Temperature-Dependent Hole Transfer from Photoexcited Quantum Dots to Molecular Species: Evidence for Trap-Mediated Transfer.

The effect of temperature on the rate of hole transfer from photoexcited quantum dots (QDs) is investigated by measuring the driving force dependence of the charge transfer rate for different sized QDs across a range of temperatures from 78 to 300 K. Spherical CdSe/CdS core/shell QDs were used with a series of ferrocene-derived molecular hole acceptors with an 800 meV range in electrochemical potential. Time-resolved photoluminescence measurements and photoluminescence quantum yield measurements in an integrating sphere were both performed from 78 to 300 K to obtain temperature-dependent rates for a series of driving forces as dictated by the nature of the molecular acceptor. For both QD sizes studied and all ligands, the Arrhenius plot of hole transfer exhibited an activated (linear) regime at higher temperatures and a temperature-independent regime at low temperatures. The extracted activation energies in the high-temperature regime were consistent across all ligands for a given QD size. This observation is not consistent with direct charge transfer from the QD valence band to the ferrocene acceptor. Instead, a model in which charge transfer is mediated by a shallow and reversible trap more accurately fits the experimental results. Implications for this observed trap-mediated transfer are discussed including as a strategy to more efficiently extract charge from QDs.

Gangrenous digital infarcts in a severe case of cutaneous polyarteritis nodosa.

Cutaneous polyarteritis nodosa (CPAN) is a rare diagnosis which is distinct from polyarteritis nodosa (PAN). PAN is a medium-vessel vasculitis which can affect multiple organs and classically produces microaneurysms in the vasculature. CPAN is limited to the skin mainly affecting small vessels. There is an absence of microaneurysms in CPAN and it does not affect internal organs. However, the histopathological findings on the skin are similar to PAN. CPAN rarely progresses to PAN but relapses more often. We will illustrate a challenging case of a patient with CPAN who developed gangrenous infarcts despite initial immunosuppressive treatment with high-dose steroids and azathioprine. His treatment had to be escalated to intravenous cyclophosphamide which induced disease remission.

Hundreds-fold Sensitivity Enhancement of Photothermal Microscopy in Near-Critical Xenon.

Photothermal absorption microscopy of single Au nanoparticles was conducted at temperatures and pressures near the critical point of Xenon (Tc = 16.583 °C, Pc = 5.842 MPa). The divergence of the thermal expansion coefficient at the critical point makes the refractive index highly sensitive to changes in temperature, which directly translates to a large enhancement of the photothermal signal. We find that measurements taken near the critical point of Xe give a signal enhancement factor of up to 440 ± 130 over those taken in glycerol. The highest sensitivity recorded here corresponds to power dissipation of 64 pW, achieving a signal-to-noise ratio of 9.4 for 5 nm Au nanoparticles with an integration time of 50 ms, making this the most sensitive of any absorption microscopy technique reported to date. Enhancing the sensitivity of absorption microscopy lowers the operating heating power, allowing the technique to be more compatible with absorbers with absorption coefficient and photochemical stability lower than that of Au.

Hole Transfer from Photoexcited Quantum Dots: The Relationship between Driving Force and Rate.

We have investigated the relationship between driving force and rate for interfacial hole transfer from quantum dots (QDs). This relationship is experimentally explored by using six distinct molecular hole acceptors with an 800 meV range in driving force. Specifically, we have investigated ferrocene derivatives with alkyl thiol moieties that strongly bind to the surface of cadmium chalcogenide QDs. The redox potentials of these ligands are controlled by functionalization of the cyclopentadiene rings on ferrocene with electron withdrawing and donating substituents, thus providing an avenue for tuning the driving force for hole transfer while holding all other system parameters constant. The relative hole transfer rate constant from photoexcited CdSe/CdS core/shell QDs to tethered ferrocene derivatives is determined by measuring the photoluminescence quantum yield of these QD-molecular conjugates at varying ferrocene coverage, as determined via quantitative NMR. The resulting relationship between rate and energetic driving force for hole transfer is not well modeled by the standard two-state Marcus model, since no inverted region is observed. Alternative mechanisms for charge transfer are posited, including an Auger-assisted mechanism that provides a successful fit to the results. The observed relationship can be used to design QD-molecular systems that maximize interfacial charge transfer rates while minimizing energetic losses associated with the driving force.

