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 m²/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 × 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 CO₂ adsorption. CO₂ 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 CeO₂ Supported Au₂₅(SCH₂CH₂Ph)₁₈ Nanoclusters

The effect of thiolate ligands was explored on the catalysis of CeO₂ rod supported Au₂₅(SR)₁₈ (SR = −SCH₂CH₂Ph) 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 O₂, and reaction mechanism and kinetics. The intact Au₂₅(SR)₁₈ on the CeO₂ rod is found not able to adsorb CO. Only when the thiolate ligands are partially removed, starting from the interface between Au₂₅(SR)₁₈ and CeO₂ 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 Au₂₅(SR)₁₈/CeO₂ 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 Au₂₅(SR)₁₈/CeO₂ rod catalyst proceeds predominantly via the redox mechanism where CeO₂ activates O₂ while CO is activated on the dethiolated gold sites. These results point to a double-edged sword role played by the thiolate ligands on Au₂₅ nanoclusters for CO oxidation