Spin-saturation transfer techniques

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

Very slow exchange can be detected and the rate measured by the transfer of spin saturation technique, a tool that can be useful in the elucidation of reaction mechanisms causing exchange. One of the signals participating in very slow exchange is saturated by an external radiofrequency (RF) field while the rest of the spectrum is observed. If exchange of the spin-saturated nuclei takes... 

The time-consuming 2D experiment can be replaced by ID selective inver-sion-recovery/saturation-transfer experiments [119]. Its application to study the heterogeneity of PS/PVME is mentioned afterwards (see Section 10.3.1.1). Furthermore, Campbell and VanderHart [109] showed that the selective techniques under multiple-pulse homonuclear decoupling are not necessary. They realized that at certain t value in a 2D exchange NMR experiment, polarization gradient necessary for spin diffusion can be achieved by the chemical shift difference. The optimum preparation period for the ID analogue of the 2D exchange NMR experiment was discussed. 

Saturation transfer is a technique that is sensitive to very slow motions with correlation times from 10 to 10 s—a region where conventional ESR is not sensitive [89]. It has been used extensively in spin label studies of biological systems [90], [91]. Spectra are recorded under saturation conditions and high modulation amplitudes, as second harmonic in-phase and quadrature spectra. The method measures the transfer of saturation throughout a spectrum by reorientational molecular motions. The line shape is sensitive to molecular motions and the saturation properties of the spin label. 

Saturation Transfer Spectroscopy of Spin-Labels Techniques and Interpretation of Spectra... 

The technique of saturation transfer has been used to measure in vivo the unidirectional rates of the ATPase and creatine kinase reactions, which will be discussed in later sections. In this technique, developed and first applied by Forsen and Hoffman (1963), the nuclear spin magnetization of one chemical species is perturbed from its equilibrium value and the appearance of nonequilibrium magnetization in a second, product, species is monitored to determine the reaction rate. The technique measures reaction rates in equilibrium or steady state conditions and has a time resolution of 1 s or less. Consider a second-order reaction ... 

Soft-pulse multiple irradiation In this method, pre-saturation is done using shaped pulses having a broader excitation profile. Therefore, it is a more suitable method for the suppression of multiplets. This technique is very effective, easy to apply and easy to implement within most NMR experiments. In aqueous solutions, however, slowly exchanging protons would be detectable due to the occurrence of transfer of saturation. In addition, the spins with resonances close to the solvent frequency will also be saturated. 

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... 

---