Nanoscale lattice dynamics in hexagonal boron nitride moiré superlattices.

Twisted two-dimensional van der Waals (vdW) heterostructures have unlocked a new means for manipulating the properties of quantum materials. The resulting mesoscopic moiré superlattices are accessible to a wide variety of scanning probes. To date, spatially-resolved techniques have prioritized electronic structure visualization, with lattice response experiments only in their infancy. Here, we therefore investigate lattice dynamics in twisted layers of hexagonal boron nitride (hBN), formed by a minute twist angle between two hBN monolayers assembled on a graphite substrate. Nano-infrared (nano-IR) spectroscopy reveals systematic variations of the in-plane optical phonon frequencies amongst the triangular domains and domain walls in the hBN moiré superlattices. Our first-principles calculations unveil a local and stacking-dependent interaction with the underlying graphite, prompting symmetry-breaking between the otherwise identical neighboring moiré domains of twisted hBN.

A mechanistically-distinct approach to fluorescence visualization of singlet oxygen.

We describe fluorescence detection of 1O2 by a new strategy. Oxidation of a non-fluorescent sulfoxide by 1O2 occurs via intramolecular oxygen atom transfer in a reactive persulfoxide intermediate. The resulting sulfone shows significantly enhanced (>50-fold) emission. This approach complements known methods, and is being extended to biological 1O2 imaging.

Engineering the Structural and Electronic Phases of MoTe2 through W Substitution.

MoTe2 is an exfoliable transition metal dichalcogenide (TMD) that crystallizes in three symmetries: the semiconducting trigonal-prismatic 2H- or α-phase, the semimetallic and monoclinic 1T'- or ß-phase, and the semimetallic orthorhombic γ-structure. The 2H-phase displays a band gap of ∼1 eV making it appealing for flexible and transparent optoelectronics. The γ-phase is predicted to possess unique topological properties that might lead to topologically protected nondissipative transport channels. Recently, it was argued that it is possible to locally induce phase-transformations in TMDs, through chemical doping, local heating, or electric-field to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements. The combination of semiconducting and topological elements based upon the same compound might produce a new generation of high performance, low dissipation optoelectronic elements. Here, we show that it is possible to engineer the phases of MoTe2 through W substitution by unveiling the phase-diagram of the Mo1-xWxTe2 solid solution, which displays a semiconducting to semimetallic transition as a function of x. We find that a small critical W concentration xc ∼ 8% stabilizes the γ-phase at room temperature. This suggests that crystals with x close to xc might be particularly susceptible to phase transformations induced by an external perturbation, for example, an electric field. Photoemission spectroscopy, indicates that the γ-phase possesses a Fermi surface akin to that of WTe2.

Thyrotrophin-releasing hormone decreases feeding and increases body temperature, activity and oxygen consumption in Siberian hamsters.

Thyrotrophin-releasing hormone (TRH) is known to play an important role in the control of food intake and energy metabolism in addition to its actions on the pituitary-thyroid axis. We have previously shown that central administration of TRH decreases food intake in Siberian hamsters. This species is being increasingly used as a physiological rodent model in which to understand hypothalamic control of long-term changes in energy balance because it accumulates fat reserves in long summer photoperiods, and decreases food intake and body weight when exposed to short winter photoperiods. The objectives of our study in Siberian hamsters were: (i) to investigate whether peripheral administration of TRH would mimic the effects of central administration of TRH on food intake and whether these effects would differ dependent upon the ambient photoperiod; (ii) to determine whether TRH would have an effect on energy expenditure; and (iii) to investigate the potential sites of action of TRH. Both peripheral (5-50 mg/kg body weight; i.p.) and central (0.5 microg/ml; i.c.v.) administration of TRH decreased food intake, and increased locomotor activity, body temperature and oxygen consumption in the Siberian hamster, with a rapid onset and short duration of action. Systemic treatment with TRH was equally effective in suppressing feeding regardless of ambient photoperiod. The acute effects of TRH are likely to be centrally mediated and independent of its role in the control of the production of thyroid hormones. We conclude that TRH functions to promote a catabolic energetic state by co-ordinating acute central and chronic peripheral (thyroid-mediated) function.

Modulating the efficiency of Ru(II) luminescence via ion binding-induced conformational restriction of bipyridyl ligands.

Conformational restriction imposed upon Ru(bpy)32+ crown ether complexes by metal ion binding leads to enhanced luminescence.

New molybdenum catalysts for alkyl olefin epoxidation. Their implications for the mechanism of oxygen atom transfer.

We report here the design, synthesis, and characterization of new (dioxo)Mo(VI) epoxidation catalysts based on monoanionic tridentate ligands. Two important features distinguish these catalysts from those previously reported. First, their coordination environment remains well-defined during the epoxidation reaction. Second, the ligand design does not permit simultaneous coordination of olefin and alkyl hydroperoxide. Based on the study of these new catalysts, we conclude that direct oxygen atom transfer from coordinated alkyl peroxide to olefin remains the simplest mechanism consistent with the available data. We discuss literature discrepancies in this regard.

Impairment in cognitive and exercise performance during prolonged antarctic residence: effect of thyroxine supplementation in the polar triiodothyronine syndrome.

