Guest-host nanostructures

This chapter describes the synthesis, properties, and biomedical applications of cyanine and squaraine dyes encapsulated in CDs, CBs, Leigh-type tetralactam macrocycles, aptamers, and micro- or nano-particles. The optical and photochemical properties of supramolecular guest-host nanostructures that are based on intra-and intermolecular complexes of crown-containing styryl dyes with metal cations, and aggregates of carbocyanine dyes are discussed in a separate review [18]. 

Inorganic Host-Guest Inclusion, Guest-Host Templation and Nanostructures... 

Structural applications. The use of porous materials offers also new opportunities in such areas as coverage chemistry, guest-host synthesis and molecular manipulations and reactions for manufacture of nano particles, nano wires and other quantum nanostructures. The International Union of Pure and Applied Chemistry (lUPAC) defines porosity scales as follows ... 

However, these elegant glycosylated nanostructures displayed only weak biological activity relative to their native glucan elicitor counterparts. Nevertheless, such glycoclusters provided unique environments for host-guest chemistry of amphi-pathic molecules owing to their lipophilic core surrounded by a hydrophilic periphery. 

Among various preparation techniques of metal/alloy particles on the nanometre scale, the templating synthesis using microporous materials as microreactors is one of the promising methods [7, 10, 11]. Uniform void spaces of porous hosts work to synthesize nanostructured metal/aUoy particles as a guest, which are... 

Figure 5 Comparison of the Fe K-edge (a) and the Co K-edge (b) XANES spectra of the nanostructured host/guest compounds A and B and reference materials.

Summarizing one can say that in case of these complex nanostructured host/guest compounds only the application of several complementary characterization techniques give reasonable results on the structure of the system. 

In biological recognition phenomena, protein-protein interactions are of primary importance. In an attempt to mimic these processes, LaBrenz and Kelly [51] synthesized the peptidic host 64. In this receptor, the dibenzofuran template separates the two peptide units by roughly 10 A and allows for the complexation of a guest peptide (65), as depicted in Fig. 21. The complex first forms a three-stranded, antiparallel /J-sheet that is stabilized by hydrogen bonds, electrostatic interactions, and aromatic-aromatic interactions between the dibenzofuran and the benzamide moieties. This complex can further self associate to form more complex structures. This example shows that structurally defined peptide nanostructures can interfere with biological recognition processes and potentially have therapeutic applications. 

Cucurbit [6] uril and increasingly its higher homologues have been used extensively in a variety of host-guest chemistry and nanostructure assemblies. Of particular appeal are rotaxanes and molecular necklaces, mechanically interlocked assemblies of molecules based on CB [6]. Efficient synthesis of ID, 2D and 3D polyrotaxanes and molecular necklaces (cucurbituril beads linked by a macrocyclic molecule string ) has been achieved by a combination of self-assembly and coordination chemistry. We discuss rotaxanes and molecular necklaces in Section 10.7, and cucurbil-based systems are summarised in a recent review.23... 

Figure 13.8 The assembly of multicomponent nanostructures by using complementary guest- and host-functionalized nanoparticles (a). The nanoparticle assembly from small to large (b) and large to small nanoparticles (c) by supramolecular interactions.

NIL patterns were also used for the assembly of nanoparticles via supramole-cular host-guest interactions.95 The NIL-patterned substrate was functionalized with CD SAMs via a three-step synthesis process. The fabrication of 3D nanostructures was achieved by the alternating assembly of multivalent guest-functionalized dendrimers and CD-fnnctionalized Au nanoparticles.88 This methodology can be applied to various nanoparticles, regardless of their size and core material. For instance, CD-functionalized silica and polystyrene nanoparticles were adsorbed onto NIL-patterned CD SAMs with preadsorbed guest-fnnctionalized dendrimers.60 92 Recently, Huskens et al. demonstrated the supramolecular LbL assembly of 3D multicomponent nanostructures of nanoparticles by alternating assembly steps of complementary ferrocenyl-functionalized silica nanoparticles and different kinds of host-fnnctionalized nanoparticles (see Fig. 13.8).66... 

Ordered mesoporous materials, due to their periodic and size-controllable pore channels and high surface areas, have been regarded as a nano-reactor to construct novel ordered and well dispersed nanostructured composites with controlled size and size distribution.[303] A number of studies have reported on the encapsulation of guest materials, such as metal oxides,[304] semiconductors, metal sulfides,[305] carbon, metals,[306] and polymers into mesoporous silica hosts. 

N. Rosch, G.N. Vayssilov, and K.M. Neyman, in Nanostructured Host/Guest Systems,... 

N. Rbsch, G.N. Vayssilov, and K.M. Neyman, in Nanostructured Host-Guest-Systems based on Nanoporous Crystals, F. Laeri, F. SchUth, U. Simon, M. Wark (eds.), Wiley-VCH, Weinheim, 2003, p. 339. 

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