Chemistry Reference
In-Depth Information
CHAPTER 11
STRUCTURE AND SELF-ASSEMBLY
OF AMPHIPHILIC DENDRIMERS
IN WATER
HUI SHAO and JON R. PARQUETTE
11.1. INTRODUCTION
The spontaneous segregation of polar and apolar segments of an amphiphilic
molecule in water is an extremely powerful driving force for the self-assembly and
folding of biological systems (Lins and Brasseur 1995; Tsai et al. 2002). The self-
assembly of lipids into micelles and bilayers represents a particularly important
example of amphiphilic self-assembly that is mediated by the phase separation of
polar and apolar regions in water. In this case, the self-assembly process sequesters
the hydrophobic lipid chains together at the interior of the micelle/bilayer, away
from both the polar head groups and the aqueous phase (Fig. 11.1).
Many biological events such as membrane translocation (Deshayes et al. 2006)
and antibiotic activity (Yount et al. 2006) are mediated by peptides that attain their
functional properties via a self-assembled state that is attained by amphiphilic
phase segregation. Molecular amphiphilicity also plays a critical role in mediating
the assembly of nonnatural amphiphiles. Many of these synthetic systems are
capable of assembling into ordered structures that mimic the functional compartmen-
talization of biological systems, and they have emerged as a new class of supramole-
cular materials displaying biomedical functions (Fuhrhop and Wang 2004; Loewik
and van Hest 2004; Jun et al. 2006; McNally et al. 2007). The structural impact of
creating amphiphilicity in dendritic structures has been of intense interest for many
years because their branched connectivity induces a globular morphology with dis-
tinct internal and external regions, apparently similar to the structures of micelles
and globular proteins (Tomalia et al. 1990). Amphiphilic dendrimer systems are
beginning to play important functional roles as artificial enzymes (Habicher et al.
