Porous glasses surface chemistry

The most commonly used approximate model for pore topology is to represent the pore volume of the adsorbent as an array of independent, chemical homogeneous, noninterconnected pores of some simple geometry usually, these are slit-shaped for activated carbons and cylindrical-shaped for glasses, silicas, and other porous oxides. Usually, the heterogeneity is approximated by a distribution of pore sizes, it being implicitly assumed that all pores have the same shape and the same surface chemistry. In this case, the excess adsorption, r(P), at bulk gas pressure P can be represented by the adsorption integral equation... 

An original approach to the problem has been to support the catalyst, in a polar phase, on an accessible surface. The conspicuous success in this area has come from Davis s work [ 149] the basic principle is shown in Fig. 44. In this, the Ru-BINAP catalyst is adsorbed in a polar solvent phase on a porous glass bead. The substrate (and product) are in a solvent phase which is immiscible with the adsorbed phase, and in the initially described work the reaction was carried out in water, with concomitant reduction in turnover rate compared to the homogeneous variant. Strikingly better results were obtained when the supported phase was ethylene glycol, and here the efficiency rivaled that of the solution chemistry [150]. 

Silica gels, porous glasses, and silica powders were prepared by A. Kiselev, Nikitin, and co-workers (Moscow State University, Moscow) (2, 3, 26, 27, 74-81) Dzisko, Fenelonov, and co-workers (Institute of Catalysis, Siberian Division of the U.S.S.R. Academy of Sciences, Novosibirsk) (82, 83) Zhdanov and co-workers (Institute of Silicate Chemistry, the U.S.S.R. Academy of Sciences, Leningrad) (84-87) Belotserkovsky, Kolosentsev, and co-workers (Technological Institute, Leningrad) (59-61) Neimark, Sheinfain, and co-workers (Institute of Physical Chemistry, the Ukrainian S.S.R. Academy of Sciences, Kiev) (28, 29) Chuiko (Institute of Surface Chemistry, the Ukrainian S.S.R. Academy of Sciences, Kiev) (88) and others. 

A variety of mammalian cells have been successfully cultured onto porous silicon surfaces. The first publications on this topic by Bayliss et al. demonstrated that attachment of Chinese hamster ovary (CHO) cells proceeded on porous silicon surfaces to a similar extent as on bulk silicon (Bayliss et al. 1997a, b). This was also confirmed with the neuronal cell line B50 (Bayliss et al. 2000). Cell viability in these studies was determined using two colorimetric assays, the MTT based on enzymatic reduction of a tetrazolium salt to a purple formazan and the neutral red uptake assay. B50 and CHO cells were cultured on bulk silicon, porous silicon, glass, and polycrystalline silicon. Both viability assays suggested that the neuronal cells showed preference for porous silicon above the other surfaces, while CHO cells showed the lowest viability on the porous silicon surface (Bayliss et al. 1999, 2000). The surfaces of the porous silicon used in these early studies were not modified post-etching, and it was not until a study utilized porous silicon surfaces with an oxide layer for cell culture that surface chemistry was found to play a crucial factor (Chin et al. 2001). Rat... 

Due to its similar chemical nature, oxidized porous Si (porous Si02) can be modified using many of the same chemistries used to modify silica or glass surfaces. This includes a wide range of conventional silanol-based chemistries (Janshoff et al. 1998 Tinsley-Bown et al. 2000 Schwartz et al. 2005). One of the most popular coupling reactions is the reagent 3-aminopropyltriethoxysilane (APTES), Eq. 17. Because it places a reactive —NH2 group on the surface, APTES is very commonly used to link molecules such as proteins and DNA to silica (Anderson et al. 2008), oxidized silicon (Nijdam et al. 2007), and oxidized porous Si (Tinsley-Bown et al. 2000) surfaces. 

The general theoretical picture described above relating pore size distribution and relaxation time spectra works satisfactorily for solid materials of reasonably uniform surface chemistry, such as many model porous systems (glass bead or particle packs), and most sandstones. A number of laboratory studies have used it to deduce pore size distributions from longitudinal or transverse decay curves in saturated porous systems. The fact that NMR and mercury porosimetry, which measure respectively the accessible surface and the throat dimensions, give comparable pore size distributions can be explained by the regular geometry of these systems. One should also mention that an empirical correlation between hydraulic permeability and some representative relaxation time value have been observed to be... 

CPG beads are currently the most suitable and most widely used solid-phase supports for oligonucleotide synthesis. These glass beads retain the same surface silanol groups and hence the same surface chemistry as silica gel particles. The surface of these beads is etched to leave behind a porous surface with mean pore sizes ranging from 75 A to several thousand angstroms. Unlike silica gel, the beads are uniformly milled into screened spherical particles that provide greatly reduced backpressure when packed into continuous-flow columns. The beads are also much less susceptible to fragmentation than silica gel. 

The most common way to functionalize the surface of sihca materials is to use silanes [28]. Silanes have been used for many years to modify the surface chemistry of dry silica materials, which are used in completely different areas such as glass-fiber-reinforced polymers [29] and liquid chromatography [30]. Especially in the field of high performance liquid chromatography (HPLC), there are numerous papers on how to surface modify porous sihca by using various silanes [28-32]. 

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