Integration of photoresponsive chromophores that initiate multistep catalysis is essential in dye-sensitized photoelectrosynthesis cells and related devices. We describe here an approach that ...incorporates a chromophore assembly surface-bound to metal oxide electrodes for light absorption with an overlayer of catalysts for driving the half-reactions of water splitting. The assembly is a combination of a core-twisted perylene diimide and a ruthenium polypyridyl complex. By altering the connection sequence of the two subunits in the assembly, in their surface-binding to either TiO2 or NiO, the assembly can be tuned to convert visible light into strongly oxidizing equivalents for activation of an electrodeposited water oxidation catalyst (NiCo2O x ) at the photoanode, or reducing equivalents for activation of an electrodeposited water reduction catalyst (NiMo0.05S x ) at the photocathode. A key element in the design of the photoelectrodes comes from the synergistic roles of the vertical (interlayer) charge transfer and lateral (intralayer) charge hopping in determining overall cell efficiencies for photoelectrocatalysis.
The action of molecular catalysts comprises multiple microscopic kinetic steps whose nature is of central importance in determining catalyst activity and selectivity. Single-molecule microscopy ...enables the direct examination of these steps, including elucidation of molecule-to-molecule variability. Such molecular diversity is particularly important for the behavior of molecular catalysts supported at surfaces. We present the first combined investigation of the initiation dynamics of an operational palladium cross-coupling catalyst at the bulk and single-molecule levels, including under turnover conditions. Base-initiated kinetics reveal highly heterogeneous behavior indicative of diverse catalyst population. Unexpectedly, this distribution becomes more heterogeneous at increasing base concentration. We model this behavior with a two-step saturation mechanism and identify specific microscopic steps where chemical variability must exist in order to yield observed behavior. Critically, we reveal how structural diversity at a surface translates into heterogeneity in catalyst behavior, while demonstrating how single-molecule experiments can contribute to understanding of molecular catalysts.
The air-ground dialog continues Marquard, Paul M; Metzger, Louis
Marine Corps Gazette,
12/1999, Letnik:
83, Številka:
12
Trade Publication Article
An article by Richard D. Camp last June made several critical comments about the performance of Marine aviation in Vietnam. In September, Steve Furimsky, Jr., wrote an extensive rebuttal. Three ...comments on the debate are provided.
The reactivity of the reduced Zr/Co and Ti/Co complexes (THF)Zr(MesNP i Pr2)3CoN2 (1, Mes = 2,4,6-trimethylphenyl) and (THF)Ti(XylNP i Pr2)3CoN2 (7, Xyl = 3,5-dimethylphenyl) toward diaryl ...ketones is explored in an effort to gain mechanistic insight into CO bond cleavage processes. Complex 1 reacts with 4,4′-dimethoxybenzophenone to generate ((p-OMeC6H4)2CO)Zr(MesNP i Pr2)3CoN2 (2), which exists as a mixture of valence tautomers in solution that interconvert via electron transfer from Co–I to the Zr-bound ketone in 2 S to form a Zr-bound ketyl radical in 2 T . The geometry of 2 in the solid state is most consistent with the singlet ketone adduct tautomer 2 S . Upon removal of the Co-bound N2 under vacuum, complex 2 cleanly coverts to the μ-oxo carbene product (η2-MesNP i Pr2)Zr(MesNP i Pr2)2(μ-O)CoC(C6H4 p-OMe)2 (5) at room temperature in solution. A diamagnetic intermediate, tentatively assigned as ketone-bridged species (η2-MesNP i Pr2)Zr(MesNP i Pr2)2Co(μ2,η1η2-OC(p-OMeC6H4)2) (6), is observed spectroscopically during the transformation of 1 to 5. Similar reactions between the Ti/Co analogue 7 and diaryl ketones reveal no evidence for electron-transfer to form triplet ketyl radical species. Complex 7 reacts with 4,4′-dimethoxybenzophenone to afford diamagnetic ((p-OMeC6H4)2CO)Ti(XylNP i Pr2)3CoN2 (8). In contrast, addition of benzophenone to 7 under N2 generates a mixture of (η2-XylNP i Pr2)Ti(XylNP i Pr2)2Co(η2-OCPh2) (9) and (Ph2CO)Ti(XylNP i Pr2)3CoN2 (10) in solution, and C 3-symmetric 10 is found to be favored in the solid state. Complex 9 can be generated exclusively and isolated in the absence of N2. Ti/Co complexes 8–10 are thermally stable and do not undergo CO bond cleavage even at elevated temperature, in stark contrast to their Zr/Co congeners.
