Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

Effects of ion-pairing reagents on the electrospray signal suppression of sulphonated dyes and intermediates

High-performance liquid chromatography/mass spectrometry (HPLC/MS) analysis of anionic species such as sulphonic acid dyes and intermediates requires volatile ion-pairing mobile phase additives. Six di- and trialkylammonium acetates were compared with tetraalkylammonium salts and ammonium acetate in the concentration range 0-20 mmol l(-1) as mobile phase additives for HPLC/MS of polysulphonated compounds. The effects of the structure and concentration of the ion-pairing reagents on the electrospray response of mono-, di- and tetrasulphonic aromatic acids and acid dyes were studied in detail. Further, five different mass analysers and instrument geometries were compared. A higher signal decrease is observed with linear geometry instruments in comparison to orthogonal or even Z-spray geometry mass spectrometers. The concentration of mobile phase additives has a significant influence on the abundance ratios of multiply charged ions in the mass spectra of polysulphonated compounds. The competing ions of sulphonic acids may also cause significant signal suppression.     

Syntheses of methylene-bridged ansa-zirconocene complexes and copolymerization studies of ethylene and norbornene

Methylene-bridged ansa-metallocene complexes bearing substituents on the cyclopentadienyl (Cp) and fluorenyl (Flu) moieties, namely methylene[9-(2,7-di-tert-butyl)fluorenyl(2-(1,3-dimethylcyclopentadienyl))]zirconium dichloride (1a) and its analogue, methylene[(9-(2,7-di-tert-butyl)fluorenyl(2-(1-methyl-3-phenyl)cyclopentadienyl))]zirconium dichloride (2a), have been prepared from (2,7-di-tert-butyl)-9-prop-2-ynyl-9H-fluorene (2). This procedure includes the use of 3-bromo-1-propyne which affords the methylene bridging unit by way of an intermolecular Pauson-Khand reaction in which norbornadiene and a pendant alkyne cyclize to form a ring that later becomes a substituted cyclopentadienyl group. Ethylene-norbornene (E-N) copolymerization was then carried out using these new complexes (1a and 1b) in the presence of methylaluminoxane (MAO) as a cocatalyst; these activities can be compared to that of isopropylene[9-fluorenyl-cyclopentadienyl]zirconium dichloride (3a). The activity of catalyst 1a was comparable to that of 3a but much higher than that of 2a. In addition, 1a shows higher norbornene insertion performance, and gives an E-N copolymer with a higher glass transition temperature (T_g) than 2a under identical conditions; both 1a and 2a give a lower T_g polymer than 3a does.     

Hepatobiliary excretion and brain distribution of caffeine in rats using microdialysis

To investigate the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine, this study uses a method based on microdialysis technique and liquid chromatography that allows continuous and concurrent in vivo monitoring of extracellular caffeine in the blood, brain and bile of anesthetized rats following the administration of caffeine (3 or 10 mg/kg, i.v.) through the femoral vein. Dialysates of the blood, brain and bile were directly injected onto the liquid chromatographic system and no further clean-up procedures were required. The study design consisted of two groups of six rats in parallel: the rats of the control group received caffeine (3 or 10 mg/kg, i.v.) alone and those of the cyclosporine treated-group were injected cyclosporine (10 mg/kg, i.v.) 10 min prior to caffeine administration (3 or 10 mg/kg, i.v.). The decline of caffeine in the blood, brain striatum and bile suggested that caffeine had rapid exchange and equilibration between the peripheral compartment and the central nervous system. In addition, the results indicated that caffeine underwent hepatobiliary excretion and was distributed into brain. When cyclosporine was co-administered, the pharmacokinetic parameters were not significantly altered. The results of this study reveal that the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine might not relate to P-glycoprotein.     

Use of Ag(II) as a removable template in porphyrin chemistry: diol cleavage products of [meso-tetraphenyl-2,3-cis-diolchlorinato]silver(II)

The use of Ag^II as a removable template in synthetic porphyrin chemistry is described. Mild procedures for the insertion of Ag^II into chlorins and the demetallation of the [chlorinato]Ag^II complexes are delineated. The UV-vis spectra of the novel [chlorinato]Ag^II complexes are discussed. The diol cleavage products of [meso-tetraphenyl-2,3-diolchlorinato]silver(II) under a number of conditions are characterized and compared to those resulting from the cleavage of the corresponding free base diol chlorin or its Ni^II complex, highlighting the unique templating effect of Ag^II. The scopes and limits of electrospray ionization mass spectrometry (ESI-MS) for the analysis of Ag^II chlorins is described. The use of Ag^II as a templating metal is superior over Ni^II or Zn^II for the preparation of free base pyrrole-modified porphyrins along metal templated pathways.     

吡啶酮系偶氮类化合物可见吸收光谱的预测

利用密度泛函的B3LYP方法, 在6-311G*基组水平对吡啶酮系偶氮类化合物进行构型优化, 并进行了自然键轨道(NBO)分析, 然后用TDDFT方法和ZINDO/S方法分别计算了它们的可见吸收光谱, 结果均与实验值十分吻合. 通过对比发现, 对于最高吸收波长的计算, ZINDO/S能以较快的速度得到较好的结果. 在用ZINDO/S计算的过程中, 回归分析发现π-π重叠加权因子(OWF_π-π)与染料分子吡啶环上两个羰基氧原子平均电荷Z_O有较好的线性关系: OWF_π-π＝0.11425－1.04178ZO, 这一关系不仅可从量子化学的角度进行解释, 而且可用于同类染料可见吸收光谱的预测. 分子轨道的研究表明, 这些化合物的最高可见吸收波长主要对应着共轭体系中给电子体到受电子体的电子跃迁.     

The Effect of Nb Loading on Catalytic Properties of Ni/Ce0.75Zr0.25O2 Catalyst for Methane Partial Oxidation

In this study,the effect of Nb loading on the catalytic activity of Ce_(0.75)Zr_(0.25)O_2-supported Ni catalysts was studied for methane partial oxidation.The catalysts were characterized by BET,H_2 chemisorption,XRD,TPR,TEM and tested for methane partial oxidation to syngas in the temperature range of 400-800℃at atmospheric pressure.The results showed that the activity of methane partial oxidation on the catalysts was apparently dependent on Nb loading.It seemed that the addition of Nb lowered the catalytic activity for methane partial oxidation and increased the extent of carbon deposition. This might be due to the strong interaction between NiO and Nb-modified support and reduction of surface oxygen reducibility.     

Extraction-spectrophotometric determination of iron with 2-(2′-benzothiazolylazo)-4,6-dimethylphenol

An extraction-spectrophotometric method for the determination of trace amounts of iron based on its extraction into chloroform with 2-(2-benzothiazolylazo)-4,6-dimethylphenol (BTADMP) from a pH 6.5 medium has been developed. The extracted 12 FeBTADMP complex species allow the determination of 4–30gmg of iron (=3.92×10⁴1·mol^–1·cm^–1 at 790 nm). The method is highly selective and has been applied to the determination of iron in polymineral-polyvitamin pharmaceutical products.