Molecules dendritic

Baars MWPL, Meijer EW (2000) Host-Guest Chemistry of Dendritic Molecules. 210 131-182 Balczewski P, see Mikoloajczyk M (2003) 223 161-214 Ballauff M (2001) Structure of Dendrimers in Dilute Solution. 212 177-194 Baltzer L (1999) Functionalization and Properties of Designed Folded Polypeptides. 202 39-76 Balzani V, Ceroni P, Maestri M, Saudan C, Vicinelli V (2003) Luminescent Dendrimers. Recent Advances. 228 159-191 Barre L, see Lasne M-C (2002) 222 201-258 Bartlett RJ, see Sun J-Q (1999) 203 121-145... 

Newkome GR, Moorefield CN, Vogtle F (1996) Dendritic molecules concepts, synthesis, perspectives. VCH, Weinheim... 

FIGURE 5.42 Chemical structures of first-generation (42) and second-generation (43) self-immolative, receiver-amplifier dendritic molecules with an enzymatic trigger (blue), cleaved by PGA and 6-aminoquinoline (red) reporter groups. 

The disassembly rate of dendritic molecules 18 and 19 was evaluated in phosphate buffered saline (PBS, pH 7.4) in the presence and absence of PGA. The release of tryptophan was monitored by a reverse-phase HPLC at a wavelength of 320 nm. The results are presented in Figs. 5.11 and 5.12. No disassembly of either system was observed in the buffer without PGA (data not shown). In the presence of PGA, dendritic molecule 18 disassembled to release tryptophan within approximately 4 days (Fig. 5.11), whereas dendritic molecule 19 released its tryptophan tail units within 40 min (Fig. 5.12). 

Under the experiment conditions, the enzymatic cleavage occurs within seconds. Therefore, the observed release time of the tryptophan is also the actual disappearance time of the intermediate forms after the enzymatic cleavage. This dramatic enhancement of tail-unit release with the elimination-based system (dendritic molecule 19) compared to the cyclization-based system (dendritic molecule 18) is best viewed by superimposition of the graphs (Fig. 5.13). 

FIGURE 5.8 Disassembly mechanism of AB3 self-immolative dendritic molecule 13. 

FIGURE 5.10 Chemical structures of AB3 self-immolative dendritic molecules with tryptophan tail units and a trigger that is activated by PGA. 

Additional support for this disassembly mechanism was obtained by monitoring the release of the pyrene tail units by fluorescence spectroscopy. The confined proximity of the pyrene units in the dendritic molecule results in formation of excimers. The excimer fluorescence generates a broad band at a wavelength of 470 nm in the emission spectrum of dendron 31 (Fig. 5.25). Upon the release of the pyrene units from the dendritic platform, the 470 nm band disappeared from... 

FIGURE 5.30 Conjugation of dendritic molecule 33 with PEG400-azide. 

FIGURE 5.31 Disassembly pathway of second-generation dendritic molecule 34 triggered by enzymatic activation of PGA. 

Dendritic molecules 33 and 34 were then incubated with PGA in PBS (pH 7.4) at 37 °C. Control solutions were composed of buffer without the enzyme. The sequential fragmentation illustrated in Fig. 5.31 was monitored by observing the disappearance of dendrons 33 or 34 and the release of 4-nitroaniline by RP-HPLC. As expected, dendron 33 could not be activated by PGA and remained intact for 72 h (data not shown). However, dendron 34 showed clear activation upon incubation with PGA and its corresponding peak completely disappeared from the HPLC chromatogram as 4-nitroaniline appeared (Fig. 5.32). No 4-nitroaniline was observed in the control experiment when dendron 34 was incubated in the buffer without PGA. 

FIGURE 5.41 Graphical structure of a receiver-amplifier dendritic molecule. (See the color version of this figure in Color Plates section.)... 

FIGURE 5.43 Signal transduction mechanism for dendritic molecule 42, through a self-immolative reaction sequence. 

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