Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt-Cu Nanoparticles

The effects of particle composition on heterogeneous catalysis were studied using dendrimer-encapsulated nanoparticles (DENs) as precursors to supported Pt-Cu catalysts. Bimetallic Pt-Cu DENs with varying Pt/Cu ratios were prepared in an anaerobic aqueous solution and deposited onto a high-purity commercial alumina support. The dendrimer template was then thermally removed to yield supported nanoparticle catalysts, which were studied with toluene hydrogenation and CO oxidation catalysis as well as infrared spectroscopy of adsorbed CO. Incorporating Cu into Pt nanoparticles had opposite effects on the two test reactions. Cu acted as a mild promoter for CO oxidation catalysis, and the promoting effect was independent of the amount of Cu present. Conversely, Cu acted as a strong poison for toluene hydrogenation catalysis, and the normalized rate tracked inversely with Cu content. Infrared spectroscopy of the supported nanoparticles indicated that electronic effects (electron donation from Cu to Pt) were minimal for these materials. Consequently, the catalysis results are interpreted in terms of potential structural differences as a function of Cu incorporation and reaction conditions

Superior Mesenteric Vein Thrombosis Mimicking Acute Appendicitis

Abdominal pain is one of the most common presenting complaints to the emergency department. Mesenteric venous thrombosis represents an important cause to consider in patients with acute abdominal pain. The diagnosis is often delayed, and cases traditionally have been identified either at laparotomy or at autopsy. In this case, we describe a 21-year-old female with acute onset of right lower quadrant pain attributable to a hyperhomocysteinemia related non-occlusive superior mesenteric vein thrombosis. This case highlights how the use of computed tomography in select cases can lead to earlier recognition of this condition and increasingly allow for non-surgical treatment

Preparation and Characterization of 3 nm Magnetic NiAu Nanoparticles

Using PAMAM dendrimers as nanoparticle templates, a synthetic route to prepare 3 nm magnetic NiAu nanoparticles was developed. Aqueous solutions of hydroxyl-terminated generation 5 PAMAM dendrimers in 25 mM NaClO4 were shown to bind aqueous NiII. Coreduction of NiII and AuIII salts yielded bimetallic dendrimer stabilized nanoparticles, which were extracted into toluene with decanethiol. Characterization of the resulting monolayer protected clusters (MPCs) with transmission electron microscopy and UV-visible, atomic absorption, and X-ray photoelectron spectroscopies suggested that the MPCs had substantial surface enrichment in Au. Superconducting quantum interference device (SQUID) measurements at 5 K show the bimetallic MPCs to have low coercivity and saturation magnetization relative to bulk Ni. Solution nuclear magnetic resonance (NMR) studies using the Evans method showed the bimetallic nanoparticles retain magnetic properties at ambient temperatures

The pinprick approach: Whitehall’s top-secret anti-communist committee and the evolution of British covert action strategy

This article examines Great Britain’s approach to covert action during the formative years of British Cold War intelligence operations, 1950–1951. Rather than shy away from such activity in the wake of the failure in Albania in the late 1940s, the British increased the number of operations they pursued. This was the start of a coherent strategy regarding covert activity that can be conceptualized as the “pinprick” approach. The strategy was overseen by a highly secretive Whitehall body, the Official Committee on Communism, which in effect became the government’s covert action committee. This article uses the commission’s recently declassified papers for the first time to assess the merits of this approach

Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt-Cu Nanoparticles

The effects of particle composition on heterogeneous catalysis were studied using dendrimer-encapsulated nanoparticles (DENs) as precursors to supported Pt-Cu catalysts. Bimetallic Pt-Cu DENs with varying Pt/Cu ratios were prepared in an anaerobic aqueous solution and deposited onto a high-purity commercial alumina support. The dendrimer template was then thermally removed to yield supported nanoparticle catalysts, which were studied with toluene hydrogenation and CO oxidation catalysis as well as infrared spectroscopy of adsorbed CO. Incorporating Cu into Pt nanoparticles had opposite effects on the two test reactions. Cu acted as a mild promoter for CO oxidation catalysis, and the promoting effect was independent of the amount of Cu present. Conversely, Cu acted as a strong poison for toluene hydrogenation catalysis, and the normalized rate tracked inversely with Cu content. Infrared spectroscopy of the supported nanoparticles indicated that electronic effects (electron donation from Cu to Pt) were minimal for these materials. Consequently, the catalysis results are interpreted in terms of potential structural differences as a function of Cu incorporation and reaction conditions. Introduction Highly dispersed supported metal nanoparticle catalysts are an important class of industrial materials, as one-third of material U. S. gross national product involves a catalytic process somewhere in the production chain. 1 State of the art heterogeneous catalysts often contain dopant metals, which are incorporated to promote a desired reaction, prevent undesirable side reactions, or enhance catalyst longevity. Recent advances in computational methods are beginning to shed light onto the fundamental properties of bimetallic catalyst systems, and predictive models are beginning to emerge. To address these fundamental issues, preparation methods for new model catalysts and appropriate control materials are needed. Inorganic and organometallic cluster compounds have been used to successfully prepare novel bimetallic catalysts, 5 particularly for metal combinations that are thermodynamically unstable in the bulk. Background Polyamidoamine (PAMAM) dendrimer-encapsulated nanoparticles (DENs) are attractive potential precursors for model heterogeneous catalysts. PAMAM dendrimers are versatile synthetic hosts, as they have been used to template a variety of metal and semiconductor nanoparticles on the order of 1-3 nm. In this work, we extend this general preparative route for heterogeneous catalysts to the Pt-Cu system (Scheme 1) and report the first study varying heterogeneous catalyst composition using DENs as catalyst precursors. Coincident with these goals is the desire to begin learning how to tune nanoparticle properties and reactivity through the controlled addition of dopant metals. Additionally, we seek to begin developing methods of rationally and systematically testing theoretical models for bimetallic catalyst systems. The Pt-Cu system is a good choice for initial investigations into composition effects because the two metals are miscible through the entire composition range. 34 Additionally, the system has been well studied and characterized, and there is current interest in its reactivity for dehydrodehalogenation, 35,36 dehydrogenation, Metal Uptake by G5-OH Dendrimers. UV-vis spectra during dendrimer-metal complexation were collected using an Ocean Optics, Inc. high-resolution fiber optic spectrometer (HR2000CG UV-NIR). For Pt 2+ uptake by G5-OH PAMAM dendrimer, 10 mL of 0.01 mM dendrimer solution was mixed in a round-bottom flask with sufficient 5 mM K 2 PtCl 4 to prepare the following Pt/dendrimer ratios: 30:1, 23:1, and 15:1. A portion of the solution was transferred to a cuvette and analyzed at various time intervals using 0.01 mM G5-OH PAMAM dendrimer solution as a reference. After 4 days the pH was increased to 7. For Cu uptake by G5-OH, 10 mL of 0.01 mM dendrimer solution was mixed in a round-bottom flask with sufficient 5 mM Cu(NO 3 ) 2 to result in the following Cu/dendrimer ratios: 30:1, 23:1, and 15:1. An aliquot of the solution was immediately transferred to a cuvette for UV-vis spectroscopic analysis. A spectrum was obtained every 3 min for 30 min, and the pH was increased to 7. For Cu uptake by the Pt-dendrimer complex, 10 mL of 0.01 mM dendrimer solution was mixed in a round-bottom flask with sufficient 5 mM K 2 PtCl 4 to result in the following Pt/dendrimer ratios: 30:1, 23:1, and 15:1. The solutions were stirred for 2 days, and the Cu uptake procedure was followed using sufficient 5 mM Cu(NO 3 ) 2 to result in a metal/dendrimer ratio of 45:1 for all solutions. Preparation of Supported Nanoparticles. The DENs were prepared based on techniques detailed in the literature. NaBH 4 solution (0.045 M) was degassed, and 1 mL was added to the flask as N 2 was continually bubbled through the SCHEME 1 Dendrimer-Templated Pt-Cu Catalysts J. Phys. Chem. B, Vol. 110, No. 17, 2006 8607 solution. The solution turned a champagne color as the metals were reduced after stirring for 20 min. The pH of the solution was then adjusted to 8.5 with NaOH and HNO 3 . The alumina support was prepared by degassing 700 mg of 60-80 mesh alumina in a Schlenk flask for 1 h. The DEN solution was then added to the degassed support via cannula, and the mixture was stirred overnight under N 2 . The solid gray catalyst was isolated from a colorless solution by vacuum filtration over a medium grain frit, washed with 95% ethanol, and dried at 80°C in a vacuum oven overnight. The supported DENs were activated by exposing the dried catalyst to flowing O 2 for 16 h at 300°C , as described previously. 