Turning Supramolecular Receptors into Chemosensors by Nanoparticle-Assisted “NMR Chemosensing”

Abstract

By exploiting a magnetization transfer between monolayer-protected nanoparticles and interacting analytes, the NMR chemosensing protocol provides a general approach to convert supramolecular receptors into chemosensors via their conjugation with nanoparticles. In this context, the nanoparticles provide the supramolecular receptor not only with the "bulkiness" necessary for the NMR chemosensing approach but also with a different selectivity as compared to the parent receptor. We here demonstrate that gold nanoparticles of 1.8 nm core coated with a monolayer of 18-crown-6 ether derivatives can detect and identify protonated primary amines in methanol and in water, and even discriminate between two biogenic diamines that are selectively detected over monoamines and α-amino acids.

Nanoparticle-Based Receptors Mimic Protein-Ligand Recognition

“…In this regard, some of us recently proposed nuclear magnetic resonance (NMR) chemosensing as a protocol that exploits the molecular recognition ability of monolayer-protected gold nanoparticles (AuNPs, about 2 nm core diameter) in order to detect target analytes 21, 22, 23, 24. Typically, these analytes are small organic molecules such as salicylate.…”

NMR-Based Chemosensing via p-H2 Hyperpolarization: Application to Natural Extracts

“…18,20 A recent implementation of the former approach relied on the combination of different highly selective NMR tools (i.e., diffusion filters, 46 NOE and relaxation filters 47 ) to reveal the weak association of primary amines to gold nanoparticles coated with receptor units, while discarding background signals. 22 The detection limit for such chemosensors, determined by the lowest measurable NMR response, is estimated to be in the submillimolar concentration range. Alternatively, NMR-based chemosensors have been realized such that analyte binding is signaled by chemical shift changes for specific resonances of the receptor.…”

“…Recent implementations of NMR chemosensing for chemical analysis report such limit in the submillimolar range. 20,22 Here, interaction with the receptor, an iridium complex, in the presence of p-H 2 , results in approximately 1000-fold amplification of the NMR response. As a consequence, a …”

1H NMR Chemosensing of Potassium Ions Enabled by Guest‐Induced Selectivity Switch of a Gold Nanoparticle/Crown Ether Nanoreceptor

“…To prove this idea, we selected 1.7‐nm gold core diameter nanoparticles coated with a 18‐crown‐6 ether derivative (Crown‐NP, Scheme ), which we early reported to be capable of detecting protonated phenethylamines in water by NOE‐pumping . Binding of these substrates to the nanoparticles is the result of a multipoint interaction (Figure b) that includes; i) the simultaneous formation of three H‐bonds between the primary ammonium moiety of the guest and the crown ether residue, ii) the hydrophobic interaction between the aromatic moiety of the guest and the inner portion of the monolayer (corresponding to the alkyl chains) . Potassium ions (K + ) are well known to be the optimal guest for 18‐crown‐6 and to effectively compete for binding with protonated primary amines .…”