A proton-relaxation enhancement study of the interaction of manganous ions with phospholipids in aqueous dispersions.
An interaction of dipalmitoylphosphatidylcholine (PC) and phosphatidylserine (PS) with manganous ions has been investigated by measuring the effect of bound manganese upon the longitudinal relaxation rate, 1/T1, of the solvent water protons and evaluating the enhancement factor epsilon b. The observed enhancement values were used to determine the number of interacting sites per polar head group, n, and the values of association constants, KA, of manganese to PC and PS. Changes in epsilon b correlate with structural changes at the interacting site. By increasing the temperature one can see an abrupt decrease in epsilon b within the temperature interval from 40 to 50 degrees C indicating the thermal phase transition of PC as established by calorimetry, fluorescence and high-resolution NMR measurements. That an enhancement of 1/T1 of the solvent-water protons occurs at all is explained by assuming a restricted rotation of the Mn2+-aquo complex in the bound state. In addition we suppose that the rotation of the Mn2+-aquo complex is the mechanism which dominates the relaxation of the water protons in teh bulk solvent when phospholipids are present.
D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008345:Manganese; D008433:Mathematics; D008968:Molecular Conformation; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D013696:Temperature; D013816:Thermodynamics
D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D008345:Manganese