Tantalum Oxide as an Efficient Alternative Electron Transporting Layer for Perovskite Solar Cells.

Electron transporting layers facilitating electron extraction and suppressing hole recombination at the cathode are crucial components in any thin-film solar cell geometry, including that of metal-halide perovskite solar cells. Amorphous tantalum oxide (Ta2O5) deposited by spin coating was explored as an electron transport material for perovskite solar cells, achieving power conversion efficiency (PCE) up to ~14%. Ultraviolet photoelectron spectroscopy (UPS) measurements revealed that the extraction of photogenerated electrons is facilitated due to proper alignment of bandgap energies. Steady-state photoluminescence spectroscopy (PL) verified efficient charge transport from perovskite absorber film to thin Ta2O5 layer. Our findings suggest that tantalum oxide as an n-type semiconductor with a calculated carrier density of ~7 × 1018/cm3 in amorphous Ta2O5 films, is a potentially competitive candidate for an electron transport material in perovskite solar cells.

Exaggerated ventilatory drive estimates from epiglottic and esophageal pressure deflections in the presence of airway occlusion.

Esophageal and epiglottic pressure deflections are widely used to quantify ventilatory effort during sleep in patients with obstructive sleep apnea (OSA). However, changes in upper airway patency will fundamentally alter pressure gradients across the respiratory system with different airflow and volume-dependent effects on esophageal versus epiglottic pressure. The magnitude of these obstruction effects on ventilatory effort assessed from pressure deflections has not been systematically investigated. This study sought to quantify the direct effect of airway occlusion on esophageal and epiglottic pressure deflections during sleep in patients with OSA compared with predictions based on classic respiratory mechanics. Pneumotachograph airflow and volume, and esophageal, epiglottic, mask, and gastric pressures were measured throughout a nonoccluded breath before and the first occluded breath after repeated external airway occlusions during sleep in 13 patients with OSA on constant positive airway pressure (CPAP). Inspiratory pressure deflections were approximately doubled with epiglottic pressure, and increased by around 40% with esophageal pressure on the occluded compared with the preoccluded breath. Differences in pressure between pre- and occluded breaths showed strong dependence on volume and flow, in line with theoretical models of respiratory mechanics. A relatively simple correction factor could account for these effects to provide more consistent measures of ventilatory effort from pressure, independent from measurement site and changing airflow conditions. These finding have important implications for interpreting ventilatory effort and arousal threshold measurements and for understanding the relationships between underlying ventilatory drive and pressure deflections in the presence of airway obstruction during sleep.NEW & NOTEWORTHY Esophageal and epiglottic pressure deflection measurements are widely used as gold-standard measures of ventilatory effort without consideration of differential obstruction effects between measurement sites. This study is the first to quantify the effect of airway occlusion on pressure recordings during sleep. The findings of substantial acute effects of occlusion itself on pressure deflections are important to consider in the planning, analysis, and interpretation of studies that make inferences regarding inspiratory effort.

Molecular Level Synthesis of InFeO3 and InFeO3/Fe2O3 Nanocomposites.

New heterometallic In-Fe alkoxides [InFe(OtBu)4(PyTFP)2] (1), [InFe2(OneoPen)9(Py)] (2), and [InFe3(OneoPen)12] (3) were synthesized and structurally characterized. The arrangement of metal centers in mixed-metal framework was governed by the In:Fe ratio and the coordination preferences of Fe(III) and In(III) centers to be in tetrahedral and octahedral environments, respectively. 3 displayed a star-shaped so-called "Mitsubishi" motif with the central In atom coordinated with three tetrahedral {Fe(OneoPen)4}- anionic units. The deterministic structural influence of the larger In atom was evident in 1 and 2 which displayed the coordination of neutral coligands to achieve the desired coordination number. Thermal decomposition studies of compounds 1-3 under inert conditions with subsequent powder diffraction studies revealed the formation of Fe2O3 and In2O3 in the case of 3 and 2, whereas 1 intriguingly produced elemental In and Fe. In contrary, the thermal decomposition of 1-3 under ambient conditions produced a ternary oxide, InFeO3, with additional Fe2O3 present as a secondary phase in a different stoichiometric ratio predetermined through the In:Fe ratio in 2 and 3. The intimate mixing of different phases in InFeO3/Fe2O3 nanocomposites was confirmed by transmission electron microscopy of solid residues obtained after the decomposition of 1 and 2. The pure InFeO3 particles demonstrated ferromagnetic anomalies around 170 K as determined by temperature-dependent field-cooled and zero-field-cooled magnetization experiments. A first-order magnetic transition with an increase in the ZFC measurements was explained by temperature-induced reduction of the Fe-Fe distance and the corresponding increase in superexchange.

