Probing the C-H Activation of Linear and Cyclic Ethers at (PNP)Ir

Interaction of the amido/bis(phosphine)-supported (PNP)Ir fragment with a series of linear and cyclic ethers is shown to afford, depending on substrate, products of α,α-dehydrogenation (carbenes), α,β-dehydrogenation (vinyl ethers), or decarbonylation. While carbenes are exclusively obtained from tert-amyl methyl ether, sec-butyl methyl ether (SBME), n-butyl methyl ether (NBME), and tetrahydrofuran (THF), vinyl ethers or their adducts are observed upon reaction with diethyl ether and 1,4-dioxane. Decarbonylation occurs upon interaction of (PNP)Ir with benzyl methyl ether, and a mechanism is proposed for this unusual transformation, which occurs via a series of C−H, C−O, and C−C bond cleavage events. The intermediates characterized for several of these reactions as well as the α,α-dehydrogenation of tert-butyl methyl ether (MTBE) are used to outline a reaction pathway for the generation of PNP-supported iridium(I) carbene complexes, and it is shown that the long-lived, observable intermediates are substrate-dependent and differ for the related cases of MTBE and THF. Taken together, these findings highlight the variety of pathways utilized by the electron-rich, unsaturated (PNP)Ir fragment to stabilize itself by transferring electron density to ethereal substrates through oxidative addition and/or the formation of π-acidic ligands

Prevalence and risk factors for vaginal Candida colonization in women with type 1 and type 2 diabetes

BACKGROUND: Diabetes mellitus increases the rate of vaginal colonization and infection with Candida species METHODS: We surveyed women with diabetes receiving care at either an urban or suburban diabetes clinic to examine the relationship between vaginal Candida colonization, diabetes type and duration, and HbA(1c) level. 101 participants completed the self-administered questionnaire and self-collected a vaginal swab for Candida culture. Candida colonization was similar by age and race. RESULTS: Type 1 diabetics were three times as likely as type 2 diabetics to be colonized with any Candida species (OR = 3.4; 95% CI: 1.03, 11.41; p = 0.04); even after adjusting for abnormal HbA(1c), which had an independent effect (OR = 1.4; 95% CI: 1.04, 1.76; p = 0.02). Recent antibiotic use (OR = 4.5; 95% CI: 1.18, 16.79; p = 0.03), lifetime history of chlamydia (OR = 5.8; 95% CI: 1.09, 30.54; p = 0.04), and performing oral sex during the past 2 weeks (OR = 4.9; 95% CI:0.84, 28.27; p = 0.08) were also associated with Candida carriage after adjusting for diabetic type and abnormal HbA(1c). C. albicans was isolated from the majority of colonized type 1 participants (56%), while C. glabrata was the most common isolate among colonized type 2 participants (54%). CONCLUSIONS: Improving glucose control and possibly modifying sexual behavior may reduce risk of Candida colonization, and potentially symptomatic infection, among women with diabetes

Magnetic Field Dependence of the Level Spacing of a Small Electron Droplet

The temperature dependence of conductance resonances is used to measure the evolution with the magnetic field of the average level spacing $\Delta\epsilon$ of a droplet containing $\sim 30$ electrons created by lateral confinement of a two-dimensional electron gas in GaAs. $\Delta\epsilon$ becomes very small ($< 30\mu$eV) near two critical magnetic fields at which the symmetry of the droplet changes and these decreases of $\Delta\epsilon$ are predicted by Hartree-Fock (HF) for charge excitations. Between the two critical fields, however, the largest measured $\Delta\epsilon= 100\mu$eV is an order of magnitude smaller than predicted by HF but comparable to the Zeeman splitting at this field, which suggests that the spin degrees of freedom are important. PACS: 73.20.Dx, 73.20.MfComment: 11 pages of text in RevTeX, 4 figures in Postscript (files in the form of uuencoded compressed tar file

Choosing an appropriate bacterial typing technique for epidemiologic studies

A wide variety of bacterial typing systems are currently in use that vary greatly with respect to the effort required, cost, reliability and ability to discriminate between bacterial strains. No one technique is optimal for all forms of investigation. We discuss the desired level of discrimination and need for a biologic basis for grouping strains of apparently different types when using bacterial typing techniques for different epidemiologic applications: 1) confirming epidemiologic linkage in outbreak investigations, 2) generating hypotheses about epidemiologic relationships between bacterial strains in the absence of epidemiologic information, and 3) describing the distributions of bacterial types and identifying determinants of those distributions. Inferences made from molecular epidemiologic studies of bacteria depend upon both the typing technique selected and the study design used; thus, choice of typing technique is pivotal for increasing our understanding of the pathogenesis and transmission, and eventual disease prevention

