Enantiopure molecules form apparently racemic monolayers of chiral cyclic pentamers.

Ultra-high vacuum scanning tunneling microscopy (UHV-STM) was used to investigate two related molecules pulse-deposited onto Au(111) surfaces: indoline-2-carboxylic acid and proline (pyrrolidine-2-carboxylic acid). Indoline-2-carboxylic acid and proline form both dimers and C5-symmetric "pinwheel" pentamers. Enantiomerically pure S-(-)-indoline-2-carboxylic acid and S-proline were used, and the pentamer structures observed for both were chiral. However, the presence of apparently equal numbers of 'right-' and 'left-handed' pinwheels is contrary to the general understanding that the chirality of the molecule dictates supramolecular chirality. A variety of computational methods were used to elucidate pentamer geometry for S-proline. Straightforward geometry optimization proved difficult, as the size of the cluster and the number of possible intermolecular interactions produced an interaction potential with multiple local minima. Instead, the Amber force field was used to exhaustively search all of phase space for chemically reasonable pentamer structures, producing a limited number of candidate structures that were then optimized as gas-phase clusters using density functional theory (DFT). The binding energies of the two lowest-energy pentamers on the Au(111) surface were then calculated by plane-wave DFT using the VASP software, and STM images predicted. These calculations indicate that the right- and left-handed pentamers are instead two different polymorphs.

Observation of Dirac monopoles in a synthetic magnetic field.

Magnetic monopoles--particles that behave as isolated north or south magnetic poles--have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac's 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10-13). Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.

Self-assembly of hydrogen-bonded two-dimensional quasicrystals.

The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate. Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups. Here we use scanning tunnelling microscopy to study self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pentamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 ångströms.

Structural Polymorphism as the Result of Kinetically Controlled Self-Assembly.

Traditionally, the goal of self-assembly and supramolecular chemistry is to engineer an equilibrium structure with a desired geometry and functionality; this is achieved through careful choice of molecular monomers, growth conditions, and substrate. Supramolecular assemblies produced under nonequilibrium conditions, in contrast, can form metastable structures with conformations quite different from those accessible in equilibrium self-assembly. The study of nonequilibrium growth of clusters potentially impacts the study of nucleation in atmospheric aerosols, nucleation in organic crystallization, and mesoscale organization for systems ranging from biological molecules to molecular electronics. In our experiments, we prepare surface monolayers of small organic and organometallic molecules through direct injection of a solution onto a substrate in high vacuum. During this process, the rapid evaporation of small solution droplets in high vacuum can lead to nonequilibrium growth conditions. The resulting structures are then characterized by scanning tunneling microscopy. Among the features observed in these experiments are cyclic, hydrogen-bonded pentamers. For carboxylic acids, the two-molecule ring dimer is the common binding motif. Large, cyclic hydrogen-bonded systems are uncommon, especially so for rings with five members. Despite this, pentagonal clusters appear to be a general phenomenon for systems containing adjacent strong and weak hydrogen-bonding elements on five-member aromatic rings. Regular pentamers have been observed as metastable structures for ferrocenecarboxylic acid, indole-2-carboxylic acid, and isatin (1-H-indole-2,3-dione). Electronic structure calculations confirm the relative stability of these structures with respect to the dimer or catemer conformations which are observed in the solid-state crystal structures. For ferrocenecarboxylic acid, cyclic pentamers undergo further self-assembly, resulting in long-range order in conjunction with local 5-fold rotational symmetry. This system is the first reported self-assembled molecular quasicrystal, and it remains the only example of a hydrogen-bonded quasicrystal. This supramolecular structure forms as a result of the cocrystallization of hydrogen-bonded cyclic pentamers with intercalated molecular dimers. The shared bonding to a single dimer is responsible for locking the adjacent pentamers in specific distances and orientations, which produces the quasicrystal. Careful analysis of experimental data provides evidence that, in some cases, metastable clusters are formed in solution and then subsequently adsorb on the surface. This is a unusual mechanism for supramolecular assembly, and it has important implications for understanding questions in crystal growth, namely: what the initial stages of crystal growth are as molecules are first precipitating from solution; what role the solvent plays in determining crystal structure; and whether solvent-mediated clustering is important in the broader phenomenon of solid-state polymorphism.

Prolonged QT dispersion in Subclinical Hypothyroid Females: A Study in University Teaching Hospital in Central Nepal.

Background QT dispersion is a simple index derived from 12 lead ECG; its prolongation has been shown to be associated with increased arrhythmia risk. Increased cardiovascular risks, particularly occurrence of the malignant arrhythmias are a common finding in patients with subclinical hypothyroidism. This increased arrhythmia risk is found to be higher mainly in patients with TSH level more than 10 milli international unit per liter. Objective To assess QT dispersion among subclinical hypothyroid and euthyroid Nepalese females aged 20-59 years attending general practice out patient department of centrally located University Teaching Hospital from November 2016 to April 2017. Method Forty-three newly detected subclinical hypothyroid females and forty-one euthyroid females were enrolled. Resting electrocardiogram (ECG) was performed. QT dispersion was analyzed from ECG and corrected for heart rate using Framingham correction formula. Independent sample t-test was applied to compare mean QT dispersion between two groups. Pearson correlation test was used to examine the association between QT dispersion and TSH level. Result Mean QT dispersion for sub-clinical hypothyroid group was 75.35 ± 43.82 whereas mean QT dispersion for euthyroid group was 59.51 ± 22.13, with p value 0.041. A weak association between QT dispersion and TSH level was seen with correlation factor of 0.23. Conclusion The result showed prolongation of QT dispersion in sub-clinical hypothyroid group and weak positive correlation between TSH level and QT dispersion suggesting arrhythmia risk in subclinical hypothyroid females.