31 Pt and Cu Analysis with Atomic Absorption Spectroscopy. Pt and Cu loadings were determined with a Varian SpectrAA 220FS atomic absorption spectrometer using an acetylene/air flame, as described previously. 32 Briefly, the sample was treated with freshly prepared aqua regia. The pH of the resulting solution was adjusted to 6.0-7.0 with ammonium hydroxide, condensed, and transferred to a 10 mL volumetric flask containing sufficient La(NO 3 ) 3 to yield a final solution of 1% La. Atomic absorption (AA) standards were prepared from Aldrich AA standard solutions and Nanopure water. FT-IR Spectroscopy. Spectra were collected using a Thermo Nicolet Nexus 470 spectrometer equipped with a deuterated triglyceride sulfate (DTGS) detector using 2 cm -1 resolution. A water-cooled stainless steel IR flow cell with NaCl windows was used to hold the pressed catalyst wafer (18-20 mg). The optical bench and beam path (outside the flow cell) were continuously purged with N 2 . A heating element wrapped around the cell with a thermocouple placed in close proximity to the catalyst sample allowed for in situ heating of samples and collection spectra at different temperatures. All spectra were collected with gases flowing at 60 mL/min; the gas composition was manipulated using the external manifold. Previously oxidized catalyst samples underwent in situ reduction (20% H 2 balance He at 300°C for 3 h) followed by flushing with He for 1 h at 300°C. The samples were then cooled under He flow, and a background spectrum was collected at room temperature. A 5% CO/He mixture was then flowed over the sample for 15 min, followed by pure He. IR spectra of CO adsorbed on the surface were collected once the gas-phase CO had been removed from the cell. CO desorption was accomplished by heating the sample under He flow. CO Oxidation Catalysis. The feed and reactor effluent composition was monitored with an SRI 8610C gas chromatograph with a thermal conductivity detector. Toluene Hydrogenation Catalysis. The oxidized catalyst was diluted 20:1 by mass with R-Al 2 O 3 . Approximately 300 mg of the diluted catalyst was loaded into a glass U-tube and reduced in flowing H 2 . The temperature was ramped 5°C/min to 200°C and soaked for 1 h. The temperature was then ramped 5°C/min to 300°C and held at that temperature for an additional 1.5 h. The reactor was then cooled to 60°C under flowing H 2 . A 3.2% toluene in H 2 feed was prepared using a two-stage bubbler. The first stage was held at approximately 40°C, and the second stage was maintained at 23°C. . Peak areas were standardized against external calibration solutions of toluene in hexanes and methylcyclohexane in toluene. by monitoring conversion as a function of flow rate. Flow rates were measured with a bubble flow meter immediately prior to each injection. Plots of conversion versus inverse space velocity were linear and had y-intercepts of 0.02% or lower. Results and Discussion Nanoparticle and Catalyst Preparation. Because PtCl 4 2-uptake is slow (1-2 days) relative to Cu 2+ (seconds), we used sequential binding of PtCl 4 2-followed by Cu 2+ to load generation 5 PAMAM dendrimers (G5-OH) with metal precursors (Scheme 1). Most previous studies with these metaldendrimer systems used G4-OH dendrimers, so the use of G5-OH dendrimers in the present study may have moderate effects on the kinetics of metal uptake. Additionally, metal-dendrimer interactions with one precursor may affect the binding of the second when preparing bimetallic nanoparticles. Accordingly, the individual metal binding steps in Scheme 1 were monitored with UV-vis spectroscopy. PtCl 4 2-uptake by G5-OH, monitored by following the disappearance of the PtCl charge transfer band at 380 nm, was complete in approximately 24 h and did not change after adjusting the solution pH to 7 (spectra in the Supporting Information). Changes in the 380 nm band were concurrent with changes in a dendrimerbased UV band at 320 nm indicating uptake into the dendrimer interior. 8608 J. Phys. Chem. B, Vol. 110, No. 17, 2006 Hoover et al. The consistent relative excess of Cu in the final materials also indicates that complexation of Pt(II) species to the dendrimer interior may not be complete in 48 h or that Cu 2+ may displace some of the Pt(II) species within the dendrimer. Our study is consistent with studies from other labs in that UVvis spectra of mixtures of PtCl 4 2-and PAMAM dendrimers cease to change after approximately 2 days. Infrared Spectroscopy of Adsorbed CO. Infrared spectra of CO adsorbed on the activated catalysts, shown in Evaluations of structural and electronic effects and their potential impact on catalytic activity are of fundamental interest and importance. CO adsorption studies are an important tool in evaluating these effects, as both can impact observed CO stretching frequencies. The absence of Cu-CO stretching