Case Report of Rarely Described Polymorphous Low-Grade Neuroepithelial Tumor of the Young and Comparison with Oligodendroglioma.

BACKGROUND: Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a central nervous system tumor that shares many qualities with oligodendroglioma but is rarely and only very recently described as a distinct entity in the literature. CASE DESCRIPTION: A previously healthy, 19-year-old man presented with new onset of seizures. Imaging showed an intracranial mass, which was treated with surgical removal. Preoperative and postoperative magnetic resonance imaging, histopathologic examination, genetic testing, and immunohistochemical staining all supported a diagnosis of PLNTY. CONCLUSIONS: Diagnostic investigation of PLNTY shows many similarities with oligodendroglioma, and thus these entities can be mistaken for one another. Certain studies are needed to distinguish PLNTY and other dysembryoplastic neuroepithelial tumors, such as oligodendroglioma.

Cooperative self-assembly of dendrimers via pseudorotaxane formation from a homotritopic guest molecule and complementary monotopic host dendrons.

Interaction of the homotritopic guest 1,3,5-tris[p-(benzylammoniomethyl)phenyl]benzene tris(hexafluorophosphate) (1a) with dibenzo-24-crown-8 (DB24C8) leads to the sequential self-assembly of [2]-, [3]-, and [4]-pseudorotaxanes 7a, 8a, and 9a, respectively. The self-assembly processes were studied using NMR spectroscopy. In CD(3)CN and CD(3)COCD(3) the individual association constants K(1), K(2), and K(3) for 1:1, 1:2, and 1:3 complexes were determined by several methods. Via Scatchard plots, the three NH(2)(+) sites of 1a were shown to behave independently in binding DB24C8. K values (4.4 x 10(2), 1.4 x 10(2), and 41 M(-)(1), respectively, in CD(3)CN) directly determined from signals for the individual complexes (7a, 8a, and 9a) were somewhat higher than those estimated from the Scatchard plot because of concentration dependence, but the ratios of association constants followed the expected statistical order (K(1):K(2):K(3) = 3:1:(1)/(3)). These are believed to be the first evaluations of association constants leading to a [4]-pseudorotaxane. In the less polar CDCl(3), association constants could not be determined because approximately 90% of the dissolved tritopic guest, which by itself is insoluble, was present as the fully loaded [4]pseudorotaxane 9a! Self-assembly of homotritopic guest 1a with benzyl ether dendrons of the first, second, and third generations functionalized at the "focal point" with DB24C8 moieties (3-5) produces pseudorotaxane dendrimers. The self-assembly processes were studied using (1)H NMR spectroscopy. In CD(3)COCD(3) for all three generations the individual association constants K(1), K(2), and K(3) for [2]-, [3]-, and [4]-pseudorotaxane complexes 7c-e, 8c-e, and 9c-e indicated that the self-assembly was cooperative; that is, the ratios of the individual association constants exceeded the expected statistical ratios. Scatchard plots confirmed this behavior. Self-assembly processes in the less polar CDCl(3) were kinetically slow, requiring ca. 1, 2, and 3 days, respectively, for the first, second, and third generation systems to reach equilibrium with 1a; the slow rate is attributed to the insolubility of the homotritopic guest 1a in this medium and the steric demands of the resulting dendrimers. However, only dendrimers of 1:3 stoichiometry, that is, the nanoscopic [4]pseudorotaxanes 9, were formed! Moreover, it is noteworthy that the extent of dissolution of 1a (reflective of the overall association constant which is too high to measure) increases with generation number, presumably because of the more effective screening of the ionic guest by the larger dendrons and perhaps favorable pi-pi and CH-pi interactions. Such cooperative effects suggest a number of applications that can take advantage of the pH-switchable nature of these self-assembly processes.

Dendritic Pseudorotaxanes.

Self-organization is the key. A series of dendritic pseudorotaxanes were efficiently constructed from complementary building blocks-namely, a three-armed, triply charged ammonium salt and the first, second, and third generations of benzyl ether dendrons bearing the dibenzo[24]crown-8 moiety. The pseudorotaxane arising from the third-generation dendron is shown in the picture.