Magnetic Field-Assisted Chemical Vapor Deposition of UO2 Thin Films.

Chemical vapor deposition (CVD) of UO2 thin films from in situ reductive decomposition using a U(VI) precursor ([U(OtBu)6]) was performed under applied magnetic fields (up to 1 T). The molecular mechanism responsible for the formation of U(IV) oxide was determined by nuclear magnetic resonance (NMR) analysis of gaseous byproducts revealed a reductive transformation of uranium hexakis-tert-butoxide into urania. Thin films were grown under zero-field and applied magnetic field conditions that clearly showed the guiding influence of the magnetic field on altering the morphology and crystallographic orientation of grains in UO2 deposits produced under an external magnetic field. Application of magnetic fields was found to reduce the grain size. Whereas films with a ⟨111⟩ preferred orientation were observed under zero-field conditions, the application of magnetic fields (500 mT to 1 T) promoted a polycrystalline growth. X-ray photoelectron spectroscopy confirmed the formation of UO2 films with traces of U(VI) centers present on the surface, which was evidently due to the surface oxidation of coordinatively unsaturated U(IV) centers, which was found to be significantly reduced in the field-assisted process. These findings emphasize the positive effect of magnetic fields on controlling the texture and chemical homogeneity of CVD-grown films. The availability of a magnetic field as an extrinsic parameter for the CVD process adds to the conventional parameters, such as temperature, deposition time, and pressure, and expands the experimental space for thin-film growth.

Magnetic Field-Assisted Chemical Vapor Deposition of Iron Oxide Thin Films: Influence of Field-Matter Interactions on Phase Composition and Morphology.

Magnetic field-assisted CVD offers a direct pathway to manipulate the evolution of microstructure, phase composition, and magnetic properties of the as-prepared film. We report on the role of applied magnetic fields (0.5 T) during a cold-wall CVD deposition of iron oxide from [FeIII(OtBu)3]2 leading to higher crystallinity, larger particulates, and better out-of-plane magnetic anisotropy, if compared with zero-field depositions. Whereas selective formation of homogeneous magnetite films was observed for the field-assisted process, coexistence of hematite and amorphous iron(III) oxide was confirmed under zero-field conditions. Comparison of the coercive field (11 vs 60 mT) indicated lower defect concentration for the field-assisted process with nearly superparamagnetic behavior. X-ray photoemission electron microscopy (X-PEEM) in absorption mode at the O-K and Fe-L3,2 edges confirmed the selective formation of magnetite (field-assisted) and hematite (zero-field) with coexisting amorphous phases, respectively, emphasizing the importance of field-matter interactions in the phase-selective synthesis of magnetic thin films.

Volatile Rhenium(I) Compounds with Re-N Bonds and Their Conversion into Oriented Rhenium Nitride Films by Magnetic Field-Assisted Vapor Phase Deposition.

New heteroleptic rhenium(I) compounds, [fac-Re(I)(CO)3(L)] (e.g., L= tfb-dmpda, (N,N-(4,4,4-trifluorobut-1-en-3-on)-dimethyl propylene diamine)), containing anionic and neutral ligands act as efficient precursors to grow polycrystalline rhenium nitride (ReN) films by their vapor phase deposition at 600 °C. Deposition of ReN films under an external magnetic field showed an orientation effect with preferred growth of crystallites along ⟨100⟩ direction. Rhenium complexes reported here unify high stability and reactivity in a single molecule through a Janus-type coordination around a Re center, constituted by a chelating tridentate ligand and three carbonyl groups imparting a facial geometry. Single-crystal diffraction analysis confirmed the structural integrity of the new rhenium compounds. The rigidity of molecular framework was validated in solution via 1D and 2D NMR spectroscopy, in the gas phase via mass spectrometry, and in the solid-state by thermogravimetric analysis and differential scanning calorimetry studies. The analytical data showed that pre-existent Re-N bonds in [fac-Re(I)(CO)3(L)] facilitated low-temperature formation of crystalline ReN deposits confirmed by grazing angle X-ray diffraction analysis. The surface chemical composition and the uniformity of microstructure were provided by X-ray photoelectron spectroscopy (XPS) and scanning and transmission electron microscopy (SEM/TEM), respectively.

