An anionic iron(II)
tetrahedral molecular cage (FeMOP) was studied
for its ability to interact with various per- and polyfluoroalkyl
substances (PFASs) in aqueous media. Liquid chromatography tandem
mass spectrometry revealed that longer-chain-length (more than six
carbons) perfluorocarboxylic, -sulfonic, and fluorotelomers were removed
from solution. In contrast, the steric bulk of N-ethyl
substituted fluorosulfonamido acetic acid PFASs hindered association
with the cage. Solution binding studies in D2O using 19F nuclear magnetic resonance (NMR) titrations and a Job plot
show a 1:1 binding stoichiometry for perfluorohexanoic acid (PFHxA)
and perfluoroheptanoic acid (PFHpA) with an association constant (K
a) of <103 and thus a favorable
free energy of association (ΔG°). Perfluorononanoic
acid (PFNA), on the other hand, forms an insoluble host–guest complex with FeMOP with a 1:1 host–guest ratio. Variable temperature (VT) NMR was used to determine
the thermodynamic parameters of binding for a 1:1 FeMOP/PFHpA complex
in water using a Curie-like model for fast-exchange processes. The
extracted parameters suggest a low binding interaction (K
a < 103) driven by an increase in entropy
from cage desolvation upon guest binding. The solid-state host–guest
complexes formed from solution complexation of PFHxA, PFHpA, and PFNA
into the cage were characterized by infrared spectroscopy (FT-IR)
and powder X-ray diffraction (PXRD) methods. FT-IR studies suggest
an interaction between the fluorocarbon groups of PFASs to the phenylsulfonate
functional groups of the ligand. A docking model predicted by computation
also indicates this interaction may occur, with the PFASs adsorbing
onto the surface of the cage rather than forming a true host–guest complex within the internal cavity. PXRD studies
reveal a crystal packing of the complex that is very similar to that
of the water-treated FeMOP, with the exception of 1:2 FeMOP/PFNA and
1:1 and 2:1 FeMOP/PFHpA.
Plants of the Digitalis genus contain a cocktail of cardenolides commonly prescribed to treat heart failure. Cardenolides in Digitalis extracts have been conventionally quantified by highperformance liquid chromatography yet the lack of structural information compounded with possible co-eluents renders this method insufficient for analyzing cardenolides in plants. The goal of this work is to structurally characterize cardiac glycosides in fresh-leaf extracts using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) that provides exact masses. Fragmentation of cardenolides is featured by sequential loss of sugar units while the steroid aglycon moieties undergo stepwise elimination of hydroxyl groups, which distinguishes different aglycones. The sequence of elution follows diginatigenin digoxigenin gitoxigenin gitaloxigenin digitoxigenin for cardenolides with the same sugar units but different aglycones using a reverse-phase column. A linear range of 0.8-500 ng g -1 has been achieved for digoxigenin, β -acetyldigoxin, and digitoxigenin with limits of detection ranging from 0.09 to 0.45 ng g -1 . A total of 17 cardenolides have been detected with lanatoside A, C, and E as major cardenolides in Digitalis lanata while 7 have been found in Digitalis purpurea including purpurea glycoside A, B, and E. Surprisingly, glucodigifucoside in D. lanata and verodoxin and digitoxigenin fucoside in D. purpurea have also been found as major cardenolides. As the first MS/MS-based method developed for analyzing cardenolides in plant extracts, this method serves as a foundation for complete identification and accurate quantification of cardiac glycosides, a necessary step towards understanding the biosynthesis of cardenolide in plants..
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.