PubMed · 580167
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D A Wilkinson, J F Nagle. 1978. A differential dilatometer.. https://doi.org/10.1016/0003-2697(78)90509-2
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The conformation of phosphatidylcholine in liquid-crystalline bilayers was studied with a novel, high-resolution method employing phosphatidylcholine species containing pyrenyl moieties in both acyl chains of variable length. Analysis of the intramolecular pyrene-pyrene collision data obtained for 30 such species in terms of a simple geometrical model showed that the sn-1 acyl chain penetrates, on the average, 0.84 +/- 0.11 methylene units (0.8 A) deeper into the bilayer than the sn-2 chain at 22 degrees C. A similar value was obtained at 37 degrees C. Since the penetration difference of the sn-1 and sn-2 acyl chains is inherently coupled to the conformation of the glycerol moiety, these data mean that the glycerol moiety of phosphatidylcholine is, on the average, only moderately tilted with respect to the bilayer plane in the liquid-crystalline state. This contrasts the perpendicular orientation observed previously for phosphatidylcholine crystals [Pearson, R. H., & Pascher, I. (1979) Nature 281, 499-501]. Importantly, addition of 50 mol % cholesterol, which is known to reduce dramatically the interactions between phosphatidylcholine molecules in bilayers, had only a small effect on the penetration difference of the acyl chains, strongly suggesting that the conformation of phosphatidylcholine in the liquid-crystalline state is determined largely by intramolecular, rather than intermolecular, interactions.
Using the semi-empirical AM1 method, 302 compounds have been studied and equilibrium properties calculated. Functions based on linear combinations of subsets of calculated properties have been fit to the 1-octanol-water partition coefficients. The best such semi-empirical approach function has 18 parameters, has a standard deviation of 0.306, and seems to describe the partition coefficients of the 302 compounds. The predictive power of the function was tested and found to be good. Since this new version is based on a much larger number of, and structurally more varied, compounds and uses an improved, new function, we expect it to be a very useful method to predict partition properties of a wide variety of compounds.
Photon correlation spectroscopy, nuclear magnetic resonance spectroscopy, electron microscopy, and small-angle X-ray scattering were used for the structural characterization of a model oil-in-water emulsion containing particles in the submicrometer size range. Additionally, small-angle X-ray diffraction, wide-angle X-ray diffraction, and differential scanning calorimetry were applied to raw materials and to binary mixtures. The majority of emulsion droplets have the characteristic of an ideal emulsion droplet, that is, a liquid lipid core covered by an emulsifier monolayer. However, the system contains a certain excess of emulsifier. Particles with bi- and/or oligolayer structures can be deduced. Double-emulsion droplets were detected. Large unilamellar vesicles were not found; however, the existence of small unilamellar liposomes (also referred to as small unilamellar vesicles or SUVs) seems likely. The proportion of all small nonmonolayer structures was quantified by nuclear magnetic resonance spectroscopy. No mixed micellar structures were detectable. Lysophospholipids were not detected in the aqueous phase, indicating their predominant incorporation into the emulsifier layers. Water-soluble phospholipid degradation products were found in the water phase. The existence of at least several monolayers of phospholipids does not seem to be a prerequisite for a stable soybean oil-in-water emulsion, in general.