Nonionic surfactant biological systems

In this section several recently published studies on the interaction of nonionic surfactants with a variety of biological systems, including enzymes, bacteria, erythrocytes, leukocytes, membrane proteins, low density lipoproteins and membranes controlling absorption from the gastrointestinal tract, nasal and rectal cavities, will be assessed. This is a selective account, work having been reviewed that throws light on structure-activity relationships and on mechanisms of surfactant action. 

In some biological systems nonionic surfactants have an intrinsic biological activity the Ci2 alkyl ethers were too toxic to be used in the experiments of drug absorption with goldfish. The activity of the C12 ethers was quantified by measurement of the fish turnover time, T. When the reciprocal of the turnover time is plotted against alkyl chain length for the series Cx and Ejq and C12 compound is distinguished by its marked effect. (12). 

In MECC anionic surfactants are most frequently used, but cationic surfactants are also very popular. In addition, chiral surfactants, nonionic surfactants, zwitterionic surfactants, biological surfactants, or mixtures of each are finding increasing use. In all categories, variations in alkyl chain length will affect resolution or selectivity, as will changes in buffer concentration, pH, and temperature or the use of additives such as metal ions or organic modifiers. Typical surfactant systems used in MECC are shown in Table 5.3. 

Information about the bound water fraction in some colloid systems, silica gels, and biological systems is usually inferred on die basis of the frequency- and time-domain DS measurements from the analysis of the dielectric decrements or die relaxation times (64, 150-152). However, the nonionic microemulsions are characterized by a broad relaxation specfrum as can be seen from the Cole-Cole plot (Fig. 33). Thus, these dielectric methods fail because of the difficulties of deconvoluting die relaxation processes associated widi the relaxations of bound water and surfactant occurring in the same frequency window. 

Choice of surfactants for the preparation of multiple emulsions can, in principle, be made from any of the four classes of surfactants discussed in Chapter 2. The choice will be determined by the characteristics of the final emulsion type desired the natures of the various phases, additives, solubilities, and so on. In many applications (e.g., foods, drugs, cosmetics), the choice may be further influenced by such questions as toxicity, interaction with other addenda, and biological degradation. For that reason, well-studied nonionic surfactants have received a great deal of attention for such applications. In a given system, different types of surfactant may produce different types of multiple emulsion (A, B, or C types), so that such questions must also be considered. 

A major disadvantage of microemulsions that contain cosurfactant is their instability on dilution with aqueous biological fluids, which generally occurs after in vivo administration through most routes of administration. Use of cosurfactants may also cause irritancy. Microemulsion systems devoid of cosurfactants could be prepared by using double alkyl chain surfactants and nonionic... 

With the aim of designing a biologically inspired carrier in which the encapsulation and the delivery of DNA can be efficiently controlled, Amar-Yuli et al. have designed two lipid-based columnar hexagonal LLCs [58], which can accomplish two opposite roles while maintaining the same liquid crystalline symmetry. The first system was based on a nonionic lipid, such as monoolein, while the second system was modified by a low additional amount of the oleyl amine cationic surfactant. DNA was enzymatically treated to generate a broad distribution of contour lengths and diffusion characteristic times [58]. 

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