Exploring Dynamics and Cage–Guest Interactions in Clathrate Hydrates Using Solid-State NMR

Interactions between guest molecules and the water cages in clathrates are dominated by isotropic van der Waals forces at low temperatures because the cage structures satisfy the hydrogen bonding propensity of the water. However, above 200 K the water molecules become more labile and may interact strongly with the guests through hydrogen bonding. In this work we compare the dynamics of tetrahydrofuran (THF) and cyclopentane (CP) guests in the hydrate cages above 200 K. Since THF can form hydrogen bonds while CP cannot, the dynamics provide insight into host–guest hydrogen bonding. We use magic angle spinning (MAS) solid-state NMR to measure proton spin–lattice relaxation times (<i>T</i>₁) of the guests as a function of temperature and find that the activation barrier to the motion of THF molecules is 4.7 kcal/mol (19.7 kJ/mol) at temperatures above 200 K. This is almost 5 times higher than the barrier at lower temperatures. In contrast, the barrier to guest motion in CP hydrate is found to be about 0.67 kcal/mol (2.8 kJ/mol), which agrees well with data at lower temperatures. These results demonstrate that hydrogen bonding interactions between the THF guest and the clathrate cage are significant above 200 K due to the host lattice mobility

Cleavage of Lignin-Derived 4‑O‑5 Aryl Ethers over Nickel Nanoparticles Supported on Niobic Acid-Activated Carbon Composites

Cleavage of lignin-derived 4-O-5 aryl ethers has been conducted over nickel nanoparticles supported on niobic acid-activated carbon composite under mild conditions. The hydrated niobic acid has been successfully supported and well dispersed on activated carbon. Due to the coexisting Brönsted and Lewis acid sites on the hydrated niobic oxide, the Ni/<i>x</i>NbAC catalysts exhibited higher activities for cleavage of C–O ether bonds and dehydration than those of the Ni/AC catalyst. With increasing content of niobic acid, a larger amount of O-free alkane is obtained owing to niobic acid-promoted removal of oxygen from lignin-derived aryl ethers. The cleavage of C–O ether bonds and dehydration of cyclohexanol to cyclohexane are both favored at high temperature. The direct cleavage of the 4-O-5 aryl ether bond can also be achieved under low H₂ pressure, forming phenol and benzene as intermediates, followed by hydrodeoxygenation of phenol to cyclohexane

Isobaric Vapor–Liquid Equilibrium Experiment of N‑Propanol and N‑Propyl Acetate at 101.3 kPa

N-Propanol (NPA) and n-propyl acetate (NPAC) can form an azeotrope under normal pressure, so their separation cannot be carried out by conventional distillation. Therefore, 1-butyl-3-methylimidazole acetate ([BMIM][OAC]) and ethylene glycol (EG) were selected as entrainers for extractive distillation of the two substances. Isobaric vapor–liquid equilibrium data were obtained by experiments of NPA + NPAC, NPA + NPAC + [BMIM][OAC], and NPA + NPAC + EG at normal pressure; the experimental results showed that the separation effect of [BMIM][OAC] is significantly better than that of EG. Finally, the data were fitted and correlated with the NRTL model. The ARD (average relative deviation) of NPA + NPAC, NPA + NPAC + [BMIM][OAC], and NPA + NPAC + EG is less than 5%, indicating that the NRTL model has good applicability to the vapor–liquid system

The early Cambrian <i>Kuamaia lata</i>, an artiopodan euarthropod with a raptorial frontal appendage

Abstract Phylogenetic analysis demonstrates that Kuamaia lata, a helmetiid euarthropod from the lower Cambrian (Series 2, Stage 3) Chengjiang Konservat-Lagerstätte, nests robustly within Artiopoda, the euarthropod clade including trilobitomorphs. Microtomography of new specimens of K. lata reveals details of morphology, notably a six-segmented head and raptorial frontal appendages, the latter contrasting with filiform antennae considered to be a diagnostic character of Artiopoda. Phylogenetic analyses demonstrate that a raptorial frontal appendage is a symplesiomorphy for upper stem-group euarthropods, retained across a swathe of tree space, but evolved secondarily in K. lata from an antenna within Artiopoda. The phylogenetic position of K. lata adds support to a six-segmented head being an ancestral state for upper stem- and crown-group euarthropods

Particulate matter and hospital admissions for stroke in Beijing, China: modification effects by ambient temperature