Reducing Avoidable Facility Transfers (RAFT): Outcomes of a Team Model to Minimize Unwarranted Emergency Care at Skilled Nursing Facilities.

BACKGROUND: Acute health care interventions for residents of skilled nursing facilities (SNFs) are often unwarranted, unwanted, and/or harmful. We describe a provider-focused care model to reduce unwarranted or unwanted acute health care utilization. OBJECTIVE: Assess the capability of the Reducing Avoidable Facility Transfers (RAFT) model to reduce unwanted and unwarranted acute health care utilization among residents in 3 rural SNFs between January 1, 2016 and June 30, 2017. DESIGN: Prospective cohort, pre/post study. SETTING: Three rural SNFs in collaboration with a geriatric practice in a tertiary academic medical center. PARTICIPANTS: Post-acute care (PAC) and long-term care (LTC) residents of 3 rural SNFs. INTERVENTION: RAFT includes the following components: (1) a small team of providers who manage longitudinal care and after hours call; (2) elicitation of advance care plans and preferences regarding acute care; (3) standardized communication process engaging the provider at the identification of an acute care event; (4) a biweekly case review of all emergency department (ED) transfers. MEASURES: ED and hospital utilization. RESULTS: RAFT demonstrated a 35% reduction in monthly ED transfers and a 30.5% reduction in monthly hospitalizations. These reductions were greatest for LTC residents. CONCLUSIONS/IMPLICATIONS: The RAFT approach substantially reduced unwarranted ED and hospital utilization in this study. Results support replication and evaluation in a larger, more diverse setting and population.

Anisotropy control in magnetic nanostructures through field-assisted chemical vapor deposition.

Chemical vapor deposition of iron pentacarbonyl (Fe(CO)5) in an external magnetic field (B = 1.00 T) was found to significantly affect the microstructure and anisotropy of as-deposited iron crystallites that could be transformed into anisotropic hematite (α-Fe2O3) nanorods by aerobic oxidation. The deterministic influence of external magnetic fields on CVD deposits was found to be substrate-independent as demonstrated by the growth of anisotropic α-Fe columns on FTO (F:SnO2) and Si (100), whereas the films deposited in the absence of the magnetic field were constituted by isotropic grains. TEM images revealed gradual increase in average crystallite size in correlation to the increasing field strength and orientation, which indicates the potential of magnetic field-assisted chemical vapor deposition (mfCVD) in controlling the texture of the CVD grown thin films. Given the facet-dependent activity of hematite in forming surface-oxygenated intermediates, exposure of crystalline facets and planes with high atomic density and electron mobilities is crucial for oxygen evolution reactions. The field-induced anisotropy in iron nanocolumns acting as templates for growing textured hematite pillars resulted in two-fold higher photoelectrochemical efficiency for hematite films grown under external magnetic fields (J = 0.050 mA cm-2), when compared to films grown in zero field (J = 0.027 mA cm-2). The dark current measurements indicated faster surface kinetics as the origin of the increased catalytic activity.

Implementation of a Workflow Initiative for Integrating Transitional Care Management Codes in a Geriatric Primary Care Practice.

We implemented a transitional care management service led by a nurse care manager. An interdisciplinary team developed a workflow using a Plan-Do-Study-Act cycle for contacting patients. Of the 146 (97.9%) eligible patients, 143 (97.9%) had a phone call within 48 hours. There were 84 of 120 (70.0%) and 117 of 120 (97.5%) attendance rates of those attending visits within 7 and 14 days. A care manager-led workflow was successfully and easily implemented within a primary care practice.

Comparative effects of glucose and water drinks on blood pressure and cardiac function in older subjects with and without postprandial hypotension.

