Surface charge is a key characteristic of nanoparticles which has great potential to impact the interactions of nanoparticles and biological systems. Understanding the role charge plays in these interactions is key to determining the ecological risks of nanoparticle exposure and informing sustainable nanoparticle design. In this study, the model freshwater algae Raphidocelis subcapitata was exposed to carbon dots (CDs) functionalized with polymers to have positive, negative, or neutral surface charges to examine the impact of nanoparticle surface charge on nano-algae interactions. Traditional toxicological endpoints of survival and growth inhibition were measured. Additionally, morphological impacts on whole cells, individual organelles, and cellular components were quantified using high-content fluorescence microscopy, demonstrating one of the first uses of high-content imaging in microalgae. Results indicate that PEI functionalized, positively charged CDs are most toxic to green algae (EC50 42.306 μg/L), but that CDs with negative charge induce sublethal impacts on algae. PEI-CD toxicity is hypothesized to be related to electrostatic interactions between CDs and the algal cell wall, which lead to significant cell aggregation. Interestingly, morphological data suggests that exposure to both positively and negatively charged CDs leads to increased neutral lipid droplet formation, a possible indicator of nutrient stress. Further investigation of the mechanisms underlying impacts of nanoparticle surface charge on algae biology can lead to more sustainable nanoparticle design and environmental protections.
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Enhanced host–guest complexation of short chain perfluoroalkyl substances with positively charged β-cyclodextrin derivatives
Short chain perfluoroalkyl substances (PFAS), replacements for long chain legacy PFAS such as perfluorooctanoic acid (PFOA), have similar toxicity, negative health effects, and exceptional persistence as long chain PFAS. β-Cyclodextrin (β-CD) is a powerful host–guest complexing agent for a number of legacy PFAS, suggesting potential β-CD-based remediation processes. We report herein that the addition of charged functional groups at the perimeter of β-CD has a pronounced influence on the strength of the β-CD:PFAS complex. The presence of a positively charged amine functionality on the perimeter of β-CD significantly increases the complexation of legacy and short chain PFAS. We assigned the enhanced complexation to electrostatic attraction between the negatively charged PFAS head group and the positively charged β-CD derivative. In comparison to neutral β-CD, addition of a negative charge to β-CD decreases complexation to PFAS due to electrostatic repulsion between the negatively charged polar head group of PFAS and the negatively charged β-CD. 19F NMR titration experiments illustrate the complexation of short chain PFAS by positive charged β-CDs over neutral β-CD, with increases up to 20 times depending on the PFAS guest. The results give further understanding to the nature of the β-CD:PFAS host–guest complex and the various intermolecular forces that drive complexation. Positively charged β-CDs appear to be potential complexing agents for remediation of short chain PFAS.
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- NSF-PAR ID:
- 10104074
- Date Published:
- Journal Name:
- Journal of Inclusion Phenomena and Macrocyclic Chemistry
- ISSN:
- 1388-3127
- Page Range / eLocation ID:
- 1 - 7
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Although most manufacturers stopped using long-chain per- and polyfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), short-chain PFASs are still widely employed. Short-chain PFASs are less known in terms of toxicity and have different adsorption behavior from long-chain PFASs. Previous studies have shown electrostatic interaction with the adsorbent to be the dominant mechanism for the removal of short-chain PFASs. In this study, we designed a high charge density cationic quaternized nanocellulose (QNC) to enhance the removal of both short- and long-chain PFASs from contaminated water. Systematic batch adsorption tests were conducted using the QNC adsorbent to compare its efficiency against PFASs with varying chain lengths and functional groups. From the kinetic study, PFBA (perfluorobutanoic acid), PFBS (perfluorobutanesulfonic acid) and PFOS showed rapid adsorption rates, which reached near equilibrium values (>95% of removal) between 1 min to 15 min, while PFOA required a relatively longer equilibration time of 2 h (it obtained 90% of removal within 15 min). According to the isotherm results, the maximum adsorption capacity ( Q m ) of the QNC adsorbent exhibited the following trend: PFOS ( Q m = 559 mg g −1 or 1.12 mmol g −1 ) > PFOA ( Q m = 405 mg g −1 or 0.98 mmol g −1 ) > PFBS ( Q m = 319 mg g −1 or 1.06 mmol g −1 ) > PFBA ( Q m = 121 mg g −1 or 0.57 mmol g −1 ). This adsorption order generally matches the hydrophobicity trend among four PFASs associated with both PFAS chain length and functional group. In competitive studies, pre-adsorbed short-chain PFASs were quickly desorbed by long-chain PFASs, suggesting that the hydrophobicity of the molecule played an important role in the adsorption process on to QNC. Finally, the developed QNC adsorbent was tested to treat PFAS-contaminated groundwater, which showed excellent removal efficiency (>95%) for long-chain PFASs (C7–C9) even at a low adsorbent dose of 32 mg L −1 . However, short-chain PFASs ( i.e. , PFBA and perfluoropentanoic acid (PFPeA)) were poorly removed by the QNC adsorbent (0% and 10% removal, respectively) due to competing constituents in the groundwater matrix. This was further confirmed by controlled experiments that revealed a drop in the performance of QNC to remove short-chain PFASs at elevated ionic strength (NaCl), but not for long-chain PFASs, likely due to charge neutralization of the anionic functional group of PFASs by inorganic cations. Overall, the QNC adsorbent featured improved PFAS adsorption capacity at almost two-fold of PFAS removal by granular activated carbons, especially for short-chain PFASs. We believe, QNC can complement the use of common treatment methods such as activated carbon or ionic exchange resin to remove a wide range of PFAS pollutants, heading towards the complete remediation of PFAS contamination.more » « less
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Abstract The oxidation of antioxidants by oxidizers imposes great challenges to both living organisms and the food industry. Here we show that the host–guest complexation of the carefully designed, positively charged, amphiphilic guanidinocalix[5]arene pentadodecyl ether (GC5A‐12C) and negatively charged oleic acid (OA), a well‐known cell membrane antioxidant, prevents the oxidation of the complex monolayers at the air–water interface from two potent oxidizers hydroxyl radicals (OH) and singlet delta oxygen (SDO). OH is generated from the gas phase and attacks from the top of the monolayer, while SDO is generated inside the monolayer and attacks amphiphiles from a lateral direction. Field‐induced droplet ionization mass spectrometry results have demonstrated that the host–guest complexation achieves steric shielding and prevents both types of oxidation as a result of the tight and “sleeved in” physical arrangement, rather than the chemical reactivity, of the complexes.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10847-019-00930-w
