The critical micelle concentration (cmc) of several lysophospholipids and of a lysophospholipid analogue was determined from surface tension measurements using the maximum bubble pressure method and/or 31P NMR. The use of the maximum bubble pressure method has now been extended to micromolar concentrations of surfactant, and the experimental parameters that effect its use have been explored. Surface activity was found to vary with changes in the chain length and in the headgroup polarity of the lysophospholipid. The cmc's for 1-decanoyl-, 1-dodecanoyl-, 1-tetradecanoyl-, and 1-hexadecanoyl-sn-glycero-3-phosphocholine are 7.0, 0.70, 0.070, and 0.007 mM, respectively. The cmc's for 1-decanoyl- and 1-dodecanoyl-sn-glycero-3-phosphoethanolamine are 4.4 and 0.33 mM, respectively. The cmc for dodecylphosphocholine, a lysophospholipid analogue, was found to be 1.1 mM. The cmc's for 1-tetradecanoyl- and 1-hexadecanoyl-sn-glycero-3-phosphoglycerol were found to be 3.0 and 0.60 mM, respectively, in pure water. In 0.1 M Tris-HCl (pH = 8.0), their cmc's are 0.16 and 0.018 mM, respectively. Surface tension and adsorption density values determined at the cmc are reported for each compound. The relationship of dynamic surface tension and lipid purity is discussed. These studies provide information about the micellization and interfacial properties of several biologically important lysophospholipids.

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7 mm i.d. quartz tube. Either type of sample was placed in a water-jacketed quartz condenser and irradiated under a continuous fine stream of nitrogen using six 8-W low-pressure Hg lamps arranged in a circular array of diameter 1.5 in. around the condenser.Samples were monitored by NMR analyses at ambient temperature. The chemical shifts (5) are reported in ppm downfield from Me4Si with methylene chloride (S 5.30) as a secondary standard.The irradiated mixtures were neutralized by dropwise addition to a rapidly stirred aqueous suspension of aqueous sodium bicarbonate and extracted with ether. GC analyses were carried out on the concentrated ether extracts by using the 10 ft X 1/8 in. o.d. column described earlier. Preparative collections were accomplished by using the 6 ft X 1/i in. o.d. column.2.6-Dimethyl-4-hydroxypyrylium Cation (1H+). GC analysis at 140 °C of the neutralized ether extract exhibited three products. Retentions of 4,6-dimethyl-2-pyrone ( 7), 5,6-dimethyl-2-pyrone (3), and 4,5-dimethyl-2-pyrone (2) relative to 2,6-dimethyl-4-pyrone (1) are 0.76, 0.80, and 1.29, respectively.2,3-Dimethy 1-4-hydroxypyrylium Cation (8H+). GC analysis at 140 °C of the neutralized ether extract exhibited five products. Retentions of 5-methyl-2-acetylfuran ( 12), 3,6-dimethyl-2-pyrone ( 11), 3,4-dimethyl-2-pyrone ( 9), 5,6-dimethyl-2-pyrone (3), and 4,5-dimethyl-2-pyrone (2) relative to 2,3-dimethyl-4-pyrone (8) are 0.23,0.64,0.94,1.27, and 2.01, respectively.2-Methyl-3-ethyl-4-hydroxypyrylium Cation (13H+). GC analysis at 140 °C of the neutralized ether extract exhibited four products. Retentions of 5-methyl-2-propionylfuran ( 17), 4methyl-3-ethyl-2-pyrone ( 14), 5-methyl-6-ethyl-2-pyrone ( 15), and 6-methyl-5-ethyl-2-pyrone ( 16) relative to 2-methyl-3-ethyl-4pyrone (13) are 0.35, 1.08, 1.38, and 1.61, respectively.2.3.6-Trimethyl-4-hydroxypyrylium Cation (18H+). GC analysis at 170 °C of the neutralized ether extract exhibited one product. The retention of 4,5,6-trimethyl-2-pyrone (19) relative to 2,3,6-trimethyl-4-pyrone ( 18) is 2.1. 2,3,5,6-Tetramethyl-4-hydroxypyrylium Cation (22H+). GC analysis at 170 °C of the neutralized ether extract exhibited one product. The retention of 3,4,5,6-tetramethyl-2-pyrone (23) relative to 2,3,5,6-tetramethyl-4-pyrone ( 22) is 2.4.

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