Synthesis and characterization of melamine-based dendrimers with potential biological applications

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Title: Synthesis and characterization of melamine-based dendrimers with potential biological applications
Author: Crampton, Hannah Louise
Abstract: The convergent strategy towards dendrimer synthesis is well -suited to generate macromolecules with a diverse periphery , at the expense of time and effort , while the divergent strategy has historically been effective at yielding higher generation dendrimers , although they are often plagued by impurities . Both the convergent and divergent routes were applied to the synthesis of melamine -based dendrimers , offering a comparison of the routes within a system . Generation -1 dendrons heterogeneously functionalized with Boc -protected amines and hydrazones were synthesized convergently and coupled to a generation -1 tris (piperazine ) core to yield a generation -2 dendrimer bearing 18 Boc -amines and three hydrazones . Although the yield for the final coupling step was rather low (56 % ) , the yields for all intermediate steps were quite high . Attempts toward obtaining a generation -3 dendrimer through this route were unsuccessful due presumably to steric hindrance . The materials obtained showed no impurities in their 1H and 13C NMR and mass spectra , although several chromatographic purifications were necessary throughout the synthesis . A divergent strategy based on addition of a dichlorotriazine monomer to polyamine cores was used to synthesize dendrimers of generations 1 -5 . All intermediates and dendrimers were either purified by precipitation , or did not need purification . 1H NMR spectroscopy indicated that reactions were complete up to G4 -NH2 by integration , and mass spectroscopy confirmed that assignment . HPLC and GPC of Gn -Cl dendrimers showed sharp peaks for G1 -G3 , but G4 -Cl appeared to have a small amount of impurities that are similar in size and polarity to the fully -substituted dendrimer . The G1 -G3 dendrimers were confidently assigned as pure by conventional organic chemistry standards , but the assignment of purity to higher generations remained tentative . A G1 -Cl dendrimer was functionalized with imidazole , and then deprotected and PEGylated with PEG5000 to yield a water soluble dendrimer . The imidazole -capped , Boc -protected dendrimer and the deprotected dendrimer were characterized by 1H and 13C NMR spectroscopy and mass spectrometry . The degree of PEGylation on the PEGylated material could not be definitively ascertained ; however , the material is capable of solubilizing very hydrophobic Zn -phthalocyanines in water .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2673
Date: 2009-05-15

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Synthesis and characterization of melamine-based dendrimers with potential biological applications. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2673 .

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