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Original scientific paper

Effects of Cholesterol Concentrations on Egg-phosphatidylcholine – Dihexadecyl-phosphate Liposomes Studied by CW ESR and FT – ESEEM Spectroscopy

Krunoslav Mirosavljević ; Department of Physical Chemistry, Ruđer Bošković Institute, Zagreb, Croatia
Vesna Noethig-Laslo ; Department of Physical Chemistry, Ruđer Bošković Institute, Zagreb, Croatia

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page 631-636

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The influence of cholesterol on water penetration depth as well as on the motional properties of
spin-labelled stearic acids (n-SASL, n = 5, 7, 10, 12, 16) in liposomes composed of egg-yolk
phosphatidylcholine (egg-PC) and dihexadecyl-phosphate (DHP) was studied by electron spin
echo envelope modulation (ESEEM) and continuous wave electron spin resonance (CW ESR)
spectroscopy. An increased amount of D2O molecules in the neighbourhood of the nitroxide
moiety bound at 5- and 7-SASL, concomitant with an absence of D2O at 10-SASL and 16-SASL
was determined in the presence of cholesterol in x = 8, 15, 29, 38, and 45 % (mole fraction). At
16-SASL, presence of cholesterol at any of the concentrations examined caused increased amplitude
of the librational motion of the nitroxide moiety as compared to that amplitude in the
absence of cholesterol. These results indicate that the inclusion of cholesterol increases water
penetration in the polar region of the bilayer and influences structural change in the hydrophobic
core of membrane.


egg-phosphatidylcholine; cholesterol; spin label; CW ESR; electron spin echo envelope; modulation (ESEEM) spectroscopy

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