Groups aminopropyl

Heteroaromatic ring systems are formed presumably with loss of functional groups, at elevated temperatures and probably under the catalytic influence of the aminopropyl groups on the sorbent surface. The compounds so formed are excited to fluorescence by long-wavelength UV light (X = 365 mn). 

Figure 2. Scheme illustrating (A) amine-silanol and (B) amine-amine interactions and (C) single site or site-isolated 3-aminopropyl groups grafted onto mesoporous silica [20]. 

Figure 3. Synthetic scheme to produce silica containing site-isolated aminopropyl groups through molecular imprinting approach [29].

Figure 5. Synthetic route to site-isolated 3-aminopropyl groups functionalized on mesoporous silica through use of 3-arninopropyltrimethoxysilane with bulky trityl group protected amine that serves as spacer [20].

Table 1. Grafting of 3-aminopropyl groups on mesoporous silica obtained in polar-protic, polar-aprotic and non-polar solvents, surface area and catalytic efficiency for Nitroaldol condensation of 4-hydroxybenzaldehyde and nitromethane [22]. 

Figure 16. Pictorial representation of Pd(ll) metal ions complexed to the 3-aminopropyl groups grafted onto mesoporous silica wall [74],...

There is also rapid development in the domain of standard silica-based zeolites. Their versatility can be extended by imprinting. For instance, Davis and Katz [15] recently successfully carried out imprinting and obtained a silica framework with pore walls anchoring three aminopropyl groups in cavities. Another achievement was reported by Ramamurthy, Schefer and coworkers [16]. The latter authors were able to obtain 90% diastereomeric excess of a product of the photochemical reaction in a commercially available zeolite containing chiral tropolone ether 433 in its pores. 

Many types of chiral stationary phase are available. Pirkle columns contain a silica support with bonded aminopropyl groups used to bind a derivative of D-phenyl-glycine. These phases are relatively unstable and the selectivity coefficient is close to one. More recently, chiral separations have been performed on optically active resins or cyclodextrins (oligosaccharides) bonded to silica gel through a small hydrocarbon chain linker (Fig. 3.11). These cyclodextrins possess an internal cavity that is hydro-phobic while the external part is hydrophilic. These molecules allow the selective inclusion of a great variety of compounds that can form diastereoisomers at the surface of the chiral phase leading to reversible complexes. 

Electroosmotic velocities of buffered solutions are shown for a bare silica capillaiy and one with aminopropyl groups (silica—Si—CHiCHiCHjNlL) covalently attached to the wall. A positive sign means that flow is toward the cathode. Explain the signs and relative magnitudes of the velocities. 

Attempts have recently been made to prepare solid acids by loading triflic acid into various inert oxides including silica,184 titania,185,186 and zirconia.187,188 Silica functionalized with anchored aminopropyl groups was also used to immobilize triflic acid.189 These new catalysts have been tested in a variety of organic transformations, such as alkane-alkene alkylation, Friedel-Crafts acylation, alkene dimerization, and acetalization. Silica nanoboxes prepared by dealumination of Na-X- and Ca-A-type zeolites were also loaded with triflic acid up to 32 wt%.190 The materials were thoroughly characterized but have not been tested as catalysts. 

Furthermore, MCM-41, MCM-48, and SBA-15 silica materials have been lined/ functionalized with, for example, alkyl,104 105 amino or aminopropyl groups,106-120 diamine,121,122 triamine,122,123 ethylenediamine,124 imidazole,120,125-127 triazol,120 A-benzylidenebutan-1 -amine,128 malonamide,129 carboxy(late),108,112,114... 

A complete FRET (Forster resonance energy transfer) system based on chlorophyll in the pores of FSM materials was accomplished by Kuroda s group.149,150 They first functionalized the FSM samples with 3-aminopropyl groups to guarantee an ideal position of the macroscopic chlorin units (in the pore center) and prevent their denaturation. Then they ligated chlorophyll derivatives that possess 3-(triethoxy-silyl)-A-methylpropan-l -amine groups to the pore walls. Zinc (for the FRET donor) and copper (for the FRET acceptor) were chosen as the central ions of the chlorins, which made it possible to initiate and record an efficient FRET process (Fig. 3.14). 

A popular method for immobilizing Schiff base complexes involves covalent linking. Sutra and Brunei (85) constructed a pentadentate Schiff base in the pores of a mesoporous silicate, starting from grafted aminopropyl groups. After complexation with Mn, material 5 catalyzed the epoxidation of cyclohexene with PhIO in 58% selectivity. 

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