Progressive saturation

The NO trap also requires the use of a low-sulphur fuel (<10ppm). In the presence of sulphur, the trap becomes progressively saturated with sulphates, more stable than nitrates, which quickly reduces its efficiency. In addition, it requires periodic desulpha-tion by running a richer fuel mixture at high temperature. 

A number of pulse-sequence methods are available for measurement of Ti values, and those most commonly used are the methods of saturation recovery (s.r.F.t.),69,70 progressive saturation (p.s.F.t.),71 inversion recovery (i.r.F.t.),72 and the Freeman-Hill modification of in-... 

IR, inversion recovery SR, saturation recovery PS, progressive saturation STEAM, progressive saturation with stimulated echo acquisition mode SE, Hahn spin-echo sel. SE, frequency selective spin-echo. 

Fig. 13.9 Carbon-13 solid-state NMR spectra of poly(ethylene) (a) cross-polarization magic angle spinning (CP/MAS), (b) progressive saturation, and (c) Torchia T, experiment.

C spin-lattice relaxation times of individual nuclei can also be measured by PFT 13C H experiments using a 90°, r, 90", r,... pulse train and noise modulation of the proton decoupling frequency. This method is known as progressive saturation [43] and is based on the following concept. 

Fig. 2.30. Determination of 13C spin-lattice relaxation times by inversion-recovery (a), progressive saturation (b), and comparative evaluation of the intensities (c) values from (a) with full, from (b) with empty characters, abscissa on top for C-2, abscissa on bottom for C-1 and C-3) sample propynol, 75% by vol. in hexadeuterioacetone. 25 C, not degassed, 15.08 MHz, 10 scans/ experiment in (a),...

The most commonly performed relaxation experiment is that of determining the spin-lattice relaxation time, 7, which is relatively easily measured by a variety of methods, such as inversion recovery30 or progressive saturation.31 All of these... 

Table reveals no major variation of bond distances on progressive saturation of the porphyrin macrocycle. 

The spin-lattice relaxation-time T, may also be measured by use of a 90°, f, 90° pulse sequence that employs decreasing values of f to produce a progressive saturation effect.173... 

Consideration of the degree of metal substitution at the carbons of the C2 fragment and the separations of the two carbon atoms, has led to the formulation of polymetallic species as permetallated ethyne (E), ethene (F), or ethane (G) (Chart 2).35 Addition of metal fragments to the unsaturated species E leads to sequential formation of F and G and progressive saturation of the C=C triple bond. These ideas are broadly consistent with the results of computational studies (Section IX.D). Compounds of type E are described below, while the more highly metallated species are discussed in Sections VII, VIII, and IX. 

FIGURE 2.8 Metabolism of phenytoin to form p-HPPH and p-HPPH glucuronide. The first step in this enzymatic reaction sequence is rate limiting and follows Michaelis-Menten kinetics, showing progressive saturation as plasma concentrations rise within the range that is required for anticonvulsant therapy to be effective. 

The above butyl-branched alkane was studied by solid-state 13C NMR, alongside its linear analogue C198H398, to establish the solid-state diffusion coefficient.150 Both alkanes were in the once-folded form. The progressive saturation experiments have shown that the longitudinal relaxation of magnetization is consistent with a solid state chain diffusion process. Reptation and one-dimensional diffusion models were demonstrated to satisfactorily represent the data. The addition of the branch to the alkane chain was shown to result in a decrease in the diffusion coefficient, which ranged from 0.0918 nm2 s 1 for the linear chain to 0.016 nm2 s 1 for the branched chain. These diffusion coefficients are consistent with those of polyethylene. 

The gated dicoupling experiment performed by Newman et al. (1980) on a New Zealand soil humic acid showed that the amount of nuclear Overhauser enhancement for all resonances except that attributed to carboxyl carbon is the same within experimental error. The authors state the results of the progressive saturation and gated decoupling experiments suggest that solution C NMR spectroscopy may be used to compare the aromaticities of humic acids, that is, the fraction of the total carbon of the sample that is aromatic. The authors reached this conclusion on the basis of results from only one sample, and even in that sample a substantial error is introduced into their calculations by the fact that the NOE for the carboxyl carbons is different from that of the other carbons. 

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