Metachronous bilateral leydig cell tumor in a male adult aged 20.

We report a young male aged 20 who has suffered two episodes of Leydig cell tumor of the testis, the second occurring 5 years after the first in the contralateral testis. The case is outlined briefly, with references taken from the literature. This young man's history is exceptional as this type of tumor is infrequent, and metachronous bilateral presentation extremely rare.

Synthesis, aggregation, and chiroptical properties of chiral, amphiphilic dendrimers.

The syntheses of amphiphilic dendrimers based on 3,5-dihydroxybenzyl alcohol containing tri- or tetrafunctional chiral central cores and allyl ester termini are described. Water solubility is imparted to the dendrimers via a palladium-catalyzed deprotection of the peripheral allyl esters. This method affords complete deprotection of the carboxylate surface because, in contrast to the basic hydrolysis of methyl ester termini, the solubility of partially hydrolyzed intermediates is maintained throughout the course of the deprotection, thereby avoiding precipitation during the reaction. Chiroptical analysis indicates that the structure of the dendrimers collapses in water, resulting in an increased steric effect upon the central core that is manifested by lower optical rotatory power. However, contributions to the chiroptical properties from the dendron branch segments were not evident in water or organic media, suggesting that chiral substructures were not developing in the branch segments of the dendrimers. Multiangle light scattering studies revealed that the dendrimers experienced significant aggregation in aqueous media that decreased at higher generations. This behavior could be rationalized by a change in conformational preference from a disklike conformation at low generations to a more globular conformation at higher generations.

A Light Scattering Study of the Association of Hydrophobically alpha- and alpha,omega-End-capped Poly(ethylene oxide) in Water.

Several hydrophobically alpha- and alpha,omega-end-capped poly(ethylene oxide) polymers were studied by light scattering below and above their critical association concentration, in order to understand their association mechanisms. In the case of monofunctionalized PEO, a one-step closed association model well fits the experimental data, with a limit number of aggregation of about 30, consistent with other experimental data and a theoretical approach. In the case of difunctionalized PEO, a good description of the experimental data is obtained by assuming a two-step association process: at low concentration, the formation of "flower-like" micelles is well described by a closed association model, whereas at higher concentration, the progressive bridging of these "flowers" can be modeled by an open association. Copyright 2000 Academic Press.