Mimicking Red Blood Cell Lipid Membrane To Enhance the Hemocompatibility of Large-Pore Mesoporous Silica

Mesoporous silica nanoparticles (MSNs) have been repeatedly demonstrated as potential drug-delivery devices. The study of biocompatibility and interaction of these materials with the various cell types is of great interest with regard to the development of viable pharmaceutical products. By mimicking the cholesterol, phosphatidylcholine, and phosphatidylethanolamine composition of the outer leaflet of a human red blood cell (RBC), lipid-bilayer-coated mesoporous silica particles show considerably improved hemocompatibility over phosphatidylcholine-coated and uncoated large-pore MSN (<i>l</i>-MSN). These inorganic/organic composite nanomaterials are shown to be capable of interfacing with RBCs without damaging the cells even at relatively high concentrations, as observed through electron microscopy, UV–vis spectroscopy, and flow cytometry analyses. Interestingly, the absence of cholesterol in the outer bilayer composition is shown to produce toxic effects without resulting in hemolysis. By maintaining the ζ potential of lipid-bilayer-functionalized MSNs similar to that of the hemolytic <i>l</i>-MSNs, we demonstrate that the bilayer composition, and not the surface charge, plays a significant role in determining the hemocompatibility of MSN-based materials

Monitoring the Stimulated Uncapping Process of Gold-Capped Mesoporous Silica Nanoparticles

To establish a new method for tracking the interaction of nanoparticles with chemical cleaving agents, we exploited the optical effects caused by attaching 5–10 nm gold nanoparticles with molecular linkers to large mesoporous silica nanoparticles (MSN). At low levels of gold loading onto MSN, the optical spectra resemble colloidal suspensions of gold. As the gold is removed, by cleaving agents, the MSN revert to the optical spectra typical of bare silica. Time-lapse images of gold-capped MSN stationed in microchannels reveal that the rate of gold release is dependent on the concentration of the cleaving agent. The uncapping process was also monitored successfully for MSN endocytosed by A549 cancer cells, which produce the cleaving agent glutathione. These experiments demonstrate that the optical properties of MSN can be used to directly monitor cleaving kinetics, even in complex cellular settings

Monitoring the Stimulated Uncapping Process of Gold-Capped Mesoporous Silica Nanoparticles

To establish a new method for tracking the interaction of nanoparticles with chemical cleaving agents, we exploited the optical effects caused by attaching 5–10 nm gold nanoparticles with molecular linkers to large mesoporous silica nanoparticles (MSN). At low levels of gold loading onto MSN, the optical spectra resemble colloidal suspensions of gold. As the gold is removed, by cleaving agents, the MSN revert to the optical spectra typical of bare silica. Time-lapse images of gold-capped MSN stationed in microchannels reveal that the rate of gold release is dependent on the concentration of the cleaving agent. The uncapping process was also monitored successfully for MSN endocytosed by A549 cancer cells, which produce the cleaving agent glutathione. These experiments demonstrate that the optical properties of MSN can be used to directly monitor cleaving kinetics, even in complex cellular settings

Universal and Versatile Route for Selective Covalent Tethering of Single-Site Catalysts and Functional Groups on the Surface of Ordered Mesoporous Carbons

A universal and benign strategy for the surface functionalization of OMCs through lithium-mediated chemistry has been reported. For this purpose, a hard templating method for the facile synthesis of monodispersed ordered mesoporous carbons (OMCs) with well-defined morphology templated from large pore mesoporous silica nanoparticles (<i>l-</i>MSN) has been used. These OMCs have high surface areas (800–1000 m²g^–1) and large pore sizes (4–6 nm) suitable for anchoring bulky inorganic complexes. It has been demonstrated that the numerous defect sites present in the graphitic structure of OMCs can be effectively utilized for selective and covalent tethering of functional groups and single-site catalysts through lithiation of OMCs. Accordingly, for the first time a copper-based single-site oxidation catalyst has been covalently anchored onto the surface of OMCs. This novel system has been thoroughly characterized with advanced techniques such as electron microscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction, and acid–base titrations along with structural insights regarding the tethered copper catalyst by X-ray photoelectron spectroscopy. As a proof-of-principle, this active catalytic system has been used to demonstrate environmentally benign, room temperature selective oxidation of benzyl alcohol. We envision that this strategy for surface functionalization would be universal and can be applied for tethering a variety of different single-site catalysts onto OMCs with high surface areas. We also believe that it would have a direct impact on the currently available limited syntheses and surface functionalization techniques of mesoporous carbons for catalytic, electrocatalytic, and biological applications