Atomically thin two-dimensional organic-inorganic hybrid perovskites.

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.

Efficiency of hole transfer from photoexcited quantum dots to covalently linked molecular species.

Hole transfer from high photoluminescence quantum yield (PLQY) CdSe-core CdS-shell semiconductor nanocrystal quantum dots (QDs) to covalently linked molecular hole acceptors is investigated. (1)H NMR is used to independently calibrate the average number of hole acceptor molecules per QD, N, allowing us to measure PLQY as a function of N, and to extract the hole transfer rate constant per acceptor, kht. This value allows for reliable comparisons between nine different donor-acceptor systems with variant shell thicknesses and acceptor ligands, with kht spanning over 4 orders of magnitude, from single acceptor time constants as fast as 16 ns to as slow as 0.13 ms. The PLQY variation with acceptor coverage for all kht follows a universal equation, and the shape of this curve depends critically on the ratio of the total hole transfer rate to the sum of the native recombination rates in the QD. The dependence of kht on the CdS thickness and the chain length of the acceptor is investigated, with damping coefficients ß measured to be (0.24 ± 0.025) Å(-1) and (0.85 ± 0.1) Å(-1) for CdS and the alkyl chain, respectively. We observe that QDs with high intrinsic PLQYs (>79%) can donate holes to surface-bound molecular acceptors with efficiencies up to 99% and total hole transfer time constants as fast as 170 ps. We demonstrate the merits of a system where ill-defined nonradiative channels are suppressed and well-defined nonradiative channels are engineered and quantified. These results show the potential of QD systems to drive desirable oxidative chemistry without undergoing oxidative photodegradation.

Heck coupling of olefins to mixed methyl/thienyl monolayers on Si(111) surfaces.

The Heck reaction has been used to couple olefins to a Si(111) surface that was functionalized with a mixed monolayer comprised of methyl and thienyl groups. The coupling method maintained a conjugated linkage between the surface and the olefinic surface functionality, to allow for facile charge transfer from the silicon surface. While a Si(111) surface terminated only with thienyl groups displayed a surface recombination velocity, S, of 670 ± 190 cm s(-1), the mixed CH3/SC4H3-Si(111) surfaces with a coverage of θSC4H3 = 0.15 ± 0.02 displayed a substantially lower value of S = 27 ± 9 cm s(-1). Accordingly, CH3/SC4H3-Si(111) surfaces were brominated with N-bromosuccinimide, to produce mixed CH3/SC4H2Br-Si(111) surfaces with coverages of θBr-Si < 0.05. The resulting aryl halide surfaces were activated using [Pd(PPh3)4] as a catalyst. After activation, Pd(II) was selectively coordinated by oxidative addition to the surface-bound aryl halide. The olefinic substrates 4-fluorostyrene, vinylferrocene, and protoporphyrin IX dimethyl ester were then coupled (in dimethylformamide at 100 °C) to the Pd-containing functionalized Si surfaces. The porphyrin-modified surface was then metalated with Co, Cu, or Zn. The vinylferrocene-modified Si(111) surface showed a linear dependence of the peak current on scan rate in cyclic voltammetry, indicating that facile electron transfer had been maintained and providing evidence of a robust linkage between the Si surface and the tethered ferrocene. The final Heck-coupled surface exhibited S = 70 cm s(-1), indicating that high-quality surfaces could be produced by this multistep synthetic approach for tethering small molecules to silicon photoelectrodes.

