Proton decouphng

For bone, the P spin-lattice relaxation time Tf is ca 100 s [36,39] and decreases by approximately 15% from the dried to the fully hydrated sample [36]. In contrast, for synthetic HA, Tf is considerably shorter and varies from 1 to 22 s [31, 36]. The cited results are for differently prepared samples, different magnetic fields and different MAS rates. Homonuclear 3ip.3ip spin-spin relaxation in the sohd state can be conveniently characterized by van Vleck second moments M [46,47].Wuetal. [41] measured Mf in bone, dental enamel and synthetic apatites, HA and CHA-B, using the P Hahn spin echo under proton decouphng. The initial P magnetization was prepared either by a nl2 pulse or... 

Proton-proton homonuclear decoupling has been performed by the ESLG decoupling sequence [46]. Quadrature detection in coj was achieved by using the time proportional phase increment method (TPPI) [47]. During the acquisition period, two pulse phase modulation (TPPM) heteronuclear decouphng ]48] was applied (Figure 7.6). 

In this technique, the frequency of a second radiofrequency transmitter (the decoupler) is set either upheld or downheld from the usual sweep width of a normal proton spectrum (i.e., off resonance). In contrast, the frequency of the decoupler is set to coincide exactly with the range of proton resonances in a true decoupling experiment. Furthermore, in off-resonance decoupling, the power of the decoupling oscillator is held low to avoid complete decouphng. 

Off-resonance decouphng can be a great help in assigning spectral peaks. The off-resonance-decoupled spectrum is usually obtained separately, along with the proton-decoupled spectrum. Figure 4.8 shows the off-resonance-decoupled spectrum of 1-propanol, in which the methyl carbon atom is split into a quartet, and each of the methylene carbons appears as a triplet. Notice that the observed multiplet patterns are consistent with the n -I-1 Rule and with the patterns shown in Figure 4.3. If TMS had been added, its methyl carbons would have appeared as a quartet centered at <5= 0 ppm. 

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