Synthesis, Structure, and Properties of 2O-BaPtO3, a Phase Derived from Hexagonal Perovskite.

We have made the compound 2O-BaPtO3 by high-pressure, high-temperature synthesis, determined its structure, and tested its catalytic activity. Compounds of the same stoichiometry have been reported and tentatively identified as hexagonal perovskites, and although no structural model was ever established, 2O-BaPtO3 is clearly different and, to the best of our knowledge, unique. It features continuous chains of face-sharing PtO6 octahedra, like the well-known 2H hexagonal perovskite type, but with a staggered offset between the chains that breaks hexagonal symmetry and disrupts the close-packed array of A = Ba and X = O that is a defining characteristic of ABX3 perovskites. We investigated this structure and its stability vs the conventional 2H form using X-ray and neutron diffraction, X-ray absorption spectroscopy, and ab initio calculations. Catalytic testing of 2O-BaPtO3 showed that it is active for hydrogen evolution.

A Picture of Disorder in Hydrous Wadsleyite-Under the Combined Microscope of Solid-State NMR Spectroscopy and Ab Initio Random Structure Searching.

The Earth's transition zone, at depths of 410-660 km, while being composed of nominally anhydrous magnesium silicate minerals, may be subject to significant hydration. Little is known about the mechanism of hydration, despite the vital role this plays in the physical and chemical properties of the mantle, leading to a need for improved structural characterization. Here we present an ab initio random structure searching (AIRSS) investigation of semihydrous (1.65 wt % H2O) and fully hydrous (3.3 wt % H2O) wadsleyite. Following the AIRSS process, k-means clustering was used to select sets of structures with duplicates removed, which were then subjected to further geometry optimization with tighter constraints prior to NMR calculations. Semihydrous models identify a ground-state structure (Mg3 vacancies, O1-H hydroxyls) that aligns with a number of previous experimental observations. However, predicted NMR parameters fail to reproduce low-intensity signals observed in solid-state NMR spectra. In contrast, the fully hydrous models produced by AIRSS, which enable both isolated and clustered defects, are able to explain observed NMR signals via just four low-enthalpy structures: (i) a ground state, with isolated Mg3 vacancies and O1-H hydroxyls; (ii/iii) edge-sharing Mg3 vacancies with O1-H and O3-H species; and (iv) edge-sharing Mg1 and Mg3 vacancies with O1-H, O3-H, and O4-H hydroxyls. Thus, the combination of advanced structure searching approaches and solid-state NMR spectroscopy is able to provide new and detailed insight into the structure of this important mantle mineral.

A Clinical Review of Surgical vs Transcatheter Aortic Valve Replacement in Geriatric Patients.

OBJECTIVE: To provide an up-to-date review of the available evidence regarding management of elderly patients after transcatheter aortic valve replacement (TAVR). DATA SOURCES: A PubMed search of articles published (September 1969-December 2016) was done using a combination of the following words: aortic valve stenosis, geriatric, elderly, transcatheter aortic valve replacement, surgical aortic valve replacement, transcatheter aortic valve implantation (TAVI), and dual antiplatelet therapy. STUDY SELECTION/DATA EXTRACTION: Relevant original research, review articles, and guidelines were assessed for the management of elderly patients after TAVR. References from the above literature were also evaluated. Articles were selected for inclusion based on relevance to the topic, detailed methods, and complete results. DATA SYNTHESIS: Aortic valve stenosis is common in the geriatric population. While patients were historically treated with surgical aortic valve replacement (AVR), more patients are now undergoing TAVR. This article reviews the current literature regarding outcomes and pharmacotherapy between surgical and TAVR in the elderly population. CONCLUSION: Appropriate management of pharmacotherapy after surgical or TAVR can help improve outcomes in elderly patients, and pharmacists can provide guidance regarding evidence-based therapy.

Hunting for hydrogen: random structure searching and prediction of NMR parameters of hydrous wadsleyite.

