Intra- and intermolecular Fe-catalyzed dicarbofunctionalization of vinyl cyclopropanes

Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach. Mechanistic studies support the diffusion of alkyl radical intermediates out of the solvent cage to participate in an intra- or intermolecular radical cascade with a range of VCPs followed by re-entering the Fe radical cross-coupling cycle to undergo (stereo)selective C(sp²)–C(sp³) bond formation. This work provides a proof-of-concept of the use of vinyl cyclopropanes as synthetically useful 1,5-synthons in Fe-catalyzed conjunctive cross-couplings with alkyl halides and aryl/vinyl Grignard reagents. Overall, we provide new design principles for Fe-mediated radical processes and underscore the potential of using combined computations and experiments to accelerate the development of challenging transformations.

Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach.     

The first fullerene-metal sandwich complex: an unusually strong electronic communication between two C(60) cages

Reaction of Rh(6)(CO)(9)(dppm)(2)(mu(3)-eta(2),eta(2),eta(2)-C(60)) (1) with C(60) in refluxing chlorobenzene followed by treatment with CNR (R = CH(2)C(6)H(5)) at room temperature affords the first fullerene-metal sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(mu(3)-eta(2),eta(2),eta(2)-C(60))(2) (2). Compound 2 has been characterized by an X-ray diffraction study. Electrochemical study of 2 reveals six well-separated reversible redox couples localized at C(60) cages due to a strong electronic communication between the two C(60) centers via the Rh(6) cluster spacer.     

Hollow fiber membrane-protected solid-phase microextraction of triazine herbicides in bovine milk and sewage sludge samples

A porous polypropylene hollow fiber membrane (HFM)-protected solid-phase microextraction (HFM-SPME) procedure in conjunction with gas chromatography/mass spectrometric analysis for use in the determination of triazine herbicides in bovine milk samples is described. A 65-microm polydimethylsiloxane-divinylbenzne (PDMS-DVB) SPME fiber was protected by an HFM. HFM-SPME experimental parameters such as fiber type, extraction time, extraction temperature and salt concentration were investigated and optimized. The relative standard deviations for the reproducibility of the optimized HFM-SPME method varied from 4.30 to 12.37%. The correlation coefficients of the calibration curves were between 0.9799 and 0.9965 across a concentration range of 0-200 microg l(-1). The method detection limits for triazines in bovine milk were in the range of 0.003-0.013 microg l(-1) and limits of quantification were in the range of 0.006-0.021 microg l(-1). The suitability of HFM-SPME was extended to the analysis of the herbicides in sewage sludge samples. The results demonstrate that HFM-SPME was an efficient pretreatment and enrichment procedure for complex matrices.     

Resveratrol derivatives potently induce apoptosis in human promyelocytic leukemia cells

Resveratrol has been shown to possess antioxidant and anticancer activities, but little is known on the effect of resveratrol derivatives. Recently we have isolated resveratrol and its dimers and trimers from peony (Paeonia lactiflora) seeds, and reported their strong antioxidant and cytotoxic activity. In the present study, we have evaluated cellular effects of resveratrol derivatives; viniferin, gnetin H, and suffruticosol B on the proliferation and apoptosis in HL-60 cells in vitro. All resveratrol and its derivatives reduced viability of HL-60 cells in a dose-dependent manner with their IC(50) values of 20-90 microM. Ascending orders of IC(50) values were suffruticosol B, gnetin H, viniferin and resveratrol respectively. HL-60 cells treated with the four stilbenes exhibited the distinct morphological changes characteristics of cell apoptosis such as chromatin condensation, apoptotic bodies, and DNA fragmentations. A time-dependent histogram of the cellular DNA analyzed by flow cytometry revealed a rapid increase in subdiploid cells and a concomitant decrease in diploid cells exposed to 100 microM resveratrol for 0-24 h. Cells treated with 25 microM of resveratrol, viniferin, gnetin H, and suffruticosol B for 24 h resulted in increment of sub-G1 population by 51, 5, 11 and 59%, respectively. Treatment of cells with 0-20 microM resveratrol for 5 h produced a concentration-dependent decrease in cytochrome P450 (CYP) 1B1 mRNA levels. Suffruticosol B also suppressed CYP1B1 gene expression. These results demonstrated that resveratrol oligomers also strongly suppressed HL-60 cell proliferation, and induced DNA damage. In addition, CYP1B1 gene supression may suggest an involvement in the resveratrol-induced apoptosis in HL-60 cells.     

Adsorption of atomic hydrogen on single-walled carbon nanotubes

We have investigated atomic and electronic structures of hydrogen-chemisorbed single-walled carbon nanotubes (SWCNTs) by density functional calculations. We have searched for relative stability of various hydrogen adsorption geometries with coverage. The hydrogenated SWCNTs are stable with coverage of H/C, theta >/= 0.3. The circular cross sections of nanotubes are transformed to polygonal shapes with different symmetries upon hydrogen adsorption. We find that the band gap in carbon nanotubes can be engineered by varying hydrogen coverage, independent of the metallicity of carbon nanotubes. This is explained by the degree of sp(3) hybridization.     

