Synthesis and properties of novel dendrimer materials

Ataei, Abdollah (2009) Synthesis and properties of novel dendrimer materials. (PhD thesis), Kingston University,


The field of drug delivery is developinq rapidly and is gaining the attention of scientists and the pharmaceutical Industry. Serious challenges in designing drug delivery systems are that many new drug entities such as cancer drugs are water-insoluble. Hyperbranched polymers, most notably dendrimers, are a class of macromolecules whose unique properties such as their degree of branching, multi-valency and defined molecular shape make them suitable as new scaffolds for drug delivery. Dendrimers can offer two different environments which are very important in drug delivery, namely the interior and the outer surface. The outer surface represents molecular features such as solubility where the terminal groups are located, and its interface with the surrounding medium. When a hydrophilic substituent is introduced into the surface (the periphery) the dendrimer becomes hydrophilic and water-soluble. The interior of these water soluble dendrimers gives a hydrophobic environment to the incorporated organic molecule. Having a hydrophobic interior and a hydrophilic surface makes dendrimers potentially very good drug delivery vehicles. The primary aim of this investigation was to synthesise a suitable water soluble dendritic material which was able to encapsulate the non-polar drugs (water insoluble dye) in a lower generation; the idea was that the large branching unit could the encapsulate drugs at lower generation. The selection of building blocks for the preparation of dendritic material was very important. In this project, the monomer selected to build the dendritic macromolecule was 3,5-dihydroxybenzyl alcohol, and initially ethyl 6- bromohexanoate as a branching unit. The cores used were 4,4- dihydroxybiphenyl and 1,1, 1-tris (4-hydroxy-phenyl) ethane; in the later stage of this project, physical and chemical properties of dendrimers such as solubility at different pH, maximum solubility at pH 7.4, Absorptivity of the molecules, and finding their CMC using dye-encapsulatlon, surface tension, and molar conductivity were investigated. The first part of this investigation was the synthesis of dendritic macromolecules achieved by attaching first and second generation dendrons to 4,4-dihydroxybipnenyl and 1,1, 1-tris(4-hydroxyphenyl) ethane, and then hydrolysis prior to measurement of their physical-chemical properties. Some of the products had properties that could improve the solubility of a water insoluble dye by encapsulation. Their critical micelle concentration was found by surface tension measurement and was verified by two other analytical techniques (molar conductivity and dye encapsulation). Study of physico-chemical results and molecular modelling of these compounds revealed that they have a potential to be used in drug delivery systems, although further modification of structure would improve their properties for this purpose.

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