The structural chemistry of materials containing low levels of nonstoichiometric hydrogen is difficult to determine, and producing structural models is challenging where hydrogen has no fixed crystallographic site. Here we demonstrate a computational approach employing ab initio random structure searching (AIRSS) to generate a series of candidate structures for hydrous wadsleyite (ß-Mg2SiO4 with 1.6 wt% H2O), a high-pressure mineral proposed as a repository for water in the Earth's transition zone. Aligning with previous experimental work, we solely consider models with Mg3 (over Mg1, Mg2 or Si) vacancies. We adapt the AIRSS method by starting with anhydrous wadsleyite, removing a single Mg(2+) and randomly placing two H(+) in a unit cell model, generating 819 candidate structures. 103 geometries were then subjected to more accurate optimisation under periodic DFT. Using this approach, we find the most favourable hydration mechanism involves protonation of two O1 sites around the Mg3 vacancy. The formation of silanol groups on O3 or O4 sites (with loss of stable O1-H hydroxyls) coincides with an increase in total enthalpy. Importantly, the approach we employ allows observables such as NMR parameters to be computed for each structure. We consider hydrous wadsleyite (∼1.6 wt%) to be dominated by protonated O1 sites, with O3/O4-H silanol groups present as defects, a model that maps well onto experimental studies at higher levels of hydration (J. M. Griffin et al., Chem. Sci., 2013, 4, 1523). The AIRSS approach adopted herein provides the crucial link between atomic-scale structure and experimental studies.

Fractional crystallisation of eclogite during the birth of a Hawaiian Volcano.

The initial melts erupted by a Hawaiian volcano have a range of alkalic compositions but are rarely observed as they are covered by enormous volumes of shield stage tholeiites. A remarkable record of the early evolution of Hawaiian volcanoes, however, is preserved by a volcanic sandstone dredged from the submarine flank of Kilauea, which contains a suite of petrogenetically related pre-shield basanite to nephelinite glasses. Here we show that the systematic variation in the rare earth element (REE) patterns of these samples requires the fractional crystallisation of garnet. A fractionating assemblage of Ca-rich garnet (32%), omphacitic clinopyroxene (63%), and minor phlogopite can explain the variation in the major and trace element contents of the suite. The results suggest fractional crystallisation of eclogite from a primitive Hawaiian melt near the base of the lithosphere (>90 km) and that a deep magma chamber is the first stage in the development of a Hawaiian volcano.

Observation of "hidden" magnesium: first-principles calculations and 25Mg solid-state NMR of enstatite.

(25)Mg NMR parameters have been determined for two polymorphs of enstatite (MgSiO(3)), an important magnesium silicate phase present as a major component of the Earth's upper mantle. The crystal structures of both polymorphs contain two crystallographically distinct magnesium sites; however, only a single resonance is observed in (25)Mg MAS NMR spectra recorded at 14.1 and 20.0 T. First-principles calculations performed on geometry-optimised crystal structures reveal that the quadrupolar interaction for the second site is expected to be very large, resulting in extensive broadening of the spectral resonance, explaining its apparent absence in the NMR spectrum. (25)Mg QCPMG NMR experiments employing variable offset cumulative spectroscopy (VOCS) are used to observe the broadened site and enable measurement of NMR parameters. The large difference in quadrupolar interaction between the two crystallographic magnesium sites is rationalised qualitatively in terms of the distortion of the local coordination environment as well as longer-range effects using a simple point charge model.

High-resolution (19)F MAS NMR spectroscopy: structural disorder and unusual J couplings in a fluorinated hydroxy-silicate.

High-resolution (19)F magic angle spinning (MAS) NMR spectroscopy is used to study disorder and bonding in a crystalline solid. (19)F MAS NMR reveals four distinct F sites in a 50% fluorine-substituted deuterated hydrous magnesium silicate (clinohumite, 4Mg(2)SiO(4)·Mg(OD(1-x)F(x))(2) with x = 0.5), indicating extensive structural disorder. The four (19)F peaks can be assigned using density functional theory (DFT) calculations of NMR parameters for a number of structural models with a range of possible local F environments generated by F(-)/OH(-) substitution. These assignments are supported by two-dimensional (19)F double-quantum MAS NMR experiments that correlate F sites based on either spatial proximity (via dipolar couplings) or through-bond connectivity (via scalar, or J, couplings). The observation of (19)F-(19)F J couplings is unexpected as the fluorines coordinate Mg atoms and the Mg-F interaction is normally considered to be ionic in character (i.e., there is no formal F-Mg-F covalent bonding arrangement). However, DFT calculations predict significant (19)F-(19)F J couplings, and these are in good agreement with the splittings observed in a (19)F J-resolved MAS NMR experiment. The existence of these J couplings is discussed in relation to both the nature of bonding in the solid state and the occurrence of so-called "through-space" (19)F-(19)F J couplings in solution. Finally, we note that we have found similar structural disorder and spin-spin interactions in both synthetic and naturally occurring clinohumite samples.

