Designing advanced functional periodic mesoporous organosilicas for biomedical applications

Periodic mesoporous organosilicas (PMOs), reported for the first time in 1999, constitute a new branch of organic-inorganic hybrid materials with high-ordered structures, uniform pore size and homogenous distribution of organic bridges into a silica framework. Unlike conventional mesoporous silicas, these materials offer the possibility to adjust the surface (hydrophilicity/hydrophobicity) and physical properties (morphology, porosity) as well as their mechanical stability through the incorporation of different functional organic moieties in their pore walls. A broad variety of PMOs has been designed for their subsequent application in many fields. More recently, PMOs have attracted growing interest in emerging areas as biology and biomedicine. This review provides a comprehensive overview of the most recent breakthroughs achieved for PMOs in biological and biomedical applications

Facile synthesis of cooperative acid-base catalysts by clicking cysteine and cysteamine on an ethylene-bridged periodic mesoporous organosilica

A periodic mesoporous organosilica (PMO) that contains ethylene bridges was functionalized to obtain a series of cooperative acid-base catalysts. A straightforward, single-step procedure was devised to immobilize cysteine and cysteamine on the support material by means of a photoinitiated thiol-ene click reaction. Likewise, PMO materials capped with hexamethyldisilazane (HMDS) were used to support both compounds. This resulted in different materials in which the amine site was promoted by carboxylic acid groups, surface silanol groups, or both. The catalysts were tested in the aldol reaction of 4-nitrobenzaldehyde and acetone. It was found that silanol groups have a stronger promoting effect on the amine than the carboxylic acid group. The highest turnover frequency (TOF) was obtained for an amine-functionalized material that contained only silanol promoting sites. The loading of the active sites also had a significant effect on the activity of the catalysts, which was rationalized on the basis of a computational study

Preparation of palladium-supported periodic mesoporous organosilicas and their use as catalysts in the Suzuki cross-coupling reaction

Three periodic mesoporous materials, i.e., two organosilicas with either ethylene or phenylene bridges and one silica, have been used as supports for Pd nanoparticles. All Pd-supported samples (1.0 wt%) were prepared by the incipient wetness method and subsequently reduced in an H2 stream at 200 °C. Both hydrogen chemisorption and temperature programmed reduction experiments revealed significant differences depending on the support. Pd2+ species were more reducible on the mesoporous organosilicas than on their silica counterpart. Also, remarkable differences on the particle morphology were observed by transmission electron microscopy. All Pd-supported samples were active in the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid

Periodic mesoporous organosilicas: hybrid porous materials with exciting applications

Periodic Mesoporous Organosilicas or commonly named “PMOs” constitute of a new family of functional hybrid materials where organic groups are covalently integrated within the pore walls of a silica framework. With well-defined pore structures and unique properties, they combine the structural characteristics of ordered mesoporous silicas with the chemical functionalization possibilities of organic groups. These advantages convert these materials into promising candidates in areas such as catalysis, adsorption, nanoelectronics, and chromatography, among others. In this chapter, we will give an overview of all these applications where PMOs with specific functional groups have been successfully reported

Silanol assisted aldol condensation on aminated silica: understanding the arrangement of functional groups

Free silanol groups are known to promote the activity of aminated silica. In this work the effect of the silanol-to-amine ratio on the aldol condensation of 4-nitrobenzaldehyde and acetone is investigated in a range from 0 to 2.4. Irrespective of the amine density, identical, moderate turnover frequencies are obtained if the silica exclusively has amines on its surface. The turnover frequency increases with increasing silanol-to-amine ratio until an upper limit is reached at a silanol-to-amine ratio of 1.7. At this upper limit the turnover frequency is a factor5 higher than the turnover frequencies obtained with the monofunctional amine-based catalysts. This increase is ascribed to hydrogen-bridge interactions between the silanols and the carbonyl moiety of the reactants that provoke a more easy interaction between the carbonyl moiety and the amine as required for the aldol condensation. The observation that higher values than one for the silanol-to-amine ratio are required is rationalized by computer simulations. It was found that amine groups were grafted on the silica surface in a clustered manner, originating from positive deviations from ideality in the synthesis mixture, that is, from clustering of the amine precursor in the liquid phase