ABSTRACT
Amphiphilic compounds, that is, those that have distinct hydrophilic and lipophilic parts, are used in most branches of industry and are ubiquitous in biological systems. They range from low molecular weight substances (like surfactants and lipids) to macromolecules (comprising synthetic graft and block copolymers) and biomacromolecules (like proteins, lipopolysaccharides, and nucleic acids) [1-4]. Amphiphilic molecules are those that have an afnity for two different types of environments. Amphiphilic molecules self-organize both in bulk solution and at interfaces. Low-molecular-weight amphiphilic compounds, mainly constituted of surfactants and polar lipids, have been thoroughly investigated extensively and are well understood both with respect to their bulk self-assembly and surface-modifying ability. The elaborate research efforts have been stimulated by numerous applications,ranging from soil removal to pharmaceutical and other formulations, as well as the biological implications-cell membranes being a prime example. The broad use of surfactants is, however, not without problems; in recent years, there has been an increased focus on the environmental and toxic effects displayed, in particular, by cationic surfactants. However, aremedy to this can often be found in designing surfactants, based on constituents derived from nature, for example, amino acids. Such work is quite recent and has been pioneered by Maria Rosa Infantes and her group in Barcelona, one of the contributors in this book. The study of high molecular weight amphiphilic molecules is of much more recent. There are two reasons for this. First, synthetic amphiphilic polymers,illustrated by block and graft copolymers, have been synthesized to any important extent only recently. Second, the recognition of amphiphilicity of biomacromolecules has been very limited and, in our view, the signicance of hydrophobic interactions in biology has not been taken into consideration, but rather given a cold shoulder. While proteins, in which the secondary structure is determined by abalance between hydrophilic and hydrophobic interactions, and lipopolysaccharidesare obvious examples of amphiphilic biological macromolecules, there are many cases where the role of amphiphilicity is not properly considered. As ameans of illustration of these aspects, one can take into consideration two typical examples: DNA and cellulose. As indicated below, the double helix structure of DNA owes its stability to hydrophobic interactions, and this aspect is also applicable to the insolubility of cellulose in water. Often, the association of DNA and cellulose is
1.1 Introduction ..............................................................................................................................1 1.2 Some Aspects of DNA Self-Assembly .....................................................................................2 1.3Dissolution of Cellulose ............................................................................................................3