Dynamics on the microsecond timescale in hydrous silicates studied by solid-state (2)H NMR spectroscopy.

Solid-state (2)H NMR spectroscopy has been used to probe the dynamic disorder of hydroxyl deuterons in a synthetic sample of deuterated hydroxyl-clinohumite (4Mg(2)SiO(4).Mg(OD)(2)), a proposed model for the incorporation of water within the Earth's mantle. Both static and magic angle spinning (MAS) NMR methods were used. Static (2)H NMR appears to reveal little evidence of the dynamic process, yielding results similar to those obtained from deuterated brucite (Mg(OD)(2)), where no dynamics on the relevant timescale are expected to be present. However, in (2)H MAS NMR spectra, considerable line broadening is observed for hydroxyl-clinohumite and a (2)H double-quantum (DQ) MAS NMR spectrum confirms that this is due to motion on the microsecond timescale. Using a model for dynamic exchange of the hydroxyl deuterons between two sites identified in previous diffraction studies, first-principles density functional theory (DFT) calculations of (2)H (spin I = 1) quadrupolar NMR parameters, and a simple analytical model for dynamic line broadening in MAS NMR experiments, we were able to reproduce the observed motional line broadening and use this to estimate a rate constant for the dynamic process. From analysis of the observed (2)H linewidths in variable-temperature MAS experiments, an activation energy for the exchange process was also determined. A simulated static (2)H NMR lineshape based on our dynamic model is consistent with the observed experimental static NMR spectrum, confirming that the motion present in this system is not easily detectable using a static NMR approach. Finally, a (2)H DQMAS NMR spectrum of fluorine-substituted (2)H-enriched hydroxyl-clinohumite shows how the dynamic exchange process is inhibited by O-DF(-) hydrogen-bonding interactions.

Comparison of acute kidney injury risk associated with vancomycin and concomitant piperacillin/tazobactam or cefepime in the intensive care unit.

PURPOSE: The objective of this study was to evaluate AKI incidence with concomitant vancomycin and piperacillin/tazobactam (PTZ) compared to vancomycin and cefepime (FEP) in critically ill patients. MATERIALS AND METHODS: A retrospective, cohort study was conducted in adult critically ill patients from January 1, 2014 to December 31, 2017. The primary aim was to compare the incidence of AKI during concomitant therapy or until hospital discharge. Secondary analyses included AKI severity, time to AKI as well as recovery, and clinical outcomes. RESULTS: Overall, 333 patients were evaluated. The AKI rate in the vancomycin/PTZ group and vancomycin/FEP group were similar (19.5% vs. 17.3%, respectively, p = .612). Renal replacement therapy (RRT) was initiated in 10.0% and 3.8% administered vancomycin/PTZ and vancomycin/FEP groups, respectively (p = .04). Multivariate regression found vancomycin/PTZ was not associated with an increased risk of developing AKI although the presence of shock was identified as an independent risk factor (odds ratio, 3.22; 95% CI, 1.66-6.26). No significant differences in hospital or ICU length of stay or in-hospital mortality were observed between study groups. CONCLUSIONS: Concomitant PTZ and vancomycin in ICU patients was not associated with an increased risk of developing AKI compared to FEP and vancomycin combinations. More patients administered vancomycin/PTZ received RRT.

Trigger alerts associated with laboratory abnormalities on identifying potentially preventable adverse drug events in the intensive care unit and general ward.

