Silica nanospheres

The nonporous spherical gels for PCHdC are often specially prepared for research purposes. However, nonporous polystyrene/divinylbenzene beads. Solid Bead, can be obtained in various particle sizes from Jordi Associates, Inc. (Bellingham, MA). Columns packed with these gels can be used for HdC of the polymers that are currently analyzed using polystyrene/divinylbenzene SEC columns. Fumed silica nanospheres are offered by Cabot (Tuscola, IL) (17), and nonporous silica (NPS) microspheres are offered by Micra Scientific, Inc. (Northbrook, IL). These nonporous silica gels may also be used for HdC. 

Kroger N, Deutzmann R, Sumper M (1999) Polycationic peptides from diatom biosilica that direct silica nanosphere formation. Science 286 1129-1132... 

E. (2003) Biomimetic control of size in the polyamine-directed formation of silica nanospheres. Angewandte Chemie-Intemational Edition, 42, 5192— 5195. 

Knecht, M.R. and Wright, D.W. (2004) Amine-terminated dendrimers as biomimetic templates for silica nanospheres formation. Langmuir, 20, 4728-4732. 

Another nice example of nanostructuring an MIP layer is the work published by Wu et al. [138, 139] who developed a label-free optical sensor based on molecularly imprinted photonic polymers. Photonic crystals were prepared by self-assembly of silica nanospheres. The space between the spheres was then filled with MIP precursor solution. After polymerization, the silica was dissolved, leaving an MIP in the form of a 3D-ordered interconnected macroporous inverse polymer opal (Fig. 15). The authors were able to detect traces of the herbicide atrazine at low concentrations in aqueous solution [139]. Analyte adsorption into the binding sites resulted in a change in Bragg diffraction of the polymer characterized by a color modification (Fig. 15). 

The study of QDs and MIPs in the development of the detection scheme for pyrethroids has very recently been reported [72]. Pyrethroids are pesticides commonly used against insects being widely used in agriculture, medicine, industry and the household. The QDs were embedded in silica nanospheres having lambda-cahalothrin imprinted sites on their surfaces. As also presented in the previous example, the principle of recognition was based on a decrease of fluorescence with an increase of analyte concentration. The lambda-cahalothrin imprinted... 

A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanoparticle caps for stimuli-responsive controlled release of neurotransmitters and drag molecules. 

Following this approach, Kopelman and coworkers have prepared a pH sensor72 using as magnetic material barium ferrite nanocrystals (BaM) and as dye the dextran-linked carboxy SNARF-1, a commercially available fluorescein derivative with a convenient pKa of 7.5 and dual excitation and emission, which allows for ratiometric pH sensing. The two components were incorporated in silica nanospheres of 300 nm... 

Figure 16.5 Design principle of nanoparticle gated mesoporous silica nanospheres. The nanoparticles cap the pores by covalent bonds trapping previously diffused guest molecules. The bonds are then broken under specific stimuli allowing the guest molecules to diffuse away.

Green, M., Harries, J., Wakefield, G. et al. (2005) The synthesis of silica nanospheres doped with polyoxometalates. Journal of the American Chemical Society, 127, 12812-12813. 

Huh S, Chen HT, Wiench JW, Pruski M, Lin V (2005) Cooperative catalysis by general acid and base bifunctionalized mesoporous silica nanospheres. Angew Chem Int Ed Engl 44 1826... 

A further example of a cooperative catalytic system is a bifunctionalized mesoporous silica nanosphere material (MSN) containing the ureidopropyl group (UDP) and 3-[2-(2-aminoethylamino)ethylamino]propyl group (AEP). All catalysts were synthesized by a sol-gel procedure similar to the previously mentioned one by using different AEP/UDP molar ratios. The MSN-AEP/ UDP catalyst was employed for the aldol, Henry and cyanosilylation reactions (Scheme 3.8 R = NO2, R" = H, Schemes 3.35 and 3.36, respectively) and TON values were compared with those observed by using MSN-AEP and MSN-UDP catalysts (Table 3.10). 

In addition to selecting peptides for metal substrates, phage display methods successfully identified peptides capable of forming silica nanospheres. Recently, many groups have isolated proteins and peptides responsible for the in vivo production of silica.Stone and coworkers have isolated additional novel peptides using phage display that are capable... 

The headline in the News of the Week section of C ENews is INORGANIC BIOCATALYSIS and reports that diatom peptide forms silica nanosphere for diffraction grating [132,133]. The peptides are embedded into a polyacrylate... 

---