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Abstract As nanotechnology becomes increasingly used in biomedicine, it is important to have techniques by which to examine the structure and dynamics of biologically-relevant molecules on the surface of engineered nanoparticles. Previous work has shown that Saturation-Transfer Difference (STD)-NMR can be used to explore the interaction between small molecules, including amino acids, and the surface of polystyrene nanoparticles. Here we use STD-NMR to further explore the different driving forces that are responsible for these interactions. Electrostatic effects are probed by using zwitterionic polystyrene beads and performing STD-NMR experiments at high, low, and neutral pH, as well as by varying the salt concentration and observing the effect on the STD buildup curve. The influence of dispersion interactions on ligand-nanoparticle binding is also explored, by establishing a structure–activity relationship for binding using a series of unnatural amino acids with different lengths of hydrophobic side chains. These results will be useful for predicting which residues in a peptide are responsible for binding and for understanding the driving forces for binding between peptides and nanoparticles in future studies.
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This content will become publicly available on April 16, 2026
Squaramide-based ion pair receptors can facilitate transmembrane transport of KCl and zwitterions including highly polar amino acids
Misregulation of transmembrane ion transport in biological systems has been linked to a variety of diseases. As a result, supramolecular chemists have been trying to develop small molecules that facilitate the transmembrane transport of several ionic species. However, ion transport by small molecules is a passive process and needs to be overall charge neutral (i.e., when an ion is transported across a membrane, another ion needs to be transported as well to avoid charge separation). Ion pair receptors could therefore have great potential as transmembrane ion transporters because they can facilitate transport of an overall neutral species. Furthermore, ditopic ion pair receptors also have the potential to transport biologically important zwitterionic species, such as amino acids. In this manuscript, we report the synthesis of a series of ditopic receptors based on squaramides as the anion binding unit and 18-crown-6 as the cation binding unit. UV-vis and NMR titrations revealed that these compounds can bind a variety of chloride salts, especially KCl. Furthermore, liquid–liquid extractions and transport experiments using bulk liquid membranes and liposomes indicate that these ditopic receptors are capable of transporting chloride salts and hydrophilic amino acids. In fact, compound 5 was even able to facilitate the transport of amino acids with charged side chains at physiological pH (arginine and glutamate), making it the first example of a small molecule that can transport these highly polar and charge-dense species. These findings open up the possibility of using these receptors in a wide range of biological applications.
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- Award ID(s):
- 2108699
- PAR ID:
- 10594085
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 16
- Issue:
- 16
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 6982 to 6990
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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