BACKGROUND: Medication safety strategies involving trigger alerts have demonstrated potential in identifying drug-related hazardous conditions (DRHCs) and preventing adverse drug events in hospitalized patients. However, trigger alert effectiveness between intensive care unit (ICU) and general ward patients remains unknown. The objective was to investigate trigger alert performance in accurately identifying DRHCs associated with laboratory abnormalities in ICU and non-ICU settings. METHODS: This retrospective, observational study was conducted at a university hospital over a 1-year period involving 20 unique trigger alerts aimed at identifying possible drug-induced laboratory abnormalities. The primary outcome was to determine the positive predictive value (PPV) in distinguishing drug-induced abnormal laboratory values using trigger alerts in critically ill and general ward patients. Aberrant lab values attributed to medications without resulting in an actual adverse event ensuing were categorized as a DRHC. RESULTS: A total of 634 patients involving 870 trigger alerts were included. The distribution of trigger alerts generated occurred more commonly in general ward patients (59.8%) than those in the ICU (40.2%). The overall PPV in detecting a DRHC in all hospitalized patients was 0.29, while the PPV in non-ICU patients (0.31) was significantly higher than the critically ill (0.25) (p = 0.03). However, the rate of DRHCs was significantly higher in the ICU than the general ward (7.49 versus 0.87 events per 1000 patient days, respectively, p < 0.0001). Although most DRHCs were considered mild or moderate in severity, more serious and life-threatening DRHCs occurred in the ICU compared with the general ward (39.8% versus 12.4%, respectively, p < 0.001). CONCLUSIONS: Overall, most trigger alerts performed poorly in detecting DRHCs irrespective of patient care setting. Continuous process improvement practices should be applied to trigger alert performance to improve clinician time efficiency and minimize alert fatigue.

Alcohol withdrawal syndrome in critically ill patients: protocolized versus nonprotocolized management.

BACKGROUND: Approximately 18% to 25% of patients with alcohol use disorders admitted to the hospital develop alcohol withdrawal syndrome (AWS). Symptom-triggered dosing of benzodiazepines (BZDs) seems to lead to shorter courses of treatment, lower cumulative BZD dose, and more rapid control of symptoms in non-critically ill patients. This study compares the outcomes of critically ill patients with AWS when treated using a protocolized, symptom-triggered, dose escalation approach versus a nonprotocolized approach. METHODS: This is a retrospective pre-post study of patients 18 years or older with AWS admitted to an intensive care unit (ICU). The preintervention cohort (PRE) was admitted between February 2008 and February 2010. The postintervention cohort (POST) was admitted between February 2012 and January 2013. The PRE patients were treated by physician preference and compared with POST patients who were given escalating doses of BZDs and/or phenobarbital according to an AWS protocol, titrating to light sedations (Richmond Agitation Sedation Scale score of 0 to -2). RESULTS: There were 135 episodes of AWS in 132 critically ill patients. POST patients (n = 75) were younger (50.7 [13.8] years vs. 55.7 [8.7] years, p = 0.03) than PRE patients (n = 60). Sequential Organ Failure Assessment (SOFA) scores were higher in the PRE group (6.1 [3.7] vs. 3.9 [2.9], p = 0.0004). There was a significant decrease in mean ICU length of stay from 9.6 (10.5) days to 5.2 (6.4) days (p = 0.0004) in the POST group. The POST group also had significantly fewer ventilator days (5.6 [13.9] days vs. 1.31 [5.6] days, p < 0.0001) as well as a significant decrease in BZD use (319 [1,084] mg vs. 93 [171] mg, p = 0.002). There were significant differences between the two cohorts with respect to the need for continuous sedation (p < 0.001), duration of sedation (p < 0.001), and intubation secondary to AWS (p < 0.001). In all of these outcomes, the POST cohort had a notably lower frequency of occurrence. CONCLUSION: A protocolized treatment approach of AWS in critically ill patients involving symptom-triggered, dose escalations of diazepam and phenobarbital may lead to a decreased ICU length of stay, decreased time spent on mechanical ventilation, and decreased BZD requirements. LEVEL OF EVIDENCE: Epidemiologic study, level III; therapeutic study, level IV.

Enteral albuterol decreases the need for chronotropic agents in patients with cervical spinal cord injury-induced bradycardia.