Postprandial hypotension (PPH) occurs frequently and is thought to reflect an inadequate increase in cardiac output to compensate for the rise in splanchnic blood flow after a meal. Gastric distension by water attenuates the postprandial fall in blood pressure (BP). Cardiac hemodynamics (stroke volume (SV), cardiac output (CO), and global longitudinal strain (GLS)) have hitherto not been measured in PPH We sought to determine the comparative effects of water and glucose drinks on cardiac hemodynamics in healthy older subjects and individuals with PPH Eight healthy older subjects (age 71.0 ± 1.7 years) and eight subjects with PPH (age 75.5 ± 1.0 years) consumed a 300 mL drink of either water or 75 g glucose (including 150 mg 13C-acetate) in randomized order. BP and heart rate (HR) were measured using an automatic device, SV, CO, and GLS by transthoracic echocardiography and gastric emptying by measurement of 13CO2 In both groups, glucose decreased systolic BP (P < 0.001) and increased HR, SV, and CO (P < 0.05 for all). The fall in systolic BP was greater (P < 0.05), and increase in HR less (P < 0.05), in the PPH group, with no difference in SV or CO Water increased systolic BP (P < 0.05) in subjects with PPH and, in both groups, decreased HR (P < 0.05) without affecting SV, CO, or GLS In subjects with PPH, the hypotensive response to glucose and the pressor response to water were related (R = -0.75, P < 0.05). These observations indicate that, in PPH, the hypotensive response to oral glucose is associated with inadequate compensatory increases in CO and HR, whereas the pressor response to water ingestion is maintained and, possibly, exaggerated.

Intermittent hypercapnic hypoxia during sleep does not induce ventilatory long-term facilitation in healthy males.

Intermittent hypoxia-induced ventilatory neuroplasticity is likely important in obstructive sleep apnea pathophysiology. Although concomitant CO2 levels and arousal state critically influence neuroplastic effects of intermittent hypoxia, no studies have investigated intermittent hypercapnic hypoxia effects during sleep in humans. Thus the purpose of this study was to investigate if intermittent hypercapnic hypoxia during sleep induces neuroplasticity (ventilatory long-term facilitation and increased chemoreflex responsiveness) in humans. Twelve healthy males were exposed to intermittent hypercapnic hypoxia (24 × 30 s episodes of 3% CO2 and 3.0 ± 0.2% O2) and intermittent medical air during sleep after 2 wk washout period in a randomized crossover study design. Minute ventilation, end-tidal CO2, O2 saturation, breath timing, upper airway resistance, and genioglossal and diaphragm electromyograms were examined during 10 min of stable stage 2 sleep preceding gas exposure, during gas and intervening room air periods, and throughout 1 h of room air recovery. There were no significant differences between conditions across time to indicate long-term facilitation of ventilation, genioglossal or diaphragm electromyogram activity, and no change in ventilatory response from the first to last gas exposure to suggest any change in chemoreflex responsiveness. These findings contrast with previous intermittent hypoxia studies without intermittent hypercapnia and suggest that the more relevant gas disturbance stimulus of concomitant intermittent hypercapnia frequently occurring in sleep apnea influences acute neuroplastic effects of intermittent hypoxia. These findings highlight the need for further studies of intermittent hypercapnic hypoxia during sleep to clarify the role of ventilatory neuroplasticity in the pathophysiology of sleep apnea.NEW & NOTEWORTHY Both arousal state and concomitant CO2 levels are known modulators of the effects of intermittent hypoxia on ventilatory neuroplasticity. This is the first study to investigate the effects of combined intermittent hypercapnic hypoxia during sleep in humans. The lack of neuroplastic effects suggests a need for further studies more closely replicating obstructive sleep apnea to determine the pathophysiological relevance of intermittent hypoxia-induced ventilatory neuroplasticity.

Changes in lung volume and diaphragm muscle activity at sleep onset in obese obstructive sleep apnea patients vs. healthy-weight controls.

Obese obstructive sleep apnea (OSA) patients potentially defend end-expiratory lung volume (EELV) during wakefulness via increased expiratory diaphragmatic activity (eEMG(dia)). A reduction in eEMG(dia) and EELV at sleep onset could, therefore, increase upper airway collapsibility via reduced tracheal traction. The aim of this study was to establish if eEMG(dia) is greater in obese OSA patients vs. healthy-weight controls during wakefulness, and to compare eEMG(dia) and EELV changes at sleep onset between groups as a function of stable breathing, hypopnea vs. apnea events developing within the first few breaths after sleep onset. Eight obese men with OSA and eight healthy-weight men without OSA were studied in the supine position while instrumented with an intraesophageal catheter to measure eEMG(dia) and magnetometer coils to assess changes in EELV. While eEMG(dia) expressed as %maximal activity was not significantly different between groups during wakefulness, OSA patients experienced a greater fall in eEMG(dia) following sleep onset (group × breath, P < 0.001) and a greater decrease when respiratory events accompanied sleep onsets (category × breath, P < 0.001). The decrease in EELV by the third postsleep onset breath was small (OSA, 61.4 ± 8.0 ml, P < 0.001; controls, 34.0 ± 4.2 ml, P < 0.001), with the decrease significantly greater in OSA patients over time (group × breath, P = 0.007). There was a greater decrease with more severe events (category × breath, P < 0.001), with EELV decreasing by 89.6 ± 14.2 ml (P < 0.001) at the onset of apneas in the OSA group. These data support that diaphragm tone and EELV frequently decrease following sleep onset, with greater falls at transitions accompanied by respiratory events. In addition to decrements in upper airway dilator muscle activity, decreasing lung volume potentially contributes to an increased propensity for upper airway collapse in OSA patients at sleep onset.

