Gordon C. Kresheck

Thermometric titration studies of the effect of head group, chain length, solvent, and temperature on the thermodynamics of micelle formation

Abstract The changes in enthalpy, entropy, and heat capacity that accompany micelle formation for sodium, octyl, decyl, and dodecyl sulfate, dimethyldecyl and dimethyldodecyl phosphine oxide, sodium dodecoyl sarcosinate, and dodecylpyridinium chloride and bromide were determined by thermometric titrations between 21 and 35° in aqueous solution. The enthalpy and entropy changes exhibited a correlation for a given chain length consistent with a compensation temperature of about 300°. In general, the enthalpy and entropy changes, which appear to be rather complex parameters, did not parallel the heat capacity change. The change in heat capacity for micellization appears mainly to reflect solvent effects. Sodium dodecyl sulfate was also studied in 6 M urea, 10% ethanol, 0.1 M sucrose, 0.1 M NaC1, 0.5 M NaCl, and 0.1 M NaBr. A comparison of enthalpy changes that have been determined by calorimetry and from the temperature dependence of the CMC indicates that the two approaches should not be assumed to yield identical results.

Enthalpy titration studies of the binding of surfactants to polyvinylpyrrolidonel

Abstract The temperature dependence of the enthalpy changes that accompany the addition of several surfactants to aqueous polyvinylpyrrolidone solutions was determined by titration calorimetry. The alkyl sulfates (octyl, decyl, and dodecyl) showed signs of binding, whereas the dodecylpyridinium halides (bromide and chloride), alkyldimethylphosphine oxides (decyl and dodecyl), and dodecylsarcosinate exhibited only a general solvent effect due to the presence of the polymer (that of a water structure-breaker). The binding of dodecyl sulfate was essentially athermal (although the heat of dilution was more endothermic due to increased dimicellization), and the binding of the octyl and decyl sulfates was endothermic near 25°C. At low dodecyl sulfate binding ratios, the monomeric form of the surfactant reacted with the polymer, but 2 3 of the surfactant was bound from the micellar state as saturation was approached. The differences between the binding properties of the various surfactants cannot be explained using existing theories of hydrophobic bonding.

Phase separation properties of several aqueous alkyldimethylphosphine oxide/phospholipid mixtures and their potential use for protein purification

Abstract The phase separation properties of several aqueous alkyldimethylphosphine oxide/phospholipid mixtures were investigated. The addition of synthetic phospholipids with acyl residues ranging from 12 to 18 carbon atoms, a soybean phospholipid extract, and a red blood cell ghost extract lowered the temperature of phase separation below that of the surfactant alone. The high relative viscosity of the top layer suggests that asymmetric mixed micelles exist, whereas the relative viscosity of the bottom layer approached the value of 2.5 expected for spherical particles. The relative concentration of lipid in the top layer decreased with increasing molecular weight for the synthetic lecithins. The addition of 0.1 M univalent salts was investigated and no dependence of the cloud point on cation size was observed. However, a set of potassium halides exhibited a trend which followed the Hofmeister series. Finally, the composition of the top and bottom layers was investigated at 38, 42, 48 and 55°C for one DodDPO/DMPC mixture, and the solute was observed to be progressively concentrated in a smaller volume as the temperature was increased for each of five initial concentrations ranging from 12 to 53.6 mg/ml.

Calorimetric studies of the interaction between asolectin vesicles and surfactants

Abstract The interaction of Asolectin vesicles with an anionic (NaDodSO 4 ), cationic (DodPyCl), and nonionic (DeDPO) surfactant was investigated by titration calorimetry at 25°C. An enthalpy change of about −2.0 kcal/mole was found for what appears to be a rapid penetration of all three of the surfactants into the vesicle bilayer. The stoichiometry for saturation of the vesicles was about 0.06 g surfactant/g of phospholipid in each case. Only NaDodSO 4 , exhibited evidence of a lamellar-micelle phase transition, which was complete at a stoichiometry of 0.24 g of surfactant/g of phospholipid. The free energy changes for interaction of the ionic surfactants were more negative than for DeDPO. The entropy change was much less for the binding of DeDPO to the vesicles (7.7 cal/moledeg) than for micelle formation (17.4 cal/mole-deg). The nonionic surfactant, Lubrol WX, did not have a measurable enthalpy of interaction with the vesicles under the conditions employed.

A calorimetric comparison of the interaction of sodium dodecyl sulfate with cytochrome c and erythrocyte glycoproteins

The interactions of sodium dodecyl sulfate with cytochrome c and erythrocyte glycoproteins have been studied by the method of titration calorimetry. It was found that the initial addition of sodium dodecyl sulfate to cytochrome c caused an endothermic unfolding of the protein, detectable by circular dichroism (CD). This was followed by the exothermic binding of sodium dodecyl sulfate to the protein, without further CD-detectable conformational changes. In contrast, sodium dodecyl sulfate bound directly to the erythrocyte glycoproteins in an exothermic reaction without any accompanying CD-detectable conformation changes. This indicates that the glycoproteins solubilized in aqueous media have exposed hydrophobic regions which can interact directly with this detergent. The enthalpy changes and stoichiometries of binding are reported.

