Nuclear relaxation methods

Electron-Nuclear Relaxation Methods for Carbon Atoms Use of Data... 

The molecular motions in inclusion complexes formed by cyclohexa-amylose with 4-methylcinnamate, 3-methylcinnamate, and 4-t-butylphenate anions have been studied by and nuclear relaxation methods. The results showed that the time taken for the substrate to reorientate increases by a factor of ca. 4 on inclusion, whereas the increase in tumbling motion depends on the substrate. It was pointed out that, in general, a molecular complex should be described not only by its thermodynamic stability and formation and dissociation kinetics, but also by the dynamic rigidity, defined by the coupling between the molecular motions of the two (or more) entities of which it is composed. 

Meiboom S and Gill D 1958 Modified spin-echo method for measuring nuclear relaxation times Rev. Sci. Instrum. 29 688-91... 

The HF results generated for representative polyatomic molecules have used the /V-derivatives estimated by finite differences, while the -derivatives have been calculated analytically, by standard methods of quantum chemistry. We have examined the effects of the electronic and nuclear relaxations on specific charge sensitivities used in the theory of chemical reactivity, e.g., the hardness, softness, and Fukui function descriptors. New concepts of the GFFs and related softnesses, which include the effects of molecular electronic and/or nuclear relaxations, have also been introduced. 

Nozzle Beams, Supersonic (Anderson, Andres, Fenn). Nuclear Magnetic Relaxation Methods for the Study of 10 275... 

Fhilippott). Relaxation Methods, Nuclear Magnetic, in the Study of 11 289... 

Study of Specific Molecular Interactions by Nuclear Magnetic Relaxation Methods (Jardetzky). ... 

Methods for measuring Ti and T2 are discussed in Chapter 5 of reference 21. Suffice it to say here that understanding the method for measuring T2 (the Carr-Purcell pulse sequence or spin-echo method) becomes important for discussing two-dimensional NMR spectra. When spin-spin coupling is present, a modulation of spin echoes is produced, and it is this fact that is important in 2-D NMR spectroscopy. Nuclear relaxation rates and mechanisms become important when discussing the effect of paramagnetic metal centers on NMR spectroscopy. 

A second steady-state method involves the analysis of the broadening of the nuclear magnetic resonance spectra of phospholipids in bilayers containing low concentrations of spin-labeled phospholipids. A theoretical analysis of the relation between this line broadening and diffusion rates has been given by Brulet and McConnell.3 [In this paper (6) is not correct the subsequent equations are nonetheless correct. For an alternative derivation, see Brulet.2] In this paper it is shown that a number of measurements of nuclear relaxation rates T71 of nuclei in phospholipids are consistent with lateral diffusion constants in the range 10 7 to 10 R cm2/s. 

Nuclear Magnetic Relaxation Methods for the Study of Specific... 

There have been many investigations of phosphotransferases by NMR and EPR methods.681,682 One approach is to use paramagnetic ions such as Mn2+, Cu2+, or Cr3+ to induce nuclear relaxation in substrate and coenzyme molecules at active sites of enzymes. Flavin radicals and specifically introduced nitroxide spin labels can serve as well. Paramagnetic ions greatly increase the rate of magnetic relaxation of nearby nuclei (Chapter 3, Section I). Thus, small amounts of... 

Nuclear relaxation in paramagnetic lan- 2.4.2. The model-free methods 376... 

One of the most important phenomenon, chemically induced dynamic nuclear polarization (CIDNP), deserves more detailed consideration, since it forms the basis of one of the most powerful modem methods for the investigation of the structure and reactivity of short-lived (from nano- to microseconds) paramagnetic precursors of the reaction products. CIDNP manifests itself in the form of unusual line intensities and/or phases of NMR signals observed when the radical reaction takes place directly in the probe of the spectrometer. These anomalous NMR signals—enhanced absorption or emission — are observed within the time of nuclear relaxation of the diamagnetic molecule (from several seconds to several minutes). Later on, the NMR spectrum re-acquires its equilibrium form. 

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