Hideyuki Itagaki

Induction of Female-to-Male Sex Change in Adult Zebrafish by Aromatase Inhibitor Treatment

This study investigated whether undifferentiated germ and/or somatic stem cells remain in the differentiated ovary of a species that does not undergo sex changes under natural conditions and retain their sexual plasticity. The effect of aromatase inhibitor (AI)-treatment on sexually mature female zebrafish was examined. A 5-month AI treatment caused retraction of the ovaries after which testes-like organs appeared, and cyst structures filled with spermatozoa-like cells were observed in sections of these tissues. Electron microscopic observations revealed that these cells appeared as large sperm heads without tails. Sperm formation was re-examined after changing the diet to an AI-free food. A large number of normal sperm were obtained after eight weeks, and no formation of ovarian tissue was observed. Artificial fertilization using sperm from the sex-changed females was successful. These results demonstrated that sex plasticity remains in the mature ovaries of this species.

Physical gelation process for cellulose whose hydroxyl groups are regioselectively substituted by fluorescent groups

Abstract Five cellulose derivatives whose hydroxyl groups are regioselectively substituted by benzyl ether and methyl ether groups were prepared, i.e. 6- O -benzylcellulose, 2,3-di- O -methyl-6- O -benzylcellulose, 2,3-di- O -benzylcellulose 23B60), 2,3-di- O -benzyl-6- O -methylcellulose and 2,3,6-tri- O -benzylcellulose. The gelation did not take place in tetrahydrofuran solutions of the cellulose derivatives whose hydroxyl group at the 6-position was substituted to methyl ether or benzyl ether groups, but only the cellulose derivative having the 6-position hydroxyl group, i.e. 23B60, was found to form gels. All the samples except 23B60 showed only usual fluorescence of benzyl group over the temperature range 200–310 K. In contrast, the fluorescence of 23B60 shifted to the red and the excimer fluorescence increased with an increase of interactions between the cellulose molecules. Thus, our fluorescent probe method could elucidate the gelation process with a change of temperature in terms of the molecular association involving a hydrogen bond. In addition, the new absorption corresponding to the red-shifted fluorescence peak was also confirmed. The new species were concluded to be a ground state dimer formed intermolecularly between benzyl groups, meaning that there exists a hydrophobic interaction between them. In conclusion, (1) the main cause for the gel formation in our system is the hydrogen bonding by means of the 6-position hydroxyl group, and (2) the hydrophobic interaction between benzyl groups also keeps 23B60 molecules associated with one another, as well as the hydrogen bonds, after it is aggregated.

Intramolecular excimer formation of oligostyrenes from dimer to tridecamer: The measurements of rate constants for excimer formation, singlet energy migration, and relaxation of internal rotation

The emission properties of styrene oligomers from dimer to tridecamer have been investigated by picosecond pulse radiolysis at room temperature. The oligomers are precisely fractionated and are considered to be models of atactic polystyrene. The rate constant for excimer formation kDM of the order of 108 s−1, increases with increasing number of monomer units n for 2≤n≤8, then levels off at the value for polystyrene. The rate constant for singlet energy migration between adjacent chromophores in polystyrene was determined to be 3×1010 s−1 (∼30 ps). An average time of 7.2 ns was found to be necessary for two adjacent chromophores to assume the excimer conformation (g−t or tg− in a racemo dyad; tt in a meso dyad) from their initial equilibrium distribution of conformations. The present result is an indication that one may investigate the dynamics of internal rotation by photophysical techniques. Moreover, from a comparison of the results of photostationary measurements with those of transient methods, it is ...

Microenvironments in poly(ethylene terephthalate) film revealed by means of fluorescence measurements

Abstract The fluorescence behaviour of poly(ethylene terephthalate) (PET) films prepared by using a spin-casting method was measured. The wavelength of the fluorescence peak was found to be dependent on the casting temperature, T cast . This fluorescence is neither from a ground state dimer nor from an excimer. It is the red-shifted fluorescence of either the phenylene group or the phenylene exciplex due to interactions involving some contributions of charge-transfer stabilization among phenylene and carbonyl groups and/or phenylene groups. Both d.s.c. and i.r. measurements clearly showed that the fluorescence reflects whether the main-chain phenylene ring of PET is in the crystal region or in the amorphous region.

