Nanosized cages

The concept of dynamic imine chemistry was further extended to the preparation of three nanosized cages 46-48 (Fig. 22) akin to nanocube 45... 

Fig. 22 Thermodynamically controlled synthesis of nanosized cages 46-48.134,135 Reprinted with permission from Ref.134 (For color version of this figure, the reader is referred to the web version of this book.)...

Table 7 H NMR spectroscopy was used for determining the yield (%) of nanosized cages 46-48 in thermodynamically controlled condensations136...

Various strategies have been pursued in order to immobilise chiral epoxidation catalysts and these encompass covalent attachment to solid supports,[41] steric occlusion in nanosized cages of zeolites,[42 44] entrapment in a polydimethylsiloxane membrane145,461 and fluorous biphasic systems.1471 However, these approaches frequently require tedious ligand modifications and often lead to a marked decrease in both selectivity and activity of the transition metal catalyst. 

Without exaggerations, the abihty of POSS to combine unique hybrid (inorganic-organic) chemical compositions with nanosized cage structures... 

Ibukuro, F. Kusukawa. T. Fujita, M.A. Thermally switchable molecular lock. Guest-templated synthesis of a kinetically stable nanosized cage. J. Am. Chem. Soc. 1998, 120. 8561-8562. 

Triazides, such as 3, are also used in the construction of nanosize cages by reacting them with the trialkyne 4 to give the cage compound 5 in 92 % yield... 

Moreover, recently the application of zeolites in organic synthesis demonstrated their ability to achieve reactions necessitating usually superelectrophilic intermediates as in superacid media.144 These results cannot be rationalized on the basis of the acidic character alone and needs the understanding of confinement effects145 in which case the zeolite cage behaves like a nanosized reactor favoring the contact between reactant and specific acidic sites. The electrostatic effects may also be important. 

It is possible to use ancillary ligands in addition to phosphonic acids in building up nanosized cluster compounds of late transition metal ions. Thus, the reaction of CuCl2 with tert-butylphosphonic acid in the presence of 3,5-dimethylpyrazole affords a dodecanuclear copper phosphonate with an interesting cage structure,3 Similarly, large vanadium phosphonate clusters with up to 18 vanadium atoms have been assembled from phosphonic acids.35... 

K. Matsutua, T. Yamashita, Y. Igami, N. Kimizuka, Nucleo-Nanocages Designed Ternary Oligodeoxyribonucleotides Spontaneously Form Nanosized DNA Cages , Chem. Commim., 376 (2003)... 

It is evident that the incorporation of POSS cages into polymeric materials often results in substantial improvements in polymer properties and offer the possibility to control the mechanical, chemical and physical properties of the system during polymerization as well. Intense efforts have recently been directed toward the development of new porous materials because of their utihty and potential utihty as catalysts and catalyst supports [208,209], dielectric materials for electronic appHcations [210], media for optical [211] and sensor [212] applications, and selectively permeabihty membranes [213] and precursors [10] for POSS nanocomposites. Significant property enhancements imparted by the inclusion of a nanosized inorganic... 

The nanosized void spaces in zeolites have been exploited to serve as hosts for interesting organic guest molecules. A large variety of organic dye molecules have been incorporated in the defined cages and channels of uniform size of the zeolites. Control of the morphology and the size of zeolite hosts allow for the optimisation of the dye-zeolite composites for a specific application.[20]... 

The size of the zeoKte crystals determines the role of the external surface and the relative importance of diffusion-based shape selectivity in catalysis. So, the external surface of zeoKte Beta, often in the form of nanosized crystallites, is crucial for catalysis. Some topologies like MWW (MCM-22) show structural features that result in the formation of typical half-cages at the external surface. Such confinement effects for molecules can also be the result of delamination of specific structures, viz. ITQ-2 [20]. 

In a great number of cases, zeolites are used as auxiliary elements. They may act either as a framework to stabilize the sensor material, as filter layers (either catalytic or size restrictive) to enhance selectivity of a sensitive film, or as a preconcentrator of specific analytes from diluted solutions. For example, due to excellent chemical and thermal stability, zeolites can be used as a substrate to prepare compounds and devices with desirable fundamental physical and chemical properties (Xu et al. 2006). For example, inorganic or organic compounds, metal and metal-organic compounds, and their clusters can be assembled into the pores and cages in zeohtes. Some nanosized metal or metal oxide particles have been successfully inserted into the caves and the pores or highly dispersed on the external surface of zeohtes. 

Avnir D., Levy D., Reisfeld R. The nature of the silica cage as reflected by spectral changes and enhanced photostability of trapped rhodamine 6G. J. Phys. Chem. 1984 88 5956-5959 Bacsa R.R., Gratzel M. Rutile formation in hydrothermally crystallized nanosized titania. J. Am. Ceram. Soc. 1996 79 2185-2188... 

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