Abstract
It is demonstrated that proteins and nucleic acids can be transported through hydrophobic organic solvents (liquid membranes) via nonspecific complex formation with detergents, whereas no macromolecule transport is observed without the latter. A protein (or a nucleic acid) first interacts with an oppositely charged detergent due to hydrophobic ion pairing in the aqueous feed phase. The resultant hydrophobic complex readily partitions into an organic solvent and then into the aqueous receiver phase, where it dissociates. Experiments with (i) different detergent/protein molar ratios, (ii) a range of unrelated organic solvents as liquid membranes, and (iii) homologous detergents with hydrophobic tails of varying lengths indicate that the protein flux through the membrane directly correlates with the partitioning of the protein-detergent complexes from the aqueous feed into the organic phase. Very little protein transport was detected at detergent concentrations above the critical micelle concentration, suggesting that individual detergent molecules, rather than micelles, play the key role. The rate of the detergent-enabled protein transport is not a function of the protein molecular weight, provided that enough detergent molecules bind to make the complex sufficiently hydrophobic; e.g., bovine serum albumin can be transported faster than insulin, which is less than 1/10th of its size.
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Selected References
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