Upper airway function and arousability to ventilatory challenge in slow wave versus stage 2 sleep in obstructive sleep apnoea.

UNLABELLED: Patients with obstructive sleep apnoea (OSA) have reduced event rates during slow wave sleep (SWS) compared with stage 2 sleep. To explore this phenomenon, ventilatory and arousal timing responses to partial and complete airflow obstruction during SWS versus stage 2 sleep were examined. METHODS: Ten patients, mean+/-SD apnoea-hypopnoea index (AHI) 49.7+/-16.5 events/h with reduced OSA frequency during SWS (SWS AHI 18.9+/-14.0 events/h) slept with an epiglottic pressure catheter and nasal mask/pneumotachograph. Patients underwent rapid continuous positive airway pressure (CPAP) dialdowns to three subtherapeutic levels and brief airway occlusions in random order. RESULTS: Post-dialdown, there were marked reductions in peak flow and minute ventilation, and progressive increases in inspiratory effort (p<0.001), but with limited ventilatory recovery and no differences between sleep stages. CPAP versus peak flow relationships on the third and second to last breath pre-arousal were not different between sleep stages. Arousals occurred later and post-dialdown arousal probability was lower during SWS compared with stage 2 sleep, Cox hazard ratio (95% CI) 0.65 (0.48 to 0.88), p=0.006. During SWS occlusions, time to arousal (mean+/-SEM) was prolonged (23.0+/-2.6 vs 17.1+/-1.7 s, p=0.02). Inspiratory effort developed more rapidly (-1.0+/-0.2 vs -0.6+/-0.1 cm H(2)O/s, p=0.019) and was more negative (-28.7+/-2.7 vs -20.3+/-1.6 cm H(2)O, p<0.001) on the breath preceding arousal. CONCLUSIONS: Except for a heightened ventilatory drive response during airway occlusion, airway function and ventilatory compensation to ventilatory challenge appear to be similar, but with consistently and substantially delayed arousal responses, in SWS versus stage 2 sleep.

Diastereoselective domino reactions of chiral 2-substituted 1-(2',2',3',3'-tetramethylcyclopropyl)-alkan-1-ols under Friedel-Crafts conditions.

The 2-substituted 1-(2',2',3',3'-tetramethylcyclopropyl)-alkan-1-ols 3-7 were prepared by carbonyl addition of tetramethylcyclopropyl lithium to the respective aldehydes or by addition of the respective substituted carbanions to tetramethylcyclopropyl carbaldehyde 16. Under Brønsted acidic conditions (HBF(4).OEt(2)), the alcohols served as substrates in Friedel-Crafts alkylation reactions with 2-methylthiophene (8) and N-tosylpyrrole (9). The alkanols 3-6 carrying the groups (t)Bu, Ph, CN, PO(OEt)(2) in 2-position delivered the rearranged substitution products 17-20 in very good chemical yields (9 examples, 81-97%). The products were formed presumably via ring-opening of the tetramethylcyclopropyl-substituted cation, which rearrange by a Wagner-Meerwein shift to allylic cations I. The latter cations are eventually attacked by the arene nucleophile. The diastereoselectivity of this process is good (anti-preference for Ph, CN, PO(OEt)(2)) to excellent (syn-preference for (t)Bu). The esters 7, carrying a methoxycarbonyl group in 2-position, yielded under the same reaction conditions products 25 and 26, which are formed by an intermolecular Friedel-Crafts reaction followed by a subsequent intramolecular Friedel-Crafts alkylation (3 examples, 80-93%).

Marked reduction in obstructive sleep apnea severity in slow wave sleep.

