Efficient shielding of phosphorescent transition metal complexes against diffusion-controlled collisional quenching by triplet molecular dioxygen as well as reduction of microenvironment-related radiationless deactivation pathways is crucial for their applications in bioimaging and optoelectronics. In this report, we present a straightforward yet efficient approach to safeguard emissive triplet states from external influences by adsorbing phosphorescent Pt(II) complexes onto a layered nanoclay, namely Laponite. These hybrids facilitate the dispersion of otherwise insoluble transition metal complexes in aqueous media while shielding them from physical quenching. Self-assembly of the nanoclay and intermolecular stacking between molecules adsorbed at different nanodisc units are mirrored in the photophysical, colloidal, and morphological properties of the hybrids, which were herein characterized by steady-state and time-resolved photoluminescence spectroscopy, dynamic light scattering, and atomic force microscopy. We also show that the hybrids are noncytotoxic and can be exploited as luminescent reporters in spectrally resolved phosphorescence lifetime imaging implemented by confocal optical microscopy.
In continuation of the search for new anthelmintic natural products, the study at hand investigated the nematicidal effects of the two naturally occurring quassinoids ailanthone and bruceine A against the reproductive system of the model nematode Caenorhabditis elegans to pinpoint their anthelmintic mode of action by the application of various microscopic techniques. Differential Interference Contrast (DIC) and the epifluorescence microscopy experiments used in the presented study indicated the genotoxic effects of the tested quassinoids (c ailanthone = 50 µM, c bruceine A = 100 µM) against the nuclei of the investigated gonadal and spermathecal tissues, leaving other morphological key features such as enterocytes or body wall muscle cells unimpaired. In order to gain nanoscopic insight into the morphology of the gonads as well as the considerably smaller spermathecae of C. elegans, an innovative protocol of polyethylene glycol embedding, ultra-sectioning, acridine orange staining, tissue identification by epifluorescence, and subsequent AFM-based ultrastructural data acquisition was applied. This sequence allowed the facile and fast assessment of the impact of quassinoid treatment not only on the gonadal but also on the considerably smaller spermathecal tissues of C. elegans. These first-time ultrastructural investigations on C. elegans gonads and spermathecae by AFM led to the identification of specific quassinoid-induced alterations to the nuclei of the reproductive tissues (e.g., highly condensed chromatin, impaired nuclear membrane morphology, as well as altered nucleolus morphology), altogether implying an apoptosis-like effect of ailanthone and bruceine A on the reproductive tissues of C. elegans.
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