Francis J. Scavitto

Bio: Francis J. Scavitto is an academic researcher from Brown University. The author has contributed to research in topics: Dipalmitoylphosphatidylcholine. The author has an hindex of 2, co-authored 2 publications receiving 129 citations.

Dilatometry of dipalmitoyllecithin-cholesterol bilayers

Abstract: The interactions of cholesterol and dipalmitoyl-phosphatidylcholine in bilayers were investigated by differential scanning dilatometry and related techniques. Dipalmitoyl-phosphatidylcholine bilayers ranging from 0 to 50 mol % cholesterol were studied over a temperature range of 0-50 degrees C. These investigations allowed construction of a three-dimensional surface with dimensions of mole fraction of cholesterol, temperature, and apparent partial specific volume. Much of the phenomenology reported for dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine-cholesterol bilayers appears and can be interrelated on this surface. In addition to the thermotropic events associated with the system, two cholesterol-induced events at 17.5-20 and 29 mol % cholesterol are particularly in evidence.

Phase equilibria of cholesterol/dipalmitoylphosphatidylcholine mixtures: 2H nuclear magnetic resonance and differential scanning calorimetry.

Abstract: Deuterium nuclear magnetic resonance spectroscopy and differential scanning calorimetry are used to map the phase boundaries of mixtures of cholesterol and chain-perdeuteriated 1,2-dipalmitoyl-sn- glycero-3-phosphocholine at concentrations from 0 to 25 mol % cholesterol. Three distinct phases can be identified: the La or liquid-crystalline phase, the gel phase, and a high cholesterol concentration phase, which we call the 0 phase. The liquid-crystalline phase is characterized by highly flexible phospholipid chains with rapid axially symmetric reorientation; the gel phase has much more rigid lipid chains, and the motions are no longer axially symmetric on the 2H NMR time scale; the 0 phase is characterized by highly ordered (rigid) chains and rapid axially symmetric reorientation. In addition, we identify three regions of two-phase coexistence. The first of these is a narrow La/gel-phase coexistence region lying between 0 and about 6 mol % cholesterol at temperatures just below the chain-melting transition of the pure phospho- lipid/water dispersions, at 37.75 OC. The dramatic changes in the *H NMR line shape which occur on passing through the phase transition are used to map out the boundaries of this narrow two-phase region. The boundaries of the second two-phase region are determined by 2H NMR difference spectroscopy, one boundary lying near 7.5 mol 5% cholesterol and running from 37 down to at least 30 OC; the other boundary lies near 22 mol 5% cholesterol and covers the same temperature range. Within this region, the gel and /3 phases coexist. As the temperature is lowered below about 30 "C, the phospholipid motions reach the intermediate time scale regime of 2H NMR so that spectral subtractions become difficult and unreliable. The third two-phase region lies above 37 OC, beginning at a eutectic point somewhere between 7.5 and 10 mol % cholesterol and ending at about 20 mol %. In this region, the La and /3 phases are in equilibrium. The boundaries for this region are inferred from differential scanning calorimetry traces, for the boundary between the La- and the two-phase region, and from a dramatic sharpening of the NMR peaks on crossing the boundary between the two-phase region and the &phase region. In this region, the technique of difference spectroscopy fails, presumably because the diffusion rate in both the La- and P-phase domains is so rapid that phospholipid molecules exchange rapidly between domains on the experimental time scale.

Molecular mechanisms of general anaesthesia

Abstract: Important constraints on possible molecular mechanisms of general anaesthesia are derived from a quantitative reappraisal of data on the potency of general anaesthetics on whole animals. Despite their popularity, theories that invoke lipids as the prime target do not look at all promising, and available data point much more plausibly to a direct effect on particularly sensitive proteins. Structural changes of proteins on binding general anaesthetics are probably small but may be sufficient to perturb normal function; alternatively, anaesthetics may compete with an endogenous ligand. The phenomenon of pressure reversal of anaesthesia may simply be due to anaesthetics being squeezed away from their target sites.