Synthetic approaches toward ecteinascidins. Part 2. Preparation of the ABCDE ring system of ecteinascidins having characteristic substituents in both benzene rings

A synthesis of an advanced ABCDE ring system (24c) having characteristic substituents in both benzene rings of ecteinascidin marine natural products is described based on our model studies.     

Studies on the charge-transfer complex and polymerization. Part XIII. Dilution and solvent effects in radical terpolymerization

In the terpolymerization of 2-chloroethyl vinyl ether—maleic anhydride—acrylonitrile and p-dioxene—maleic anhydride—acrylonitrile systems the compositions of the terpolymers obtained from feed of the same mole fraction were found to be changed beyond the limit of error for the given amounts and kinds of solvent. This change was considered to be divided into two parts. The first part, discussed quantitatively, was due to a dilution effect on the equilibrium complex formation between donor and acceptor monomer, and the second, as tentatively proposed, was due to a solvent effect on the reactivity of the complex.     

Quantification of end groups in polystyrenes by pyrolysis–gas chromatography

The determination of end groups in polystyrenes (PSts) polymerized anionically with n-butyllithium as the initiator was carried out by pyrolysis-gas chromatography (Py-GC). The relative proportions of the end groups decrease with increasing molecular weight (MW). Consequently, the peaks which reflect the structure of the end groups can be distinguished by comparing pyrograms of samples with different MW. By comparing the intensities of these peaks relative to total intensities of all the peaks in the pyrogram, the numberaverage molecular weight (M_n) of the polymer can be estimated. The observed M_n values of PSts estimated by this method are compared with those determined by size exclusion chromatography (SEC). By this method it was possible to make direct determination of M_n values of PSts with MWs between 1000 and ca. 1 million. Furthermore, the calibration curve produced by the relative intensity of one of the most characteristic peaks (2-phenyl-1-heptene; C₄H₉? CH₂C (Ph) = CH₂) for the end group to total intensity of all the peaks in the pyrogram, gave rapid and highly reproducible M_n values. © 1994 John Wiley & Sons, Inc.     

Catalytic degradation of polyolefins over hexagonal mesoporous silica: Effect of aluminum addition

Degradations of polypropylene (PP) and polyethylene (PE) over pure hexagonal mesoporous silica and aluminum-containing hexagonal mesoporous silica catalysts were studied in a fixed bed catalytic reactor at 380 and 430 °C, respectively. The thermal and catalytic degradations of both PP and PE in liquid-phase-contact and vapor-phase-contact modes over pure hexagonal mesoporous silica had no significant effect on the product yields. The liquid products were widely distributed in hydrocarbons with boiling point ranges of 36–405 °C. By adding a small amount of aluminum to the hexagonal mesoporous material, aluminium-containing hexagonal mesoporous silica exhibited good performance in cracking heavy molecular weight hydrocarbons into light hydrocarbons. High liquid yields and less coke deposits were obtained in liquid-phase-contact reaction with increasing aluminum content. The liquid products were mainly composed of C₅–C₁₀ hydrocarbons with boiling points of 36–174 °C, and propene, butene, and butane were main components in gaseous products. The effect of degradation temperature was not observed on product yields though degradation rate of polyolefin into liquid products was faster. Conversely, in vapor-phase-contact reaction, an increase in gaseous yield was observed when increasing the amount of aluminum and temperature of the cracking reactor, while the residue yield remained constant.     

Synthesis of 1,1,9,9-tetrafluoro[2.2]paracyclophane and its polymerization by vapor deposition method

1,1,9,9-Tetrafluoro[2.2]paracyclophane ( 1 ) was prepared successfully as white crystals in 72% yield via two-step reactions from 1,9-diketo[2.2]-paracyclophane. The polymerization of 1 by the vapor deposition method was carried out at pyrolysis temperature range of 400 to 800°C and deposition temperature range of ?20 to 20°C, and a tough, transparent poly(α,α-difluoro-p-xylylene) film was obtained in 72% yield at the pyrolysis temperature of 750°C and the deposition temperature of ?20°C. It was found that the pyrolysis of 1 gave a reactive α,α-difluoro-p-xylylene, which polymerized on the head-to-tail addition to give poly(α,α-difluoro-p-xylylene). Some properties such as solubility, thermal stability, glass transition temperature, and density for poly(α,α-difluoro-p-xylylene) were studied. © 1995 John Wiley & Sons, Inc.     

