New [60]fullerene-steroid conjugates (4-6) have been synthesized by 1,3-dipolar cycloaddition and Bingel-Hirsch cyclopropanation reactions from suitably functionalized epiandrosterone and [60]fullerene. Since a new stereocenter is created in the formation of the Prato monoaduct, two different diastereomers were isolated by HPLC (4, 5) whose absolute configurations were assigned according to the highly reliable "sector rule" on fullerenes. A further reaction of the malonate-containing diastereomer 5 with a second C60 molecule has afforded dumbbell fullerene 6 in which the two fullerene units are covalently connected through an epiandrosterone moiety. The new compounds have been spectroscopically characterized and their redox potentials, determined by cyclic voltametry, reveal three reversible reduction waves for hybrids 4 and 5, whereas these signals are split in dumbbell 6. Theoretical calculations at semiempirical (AM1) and single point B3LYP/6-31G(d) levels have predicted the most stable conformations for the hybrid compounds (4-6), showing the importance of the chlorine atom on the D ring of the steroid. Furthermore, TDDFT calculations have allowed assignments of the experimentally determined circular dichroism (CD) of the [60]fullerene-steroid hybrids based on the sign and position of the Cotton effects, despite the exceptionally large systems under study.

Structural and conformational study of a new steroid derivative using X-ray and density functional calculations.

Pyrrolil-silicon compounds were investigated by different theoretical approaches.Model monomers consisted in pyrrole ring N-substituted with silylmethoxy and silylhydroxy end-groups through propyl chain spacer, designated as PySi and PySiOH. Geometrical, vibrational and electronic properties, as well as chemical reactivity, are discussed and compared with Pyrrole (Py) and N-propylpyrrole (N-PrPy) that were studied in parallel for reference purposes and methods validation. The electronic distribution between PySi and PySiOH importantly differs, being the former electron donor, as Py and N-PrPy. Conversely, PySiOH presents donor-acceptor character with LUMO energy level localized on the silanol end-group.Global and local reactivity descriptors predict PySiOH more reactive than PySi with two preferential reactive sites: electron-rich Py ring and electron-deficient silanol group. Based on experimental studies, oligomers of PySiOH linked α−α' via Py rings (α−α'Py n SiOH, n = 2,3) were considered as model molecules of hydrolyzed PySi. The most stable structures were derived from randomly generated α−α'Py n SiOH that were optimized at semiempirical AM1 and refined with M05-2X/6-31G(d,p). Conformational analysis of dimer and trimer structures points to stability enhanced by molecular packing. Nonetheless, NBO and RDG results indicate that oligomers stability is dictated by the cooperative contribution of hydrogen bonding between silanol end-groups and dispersive vdW interactions between silanol and the π system of Py ring.The latter interaction resulting from electron delocalization induced by electron deficient silanol group seems to determine the smaller gap energy of T-shaped OH-π arrangements. The theoretical findings support the peculiar chemical behavior revealed by experiment.

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