Electrochemical, theoretical, and morphological studies of antioxidant fullerosteroids

Abstract

Four fullerosteroidal conjugates, previously confirmed to express two-to threefold better antioxidant activity in vitro than C 60 , were subjected to additional studies, including electrochemical, theoretical, and morphological examination. All tested compounds underwent reversible, diffusion-controlled reductions. A notable influence of the solvent properties on the reduction potential, the level of aggregation, and the lowest unoccupied molecular orbital (LUMO) energy was observed. Theoretical calculations indicated that the energy gain obtained by an intermediate formation, together with compounds' polarizability, polarity, and lipophilicity contributed to the radical quenching capacity. Very large supramolecular aggregates of all fullerosteroidal esters with no hierarchical arrangement were observed in precipitated samples, while solvent induced self-assembling led to round nanoplates, which further arranged to flowershaped hierarchically ordered architectures or uniformly distributed discoid particles. As in electrochemical studies, fine tuning of the aggregation level was achieved by the solvent.

Steroid–Fullerene Hybrids from Epiandrosterone: Synthesis, Characterization and Theoretical Study

“…ral products. [17,18,20,21] Gathering these two entities has allowed these conjugates to be more soluble than pristine [60]fullerene in aqueous medium as well as in organic solvents. [13,14] It has also been shown that certain structural modifications induced the change of biological response, giving compounds with a wide scope of biological activity.…”

“…[17,18,20,21] Gathering these two entities has allowed these conjugates to be more soluble than pristine [60]fullerene in aqueous medium as well as in organic solvents. Thus, some studies have been published reporting on the antioxidant activity of fulleropyrrolidines endowed with an steroid unit, [20,21,27] the effect of steroid-fullerene adducts on sarcoplasmic reticulum (SR) Ca 2+ -ATPase and survival of human lung adenocarcinoma cancer A549 cells. [23] The synthetic methods for preparing hybrid steroid-fullerenes are based on the electrophilic character of C 60 , the most common reactions reported for the modifications of fullerenes being the cycloadditions.…”

“…[18,19] The synthesis of hybrid molecules by covalent linkage of steroids to [60]fullerene is an interesting topic, and nowadays is a common approach in the pursuit of compounds for biomedical and chemical applications. [17,18,20,21] Gathering these two entities has allowed these conjugates to be more soluble than pristine [60]fullerene in aqueous medium as well as in organic solvents. [22] The hybrids thus formed not only may modulate the properties of each one of the components, but also allow obtaining chimeric molecular entities with completely new properties and functions.…”

“…[26] A variety of biological activities have been reported for fullerene-steroid conjugates. Thus, some studies have been published reporting on the antioxidant activity of fulleropyrrolidines endowed with an steroid unit, [20,21,27] the effect of steroid-fullerene adducts on sarcoplasmic reticulum (SR) Ca 2+ -ATPase and survival of human lung adenocarcinoma cancer A549 cells. [25] Employing cholesterol, or cholesterol derivatives, attached to [60]fullerene through a pyrrolidine ring, some hybrids have been described, demonstrating that the steroid moiety can confer useful solubility in components of biological fluids, impacting on the biodistribution of the fullerenes, which makes these derivatives useful in imaging, diagnosis, and in the treatment or in management of disease.…”

Fulleropeptide esters as potential self-assembled antioxidants

“…Additionally, morphological characterization of self-organized structures of fullerene–steroid [26] and fullerene–peptide–steroid hybrids [25] in solution and in the solid state was studied by SEM. In our previous work [27], we described the synthesis and provided a thorough spectral characterization of a series of fulleropeptide tert -butyl esters ( 2 – 12 , Fig.…”