BACKGROUND: Cervical spinal cord injury (CSCI) is often complicated by autonomic instability and life-threatening bradycardia. ß-adrenergic receptors offer a potential target for modulating cardiac vagal activity and heart rate. Enteral albuterol may mitigate symptomatic bradycardia in CSCI patients. The purpose of this study was to examine the effect of enteral albuterol on the frequency of symptomatic bradycardia and the need for rescue therapy in CSCI patients. METHODS: The charts of CSCI patients admitted to a Level I trauma center from February 2008 through March 2012 were reviewed for demographics, episodes of symptomatic bradycardia (defined as heart rate < 60 beats per minute and systolic blood pressure < 90 mm Hg), use of enteral albuterol, hospital days requiring chronotropic use, and total atropine administered. In the albuterol group, patients received scheduled enteral albuterol after experiencing symptomatic bradycardia, with chronotropic agents used as needed for rescue treatment. In the no-albuterol group, only chronotropic agents were used as needed for rescue treatment. The albuterol and no-albuterol groups were compared using independent-samples Kruskal-Wallis test for total number of bradycardic episodes, hospital days requiring chronotropic use, and total atropine administered. RESULTS: Eighteen patients with CSCI-induced bradycardia were identified. Eight patients received treatment with enteral albuterol, and 10 patients did not. The median age did not differ significantly between the two groups. However, the median Injury Severity Score (ISS) was higher in the albuterol group (median ISS, 36.5; interquartile range, 35-66.5 vs. median ISS 26; interquartile range, 27-37.25 in no-albuterol group). Patients receiving albuterol experienced 1.8 symptomatic bradycardic episodes versus 4.3 episodes in those patients not receiving albuterol (p = 0.08). Hospital days on chronotropic agents were significantly less in the albuterol group (1.8 vs. 8.6, p = 0.01). One patient, in the no-albuterol group, required pacemaker placement. CONCLUSION: Enteral albuterol may reduce the frequency of symptomatic bradycardia in patients with CSCI, resulting in less rescue therapy using chronotropic agents. LEVEL OF EVIDENCE: Therapeutic study, level IV.

Clinical utility of treprostinil in the treatment of pulmonary arterial hypertension: an evidence-based review.

Pulmonary arterial hypertension (PAH) remains a progressive disease without a cure, despite the development of several treatment options over the past several decades. Its management strategy consists of the endothelin receptor antagonists (ambrisentan, bosentan, macitentan), phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil), and prostacyclin analogs (epoprostenol, treprostinil, iloprost). Treprostinil, a stable prostacyclin analog, displays vasodilatory effects in the pulmonary vasculature, as well as antiplatelet aggregation properties. Clinical practice guidelines recommend oral endothelin receptor antagonist or phosphodiesterase inhibitor therapy in mild to moderate PAH. Epoprostenol is specifically suggested as first-line therapy in moderate to severe PAH patients (ie, World Health Organization/New York Heart Association functional class III-IV). However, treprostinil may be an alternative option in these severe PAH patients. The longer half-life and stability at room temperature with treprostinil may be associated with lower risk of pulmonary hemodynamic worsening as a result of abrupt infusion discontinuation and less frequent drug preparation. These characteristics make treprostinil an attractive alternative to continuous infusion of epoprostenol, due to convenience and patient safety. The purpose of this review is to evaluate the safety and efficacy of continuous infusion of treprostinil as well as the inhaled and oral routes of administration in PAH.

First-principles calculations of solid-state (17)O and (29)Si NMR spectra of Mg(2)SiO(4) polymorphs.

