We describe in detail a strategy for creating foldamers in which interactions between mechanically interlocked components dictate the single-molecule assembly of a folded secondary structure. This ...unique folding motif is based on a flexible polyether dumbbell bearing 1,5-dioxynaphthalene (DNP) donors, which folds its way through a series of cyclobis(paraquat-p-phenylene) (CBPQT super(4+)) acceptor rings in a serpentine fashion to enable extended donor-acceptor (D-A) stacking between DNP and the electron-poor 4,4'-bipyridinium (BIPY super(2+)) units in CBPQT super(4+). These oligorotaxanes can be prepared in a wide range of sizes, with molecular weights up to >15 000 Da, on account of novel one-pot reactions we developed to generate the necessary oligo-DNP precursors. The product distributions from the final kinetically controlled stoppering reactions are highly biased towards oligorotaxanes in which approximately half of the DNP units are encircled by rings, a fact which can be rationalized if the dominant solution-state structures of the pseudorotaxane precursors reflect the solid-state superstructures of analogous compounds, which express 50% recognition site occupancy because of their proclivity to pack into continuous D-A-D-A stacks. The presence of well-defined folded structures in solution have been confirmed by super(1)H NMR spectroscopy in CD sub(3)CN. Moreover, we discovered an empirical selection rule forbidding CBPQT super(4+) rings to occupy adjacent DNP sites, which elegantly explains both the product distributions and the super(1)H NMR spectra. Depending on their adherence to this selection rule, all of the oligorotaxanes belong to one of three families: whereas 'Confused' oligorotaxanes adopt multiple translational isomers that satisfy the rule and 'Frustrated' species cannot obey it at all, members of the 'Happy' family each express only one rule-compliant 'Goldilocks' isomer. The NMR spectra of these oligorotaxanes also shed light on their dynamics; rapid 180 degree rotations of DNP units cause pairs of heterotopic BIPY super(2+) protons in the accompanying CBPQT super(4+) rings to exchange sites, giving rise to time-averaged signals. This process, which we term 'superrotation', will apply much more generally to other mechanically interlocked systems.
Metal–organic frameworks (MOFs) have been proposed as a promising material for non‐thermal chemical separations owing to their high structural diversity and tunability. Here, we report the synthesis ...of a zinc‐based MOF containing a three‐dimensional (3D) linker, bicyclo2.2.2octane‐1,4‐dicarboxylic acid, with high thermal stability towards the separation of hexane isomers. The incorporation of the 3D linker enhances the structural stability and provides well‐defined pore apertures/channels with sub‐Ångstrom precision. This precision allowed for the separation of similarly sized hexane isomers based on subtle differences in their kinetic diameters. Multi‐component liquid phase batch experiments confirmed the separation of hexanes mixture into linear, monobranched, and dibranched isomers. This work represents a significant milestone in the construction of stable Zn‐based MOFs and the incorporation of 3D linkers as a potential solution to challenging separations.
Sub‐Ångstrom tuning and control of pore aperture in metal–organic frameworks was achieved through expansion of linker dimensionality for selective separation of linear, monobranched, and dibranched hexane isomers.
We recently engineered the first female reproductive tract on a chip (EVATAR), to enable sex-based ex vivo research. To increase the scalability and accessibility of EVATAR, we turned to 3D printing ...(3DP) technologies, selecting two biocompatible 3DP resins, Dental SG (DSG) and Dental LT (DLT) to generate 3DP microphysiologic platforms. Due to the known sensitivity of reproductive cells to leachable compounds, we first screened for toxicity of these biomaterials using an in vitro mammalian oocyte maturation assay. Culture of mouse oocytes in 3DP plates using conventionally treated DSG resin resulted in rapid oocyte degeneration. Oxygen plasma treatment of the surface of printed DSG resin prevented this degeneration, and the majority of the resulting oocytes progressed through meiosis in vitro. However, 57.0% ± 37.2% of the cells cultured in the DSG resin plates exhibited abnormal chromosome morphology compared to 19.4% ± 17.3% of controls cultured in polystyrene. All tested DLT resin conditions, including plasma treatment, resulted in complete and rapid oocyte degeneration. To identify the ovo-toxic component of DLT, we analyzed DLT leachate using mass spectroscopy. We identified Tinuvin 292, a commercial light stabilizer, as a major component of the DLT leachate, which resulted in a dose-dependent disruption of meiotic progression and increase in chromosomal abnormalities with oocyte exposure, showing significant ovo-toxicity in mammals. Severe reproductive toxicity induced by in vitro exposure to these 3D-printed resins highlights potential risks of deploying insufficiently characterized materials for biomedical applications and underscores the need for more rigorous evaluation and designation of biocompatible materials.
•Exposure to dental resins commonly used for 3D printing technology causes mammalian oocyte toxicity in vitro .•Dental LT resin exposure results in more severe oocyte toxicity compared to Dental SG.•The commercial light stabilizer Tinuvin 292 leaches from Dental LT resin.•Exposure to Tinuvin 292 mimics the oocyte toxicity observed with dental resins.•Our findings underscore the need for more rigorous evaluation and designation of biocompatible materials.
