Microporous Magnesium and Manganese Formates for Acetylene Storage and Separation

Acetylene sorption of microporous metal formates M(HCOO)₂ (M=Mg and Mn) was investigated. Measurements of acetylene sorption at 196, 275, and 298 K showed a Type I isotherm with quick saturation at low pressures, and 50–75 cm³ g^?1 uptake at 1.0 atm. The single‐crystal X‐ray structure analysis of the acetylene‐adsorbed metal formates revealed that acetylene molecules occupy two independent positions in the zigzag channels of the frameworks with a stoichiometry of M(HCOO)₂?1/3C₂H₂, which is consistent with the gas sorption experiments. No specific interaction except van der Waals interactions between the adsorbed acetylene molecules and the walls of the frameworks was found. Sorption properties of other gases, including CO₂, CH₄, N₂, O₂, and H₂, were also investigated. When the temperature was increased to 298 K, the amount of adsorbed acetylene was still above 60 cm³ g^?1 for Mg(HCOO)₂ and 50 cm³ g^?1 for Mn(HCOO)₂, whereas the uptake of other gases decreased substantially. The microporous metal formates may thus be useful not only for the storage of acetylene but also its separation from other gases at room or slightly higher temperatures.     

Multicopy suppressors for novel antibacterial compounds reveal targets and drug efflux susceptibility

Gene dosage has frequently been exploited to select for genetic interactions between a particular mutant and clones from a random genomic library at high copy. We report here the first use of multicopy suppression as a forward genetic method to determine cellular targets and potential resistance mechanisms for novel antibacterial compounds identified through high-throughput screening. A screen of 8640 small molecules for growth inhibition of a hyperpermeable strain of Escherichia coli led to the identification of 49 leads for suppressor selection from clones harboring an E. coli genomic library. The majority of suppressors were found to encode the multidrug efflux pump AcrB, indicating that those compounds were substrates for efflux. Two leads, which produced clones containing the gene folA, encoding dihydrofolate reductase (DHFR), proved to target DHFR in vivo and were competitive inhibitors in vitro.     

Structural and conformational properties of 1,2-propadienylphosphine (allenylphosphine) studied by microwave spectroscopy and quantum chemical calculations

1,2-Propadienylphosphine (allenylphosphine), H(2)C=C=CHPH(2), has been investigated by Stark and Fourier transform microwave spectroscopy. Two rotameric forms denoted syn and gauche have been assigned. The syn form has a symmetry plane (C(s)() symmetry) where the lone electron pair of phosphorus points toward the double bonds. The phosphino group is rotated roughly 120 degrees from this position in the gauche rotamer. The dipole moment of syn was determined to be mu(a) = 1.613(23), mu(b) = 2.347(24), mu(c) = 0 (for symmetry reasons), and mu(tot) = 2.848(28) x 10(-30) C m [0.854(8) D]. The energy difference between the two forms was found to be 2.1(4) kJ/mol from relative intensity measurements with syn as the more stable conformer. Extensive quantum chemical calculations have been carried out and accurate equilibrium structures have been determined for these two rotamers, as well as for the corresponding two conformers of vinylphosphine (H(2)C=CHPH(2)).     

Theoretical characterization of the low-lying electronic states of NbC

We have studied the potential-energy curves and the spectroscopic constants of the ground and low-lying excited states of NbC by employing the complete active space self-consistent field method with relativistic effective core potentials followed by multireference configuration-interaction calculations. We have identified 23 low-lying electronic states of NbC with different spin multiplicities and spatial symmetries within 40,000 cm(-1). At the multireference single and double configuration interaction level of theory the 2sigma+ and 2delta states are nearly degenerated, with the 2delta state located 187 cm(-1) lower than the 2sigma+ state. The estimated spin-orbit splitting for the 2delta state results in a 2delta(3/2) ground state and A 2sigma+ which is placed 650 cm(-1) above the ground state, in reasonable agreement with the experimental result, 831 cm(-1). Our computed spectroscopic constants are in good agreement with experimental values although our results differ from those of a previous density-functional investigation of the excited states of NbC, mainly due to the strong multiconfigurational character of NbC. In the present work we have not only suggested assignments for the observed states but also computed more electronic states that are yet to be observed experimentally.     

