5 research outputs found
<sup>1</sup>H MAS NMR Study of Cysteine-Coated Gold Nanoparticles
<sup>1</sup>H 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 <sup>1</sup>H NMR suggests that the cysteine in the outer layer exhibits large
amplitude motion about specific carbonâcarbon bonds
<sup>1</sup>H MAS NMR Study of Cysteine-Coated Gold Nanoparticles
<sup>1</sup>H 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 <sup>1</sup>H NMR suggests that the cysteine in the outer layer exhibits large
amplitude motion about specific carbonâcarbon bonds
<sup>1</sup>H MAS NMR Study of Cysteine-Coated Gold Nanoparticles
<sup>1</sup>H 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 <sup>1</sup>H NMR suggests that the cysteine in the outer layer exhibits large
amplitude motion about specific carbonâcarbon bonds
lâCysteine Interaction with Au<sub>55</sub> 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 Au<sub>55</sub>. 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 (âSH)
groups oriented outward. Such a structure has high potential for further
biofunctionalization
DrugâPolymer 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 drugâpolymer 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 (1Hâ13C through-space heteronuclear correlation experiments identify proximity
between aromatic protons in acetaminophen with cellulose backbone
protons in HPMC-AS. We also show that 14Nâ1H 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