Yoshihiro Kimura

Synthesis and properties of all members of methylated tropylium ions

Abstract An members of the methylated tropylium perchlorates have been synthesized and their properties (UV absorptions, 1H NMR spectra, and charge-transfer spectra with pyrene) determined. The methylated tropylium ions other than the hexa- and hepta-methyl homologues have been prepared by abstracting a hydride ion with trityl perchlorate from the corresponding methylated tropilidenes. The preparation of the hexa- and hepta-methyltropylium ions has been effected by utilizing phosphorus pentachloride as the hydride-abstraction reagent. The methylated tropilidenes have been prepared via one of the three known routes, i.e. the ring expansion of methylated benzenes with diazomethane (Route 1) or with ethyl diazoacetate (Route 2), and the cycloaddition of cyclopropene or methylcyclopropenes with methylated thiophene 1,1-dioxides accompanied with the exclusion of sulfur dioxide (Route 3). The methyl 1H NMR chemical-shift values have been assigned, partly with the aid of the Me 13C NMR chemical-shift data for the tropylium ions containing the Me groups on contiguous ring-carbons (3a, 4a, 5a, 6 and 7). The transition energy for the charge-transfer band of the tropylium ions with pyrene increases with the increase in the number of the Me group, indicating that the more methylated the tropylium ion, the more stable is the ion.

Regulatory Mechanisms of Granulosa Cell Apoptosis in Ovarian Follicle Atresia

Porcine ovary samples were prepared for histochemical and ultrastructural analyses. In situ analysis of DNA fragmentation was performed on histological sections of follieles using the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end-labeling TUNEL) method. No apoptotic cells were observed in healthy follicles. In atretic follicles, apoptotic TUNEL staining was seen in scattered granulosa cells located on the inner surface of the follicular wall, but not in cumulus cells, internal or external theca cells, or oocytes. Nuclear condensation, a typical feature of apoptosis was seen only in scattered granulosa cells. The neutral Ca2+/Mg2+-dependent endonuclease is involved in granulosa cell apoptosis. No endonuclease activity was detected in cumulus cells. An IgM monoclonal antibody (PFG-1) capable of inducing granulosa cell apoptosis was then produced against granulosa cells prepared from healthy antral follicles. Two-dimensional (2D) Western blotting analysis revealed that PFG-1 specifically recognized a cell-membrane protein (PFG-1 antigen, 55 kD, pl 5.9). PFG-1 immunohistochemically reacted with granulosa cells of healthy follicles but not those of atretic follicles. When the isolated granulosa cells prepared from healthy follicles were cultured in medium containing 0.1 μg/ml of PFG-1, the cells underwent apoptosis. These observations indicated that apoptosis occurs in granulosa cells but not cumulus cells in the atretic follicles and that the PFG-1 antigen, a novel cell death receptor, is different from the apoptosis-mediating receptors Fas antigen or tumor neerosis factor receptor 1 (TNFR-1).

The one-electron reduction of carbonium ions. Part 14. Effect of successive introduction of methyl substituents on the reducibility of tropylium ion in chromium(II) ion and cathodic reductions

The second-order rate constants (k2) of one-electron reduction with CrII ion of methylated tropylium ions [C7H7 –n(CH3)n+ClO4–, n= 0–7] were determined in 10% hydrochloric acid at 25.0°C. Reduction peak potentials determined by means of triangular wave cyclic voltammetry and charge transfer energies with pyrene were compared with the rates of CrII ion reduction in terms of the effect of methyl substituents. The log k2 values decrease linearly with an increase in the number of methyl groups up to n= 4. However, the decelerating effect per extra methyl substituent becomes smaller when n is 5 or 6, and the seventh methyl substituent accelerates the reduction. The methyl substituent effect on the reduction peak potentials of the carbocations is similar to that found for the CrII ion reduction, giving rise to a linear correlation. A Marcus treatment suggests that CrII ion reduction proceeds through an outer-sphere mechanism. The charge transfer energies with pyrene are linearly correlated with reduction potentials for ions with n= 0–6, but considerable deviation is noted when n is 7. The charge transfer energies are linearly correlated with the LUMO energy levels of the methylated tropylium ions, suggesting that the unexpectedly pronounced reducibilities of hexa- and hepta-methyltropylium ions are attributable to steric factors. The deviation from linearity in the CrII ion reduction and the reduction potential are reasonably explained by assuming that non-bonded repulsive interactions among congested methyl substituents in the carbocations are relieved upon reduction to their corresponding radicals. This explanation is consistent with our previous conclusion from a 13C n.m.r. study that the methyl substituents of 1,2,3,4,5-penta-, hexa-, and hepta-methyltropylium ions are highly congested and distorted out of plane.