frequencies provides important indirect information regarding the state of Cu in the catalysts. CO is relatively unstable and easily removed from fully reduced Cu surfaces (i.e., during the He flush required to remove gas-phase CO) yet is stable at ambient temperatures when adsorbed on cationic Cu species. The shifts in Pt-CO stretching frequencies are attributable to a combination of electronic and dipole-dipole coupling effects. Electronic effects arise from a net (partial) electron donation from Cu to the more electronegative Pt. This enhances population of Pt d-bands (relative to a pure Pt material), increasing CO back-bonding and resulting in a lower CO stretching frequency. Dipole-dipole coupling, which is thoughspace interaction between adsorbed dipoles vibrating at the same frequency (Pt-CO adsorbates), also plays an important role in CO stretching frequencies on supported catalysts. Increased dipole coupling, which occurs when vibrating dipoles are close to one another, causes a blue shift in the observed CO stretching frequency. Consequently, as one metal dilutes another, dipole coupling effects are diminished, and a resulting red shift is observed in the CO stretching frequency. Dendrimer-Templated Pt-Cu Catalysts J. Phys. Chem. B, Vol. 110, No. 17, 2006 8609 To evaluate the relative importance of dipole coupling effects, low-coverage CO stretching frequencies Catalytic Test Reactions. Catalytic activity of the supported nanoparticles was evaluated with the toluene hydrogenation and CO oxidation test reactions. Toluene hydrogenation activities, collected in The data in CO oxidation activity data for the Pt-containing catalysts is shown in Structural and Electronic Effects on Catalytic Activity. It is appropriate and important to reconcile the divergent effects of Cu incorporation on the two test reactions, particularly since they are opposite in both direction and magnitude (mild promotion of CO oxidation that is independent of Cu content versus strong inhibition of toluene hydrogenation that is Cudependent). Structural and electronic factors can affect the catalytic activity for these oxidation-reduction reactions. Pt is 8610 J. Phys. Chem. B, Vol. 110, No. 17, 2006 Hoover et al. slightly more electronegative than Cu, so it is possible that the more active metal is enriched in electron density upon incorporation of Cu. However, the electronegativity difference is small (2.2 vs 1.9), and the IR spectroscopy data indicate that any electronic differences between the mono-and bimetallic catalysts are correspondingly mild. The low-coverage Pt-CO stretching frequencies show only a weak trend with Cu incorporation, but the shifts are fairly small and are in the range of singleton Pt-CO stretching frequencies for monometallic Pt catalysts. Although these small potential electronic effects might be a reasonable explanation for the copper's promotion of CO oxidation catalysis (vide infra), we do not believe that they are sufficient to explain the 100-fold decrease in Pt activity for toluene hydrogenation. The trend in hydrogenation activity tracks directly with the metal stoichiometry, which is set and controlled in the initial nanoparticle synthesis. This reduction in catalytic activity with increasing Cu content is likely due to surface enrichment in copper under a reducing atmosphere. Cu surface enrichment in this system been postulated for a number of traditionally prepared supported Pt-Cu catalysts, particularly under reducing atmospheres. The simplest structural explanation is that surface Cu atoms provide a new type of surface site that binds CO more weakly than monometallic Pt sites. The E app values for the bimetallic nanoparticles, which strongly depend on heats of adsorption, are 30% lower than that of the monometallic Pt catalyst. This explanation is also attractive in light of models for this reaction over Pt, which implicates desorption of a key weakly bound CO-based intermediate as the rate-determining step. Oxygen is also more competitive for binding on Cu than Pt (Cu-CO bonds are weak, vide supra), so Cu incorporation may simply increase the amount of surface oxygen available on the particle. Because CO binding appears to enrich the surface in Pt, the surface stoichiometry under the reaction conditions is unclear. It is also possible that, in the presence of CO, the bimetallic particles result in Pt-on-Cu subsurface alloys that have been predicted by some computational models. 6-9 These subsurface alloys can be activated through electronic influences or structurally through the epitaxial compression of surface Pt atoms. This explanation is consistent with a mild electronic effect on Pt observed in the infrared spectra. At the same time, correlations between IR spectra and catalytic activity must be drawn with extreme care, since there is no guarantee that the strongly bound Pt-CO species observed in the IR are the active species in CO oxidation catalysis. Additionally, the expected influence of the electronic effect (enhanced metal-ligand back-bonding inferred from a slightly weaker CO bond) would predict stronger Pt-C bonds and is inconsistent with a model involving desorption in the slow step. 47 Although we cannot rule out an electronic nature of the activity enhancement, we favor structural explanations

