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41.
Warshauer-Baker E Bonham VL Jenkins J Stevens N Page Z Odunlami A McBride CM 《Community genetics》2008,11(6):352-358
Greater attention towards genetics as a contributor to group health differences may lead to inappropriate use of race/ethnicity and gender as genetic heuristics and exacerbate health disparities. As part of a web-based survey, 1,035 family physicians (FPs) rated the contribution of genetics and environment to racial/ethnic and gender differences in health outcomes, and the importance of race/ethnicity and gender in their clinical decision-making. FPs attributed racial/ethnic and gender differences in health outcomes equally to environment and genetics. These beliefs were not associated with rated importance of race/ethnicity or gender in clinical decision-making. FPs appreciate the complexity of genetic and environmental influences on health differences by race/ethnicity and gender. 相似文献
42.
Brendan J. Graziano Thais R. Scott Matthew V. Vollmer Michael J. Dorantes Victor G. Young Jr Eckhard Bill Laura Gagliardi Connie C. Lu 《Chemical science》2022,13(22):6525
Odd-electron bonds have unique electronic structures and are often encountered as transiently stable, homonuclear species. In this study, a pair of copper complexes supported by Group 13 metalloligands, M[N((o-C6H4)NCH2PiPr2)3] (M = Al or Ga), featuring two-center/one-electron (2c/1e) σ-bonds were synthesized by one-electron reduction of the corresponding Cu(i) ⇢ M(III) counterparts. The copper bimetallic complexes were investigated by X-ray diffraction, cyclic voltammetry, electron paramagnetic spectroscopy, and density functional theory calculations. The combined experimental and theoretical data corroborate that the unpaired spin is delocalized across Cu, M, and ancillary atoms, and the singly occupied molecular orbital (SOMO) corresponds to a σ-(Cu–M) bond involving the Cu 4pz and M ns/npz atomic orbitals. Collectively, the data suggest the covalent nature of these interactions, which represent the first examples of odd-electron σ-bonds for the heavier Group 13 elements Al and Ga.Hanging on by a thread. Formally zerovalent copper complexes with an Al(iii) or Ga(iii) support were investigated. The combined experimental and theoretical data corroborate the presence of an odd-electron σ-bond between Cu and the Group 13 center.Odd-electron σ-bonds, where the electrons are delocalized between two atoms, can occur as two-center/one-electron (2c/1e) or two-center/three-electron (2c/3e) interactions. Proposed by Pauling in 1931,1 odd-electron σ-bonds have garnered attention because of their fundamental importance to chemical bonding and their relationship to radical species generated during oxidative stress in biological systems.2–14 Examples of compounds exhibiting odd-electron bonding are typically homonuclear (like H2+, He2+, and alkali metal dimers) and transiently stable, limiting them to spectroscopic characterization.1,11,15–18The first solid-state structure of a formally one-electron σ-bond was a tetraphosphabenzene species (Fig. 1a) which was formed by the coupling of two diphosphirenyl radicals.19 Following this discovery, the formation of discrete 2c/1e σ-bonds, where the odd-electron is delocalized between two homonuclear main group centers, was reported for B·B and then extended to P·P.8,17,20 Of note, the first solid-state structure of a B·B compound was reported in only 2014 (Fig. 1b).21 Examples of 2c/1e σ-bonds between the heavier Group 13 congeners are even more lacking because of the greater propensity for their unpaired spins to couple, forming larger more stable clusters.8 To our knowledge, there are only three structurally characterized examples of odd-electron bonds for the heavy Group 13 atoms,22 and these examples are all homonuclear π-radicals (Fig. 1c).23–26Open in a separate windowFig. 1Select examples of structurally characterized molecules (a–d) featuring odd-electron bonds.Heteronuclear odd-electron σ-bonds are also rare. The Cu(TPB) complex, where TPB is a trisphosphinoborane, is the single structural example of a 2c/1e bond between heteroatoms (Fig. 1d).27 The authors described the bonding as Cu·B, where the unpaired electron is heavily polarized toward B. A theoretical study predicted that such a bond would also exist between Cu and Al, but no heavier analogues of Cu(TPB) have been synthesized to date.28 Furthermore, the heavier Group 13 elements by virtue of their lower electronegativity compared to B should facilitate greater covalent interactions with the Cu center.Hence, we sought to target formally zerovalent Cu complexes supported by Al(III) or Ga(III) as an extension of the previously reported isoelectronic nickelate species and Cu(TPB).29 Herein, we describe the synthesis, structure, spectroscopic characterization, and DFT calculations of cationic [CuML]+ complexes (L = [N((o-C6H4)NCH2PiPr2)3]3−; M = Al and Ga) as well as their one-electron reduced metalloradical counterparts that feature discrete 2c/1e bonds. 相似文献
43.
