PubMed · 5697033
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B Piccolo, R T O'Connor. 1968. Atomic absorption spectroscopy.. https://doi.org/10.1007/bf02631956
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The reaction of ozone with double bonds present in glycerophosphocholine lipids results in formation of ozonides that can be directly analyzed by mass spectrometry as either positive or negative molecular ion species generated by electrospray ionization. Polyunsaturated fatty acyl groups esterified to the phospholipid yielded a mixture of ozonide species with the maximum number of ozone molecules added equal to the total number of double bonds. Ozonide decomposition resulted in omega-aldehyde and omega-carboxylic acid products as revealed by ESI-MS. Collisional activation of the ozone adducts for mono- and polyunsaturated phospholipids gave rise to fragment ions indicative of the position of the double bonds in these molecules. The major decomposition pathway for either positive or negative ozonide ion species involved charge remote fragmentation of the ozonide initiated by homolytic cleavage of the peroxide bridge followed by rearrangement to form the omega-aldehyde and omega-carboxylate acyl species. The reaction of ozone with phospholipids containing polyunsaturated fatty acyl groups is a useful method to probe the position of double bonds by electrospray ionization mass spectrometry.
Extents of hydration of different lipids such as cholesterol, lecithin, lysolecithin, gangliosides, hydroxy cerebrosides, sphingomyelin, Dalda (hydrogenated fat), coconut oil and sunflower oil in the presence and absence of some inorganic electrolytes, sucrose and urea have been studied using the isopiestic vapour pressure technique. Except triglycerides, the shape of the water vapour adsorption isotherms for other lipids are in agreement with type II or type III BET isotherms respectively. The overall shape of each curve for triglycerides does not agree with any of the shapes of five types of BET isotherms. At water activity (1) approaching unity, maximum number of moles of water bound (delta n1zero) per mole of cholesterol are 1.6 and 2.6 at 28 degrees C and 37 degrees C, respectively. Values of delta n1zero at 23 degrees C stand in the following order: Ganglioside > lysolecithin > sphingomyelin > hydroxy cerebrosides. For triglycerides n1 increases with increase of a1 and reaches maximum in between 0.95 to 0.98 beyond which it sharply decreases to zero as a1 approaches unity. Standard free energy changes (delta Gzero) and enthalpy changes (delta Hzero) for cholesterol and lysolecithin have been evaluated from the experimental data. The excess hydration of cholesterol in the presence of several inorganic salts, urea and sucrose have been estimated from isopiestic experiments and free energies of excess hydration have been evaluated.
In order to test how well the lipophilicity of large and flexible molecules can be predicted by theoretical approaches, renin inhibitors and their building blocks have been investigated. Different experimental methods have been used for the determination of lipophilicity of the selected compounds, including RP-HPLC and a new pH-metric or two-phase titration method. This latter method appears to be well-suited for the log P measurement of lipophilic compounds. The experimental results have been compared to computer-assisted log P calculations (CLOGP and PrologP). Different correction terms have been introduced to correlate the experimental to the calculated results. Finally, in view of the poor oral bioavailability of most renin inhibitors, we have investigated the correlation between aqueous solubility data and their log P values.