Humans who work in Antarctica display deficits in cognition, disturbances in mood, increased energy requirements, a decline of thyroid hormone products, and an increase of serum TSH. We compared measurements in 12 subjects, before deployment (baseline), with 11 monthly studies during Antarctic residence (AR). After 4 months of AR (period 1), half of the subjects (T(4) group) received L-thyroxine [64 nmol.day(-)(1) (0.05 mg.day(-)(1))]; and the other half, a placebo (placebo group) for the next 7 months of AR (period 2). During period 1, there was a 12.3 +/- 5.1% (P < 0.03) decline on the matching-to-sample (M-t-S) cognitive task and an increase in depressive symptoms, compared with baseline. During the intervention in period 2, M-t-S scores for the T(4)-treated group returned to baseline values; whereas the placebo group, in contrast, showed a reduced M-t-S score (11.2 +/- 1.3%; P < 0.0003) and serum free T(4) (5.9 +/- 2.4%; P < 0.02), compared with baseline. The change in M-t-S score was correlated with the change in free T(4) (P < 0.0003) during both periods, and increases in serum TSH preceded worsening scores in depression, tension, anger, lack of vigor, and total mood disturbance (P < 0.001) during period 2. Additionally, the submaximal work rate for a fixed O(2) use decreased 22.5 +/- 4.9% in period 1 and remained below baseline in period 2 (25.2 +/- 2.3%; P < 0.005) for both groups. After 4 months of AR, the L-thyroxine supplement was associated with improved cognition, which seems related to circulating T(4). Submaximal exercise performance decrements, observed during AR, were not changed with this L-thyroxine dose.

Circannual pattern of hypothalamic-pituitary-thyroid (HPT) function and mood during extended antarctic residence.

The seasonal variation in thyroid function and mood was examined in 10 men and two women who spent the 1997 or 1998 austral winter at McMurdo Station, Antarctica. Serum samples of TSH, free T3 and free T4 were collected each month over a 10-month period (October-August), along with responses to the Profile of Mood States (POMS) and the Center for Epidemiologic Studies - Depression (CES-D) Scale. Both TSH and mood (a summary score created from the POMS depression, anger, fatigue and confusion subscales) exhibited a circannual pattern with peaks during the months of November and July and a trough during the months of March and April. High levels of tension-anxiety and confusion were preceded by declines in free T3 and T4. However, increases in tension-anxiety and total mood disturbance also preceded a decline in free T3 levels, suggesting a feedback of mood on T3 levels. Levels of free T4 were independently associated with preceding increases in anger scores. These results support the hypothesis that the symptoms characteristic of the winter-over syndrome is a state of relative CNS hypothyroidism. This model of seasonal variation in thyroid function and mood also has implications for an understanding of potential mechanisms underlying the association between latitude and SAD or S-SAD.

Convenient synthesis and transformation of 2,6-dichloro-4-iodopyridine.

We describe a convenient scalable synthesis of 2,6-dichloro-4-iodopyridine and demonstrate its utility by stepwise elaboration to a number of 2,4,6-trisubstituted pyridines. [reaction: see text]

Enantioselective epoxide hydrolysis: catalysis involving microbes, mammals and metals.

Although alkyl epoxides are difficult to synthesize in enantiomerically pure form they can often be prepared by the enantioselective hydrolysis of racemic epoxide. The best methods for this transformation are all catalytic and they illustrate the complementary role that biological and synthetic catalysts can play in organic chemistry.

Fluorescence assays for screening combinatorial libraries of drug candidates.

The following subjects will be addressed sequentially: recent advances in the application of the green fluorescent protein (GFP) to monitoring biological processes; a new fluorescent reporter for monitoring b-lactamase expression; a new fluorescent reporter for monitoring membrane potential; and, some wild speculation about the future.

Intrathoracic biopsies, pulmonary wedge excision, and management of pleural disease: is video-assisted closed chest surgery the approach of choice?

Few studies define differences between video-assisted thoracic surgery (VATS) over conventional posterolateral thoracotomy (PLT) for limited procedures. We propose that length of hospital stay (LOS), the days of requirement for narcotic analgesia (DNA) by epidural, intravenous, intramuscular, or oral administration, operating time (OT), return to pre-operative functional status (RT), and the achievement of a therapeutic objective are not dependent on the approach taken (VATS or PLT) for selected diagnostic and therapeutic procedures for pleural, pulmonary, or mediastinal disease. A total of 102 consecutive patients (52 males, 50 females, age 48 +/- 16 years) were eligible to undergo (VATS) for diagnosis and/or treatment of lung lesions, pleural disease, persistent pneumothorax or mediastinal lesions. Seventy-two underwent VATS only and 21, conventional posterolateral thoracotomy (PLT). Nine VATS patients were converted to PLT, for completion of lobectomies after VATS staging of resectable malignancy (6), extensive decortication (2), and giant bullectomy (1). VATS and PLT were compared according to OT, LOS, DNA, RT, achievement of diagnostic and/or therapeutic objective, and morbidity and mortality. After VATS only and PLT only, LOS was 4.8 +/- 2.7 and 7.8 +/- 4.6 days, respectively (P < .03). DNA was 3.4 +/- 2.1 and 6.1 +/- 3.6 days after surgery, respectively (P < .01). RT was 12.0 +/- 11.2 and 21.4 +/- 9.5 days, respectively (P < .01). OT was 80 +/- 34 and 95 +/- 32 minutes, respectively (P = ns). Among 9 conversions from VATS to PLT LOS was 11.4 +/- 5.5, DNA 6.9 +/- 4.4 and RT 20.1 +/- 6.0 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthetic and biological catalysts in chemical synthesis: how to assess practical utility.

Enzymes, synthetic catalysts, and catalytic antibodies can all be used to perform asymmetric reactions, but their practical utility is not always easy to evaluate. Criteria with which to compare such catalysts are proposed and illustrated for asymmetric epoxidation, a reaction to which all three approaches have been applied.