The nuclear magnetic resonance (NMR) shielding and electric field gradient (EFG) tensors of three polymorphs of Mg(2)SiO(4), forsterite (alpha-Mg(2)SiO(4)), wadsleyite (beta-Mg(2)SiO(4)) and ringwoodite (gamma-Mg(2)SiO(4)), have been calculated using a density functional theory (DFT) approach with a planewave basis set and pseudopotential approximation. These Mg(2)SiO(4) polymorphs are the principal components of the Earth down to depths of 660 km and have been proposed as the hosts of water in the Earth's upper mantle and transition zone. A comparison of our calculations with single-crystal spectroscopic data in the literature for the alpha-polymorph, forsterite, shows that both the magnitude and orientation of the shielding and EFG tensors for O and Si can be obtained with sufficient accuracy to distinguish subtle differences in atomic positions between published structures. We compare calculated (17)O MAS NMR quadrupolar powder lineshapes directly with experimental lineshapes and show that we are able to reproduce them within the precision with which the NMR parameters may be determined from multi-parameter fitting. The relatively small amounts of sample available for the beta- and gamma-polymorphs, arising from the high pressures required for synthesis, has hindered the extraction of NMR parameters in previous work. The application of DFT calculations to these high-pressure polymorphs confirms previous spectral assignments, and provides deeper insight into the empirical correlations and observations reported in the literature. These first-principles methods are highly promising for the determination of local bonding in more complex materials, such as the hydrated forms of Mg(2)SiO(4), by aiding analysis of their multinuclear NMR spectra.

17O and 29Si NMR parameters of MgSiO3 phases from high-resolution solid-state NMR spectroscopy and first-principles calculations.

The 29Si and 17O NMR parameters of six polymorphs of MgSiO3 were determined through a combination of high-resolution solid-state NMR and first-principles gauge including projector augmented wave (GIPAW) formalism calculations using periodic boundary conditions. MgSiO3 is an important component of the Earth's mantle that undergoes structural changes as a function of pressure and temperature. For the lower pressure polymorphs (ortho-, clino-, and protoenstatite), all oxygen species in the 17O high-resolution triple-quantum magic angle spinning (MAS) NMR spectra were resolved and assigned. These assignments differ from those tentatively suggested in previous work on the basis of empirical experimental correlations. The higher pressure polymorphs of MgSiO3 (majorite, akimotoite, and perovskite) are stabilized at pressures corresponding to the Earth's transition zone and lower mantle, with perovskite being the major constituent at depths >660 km. We present the first 17O NMR data for these materials and confirm previous 29Si work in the literature. The use of high-resolution multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments allows us to resolve distinct oxygen species, and full assignments are suggested. The six polymorphs exhibit a wide variety of structure types, providing an ideal opportunity to consider the variation of NMR parameters (both shielding and quadrupolar) with local structure, including changes in coordination number, local geometry (bond distances and angles), and bonding. For example, we find that, although there is a general correlation of increasing 17O chemical shift with increasing Si-O bond length, the shift observed also depends upon the exact coordination environment.

High-resolution 17O NMR spectroscopy of wadsleyite (beta-Mg2SiO4).

The sensitivity of high-resolution 17O (I = 5/2) NMR spectroscopy of solids has advanced significantly in recent years. Here, we show that excellent results are now obtainable from milligram quantities of 17O-enriched materials, thereby allowing the technique to be applied to silicate phases synthesized under very high pressures in a multiple-anvil apparatus. We report the first 17O NMR study of beta-Mg2SiO4 (9.6 mg of 35% 17O-enriched material, synthesized at p = 16 GPa and T = 1873 K), a dense phase believed to have a significant role in the Earth's mantle. Using STMAS at magnetic fields of B0 = 9.4 and 11.7 T and MQMAS at B0 = 18.8 T, we have resolved and assigned all four crystallographically distinct O sites and determined their chemical shift and quadrupolar parameters.

A furnace design for XANES spectroscopy of silicate melts under controlled oxygen fugacities and temperatures to 1773 K.

A controlled-atmosphere furnace has been constructed for X-ray absorption spectroscopy experiments under imposed oxygen fugacities at temperatures up to 1773 K. The use of the furnace is demonstrated in a study of the oxidation state of Cr in a basaltic silicate melt (mid-ocean ridge basalt) by K-edge XANES spectroscopy. This is the first time the Cr(2+)/Cr(3+) ratio has been identified directly in an Fe-bearing melt. At typical terrestrial oxygen fugacities around half the Cr is present as Cr(2+), even though this oxidation state has never been identified in a terrestrial material and only Cr(3+) is observed after quenching to a glass. Cr(2+) oxidizes to Cr(3+) on cooling in the presence of Fe(3+) according to the electron exchange reaction Cr(2+) + Fe(3+) --> Cr(3+) + Fe(2+). This illustrates the importance of the in situ determination of metal oxidation states in melts.