Proton relaxation times

By measuring the proton relaxation times, and T,p, it is possible to estimate the mobility of polymer chains within the cell wall (11). Proton spin relaxation editing (PSRE) is a method of expressing these results. It separates the components seen in a conventional CP-MAS C spectra into low-mobility and intermediate-mobility components. If PSRE is applied to a experiment (12) the mobility of the... 

Carbon nanotubes have been also used as a macromolecular scaffold for Gdm complexes. An amphiphilic gadolinium(III) chelate bearing a C16 chain was adsorbed on multiwalled carbon nanotubes (264). The resulting suspensions were stable for several days. Longitudinal water proton relaxivities, r] showed a strong dependence on the GdL concentration, particularly at low field. The relaxivities decreased with increasing field as predicted by the SBM theory. Transverse water proton relaxation times, T2, were practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been... 

In the previous discussion, the electron-nucleus spin system was assumed to be rigidly held within a molecule isotropically rotating in solution. If the molecule cannot be treated as a rigid sphere, its motion is in general anisotropic, and three or five different reorientational correlation times have to be considered 79). Furthermore, it was calculated that free rotation of water protons about the metal ion-oxygen bond decreases the proton relaxation time in aqua ions of about 20% 79). A general treatment for considering the presence of internal motions faster than the reorientational correlation time of the whole molecule is the Lipari Szabo model free treatment 80). Relaxation is calculated as the sum of two terms 8J), of the type... 

There have been several initial applications of the NMR method to the study of solids of catalytic interest. Selwood and co-workers (14) have measured proton relaxation times (Ti) of water-soaked 7-aluminas containing iron oxide, copper oxide, and chromium oxide. 

On the other hand, Connor and Hartland ( ) have reported results of a proton NMR study for a series of polyethylene oxide samples by rotating frame proton relaxation time T p meastirements. Ti was also determined. For their lowest molecular weight sam-... 

The Cl carbon resonances for the aryl groups, unlike the C resonances of the alky groups are too broad for detection. The proton relaxation times and as well as the linewidths in three different magnetic fields, corresponding to proton frequencies of 250, 400, and 600 MHz, show an increase with the field strength. 

NMR proton relaxation times for water in living tissues are found to be shorter than in ordinary water, and the lines correspondingly broader. Some workers have interpreted this fact as indicating that water in living cells may be in a semicrystalline state, rather than a liquid state the... 

Figure 6. Proton relaxation times for water adsorbed on sample of 70-n diameter NaX crystals before and after hydrolysis (sample furnished by L.

In zeolites the mobility of hydrocarbon molecules with double bonds is specifically restricted because of a specific interaction between the 7r-elec-trons and the zeolite (2). As expected, proton spin relaxation of benzene, cyclohexadiene, cyclohexene, and cyclohexane adsorbed on NaY reveals an increasing restriction of mobility with increasing number of -electrons (8, 4, 8). This is shown in Figure 1, where the longitudinal (7 ) and transverse (T2) proton relaxation times are plotted. 

Figure 1. Temperature dependence of proton relaxation times of cyclic hydrocarbons (C Ht, C Hs, C flio, CqHi2) adsorbed on NaY. Pore filling factor 0 = 0.8.

Figure 3. Temperature dependence of proton relaxation time Ti of water in NaPtY. Pore filling factor 6 0.8. Pretreatment procedure for 20 hours at 100° Ifi0°C. For comparison the results for NaY without platinum are also plotted.

Fig. 58. Proton relaxation times T, and T2 for water adsorbed in zeolite Na-X at 12 MHz...

Meiler and Pfeifer (493) measured 13C and H NMR spectra of carbon monoxide, carbon dioxide, and benzene adsorbed on ZSM-5 and silicalite. The 13C signal from benzene was a superimposition of two lines corresponding to relatively mobile molecules (narrow Lorentzian line) and strongly adsorbed molecules (broad asymmetric line similar to that in polycrystalline benzene). Quantitative interpretation of the spectrum was possible via the measurement of the transverse proton relaxation times, T2, as a function of temperature and coverage. Recent work involving 13C NMR studies of sorbed species is summarized in Table XX. 

Lanthanides have been used as substitutes for calcium in calcium binding proteins since the early days in NMR [155,156]. Remarkable information was obtained on systems such as Yb(III)-substituted parvalbumin (which contains a typical calcium binding site called EF-hand [157,158]) from ID spectroscopy alone [159-164], later complemented by 2D spectroscopy [165]. More recently, pseudocontact shifts and longitudinal proton relaxation times have been used to... 

Cross Polarisation not only provides a better signal-to-noise ratio, but the experiment can also be done faster, because the repetition rate of the pulses is now determined by the proton relaxation times, which are a factor 10-100 smaller than those of the carbons. 

Williamson P, Pelz D, Merskey H, Morrison S, Karlik S, et al. 1992. Frontal, temporal, and striatal proton relaxation times in schizophrenic patients and normal comparison subjects. Am J Psychiatry 149 549-551. 

Bloembergen, N. (1957) Proton relaxation times in paramagnetic solutions. Journal of Chemical Physics, 27, 572-573. 

Fig. 17. Longitudinal H NMR relaxation parameters at 30 MHz for water adsorbed on lysozyme powders derived from the cross-relaxation model after setting the protein relaxation rate equal to 0. Tis the water proton relaxation time and 7", is the time constant characterizing spin transfer between the protein protons and the water protons. From Hilton etal. (1977).

The invariably opposite signs of the Cand isotropic shifts of the (x-CH2 nuclei (Table IV) are clear evidence of 71-delocalization. (69) Table IV also lists proton relaxation times. The 7] values have been analysed in terms of dipolar (DD) and hyperfine contributions. For the... 

The existence of a second solvation sphere around iron(iii) perchlorate has been deduced from proton relaxation times (Tim and T2m) of dimethyl sulphoxide molecules. (278) The results imply that... 

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