Carboranes as model hypercarbon systems; structural and bonding patterns in selected isoelectronic closo-borane and carborane systems; [BnHn](2-), [1-CBn-1Hn](-) and 1,n-C2Bn-2Hn (n=5, 6, 7, 10 or 12)

Computations have been carried out on the title boranes and carboranes, model hypercarbon cluster systems chosen to explore how effectively an individual carbon atom, whilst bonding by a normal 2-electron 2-centre bond to an exo-hydrogen atom, can also bond to sets of three, four or five equivalent boron atoms within a series of carborane clusters which have carbon atoms in axial sites of C3v, C4v or C5v local symmetry. The calculated interatomic distances and bond orders and CH and BH group charges are reported, and the manner in which the introduction of CH units to replace BH− units in closo-borane cages perturbs the distribution of the skeletal electrons in these clusters is discussed

19F and 13C GIAO-NMR chemical shifts for the identification of perfluoro-quinoline and -isoquinoline derivatives

Reaction of perfluoroquinoline 1 and perfluoroisoquinoline 2 with benzylamine gave mono- and di-aminated quinoline and isoquinoline systems, respectively, depending upon the reaction conditions by selective SNAr processes. Optimised model geometries of the aminated derivatives at MP2/6-31G* were in very good agreement with available X-ray crystallographic data and were used to compute 19F and 13C GIAO-NMR shifts. Comparison with observed 19F and 13C NMR shifts give excellent correlations, indicating that 19F and 13C GIAO-NMR computations are powerful tools in structurally identifying polyfunctional, polycyclic perfluoroheteroaromatic compounds and aiding NMR resonance assignment

Saxion Emission from SN1987A

We study the possibility of emission of the saxion, a superpartner of the axion, from SN1987A. The fact that the observed neutrino pulse from SN1987A is in excellent agreement with the current theory of supernovae places a strong bound on the energy loss into any non-standard model channel, therefore enabling bounds to be placed on the decay constant, f_a, of a light saxion. The low-energy coupling of the saxion, which couples at high energies to the QCD gauge field strength, is expected to be enhanced from QCD scaling, making it interesting to investigate if the saxion could place stronger bounds on f_a than the axion itself. Moreover, since the properties of the saxion are determined by f_a, a constraint on this parameter can be translated into a constraint on the supersymmetry breaking scale. We find that the bound on f_a from saxion emission is comparable with the one derived from axion emission due to a cancellation of leading-order terms in the soft-radiation expansion.Comment: 18 pages, 2 figures; minor changes, typos corrected, version to appear in JHE

Common gauge origin of discrete symmetries in observable sector and hidden sector

An extra Abelian gauge symmetry is motivated in many new physics models in both supersymmetric and nonsupersymmetric cases. Such a new gauge symmetry may interact with both the observable sector and the hidden sector. We systematically investigate the most general residual discrete symmetries in both sectors from a common Abelian gauge symmetry. Those discrete symmetries can ensure the stability of the proton and the dark matter candidate. A hidden sector dark matter candidate (lightest U-parity particle or LUP) interacts with the standard model fields through the gauge boson Z', which may selectively couple to quarks or leptons only. We make a comment on the implications of the discrete symmetry and the leptonically coupling dark matter candidate, which has been highlighted recently due to the possibility of the simultaneous explanation of the DAMA and the PAMELA results. We also show how to construct the most general U(1) charges for a given discrete symmetry, and discuss the relation between the U(1) gauge symmetry and R-parity.Comment: Version to appear in JHE

A novel, efficient synthesis of N-aryl pyrroles via reaction of 1-boronodienes with arylnitroso compounds

A one-pot hetero-Diels–Alder/ring contraction cascade is presented from the reaction of 1-boronodienes and arylnitroso derivatives to derive N-arylpyrroles in moderate to good yields (up to 82%)

An experimental and computational approach to understanding the reactions of acyl nitroso compounds in [4+2]-cycloadditions

Catalytic aerobic oxidation of phenyl hydroxycarbamate 1 and 1-hydroxy-3-phenylurea 2 using CuCl2 and 2-ethyl-2-oxazoline in methanol gave acyl nitroso species in situ, which were trapped in nitroso-Diels–Alder (NDA) reactions with various dienes to afford the corresponding cycloadducts in high yields (90–98%). Competing ene products were also present for dienes containing both alkene π-bonds and allylic σ-bonds, and the ene yields are higher with 1 than with 2. The use of the chiral hydroxamic acid, (R)-1-hydroxy-3-(1-phenylethylurea) 3 (same conditions) gave NDA cycloadducts in high yields (97–99%) with no ene product from 2,3-dimethyl-1,3-butadiene. NDA cycloadducts were not obtained from other hydroxamic acid analogues [RCONHOH (R = PhCH2 4; Ph(CH2)2 5; Ph(CH2)3 6; Ph(CH2)4 7; Ph 8; 2-pyridyl 9; 3-pyridyl 10] with various dienes using copper-oxidation but rather were obtained using sodium periodate, resulting in variable NDA yields (13–51%) from hydroxamic acids 1–10 with cyclohexa-1,3-diene and 2,3-dimethyl-1,3-butadiene (several cycloadducts characterized by X-ray crystallography). The NDA and nitroso-ene reaction pathways of nitroso intermediates with dienes were mapped by DFT computations (B3LYP/6-31G*), which showed that the acyl nitroso species are super-reactive and that activation energies in the NDA processes are lower than the isomerization barriers between some cis- and trans-butadienes

