Quantification of oxyresveratrol analog trans-2,4,3',5'-tetramethoxystilbene in rat plasma by a rapid HPLC method: application in a pre-clinical pharmacokinetic study

A rapid HPLC method was developed and validated for the quantification of oxyresveratrol analog trans‐2,4,3′,5′‐tetramethoxystilbene (oxyresveratrol tetramethyl ether, OTE) in rat plasma. Chromatographic separation was achieved on an RP‐HPLC column, which was protected by a guard column through a 12 min gradient delivery of a mixture of acetonitrile–water at 50°C. The UV absorbance at 325 nm was recorded. The retention time of OTE and trans‐stilbene (internal standard) was about 7.7 and 8.4 min, respectively. The calibration curves were linear (R² ≥ 0.9986) with a lower limit of quantification of 15 ng/mL. The intra‐ and inter‐day variations, in terms of RSD, were all lower than 9.8% while the intra‐day and inter‐day bias ranged from ?8.3 to +9.2%. The pharmacokinetics of OTE was assessed in rats using 2‐hydroxypropyl‐β‐cyclodextrin as a dosing vehicle. After intravenous administration, OTE possessed a long terminal elimination half‐life (t_{1/2 λz} = 481 ± 137 min) and slow clearance (Cl = 29.1 ± 3.7 mL/min/kg). Upon oral administration, OTE was rapidly absorbed. However, it only displayed minimal plasma exposure and its absolute oral bioavailability (F) was as low as 4.5 ± 3.2%. Fortunately, the levels of OTE after single oral administration were sufficient to inhibit human cytochrome P450 1B1. Copyright © 2010 John Wiley & Sons, Ltd.     

Density functional theory and RRKM calculations of decompositions of the metastable E‐2,4‐pentadienal molecular ions

The potential energy profiles for the fragmentations that lead to [C₅H₅O]⁺ and [C₄H₆]^+? ions from the molecular ions [C₅H₆O]^+? of E‐2,4‐pentadienal were obtained from calculations at the UB3LYP/6‐311G + + (3df,3pd)//UB3LYP/6‐31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice–Ramsperger–Kassel–Marcus calculations of individual rate coefficients for a large number of reaction steps. The pre‐equilibrium and rate‐controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C? H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E‐2,4‐pentadienal ions. The direct dissociation, however, can only become important in the high‐energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2‐hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion‐neutral complex which, in turn, decomposes rapidly to the s‐trans‐1,3‐butadiene ion [C₄H₆]^+?. The predominating metastable channel is the second one, that is, a multi‐step ring closure which starts with a rate‐limiting cis—trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C₅H₅O]⁺. These results can be used to rationalize the CID mass spectrum of E‐2,4‐pentadienal in a low‐energy regime. Copyright © 2010 John Wiley & Sons, Ltd.     

Biaxial ordering of terminal diene groups in lipid membranes: an infrared linear dichroism study

The molecular order within the hydrophobic core of membranes of the diene lipid di-tetradecadienoylphosphatidylcholine was studied by means of infrared spectroscopy on multibilayer assemblies which orient macroscopically on the surface of an attenuated total reflection crystal. The relative humidity and temperature were used as variable parameters to demonstrate that there were profound differences in the melting transition of lipids possessing predominantly cis and trans diene groups. The cis isomer undergoes the phase transition at a vapor pressure which is increased by 0.15 GPa when compared with that of the trans isomer. The methylene wagging band progression gives no indication of differences between the acyl chain conformation of the cis and trans forms in the gel state. The frequencies of a number of absorption bands of the diene groups reveal that these moieties are predominantly in the s-trans conformation to accommodate a favorable packing within the bilayer. The linear dichroism of selected in-plane and out-of-plane vibrations of the diene groups gives indications of the biaxial ordering of these moieties. We present the basic equations for the quantitative analysis of IR dichroism data of lamellar structures in terms of transverse and longitudinal molecular order parameters. It turns out that the planes of the rigid diene groups orient preferentially in a perpendicular direction with respect to the bilayer surface and parallel to each other forming in this way a layer of well-aligned diene groups in the bilayer center. This finding is confirmed by the results of X-ray measurements. We suggest that the partial interdigitation of the diene groups of the sn-1 acyl chains promotes the formation of the inverse H_II phase and/or enables the formation of covalent bonds between both the monolayers upon polymerization of diene lipids.     

Synthesis of propylene carbonate from carbon dioxide using trans‐dichlorotetrapyridineru‐ thenium(II) as catalyst

trans‐Dichlorotetrapyridineruthenium(II) [trans‐RuCl₂(py)₄] was synthesized and the structure was determined by single crystal X‐ray crystallography. Highly efficient formation of propylene carbonate (PC) from carbon dioxide and propylene oxide was achieved by using a catalyst system composed of trans‐RuCl₂(py)₄ and hexadecyl trimethyl ammonium bromide under mild conditions (4h, 80 °C, 3.0 MPa). PC was obtained in nearly 100% selectivity without the formation of a polymer. The catalyst could be recycled constantly many times without any significant loss of its catalytic activity. On the basis of the results, a mechanism for the reaction was proposed. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Investigation on dual properties of photosensitive thermotropic liquid‐crystalline poly(benzylidene‐ether)s containing alkanones and methylene spacers in the main chain