Hong C Bao D Thomas MS Clift JM Vullev VI 《Langmuir : the ACS journal of surfaces and colloids》2008,24(16):8439-8442
We describe a facile and expedient approach for the fabrication of arrays of microelectrodes on smooth substrates. A sequence of print-and-peel procedures allowed for the microfabrication of capacitance microsensors using office equipment and relatively simple wet chemistry. Microfluidic assemblies with reversibly adhered elastomer components allowed for the transfer of patterns of metallic silver, deposited via Tollens' reaction, onto the substrate surfaces. Electroplating of the silver patterns produced an array of micrometer-thick copper electrodes. Capacitance sensors were assembled by placing nonlithographically fabricated flow chambers over the microelectrode arrays. Triangular-waveform current-voltage (I/V) measurements showed a linear correlation between the capacitance of the print-and-peel fabricated devices and the dielectric constant of the samples injected into their flow chambers. 相似文献
44.
Soyoung Kim Connie B. Roth John M. Torkelson 《Journal of polymer science. Part A, Polymer chemistry》2008,46(24):2754-2764
The effect of nanoscale confinement on the glass transition temperature, Tg, of freely standing polystyrene (PS) films was determined using the temperature dependence of a fluorescence intensity ratio associated with pyrene dye labeled to the polymer. The ratio of the intensity of the third fluorescence peak to that of the first fluorescence peak in 1-pyrenylmethyl methacrylate-labeled PS (MApyrene-labeled PS) decreased with decreasing temperature, and the intersection of the linear temperature dependences in the rubbery and glassy states yielded the measurement of Tg. The sensitivity of this method to Tg was also shown in bulk, supported PS and poly(isobutyl methacrylate) films. With free-standing PS films, a strong effect of confinement on Tg was evident at thicknesses less than 80–90 nm. For MApyrene-labeled PS with Mn = 701 kg mol−1, a 41-nm-thick film exhibited a 47 K reduction in Tg relative to bulk PS. A strong molecular weight dependence of the Tg-confinement effect was also observed, with a 65-nm-thick free-standing film exhibiting a reduction in Tg relative to bulk PS of 19 K with Mn = 701 kg mol−1 and 31 K with Mn = 1460 kg mol−1. The data are in reasonable agreement with results of Forrest, Dalnoki-Veress, and Dutcher who performed the seminal studies on Tg-confinement effects in free-standing PS films. The utility of self-referencing fluorescence for novel studies of confinement effects in free-standing films is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2754–2764, 2008 相似文献
45.
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47.
