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Issue 4, 2011
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Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles

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Abstract

We report a study on encapsulation of various amino acids into gas-phase sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) reverse micelles, using electrospray ionization guided-ion-beam tandem mass spectrometry. Collision-induced dissociation of mass-selected reverse micellar ions with Xe was performed to probe structures of gas-phase micellar assemblies, identify solute–surfactant interactions, and determine preferential incorporation sites of amino acids. Integration into gas-phase reverse micelles depends upon amino acid hydrophobicity and charge state. For examples, glycine and protonated amino acids (such as protonated tryptophan) are encapsulated within the micellar core via electrostatic interactions; while neutral tryptophan is adsorbed in the surfactant layer. As verified using model polar hydrophobic compounds, the hydrophobic effect and solute-interface hydrogen-bonding do not provide sufficient driving force needed for interfacial solubilization of neutral tryptophan. Neutral tryptophan, with a zwitterionic structure, is intercalated at the micellar interface between surfactant molecules through complementary effects of electrostatic interactions between tryptophan backbone and AOT polar heads, and hydrophobic interactions between tryptophan side chain and AOT alkyl tails. Protonation of tryptophan could significantly improve its incorporation capacity into gas-phase reverse micelles, and displace its incorporation site from the micellar interfacial zone to the core; protonation of glycine, on the other hand, has little effect on its encapsulation capacity. Another interesting observation is that amino acids of different isoelectric points could be selectively encapsulated into, and transported by, reverse micelles from solution to the gas phase, based upon their competition for protonation and subsequent encapsulation within the micellar core.

Graphical abstract: Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles

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Publication details

The article was received on 08 Jun 2010, accepted on 16 Nov 2010 and first published on 07 Dec 2010


Article type: Paper
DOI: 10.1039/C0CP00823K
Citation: Phys. Chem. Chem. Phys., 2011,13, 1466-1478
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    Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles

    Y. Fang, A. Bennett and J. Liu, Phys. Chem. Chem. Phys., 2011, 13, 1466
    DOI: 10.1039/C0CP00823K

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