Chiral probe development for circularly polarised luminescence: comparative study of structural factors determining the degree of induced CPL with four heptacoordinate europium(III) complexes

A series of bright, europium(III) complexes has been prepared based on an achiral heptadentate triazacyclononane ligand bearing two strongly absorbing, coordinated aralkynyl pyridyl moieties. The binding of chiral carboxylates, including α-hydroxy acids such as lactate and mandelate, has been monitored by emission spectroscopy and is signalled by the switching on of strong circularly polarised emission. In each case, an R-chiral carboxylate gave rise to emission typical of a Δ complex, most clearly shown in the form of the ΔJ = 4 transition manifold around 700 nm. Variations in the sign and magnitude of the CPL allow the enantiomeric purity and absolute configuration of the acid to be assessed in a sample. Analysis of the relative energies of the parent aqua complexes and their stereoisomeric adducts has been aided by lifetime measurements and density functional theory calculations

Crystal structures of the carborane dianions, [1,4-(PhCB10H10C)2C6H4]2- and [1,4-(PhCB10H10C)2C6F4]2-, and the stabilizing role of the para-phenylene unit on unusual 2n+3 SE clusters

While carboranes with 2 n+2 and 2 n+4 (n=number of skeletal atoms) skeletal electrons (SE) are widely known, little has been reported on carboranes with odd SE numbers. Electrochemical measurements on two-cage assemblies, where two C-phenyl-ortho-carboranyl groups are linked by a para-phenylene or a para-tetrafluorophenylene bridge, revealed two well separated and reversible two-electron reduction waves indicating formation of stable dianions and tetraanions. The salts of the dianions were isolated by reduction with sodium metal and their unusual structures were determined by X-ray crystallography. The diamagnetic dianions contain two 2 n+3 SE clusters where each cluster has a notably long carborane C–carborane C distance of ca 2.4 Å. The π conjugation within the phenylene bridge plays an important role in the stabilization of these carboranes with odd SE counts

Sulfonyl-Substituted Heteroleptic Cyclometalated Iridium(III) Complexes as Blue Emitters for Solution-Processable Phosphorescent Organic Light-Emitting Diodes

The synthesis is reported of a series of blue-emitting heteroleptic iridium complexes with phenylpyridine (ppy) ligands substituted with sulfonyl, fluorine, and/or methoxy substituents on the phenyl ring and a picolinate (pic) ancillary ligand. Some derivatives are additionally substituted with a mesityl substituent on the pyridyl ring of ppy to increase solubility. Analogues with two ppy and one 2-(2′-oxyphenyl)pyridyl (oppy) ancillary ligand were obtained by an unusual in situ nucleophilic displacement of a fluorine substituent on one of the ppy ligands by water followed by N^O chelation to iridium. The X-ray crystal structures of seven of the complexes are reported. The photophysical and electrochemical properties of the complexes are supported by density functional theory (DFT) and time-dependent DFT calculations. Efficient blue phosphorescent organic light-emitting devices (PhOLEDs) were fabricated using a selection of the complexes in a simple device architecture using a solution-processed single-emitting layer in the configuration ITO/PEDOT:PSS/PVK:OXD-7(35%):Ir complex(15%)/TPBi/LiF/Al. The addition of a sulfonyl substituent blue-shifts the electroluminescence by ca. 12 nm to λmaxEL 463 nm with CIEx,y coordinates (0.19, 0.29), compared to the benchmark complex FIrpic (λmaxEL 475 nm, 0.19, 0.38) in directly comparable devices, confirming the potential of the new complexes to serve as effective blue dopants in PhOLEDs. Replacing a fluorine by a methoxy group in these complexes red shifts the PL and EL λmax by ca. 4–6 nm. The efficiency of the blue PhOLEDs of the sulfonyl-substituted complexes is, in most cases, significantly enhanced by the presence of a mesityl substituent on the pyridyl ring of the ppy ligands

Systems Biology Approach Pinpoints Minimum Requirements for Auxin Distribution during Fruit Opening : Plant Systems Biology

The phytohormone auxin is implied in steering various developmental decisions during plant morphogenesis in a concentration-dependent manner. Auxin maxima have been shown to maintain meristematic activity, for example, of the root apical meristem, and position new sites of outgrowth, such as during lateral root initiation and phyllotaxis. More recently, it has been demonstrated that sites of auxin minima also provide positional information. In the developing Arabidopsis fruit, auxin minima are required for correct differentiation of the valve margin. It remains unclear, however, how this auxin minimum is generated and maintained. Here, we employ a systems biology approach to model auxin transport based on experimental observations. This allows us to determine the minimal requirements for its establishment. Our simulations reveal that two alternative processes—which we coin “flux-barrier” and “flux-passage”—are both able to generate an auxin minimum, but under different parameter settings. Both models are in principle able to yield similar auxin profiles but present qualitatively distinct patterns of auxin flux. The models were tested by tissue-specific inducible ablation, revealing that the auxin minimum in the fruit is most likely generated by a flux-passage process. Model predictions were further supported through 3D PIN localization imaging and implementing experimentally observed transporter localization. Through such an experimental–modeling cycle, we predict how the auxin minimum gradually matures during fruit development to ensure timely fruit opening and seed dispersal.Peer reviewe