Dietary patterns associated with dental caries in adults in the United States

ObjectivesDental caries experience, which affects 91% of US adults, is a consequence of a carious process influenced by diet. Although individual foods have been implicated, we hypothesized that dietary patterns might be important predictors of caries presence.MethodsWe analysed data from 4467 people ≥18 years old participating in the 2013‐2014 National Health and Nutrition Examination Survey, a nationally representative sample of the US population. Data from 24‐hour dietary recalls were classified into standard food categories and reduced to three dietary patterns using principal components (PCs) analysis. We used regression to model the log‐transformed decayed, missing and filled teeth (DMFT) score and the prevalence of any caries experience by quartiles of PC scores, controlling for potential confounders. Dietary patterns differed by age with respect to dental caries so 18‐30‐year‐olds (n = 1074) and >30‐year‐olds (n = 3393) were analysed separately.ResultsSimilar dietary patterns existed among individuals aged 18‐30 and >30 years, but the prevalence of DMFT score >0 and the median of DMFT was greater in those >30:78.7% (95% CI: 76.1, 81.3) vs 92.6% (95% CI: 91.4, 93.7) and 4 (95% CI: 4, 5) vs 12 DMFT (95% CI: 11, 13), respectively. In those 18‐30, no dietary pattern was associated with greater prevalence or severity of dental caries experience. Among those >30, the prevalence of DMFT>0 was higher by 2% for those in each subsequent quartile of a diet high in sugar‐sweetened beverages and sandwiches (adjusted PR: 1.02, 95% CI: 1.001, 1.03)—thus, the prevalence of dental caries experience was 6% higher among those in the uppermost quartile than in the lowest quartile. For every subsequent quartile in the same pattern, there was a 1.98% higher (95% CI: 0.15, 3.85) DMFT score. However, analysis using the two strongest loading food groups from any of the PCs did not identify any predictors of caries experience.ConclusionsDietary patterns were associated with the prevalence of dental caries experience, with differing findings by age. Although effect sizes were small, the population impact may be substantial. While food groups high in sugar were associated with caries prevalence and severity, associations were more apparent in the context of overall diet. Prospective studies are needed to confirm whether particular dietary patterns are causally related to the development of dental caries.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154279/1/cdoe12509_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154279/2/cdoe12509.pd

Single Wall Nanotubes: Atomic Like Behaviour and Microscopic Approach

Recent experiments about the low temperature behaviour of a Single Wall Carbon Nanotube (SWCNT) showed typical Coulomb Blockade (CB) peaks in the zero bias conductance and allowed us to investigate the energy levels of interacting electrons. Other experiments confirmed the theoretical prediction about the crucial role which the long range nature of the Coulomb interaction plays in the correlated electronic transport through a SWCNT with two intramolecular tunneling barriers. In order to investigate the effects on low dimensional electron systems due to the range of electron electron repulsion, we introduce a model for the interaction which interpolates well between short and long range regimes. Our results could be compared with experimental data obtained in SWCNTs and with those obtained for an ideal vertical Quantum Dot (QD). For a better understanding of some experimental results we also discuss how defects and doping can break some symmetries of the bandstructure of a SWCNT.Comment: 8 pages, 4 figure

Superposition of photon- and phonon- assisted tunneling in coupled quantum dots

We report on electron transport through an artificial molecule formed by two tunnel coupled quantum dots, which are laterally confined in a two-dimensional electron system of an Al$_x$Ga$_{1-x}$As/GaAs heterostructure. Coherent molecular states in the coupled dots are probed by photon-assisted tunneling (PAT). Above 10 GHz, we observe clear PAT as a result of the resonance between the microwave photons and the molecular states. Below 8 GHz, a pronounced superposition of phonon- and photon-assisted tunneling is observed. Coherent superposition of molecular states persists under excitation of acoustic phonons.Comment: 5 pages, 4 figure

Correlations between Ground and Excited State Spectra of a Quantum Dot

We have studied the ground and excited state spectra of a semiconductor quantum dot for successive numbers of electron occupancy using linear and nonlinear magnetoconductance measurements. We present the first observation of direct correlation between the mth excited state of the N electron system and the ground state of the N+m electron system for m up to 4. Results are consistent with a non-spin-degenerate single particle picture of the filling of levels. Electron-electron interaction effects are also observed as a perturbation to this model. Magnetoconductance fluctuations of ground states are shown as anticrossings where wavefunction characteristics are exchanged between adjacent levels.Comment: 8 pages pdf; gzipped ps available at http://www-leland.stanford.edu/group/MarcusLab/grouppubs.htm

4-Ferrocenylphenol

The title compound, [Fe(C5H5)(C11H9O)], is of inter­est as a precursor to the synthesis of cheap ferrocene-based liquid crystals. The –OH substituent only results in weak C—H⋯O weak inter­actions between one of cyclo­penta­dienyl (Cp) ring H atoms and the O atom of a neighbouring mol­ecule with a distance of 3.308 (3) Å between the donor and acceptor atoms. The inter­planar angle between the Cp and benzene rings is 13.0 (4)°. There are also weak O—H⋯π and C—H⋯π inter­actions involving the unsubstituted Cp and the benzene ring, respectively

From the Kondo Regime to the Mixed-Valence Regime in a Single-Electron Transistor

We demonstrate that the conductance through a single-electron transistor at low temperature is in quantitative agreement with predictions of the equilibrium Anderson model. When an unpaired electron is localized within the transistor, the Kondo effect is observed. Tuning the unpaired electron's energy toward the Fermi level in nearby leads produces a cross-over between the Kondo and mixed-valence regimes of the Anderson model.Comment: 3 pages plus one 2 page postscript file of 5 figures. Submitted to PR