Structural Relationships between the Hemiporphyrazine Macrocyclic Ligand and its Metal Complexes. II.: Planar Neutral Ligand,C26H16N8, and Four Isomorphous Metal Complexes, [M(C26H16N8)(H2O)], M=Mn(II), Co(II), Cu(II), Zn(II)

Crystal and molecular structures of the planar neutral ligand, C₂₆H₁₆N₈, and the four isomorphous five-coordinated metal complexes, [M(C₂₆H₁₆N₈)(H₂O)], M = Mn(II), Co(II), Cu(II), Zn(II), have been determined from three-dimensional X-ray diffraction data. The free ligand hpH₂, C₂₆H₁₆N₈, belongs to the P 2₁/c space group with Z=2, a=4.142(3), b=23.736(6), c=10.338(3) Ä, β=94.66(6)°. The metal complexes monohydrate Mhp-H₂O all belong to the orthorhombic Pcab space group with Z=8. The dimensions are roughly 8.8×19.3×23.7 ų. In each structure, the macrocyclic ligand has an almost planar conformation which differs from the saddle shaped ligand hydrate (hpH₂·H₂O) and the nickel complex [Nihp]⁵. The distances from the center of the macrocyclic ring to the nitrogen atom of the free ligand are 1.907(6) and 2.245(6)Å. The coordination geometry in these four complexes is square pyramidal with a water molecule as an axial ligand. The bond distances of M(II)-O(H₂O), M(II)-N1 (imine), M(II)-N3 (pyridine) are: 2.19(1), 2.00(2), 2.27(2)Å respectively for the manganese complex; 2.08(1), 1.97(1), 2.23(1)Å for the cobalt complex; 2.33(1), 1.92(3), 2.18(1)Å for the copper complex; 2.110(5), 1.964(6), 2.252(6)Å for the zinc complex. The variation of metal-ligand distances can be correlated to the metal d orbital occupancy. A comparison with similar ligands will be presented.     

Differential 3ω calorimeter

We have developed a new dynamic calorimeter using the differential 3ω detection method. The differential 3ω calorimeter is capable of measuring dynamic heat capacity of liquid samples. The new calorimeter consists of a Wheatstone bridge made of two identical heater/sensors, and is based on the sensitive null detection method. The balancing is done automatically at all frequencies and is independent of temperature; once a sample is placed on one heater/sensor, a third harmonic signal is produced due to the difference in the two arms of the bridge. The differential 3ω calorimeter provides enhancements over traditional dynamic methods in dynamic range (up to 30 kHz), resolution, and ease of operation.     

Novel titanium complexes of a multidentate dicarbollide ligand. Synthesis and structural characterization of a constrained geometry complex

The multidentate dicarbollide ligand nido-7,8-(NMe2CH2)2-7,8-C2B9H11 has been prepared, structurally characterized, and employed in the preparation of the novel mono- and trimetallic titanium complexes [eta5:eta1-(NMe2CH2)C2B9H9CH2NMe2]Ti(NMe2)2 and [eta5:eta1-[(NMe2CH2)C2B9H9CH2NMe2]Ti(NMe2)]2-mu3-O-Ti(NMe2)2.     

14‐Membered Cyclopeptides from Paliurus ramosissimus and P. hemsleyanus

Six 14‐membered cyclopeptide alkaloids, i.e., ramosines A–C, mucronine J, and lotusines A and D, were isolated from the roots of Paliurus ramosissimus, and an additional four, hemsines A–D, from the roots of P. hemsleyanus. Among these, ramosines A–C ( 1, 5 , and 6 , resp.) and hemsines A and B ( 7 and 8 , resp.) are new bases of the amphibine‐B type, and hemsines C and D ( 9 and 10 , resp.) are new integerrine‐type alkaloids. Additionally, ramosine C ( 6 ) represents the first 14‐membered cyclopeptide alkaloid possessing a substitution (? OH) at C(13′). Their structural elucidations were based on spectral analysis and molecular‐modeling studies. Pronounced solvent effects in the ¹H‐ and ¹³C‐NMR spectra of these two types of alkaloids were observed.     

Cluster size effects on CO oxidation activity, adsorbate affinity, and temporal behavior of model Au(n)/TiO2 catalysts

Model catalysts were prepared by deposition of size-selected Au(n) (n = 1-7) on rutile TiO2(110), and characterized by a combination of electron spectroscopy, ion scattering, temperature-programmed desorption, and pulse-dosing mass spectrometry. CO oxidation activity was found to vary strongly with deposited cluster size, with significant activity appearing at Au3. Activity is not obviously correlated with affinity for CO, or with cluster morphology, but is strongly correlated with the clusters' ability to bind oxygen (during O2 exposure) on top of the gold. The temporal dependence of CO2 evolution in reaction of O2 pre-exposed samples with CO pulses shows an interesting cluster size dependence. For Au5 and Au6, the peak CO2 production is coincident with the peak CO flux, but for Au3, Au4, and Au7, there are significant induction periods for CO2 evolution. In addition, it is observed that some of the most active cluster sizes have the slowest CO2 evolution rates. Several mechanistic scenarios capable of accounting for the observations are laid out.