Wave grouping of a meandering spiral induced by Doppler effects and oscillatory dispersion

A new type of meandering spiral pattern, in which the dense waves form groups while the sparse waves keep evenly spaced, is observed in a spatial open reactor using a ferroin-catalyzed Belousov-Zhabotinsky reaction. Such a phenomenon is related to both the Doppler effect of a meandering spiral and the oscillatory dispersion relation of the system. Simulation in the two-dimensional Oregonator reaction-diffusion model with an oscillatory dispersion relation gives very similar results.     

Structure and exchange in silicon-linked tetraradicals

The EPR spectroscopy, crystallography, and magnetic susceptibility of tetrakis(N-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)silane and tetrakis(4-N-tert-butyl-N-aminoxylphenyl)silane show that silicon acts as a weak intramolecular exchange linker for polynitroxides, although both tetraradicals show onset of inter-spin exchange at reduced temperatures.     

2,7-Bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine: an ultrasensitive fluorescent probe for glucopyranoside

[structure: see text] A push-pull conjugated molecule, 2,7-bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN), has been designed to bind selectively with octyl glucopyranoside (OGU). The BPN/OGU quadruple hydrogen-bonding complex adopts a rigid BPN conformation in which the proton donor (d) and acceptor (a) relays (daad) are resonantly conjugated through the ethynyl bridge, inducing pi-electron delocalization, i.e., a charge transfer effect. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM.     

Josephson junction through a thin ferromagnetic layer: negative coupling

We investigate Josephson coupling through a ferromagnetic thin film using superconductor-insulator-ferromagnet-superconductor planar junctions. Damped oscillations of the critical current are observed as a function of the ferromagnetic layer thickness. We show that they result from the exchange energy gained or lost by a quasiparticle Andreev-reflected at the ferromagnet-superconductor interface. The critical current cancels out at the transition from positive ("0") to negative ("pi") coupling, in agreement with theoretical calculations.     

Transition-metal-catalyzed formation of trans alkenes via coupling of aldehydes

[reaction: see text] Rh(2)(OAc)(4) catalyzed the formation of exclusively trans fluorinated alkenes from aldehydes and pentafluorobenzaldehyde tosylhydrazone salts, which were readily prepared from pentafluorobenzaldehyde using the Bamford-Stevens reaction. A series of pentafluorophenyl-containing alkenes were synthesized from aldehydes in moderate to good yields under mild reaction conditions in a one-pot reaction. It is the first report of coupling two different aldehydes to form exclusively trans alkenes.     

Synthesis and structure of a novel one-dimensional chain compound formed by copper(II) and nitronyl nitroxide radical

A novel compound formed by copper(II) and a carboxy-substituted nitronyl nitroxide of formula [Cu₂(NITpBAH)₂Cl₄] (NITpBAH = [2-(4-carboxy-phenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-oxide]) has been synthesized. The compound crystallizes in the monoclinic space group P2₁/c with a = 9.5464(10), b = 12.4501(12), c = 14.3627(14) Å, = 95.200(2)°, and Z = 2. X-ray analysis reveals [Cu₂(NITpBAH)₂Cl₄] units to be linked into infinite chains by radical bridging ligands with N O of nitronyl nitroxide and substituted carboxy; there are the weak hydrogen bond interactions between chains.     

Cu(L)Mn(N3)2]n: the first complex containing both macrocyclic oxamido and alternate (mu-1,1 and mu-1,3) azido bridges

A wattle-type heteropolynuclear complex [(CuL)Mn(N(3))(2)](n) (1) (H(2)L = 2,3-dioxo-5,6:15,16-dibenzo-1,4,8,13-tetraazacyclo-pentadeca-7,13-diene), which represents the first system with macrocyclic oxamido and alternate azido bridges, forming a one-dimensional chain structure, has been synthesized and characterized by a low temperature magnetic study. The chains are stacked with interchain hydrogen and lead to the structure of a three-dimensional network.     

A zeolitic organo-metallophosphate hybrid material with bimodal porosity

The first metal carboxylatophosphate, NTHU-2, contains inorganic ZnHPO4 layers linked by BDC units (BDC = 1,4-benzene dicarboxylate or terephthalic anion); the three-dimensional anionic framework has large pores with the smallest diameter being 1.36 nm; N2 sorption isotherms reveal both micro- and mesoporosity; the new material is photoluminescent and disassembles in water wherein the discharged organic fragments form mixed crystals.     

A reactivity/affinity switch for parallel kinetic resolution: alpha-amino acid quasienantiomers and the resolution of cyclopropene carboxylic acids

A new type of parallel kinetic resolution (PKR) is reported in which quasienantiomers with very similar reactivities give products whose chromatographic properties diverge upon the addition of fluoride. This concept of a reactivity/affinity switch is applied to the PKR of cyclopropene carboxylic acids with all-carbon quaternary centers. This is the first application of alpha-amino acid quasienantiomers in PKR, and it is a complementary approach for acyltransfer systems where the asymmetry is induced by the nucleophile rather than the leaving group. Excellent diastereoselectivities (ranging from 90:10 to 99.5:5) and good yields were obtained for both quasienantiomeric products, and the reactions can be run on significant scale because the separation is trivial. High-level DFT calculations (B3LYP functional with the 6-31+G(d,p) basis set) provided transition-state structures with relative energies that are in accord with the experimental observations.