3 research outputs found
Sub 2‑μm Macroporous Silica Particles Derivatized for Enhanced Lectin Affinity Enrichment of Glycoproteins
A new, mechanically stable silica microparticle with
macrosized
internal pores (1.6 μm particles with 100 nm pores) has been
developed for chromatography. The particles are characterized by an
extensive network of interconnected macropores with a high intraparticle
void volume, as observed by transmission electron microscopy (TEM).
They are synthesized by an aerosol assembly technique called ultrasonic
spray pyrolysis (USP). The particles have a high surface area for
a macroporous material, ∼200 m<sup>2</sup>/g, making them suitable
for large biomolecular separations. To demonstrate their potential
for bioseparations, they have been functionalized with lectins for
affinity enrichment of glycoproteins. The material was derivatized
with two lectins, Concanavalin A (Con A) and Aleuria
aurantia lectin (AAL), and binding properties were
tested with standard glycoproteins. The columns exhibited excellent
binding capacities for microaffinity enrichment: Con A was able to
bind 75 μg of a standard glycoprotein in a 50 Ă— 1 mm column.
Following initial tests, the lectin microcolumns were utilized for
enrichment of glycoproteins from 1 μL volumes of blood serum
samples, performed in triplicate for each lectin. The enriched serum
fractions were subjected to side-by-side glycomic and glycoproteomic
profiling analyses with mass spectrometry to show that the new particles
offer excellent sensitivity for microscale analyses of precious biological
sample materials. The unique combination of the macroporous architecture
and small particle diameter suggests the material may have advantages
for conventional modes of chromatographic separation of macromolecules
in an ultra-high-pressure liquid chromatography (UHPLC) format
Spectroscopic Investigation of Surface-Dependent Acid–Base Property of Ceria Nanoshapes
In addition to their well-known redox
character, the acid–base
property is another interesting aspect of ceria-based catalysts. Herein,
the effect of surface structure on the acid–base property of
ceria was studied in detail by utilizing ceria nanocrystals with different
morphologies (cubes, octahedra, and rods) that exhibit crystallographically
well-defined surface facets. The nature, type, strength, and amount
of acid and base sites on these ceria nanoshapes were investigated
via in situ IR spectroscopy combined with various probe molecules.
Pyridine adsorption shows the presence of Lewis acid sites (Ce cations)
on the ceria nanoshapes. These Lewis acid sites are relatively weak
and similar in strength among the three nanoshapes according to the
probing by both pyridine and acetonitrile. Two types of basic sites,
hydroxyl groups and surface lattice oxygen are present on the ceria
nanoshapes, as probed by CO<sub>2</sub> adsorption. CO<sub>2</sub> and chloroform adsorption indicate that the strength and amount
of the Lewis base sites are shape dependent: rods > cubes >
octahedra.
The weak and strong surface dependence of the acid and base sites,
respectively, are a result of interplay between the surface structure
dependent coordination unsaturation status of the Ce cations and O
anions and the amount of defect sites on the three ceria nanoshapes.
Furthermore, it was found that the nature of the acid–base
sites of ceria can be impacted by impurities, such as Na and P residues
that result from their use as structure-directing reagent in the hydrothermal
synthesis of the ceria nanocrystals. This observation calls for precaution
in interpreting the catalytic behavior of nanoshaped ceria where trace
impurities may be present
Thiolate Ligands as a Double-Edged Sword for CO Oxidation on CeO<sub>2</sub> Supported Au<sub>25</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>18</sub> Nanoclusters
The effect of thiolate ligands was
explored on the catalysis of
CeO<sub>2</sub> rod supported Au<sub>25</sub>(SR)<sub>18</sub> (SR
= −SCH<sub>2</sub>CH<sub>2</sub>Ph) by using CO oxidation as
a probe reaction. Reaction kinetic tests, in situ IR and X-ray absorption
spectroscopy, and density functional theory (DFT) were employed to
understand how the thiolate ligands affect the nature of active sites,
activation of CO and O<sub>2</sub>, and reaction mechanism and kinetics.
The intact Au<sub>25</sub>(SR)<sub>18</sub> on the CeO<sub>2</sub> rod is found not able to adsorb CO. Only when the thiolate ligands
are partially removed, starting from the interface between Au<sub>25</sub>(SR)<sub>18</sub> and CeO<sub>2</sub> at temperatures of
423 K and above, can the adsorption of CO be observed by IR. DFT calculations
suggest that CO adsorbs favorably on the exposed gold atoms. Accordingly,
the CO oxidation light-off temperature shifts to lower temperature.
Several types of Au sites are probed by IR of CO adsorption during
the ligand removal process. The cationic Au sites (charged between
0 and +1) are found to play the major role for low-temperature CO
oxidation. Similar activation energies and reaction rates are found
for CO oxidation on differently treated Au<sub>25</sub>(SR)<sub>18</sub>/CeO<sub>2</sub> rod catalysts, suggesting a simple site-blocking
effect of the thiolate ligands in Au nanocluster catalysis. Isotopic
labeling experiments clearly indicate that CO oxidation on the Au<sub>25</sub>(SR)<sub>18</sub>/CeO<sub>2</sub> rod catalyst proceeds predominantly
via the redox mechanism where CeO<sub>2</sub> activates O<sub>2</sub> while CO is activated on the dethiolated gold sites. These results
point to a double-edged sword role played by the thiolate ligands
on Au<sub>25</sub> nanoclusters for CO oxidation