Nuclear magnetic resonance-proton relaxation

Richardson, S.J. 1989. Contribution of proton exchange to the oxygen-17 nuclear magnetic resonance transverse relaxation rate in water and starch-water systems. Cereal Chem. 66, 244-246. Richardson, M.J. and Saville, N.G. 1975. Derivation of accurate glass transition temperatures by differential scanning calorimetry. Polymer 16, 753-757. 

Figure 3 Molecular relaxivities of liposomes with different Gd-containing membranotropic chelators. Liposomes (egg lecithin cholesterol chelator = 72 25 3) were prepared by consecutive extrusion of lipid suspension in HEPES buffered saline, pH 7.4, through the set of polycarbonate filters with pore size of 0.6, 0.4, and 0.2 mm. Liposome final size was between 205 and 225 nm. Gd content determination was performed by Galbraith Laboratories, Inc. The relaxation parameters of all preparations were measured at room temperature using a 5-MHz RADX nuclear magnetic resonance proton spin analyzer. The relaxivity of liposomes with polymeric chelators is noticeably greater because of the larger number of Gd atoms bound to a single lipid residue [16].

The dynamics of the so-called biological water molecules in the immediate vicinity of a protein have been studied using dielectric relaxation [18], proton and O NMR relaxation [19], reaction path calculation [20], and analytical statistical mechanical models [21]. While the dielectric relaxation time of ordinary water molecules is 10 ps [16], both the dielectric [18] and nuclear magnetic resonance (NMR) relaxation studies [19], indicate that near the protein surface the relaxation dynamics are bimodal with two components in the 10-ns and 10-ps time scale, respectively. The 10-ns relaxation time cannot be due to the motion of the peptide chains, which occurs in the 100-ns time scale. From the study of NMR relaxation times of " O at the protein surface, Halle et al. [19c,d] suggested dynamic exchange between the slowly rotating internal and the fast external water molecules. 

Nuclear magnetic resonance (NMR) relaxation times are known to be very sensitive to molecular motions and their measurement does not require the Introduction of external probes. The spin-spin relaxation time (T2) of protons Is especially sensitive to local motions with large amplitude (19, 20) which in turn are the most sensitive ones to changes In packing. On the other hand, the major factor which affects the ESR... 

The proton spin-lattice relaxation-rate (R,) is a well established, nuclear magnetic resonance (n.m.r.) parameter for structural, configurational, and conformational analysis of organic molecules in solution. " As yet, however, its utility has received little attention in the field of carbohydrate chemistry,... 

This is based on spatial nuclear magnetic resonance of water protons within the body. For a contrast agent to be effective, direct coordination of water molecules to the lanthanide is necessary to impart efficient relaxation of the water protons. Therefore, whilst this has been covered comprehensively in a number of recent reviews... 

Nuclear magnetic resonance (NMR) has been used to study segmental motions in block copolymer solutions. The mobility of protons in polymer chains in dilute solutions has been probed using high-resolution H NMR. Association of chains into micelles leads to a reduction in mobility in the core, which leads to a broadening of the respective NMR lines that has been studied for a number of systems, as described by Tuzar and Kratochvil (1993). The sol-gel transition in concentrated solutions has been located via ]H transverse relaxation time experiments, as outlined in Chapter 4. 

In protein solutions the water protons may be considered to reside in two different environments, i.e. the bulk water, and the hydration spheres of the protein molecules. If there is fast exchange of protons between these environments a single proton nuclear magnetic resonance will be observed, which corresponds to the average of the resonances in the different environments. Following McConnell (74) the observed longitudinal relaxation time is to a good approximation... 

Figure 15.16. H Relaxation of 1-naphthol protons with increasing humic acid concentration at pH 7. All protons are observed to relax at a similar rate, suggesting a nonselective interaction between the protons of 1-naphthol and humic acid. Reprinted from Simpson, M. I, Simpson, A. J., and Hatcher, R G. (2004). Noncovalent interactions between aromatic compounds and dissolved humic acid examined by nuclear magnetic resonance spectroscopy. Environ. Toxi. Chem. 23, 355-362, with permission from the Society of Environmental Toxicology and Chemistry.

---