Determination of prostatic androgens in 10 mg of tissue using liquid chromatography–tandem mass spectrometry with charged derivatization

A practical liquid chromatography–tandem mass spectrometric (LC-MS-MS) method for the determination of prostatic 5-dihydrotestosterone (DHT) and testosterone (T) has been developed. The prostatic androgens were extracted with MeOH–H₂O (3: 7, v/v), purified with an Oasis HLB cartridge, derivatized with the permanently charged reagent 2-hydrazino-1-methylpyridine (HMP), and subjected to LC–MS-MS analysis using electrospray ionization (ESI) operated in the positive ion mode. The derivatization with HMP was very effective at increasing the detectability using the positive-ESI-MS. The method allowed the reproducible and accurate quantification of ng g^–1 tissue levels of prostatic androgens in 10 mg of tissue. That is, the intra- and inter-assay coefficients of variation were below 8.1 and 9.3%, respectively, and the analytical recoveries of the androgens were quantitative. The limits of quantitation for DHT and T were both 1.0 ng g^–1 tissue. The developed method was used to determine DHT and T in the prostates of patients with benign prostatic hyperplasia and prostate cancer, and satisfactory results were obtained.     

ESR spectra fo matrix-isolated bromobenzene cations formed by radiolysis

Exposure of dilute solution of bromobenzene and p-dibromobenzene in fluorotrichloromethane to ⁶⁰Co_γ-rays at 77 K gave the corresponding cations characterized by ESR spectra. Estimated spin densities on bromine of ≈ 30% and 23%, respectively, are greater than those predicted by comparison with neutral α-bromo radicals, R₂CBr (≈ 15%). Evidence for dimer cation formation in more concentrated solutions is presented.     

Crystal structure analysis of β-tricalcium phosphate Ca3(PO4)2 by neutron powder diffraction

The crystal structure of sintered β-tricalcium phosphate, Ca₃(PO₄)₂, was refined using a high-resolution neutron powder diffraction data and the Rietveld method. This material was confirmed to have a rhombohedral structure (space group R3c, Z=21). Unit-cell parameters with higher precision (a=b=10.4352(2) Å, c=37.4029(5) Å, α=β=90°, and γ=120° in the hexagonal setting) and positional parameters for oxygen with equal precision were obtained by the neutron powder diffraction technique, compared with the single-crystal X-ray diffraction data by Dickens et al. (J. Solid State Chem. 10 (1974) 232). The site Ca(4) with atomic coordinates [0.0, 0.0, −0.0851(6)] was confirmed to be very different from the other four Ca sites: The position Ca(4) is three-fold coordinated with oxygen atoms, and has lower occupancy factor of 0.43(4), and a higher isotropic thermal parameter. On the contrary, each of the Ca(1), Ca(2), Ca(3), and Ca(5) is fully occupied by one Ca atom and these positions are coordinated with seven, eight, eight, and six oxygen atoms, respectively. The bond valence sums of Ca(4) and Ca(5) are lower (0.7) and higher (2.7), respectively, than the others (1.8-2.1).     

The role of Fe3+ on Fe2+-dependent lipid peroxidation in phospholipid liposomes

Fe2+-dependent lipid peroxidation in phosphatidylcholine (PC) liposomes, assessed by thiobarbituric acid-reactive substances (TBARS) production, was stimulated in the presence of Fe3+ in a concentration-dependent manner. The rates of nitroblue tetrazolium (NBT) reduction and Fe2+ oxidation (Fe2+ disappearance and Fe3+ formation) were also enhanced by the addition of Fe3+ to the reaction mixture, and there is a good linear relationship between these parameters. These results suggest that the facilitation of reactive oxygen species (ROS) production via Fe2+ oxidation is closely related to the onset of the stimulatory effect of Fe3+ on Fe2+-dependent lipid peroxidation. On the other hand, results using the liposomes containing various concentrations of endogenous lipid hydroperoxides (LOOH) indicated that endogenous LOOH is not directly involved in the onset of the Fe3+ stimulatory effect on Fe2+-dependent TBARS production and ROS production. This hypothesis was further confirmed by the evidence that Fe2+-dependent ROS production and Fe2+ oxidation of dipalmitoylphosphatidylcholine liposomes were also stimulated by the addition of Fe3+. The results with several antioxidants and radical scavengers suggested that ROS related to Fe2+-dependent lipid peroxidation and its stimulation by Fe3+ are ferrous-oxygen complexes rather than superoxide anion, hydrogen peroxide and hydroxyl radicals. Based on these results, we proposed a possible mechanism for the onset of the Fe3+ stimulation in Fe2+-dependent lipid peroxidation.