Macrocyclic structures dendrimers

Fig. 27. Chemical structures of PPE and its derivatives (a) molecular unit structure of PPE, (b) macrocycles, (c) dendrimers, and (d) nanoarchitecture.

In this review, we tried to cover all the supramolecular species that maybe classified as rotaxane dendrimers. We classified them by their structures - where in dendrimer rotaxane-hke features are introduced. Several different types of macrocycles have been employed as a ring component in the templated synthesis of rotaxane dendrimers. While the synthesis of Type I and II rotaxanes dendrimers is relatively straightforward, that of well-defined Type III rotaxane dendrimers, particularly those of second and higher generations, is still challenging. 

Simanek el al. investigated the structure dependence of the kinetics of thiol-disulfide exchange reactions.[44] In general, the rate of exchange decreased as the size of the dendrimers increased. Dendrimers with disulfides attached near the core undergo exchange more slowly than dendrimers with disulfides at the periphery. No evidence was found for intramolecular macrocyclization (cooperative) exchange. 

Over the years, molecular design has allowed the synthesis of functional dendrimers possessing metal and semiconductor nanoparticles, metal complexes and macrocycles, dyes and biologically important carrier molecules in various parts of the dentritic structures [31-39], Such dendrimers incorporating functional units are considered as supramolecular species [16, 21], Functional dendrimers have been proved to be very useful for specific applications [40, 41], Some examples of functional dendrimers are shown in Fig.5. 

Advances in techniques include sophisticated NMR methods, both in solution and the solid-state, and computational methods, and these, coupled with X-ray diffraction and other established methods, have been applied to the study of a wide variety of structures. Topics covered in the book include Sn(II) clusters, tin Zintl ions, Sn(II) heterobimetallic compounds, RsSn+ cations, stannylenes (R2Sn ), stannenes (R2Sn=SnR2 and R2Sn=CR2), stannynes (RSn=SnR), organotin oxide, carboxylate and sulfonate clusters, dendrimers and macrocycles, organotin polymers, Sh-tt interactions, unusual bondings and structures, and compounds with non-linear optical properties. 

Other groups have also studied such macrocycles. For example, extending the molecular chain with a single carbon that connects the dendrimers with the porphyrins on the outer shell (Fig. 5.13) resulted in a significant improvement in the electron transfer process [67]. The authors reported that only 10% of the excitation intensity was needed for 64 Zn(II) porphyrin-based structure with a longer connecting chain to... 

Macrocyclic metal complexes are the principal materials incorporated in the dendrimer structure (for reviews see [192,193]). Examples are metallo dendrimers with a porphyrin core [194-204], with a phthalocyanine core [205-209], with crown ethers in the repeat unit [210-212] or with a cyclic amine core [213],... 

Other polymers whose structure has been examined by SEC-MS include poly-3-hexylthiophene [34], styrene oligomers [35], PS [5, 36-38], e-caprolactone [39, 40], polytetrahydrofuran [41] macrocyclic vinyl polymers [42], bis (metholol propionic acid) dendrimers [43], poly-isocyanates [44], isosorbide diols [45], 3,5-diacetoxybenzoic acid polyesters [46], polyethylene and polypropylene oxide condensates and PEG containing a 1,3 disubstituted phenolic group [37]. 

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