Two florescent xanthene-cyanamide lysosomal trackers emitting strongly at ~525 nm were prepared from fluorescein and rhodol methyl esters in microwave-assisted reactions. Both forms named "off" (nonfluorescent lactam) and "on" (strongly fluorescent ring-opened amide) have been comprehensively characterized out by using a combination of NMR spectroscopy, X-ray analysis, fluorimetry and confocal microscopy. Known rhodamines bearing electron-withdrawing groups (EWGs) exhibit an equilibrium between non-fluorescent (off) and fluores-cent (on) depending on the dielectric constant of the medium. Here, cyanamide was introduced as EWG amine into the fluorescein and rhodol framework. Unlike rhodamine-type dyes, the ring-opened forms of fluorescein-and rhodol-cyanamides are stable in protic solvents under circumneutral and basic pH conditions. The osteoblastic cell line MC3T3-E1 from C57BL/6 mouse calvaria was used for confocal imaging where the different organelles and nuclei were distinguished by using an orthogonal combination of fluorescent dyes.
In the prebiotic world, the chemical assembly of biotic building blocks led to racemic mixtures; however, homo-chirality emerged in the racemic prebiotic soup. Polymers and other molecules assembled from mixtures of enantiomers rather than racemic ones. Understanding how symmetry breaking happens is one of the most challenging fields of research in origin of life studies. With this article, we aim to shed light on one of the problems: in the absence of physical examples for use in a laboratory scale, what are the best models to use to simulate the conditions and lead to homo-chiral symmetry breaking? In this perspective, we suggest looking to chemical models that can represent a poorly studied class of prebiotic compounds in the context of symmetry breaking: the phospholipids.
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