Ligand-protein interactions via nuclear magnetic resonance of quadrupolar nuclei

Mixed lipid aggregates containing gangliosides impose different2H-NMR dynamical parameters on water environment depending on their lipid composition

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 degrees 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.

Identification of Al(III) Species in a Solution Containing Equimolar Concentrations of Al(III) and Citric Acid Using Varying-Temperature 27Al NMR Spectrometry

27Al NMR spectra of an equimolar (10 mM) Al(III)-citrate system were obtained at different temperatures. The linewidths of the signals decreased in the spectra recorded at elevated temperatures, which enabled us to unequivocally identify the resonance lines. From the spectrum recorded at 65 approximately C, a mononuclear Al(III)-citrate complex was identified at a solution pH of 3.0 in addition to trinuclear Al(III)-citrate complex, which dominated at pH 4.0.

Nuclear magnetic resonance spectra for l > 1 spins in dynamically heterogeneous systems with chemical exchange among environments

Nuclear magnetic resonance spectra for nuclei with spin l > 1 are considered in cases in which the observed nucleus may sample a rotationally immobilized and an isotropic environment that are coupled by a chemical exchange process. Spectra are simulated for the central (1/2, -1/2) transition for a 3/2 nucleus as a function of the concentrations of the two environments and as a function of the exchange rate between them. It is shown that a crucial feature determining the shape of the observable spectra is the spatial extent or the local order in the immobilized phase. In the case for which all rotationally immobilized sites sampled by the exchanging nucleus are identically oriented but where there is a distribution of these microdomain orientations with respect to the magnetic field direction, a powder pattern for the central transition is observed that carries whatever dynamic information may be derived from it. In the fast exchange limit, the width of the powder pattern scales inversely with the concentration of the isotropic environment as usual. In the intermediate exchange regimes, a complex line shape results that may mask the anisotropic character of the spectrum. In the slow exchange limit, superposition of the spectral contributions results; however, if the isotropic environment concentration is significantly larger than the anisotropic environment concentration, the anisotropic contribution is very difficult to detect because of the dynamic range problem and the possibly large difference in the effective line widths. In the case for which the exchanging nucleus samples a considerable distribution of rotationally immobilized site orientations, the anisotropic character of the spectrum is lost and a super-Lorentzian line shape results. These effects are demonstrated experimentally by 35Cl nuclear magnetic resonance spectra obtained on a lamellar liquid crystal that is modified with the addition of a thiolmercurate to provide a site of large quadrupole coupling constant and with cross-linked bovine serum albumin gels.