In the nervous system, NMDA receptors (NMDARs) participate in neurotransmission and modulate the viability of neurons. In contrast, little is known about the role of NMDARs in pancreatic islets and ...the insulin-secreting beta cells whose functional impairment contributes to diabetes mellitus. Here we found that inhibition of NMDARs in mouse and human islets enhanced their glucose-stimulated insulin secretion (GSIS) and survival of islet cells. Further, NMDAR inhibition prolonged the amount of time that glucose-stimulated beta cells spent in a depolarized state with high cytosolic Ca(2+) concentrations. We also noticed that, in vivo, the NMDAR antagonist dextromethorphan (DXM) enhanced glucose tolerance in mice, and that in vitro dextrorphan, the main metabolite of DXM, amplified the stimulatory effect of exendin-4 on GSIS. In a mouse model of type 2 diabetes mellitus (T2DM), long-term treatment with DXM improved islet insulin content, islet cell mass and blood glucose control. Further, in a small clinical trial we found that individuals with T2DM treated with DXM showed enhanced serum insulin concentrations and glucose tolerance. Our data highlight the possibility that antagonists of NMDARs may provide a useful adjunct treatment for diabetes.
The tris(phosphinoamide)-linked heterobimetallic Co/Zr complex (THF)Zr(MesNP i Pr2)3CoN2 (1) has been investigated as a catalyst for the hydrosilylation of ketones with PhSiH3. Catalytic activity ...superior to monometallic Co or Zr analogues has been observed, demonstrating the importance of cooperative reactivity between Co and Zr. Upon examining stoichiometric reactions, complex 1 was found to be unreactive toward PhSiH3, implying that the mechanism diverges from the typical Chalk–Harrod-type hydrosilylation pathway. In contrast, 1 reacts readily with ketones, and in the case of benzophenone, a radical coupling product (Ph2CO)Zr(MesNP i Pr2)3CoN22 (3) was isolated, implying the intermediacy of a Zr-bound ketyl radical fragment. A radical-based hydrosilylation mechanism is proposed involving hydrogen atom transfer from PhSiH3 to the Zr-bound ketyl-radical.
Three loop cusp anomalous dimension in QCD Grozin, Andrey; Henn, Johannes M; Korchemsky, Gregory P ...
Physical review letters,
02/2015, Letnik:
114, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We present the full analytic result for the three loop angle-dependent cusp anomalous dimension in QCD. With this result, infrared divergences of planar scattering processes with massive particles ...can be predicted to that order. Moreover, we define a closely related quantity in terms of an effective coupling defined by the lightlike cusp anomalous dimension. We find evidence that this quantity is universal for any gauge theory and use this observation to predict the nonplanar n(f)-dependent terms of the four loop cusp anomalous dimension.
We study the chiral Ising, the chiral XY, and the chiral Heisenberg models at four-loop order with the perturbative renormalization group in 4−ε dimensions and compute critical exponents for the ...Gross-Neveu-Yukawa fixed points to order O(ε4). Further, we provide Padé estimates for the correlation length exponent, the boson and fermion anomalous dimension, as well as the leading correction to scaling exponent in 2+1 dimensions. We also confirm the emergence of supersymmetric field theories at four loops for the chiral Ising and the chiral XY models with N=1/4 and N=1/2 fermions, respectively. Furthermore, applications of our results relevant to various quantum transitions in the context of Dirac and Weyl semimetals are discussed, including interaction-induced transitions in graphene and surface states of topological insulators.
To determine the rate of embryonic chromosomal abnormalities, thrombophilias, and uterine anomalies in women over the age of 35 years with recurrent pregnancy loss (RPL).
Retrospective cohort study.
...Academic reproductive endocrinology and infertility clinic.
Women>or=35 years old with >or=3 first trimester miscarriages.
None.
Age, number of prior losses, cytogenetic testing of the products of conception (POC), uterine cavity evaluation, parental karyotype, TSH, and antiphospholipd antibody (APA) and thrombophilia testing. Aneuploidy in the POC in women with RPL was compared with sporadic miscarriages (<or=2 losses) in women>or=35 years.
Among 43 RPL patients, there were 50 miscarriages in which cytogenetic analysis was performed. In the RPL group, the incidence of chromosomal abnormalities in the POC was 78% (39 out of 50) compared with a 70% incidence (98 out of 140) in the sporadic losses. Thrombophilia results in the RPL patients were normal in 38 patients, four patients had APA syndrome, and one had protein C deficiency. Forty out of 43 had normal uterine cavities. Both TSH and parental karyotypes were normal in all of the patients tested. When the evaluation of RPL included karyotype of the POC, only 18% remained without explanation. However, without fetal cytogenetics, 80% of miscarriages would have been unexplained.
In older patients with RPL, fetal chromosomal abnormalities are responsible for the majority of miscarriages. Other causes were present in only 20% of cases.
Complete renormalization of QCD at five loops Luthe, Thomas; Maier, Andreas; Marquard, Peter ...
The journal of high energy physics,
3/2017, Letnik:
2017, Številka:
3
Journal Article
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