Marlier EE Tereniak SJ Ding K Milliken JE Mulliken JE Lu CC 《Inorganic chemistry》2011,50(19):9290-9299
The diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran (abbreviated as (iPr)DPDBFphos) has been metalated with transition metal dichlorides of zinc, cobalt, and nickel to yield ((iPr)DPDBFphos)MCl(2) complexes. Within these compounds, the diphosphine (iPr)DPDBFphos adapts a wide range of bite angles (115 to 180°) as determined by X-ray crystallography. A three-coordinate planar Ni(I) species was isolated from the reduction of ((iPr)DPDBFphos)NiCl(2) with KC(8). Low-temperature electron paramagnetic resonance (EPR) measurements of ((iPr)DPDBFphos)NiCl allow the determination of g values (2.09, 2.14, 2.37) and hyperfine coupling constants to two (31)P nuclei, A(iso) = 46 × 10(-4) cm(-1), and one (37)Cl/(35)Cl nucleus, A = (12, 0.7, 35) × 10(-4) cm(-1). Density functional theory (DFT) studies reveal the nature of the magnetic orbital to be d(xy), which has σ-antibonding and π(∥)-antibonding interactions with the phosphorus and chloride atoms, respectively. The monovalent nickel complex reacts with substrates containing C-X bonds; and in the case of vinyl chloride, a Ni(II) vinyl species ((iPr)DPDBFphos)Ni(CH═CH(2))Cl is generated along with the Ni(II) dichloride complex. The monovalent Ni(I) chloride is an active catalyst in the Kumada cross-coupling reaction of vinyl chloride and phenyl Grignard reagent. 相似文献
48.
Kenneth V Christensen Henrik Leffers William P Watson Connie Sánchez Pekka Kallunki Jan Egebjerg 《BMC neuroscience》2010,11(1):9
Background
The amygdala-kindled rat is a model for human temporal lobe epilepsy and activity-dependent synaptic plasticity. Hippocampal RNA isolated from amygdala-kindled rats at different kindling stages was analyzed to identify kindling-induced genes. Furthermore, effects of the anti-epileptic drug levetiracetam on kindling-induced gene expression were examined. 相似文献49.
Use of in‐situ atomic force microscopy to monitor the biodegradation of polyhydroxyalkanoates (PHAs)
Connie J. Rossini Justinn F. Arceo Evan R. McCarney Brian H. Augustine Douglas E. Dennis Michael D. Flythe Stephen F. Baron 《Macromolecular Symposia》2001,167(1):139-151
Thin films of a co‐polymer mixture of poly 3‐hydroxybutyrate and poly 3‐hydroxyvalerate P(3HB‐3HV) were spun‐cast onto glass slides resulting in 35 nm thick layers with a spherulitic microstructure. An untyped strain of Streptomyces sp. bacteria was isolated from soil samples, and it's PHA depolymerase was used to degrade the P(3HB‐3HV) thin films. Both ex‐situ and in‐situ atomic force microscopy (AFM) biodegradation studies were performed to determine the kinetics of the biodegradation over the course of three hours at room temperature. Ex‐situ AFM was performed in Tapping Mode and in‐situ AFM was performed in the PHA depolymerase using contact mode AFM in the liquid cell, allowing for the real‐time analysis of P(3HB‐3HV) biodegradation. Biodegradation is observed uniformly throughout the surface, and can be observed within 30 min. of depolymerase exposure. In‐situ AFM analysis yields a linear degradation rate as a function of time, while the ex‐situ study suggests a more complex kinetics. 相似文献
50.
Russell A. Bonham 《Chemical physics letters》1974,27(3):332-337
It is proposed that low energy secondary electrons produced in medium energy electron impact experiments may play an important role in the excitation of triplet states even at low sample gas densities. A model calculation is carried out which shows that the population of the 43S, S3P and 43D triplet states in He from secondary electron excitation can be comparable to the population of these states by direct excitation at an incident electron energy of 1000 eV and sample gas pressures as low as 10?3 torr. The model calculations show that the secondary electron mechanism becomes more important as the incident energy increases and that the produced populations are of a similar magnitude for the 33P and 43D states which in turn are about a factor of 4 larger than the population found for the 43S state. The results indicate that the effect of secondary electron excitation in careful experimental measurements of electron impact total triplet state cross sections may have to be considered when incident electron excitation energies in the range of 1 keV or higher are used. 相似文献