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

Journal Article · Tue Jan 16 00:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00454a021· OSTI ID:6710086

Vist, M R; Davis, J H ^[1]

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1. Univ. of Guelph, Ontario (Canada)

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. These distinct phases can be identified: the L{sub {alpha}} or liquid-crystalline phase, the gel phase, and a high cholesterol concentration phase, which we call the {beta} 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 {sup 2}H NMR time scale; the {beta} phase is characterized by highly ordered (rigid) chains and rapid axially symmetric reorientation. In addition, the authors identify three regions of two-phase coexistence. The first of these is a narrow L{sub {alpha}}/gel-phase coexistence region lying between 0 and about 6 mol % cholesterol at temperatures just below the chain-melting transition of the pure phospholipid/water dispersions, at 37.75{degree}C. The dramatic changes in the {sup 2}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 {sup 2}H NMR difference spectroscopy, one boundary lying near 7.5 mol % cholesterol and running from 37 down to at least 30{degree}C; the other boundary lies near 22 mol % cholesterol and covers the same temperature range. The third two-phase lies above 37{degree}C, beginning at a eutectic point somewhere between 7.5 and 10 mol% cholesterol and ending at about 20 mol %. In this region, the L{sub {alpha}} and {beta} phases are in equilibrium.

• OSTI ID: 6710086
• Journal Information: Biochemistry; (USA), Vol. 29:2; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CHOLESTEROL
PHASE STUDIES
MEMBRANES
MOLECULAR STRUCTURE
PHOSPHOLIPIDS
CALORIMETRY
CHOLINE
DEUTERIUM COMPOUNDS
NUCLEAR MAGNETIC RESONANCE
TEMPERATURE EFFECTS
ALCOHOLS
AMINES
AMMONIUM COMPOUNDS
DRUGS
ESTERS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
LIPIDS
LIPOTROPIC FACTORS
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
QUATERNARY COMPOUNDS
RESONANCE
STEROIDS
STEROLS
550201* - Biochemistry- Tracer Techniques