if two AETES
+ molecules are attached. We do expect that complete sealing is also
achieved by using TCPCU (Fig. 9), as another example. The ability of guest
molecules to access the channel interior is strongly diminished for larger molecules
even with one AETES
+ molecule attached.
4.2 Functionalization of the Whole Outer Surface
Functionalization of the whole surface of ZL and of ZL composites is often desirable
for achieving specific properties such as avoidance of agglomeration of the particles,
solubilization in a specific environment, and refractive index matching, for attaching
reactive groups, and for obtaining biocompatibility or bio-reactivity. Methods rely
essentially on reactions with the surface OH groups of ZL. Popular reagents are
AETES, APTES, MPTMS, CPTES, MeImz
+
Sil, and BuImz
+ Sil, but also DEGAC,
MATMS, and PAH have been used [16, 92, 99, 101–104]. Two principles for
obtaining surface modification are illustrated in Fig. 11; optimal choice of the
solvent and details of the reaction conditions are important for achievement of the
desired result. Reaction (a) illustrates modification of stopcock-modified composites
where the stopcocks have no affinity to the modifying reagent. Reaction (b) includes
sealing the channel entrances. This means that the molecules must bear a tail which
has good affinity to the channel entrance and a base which is not reactive in the selforganization step. Change of the solvent may be necessary for the fixation step. For
example, ZL can be functionalized with APTES leading to amino-functionalized
particles, or it can be reacted with BuImz
+
Sil leading to composites bearing very
different properties.
Progress regarding selective surface modification has been reported by several
authors. The site-selective immobilization of dyes and different proteins recognizing
entities at the surface of ZL crystals using mild radical nitroxide exchange reactions
opens interesting possibilities for obtaining new properties [105, 106]. De Cola et al.
reported that modification of ZL with magnetically active Fe 3 O 4 particles can be
achieved by simply mixing the ZL with a large excess of Fe 3 O 4 nanoparticles in
water [107]. A novel type of ZL/polymer hybrid material was obtained by Studer
et al. who described the preparation of polymer brush particles using surfacefunctionalized ZL crystals as macro initiators in controlled radical polymerization
processes. Copolymerization of a photo-cleavable monomer and subsequent spin
trapping of functionalized nitroxides under UV irradiation lead to a variety of highly
functionalized ZL-based core-shell particles in a modular approach. These
ZL/polymer hybrids feature a softer surface and higher densities of functionalities,
in comparison to crystals modified with monolayers, and thus exhibit a higher
capability to interact [108, 109].
22
G. Calzaferri
+ molecules are attached. We do expect that complete sealing is also
achieved by using TCPCU (Fig. 9), as another example. The ability of guest
molecules to access the channel interior is strongly diminished for larger molecules
even with one AETES
+ molecule attached.
4.2 Functionalization of the Whole Outer Surface
Functionalization of the whole surface of ZL and of ZL composites is often desirable
for achieving specific properties such as avoidance of agglomeration of the particles,
solubilization in a specific environment, and refractive index matching, for attaching
reactive groups, and for obtaining biocompatibility or bio-reactivity. Methods rely
essentially on reactions with the surface OH groups of ZL. Popular reagents are
AETES, APTES, MPTMS, CPTES, MeImz
+
Sil, and BuImz
+ Sil, but also DEGAC,
MATMS, and PAH have been used [16, 92, 99, 101–104]. Two principles for
obtaining surface modification are illustrated in Fig. 11; optimal choice of the
solvent and details of the reaction conditions are important for achievement of the
desired result. Reaction (a) illustrates modification of stopcock-modified composites
where the stopcocks have no affinity to the modifying reagent. Reaction (b) includes
sealing the channel entrances. This means that the molecules must bear a tail which
has good affinity to the channel entrance and a base which is not reactive in the selforganization step. Change of the solvent may be necessary for the fixation step. For
example, ZL can be functionalized with APTES leading to amino-functionalized
particles, or it can be reacted with BuImz
+
Sil leading to composites bearing very
different properties.
Progress regarding selective surface modification has been reported by several
authors. The site-selective immobilization of dyes and different proteins recognizing
entities at the surface of ZL crystals using mild radical nitroxide exchange reactions
opens interesting possibilities for obtaining new properties [105, 106]. De Cola et al.
reported that modification of ZL with magnetically active Fe 3 O 4 particles can be
achieved by simply mixing the ZL with a large excess of Fe 3 O 4 nanoparticles in
water [107]. A novel type of ZL/polymer hybrid material was obtained by Studer
et al. who described the preparation of polymer brush particles using surfacefunctionalized ZL crystals as macro initiators in controlled radical polymerization
processes. Copolymerization of a photo-cleavable monomer and subsequent spin
trapping of functionalized nitroxides under UV irradiation lead to a variety of highly
functionalized ZL-based core-shell particles in a modular approach. These
ZL/polymer hybrids feature a softer surface and higher densities of functionalities,
in comparison to crystals modified with monolayers, and thus exhibit a higher
capability to interact [108, 109].
22
G. Calzaferri