Metal–organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules ...with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo1.1.1pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different sizes and shapes of these isomers.
Legionella pneumophila, the agent of Legionnaires' disease, secretes a siderophore (legiobactin) that promotes bacterial infection of the lung. In past work, we determined that cytoplasmic LbtA (from ...Legiobactin gene A) promotes synthesis of legiobactin, inner membrane LbtB aids in export of the siderophore, and outer membrane LbtU and inner membrane LbtC help mediate ferrilegiobactin uptake and assimilation. However, the past studies examined legiobactin contained within bacterial culture supernatants. By utilizing high-pressure liquid chromatography that incorporates hydrophilic interaction-based chemistry, we have now purified legiobactin from supernatants of virulent strain 130b that is suitable for detailed chemical analysis. High-resolution mass spectrometry (MS) revealed that the molecular mass of (protonated) legiobactin is 437.140 Da. On the basis of the results obtained from both MS analysis and various forms of nuclear magnetic resonance, we found that legiobactin is composed of two citric acid residues linked by a putrescine bridge and thus is identical in structure to rhizoferrin, a polycarboxylate-type siderophore made by many fungi and several unrelated bacteria. Both purified legiobactin and rhizoferrin obtained from the fungus Cunninghamella elegans were able to promote Fe(3+) uptake by wild-type L. pneumophila as well as enhance growth of iron-starved bacteria. These results did not occur with 130b mutants lacking lbtU or lbtC, indicating that both endogenously made legiobactin and exogenously derived rhizoferrin are assimilated by L. pneumophila in an LbtU- and LbtC-dependent manner.
Metal–organic frameworks (MOFs) have been proposed as a promising material for non‐thermal chemical separations owing to their high structural diversity and tunability. Here, we report the synthesis ...of a zinc‐based MOF containing a three‐dimensional (3D) linker, bicyclo2.2.2octane‐1,4‐dicarboxylic acid, with high thermal stability towards the separation of hexane isomers. The incorporation of the 3D linker enhances the structural stability and provides well‐defined pore apertures/channels with sub‐Ångstrom precision. This precision allowed for the separation of similarly sized hexane isomers based on subtle differences in their kinetic diameters. Multi‐component liquid phase batch experiments confirmed the separation of hexanes mixture into linear, monobranched, and dibranched isomers. This work represents a significant milestone in the construction of stable Zn‐based MOFs and the incorporation of 3D linkers as a potential solution to challenging separations.
Sub‐Ångstrom tuning and control of pore aperture in metal–organic frameworks was achieved through expansion of linker dimensionality for selective separation of linear, monobranched, and dibranched hexane isomers.
We describe in detail a strategy for creating foldamers in which interactions between mechanically interlocked components dictate the single-molecule assembly of a folded secondary structure. This ...unique folding motif is based on a flexible polyether dumbbell bearing 1,5-dioxynaphthalene (DNP) donors, which folds its way through a series of cyclobis(paraquat-
p
-phenylene) (CBPQT
4+
) acceptor rings in a serpentine fashion to enable extended donor-acceptor (D-A) stacking between DNP and the electron-poor 4,4′-bipyridinium (BIPY
2+
) units in CBPQT
4+
. These oligorotaxanes can be prepared in a wide range of sizes, with molecular weights up to >15 000 Da, on account of novel one-pot reactions we developed to generate the necessary oligo-DNP precursors. The product distributions from the final kinetically controlled stoppering reactions are highly biased towards oligorotaxanes in which approximately half of the DNP units are encircled by rings, a fact which can be rationalized if the dominant solution-state structures of the pseudorotaxane precursors reflect the solid-state superstructures of analogous compounds, which express 50% recognition site occupancy because of their proclivity to pack into continuous D-A-D-A stacks. The presence of well-defined folded structures in solution have been confirmed by
1
H NMR spectroscopy in CD
3
CN. Moreover, we discovered an empirical selection rule forbidding CBPQT
4+
rings to occupy adjacent DNP sites, which elegantly explains both the product distributions and the
1
H NMR spectra. Depending on their adherence to this selection rule, all of the oligorotaxanes belong to one of three families: whereas '
Confused
' oligorotaxanes adopt multiple translational isomers that satisfy the rule and '
Frustrated
' species cannot obey it at all, members of the '
Happy
' family each express only one rule-compliant 'Goldilocks' isomer. The NMR spectra of these oligorotaxanes also shed light on their dynamics; rapid 180° rotations of DNP units cause pairs of heterotopic BIPY
2+
protons in the accompanying CBPQT
4+
rings to exchange sites, giving rise to time-averaged signals. This process, which we term 'superrotation', will apply much more generally to other mechanically interlocked systems.
We describe in detail a strategy for creating foldamers in which interactions between mechanically interlocked components dictate the single-molecule assembly of a folded secondary structure.
PDF
