Abstract
Water dynamics in samples of ceramide tetrasaccharide (Gg4Cer) vesicles and GM1 ganglioside micelles at 300:1 water/lipid mole ratio were studied by using deuterium nuclear magnetic resonance (2H-NMR). GM1 imposes a different restriction on water dynamics that is insensitive to temperatures either above or below its phase transition temperature or below the freezing point of water. The calculated correlation times are in the range of 10−10 s, typical of water molecules near to the polar groups. Pure GM1 micelles have two distinct water microenvironments dynamically characterized. Their dynamic parameters remain constant with temperature ranging from −18 to 32°C, but the amount of strongly associated water is modified. By contrast, a mixture of single soluble carbohydrates corresponding to GM1 polar head group does not preserve the dynamic parameters of water hydration when the temperature is varied. Incorporation of cholesterol or lysophosphatidylcholine into GM1 micelles substantially increases the mobility of water molecules compared with that found in pure GM1 micelles. The overall results indicate that both the supramolecular organization and the local surface quality (lipid–lipid interaction) strongly influence the interfacial water mobility and the extent of hydration layers in glycosphingolipid aggregates.
2H-NMR, Nuclear Magnetic Resonance of Deuterium; FFT, Fast Fourier Transform; FID, Free Induction Decay; T1, spin–lattice relaxation time; T2, spin–spin relaxation time; GM1, Gal(β1–3)GalNac(β1–4)Gal(3-2α)NeuAc(β1–4)Glc(β1-1′)N-acylsphingosine; Gg4Cer, Gal((β1–3)GalNac(β1–4)Gal(β1–4)Glc(β1-1′)N-acylsphingosine; Chol, cholesterol; LPC, egg lysophosphatidylcholine; Tm, gel→liquid lipid phase transition temperature (temperature of maximal excess heat capacity; T1/2 of endothermic peak means the temperature width at half height of excess heat capacity trace; τc, correlation time
2H-NMR, Nuclear Magnetic Resonance of Deuterium; FFT, Fast Fourier Transform; FID, Free Induction Decay; T1, spin–lattice relaxation time; T2, spin–spin relaxation time; GM1, Gal(β1–3)GalNac(β1–4)Gal(3-2α)NeuAc(β1–4)Glc(β1-1′)N-acylsphingosine; Gg4Cer, Gal((β1–3)GalNac(β1–4)Gal(β1–4)Glc(β1-1′)N-acylsphingosine; Chol, cholesterol; LPC, egg lysophosphatidylcholine; Tm, gel→liquid lipid phase transition temperature (temperature of maximal excess heat capacity; T1/2 of endothermic peak means the temperature width at half height of excess heat capacity trace; τc, correlation time