Unusual enthalpy changes which accompany the titration of dimyristoylphosphatidylcholine vesicles with triton X-100

The enthalpy changes which accompany the titration of 0.1% and 0.25% small unilamellar and multiameller vesicle samples of dimyristoylphosphatidylcholine with 2% Triton X-100 in 0.067 M phosphate buffer (pH 7.4) containing 0.15 M NaCl have been determined by titration calorimetry at 21 degrees C and 28 degrees C, the enthalpy change for both type of vesicles was zero within the limits of experimental error. At 21 degrees C, the multilamellar vesicle samples exhibited an enthalpy change of 1.35 +/- 0.48 and 2.47 +/- 0.98 kcal/mol dimyristoylphosphatidylcholine which was complete at a molar ratio of dimyristoylphosphatidylcholine to Triton of 3.21 +/- 0.84 and 5.77 +/- 1.05 for 0.1% and 0.25% dimyristoylphosphatidylcholine solutions, respectively. An exothermic transition of -2.39 +/- 0.30 and -2.05 +/- 0.69 kcal/mol phospholipid followed by an endothermic transition of 1.37 +/- 0.12 and 1.94 +/- 0.20 kcal/mol dimyristoylphosphatidylcholine was observed at 21 degrees C for 0.1% and 0.25% small unilamellar vesicle samples, respectively. In addition the nearly athermal association of the small unilemellar vesicle samples at 21 degrees C was observed, which may be an appropriate model for biological membrane fusion.

Precipitous effect of dimyristoyl phosphatidylcholine on the reversible thermotropic phase separation of aqueous dimethylalkylphosphine oxide solutions

Abstract The addition of dimyristoyl phosphatidylcholine (DMPC) to aqueous dimethylalkylphosphine oxide solutions decreases the concentration of surfactant required to reach the temperature at which phase separation occurs (cloud point). The cloud point was shown to depend on the mole fraction of surfactant to phospholipid present. The solution below the cloud point contains mixed micelles which may increase in size as the temperature is raised faster than surfactant micelles without phospholipid. The stability of the cloud phase was found to depend upon the amount of phospholipid added. Solutions which were rich in phospholipid and held above the cloud point, produced multilamellar structures that eventually precipitated from a clear monomeric surfactant solution. The possible significance of an abrupt phase inversion from a multilamellar to mixed micellar state for biological membranes was discussed.

Micelle formation by 31P NMR

An investigation of the process of micelle formation of amphiphilic molecules in dilute solution is described. This report shows that nuclear magnetic resonance using plutonium-31 is effective. Plutonium-31 measurements were made with a spectrometer under ambient conditions. The spectra were measured with proton decoupling, and the shifts are reported with respect to an internal capillary containing 85% H/sub 3/PO/sub 4/. The number of transients accumulated varied from 100 to 10,000. The critical micelle concentration in water is consistent with that previously determined. The spectra of the sample were compatible with the trialkylphosphine oxide structure reported previously. 17 references.

Relationships between micellar properties and the cloud point of aqueous dimyristoyl phosphatidylcholine―dimethyldecylphosphine oxide solutions

Abstract The molecular weight and shape of mixed micelles containing different ratios of decyldimethylphosphine oxide (DecDPO) and dimyristoyl phosphatidylcholine (DMPC) were determined in order to account for the depression of the cloud point of aqueous DecDPO by the addition of DMPC (Kresheck, G. C., Chem. Phys. Lipids 29, 69 (1981)). The molecular weight from gel filtration chromatography and sedimentation equilibrium studies increased from 25,000 g/mole to 48,000, 165,000, and 310,000 g/mole as the mole fraction of DecDPO to DMPC decreased from 1.0 to 0.9, 0.95, and 0.8, respectively. The hydrodynamic shape of the mixed micelles containing the least amount of phospholipid appeared to be the least asymmetric, and the sample with a DecDPO mole fraction of 0.8 resembled a prolate particle with an axial ratio of 40. The cloud point lowering action of DMPC was correlated with an increased molecular weight of the resulting mixed micelles in analogy with the molecular weight of the cloud point for aqueous polymer solutions using the theory of Flory and Huggins.

Block poly(Ala)-poly(Lys). A water-soluble model for intrinsic membrane proteins?

Block poly(Ala)16-poly(Lys)13.5 was synthesized by the Leuchs anhydride method. This polypeptide is water soluble in a largely monomeric form, but binds rapidly and spontaneously to unilamellar vesicles of dimyristoyl phosphatidylcholine at pH 7.4. The interaction is evidently of a hydrophobic nature since the complex is not disrupted by salt and no similar reaction is given by polylysine. Evidence for the interaction was obtained by ultrafiltration, chromatography on Sepharose 4B, and sedimentation velocity ultracentrifugation. While direct information on the molecular structure of the complex is still lacking, we propose that this amphipathic block copolymer binds to lipids in a similar manner as intrinsic membrane proteins and hence can be used to study the interactions of intrinsic proteins with lipids.