herein, we present short-term outcomes of combination therapy for CAMR. METHODS: We identified nine patients with CAMR or suspicious CAMR who were treated with antihumoral therapy from 2010 to 2011 and analyzed their medical records retrospectively. RESULTS: Five patients had CAMR, and four patients had suspicious CAMR. Severe transplant glomerulopathy (TG) was observed in seven patients. The estimated glomerular filtration rate (eGFR) was decreased in all patients before treatment. We used three different treatment regimens: (i) high-dose intravenous immunoglobulin (IVIG) and rituximab; (ii) high-dose IVIG, rituximab, and bortezomib; and (iii) plasmapheresis with low-dose IVIG, rituximab and bortezomib. After treatment with one of these three regimens, graft function improved or stabilized in six patients, whereas three patients showed further deterioration of eGFR. The third regimen suppressed deterioration of renal function in all patients. Most patients showed no progression of proteinuria. Infectious complications due to Pneumocystis jirovecii pneumonia and herpes zoster occurred in two patients. CONCLUSION: Combination therapy for CAMR might be effective, even in patients with relatively late-stage CAMR.

Impact of parathyroidectomy on allograft outcomes in kidney transplantation.

We performed retrospective, multi-center study of the impacts of parathyroidectomy (PTX) after or before kidney transplantation on allograft outcomes. A total of 63 patients who underwent PTX after kidney transplantation were identified. Deterioration in eGFR by more than 25% at 1 month after PTX occurred in 20% of the patients. The baseline eGFR was significantly lower in impairment group than nonimpairment group [adjusted odds ratio (OR) 0.87, 95% confidence interval (CI) 0.77-0.99, P = 0.033]. Low iPTH concentration after PTX was also a significant risk factor for the renal impairment (OR 0.96, CI 0.94-0.99, P = 0.009). A total of 37 patients who underwent PTX before transplantation were identified. Thirty-six percent of the patients had persistent hyperparathyroidism by 1 year after transplantation. A high iPTH level before PTX was a significant risk factor for persistent post-transplant hyperparathyroidism (adjusted OR 1.002, CI 1.000-1.005, P = 0.039). Finally, eGFR values during the first 5 years after transplantation were significantly lower in the patients who underwent PTX at less than 1 year after transplantation, than the pretransplant PTX patients (P = 0.032). As PTX after kidney transplantation has a risk of deterioration of allograft function, pretransplant PTX should be considered for patients with severe hyperparathyroidism, who could undergo post-transplant PTX.

Clinical outcomes of patients with hepatorenal syndrome after living donor liver transplantation.

Liver transplantation (LT) is the treatment of choice for hepatorenal syndrome (HRS). However, the clinical benefits of living donor liver transplantation (LDLT) are not yet well established. We, therefore, investigated the outcomes of patients with HRS who underwent LDLT and patients with HRS who received transplants from deceased donors. This study focused on 71 patients with HRS out of a total of 726 consecutive adult Korean patients who underwent LT at a single Asian center. We compared 48 patients who underwent LDLT with 23 patients who underwent deceased donor liver transplantation (DDLT). Patients with HRS showed poorer survival than patients without HRS (P = 0.01). Poorer survival was associated with higher in-hospital mortality for patients with HRS (18.3% versus 5.2%, P < 0.001). In comparison with DDLT, LDLT was associated with younger donors and shorter ischemic times. The survival rate with LDLT was significantly higher than the survival rate with DDLT (P = 0.02). Among patients with high Model for End-Stage Liver Disease scores (≥30) or type 1 HRS, the survival rates for the LDLT group were not inferior to those for the DDLT group. LDLT significantly improved recipient survival after adjustments for several risk factors (hazard ratio = 0.20, 95% confidence interval = 0.05-0.85, P = 0.03). Kidney function was significantly improved after LT, and there was no difference between LDLT and DDLT. No patients in the HRS cohort required maintenance renal replacement therapy. In conclusion, LDLT may be a beneficial option for patients with HRS.

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.

A rare case with primary undifferentiated carcinoma of pericardium.

A primary pericardial tumor is very rare. A 77-year-old woman was admitted to our hospital with chief complaint of exertional dyspnea due to large amount of pericardial effusion. She was finally diagnosed as pericardial undifferentiated carcinoma without definite histopathologial, immunochemistry feature. Despite palliative radiation therapy, the patient died of multiple organ failure. The prognosis of primary pericardial undifferentiated carcinoma is known to be very poor, especially in old people.

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).