Neutropenia in patients receiving anti-tumor necrosis factor therapy.

OBJECTIVE: To examine the rates of and risk factors for neutropenia together with the dynamics of neutrophil and other white cell subset counts in a cohort of patients treated with a tumor necrosis factor (TNF) inhibitor for inflammatory arthritis. METHODS: We performed a retrospective cohort study examining the association between baseline demographics, clinical features, medications used, and development of neutropenia, and behavior of neutrophil and other white cell subset counts during TNF inhibitor therapy. RESULTS: In 367 patients (298 [81.2%] with rheumatoid arthritis, 38 [10.4%] with ankylosing spondylitis, and 31 [8.4%] with psoriatic arthritis), 69 (18.8%) had at least one episode of neutropenia (<2.0 x 10(9)/liter) during TNF inhibitor therapy, and of these, 6% developed serious infections secondary to neutropenia. There was no significant difference in disease, demographic, or drug variables between patients with and without neutropenia. However, patients with neutropenia had significantly lower baseline neutrophil counts (4.2 x 10(9)/liter; 95% confidence interval [95% CI] 3.8, 4.6 versus 6.2 x 10(9)/liter; 95% CI 6.0, 6.5), and a previous history of neutropenia while receiving disease-modifying antirheumatic drugs increased the risk while receiving TNF inhibitors (hazard ratio 2.97; 95% CI 1.69, 5.25). A significant drop in mean neutrophil count (1.12 x 10(9)/liter; 95% CI 0.92, 1.32) was observed after 2 weeks of TNF inhibitor therapy. Other white cell subsets tended to significantly increase. CONCLUSION: TNF inhibitor therapy is associated with a significant reduction in peripheral blood neutrophil count, leading to 19% of patients becoming neutropenic. Risk of neutropenia is significantly higher in patients with a low baseline neutrophil count or previous history of neutropenia. We suggest that patients receiving TNF inhibitor therapy would benefit from regular complete blood cell count monitoring.

Trends in underinsurance and the affordability of employer coverage, 2004-2007.

Based on simulated bill paying, this paper examines trends in comprehensiveness of coverage, out-of-pocket spending for medical services, underinsurance, and the affordability of employer-based insurance from 2004 to 2007. Data are from MarketScan medical claims and an annual survey of employer health benefits. Health plans covered slightly fewer expenses in 2007 than in 2004, but out-of-pocket spending grew more than one-third because of growth in overall health spending. For people at 200 percent of poverty, the percentage spending more than 10 percent of their income out of pocket on premiums plus services increased from 13 percent to 18 percent.

Ambulatory care visits for treating adverse drug effects in the United States, 1995-2001.

BACKGROUND: Adverse d[rug events (ADEs) are a well-recognized patient safety 4concern, but their magnitude is unknown. Ambulatory viisits for treating adverse drug effects (VADEs) as recordeed in national surveys offer an alternative way to estimatte the national prevalence of ADEs because each VA]DE indicates that an ADE occurred and was seriousenough to require care. METHODS: A nationallyrepresentative sample of visits to physician offices, hospital outpatient departments, and emergency departments was analyzed. VADEs were identified as tthe first-listed cause of injury. RESULTS: In 2001, there Awere 4.3 million VADEs in the United States, averaging 15 visits per 1,000 population. VADE rates at physicianoffices, hospital outpatient departments, and hospittal emergency departments were at 3.7, 3.4, and 7.3 lper 1,000 visits, respectively. There was an upward tr'end in the total number of VADEs from 1995 to 2001 ((p < .05), but the increases in VADEs per 1000 visits an.d per 1,000 population were not statistically significant. VADEs were lower in children younger than 15 and higher in the elderly aged 65-74 than in adults aged 225-44 (p < .01) and were more frequent in females than irn males (p < .05). DISCUSSION: Although methodologically conservative, the study suggests that ADEs are a significant threat to patient safety in the United States.