Multifunctional fourfold interpenetrating diamondoid network: gas separation and fabrication of palladium nanoparticles

A fourfold interpenetrating diamondoid network, [{[Ni(cyclam)]2-(mtb)}(n)].8n H2O.4n DMF (1) (MTB=methanetetrabenzoate, DMF=dimethylformamide), has been assembled from [Ni(cyclam)][ClO4]2 (cyclam=1,4,8,11-tetraazacyclotetradecane) and methanetetrabenzoic acid (H4MTB) in DMF/H2O (7:3, v/v) in the presence of triethylamine (TEA). Despite the high-fold interpenetration, 1 generates 1D channels that are occupied by water and DMF guest molecules. Solid 1, after removal of guest molecules, exhibits selective gas adsorption behavior for H2, CO2, and O2 rather than N2 and CH4, suggesting possible applications in gas separation technologies. In addition, solid 1 can be applied in the fabrication of small Pd (2.0+/-0.6 nm) nanoparticles without any extra reducing or capping agent because a Ni II macrocyclic species incorporated in 1 reduces Pd II ions to Pd 0 on immersion of 1 in the solution of Pd(NO3)2.2H2O in MeCN at room temperature.     

Characterization of in vitro metabolites of deoxypodophyllotoxin in human and rat liver microsomes using liquid chromatography/tandem mass spectrometry

The in vitro metabolism of deoxypodophyllotoxin (DPT), a medicinal herbal product isolated from Anthriscus sylvestris (Apiaceae), was investigated in rats and human microsomes and human recombinant cDNA-expressed CYPs. The incubation of DPT with pooled human microsomes in the presence of NADPH generated five metabolites while its incubation with dexamethasone (Dex)-induced rat liver resulted in seven metabolites (M1-M7) with major metabolic reactions including mono-hydroxylation, O-demethylation and demethylenation. Reasonable structures of the seven metabolites of DPT could be proposed, based on the electrospray tandem mass spectra. Chemical inhibition by ketoconazole and metabolism studies with human recombinant cDNA-expressed CYPs indicated that CYP 3A4 and 2C19 are the major CYP isozymes in the metabolism of DPT in human liver microsomes.     

Products of Bergman space Toeplitz operators on the polydisk

Motivated by recent works of Ahern and uković on the disk, we study the generalized zero product problem for Toeplitz operators acting on the Bergman space of the polydisk. First, we extend the results to the polydisk. Next, we study the generalized compact product problem. Our results are new even on the disk. As a consequence on higher dimensional polydisks, we show that the generalized zero and compact product properties are the same for Toeplitz operators in a certain case.The first three authors were partially supported by KOSEF(R01-2003-000-10243-0) and the last author was partially supported by the National Science Foundation.     

A Brønsted acid catalyst for the enantioselective protonation reaction

A highly reactive and robust chiral Br?nsted acid catalyst, chiral N-triflyl thiophosphoramide, was developed. The first metal-free Br?nsted acid catalyzed enantioselective protonation reaction of silyl enol ethers was demonstrated using this chiral Br?nsted acid catalyst. The catalyst loading could be reduced to 0.05 mol % without any deleterious effect on the enantioselectivity.     

Different elution modes and field programming in gravitational field-flow fractionation. Effect of channel angle

Gravitational field-flow fractionation (GrFFF) has been shown to be useful for separation and characterization of various types of micrometer-sized particles. It has been recognized however that GrFFF is less versatile than other members of FFF because the external field (Earth's gravity) in GrFFF is relatively weak and is not tunable (constant), which makes the force acting on the particles constant. A few approaches have been suggested to control the force acting on particles in GrFFF. They include (1) changing the angle between the Earth's gravitational field and the longitudinal axis of the channel, and (2) the use of carrier liquid having different densities. In the hyperlayer mode of GrFFF, the hydrodynamic lift force (HLF) also act on particles. The existence of HLF allows other means of changing the force acting on the particles in GrFFF. They include (1) the flow rate programming, or (2) the use of channels having non-constant cross-section. In this study, with polystyrene latex beads used as model particles, the channel angle was varied to study its effect on elution parameters (such as selectivity, band broadening and resolution) in the steric or in the hyperlayer mode of GrFFF. In addition, the effects of the channel thickness and the flow rate on the elution parameters were also investigated. It was found that, in the steric mode, the resolution decreases as the flow rate increases due to increased zone broadening despite of the increase in the selectivity. At a constant volumetric flow rate, both the zone broadening and the selectivity increase as the channel thickness increases, resulting in the net increase in the resolution. It was also found that the retention time decreases as the channel angle increases in both up- and down-flow positions. The zone broadening tends to increase almost linearly with the channel angle, while no particular trends were found in selectivity. As a result, the resolution decreases as the channel angle increases.     

Water soluble cucurbit[6]uril derivative as a potential Xe carrier for 129Xe NMR-based biosensors

The water soluble cucurbit[6]uril derivative CB*[6] forms a thermodynamically and kinetically stable host-guest complex with xenon in water, the binding affinity of which is about 3 x 10(3) M(-1), comparable to those of cryptophanes, suggesting that it may serve as an effective molecular "carrier" for 129Xe NMR-based biosensors.     

Synthesis and activity of largazole analogues with linker and macrocycle modification

To characterize largazole's structural requirements for histone deacetylase (HDAC) inhibitory and antiproliferative activities, a series of analogues with modifications to the side chain or 16-membered macrocycle were prepared and biologically evaluated. Structure-activity relationships suggested that the four-atom linker between the macrocycle and octanoyl group in the side chain and the (S)-configuration at the C17 position are critical to repression of HDAC activity. However, the valine residue in the macrocycle can be replaced with alanine without significant loss of activity.     

Time-dependent binding mode of a cationic porphyrin dimer to poly[d(G-C)2] and Poly[d(A-T)2

The time-dependent binding mode of a porphyrin dimer to poly[d(G-C)2] and poly[d(A-T)2] was investigated by spectroscopic methods including absorption and circular and linear dichroism (CD and LD) spectroscopy. Immediately after mixing with poly[d(G-C)2], the porphyrin dimer exhibited red-shift and hypochromism in the absorption spectrum and negative CD and LD spectra. With further red-shift in absorption, the CD and LD magnitude in the Soret region became increasingly negative over time. After it was stabilized, the magnitude of the reduced LD (LDr) in the Soret region was larger than that in the DNA absorption region, indicating that the second porphyrin was also intercalated. Following the rapid intercalation of the first porphyrin, the very slow intercalation of the second followed with first-order kinetics. In the poly[d(A-T)2] case, a bisignate CD spectrum was observed in the Soret region suggesting stacking of the porphyrins. The small alteration in the CD spectrum and increased absorbance, which followed the initial rapid spectral change, was of the second order. This alteration in the spectral properties was attributed to the conformational change of poly[d(A-T)2] near the binding site because the overall shape of the CD spectrum was conserved in spite of the changes in the absorption spectrum.     

Measurement of the near-threshold e+e- --> D(*)+/-D(*)-/+ cross section using initial-state radiation

We report a measurement of the exclusive e+e- -->D(*)+/-D*-/+ cross section as a function of center-of-mass energy near the D(*)+/-D*-/+ threshold with initial-state radiation. A partial reconstruction technique is used to increase the efficiency and to suppress background. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 547.8 fb(-1).