RNA:protein ratio of the unicellular organism as a characteristic of phosphorous and nitrogen stoichiometry and of the cellular requirement of ribosomes for protein synthesis

Background Mean phosphorous:nitrogen (P:N) ratios and relationships of P:N ratios with the growth rate of organisms indicate a surprising similarity among and within microbial species, plants, and insect herbivores. To reveal the cellular mechanisms underling this similarity, the macromolecular composition of seven microorganisms and the effect of specific growth rate (SGR) on RNA:protein ratio, the number of ribosomes, and peptide elongation rate (PER) were analyzed under different conditions of exponential growth. Results It was found that P:N ratios calculated from RNA and protein contents in these particular organisms were in the same range as the mean ratios reported for diverse organisms and had similar positive relationships with growth rate, consistent with the growth-rate hypothesis. The efficiency of protein synthesis in microorganisms is estimated as the number of active ribosomes required for the incorporation of one amino acid into the synthesized protein. This parameter is calculated as the SGR:PER ratio. Experimental and theoretical evidence indicated that the requirement of ribosomes for protein synthesis is proportional to the RNA:protein ratio. The constant of proportionality had the same values for all organisms, and was derived mechanistically from the characteristics of the protein-synthesis machinery of the cell (the number of nucleotides per ribosome, the average masses of nucleotides and amino acids, the fraction of ribosomal RNA in the total RNA, and the fraction of active ribosomes). Impairment of the growth conditions decreased the RNA:protein ratio and increased the overall efficiency of protein synthesis in the microorganisms. Conclusion Our results suggest that the decrease in RNA:protein and estimated P:N ratios with decrease in the growth rate of the microorganism is a consequence of an increased overall efficiency of protein synthesis in the cell resulting from activation of the general stress response and increased transcription of cellular maintenance genes at the expense of growth related genes. The strong link between P:N stoichiometry, RNA:protein ratio, ribosomal requirement for protein synthesis, and growth rate of microorganisms indicated by the study could be used to characterize the N and P economy of complex ecosystems such as soils and the oceans

A chemotherapy privileging process for advanced practice providers at an academic medical center

Purpose: Nurse practitioners, physician assistants, and pharmacists are advanced practice providers who are highly trained and qualified healthcare professionals that can help support traditional demands on oncologists' increased time in direct patient care. The purpose of this study was to detail and assess the creation of a privileging process for this group of medical professionals within an academic medical center. Obtaining the designation of limited oncology practice provider (LOPP) gives the right to modify chemotherapy orders and to order supportive care medications. Methods: An interdisciplinary team developed a comprehensive training process inclusive of required educational domains, knowledge goals, and educational activities to become an LOPP. In 2018, five years after the implementation of the privileging process, a survey was distributed to assess perceptions of the training process and integration of LOPPs within oncology practice. Results: Most oncologists noted that working with LOPPs is beneficial to oncology practice (94%) and that they make modifying chemotherapy orders more efficient (87%). Greater than 82% of LOPPs also reported that their privileges streamline the chemotherapy process and make them feel valuable. Conclusion: The creation of the LOPP designation is an effective way to integrate nurse practitioners, physician assistants, and pharmacists within oncology practice. The inclusion of a focused privileging process ensures the safety of cancer care provided and has created a streamlined process for chemotherapy modifications and supportive care

