Solubility properties of the alkylmethylglucamide surfactants.
The critical micelle concentration (CMC) and the ability to solubilize and form vesicles from phospholipids are important criteria for the selection of a surfactant for reconstitution protocols. The CMC and its temperature dependence were determined for an homologous series of alkylmethylglucamides (MEGA-8, MEGA-9, MEGA-10). Each detergent was added continuously from a concentrated solution to a saline buffer with the environment-sensitive fluorescent probe ANS, held in a thermojacketed cuvette; ANS fluorescence increases at the CMC. The CMCs at 25 degrees C were 51.3, 16.0 and 4.8 mM for MEGA-8, MEGA-9 and MEGA-10. The free energy change for transfer to a micellar environment per -CH2- was -740 cal/mol, similar to other alkyl series. The CMCs decreased slightly with increasing temperature (T = 5-40 degrees C) for MEGA-9 and MEGA-10 while that of MEGA-8 was virtually insensitive to temperature in this range. MEGA-9 solubilization of egg PC in aqueous solutions was determined as a function of [PC] and temperature. The lamellar-micellar phase boundaries were determined by simultaneous 90 degrees light scattering and the resonance energy transfer using the headgroup labeled lipid probes NBD-PE and Rho-PE. The [MEGA-9] at solubilization was linear with [PC]; the MEGA-9 to egg PC ratio in the structures at optical clarity was 2.3 while the monomeric [MEGA-9] was 14.3 mM or slightly lower than the CMC at 25 degrees C. Solubilization of egg PC by MEGA-9 was somewhat more temperature-dependent than the CMC of this detergent. Vesicles formed from MEGA-9 tended to be multilamellar. MEGA-9 is clearly different from octyl glucoside, despite its chemical similarity, in terms of its temperature sensitivity and vesicle forming characteristics.
Walter
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Department of Physiology and Biophysics, Wright State University, Dayton, OH 45435.
Suchy
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Vinson
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D005227:Fatty Acids / Q000737:chemistry* / Q000378:metabolism; D005453:Fluorescence; D005944:Glucosamine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D008823:Micelles; D010063:Ovum; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism; D012995:Solubility; D013012:Sorbitol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D013501:Surface-Active Agents / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature
D005227:Fatty Acids; D008823:Micelles; D010713:Phosphatidylcholines; D013501:Surface-Active Agents; D013012:Sorbitol; C042222:nonanoyl-N-methylglucamide; C042221:decanoyl-N-methylglucamide; C063161:MEGA 8; D005944:Glucosamine