Solvent-Induced Reversal of Activities between Two Closely Related Heterogeneous Catalysts in the Aldol Reaction

The relative rates of the aldol reaction catalyzed by supported primary and secondary amines can be inverted by 2 orders of magnitude, depending on the use of hexane or water as a solvent. Our analyses suggest that this dramatic shift in the catalytic behavior of the supported amines does not involve differences in reaction mechanism, but is caused by activation of imine to enamine equilibria and stabilization of iminium species. The effects of solvent polarity and acidity were found to be important to the performance of the catalytic reaction. This study highlights the critical role of solvent in multicomponent heterogeneous catalytic processes

Palladium Intercalated into the Walls of Mesoporous Silica as Robust and Regenerable Catalysts for Hydrodeoxygenation of Phenolic Compounds

Nanostructured noble-metal catalysts traditionally suffer from sintering under high operating temperatures, leading to durability issues and process limitations. The encapsulation of nanostructured catalysts to prevent loss of activity through thermal sintering, while maintaining accessibility of active sites, remains a great challenge in the catalysis community. Here, we report a robust and regenerable palladium-based catalyst, wherein palladium particles are intercalated into the three-dimensional framework of SBA-15-type mesoporous silica. The encapsulated Pd active sites remain catalytically active as demonstrated in high-temperature/pressure phenol hydrodeoxygenation reactions. The confinement of Pd particles in the walls of SBA-15 prevents particle sintering at high temperatures. Moreover, a partially deactivated catalyst containing intercalated particles is regenerated almost completely even after several reaction cycles. In contrast, Pd particles, which are not encapsulated within the SBA-15 framework, sinter and do not recover prior activity after a regeneration procedure

Aerobic Epoxidation of Olefin by Platinum Catalysts Supported on Mesoporous Silica Nanoparticles

We report platinum catalysts for the efficient aerobic oxidation of olefins to form epoxides and/or derived glycol monoethers. The catalystsdiaqua and dichloro Pt^II complexes supported by the ligand di­(2-pyridine)­methanesulfonate (dpms)are most active when they are covalently tethered to mesoporous silica nanoparticles (MSNs). Supporting the molecular Pt complexes on the MSNs prevents bimolecular catalyst deactivation. Using this strategy, >40 000 turnovers are achieved for the aerobic oxidation of norbornene in 2,2,2-trifluoroethanol. The position of the tether and the nature of other ligands in the metal coordination sphere (aqua, hydroxo, or chloro) are shown to affect the catalyst activity. The new MSN-supported Pt materials were characterized by nuclear magnetic resonance (NMR) spectroscopy, nitrogen physisorption, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA)

Organometallic Complexes Anchored to Conductive Carbon for Electrocatalytic Oxidation of Methane at Low Temperature

Low-temperature direct methane fuel cells (DMEFCs) offer the opportunity to substantially improve the efficiency of energy production from natural gas. This study focuses on the development of well-defined platinum organometallic complexes covalently anchored to ordered mesoporous carbon (OMC) for electrochemical oxidation of methane in a proton exchange membrane fuel cell at 80 °C. A maximum normalized power of 403 μW/mg Pt was obtained, which was 5 times higher than the power obtained from a modern commercial catalyst and 2 orders of magnitude greater than that from a Pt black catalyst. The observed differences in catalytic activities for oxidation of methane are linked to the chemistry of the tethered catalysts, determined by X-ray photoelectron spectroscopy. The chemistry/activity relationships demonstrate a tangible path for the design of electrocatalytic systems for C–H bond activation that afford superior performance in DMEFC for potential commercial applications

Conserved Activity of Reassociated Homotetrameric Protein Subunits Released from Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticles (MSN) with enlarged pores were prepared and characterized, and reversibly dissociated subunits of concanavalin A were entrapped in the mesopores, as shown by multiple biochemical and material characterizations. When loaded in the MSN, we demonstrated protein stability from proteases and, upon release, the subunits reassociated into active proteins shown through mannose binding and <i>o</i>-phthalaldehyde fluorescence. We have demonstrated a versatile and facile method to load homomeric proteins into MSN with potential applications in enhancing the delivery of large therapeutic proteins