The Influence of Drawing in Hot Water on The Morphological Properties of Pet Films as Measured by DSC and Modulated DSC

PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition is studied by MDSC which allows to access the glass transition temperature T _g and the variations of ΔC _p=C _p1−C _pg (difference between thermal capacity in the liquid-like and glassy states at T=T _g). Variations of T _g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed with regard to the structure engaged in these materials. The increments of ΔC _p at T _g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’ of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and reactivity towards tetrafluoroboric acid of a new family of heterobimetallic polyhydride complexes [(CO)(PPh3)2HRe(μ-H)3RhL2] (L = PPh3, 1,2,5-triphenylphosphole, or P(OMe)3)

The reaction of K[ReH₆(PPh₃)₂] with [RhCl(CO)L₂] [L= PPh₃, 1,2,5-triphenylphosphole (TPP), or P(OMe)₃] leads to the new electronically unsaturated heterobimetallic polyhydride complexes [(CO)(PPh₃)₂HRe(μ-H)₃RhL₂] in moderate-to-good yields. The structures of these complexes have been established on the basis of spectroscopic data, especially ¹H and ³¹P NMR. The bridging hydride ligands are fluxional but there is either a slow or nonexistent exchange between terminal and bridging hydrides. For L = PPh₃ or TPP, protonation with tetrafluoroboric acid affords quantitatively the cationic complexes [(CO)(PPh₃)₂HRe(μ-H)₃RhHL₂]⁺, isolated as the BF₄⁻ or the BPh₄⁻ salts.     

First 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from plants: structure elucidation,synthesis and antifungal activity

Two new 2-hydroxy-3-methylbut-3-enyl substituted xanthones, (+/-)-caledol 1 and (+/-)-dicaledol 2 were isolated from a dichloromethane extract of the leaves of Calophyllum caledonicum (Clusiaceae). Compounds 1 and 2 are the first 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from natural source. Their structures were elucidated by means of combined analytical methods including HRFABMS, 1D and 2D NMR spectroscopies and also confirmed by total synthesis using biomimetic ortho-prenylphenols photooxygenation (1O2) as a key step. The antifungal activity against Aspergillus fumigatus is reported.     

Invariant subrings of ℂ[X,Y,Z] which are complete intersections

It is known that for every finite subgroup G of SL(2,), the invariant subring [X,Y]^G is a hyper-surface. In this note we treat finite subgroups of SL(3,) and give complete classification of the finite subgroups of SL(3,) whose invariant subrings are complete intersections.     

Order-disorder transition in the complex lithium spinel Li2CoTi3O8

Li₂CoTi₃O₈ has an ordered Li₂BB′₃O₈ spinel structure, space group P4₃32, at room temperature with 3:1 ordering of Ti and Li on the octahedral sites, and Li, Co disordered over the tetrahedral site. Rietveld refinement of variable temperature neutron powder diffraction data has shown an order-disorder phase transition in Li₂CoTi₃O₈ which commences at ∼500 °C with Li and Co mixing on the tetrahedral and 4-fold octahedral sites and is complete at a first order structural discontinuity at ∼915 °C. The fraction of Ti on the 12-fold octahedral site exhibits a small decrease with increasing temperature, which may suggest that the disordering involves all three cations. Above 930 °C, the structure, space group Fd3¯m, has Li, Co and Ti sharing a single-octahedral site and Li, Co sharing a tetrahedral site, although Co still exhibits a preference for tetrahedral coordination. A labelling scheme for ordered and partially ordered 3:1 spinels is devised which focuses on the occupancy of the Li,B cations.     

Remarkable diastereoselectivity in the addition of allylic and unsaturated diorganozinc reagents to beta-(N,N-dialkylamino)-aldehydes

1,3-Anti amino alcohols 5(a)-18(a) are obtained with high diastereoselectivity by use of diorganozinc reagents in additions to amino aldehydes 2a and 2b. The corresponding Grignard reagents exhibit low to modest diastereoselectivity. The highly diastereoselective zinc-based method makes available a wide range of 4,4-disubstituted cyclohexenone derivatives containing contiguous stereocenters.