Background-—The impact of particulate matter (PM) on stroke may vary by particle size, stroke subtype, and patient characteristics and temperature. We examined the association of stroke admissions with PM in different subgroups in Beijing, China, during 2013–2014. Methods and Results-—A time-stratified case-crossover design was used to assess the relation between PM of different particle sizes and hospital admissions for ischemic and hemorrhagic stroke. Stratified analyses were performed by age, sex, and temperature. In total, there were 147 624 stroke admissions during the study period. In the whole-period analysis, both PM2.5 and PM10 were positively associated with ischemic stroke admissions on the day of hospital admission and negatively associated with ischemic stroke at lag2 and lag3 day. In warm days (>13.5°C), the odds ratios of ischemic stroke admissions were 2.071 (95% CI 1.959–2.190), 1.470 (95% CI 1.391–1.554), and 1.590 (95% CI 1.493–1.694) per IQR increase in the same-day PM2.5 (82.0 lg/ m3), PM2.5–10 (36.6 lg/m3), and PM10 (93.5 lg/m3), respectively. For hemorrhagic stroke, the corresponding values were 1.941 (95% CI 1.658–2.273), 1.590 (95% CI 1.366–1.851), and 1.527 (95% CI 1.278–1.826). The positive associations were also observed in the other lag structures and were higher than in cold days (≤13.5°C). Conclusions-—This study suggests that the associations of PM2.5, PM2.5–10, and PM10 with stroke admissions differed across levels of temperature. Short-term exposure to PM2.5, PM2.5–10, and PM10 was positively associated with hospital admissions for ischemic and hemorrhagic stroke on warm days (>13.5°C)

Predictive performance of the urine and plasma value of miR-21 for the progression of AKI.

<p>Receiver-operating characteristic (ROC) curves show the predictive performance of the clinical model, clinical model+urine miR-21, and clinical model+plasma miR-21. MiR-21 levels obtained from progressors (<i>n</i> = 39) and non-progressors (<i>n</i> = 41) of AKI group.</p

The early Cambrian Kylinxia zhangi and evolution of the arthropod head

The early Cambrian Kylinxia zhangi occupies a pivotal position in arthropod evolution, branching from the euarthropod stem lineage between radiodonts (Anomalocaris and relatives) and “great-appendage” arthropods.1,2 Its combination of appendage and exoskeletal features is viewed as uniquely bridging the morphologies of so-called “lower” and “upper” stem-group euarthropods.3,4 Microtomographic study of new specimens of Kylinxia refines and corrects previous interpretation of head structures in this species. Phylogenetic analyses incorporating new data reinforce the placement of Kylinxia in the euarthropod stem group but support new hypotheses of head evolution. The head of Kylinxia is composed of six segments, as in extant mandibulates, e.g., insects.5 In Kylinxia, these are an anterior sclerite associated with an unpaired median eye and paired lateral eyes (thus three rather than five eyes as was previously described1), deutocerebral frontal-most appendages, and four pairs of biramous appendages (rather than two pairs of uniramous appendages). Phylogenetic trees suggest that a six-segmented head in the euarthropod crown group was already acquired by a common ancestor with Kylinxia. The segmental alignment and homology of spinose frontal-most appendages between radiodonts and upper stem-group euarthropods6,7,8,9,10 is bolstered by morphological similarities and inferred phylogenetic continuity between Kylinxia and other stem-group euarthropods.</p

Performance characteristics of urine and plasma miR-21 as prognostic AKI biomarkers among patients with AKI at the time of sample collection (n = 80).

<p>PPV, positive predictive value; NPV, negative predictive value; RRT, renal replacement therapy; AKIN, Acute Kidney Injury Network; ICU, intensive care unit.</p>a<p>The percentage and number of patients who were above and equal to the best PPV cut-off.</p>b<p>Death defined as 30 day in-hospital mortality.</p>c<p>Defined as discharge >10 days from sample collection.</p>d<p>Defined as length of ICU stay >4 days.</p

Performance of urine miR-21 and plasma miR-21 for established AKI detection.

<p>Receiver-operating characteristic (ROC) curves show the distinguishing performance of urine and plasma miR-21 levels that obtained from 40 patients in the non AKI group and 80 patients in the AKI group.</p

Predictive power for AKI progression (urine and plasma miR-21 versus routine measurements).

<p>SCr, plasma creatinine; AUC, area under the curve; CI, confidence interval; OR, odds ratio.</p>a<p>Adjusted for the clinical mode, which include Cleveland score, preoperative eGFR(30–60,60–90,and >90,), operation time, and CPB time >120minutes (clinical model AUC = 0.75).</p>b<p>Defined as percent change in postoperative plasma creatinine from baseline at the time of AKI diagnosis.</p>c<p>Proteinuria by dipstick urinalysis, heavy (≥2+).</p