Microgel templating

Fig. 19 Reactions used for testing the activity of enzymes (P-D-glucosidase) immobilized in the thermo sensitive core-shell microgel template at different temperatures. Enzymatic hydrolysis of the substrate oNPG produces d-glucose and o-nitrophenol. The concentration of the resulting o-nitrophenol can be monitored photometrically...

Table 3.3 Catalytic activity and selectivity of microgel-templated mesoporous alumina in the hydrogenation of acetylene alcohols. ...

On the other hand, in the hydrogenation of DMEC and DHL these catalysts are much less active and selective than PS-l)-P4VP-Pd or PEO-h-P2VP-Pd. The lower activity may be due to the formation of comparatively large particles (compare 2nm nanoparticles in block copolymer-based catalysts and the nanoparticles formed in microgel-templated catalysts). The lower selectivity can be caused by the absence of modifying groups on the nanoparticle surface. 

Such monomer interacts with a suitable p-di ketone forming an isolable enamide which effectively mimicks the transition state of the reaction. Copolymerisation of this adduct with the crosslinker and acrylamide followed by template removal yields small microgels (around 20 nm) that are able to catalyse the aldol condensation reaction about 19 times faster than nonimprinted controls. 

Keywords. Imprinting, Colloids, Microgels, Molecular Recognition, Templates... 

The template monomer was designed for imprinting by inclusion in the microgels formed, followed by hydrolysis during suspension in methanol/water (1 1, v/v). Thus, the boronic ester was split and phenyl-a-D-mannopyranoside 2 (Fig. 2) was removed, leaving free binding sites in the polymer network. 

Fig. lOa-c. Molecular structure of BFA and 1H-NMR spectra of a the pure template BFA b imprinted microgel dispersed in THF-d8 before extraction showing BFA-signals of high intensity c imprinted microgel after extraction with BFA signals of very low intensity. The barred signals are attributed to the solvent THF-d8 and water [30]... 

Recently it has been shown that hydrogel layers of variable thickness can be prepared on solid substrates by photolithographic technique [47], The technique called PRINT (particle replication in non-wetting templates) [48,49] utilizes elastomeric molds from a low surface energy perfluoropolyether network. The molds prevent the formation of an interconnecting film between molded objects and allow production of monodisperse microgel particles of different sizes, shapes, compositions, and surface functionalities. 

The unique property of conjugated polymers to uptake/release the anions upon transformation from oxidized to reduced state can be used for the targeted deposition of NPs. To demonstrate the principal viability of such approach, VCL/AAEM/PEDOT microgels have been used as templates for the incorporation of AuNPs [148], Figure20 shows the procedure of AuNP deposition into microgels filled with PEDOT nanorods. 

Such microgel nanoparticles with varying gelatin concentration and crosslinking density have a high potential for use in drug delivery applications. The gelatin nanoparticles can also be used as template particles for the formulation of apatite... 

In general, microgels obtained by radiation methods can be used in various applications in the same way as conventional synthesized systems, e.g., as drug delivery templates, for encapsulation, or as microreactors [29, 30], PAAm for example can be used as template material to synthesize hollow cadmium selenide nanospheres [24], and PVP can be used for the incorporation of ferromagnetic nanoparticles to obtain magnetic hydrogel microspheres [13],... 

As an example, thermosensitive PVME microgels can be used as template and stabilizer for the synthesis of composite polypyrrole (PPy) particles [32], The PVME microgels were obtained by electron beam irradiation above the phase transition temperature as described in Sect. 3.2.1 [3,4], Pyrrole (Py) was polymerized by oxidative polymerization with ferric chloride in the presence of the PVME microgels in water/ethanol mixtures as reaction medium. For comparison, the synthesis was also carried out in the presence of uncross-linked PVME. 

Armes et al. [49] have reported the use of pH-responsive microgels based solely on 2-(diethylamino)ethyl methacrylate (DEA) as colloidal templates for the in situ synthesis of Pt nanoparticles (PtNPs). The swollen microgels can be used as nanoreactors efficient impregnation with PtNPs can be achieved by incorporating precursor platinum compounds, followed by metal reduction. Addition of platinic acid, H2PtCl6, to the latex particles causes the protonation of the tertiary amine... 

Recently, we have successfully used these thermosensitive core-shell microgel particles as templates for the deposition of metal nanoparticles (Ag, Au, Pd, Pt, and Rh) [29, 59, 60], The reduction to metallic nanoparticles in the presence of microgel particles was done at room temperature via the addition of NaBPL and could be followed optically by the color change of the suspensions, as shown in Fig. 3. The immobilization of metal nanoparticles might be due to the strong localization of... 

The move towards catalytic reactions was initiated in 1983 by Hopkins and William. Phthalimide attached to a methacrylate residue acted as template. Hydrolysis after microgel formation with methyl methacrylate, 2-ethoxyethyl-methacrylate and ethylene glycol dimethacrylate left behind cavities possessing primary amine groups. Sha selectivity was confirmed by determination of hydrolysis rates between different 4-nitrophenyl esters. An acetate was hydrolysed considerably faster than a caproate [147]. Four years later Leonhardt and... 

This approach was first described in [64, 65]. When metal nanoparticles are located in the block copolymer micelle cores [64] or in microgels [65] and these polymeric systems are used as templates for silica casting, both pore size and... 

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