Structure-activity relationships in cholapod anion carriers: enhanced transmembrane chloride transport through substituent tuning

Chloride transport by a series of steroid-based "cholapod" receptors/carriers was studied in vesicles. The principal method involved preincorporation of the cholapods in the vesicle membranes, and the use of lucigenin fluorescence quenching to detect inward-transported Cl-. The results showed a partial correlation between anion affinity and transport activity, in that changes at the steroidal 7 and 12 positions affected both properties in concert. However, changes at the steroidal 3-position yielded irregular effects. Among the new steroids investigated the bis-p-nitrophenylthiourea 3 showed unprecedented activity, giving measurable transport through membranes with a transporter/lipid ratio of 1:250 000 (an average of <2 transporter molecules per vesicle). Increasing transporter lipophilicity had no effect, and positively charged steroids had low activity. The p-nitrophenyl monourea 25 showed modest but significant activity. Measurements using a second method, requiring the addition of transporters to preformed vesicle suspensions, implied that transporter delivery was problematic in some cases. A series of measurements employing membranes of different thicknesses provided further evidence that the cholapods act as mobile anion carriers.     

Palladium-Catalyzed Hydroaminocarbonylation of Olefins with Aliphatic Amines without Additives

Palladium-catalyzed hydroaminocarbonylation reactions of olefins using aliphatic amines were performed under carbon monoxide atmosphere. Despite the strong basicity of the applied nucleophiles, the targeted amides were successfully synthesized in the absence of acidic additives. Styrene, oct-1-ene and isoprene were transformed to the corresponding amide isomers in moderate to good isolated yields under optimized reaction conditions. Various aliphatic amines were used as N-nucleophiles. The effect of chiral diphosphines on product distribution, that is, on chemo-, regio- and enantioselectivities was also studied. Plausible explanation was given for the additive-free hydroaminocarbonylation reaction.     

Synthesis and absolute configuration of a constitutionally-new [5.6] spiroacetal from B. tryoni (Queensland fruit fly)

A novel spiroacetal, (2S,6R,8S)-2-methyl-8-ethyl-1,7-dioxaspiro[5.6]dodecane (1), has been identified from the volatile secretions of female B. tryoni by mass spectral analysis and synthesis of an authentic, enantioenriched sample.     

Complete (1)H and (13)C assignments of the four major saponins from Dioscorea villosa (wild yam)

Complete (1)H and (13)C spectral assignments for the four major steroidal saponins isolated by methanolic extraction of the roots of Dioscorea villosa, collected in North Carolina, United States (in summer and autumn), are presented in this paper. The structures were determined by a combination of (1)H, (13)C and 2D NMR techniques and were found to be ((3beta,25R)-26-(beta-D-glucopyranosyloxy)-22-methoxyfurost-5-en-3-yl-O-beta-D-glucopyranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 4)-O-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (1) (or methyl parvifloside), ((3beta,25R)-26-(beta-D-glucopyranosyloxy)-22 methoxyfurost-5-en-3-yl-O-alpha-L-rhamnopyranosyl-(1 --> 2)-O-[beta-D-gluco- pyranosyl-(1 --> 4)]-beta-D-glucopyranoside (2) (or methyl protodeltonin), (3beta,25R)-spirost-5-en-3-yl-O-beta-D-glucopy ranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 4)-O-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (3) (or Zingiberensis saponin I) and (3beta,25R)-spirost-5-en-3-yl-O-alpha-L-rhamnopyranosyl-(1 --> 2)-O-[beta-Ds-glucopyranosyl -(1 --> 4)]-beta-D-glucopyranoside (4) (or deltonin).     

Identification, characterization and quantitation of pyrogenic polycylic aromatic hydrocarbons and other organic compounds in tire fire products

On 15 August 2001, a tire fire took place at the Pneu Lavoie Facility in Gatineau, Quebec, in which 4000 to 6000 new and recycled tires were stored along with other potentially hazardous materials. Comprehensive gas chromatography-mass spectrometry (GC-MS) analyses were performed on the tire fire samples to facilitate detailed chemical composition characterization of toxic polycyclic aromatic hydrocarbons (PAHs) and other organic compounds in samples. It is found that significant amounts of PAHs, particularly the high-ring-number PAHs, were generated during the fire. In total, 165 PAH compounds including 13 isomers of molecular weight (MW) 302, 10 isomers of MW 278, 10 isomers of MW 276, 7 isomers of MW 252, 7 isomers of MW 228, and 8 isomers of MW 216 PAHs were positively identified in the tire fire wipe samples for the first time. Numerous S-, O-, and N-containing PAH compounds were also detected. The identification and characterization of the PAH isomers was mainly based on: (1) a positive match of mass spectral data of the PAH isomers with the NIST authentic mass spectra database; (2) a positive match of the GC retention indices (I) of PAHs with authentic standards and with those reported in the literature; (3) agreement of the PAH elution order with the NIST (US National Institute of Standards and Technology) Standard Reference Material 1597 for complex mixture of PAHs from coal tar; (4) a positive match of the distribution patterns of PAH isomers in the SIM mode between the tire fire samples and the NIST Standard Reference Materials and well-characterized reference oils. Quantitation of target PAHs was done on the GC-MS in the selected ion monitoring (SIM) mode using the internal standard method. The relative response factors (RRF) for target PAHs were obtained from analyses of authentic PAH standard compounds. Alkylated PAH homologues were quantitated using straight baseline integration of each level of alkylation.     

Electrostatic forces in micromanipulation: Experimental characterization and simulation including roughness

Manipulation by contact of objects between 1 m and 1 mm are often disturbed by adhesion between the manipulated object and the gripper. Electrostatic forces are among the phenomena responsible for this adhesive effect. Analytical models have been developed in the literature to predict electrostatic forces. Most models have been developed within the framework of scanning probe microscopy, i.e. for a contact between a conducting tip and a metallic surface. In our study, we developed a simulation tool based on finite elements modeling. The strength of this model lies in the fact that it integrates roughness parameters. Measurements of electrostatic forces in function of roughness were conducted by atomic force microscopy. The experimental results were compared with the simulation results showing very good correlation. This demonstrates the influence of surface topography on electrostatic forces, especially for very small separation distances and proves the utility of the simulation tool in designing surfaces with controlled adhesion. Some application fields to which these results can be applied are drug delivery devices and micromanipulation tools.     

甘氨酸在SiO2表面的吸附及热缩合反应

 考察了甘氨酸水溶液平衡浓度和pH值对其在SiO2表面吸附行为的影响,采用DTG,XRD和FT-IR等手段对甘氨酸在SiO2表面的吸附量及晶相结构等进行了表征. 结果表明,甘氨酸在SiO2上的吸附不符合Langmuir吸附模型,当甘氨酸水溶液平衡浓度小于0.073 mol/L时,主要为特定位置吸附,此时SiO2对甘氨酸的吸附源于其表面≡Si-O-基团与甘氨酸离子的-NH+3 端的相互作用; 当平衡浓度大于0.073 mol/L时,呈多层吸附,形成α和β两种晶型的甘氨酸. 用TPD-MS对甘氨酸的热缩合行为进行了考察,结合FT-IR结果表明,产物为环状二聚体哌嗪二酮(DKP),没有检测到线式二聚体以及表面硅酯类物种形成. SiO2对表面吸附的甘氨酸分子产生了诱导活化,使其热缩合温度与体相α甘氨酸相比降低了50 ℃左右.