GANGLIOSIDE HYDRATION STUDY BY H-2-NMR - DEPENDENCE ON TEMPERATURE AND WATER LIPID RATIO/

Dynamic properties of (H2O)-H-2 in samples of ganglioside aggregates h ydrated at water/lipid ratios ranging from 25:1 to 8000:1 mole/mole we re studied by using deuterium nuclear magnetic resonance (H-2-NMR). We present a physical model for the interpretation of the measured spin- spin relaxation times (T-2). For all the concentrations studied the mo del provides evidence for the existence of at least two kinds of water environments: one in which the rotational correlation time is in the range of 10(-9) to 10(-8) s, and a second in which it lies between 10( -11) to 10(-10) s. A detailed study on the temperature dependence was performed for two of the concentrations, one corresponding to the hexa gonal phase (100: 1 mole/mole) and the other involving a micellar phas e (200: 1 mole/mole). In the 100:1 (H2O)-H-2/ganglioside molar ratio s ample, most of the water is tightly bound to long cylindrical structur es. For the 200:1 sample, there are on average approximately 30 water molecules tightly bound to the polar head group of each ganglioside mo lecule. The relative number and dynamics of molecules in this environm ent are essentially insensitive to temperature variations in the range 220-300K The rest of water molecules are also influenced by the aggre gate, having a different mobility from that observed in the free liqui d state.