Design, molecular structure oriented

Surfactants are organic molecules that possess a nonpolar hydrocarbon tail and a polar head. The polar head can be anionic, cationic, or nonionic. Because of the existence of the two moieties in one molecule, surfactants have limited solubility in polar and nonpolar solvents. Their solubility is dependent on the hydrophile-lipophile balance of their molecular structure. At a critical concentration, they form aggregates in either type of solvent. This colloidal aggregation is referred to as micellization, and the concentration at which it occurs is known as the critical micelle concentration. The term micelle was coined by McBain (7) to designate the aggregated solute. In water or other polar solvents, the micellar structure is such that the hydrophobic tails of the surfactant molecules are clustered together and form the interior of a sphere. The surface of the sphere consists of the hydrophilic heads. In nonpolar solvents, the orientation of the molecules is reversed. 

As target molecules of multistep organic synthesis, the molecular structure of the monomers that form synthetic ion channels and pores is always known from routine analytical methods. Structural studies, therefore, ask the question how these monomers form active ion channels and pore, i.e. focus on conformational or supramolecular analysis. Being the outcome of rational design based on known structural information, this question often comes down to the not very inspired question whether or not synthetic ion channels and pores that are already known to function as expected also form the expected active structure. Added to a lipid bilayer, a monomer of known structure can avoid the membrane (Fig. 11.13, Aa) or accumulate in transmembrane orientation (Figure 11.13, Ab), in the middle ofthe... 

While some of the above discussion is in the general reedm of prognostication, some mote specific comments are appropriate. It is appeuent that em increase in both the number and types of solid-state polymerization is a desirable research objective. Here, the major initial burden lies with the chemist to design (, new reactive molecular structure and appropriately oriented monomer crystal structures. Successful development of new lattice-controlled processes resulting in the availability of well-defined fully ordered mticromolecules will readily attract the more physically and theoreticedly oriented research communities. The PDA and poly (sulfur nitride) cases bear strong witness to this point. 

The naming and numbering of each parent system follow current practice by Chemical Abstracts. To assist the reader, the number 1 position in the structural formula and the number position of each heterosulfur atom are shown. However, the molecular structure is oriented so as to emphasize the relationship to the structure of its benzolog rather than to conform with the rules of Chemical Abstracts. Each system wherein the parent compound has been synthesized and described is designated by an asterisk. Selected data on this parent are presented in Table III. Some key references to the thiophene system are listed in each case. 

---