24-h personal monitoring of exposure to Power Frequency Magnetic Fields in adolescents - Results of a National Survey.

OBJECTIVES: The aim of this exposure assessment study was to gain information about the exposure levels of adolescents in Israel to power frequency (50Hz) magnetic fields (MF) through personal monitoring, and to provide reliable data for national policy development. METHODS: 84 adolescents, 6-10th grade students, carried an EMDEX II meter attached to their body for 24h. The meter recorded the MF every 1.5s. The students documented their activities and microenvironments, such as apartment (awake or asleep), school, transportation, open public areas and other indoor environments. RESULTS: The geometric mean (GM) of the daily time weighted average (TWA) of all the participants was 0.059 µT (STD = 1.83). This result is similar to those of personal exposure surveys conducted in the UK (GM 0.042-0.054µT), but lower than levels found in the US (GM 0.089 - 0.134µT). The arithmetic mean was 0.073µT, 23% higher than the GM. Fields were lowest at school (GM 0.033µT), and average outdoor exposures were higher than indoor ones. 3.6% of the participants were exposed to daily TWA above 0.2µT. The typical time spent above 0.2µT ranged from few minutes to few hours. The time spent above 0.4µT and 1µT were much shorter, around 1-15min and from few seconds to 2min, respectively. Momentary peaks ever recorded were in the range of 0.35-23.6µT CONCLUSIONS: Exposure of adolescents in Israel is similar to data reported in other countries, being below 0.1µT for the vast majority, with very few average exposures above 0.2µT. Analysis of the different microenvironments allows for a cost-effective and equitable policy development.

Hydrogen-bonded clusters of 1, 1'-ferrocenedicarboxylic acid on Au(111) are initially formed in solution.

Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

Synthesis of a Neutral Mixed-Valence Diferrocenyl Carborane for Molecular Quantum-Dot Cellular Automata Applications.

The preparation of 7-Fc(+) -8-Fc-7,8-nido-[C2 B9 H10 ](-) (Fc(+) FcC2 B9 (-) ) demonstrates the successful incorporation of a carborane cage as an internal counteranion bridging between ferrocene and ferrocenium units. This neutral mixed-valence Fe(II) /Fe(III) complex overcomes the proximal electronic bias imposed by external counterions, a practical limitation in the use of molecular switches. A combination of UV/Vis-NIR spectroscopic and TD-DFT computational studies indicate that electron transfer within Fc(+) FcC2 B9 (-) is achieved through a bridge-mediated mechanism. This electronic framework therefore provides the possibility of an all-neutral null state, a key requirement for the implementation of quantum-dot cellular automata (QCA) molecular computing. The adhesion, ordering, and characterization of Fc(+) FcC2 B9 (-) on Au(111) has been observed by scanning tunneling microscopy.

Factors influencing parental consent for participation in clinical research involving their children in Egypt.

Factors affecting parents' decision to involve their children in clinical research have not been studied in all cultural backgrounds. We aimed to explore the attitudes and beliefs influencing parents' decision to involve their children in clinical research in Mansoura, Egypt. Of 523 families approached, 357 filled the questionnaire. Only 98 (27.5%) parents consented to involve their child in clinical research. The children of consenters were significantly older than refusers: 8.6 (SD 7.2) versus 2.6 (SD 1.2) years. Factors favouring consent were: research of benefit to child (84.7%), enough explanation about the benefits (40.8%) and to learn more about child's condition (29.6%). Factors favouring refusal were: use of new drugs or vaccines (89.6%) and invasive procedures (84.2%). Parents' rate of consent was positively correlated with the research being non-invasive and the belief that research was of benefit to their child and negatively correlated with belief that refusal may negatively affect the care provided to their child.

Normothermic acellular ex vivo liver perfusion reduces liver and bile duct injury of pig livers retrieved after cardiac death.

We compared cold static with acellular normothermic ex vivo liver perfusion (NEVLP) as a novel preservation technique in a pig model of DCD liver injury. DCD livers (60 min warm ischemia) were cold stored for 4 h, or treated with 4 h cold storage plus 8 h NEVLP. First, the livers were reperfused with diluted blood as a model of transplantation. Liver injury was determined by ALT, oxygen extraction, histology, bile content analysis and hepatic artery (HA) angiography. Second, AST levels and bile production were assessed after DCD liver transplantation. Cold stored versus NEVLP grafts had higher ALT levels (350 ± 125 vs. 55 ± 35 U/L; p < 0.0001), decreased oxygen extraction (250 ± 65 mmHg vs. 410 ± 58 mmHg, p < 0.01) and increased hepatocyte necrosis (45% vs. 10%, p = 0.01). Levels of bilirubin, phospholipids and bile salts were fivefold decreased, while LDH was sixfold higher in cold stored versus NEVLP grafts. HA perfusion was decreased (twofold), and bile duct necrosis was increased (100% vs. 5%, p < 0.0001) in cold stored versus NEVLP livers. Following transplantation, mean serum AST level was higher in the cold stored versus NEVLP group (1809 ± 205 U/L vs. 524 ± 187 U/L, p < 0.05), with similar bile production (2.5 ± 1.2 cc/h vs. 2.8 ± 1.4 cc/h; p = 0.2). NEVLP improved HA perfusion and decreased markers of liver duct injury in DCD grafts.