Investigating the Interactions of Tri-peptides on Gold Nanoparticles using Solid-state NMR Spectroscopy and the Development of 1H- 2H Dipolar Recoupling Experiments

Solid-state NMR spectroscopy is a powerful technique to study the structure of biological and inorganic systems, especially non-crystalline and insoluble samples that are difficult to study for X-ray diffraction and solution NMR spectroscopy methods. We used solid-state NMR spectroscopy to elucidate the structure and interactions of tri-peptides on gold nanoparticles. Tri-peptides CysAlaAla (CAA) and AlaAlaCys (AAC) are the focus of this work. These peptides are incorporated on gold surfaces through thiol-gold interactions and their structures on gold surfaces are studied using 1H and 13C solid-state NMR spectroscopy. NMR spectroscopy shows that CAA forms a uniform monolayer on gold nanoparticles while a bilayer of AAC forms on gold nanoparticles. The evidence of monolayer and bilayer of CAA and AAC gold nanoparticles was also supported by TGA analysis by calculating the number density of CAA and AAC on gold nanoparticles. The number of CAA and AAC on AuNPs was found to be 6 and 16 peptides/nm2 respectively.;1H-observe Rotational-Echo Double Resonance (REDOR) NMR spectroscopy and rotary resonance recoupling experiments with fast sample spinning have potential for measuring 1H-2H dipolar couplings. Both of these dipolar recoupling experiments were successful in measuring heteronuclear dipolar couplings of 2H with 1H nuclei. Potential limitations of the experiments include 1H background signals arising from the probe and Bloch-Siegert effects.