Thermotropic main chain liquid‐crystalline poly (benzylidene‐ether)s were synthesized by Claisen‐Schmidt polycondensation reaction of 4,4′‐diformyl‐2,2′‐dimethoxy‐α,ω‐diphenoxyalkanes with acetone, cyclopentanone, and cyclohexanone. The diformyl precursors were synthesized from 4‐hydroxy‐3‐methoxybenzaldehyde with dibromoalkanes of varying spacer lengths. The structure of monomers and polymers was confirmed by elemental analyses, Fourier‐transform infrared, ¹H NMR, and ¹³C NMR spectral analyses. The thermal properties were studied by thermogravimetric analysis and differential scanning calorimetry. Thermogravimetric analysis (TGA) data revealed that the polymers were stable up to 285 °C and start degrading thereafter. Cyclopentanone‐containing polymers are more stable than cyclohexanone‐ and acetone‐containing polymers. The self‐extinguishing property of the synthesized polymers was studied by calculating the limiting oxygen index values using Van Krevelen's equation. The influence of the length of methylene spacer on phase transition was investigated using differential scanning calorimetry (DSC), and it was proved that the isotropic temperature decreases with an increase in the length of the spacer. Polarized optical microscopic study showed that cyclohexanone‐containing polymers exhibit nematic threadlike and nematic droplet texture. The photolysis of liquid‐crystal poly(benzylidene‐ether)s revealed that the Entgegen, Zusammen (EZ) photoisomerization proceeds in the system. The band gap energy was calculated from absorption spectra and is in the range of 3.05–3.37 eV and proved that the length of spacers has a significant influence on their absorption and emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polyethylene terephthalate–multiwall nanotubes nanocomposites: Effect of nanotubes on the conformations,crystallinity and crystallization behavior of PET

PET‐nanotube composite samples were manufactured by mixing neat PET with a PET‐multiwall carbon nanotube masterbatch. Fourier transform infrared (FTIR) spectroscopy was utilized to monitor the gauche and trans conformations of the polymeric chains with respect to the nanotube content. The crystallinity as well as the crystallization behavior of the polymer were studied via differential scanning calorimetry (DSC). An increase of the trans conformations and crystallinity was recorded at low NT contents followed by a sharp decrease at 1 wt % of nanotubes, further addition of nanotubes led once again to increase of the trans conformations and crystallinity. This behavior was attributed to the aggregations formation which as shown via transmission electron microscopy (TEM) was initiated at concentrations above 0.5 wt %. Discordance between the FTIR and DSC results in the case of the PET sample showed that the later bears relatively more trans non‐crystalline conformers than the nanocomposite samples. Thus it appears that the nanotubes incorporate the trans non‐crystalline segments into the crystalline phase. This work has shown that even a minor addition of carbon nanotubes (even 0.1 wt %) alters the crystallization behavior of the polymer dramatically, yielding a novel nanocomposite material rather than a simple mixture of two ingredients. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 668–676, 2008     

High‐performance liquid chromatography separation of unsaturated organic compounds by a monolithic silica column embedded with silver nanoparticles

The optimization of a porous structure to ensure good separation performances is always a significant issue in high‐performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high‐performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high‐performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high‐performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36 000 m^?1. Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans‐stilbene with separation factor as 7 and theoretical plate number as 76 000 m^?1 for cis‐stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long‐ established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes.     

Precision Chain‐Walking Polymerization of trans‐4‐Octene Catalyzed by α‐Diimine Nickel(II) Catalysts Bearing ortho‐sec‐Phenethyl Groups

α‐Diimine nickel complexes bearing bulky ortho‐sec‐phenethyl groups (bis{[N,N′‐(4‐methyl‐2,6‐di‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel ( 1 ), bis{[N,N′‐(4,6‐dimethyl‐2‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel ( 2 ), bis{[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel ( 3 )) and {bis[N,N′‐(2,4,6‐trimethylphenyl)imino]‐1,2‐dimethylethane}dibromidonickel ( 4 ) are used as a precatalyst for the polymerization of trans‐4‐octene upon activation with modified methylaluminoxane. These catalysts conduct chain‐walking polymerization of trans‐4‐octene to give polymers possessing propyl and butyl branches with high molecular weight and narrow molecular weight distribution. The branching structure depends on the nickel complex as well as the polymerization temperature, and the ratio of propyl branch was increased with increasing the bulkiness of the ligand and decreasing the polymerization temperature. Consequently, the most bulky 1 among the complexes used is found to polymerize trans‐4‐octene with high 1,5‐regioselectivity at −20 °C to give poly(1‐propylpentan‐1,5‐diyl).

     

Die Akzeptoreigenschaften der Metall—Metall-Einheit in den zweikernigen Komplexen cis-M2(O2CCH3)2Cl4L2, M = Tc,Re; L = neutrale Base

The Acceptor Properties of the Metal—Metal Unit in the Dinuclear Complexes cis-M₂(O₂CCH₃)₂Cl₄L₂, M = Tc, Re; L = neutrale Base The weakly bound H₂O molecules in axial positions of the dimetalates cis-M₂(O₂CCH₃)₂Cl₄L₂, M = Tc, Re, are easily substituted on reaction with stronger donor bases. With increasing donor number D_N or donor strength D_S of the axial ligands, the metal—metal stretching frequency v₁ is lowered. The linearity between v₁ and the hard D_N scale shows, that the M₂ unit acts as a hard Lewis acid in the axial direction, according to the observation that no coordination of soft donor bases takes place. The trans influence of the metal—metal multiple bond is estimated from the ratio of the shifts observed for v₁ and the equatorial metal-ligand stretching modes after formation of adducts. The ratio is about 5: 1 in the ditechnetates and thus considerable higher than in the dirhenates with about 2: 1.