Spin-lattice relaxation of protons

NOE factors smaller than 1.988 indicate participation of other mechanisms in the spin-lattice relaxation of protonated 13C nuclei. The percentange contribution of the DD mechanism can be ascertained from the measured NOE factor according to eq. (3.19) ... 

Figure 8 shows the time course of the laboratory and rotating frame spin-lattice relaxation of protons in lyophilized y-globulin formulations containing dextran, determined at 55°C using a pulsed NMR spectrometer [26]. 

The efficiency of spin-lattice relaxation of a given nucleus is also dependent on the number of nearby nuclear dipoles. In fortunate cases this can be used to obtain structural information. For example, there are more protons spatially close to the methine carbons in the c/.v-configurated tricyclic compound 3 than in the trans-isomer220. Thus, the 7 value of the methine carbons in the (Tv-isomer is considerably smaller. 

The measurement of the spin-lattice relaxation of solvent water protons in solutions of Co11 carbonic anhydrase leads to the establishment of pKa values of 6.1 and 8.5. The former value probably refers to the Co—OH2 group, while the latter piC, is suggested to be due to enzyme-bound bicarbonate.501... 

The results are shown in Table 16. The spin-lattice relaxations of the o-methyl and methoxy protons were found to arise mainly from the dipolar interactions between the protons in the methyl group itself. In the relaxation of backbone methylene protons the contributions from the protons in the neighbour-... 

Enolization of triplet 5,8-dimethyl-1-tetralone by hydrogen transfer effects" ", spin-lattice relaxation of pentacen-6,13-quinone triplets in a benzoic acid host crystal involves proton tunnelling", and photoreduction of benzophenone and thioxanthen-9-one by amines" are other researches of photochemical significance. Interactions of formate ions with triplet states of benzophenone-4-carboxylate and -4-sulphonate, 1,4-naphthoquinone, and anthraquinone-2-sulphonate have been examined systematically by laser flash photolysis". ... 

Figure 34.3 shows the results of a variable contact time CP experiment, in which the Si CP contact period (tcp) is varied in order to elucidate the Si CP (relaxation) time constant (ThsO for each Si peak. The early (small tcp) part of such curves is typically dominated by the rate of CP transfer, as characterized by the rate constant and the latter part of such curves is usually determined by the rate constant of the rotating frame spin-lattice relaxation of the protons responsible for polarization transfer to the observed silicons, as characterized by the time constant, (assuming > Thsi). These curves can be analyzed mathematically in terms of well-known equations [17]. 

Measurement of relaxation is usually easier then but also time consuming. It should be borne in mind that spin-lattice relaxation of is bi-exponential [86] unless protons are decoupled during the relaxation delay. at natural abundance and nuclei are often used as probe of dynamic processes. Parameters such as and spin-lattice relaxation times and Tj), carbon and proton-rotating-frame relaxation... 

FIGURE 1.112 Water-proton HT NMRD profiles for colloid silica (Sbet=265 mVg) sols (2.2 wt%) at 4°C alone and with metal ions. (Adapted from J. Magn. Resort. A., 120, Roose, R, Van Craen, J., Andriessens, G., and Eisendrath, H., NMR study of spin-lattice relaxation of water protons by Mn adsorbed onto colloidal silica, 206-213, 1996. Copyright 1996, with permission from Elsevier.)... 

Roose, P., Van Craen, J., Andriessens, G., and Eisendrath, H. 1996. NMR study of spin-lattice relaxation of water protons by Mn adsorbed onto colloidal silica. J. Magn. Reson. A 120 206-213. 

Lynch, L.J., and Webster, D.S. Proton spin-lattice relaxation of water associated with brown coal. J. Magn. Reson. 1980 40 259-272. 

Conformations and Dynamic Situations.—Rotation about single bonds " and partial double bonds, carbonium-ion rearrangements, conformational processes in rings, and spin-lattice relaxation times and the mobility of organic molecules in solution have been reviewed. The proton spin-lattice relaxation of polycrystalline bicyclo[2,2,2]oct-2-ene has been measured and the enthalpy of activation or reorientational motion calculated. 

Values of B for many ions at 25°C are shown in Table 2.11, snpplonented by data from the NMR spin-lattice relaxation of D O molecnles in aqneons salt solutions, again split according to B (K ) = B ,j(Cr). These valnes [127] agree in sign and generally in magnitude with the proton NMR also shown in Table 2.11. 

Figure 5.8. Paramagnetic ion-induced spin-lattice relaxation rates (rp) of the protons of 5.1c and 5.1 f in CTAB solution and of CTAB in the presence of 5.1c or 5.1 f, normalised to rpfor the surfactant -CH-j. The solutions contained 50 mM of CTAB, 8 mM of 5.1c or 5.1f and 0 or 0.4 mM of [Cu (EDTA) f ...

If the amount of the sample is sufficient, then the carbon skeleton is best traced out from the two-dimensional INADEQUATE experiment. If the absolute configuration of particular C atoms is needed, the empirical applications of diastereotopism and chiral shift reagents are useful (Section 2.4). Anisotropic and ring current effects supply information about conformation and aromaticity (Section 2.5), and pH effects can indicate the site of protonation (problem 24). Temperature-dependent NMR spectra and C spin-lattice relaxation times (Section 2.6) provide insight into molecular dynamics (problems 13 and 14). 

Different solid-state NMR techniques CPMAS NMR, the second moment of the signal, the spin-lattice relaxation time in the rotating frame T p) were combined to reach the conclusion that in the case of por-phine H2P the double-proton transfer is followed by a 90° rotation within the crystal (see Scheme 2). 

NMR Spectroscopy. All proton-decoupled carbon-13 spectra were obtained on a General Electric GN-500 spectrometer. The vinylldene chloride isobutylene sample was run at 24 degrees centigrade. A 45 degree (3.4us) pulse was used with a Inter-pulse delay of 1.5s (prepulse delay + acquisition time). Over 2400 scans were acquired with 16k complex data points and a sweep width of +/- 5000Hz. Measured spin-lattice relaxation times (Tl) were approximately 4s for the non-protonated carbons, 3s for the methyl groups, and 0.3s for the methylene carbons. 

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