Artificial micelles

In their stability to dialysis, ethanol addition, heating, and applied pressure, the artificial micelles generally were more similar to native micelles than micelles made with Ca2+ alone (Schmidt and Koops, 1977 Schmidt et al., 1979). 

Explosive research activity is going on in micellar photochemistry. This is related to the development of artificial photosynthetic systems, and the anisotropic nature of globular micelles and bilayer membranes is used for conservation of excitation energy. The subject has been recently reviewed (Kalyanasundaram, 1978). 

We have also learned that self-replication is not a prerogative only of nucleic acids, but it can be shared by different kinds of chemical families see the formose reaction, the self-replicating peptides, and the self-reproducing micelles and vesicles. The list should include the cellular automata and the corresponding devices of artificial life. Self-reproduction of vesicles and liposomes is important because it represents a model for cell reproduction. 

Micelles and vesicles can be formed above a certain concentration. For instance, small micelles are formed above critical micellar concentration, cmc. (The latter abbreviation is often used for critical vesicle concentration, too. However, sometimes a more general term critical aggregate concentration, cac is also applied.) Bilayers of specific amphiphiles with two tails are typical of the central part of cell membranes discussed in some detail in the next chapter. Studying artificial mono- and bilayers (uniform or with built in pores) is indispensable for gaining information about the structure and functioning of cell membranes involving the transport through them. 

This last problem is perhaps not strictly within the realm of photochemistry. It is however so important potentially that it cannot be overlooked on grounds of arbitrary separations between different branches of scientific research (perhaps the expression of interdisciplinary approach would best describe it). A few pages will therefore be devoted to the science and technology of artificially organized molecular systems such as monomolecular and multimolecular layers, micelles and spatially restricted environments like zeolites and since we reach here another of the frontiers of photochemistry, section 8.4 in the final chapter is devoted to these systems. 

In summary, while the nonionic surfactant dimethyldo-decylamine oxide forms only spherical micelles even in 0.20 M NaCl (see above and ref. 498), micelles of dimethyloleylamine oxide are subject to a sphere-rod equilibrium in aqueous solutions of NaCl as dilute as 10 4 M and even in water alone (ref. 500). Thus, Imae and Ikeda (ref. 479) conclude the rodlike micelles are stabilized more, as compared with the spherical micelles, when the hydrocarbon chain of the surfactant molecule is longer. This conclusion is, therefore, consistent with the earlier-mentioned belief of these authors that the rodlike micelles are more stable when the polar head group of the surfactant molecule is smaller and the chain length of its hydrocarbon part is longer (ref. 473). Since the surfactants referred to all behave as nonionics, these findings of rodlike micelle production have direct relevance to the formation of artificial gas microbubbles (see Section 10.3) with either the earlier-mentioned surfactant mixture Filmix 3 (see Chapter 9 and Section 10.4) or another, related surfactant preparation (see Section 10.4). 

Fig. 10.1. Particle size distribution determined for artificial, surfactant-stabilized microbubbles (and micelles) in distilled water.

The surfactant mixture used (CAV-CON Filmix 3) is identical to that used to form the artificial gas-in-water emulsions described in Chapter 9, where the concentrated emulsion particles observed were all above 0.3 pm in diameter (which is the lower detection limit of the laser-based flow cytometer instrument) and therefore did not include the co-existing micelles. 

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