¹H MAS NMR Study of Cysteine-Coated Gold Nanoparticles

¹H MAS NMR experiments were performed on gold nanoparticles coated with l-cysteine. The experiments show that l-cysteine molecules are zwitterions and support a structural model of cysteine forming two layers. The inner layer is composed of cysteine molecules chemisorbed to the gold surface via the sulfur atom. The outer layer interacts with the chemisorbed layer. The ¹H NMR suggests that the cysteine in the outer layer exhibits large amplitude motion about specific carbon–carbon bonds

¹H MAS NMR Study of Cysteine-Coated Gold Nanoparticles

¹H MAS NMR experiments were performed on gold nanoparticles coated with l-cysteine. The experiments show that l-cysteine molecules are zwitterions and support a structural model of cysteine forming two layers. The inner layer is composed of cysteine molecules chemisorbed to the gold surface via the sulfur atom. The outer layer interacts with the chemisorbed layer. The ¹H NMR suggests that the cysteine in the outer layer exhibits large amplitude motion about specific carbon–carbon bonds

¹H MAS NMR Study of Cysteine-Coated Gold Nanoparticles

¹H MAS NMR experiments were performed on gold nanoparticles coated with l-cysteine. The experiments show that l-cysteine molecules are zwitterions and support a structural model of cysteine forming two layers. The inner layer is composed of cysteine molecules chemisorbed to the gold surface via the sulfur atom. The outer layer interacts with the chemisorbed layer. The ¹H NMR suggests that the cysteine in the outer layer exhibits large amplitude motion about specific carbon–carbon bonds

l‑Cysteine Interaction with Au₅₅ Nanoparticle

Simulations of l-cysteine molecules attaching on Au nanoparticles provide insight on how larger biomolecules (such as proteins and peptides) can interact with Au nanoparticles. The attaching mode is still in debate and of strong impact on the fundamental research in biosensors and biomedicine. We used a density functional theory (DFT) approach to calculate the interactions between l-cysteine molecules and the quantum sized Au nanoparticle Au₅₅. Our results support the attaching mode recognized in solid-state NMR studies, which indicate that a double layer of l-cysteine molecules is the likely configuration. A strong electronic interaction between gold and sulfur atoms establishes a strong-bonding inner layer, while a hydrogen-bond network between zwitterion-structured cysteine molecules stabilizes the existence of a second layer with thiol (−SH) groups oriented outward. Such a structure has high potential for further biofunctionalization

Drug–Polymer Interactions in Acetaminophen/Hydroxypropylmethylcellulose Acetyl Succinate Amorphous Solid Dispersions Revealed by Multidimensional Multinuclear Solid-State NMR Spectroscopy

The bioavailability of insoluble crystalline active pharmaceutical ingredients (APIs) can be enhanced by formulation as amorphous solid dispersions (ASDs). One of the key factors of ASD stabilization is the formation of drug–polymer interactions at the molecular level. Here, we used a range of multidimensional and multinuclear nuclear magnetic resonance (NMR) experiments to identify these interactions in amorphous acetaminophen (paracetamol)/hydroxypropylmethylcellulose acetyl succinate (HPMC-AS) ASDs at various drug loadings. At low drug loading (1H–13C through-space heteronuclear correlation experiments identify proximity between aromatic protons in acetaminophen with cellulose backbone protons in HPMC-AS. We also show that 14N–1H heteronuclear multiple quantum coherence (HMQC) experiments are a powerful approach in probing spatial interactions in amorphous materials and establish the presence of hydrogen bonds (H-bond) between the amide nitrogen of acetaminophen with the cellulose ring methyl protons in these ASDs. In contrast, at higher drug loading (40 wt %), no acetaminophen/HPMC-AS spatial proximity was identified and domains of recrystallization of amorphous acetaminophen into its crystalline form I, the most thermodynamically stable polymorph, and form II are identified. These results provide atomic scale understanding of the interactions in the acetaminophen/HPMC-AS ASD occurring via H-bond interactions