Peripheral group

There is also evidence that individual chlorophyll derivatives exhibit cytostatic and cytotoxic activities against tumor cells. Studies have been started on electronic structures, in particular the electronic state of the phorphyrin macrocycle, and progress in this area is expected regarding photodynamic therapy for tumors, since the strong absorption of hght in the visible region is effective for laser excitation. Nevertheless, httle is known to date about the influences of peripheral groups on the electronic state of the macrocycle n system in chlorophyll derivatives. ... 

Zhu, Z. and Moore, J.S., Synthesis and characterization of 9-phenylcarbazole monodendrons an exploration of peripheral groups to facilitate purification, Macromolecules, 33, 801, 2000. 

Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

Dendrimer interior functional groups and cavities can retain guest molecules selectively, depending on the nature of the guest and the dendritic endoreceptors, the cavity size, the structure, and the chemical composition of the peripheric groups. Two main methods are known for the synthesis of metal nanoparticles inside dendrimers. The first method consists of the direct reduction of dendrimer-encapsulated metal ions (Scheme 9.4) the second method corresponds to the displacement of less-noble metal clusters with more noble elements [54]. 

Assuming that in the course of the functionalization, each reaction between the reagent and a still free peripheral group occurs without being influenced by the number of already converted moieties,1231 the total yield A of perfectly reacted dendrimer can be calculated by means of the product formula for a stochastically independent event, if the yield of the individual reaction a is known. The yield A is given by a" where n is the number of peripheral functional groups of the dendrimer. 

Next let us examine a QM/MM model system of complex 3 where the steric influence of the phenyl substituents and of the ferrocene is accounted for but the electronic effects have been largely eliminated (model B). In other words, the peripheral groups have been delegated to the MM region, while keeping the molecular system used for electronic structure calculation identical to that in model A. 

Fig. 7.10 Matching of RR from 7 a (thick lines) with the extended form of bilirubin IX (dashed lines). The extended conformation of bilirubin is one of several possibilities and it is uncertain which of these it adopts when binding to albumin. The iron atom of 7a is placed at the central methylene of bilirubin. A number of the peripheral groups have been omitted from the structures for clarity. Reproduced with permission from R. B. Lauffer, A. C. Vincent, S. Padmanabhan and T. I. Meade, J. Amer. Chem. Soc. 109, 2216 (1987). (1987) American Chemical Society.

Another noteworthy difference between core- and periphery-functionalized dendrimers is that much higher costs are involved in the application of core-functionalized dendrimers due to their higher molecular weight per catalytic site. Furthermore, applications may be limited by the solubility of the dendrimer. (To dissolve 1 mmol of catalyst/L, 20 g/L of core-functionalized dendrimer is required (MW 20 000 Da, 1 active site) compared to 1 g/L of periphery-functionalized dendrimer (MW 20 000 Da, 20 active sites). On the other hand, for core-functionalized systems, the solubility of the dendritic catalyst can be optimized by changing the peripheral groups. 

The physical properties of dendrimers such as solubility, arising from their hyperbranched globular shapes and the peripheral groups, can be modified by end-group modification. In core-functionalized dendrimers, the immiscibility of the wedges with a solvent enables precipitation and subsequent separation by filtration. 

Fig. 6 The typical disorder of CX3 peripheral groups about the pseudo threefold axis left) and the t) pical pedal motion disorder about the central double bond in E-stilbene kind of molecules right)...

Bhave, G., Karim, F., Carlton, S. M., Gereau, R. W. Peripheral group I metabotropic glutamate receptors modulate nociception in mice, Nature Neurosci. 2001, 4, 417-423. 

It is also possible to attach chiral peripheral groups to benzo[15]crown-5 as demonstrated by Shinkai [28]. In 8 (Scheme 4), a cholesteryl subunit was attached using an ester group as linker and a chiral nematic phase was observed. 

Lattermann found that the sixfold symmetry is not important for the presence of columnar mesophases in [14]-N4 when appropriate peripheral groups are chosen [105]. As substituents with one terminal alkyl (88a-d) chain and with three terminal alkyl chains (88e) are not able to induce liquid crystalline behavior in 88 (Table 5) [104], a substituent with two alkyl chains, namely 3,4-bis(alkyloxy) benzoyl, was chosen since it has been known to induce liquid crystalline phases in other systems. A mesophase (most likely Colh due to the texture) was observed between 96 and 132 °C for 90 (Scheme 44). 

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