SARS-CoV-2 Mitigation Strategies, Testing, and Cases at 254 Jails in the US Southeast, October 2020 to May 2021

Objectives. To characterize severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mitigation strategies, testing, and cases across county jails in the Southeastern United States, examining variability by jail characteristics. Methods. We administered a 1-time telephone survey to personnel of 254 jails in Alabama, Georgia, North Carolina, and South Carolina between October 2020 and May 2021. Results. Some SARS-CoV-2 mitigation strategies (e.g., screening at intake, isolation and masking for symptomatic persons) were commonly reported (≥ 75% of jails). Other measures, such as masking regardless of symptoms (52%) and screening at release (26%), were less common and varied by jail state or population size. Overall, 41% of jails reported no SARS-CoV-2 testing in the past 30 days. Jails with testing (59%) tested a median of 6 per 100 incarcerated persons; of those jails, one third reported 1 or more cases of positive tests. Although most jails detected no cases, in the 20% of all jails with 1 or more case in the past 30 days, 1 in 5 tests was positive. Conclusions. There was low testing coverage and variable implementation of SARS-CoV-2 mitigation strategies in Southeastern US jails during the first year of the COVID-19 pandemic

A qualitative study of patient and provider perspectives on using web-based pain coping skills training to treat persistent cancer pain

Objective: Persistent pain is common and inadequately treated in cancer patients. Behavioral pain interventions are a recommended part of multimodal pain treatments, but they are underused in clinical care due to barriers such as a lack of the resources needed to deliver them in person and difficulties coordinating their use with clinical care. Pain coping skills training (PCST) is an evidence-based behavioral pain intervention traditionally delivered in person. Delivering this training via the web would increase access to it by addressing barriers that currently limit its use. We conducted a patient pilot study of an 8-week web-based PCST program to determine the acceptability of this approach to patients and the program features needed to meet their needs. Focus groups with healthcare providers identified strategies for coordinating the use of web-based PCST in clinical care.Method: Participants included 7 adults with bone pain due to multiple myeloma or metastasized breast or prostate cancer and 12 healthcare providers (4 physicians and 8 advanced practice providers) who treat cancer-related bone pain. Patients completed web-based PCST at home and then took part in an in-depth qualitative interview. Providers attended focus groups led by a trained moderator. Qualitative analyses identified themes in the patient and provider data.Results: Patients reported strongly favorable responses to web-based PCST and described emotional and physical benefits. They offered suggestions for adapting the approach to better fit their needs and to overcome barriers to completion. Focus groups indicated a need to familiarize healthcare providers with PCST and to address concerns about overburdening patients. Providers would recommend the program to patients they felt could benefit. They suggested applying a broad definition of cancer pain and having various types of providers help coordinate program its use with clinical care.Significance of results: Web-based PCST was acceptable to patients and providers. Our findings suggest that patients could benefit from this approach, especially if patient and provider barriers are addressed

Drug Use Mediates the Relationship Between Depressive Symptoms and Adherence to ART Among Recently Incarcerated People Living with HIV

Depression is a known risk factor for antiretroviral therapy (ART) non-adherence, but little is known about the mechanisms explaining this relationship. Identifying these mechanisms among people living with HIV (PLHIV) after release from prison is particularly important, as individuals during this critical period are at high risk for both depression and poor ART adherence. 347 PLHIV recently released from prison in North Carolina and Texas were included in analyses to assess mediation of the relationship between depressive symptoms at 2 weeks post-release and ART adherence (assessed by unannounced telephone pill counts) at weeks 9–21 post-release by the hypothesized explanatory mechanisms of alcohol use, drug use, adherence self-efficacy, and adherence motivation (measured at weeks 6 and 14 post-release). Indirect effects were estimated using structural equation models with maximum likelihood estimation and bootstrapped confidence intervals. On average, participants achieved 79% ART adherence. The indirect effect of depression on adherence through drug use was statistically significant; greater symptoms of depression were associated with greater drug use, which was in turn associated with lower adherence. Lower adherence self-efficacy was associated with depressive symptoms, but not with adherence. Depression screening and targeted mental health and substance use services for depressed individuals at risk of substance use constitute important steps to promote adherence to ART after prison release