Surfactants biologically active

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

In recent years bi- and polyfunctional phosphorus-containing surfactants have attracted interest, mainly due to their combination of surface activity and sequestering ability. However, anticorrosiveness and biologically active behavior are also effects that are sought after. 

Esters represent an important class of chemical compounds with applications as solvents, plasticizers, flavors and fragrances, pesticides, medicinals, surfactants, chemical intermediates, and monomers for resins. Recently, esters of amino acids have attracted attention regarding their use as biobased surfactants with excellent adsorption and aggregation properties, low toxicity, and broad biological activity. 

Sample preparation used to extract proteins from cells prior to analysis is an important step that can have an effect on the accuracy and reproducibility of the results. Proteins isolated from bacterial cells will have co-extracted contaminants such as lipids, polysaccharides, and nucleic acids. In addition various organic salts, buffers, detergents, surfactants, and preservatives may have been added to aid in protein extraction or to retain enzymatic or biological activity of the proteins. The presence of these extraneous materials can significantly impede or affect the reproducibility of analysis if they are not removed prior to analysis. 

An interesting vertical profile of the metabolite concentrations was observed the compounds showed a tendency to accumulate at the two-phase boundaries of air-freshwater and freshwater-saline water (the halocline). Thus, concentration maxima were observed at depths of 0 and 2 m (see Fig. 6.4.1) [6]. The observed distribution may result from either the physicochemical properties of these compounds (surface activity and hydrophobicity), or their formation at the interface due to increased biological activity. For the parent surfactants a similar but less pronounced vertical distribution pattern was observed (with maxima at 0 and 2 m of 17 and 9 xg L 1, respectively) [5],... 

It has been recognised for some time (see for example reference 1), that surfactants can increase the rate and extent of transport of solute molecules through biological membranes by fluidisation of the membrane. It is only recently, however, that sufficient work has been carried out to allow some analysis of structure-action relationships. In this overview an attempt is made, by reference to our own work and to work in the literature, to define those structural features in polyoxyethylene alkyl and aryl ethers which give rise to biological activity, especially as it is manifested in interactions with biomembranes and subsequent increase in the transport of drug molecules. 

However the reduction in biological activity with increasing hydrocarbon chain length beyond the optimum (Figure la) and the increase in biological activity on initially increasing the hydrophilic nature of the surfactants (Figure lb) requires elucidation, especially at lower concentrations. 

The difficulty with HLB as an index of physicochemical properties is that it is not a unique value, as the data of Zaslavsky et al. (1) on the haemolytic activity of three alkyl mercaptan polyoxyethylene derivatives clearly show in Table 1. Nevertheless data on promotion of the absorption of drugs by series of nonionic surfactants, when plotted as a function of HLB do show patterns of behaviour which can assist in pin-pointing the necessary lipophilicity required for optimal biological activity. It is evident however, that structural specificity plays a part in interactions of nonionic surfactants with biomembranes as shown in Table 1. It is reasonable to assume that membranes with different lipophilicities will"require" surfactants of different HLB to achieve penetration and fluidization one of the difficulties in discerning this optimal value of HLB resides in the problems of analysis of data in the literature. For example, Hirai et al. (8 ) examined the effect of a large series of alkyl polyoxyethylene ethers (C4,C0, Cj2 and C 2 series) on the absorption of insulin through the nasal mucosa of rats. Some results are shown in Table II. 

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). 

Cserhati T., E. Forgacs, and G. Oros (2002). Biological activity and environmental impact of anionic surfactants. Environment International 28 337-348. 

Although supercritical CO2 is an effective solvent for oils, fats, and similar substances, it is a poor one for nonvolatile hydrophilic (water-loving) substances such as proteins or metallic salts. Adding water as such to the supercritical CO2 is of little help, as the solubility of water in it is limited. Johnson and co-workers216 overcame the latter limitation by forming water-in-C02 emulsions with the aid of an added nontoxic perfluoropolyether surfactant that forms reverse micelles around the water microdroplets, in effect combining the special properties of supercritical CO2 with the solvent power of water. These emulsions can dissolve a variety of biomolecules at near-ambient temperatures, without loss of their biological activity. 

Modified and natural lipids and polymeric surfactants are increasingly being used in pharmaceutical formulations to increase the bioavailability of difficult drugs difficult usually because they have very poor solubility in aqueous environments. While these molecules may not themselves be biologically active, what happens to them in the gastrointestinal (GI) tract may influence their intended function, especially if they are acting to protect the active principle, for example, in the case of therapeutic peptides. 

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