On the interaction of TEMPO radicals with gold clusters

The effectiveness of radicals as fluorescence quenchers of nanostructures has been widely described. Gold nanoclusters (AuNCs) have shown to be highly fluorescent, photostable and versatile in their capping functional group... [ view full abstract ]

The effectiveness of radicals as fluorescence quenchers of nanostructures has been widely described. Gold nanoclusters (AuNCs) have shown to be highly fluorescent, photostable and versatile in their capping functional group employed to provide their bio-compatibility when compared to organic fluorescent dyes.

In an attempt to describe the interaction of a free radical with a nanoparticle, by using EPR such interaction was proposed as a “strong adsorption” when 4-aminoTEMPO radical was exposed to gold nanoparticles, suggesting that the radical adsorbs flat parallel to the metal surface¹. In a more recent publication the quenching ability of AuNC by the 4-aminoTEMPO was confirmed with Stern-Volmer plots that were taken as indications of a direct binding between the nitroxyl radical and the metallic surface through the oxygen atom² If this binding exists, it should occur for TEMPO itself, a fact which was not observed in another study on the interaction of nitroxide radicals with quantum dots.³

In the present study we employed a series of nitroxides among them 4-hydroxy- and 4-carboxyTEMPO radicals to quench the fluorescence of the AuNC and recorded their corresponding EPR spectra under the same quenching conditions. We observed that EPR signal intensities and shapes did not change. We also performed reactivity studies, confirming that when a hydrogen donor such as Trolox is exposed to AuNC-nitroxide, observing that the nitroxide moieties react with the same rate constant as in homogeneous phase.

SEM and TEM imagery, and microcalorimetry were also performed.

1         L. Zhang and E. Wang, Nano Today, 2014, 9, 132–157.

2         C.-P. Liu, T.-H. Wu, C.-Y. Liu, H.-J. Cheng and S.-Y. Lin, J. Mater. Chem. B, 2015, 3, 191–197.

3         J. C. Scaiano, M. Laferrière, R. E. Galian, V. Maurel and P. Billone, Phys. Status Solidi Appl. Mater. Sci., 2006, 203, 1337–1343.