INTRODUCTION: Obstructive sleep apnea (OSA) is widely accepted to improve during slow wave sleep (SWS) compared to lighter stages of NREM sleep. However, supporting data to establish the magnitude and prevalence of this effect is lacking. Consequently, we examined this phenomenon, controlling for posture, in a large group of patients investigated for OSA at an academic clinical sleep service. METHODS: A detailed retrospective analysis was conducted on data obtained from each 30-sec epoch of sleep in 253 consecutive full-night diagnostic polysomnography studies performed over a 3-month period. Respiratory and arousal event rates were calculated within each stage of sleep, in the supine and lateral postures, and across the whole night, with OSA patients classified on the basis of an overall apnea-hypopnea index (AHI) > or =15 events/h. Central sleep apnea (CSA) patients were defined by a central apnea index > 5/h. Sleep latency and time, and respiratory and arousal event rates in OSA, CSA, and non-OSA patients were compared between sleep stages and postures using linear mixed model analysis. The numbers of patients achieving reduced event rates in SWS and in the lateral posture were also examined. RESULTS: There were 171 patients with OSA, 14 with CSA, and 68 non-OSA patients. OSA patients took significantly longer to achieve slow wave and REM sleep (p < 0.001) than non-OSA patients and had less stage 4 sleep (p = 0.037). There were striking improvements in AHI and arousal index (Al) from stage 1 to 4 NREM sleep (p <0.001), with intermediate levels in REM sleep. AHI and Al were also markedly reduced in lateral versus supine sleep in all sleep stages (p < 0.001), with an effect size comparable to that of the slow wave sleep effect. The majority of OSA patients achieved low respiratory event rates in SWS. Eighty-two percent of patients achieved an AHI <15 and 57% < 5 events/hour during stage 4 sleep. CONCLUSION: Although OSA patients demonstrate both a delayed and reduced proportion of SWS compared to non-OSA subjects, once they achieved SWS, AHI, and Al markedly improved in most patients.

Abdominal compression increases upper airway collapsibility during sleep in obese male obstructive sleep apnea patients.

STUDY OBJECTIVES: Abdominal obesity, particularly common in centrally obese males, may have a negative impact on upper airway (UA) function during sleep. For example, cranial displacement of the diaphragm with raised intra-abdominal pressure may reduce axial tension exerted on the UA by intrathoracic structures and increase UA collapsibility during sleep. DESIGN: This study aimed to examine the effect of abdominal compression on UA function during sleep in obese male obstructive sleep apnea patients. SETTING: Participants slept in a sound-insulated room with physiologic measurements controlled from an adjacent room. PARTICIPANTS: Fifteen obese (body mass index: 34.5 +/- 1.1 kg/m2) male obstructive sleep apnea patients (apnea-hypopnea index: 58.1 +/- 6.8 events/h) aged 50 +/- 2.6 years participated. INTERVENTIONS: Gastric (PGA) and transdiaphragmatic pressures (P(DI)), UA closing pressure (UACP), UA airflow resistance (R(UA)), and changes in end-expiratory lung volume (EELV) were determined during stable stage 2 sleep with and without abdominal compression, achieved via inflation of a pneumatic cuff placed around the abdomen. UACP was assessed during brief mask occlusions. MEASUREMENTS AND RESULTS: Abdominal compression significantly decreased EELV by 0.53 +/- 0.24 L (P=0.045) and increased PGA (16.2 +/- 0.8 versus 10.8 +/- 0.7 cm H2O, P < 0.001), P(DI) (11.7 +/- 0.9 versus 7.6 +/- 1.2 cm H2O, P < 0.001) and UACP (1.4 +/- 0.8 versus 0.9 +/- 0.9 cm H2O, P = 0.039) but not R(UA)(6.5 +/- 1.4 versus 6.9 +/- 1.4 cm H2O x L/s, P=0.585). CONCLUSIONS: Abdominal compression negatively impacts on UA collapsibility during sleep and this effect may help explain strong associations between central obesity and obstructive sleep apnea.

Chiral benzylic carbocations: low-temperature NMR studies and theoretical calculations.