Photophysical studies of amorphous solids of bisphenol A polycarbonate

Abstract The fluorescence properties of bisphenol A polycarbonate (PC) solids were studied in detail as a function of casting and annealing temperatures (40–180°C), resulting in the establishment of a method to measure the pure fluorescence spectrum of PC solids. The spectrum was subject to contamination by a photoproduct of PC, which was assumed to have a similar structure to 2,2′-dihydroxydiphenyl. The existence of an excimer, formed between intermolecular phenyl groups in the PC main chain, was ascertained, showing that some main chains are located with a distance of 0.35 nm between one another in the amorphous area of PC solids.

Dynamic process of cold crystallization of poly(butylene terephthalate) solids revealed by fluorescence spectroscopy

The crystallinity of poly(ethylene terephthalate) (PET) films was investigated by comparing measurements of fluorescence, differential scanning calorimetry and density. It was found that the ratio of the fluorescence intensity at 330 nm to that at 370 nm can be an effective indicator of crystallinity. The dynamic process of recrystallization was directly observed for PET prepared using a spin-casting method on quartz disks by means of fluorescence measurements at several temperatures between 380 and 400 K. The recrystallization of such films was found to proceed one-dimensionally under the mechanism of heterogeneous nucleation, since the Avrami exponent, n, was determined to be one. The apparent activation energy of recrystallization was determined to be 120 kJ/mol, indicating that more than a few monomer units of PET participate in reorientation and crystallization. The present work should provide a quick and nondestructive method for determining the crystallinity of PET factory products.

Gelation of cellulose whose hydroxyl groups are specifically substituted by the fluorescent groups

SummaryThe hydroxyl groups of cellulose molecules were specifically substituted by fluorescent probe groups and their fluorescence behavior was studied with the change in the concentration of the THF solution. The results show that the fluorescent probes yield microscopic information on aggregation and that the hydroxyl groups at the 6-position of the cellulose repeating unit play an important role in this gelation process.

On the theory of concentration depolarization of fluorescence in one‐ and two‐component systems for multipole interactions in one, two, and three dimensional medium

A theoretical analysis of the emission anisotropy of one‐ and two‐component systems for multipole interactions in one, two, and three dimensional medium is presented. The developed model explores an alternative extension of the Huber et al. theory [Phys. Rev. B 16, 4642(1977)] for higher concentrations where pair approximation is not fulfilled. A detailed analysis of emission anisotropy for three dimensional medium and dipole–dipole interactions has been presented. Inclusion of the possibility of return of the excitation to the originally excited donor molecule from more and more remote donor molecules lead to a substantial increase in the fluorescence emission anisotropy. Numerical analysis shows that experimental results of the emission anisotropy for rhodamine B in the presence of malachite green are well described by the equations presented here for a two‐component system. A comparison with models developed by other authors has been presented.

Information on amorphous area and recrystallization process of poly(ethylene terephthalate) solids revealed by means of fluorescence measurements

Abstract The crystallinity of poly(ethylene terephthalate) (PET) solids was shown to be monitored by measuring PET fluorescence: fluorescence at 330 nm for crystal region and one at 370 nm for amorphous region. Thus, the recrystallization process of the amorphous region was directly observed by annealing PET films above 380 K. The time change of the crystallinity accompanied by the recrystallization process was best fitted to an exponential function; time constant at 390 K was determined to be 33 ± 5 min.

Normal and second excimers in macromolecules—II: Poly(1-methoxy-4-vinylnaphthalene) in polystyrene solid solution

Abstract Normal and second excimer formation has been examined for poly(1-methoxy-4-vinylnaphthalane) (PMVN) in polystyrene solid films as a function of measurement temperature from 420 to 77 K and film casting temperature between 369 and 303 K. It became clear that the conformation of the second excimer forming site is different from that of the normal excimer forming site. The difference in energy between the most stable conformation and the excimer forming site is 2.0 kcal/mol for the normal excimer and less than 1 kcal/mol for the second excimer. Moreover the temperature dependence of the second excimer to monomer intensity ratio is found to give information about Tγ (γ dispersion temperature) of the host polystyrene films, below which the motion of phenyl rings is restricted.