3 research outputs found
Solution-Based Synthesis of GeTe Octahedra at Low Temperature
GeTe
octahedra were prepared by reaction of equimolar amounts of
GeCl<sub>2</sub>·dioxane and TeÂ(SiEt<sub>3</sub>)<sub>2</sub> in oleylamine, whereas a slight excess of the Te precursor yielded
GeTe octahedra decorated with elemental Te nanowires, which can be
removed by washing with TOP. The mechanism of the GeTe formation is
strongly influenced by the solvent. The expected elimination of Et<sub>3</sub>SiCl (dehalosilylation) only occurred in aprotic solvents,
whereas TeÂ(SiEt<sub>3</sub>)<sub>2</sub> was found to react with primary
and secondary amines with formation of silylamines. Temperature-dependent
studies on the reaction in oleylamine showed that crystalline GeTe
particles are formed at temperatures higher than 140 °C. XRD,
SAED, and HRTEM studies proved the formation of rhombohedral GeTe
nanoparticles. These findings were confirmed by a single-crystal and
powder X-ray analysis. The rhombohedral structure modification was
found, and the structure was solved in the acentric space group <i>R</i>3<i>m</i>
Ultrastructure and Surface Composition of Glutathione-Terminated Ultrasmall Silver, Gold, Platinum, and Alloyed Silver–Platinum Nanoparticles (2 nm)
Alloyed ultrasmall silver–platinum nanoparticles
(molar
ratio Ag:Pt = 50:50) were prepared and compared to pure silver, platinum,
and gold nanoparticles, all with a metallic core diameter of 2 nm.
They were surface-stabilized by a layer of glutathione (GSH). A comprehensive
characterization by high-resolution transmission electron microscopy
(HRTEM), electron diffraction (ED), X-ray diffraction (XRD), small-angle
X-ray scattering (SAXS), differential centrifugal sedimentation (DCS),
and UV spectroscopy showed their size both in the dry and in the water-dispersed
state (hydrodynamic diameter). Solution NMR spectroscopy (1H, 13C, COSY, HSQC, HMBC, and DOSY) showed the nature
of the glutathione shell including the number of GSH ligands on each
nanoparticle (about 200 with a molecular footprint of 0.063 nm2 each). It furthermore showed that there are at least two
different positions for the GSH ligand on the gold nanoparticle surface.
Platinum strongly reduced the resolution of the NMR spectra compared
to silver and gold, also in the alloyed nanoparticles. X-ray photoelectron
spectroscopy (XPS) showed that silver, platinum, and silver–platinum
particles were at least partially oxidized to Ag(+I) and Pt(+II),
whereas the gold nanoparticles showed no sign of oxidation. Platinum
and gold nanoparticles were well crystalline but twinned (fcc lattice)
despite the small particle size. Silver was crystalline in electron
diffraction but not in X-ray diffraction. Alloyed silver–platinum
nanoparticles were almost fully amorphous by both methods, indicating
a considerable internal disorder
The Molecular Footprint of Peptides on the Surface of Ultrasmall Gold Nanoparticles (2 nm) Is Governed by Steric Demand
Ultrasmall gold nanoparticles were functionalized with
peptides
of two to seven amino acids that contained one cysteine molecule as
anchor via a thiol–gold bond and a number of alanine residues
as nonbinding amino acid. The cysteine was located either in the center
of the molecule or at the end (C-terminus). For comparison, gold nanoparticles
were also functionalized with cysteine alone. The particles were characterized
by UV spectroscopy, differential centrifugal sedimentation (DCS),
high-resolution transmission electron microscopy (HRTEM), and small-angle
X-ray scattering (SAXS). This confirmed the uniform metal core (2
nm diameter). The hydrodynamic diameter was probed by 1H-DOSY NMR spectroscopy and showed an increase in thickness of the
hydrated peptide layer with increasing peptide size (up to 1.4 nm
for heptapeptides; 0.20 nm per amino acid in the peptide). 1H NMR spectroscopy of water-dispersed nanoparticles showed the integrity
of the peptides and the effect of the metal core on the peptide. Notably,
the NMR signals were very broad near the metal surface and became
increasingly narrow in a distance. In particular, the methyl groups
of alanine can be used as probe for the resolution of the NMR spectra.
The number of peptide ligands on each nanoparticle was determined
using quantitative 1H NMR spectroscopy. It decreased with
increasing peptide length from about 100 for a dipeptide to about
12 for a heptapeptide, resulting in an increase of the molecular footprint
from about 0.1 to 1.1 nm2