The alpha-chiral secondary and tertiary benzylic carbocations 19-30 were generated from the corresponding benzylic alcohols 1, 2, and 5-14 by treatment with FSO(3)H or FSO(3)H/SbF(5) in SO(2)ClF as the solvent at -70 degrees C and characterized by one- and two-dimensional NMR spectroscopy. Coupling constants and NOESY measurements suggest a preferred conformation in which the alpha-hydrogen atom occupies the 1,3-allylic-strain position and the diastereotopic faces of the cations are differentiated by the alkyl substituent and a functional group (FG). The existence of this preferred conformation is further supported by calculations using a DFT method at the B3LYP/6-311+G** level. Quenching experiments with an arene nucleophile showed a preferential attack from the less shielded diastereotopic face delivering high diastereomeric ratios, supporting the hypothesis that these carbocations are involved as intermediates in previously studied S(N)1 reactions. A strong shielding effect at the benzylic carbocationic center is observed for most of the secondary benzylic carbocations (derived from precursors 5-13) investigated, indicating a strong mesomeric distribution of the positive charge to the carbon atom in the para-position of the anisyl substituent. For alpha-halogen-substituted carbocations (5-7, 12), no neighboring halogen participation leading to halonium ion formation was observed.

Highly diastereoselective Friedel-Crafts alkylation reactions via chiral alpha-functionalized benzylic carbocations.

A series of chiral 1-aryl-1-alkanols, which carry different functional groups (FGs) at the 2-position, were subjected to an acid (HBF4)-catalyzed reaction with various arenes. An S(N)1 substitution reaction was observed, in the course of which 1,1-diarylalkanes were formed. In most cases (40 out of 51 reactions), yields were very good to excellent (75-99 %). The diastereoselectivity of the reaction was heavily dependent on the FG at the 2-position. If the FG was methoxycarbonyl, nitro, hydroxy, cyano, trimethylsilylethynyl, or chloro, the corresponding anti products were favored and with a decreasing preference in this order. The methoxycarbonyl-substituted substrates gave the anti products with diastereomer ratios (d.r.) that exceeded 92:8 (16 examples). Nitro- and hydroxy-substituted products were obtained in most instances with d.r. > or = 90:10, whereas cyano-, trimethylsilylalkynyl-, or chloro-substituted substrates delivered only with certain arenes products with high selectivity (d.r. > or = 90:10). The sterically more demanding FGs ethylsulfonyl, ethoxysulfonyl, and diethoxyphosphonyl induced diastereofacial selectivity in favor of the corresponding syn products, with diethoxyphosphonyl being the most effective. The substrate with FG = PO(OEt)2 delivered, with eight different arenes, the corresponding syn substitution products (d.r. = 80:20 - >95:5). The relative configuration of the products was elucidated by spectroscopic and synthetic methods. On selected examples, the reactions were shown to proceed stereoconvergently, under kinetic control, and without racemization. Depending on the functional group, the onset of the reactions between 2-methylthiophene and some representative alcohols was found to occur at a temperature Theta between -78 and -40 degrees C. There was no correlation between the selectivity and theta. A model is suggested to explain the facial diastereoselectivity based on a preferred conformation of the putative intermediate carbocation.

Chiral alpha-branched benzylic carbocations: diastereoselective intermolecular reactions with arene nucleophiles and NMR spectroscopic studies.

The chiral benzylic alcohols 1-6 were prepared and subjected to S(N)1-type displacement reactions with various arene nucleophiles in acidic medium. Under optimized conditions (HBF(4).OEt(2), CH(2)Cl(2), -78 degrees C --> r.t.) the corresponding 1,1-diarylalkanes 11-18 and 20 were obtained in good chemical yields (48-99%). The facial diastereoselectivity of the reaction is high (d.r. = 91/9-97/3) when the substrate bears a stereogenic carbon center -CHtBuMe in the alpha-position to the electrophilic carbon atom. If the starting material was enantiomerically pure, no significant racemization was observed (94% ee --> 92% ee). The reactions proceed stereoconvergently as demonstrated by the conversion of the separated diastereoisomers syn-1a and anti-1a in separate reactions to the same product syn-11 (d.r. = 97/3). Further evidence for long-lived chiral benzylic carbocations as reaction intermediates was obtained from NMR studies in superacidic medium. The chiral cation 24 was generated in SO(2)ClF as the solvent at -70 degrees C employing SbF(5) as the Lewis acid and characterized by its (1)H and (13)C NMR spectra. NOE measurements suggest a preferred conformation in which the diastereotopic faces of the cation are differentiated by the two carbon substituents R and Me at the stereogenic carbon center in the alpha-position. The hypothesis is further supported by the observation that the diastereoselectivity of the substitution reaction decreases if the bulky tert-butyl (R = tBu) substituent in the substrate 1a is replaced by a smaller ethyl group (2a, R = Et).